Questions re. Malossi 177 cast iron kit for Stella.
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Enthusiast
2005 Stella 2T
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Mon Sep 28, 2020 5:11 am quote
The prospect of a horsepower bump approaching 50% using plug & play parts costing $245 shipped has proven irresistible. I have succumbed to temptation and pulled the trigger on a Malossi 177 cast iron cylinder kit for my Stella (not to be confused with Malossi’s older 166 kit). I chose the Malossi over the comparable DR and Polini kits because the design is at least 10 years newer and I imagine the industry must have learned something in that time. I chose it over the comparable VMC kit because the VMC kit is not readily available in the US and shipping from Europe makes the VMC kit too expensive.

I have a couple of questions to ponder while I await delivery.

First, Malossi does not recommend a larger carb. It only recommends using the jetting supplied with the kit, which seems very rich (52-140 idle jet and BE4 mixer tube). For a main jet, they supply a 105 and a 115, the choice depending on whether some of the rotary valve is cut away. Of course, the Stella has a reed valve. Am I right to think that means I should start with the 115?

Second, I was expecting to upgrade from a 21 to a 22 tooth clutch, but Malossi recommends a 23/64 clutch/primary combo, a straight cut version of which Malossi just happens to sell. Overkill?

Last edited by Kowalski on Fri Oct 02, 2020 7:55 am; edited 1 time in total
Molto Verboso
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Mon Sep 28, 2020 5:39 am quote
The 23/64 is not necessarily overkill, but it is a lot of work to install. Certainly not P&P. You do have an option above 22T with your existing 68T primary, and that is a DRT. or BGM 23T clutch gear in a Cosa/Superstrong/Ultrastrong clutch. Whether you need 22 or 23 will depend on a number of factors: weight, terrain around where you ride, other performance mods, solo or pillion etc.

I have had a lot of success with a DRT 23T / 68T combo on a PX177 (BGM kit), but I don't weigh too much
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
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Location: London UK
Mon Sep 28, 2020 5:45 am quote
What made you choose this Malossi 177 cast iron cylinder kit over all the more powerful kits? The answer to this is the key to replying to your next questions.
Enthusiast
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Mon Sep 28, 2020 6:18 am quote
Jack221 wrote:
What made you choose this Malossi 177 cast iron cylinder kit over all the more powerful kits? The answer to this is the key to replying to your next questions.
Cost? I do not know of any more powerful kits costing $245 delivered to my front door. Combined with a big box exhaust and a drilled air filter, I expect to get around 15 hp at the crank out of this kit. I think I will be happy with that.
Jet Eye Master
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Mon Sep 28, 2020 9:01 am quote
Ok, low cost and 15bhp being the target. You're on the right track, properly set up it will go as expected.

177 kit, some exhaust, adjust ignition timing and full carb re-jet is all you need to do. If your gearing is actually 21/68 it may be ok. As you're reed it will rev higher. If not a 22 or 23 clutch cog is an easy change later when you actually know how it goes. Might need some better reeds and ones that run without the restriction bar.

Malossi assume the jetting is for a PX on a 20/20 carb. Yours will may need more than the jets supplied.
Enthusiast
2005 Stella 2T
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Mon Sep 28, 2020 10:30 am quote
swa45 wrote:
The 23/64 is not necessarily overkill, but it is a lot of work to install. Certainly not P&P. You do have an option above 22T with your existing 68T primary, and that is a DRT. or BGM 23T clutch gear in a Cosa/Superstrong/Ultrastrong clutch. Whether you need 22 or 23 will depend on a number of factors: weight, terrain around where you ride, other performance mods, solo or pillion etc.

I have had a lot of success with a DRT 23T / 68T combo on a PX177 (BGM kit), but I don't weigh too much
This is great info. I guess I might be a 23T candidate since I weigh about 175 lbs (12.5 stone), ride solo and live on the coast. It is good to know there is a simple option if I decide to go that route.
Enthusiast
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Mon Sep 28, 2020 10:38 am quote
Jack221 wrote:
Ok, low cost and 15bhp being the target. You're on the right track, properly set up it will go as expected.

177 kit, some exhaust, adjust ignition timing and full carb re-jet is all you need to do. If your gearing is actually 21/68 it may be ok. As you're reed it will rev higher. If not a 22 or 23 clutch cog is an easy change later when you actually know how it goes. Might need some better reeds and ones that run without the restriction bar.

Malossi assume the jetting is for a PX on a 20/20 carb. Yours will may need more than the jets supplied.
Thanks Jack. A little expert affirmation goes a long way.

Re. jetting, I suspected as much because the Malossi literature only talks about rotary valves. I plan to start with their jetting--using the 115 MJ--and take it from there.
Ossessionato
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Mon Sep 28, 2020 10:54 am quote
Their jetting and literature is shit. Broken engrish at best. Ignore it. Start with a 125-130 and work your way down.

For my friends Stella with a bolt on Pinasco, SIP Road 2.0, 20/20, stock clutch cog he’s running a 125 MJ (broken in) riding hard (260 lbs).

My Malossi 166, 24/24, Polini exh, 22 tooth cog im running a 120 MJ. 200 lbs. Both at sea level riding WOT like assholes.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
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Location: London UK
Mon Sep 28, 2020 2:41 pm quote
Kowalski wrote:
Re. jetting, I suspected as much because the Malossi literature only talks about rotary valves. I plan to start with their jetting--using the 115 MJ--and take it from there.
There's probably a million years of scooter knowledge on this forum; ignore jetting advice at your peril. Learning yourself is fun but it can get rather expensive.
AC140 BE5 MJ125 minimum to start running in with. If any good it might need richer still.
Enthusiast
2005 Stella 2T
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Posts: 61
Location: MA
Mon Sep 28, 2020 3:04 pm quote
Jack221 wrote:
Kowalski wrote:
Re. jetting, I suspected as much because the Malossi literature only talks about rotary valves. I plan to start with their jetting--using the 115 MJ--and take it from there.
There's probably a million years of scooter knowledge on this forum; ignore jetting advice at your peril. Learning yourself is fun but it can get rather expensive.
AC140 BE5 MJ125 minimum to start running in with. If any good it might need richer still.
Maybe I was too subtle but that is exactly the kind of advice I was fishing for. I'm already running the AC140 and the BE5. I will get the MJ125. Thank you.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
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Mon Sep 28, 2020 6:54 pm quote
Kowalski wrote:
I expect to get around 15 hp at the crank out of this kit. I think I will be happy with that.
You may be a little disappointed. I rode a friend's VBC with this kit, from memory it had a slightly longer intake crank, Sip Road, 20/20 and nicely matched 3 port case. My feeling at the time was that it was probably not quite in P200 territory which surprised me a little. He was really happy with it because it replaced a stock VBC 150 cylinder.

Make sure you measure it when it arrives; Jack will be able to advise you on improvements that will mostly on cost you time.
Hooked
Rat 2003 Stella 2T; 1979 P125x (in pieces, out for paint)
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Location: Madtown
Tue Sep 29, 2020 4:08 am quote
MJRally wrote:
Their jetting and literature is shit. Broken engrish at best. Ignore it. Start with a 125-130 and work your way down.

For my friends Stella with a bolt on Pinasco, SIP Road 2.0, 20/20, stock clutch cog he’s running a 125 MJ (broken in) riding hard (260 lbs).

My Malossi 166, 24/24, Polini exh, 22 tooth cog im running a 120 MJ. 200 lbs. Both at sea level riding WOT like assholes.
Agreed with the 120-130 range. Was at 122 on a Malossi 166, with my polini Venturi now at 140.
Enthusiast
2005 Stella 2T
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Tue Sep 29, 2020 4:21 am quote
Any thoughts on the 52/140 idle jet that comes with the kit? That seems very rich to me.

I have a 55/160 that was too rich for the stock 150cc jug. Might that work on the 177?

Thanks.
Hooked
Rat 2003 Stella 2T; 1979 P125x (in pieces, out for paint)
Joined: 12 Sep 2015
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Location: Madtown
Tue Sep 29, 2020 7:21 am quote
Kowalski wrote:
Any thoughts on the 52/140 idle jet that comes with the kit? That seems very rich to me.

I have a 55/160 that was too rich for the stock 150cc jug. Might that work on the 177?

Thanks.
I had a 55/160 (which worked great with the 122 main jet) until the Venturi required me to go up to a 140 main jet, which made the 55/160 too rich at partial throttle. I went down to I think a 48/160 (or whatever is closest to that).
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 61
Location: MA
Fri Oct 02, 2020 6:53 am quote
Cylinder kit arrived yesterday. MJ125 won’t be here ‘til Monday.

I am approaching this as a plug & play exercise to start. I will, however, trace and measure the ports in the name of science. I want to leave the scooter rideable over the weekend, so it probably will be Monday before I can measure the distance to the piston at TDC. No point in talking about port heights until then. In the meantime, a tracing is attached. Everything seems very plain vanilla. No doubt the exhaust port could be raised and widened some if one was inclined to do so.

I noticed the intake ports are slightly stepped. The rear (boost?) ports are .5mm lower than the next ports, which are then .5mm lower than the largest, forward-most ports. Am I right that I want to use the highest ports when calculating blow-down duration?

There is nothing in the instructions about piston ring gap. I am getting .175 millimeters. Does that sound about right?

I am thinking of using some Permatex copper spray-a-gasket on the base gasket. Good idea?

Thanks.[/img]

malossi.kit.jpg

malossi.177.port.tracing.jpg

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7949
Location: Victoria, Australia
Fri Oct 02, 2020 6:21 pm quote
Kowalski wrote:
Cylinder kit arrived yesterday. MJ125 won’t be here ‘til Monday.

I am approaching this as a plug & play exercise to start. I will, however, trace and measure the ports in the name of science. I want to leave the scooter rideable over the weekend, so it probably will be Monday before I can measure the distance to the piston at TDC. No point in talking about port heights until then. In the meantime, a tracing is attached. Everything seems very plain vanilla. No doubt the exhaust port could be raised and widened some if one was inclined to do so.

I noticed the intake ports are slightly stepped. The rear (boost?) ports are .5mm lower than the next ports, which are then .5mm lower than the largest, forward-most ports. Am I right that I want to use the highest ports when calculating blow-down duration?

There is nothing in the instructions about piston ring gap. I am getting .175 millimeters. Does that sound about right?

I am thinking of using some Permatex copper spray-a-gasket on the base gasket. Good idea?

Thanks.[/img]
Kowalski, want to put some measurements on that? That would be a bit more telling.

The base gasket doesn't need the high temp solution that a head gasket does, as long as your cases match really flat. Otherwise perhaps an RTV sealant is a little more reliable? My favourite (not strictly RTV) is Threebond 1104, same thing as Hondabond/Yamabond. It'll fill any imperfections very well.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
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Location: London UK
Fri Oct 02, 2020 11:21 pm quote
Nice job on the port map, better than most of mine. As said, need the width and height to deck (measured from inside) of each port to be of much use. Blowdown is usually measured from the largest transfer next to the exhaust, which is usually the first to open on most.

Be sure to chamfer the ports top and bottom. Normally a little rough from new. This will help with ring wear. 0.2mm gap is fine.

Try to set the squish at 1.0mm. This might need the head sanded down or more base gaskets, or both being the best option.
Enthusiast
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Sat Oct 03, 2020 4:55 am quote
Good stuff guys.

Measurements coming. As I undertand it, you can't do much without the distance to the piston at TDC. I won't have that until I pull the old jug and start installing the new one, and I won't be doing that until I am closer to having the MJ125 in hand.

Re. measuring port widths, am I measuring on the arc or the chord?

Thanks.
Jet Eye Master
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Sat Oct 03, 2020 3:39 pm quote
The measurements measure the same even with no piston. Where the piston sits at TDC is up to you. Do some calculations at zero until you know what you're working with.

You have an AC140 and BE5 to go with that 125MJ?
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
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Sat Oct 03, 2020 4:43 pm quote
Kowalski wrote:
Re. measuring port widths, am I measuring on the arc or the chord?
Arc. So you can simply measure the paper flat on the table.
Enthusiast
2005 Stella 2T
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Location: MA
Sun Oct 04, 2020 4:56 am quote
Port tracing with measurements attached. Heights are from cylinder top (i.e., no deduction for distance to piston top).

Timing calculation also attached. Exhaust 171.3°. Intake 115.4°. Blowdown 55.9°.

malossi.177.dimension.0.jpg

malossi177timing0_55496.jpg

Molto Verboso
2007 Stella 150
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Posts: 1112
Location: Rochester, Minnesota
Sun Oct 04, 2020 6:35 am quote
Lets see the bottom side of the head, does it have a built in squish band? If it does and it's about 1mm, then you know you'll be running close to a "0" PBT.
Enthusiast
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Sun Oct 04, 2020 7:12 am quote
Christopher_55934 wrote:
Lets see the bottom side of the head, does it have a built in squish band? If it does and it's about 1mm, then you know you'll be running close to a "0" PBT.
"PBT," I like that. It does appear to have a squish band. I measure a recess of about 0.70mm at the outer edge. Should have a hard number for PBT later today or tomorrow.

malossi.177.head.jpg

Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1112
Location: Rochester, Minnesota
Sun Oct 04, 2020 7:16 am quote
Kowalski wrote:
Christopher_55934 wrote:
Lets see the bottom side of the head, does it have a built in squish band? If it does and it's about 1mm, then you know you'll be running close to a "0" PBT.
"PBT," I like that. It does appear to have a squish band. I measure a recess of about 0.70mm at the outer edge. Should have a hard number for PBT later today or tomorrow.
If you're getting 0.7mm for squish band, try using PBT of 0.3 mm and see what you get.

Last edited by Christopher_55934 on Sun Oct 11, 2020 11:46 am; edited 1 time in total
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
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Sun Oct 04, 2020 10:09 am quote
Transfers are quite low but exhaust port is a good shape. It will go ok just bolted on. Blowdown is half the total, so you have 28 degrees. This is plenty to work with if you wanted to improve the situation. Put on the thickest base gaskets you feel comfortable with to get the transfers as high as possible.

Btw, BGM 177 has a 48mm wide exhaust port.
Enthusiast
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Sun Oct 04, 2020 1:59 pm quote
Let the games begin! Tip of the hat to Mr. Freakmoped who just happened to post a 2 part how-to video last week. Very helpful. Old jug and piston did not fight me at all coming off. Internals seem ok (scooter only has 2500 miles on it).

For actual PBT I am measuring 0.50 mm. Revised calculations attached. Exhaust 173.4°. Intake 118.1°. Blowdown 27.65°.

Expect to have the new jug buttoned up tomorrow and first test ride on Tuesday.

Screenshot (3).png

Enthusiast
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Mon Oct 05, 2020 12:26 pm quote
Everything seemed to go back together smoothly. Some thoughts while waiting for sealant to cure.

1. I resolved at the outset not to split the cases, and not to grind on them in situ. Nonetheless, I thought others might want to see how the Malossi cylinder matches up to the Stella cases. See 1st photo.

2. There is one spot where the case opening is actually bigger than the cylinder opening. See 2nd photo. In this case, I did elect to grind out some of the cylinder to match. See 3rd photo. So now I am at about 99% plug & play.

3. So far, this seems like a pretty nice kit. For one thing, it is compatible with the electric start right out of the box; no grinding needed there. For another thing, it seems to have been manufactured to precise tolerances. I say that mostly because the specification for squish is 1.2mm. As noted earlier, I measured the edge of the squish band at 0.70mm, and I measured PBT at 0.50mm. Add them together and you get exactly 1.2mm.

4. For a spark plug, I will start with an NGK BR8ES. That is the NGK equivalent for the ND plug Malossi recommends.

5. For a main stack, I will start with what has been recommended here: AC140, BE5, MJ125. For an idle jet, I will start with a 55/160.

stella.case.jpg

malossi.cylinder.jpg

malossi.cylinder.2.jpg

Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1112
Location: Rochester, Minnesota
Mon Oct 05, 2020 4:18 pm quote
Christopher_55934 wrote:
Kowalski wrote:
Christopher_55934 wrote:
Lets see the bottom side of the head, does it have a built in squish band? If it does and it's about 1mm, then you know you'll be running close to a "0" PBT.
"PBT," I like that. It does appear to have a squish band. I measure a recess of about 0.70mm at the outer edge. Should have a hard number for PBT later today or tomorrow.
If you're getting 0.7mm for squish band, try using PBT of 0.3 mm and see what you get.
Hooked
Stella 2T 150, Honda C70
Joined: 25 Sep 2019
Posts: 136
Location: Seattle
Mon Oct 05, 2020 4:33 pm quote
This keeps getting better and better. After this summer I thought I'd be happy with my stock-ish Stella setup but this thread is giving me upgrade-itis. I'm just going to wait and watch and let you work out the jetting and then maybe I'll join the club.

Hal
Enthusiast
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Posts: 61
Location: MA
Tue Oct 06, 2020 1:36 pm quote
Initial test rides were mostly positive. The kit runs smoothly and clearly makes a lot more power than the old setup. Just based on seat of the pants, it accelerates much more quickly than before; even lifted the front wheel a little at one point without meaning to. It is also obvious that top speed will be much improved. How much remains to be seen because I am trying to take it easy during break-in.

The recommended mainstack (AC140, BE5, MJ125) seems about right; certainly good enough for breaking-in.

Spark plug looks decent. See attached photo.

The only fly in the ointment is some pretty bad bogging up to about ¼ throttle. After that, the scooter takes off like a rocket. I tried 4 different idle jets covering a wide range (52/140, 55/160, 40/130, 42/140) and twiddled the mixture screw in and out for each, but nothing seemed to have much effect. At this point, I can’t even tell if the bogging is from too little or too much fuel. Any suggestions from the resident gurus would be gratefully received.

plug.20.10.06.jpg

Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1112
Location: Rochester, Minnesota
Tue Oct 06, 2020 1:40 pm quote
Kowalski wrote:
Initial test rides were mostly positive. The kit runs smoothly and clearly makes a lot more power than the old setup. Just based on seat of the pants, it accelerates much more quickly than before; even lifted the front wheel a little at one point without meaning to. It is also obvious that top speed will be much improved. How much remains to be seen because I am trying to take it easy during break-in.

The recommended mainstack (AC140, BE5, MJ125) seems about right; certainly good enough for breaking-in.

Spark plug looks decent. See attached photo.

The only fly in the ointment is some pretty bad bogging up to about ¼ throttle. After that, the scooter takes off like a rocket. I tried 4 different idle jets covering a wide range (52/140, 55/160, 40/130, 42/140) and twiddled the mixture screw in and out for each, but nothing seemed to have much effect. At this point, I can’t even tell if the bogging is from too little or too much fuel. Any suggestions from the resident gurus would be gratefully received.
Perform a 1/4 throttle plug chop, nothing says one has to be performed at WOT.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
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Tue Oct 06, 2020 2:51 pm quote
It's very tempting to start jetting in immediately but with an iron bore it's best not to. If it rides ok just take the whole day and go empty two tanks of gas. After about 150 miles, jetting can be set a bit better. The 42/140 is best for now but this will change later.
Enthusiast
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Wed Oct 07, 2020 8:36 am quote
Jack221 wrote:
It's very tempting to start jetting in immediately but with an iron bore it's best not to. If it rides ok just take the whole day and go empty two tanks of gas. After about 150 miles, jetting can be set a bit better. The 42/140 is best for now but this will change later.
Thank you. Put the 42/140 back in and it does seem the least bad of the lot. Still pretty bad bogging, spluttering, 4-stroking or whatever you want to call it, but confined to a slightly narrower range, perhaps the first 1/8 of the throttle. It seems counter-intuitive that a bigger jug would need a leaner idle jet, but everything seems to point in that direction. In any event, I can understand the wisdom of not wanting to go leaner during break-in.
Enthusiast
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Sun Oct 11, 2020 11:01 am quote
As suggested, I have put a little over 150 miles on the new cylinder kit. I still think some jetting changes are in order.

The idle jet is a 42/140. The bogging, spluttering, 4-stroking or whatever up to ¼ throttle remains mostly unchanged. As already stated, it seems counter-intuitive that an idle jet which is pretty damn lean to begin with, and which was fine in a 150, appears to be too rich in a 177. I would feel more confident if someone could tell me why that might (or might not) be the case. In any event, there are only a couple of available idle jets leaner than a 42/140. Is it too early to try a 45/160?

I am also starting to suspect the MJ125 is too lean. Obviously, I am not doing sustained WOT runs yet. During brief flirtations with WOT in 2nd and 3rd gear, however, the engine seems unduly harsh and nowhere near being over-fueled. If there is a 45/160 idle jet in my future, would it make sense to add an MJ128 and an MJ130 to my order?

Thanks in advance for any additional advice.
Hooked
Rat 2003 Stella 2T; 1979 P125x (in pieces, out for paint)
Joined: 12 Sep 2015
Posts: 252
Location: Madtown
Sun Oct 11, 2020 11:30 am quote
Kowalski wrote:
As suggested, I have put a little over 150 miles on the new cylinder kit. I still think some jetting changes are in order.

The idle jet is a 42/140. The bogging, spluttering, 4-stroking or whatever up to ¼ throttle remains mostly unchanged. As already stated, it seems counter-intuitive that an idle jet which is pretty damn lean to begin with, and which was fine in a 150, appears to be too rich in a 177. I would feel more confident if someone could tell me why that might (or might not) be the case. In any event, there are only a couple of available idle jets leaner than a 42/140. Is it too early to try a 45/160?

I am also starting to suspect the MJ125 is too lean. Obviously, I am not doing sustained WOT runs yet. During brief flirtations with WOT in 2nd and 3rd gear, however, the engine seems unduly harsh and nowhere near being over-fueled. If there is a 45/160 idle jet in my future, would it make sense to add an MJ128 and an MJ130 to my order?

Thanks in advance for any additional advice.
I couldn't get my Stella/malossi 166 to idle correctly with anything other than XX/160 idle jets. I ended up with a 55/160, but have now gone down one size (I think 48/160).

And yes you should definitely order the extra main jets. It's worth it to have a collection.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
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Sun Oct 11, 2020 2:29 pm quote
Now that's interesting. 125MJ is not close to spluttering at WOT. Instead of increasing jet change the air corrector. Swap the AC140 for an AC120. Keep the BE5 for now and the 42/140. See where the main jet ends up first.
Make sure you order a BE3 if you don't have one. And a box of main jets; all jets between 110 and 130 is usually enough.

And another thing, did you drill your carb yet?
Enthusiast
2005 Stella 2T
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Sun Oct 11, 2020 4:32 pm quote
Jack221 wrote:
Now that's interesting. 125MJ is not close to spluttering at WOT. Instead of increasing jet change the air corrector. Swap the AC140 for an AC120. Keep the BE5 for now and the 42/140. See where the main jet ends up first.
Make sure you order a BE3 if you don't have one. And a box of main jets; all jets between 110 and 130 is usually enough.

And another thing, did you drill your carb yet?
Carb has not been drilled. I did not expect that would be necessary just to go to a plain vanilla 177 kit.

Which do you think I should try first, drilling the carb or the AC120?

Probably will wait and see where that puts me before I start buying main jets by the dozen. Already have the BE3 should that appear beneficial.

Thank you for all the help.
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1112
Location: Rochester, Minnesota
Sun Oct 11, 2020 7:07 pm quote
Drilling the carburetor isn't going to hurt anything, it's good insurance to make sure that the channel isn't your bottle neck.
Enthusiast
2005 Stella 2T
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Location: MA
Mon Oct 12, 2020 4:57 am quote
Christopher_55934 wrote:
Drilling the carburetor isn't going to hurt anything, it's good insurance to make sure that the channel isn't your bottle neck.
Re. drilling the carb, I'm seeing references to 1.8mm, 2.0mm, 2.1mm and 2.5mm. I have a 20/20 and some of those relate to a 24/24. Don't know if that makes a difference. Would 5/64" (1.98mm) likely do the trick on a 20/20?

Thanks.
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1112
Location: Rochester, Minnesota
Mon Oct 12, 2020 7:32 am quote
Kowalski wrote:
Christopher_55934 wrote:
Drilling the carburetor isn't going to hurt anything, it's good insurance to make sure that the channel isn't your bottle neck.
Re. drilling the carb, I'm seeing references to 1.8mm, 2.0mm, 2.1mm and 2.5mm. I have a 20/20 and some of those relate to a 24/24. Don't know if that makes a difference. Would 5/64" (1.98mm) likely do the trick on a 20/20?

Thanks.
I drilled my 20/20 to something around a 2.0mm, on these carburetors a 135 main jet is 1.35mm to a point. Drilling the channel to 2.0 mm hole, gives you over double the area for flow of a 1.35mm hole, shouldn't be your restriction any longer. If I had a 5/64 drill bit on my bench that is what I would use.

Also where did you get your jets from? Some of the generic jets have poor quality control and the marked size doesn't match the actual size. Also the numbering scheme isn't the same. I've had this happen and so have a few others here. I bought two boxes of jets from SIP to cure that issue. I had the same manufacturer for all my jets and when I made a change, the expected results happened.

There is a chart from SIP that shows this for them. I was mixing Dellorto and SIP jets when I started having issues. I went from a 160 to a 140 air corrector to put me back into the assortment of SIP jets I had.

https://www.sip-scootershop.com/en/products/jet+si+sip+performance+114+_40261140
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