Questions re. Malossi 177 cast iron kit for Stella.
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Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Mon Oct 12, 2020 1:48 pm quote
Taking things one step at a time.

Drilled the carb using the 5/64" (1.98mm) drill bit and took the scooter for a test drive. Not noticing any real difference. Still feels harsh at high revs and nothing I would call splutter.

Will try the AC120 next.
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1116
Location: Rochester, Minnesota
Mon Oct 12, 2020 4:17 pm quote
Kowalski wrote:
Taking things one step at a time.

Drilled the carb using the 5/64" (1.98mm) drill bit and took the scooter for a test drive. Not noticing any real difference. Still feels harsh at high revs and nothing I would call splutter.

Will try the AC120 next.
That is interesting, what is your cylinder head temperature? Would be interesting to get a short run at wot to see the plug color.
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Mon Oct 12, 2020 5:08 pm quote
Christopher_55934 wrote:
That is interesting, what is your cylinder head temperature? Would be interesting to get a short run at wot to see the plug color.
I'm not equipped to measure cylinder head temp. I'm only doing intermittent bursts of WOT and air temps have been cool so I'm sure it's not getting too hot. I will see if I can get a look at plug color based on WOT. In the meantime, I can just tell it is too lean based on sound and feel.

On the plus side, the scooter is much quicker than before. The leaness only shows up at high rpms. I don't have a tach but it corresponds to speeds over 45 mph in 3rd and over 60 mph in 4th. For normal riding, the over-richness up to 1/4 throttle is actually the bigger nuisance.
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1116
Location: Rochester, Minnesota
Mon Oct 12, 2020 5:31 pm quote
Kowalski wrote:
Christopher_55934 wrote:
That is interesting, what is your cylinder head temperature? Would be interesting to get a short run at wot to see the plug color.
I'm not equipped to measure cylinder head temp. I'm only doing intermittent bursts of WOT and air temps have been cool so I'm sure it's not getting too hot. I will see if I can get a look at plug color based on WOT. In the meantime, I can just tell it is too lean based on sound and feel.

On the plus side, the scooter is much quicker than before. The leaness only shows up at high rpms. I don't have a tach but it corresponds to speeds over 45 mph in 3rd and over 60 mph in 4th. For normal riding, the over-richness up to 1/4 throttle is actually the bigger nuisance.
That's interesting, something isn't right, from my limited experience. My DR177 and Sito + or the PM Tuning pipe I tried using a 140 air corrector was in the 120 area for a main jet I would have to go pull it and look. I had a venturi on my 20/20 and I had to raise the jetting up 10 points. So your jet is about 15 sizes bigger than mine at a 140 air corrector. Then you put in a 120 air corrector and you Are still lean? Are you using a stock air filter? Have you pressure tested the motor to make sure you don't have an air leak.
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Mon Oct 12, 2020 5:57 pm quote
Christopher_55934 wrote:
That's interesting, something isn't right, from my limited experience. My DR177 and Sito + or the PM Tuning pipe I tried using a 140 air corrector was in the 120 area for a main jet I would have to go pull it and look. I had a venturi on my 20/20 and I had to raise the jetting up 10 points. So your jet is about 15 sizes bigger than mine at a 140 air corrector. Then you put in a 120 air corrector and you Are still lean? Are you using a stock air filter? Have you pressure tested the motor to make sure you don't have an air leak.
Results so far have been using an AC140, BE5 and MJ125. Scooter has a new Polini box and a predrilled Piaggio air filter. The AC120 is pending and I'll probably go full "Jack Stack" and combine that with a BE3 I already have. I'm fairly sure that plus an MJ in the 120-130 range will get me where I need to be.

If I'm not spluttering with a Jack Stack plus an MJ130, then I'll start to worry about an air leak.
Member
PX
Joined: 28 May 2020
Posts: 20
Location: Bognor Regis
Tue Oct 13, 2020 5:43 am quote
Out of curiosity, do you get the spluttering as bad with low throttle if you put in a B7ES plug? Im not sure what distances you are travelling but i have three plugs to hand on my DR177. I put a BE7 in for my short runs, like to work which is 6 miles away. I have a BE8 for longer runs and and a BE9 for very long runs. If i forget the BE9 is still in it splutters big time exactly how you describe it with a small amount of throttle applied in 1st 2nd and 3rd gear.
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Tue Oct 13, 2020 12:42 pm quote
ferriswolf wrote:
Out of curiosity, do you get the spluttering as bad with low throttle if you put in a B7ES plug? Im not sure what distances you are travelling but i have three plugs to hand on my DR177. I put a BE7 in for my short runs, like to work which is 6 miles away. I have a BE8 for longer runs and and a BE9 for very long runs. If i forget the BE9 is still in it splutters big time exactly how you describe it with a small amount of throttle applied in 1st 2nd and 3rd gear.
I did try going to a B7ES (actually a BR7ES). Nothing seemed to change. I plan to follow the advice I am getting here to dial in the main stack before tackling the idle jet. I will go back to a BR8ES while I do that.
Ossessionato
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 61 Ser 2, 65 Silver Special, 86 & 96 Elite 80s, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 3754
Location: Oceanside, CA
Tue Oct 13, 2020 1:10 pm quote
Did you drill out the heart in your air filter?
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Tue Oct 13, 2020 1:24 pm quote
MJRally wrote:
Did you drill out the heart in your air filter?
I am using the Piaggio airfilter that comes with the holes already drilled.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2449
Location: London UK
Tue Oct 13, 2020 10:55 pm quote
Depending on where the main jet ends up on the AC120, it could be beyond the capability of a stock filter.
When this happens the stock filter chokes up the low throttle positions
Addicted
63 Lambretta LI 125 series 3, 71 Sprint Veloce , 2005 Vespa PX150, 1979 P200E
Joined: 04 Jul 2011
Posts: 880
Location: Tucson, AZ
Sat Oct 17, 2020 8:49 am quote
My malossi 166cc kit came with a 115 main so base on this fact I would say go with the bigger of the two mains that you received. As per the cylinder being cast iron, nothing wrong with that as long as you use quality synthetic oil.
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Tue Oct 20, 2020 1:01 pm quote
As far as the main stack, it seems like the AC120 did the trick. Running an AC120, BE3, MJ125, I would say I am getting just a bit of splutter at WOT.

Plug looks ok (center is more brown in real life than in the photo).

I suspect I could pick up a couple of additional mph in top speed with an MJ122, but I plan to leave things as they are for now while I put a few more break-in miles on this kit.

My biggest quality of life issue by far continues to be the bogging, spluttering, four-stroking, machine-gunning or whatever else you want to call it up to ¼ throttle. The idle jet is a 42/140, which is pretty lean already. Is it plausible that this kit needs a 45/160? In addition to knowing the “what,” I always like to know the “why.” Anyone out there care to offer a scientific explanation for why an idle jet that worked fine on a 150 appears to be too rich on a 177?

Many thanks for all the help.[/img]

plug.20.10.20.jpg

Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2449
Location: London UK
Tue Oct 20, 2020 2:33 pm quote
If you can actually feel WOT splutter with a 125 main jet, then you could get away with a 120 main jet. Certainly change to 122.

Forget anything you know about other carbs you have ever worked on. With an SI carb the main jet is online from zero. If the main jet is too big, it will bleed all over the pilot Jet. So if you are over rich at 1/4, it is absolutely confirmed, main jet is too big.
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Tue Oct 20, 2020 4:44 pm quote
Jack221 wrote:
If you can actually feel WOT splutter with a 125 main jet, then you could get away with a 120 main jet. Certainly change to 122.

Forget anything you know about other carbs you have ever worked on. With an SI carb the main jet is online from zero. If the main jet is too big, it will bleed all over the pilot Jet. So if you are over rich at 1/4, it is absolutely confirmed, main jet is too big.
Thank you for that feedback. If right-sizing the main jet cures the low throttle bogging too, I will be a very happy scooterist.
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Wed Oct 21, 2020 3:11 pm quote
While waiting for an MJ120 and MJ122 to be delivered, I did some experiments aimed at diagnosing my partial throttle bogging.

First, to see whether the MJ 125 was drowning out the idle jet, I ran the MJ115 that came with the kit (being careful to avoid WOT). The bogging was as bad as ever.

Second, to see whether a really lean idle jet would help, I took a 1/16” bit and drilled my 42/140 idle jet out to a 42/159. Again, no appreciable difference.

I am starting to think this is not a jetting issue but, rather, something intrinsic to the way the SI 20/20 interacts with this kit. The only other thing I can think of changing on the existing carburetor is the throttle slide. Otherwise, I am thinking I should just bin the whole thing and start over with an SI 24/24.

Thoughts?
Hooked
Rat 2003 Stella 2T; 1979 P125x (in pieces, out for paint)
Joined: 12 Sep 2015
Posts: 260
Location: Madtown
Wed Oct 21, 2020 3:53 pm quote
Kowalski wrote:
While waiting for an MJ120 and MJ122 to be delivered, I did some experiments aimed at diagnosing my partial throttle bogging.

First, to see whether the MJ 125 was drowning out the idle jet, I ran the MJ115 that came with the kit (being careful to avoid WOT). The bogging was as bad as ever.

Second, to see whether a really lean idle jet would help, I took a 1/16” bit and drilled my 42/140 idle jet out to a 42/159. Again, no appreciable difference.

I am starting to think this is not a jetting issue but, rather, something intrinsic to the way the SI 20/20 interacts with this kit. The only other thing I can think of changing on the existing carburetor is the throttle slide. Otherwise, I am thinking I should just bin the whole thing and start over with an SI 24/24.

Thoughts?
There is no reason why the 20.20 shouldn't work unless it is mis-manufactured somehow.

Is the choke fully disengaging? I would remove it and inspect. Also re-clean the carb (removing, disassembling).

It seems like the bike is running too well for it to be the piston upside down! I did that once with this kit. Fun times!
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Wed Oct 21, 2020 4:38 pm quote
yackee wrote:
There is no reason why the 20.20 shouldn't work unless it is mis-manufactured somehow.

Is the choke fully disengaging? I would remove it and inspect. Also re-clean the carb (removing, disassembling).

It seems like the bike is running too well for it to be the piston upside down! I did that once with this kit. Fun times!
I agree, the choke is suspicious. Externally, it appears to be working as it should, but maybe something is getting hung up inside. I will take a look at that.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2449
Location: London UK
Wed Oct 21, 2020 11:40 pm quote
This will set up. The 24/24 would be no easier.
If the choke isn't stuck on (which is very common), it could be that it's not rich bogging at 1/4 but lean. They feel very similar, you wouldn't be the first.
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1116
Location: Rochester, Minnesota
Thu Oct 22, 2020 2:44 am quote
Kowalski wrote:
While waiting for an MJ120 and MJ122 to be delivered, I did some experiments aimed at diagnosing my partial throttle bogging.

First, to see whether the MJ 125 was drowning out the idle jet, I ran the MJ115 that came with the kit (being careful to avoid WOT). The bogging was as bad as ever.

Second, to see whether a really lean idle jet would help, I took a 1/16” bit and drilled my 42/140 idle jet out to a 42/159. Again, no appreciable difference.

I am starting to think this is not a jetting issue but, rather, something intrinsic to the way the SI 20/20 interacts with this kit. The only other thing I can think of changing on the existing carburetor is the throttle slide. Otherwise, I am thinking I should just bin the whole thing and start over with an SI 24/24.

Thoughts?
I agree with Jack, there is no reason a 20/20 shouldn't work. I ran one on mine with no issues. With the odd jetting your getting. Did you try going richer on the bottom end to see if that improves your situation? How about a plug chop at that throttle position to verify rich or lean?

Did you ever perform a leak down test to make sure you don't have an air leak? Did you ever get a cylinder head temperature gauge to see how your temperature is?
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 62
Location: MA
Thu Oct 22, 2020 8:26 am quote
Took the choke out. It seems fine. Might replace it anyway because they are dirt cheap. Nonetheless, I do not think that is the problem.

Also revisited some richer idle jets with perhaps encouraging results. A 55/160 seemed slightly better, and the 52/140 that came with the kit seemed slightly better still. So, it does seem possible that what I thought might be a rich bog could be a lean bog instead.

While the scooter is more rideable with the 52/140, it still bogs pretty badly from a standing start. The 52/140 trims out at a hair less than 2 turns on the mixture screw. Am I right to think that means there is room to go with an even richer idle jet? The next richer idle jet is a 45/120, but the difference between that (2.67) and the 52/140 (2.69) is minimal. Looks like you would have to go to a 50/120 (2.4) to get noticeable results.

My MJ120 and MJ122 will be here Monday. I am fairly certain the MJ122 will get the main stack where it needs to be. In the meantime, I am going to put this low rpm bogging on the back burner.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2449
Location: London UK
Thu Oct 22, 2020 2:22 pm quote
Lean bog it is then. You won't be the last. 52/140 is quite strong. If that isn't enough you have other issues. When you drop to 122, the pilot will need to be even richer. This means, most likely, the BE3 needs to change to a BE5. Once you do this, start jetting again from the top. Getting ever closer.
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