Modern Vespa

I'm running a 30mm PHBH Dellorto on a 90's era Malossi cylinder. I have a Mikuni fuel pump connected at the Malossi reed valve manifold to provide pressure for the pump, it works fine.

On the by pass line I do not have any restriction. Is there any recommendation on what could be used in the by pass line to provide the appropriate pressure?

Have read the float valve jet should be around 300 would that also be the same for fuel pump carb?

What is the philosophy on float weight? Heavy float or lighter float?

When pumped it all doesn't matter in the carb. 250 will work fine.

We all use the top of a spark plug as the bypass restrictor.

Are you having any issue or just concerned about this?

What scooter?
What model?
What size motor?
What mods?

or

Try SEARCH first...
http://modernvespa.com/forum/search.php?mode=results

Thanks Jack I will give that a try. Should add a little more restriction than what I have now.


Engine stats; 200 Malossi Alum cylinder- 60mm crank, o-ringed profiled (HRA) Piaggio head, PK flywheel, Malossi reed valve, 30mdelOrto, Mikuni fuel pump, Polini 8% OD, banded clutch Pinasco springs, PM Tuning exhaust LH

On the float weight seems like one can choose 6g to 12g whats the average and do you go lighter for fuel pump?

Would only need to go lighter if you were having toruble with delivery, which I am sure you're not.

Why you put the return pipe back in the tank, could have been connected to the outlet and out the way?

Here is my Dellorto PHBH info...

I've found a note saying that this is great info...
http://jonathanvingiano.com/misc/dellorto-manual.pdf

This looks like what I remember printing the most... Good tech info (incl float weights & needle options.
http://www.ducatimeccanica.com/dellorto_guide/dellorto_3_2.html

BAsics?
http://www.smellofdeath.com/lloydy/jetting.htm

Parts Catalogue
http://www.dellorto.co.uk/product-category/dellorto-motorcycle-carburettors-parts/carburettor-parts/phbh-parts/

You don't need any restriction if you're going back into the tank and don't have any running issues.

Most people connect the hoses in and out of the fuel pump. The restriction goes into this connector hose to fine tune the pressure that the carb float needle sees.

In your system if you are not getting adequate flow to the carb, a restrictor in the hose going back to the tank will increase the pressure to the carb.

wow great info on the carb never seen that much detail. Really like the smell of death tuning guide I'm going to start with that procedure THANKS.

thank you for the tip on Eurocarb they kindly processed my very small order and I have my parts!

Going back through this scooter to bring it back to better condition. Just got the stator plate re-wired at scooterwest with a new pick up installed.

Going to go through the jetting process again, it was not running that good at higher speed. Here is where I am now:

P200 Malossi CVF II - 60mm crank Profiled stock o-ringed head 8% overdrive PK flywheel PM Tuning Exhaust

Malossi Reed Valve
Mikuni Fuel Pump

PHBH 30
Slide 50
Pilot 64
Main 148
Atomiser AS266
Needle X4
Float valve 250
Float 8.3 gr

Seems from reviewing other's jetting stats my pilot seems big. Malossi instructions call for a 63 pilot is this antiquated?

The main also seems big which may explain it's poor running. I have purchased the BGM pilot pack 50-72 the main jet pack 125-147 and the needle pack x2, x3, x4, x5, x7, x13, x25, xx32, x44 and x61. Going to try and follow the tuning procedure hoping I find a good arrangement. I'm not clear on where to begin in the needle selection any suggestions?

Seems like its too rich all round. You might want to get an AS264 as well. There is a chance you might need it.

Thanks Jack! Is there a reference on the needle values for the set I'm testing with?

Got the stator back in and timed to 17 degrees. Rebuilt carb with new o-rings and new jets.

Engine started easy with a 55 pilot x4 needle 2nd clip and 135 main. Air fuel was 1 turn out. Adjusted throttle stop to set idle speed. Scooter idled on it's own not perfect but seemed decent maybe a little fast. Engine revved clean on stand. Engine speed reduced quickly. That is as far as I got.

This was replaced when I put things back together.

When the idle won't set really slowly the pilot jet is too big. With the correct (smaller) pilot jet the mixture screw will be a little further out. On this carb, slightly more than 2 turns would be ideal to start the jetting in process with.

For exactly this reason, for very many years a spare carb rubber mount is one of the parts always in my glove box. Some cables, a new CDI and duck tape are some of the others.

Not sure what you mean by needle reference. Almost certain the X4 will be too rich at 1/8 but we'll go through the process and see where it ends up.

Is yours and old Malossi 210? Any tuning on it? How thick is the base gasket? And squish clearance?

17 degrees timing is usually a cautious starting point but not where the power is Leave it there until jetted closer to correct.

This was interesting to me since I don't remember it as many years pass. Started with 3mm solder and compressed. Measured 2mm so I tried again making sure I got the solder to the cylinder wall and edge of piston. This time at the edge I measure just under 2mm and tapers (gets bigger) as it comes to center but I'd call squish at 2mm.

It is the old Malossi, I built it in 1994. I'm on a 2nd piston, the 1st one had a piece of piston break between the rings and fortunately it behaved like a ring for a time and no destruction. The case ports are matched upper transfers lengthened for longer stroke 1.5mm base gasket minimal exhaust port mod no mods to piston.

What I meant by reference was how to understand the needle value. I have the needle pack from BGM that has 10 needles but don't understand the rich/lean characteristics for each size. Thanks for walking me through this.

Going to need to need to fix that squish while you're waiting for the jets to arrive.

Put the base packer down to 1.00mm and skim the rest off the head (180 to 600 wet & dry paper, sheet of glass) until down to less than 1.20mm clearance. Nearer to 1.00mm clearance is better. That gives you 0.50mm to take off the head......or about 30 minutes on the glass.

Unless you have the 0.50mm head gasket on there. If so forget that and job done

well that's not exactly what I wanted to hear.

Was able to do some initial testing.

Removed carb to adjust air fuel mixture 2 complete turns out.

Took scooter for a ride. Scooter ran good. Engine would pull itself into power band at 1/2 throttle. I allowed engine to perform by itself and did not force it into the power band.

Once I felt more comfortable I ran the engine hard and held it open to feel the length of power band. In 3rd gear at about 1/2-3/4 throttle once the power band began so did some pinging. When I forced the power with more throttle there would be pinging in 3rd gear.

4th gear was gutless. If I got into a tuck the engine would eventually begin to pull closing the throttle improved the power not by much.

When I got back I adjusted the air fuel. 1/4 turn OUT the engine stumbled and died. 1/4 turn IN the idle was more stable than 2 turns OUT.

Removed the spark plug to check color.

Goes pretty much garbage, as expected. Get the squish fixed and cylinder down 0.5mm and she will be a whole load better right away.

I found this which covers all of the needles I have with exception to the X61





Last edited by hibbert on Thu May 17, 2018 11:15 am; edited 1 time in total

I charted the needles I have so I could work on getting a better understanding. Am I correct A) is the initial diameter B) is the final diameter and C) the length of taper?

I’m running a PHBH28, Malossi 166 & LOTS of mods...

Here is some (probably) useful jetting info:

X2 2.50-1.8-24
ok except leaning @ top of revs

X21 2.50-1.0-20
too rick @ mid range & cruise
Great above 1/2 rev when hard on gas

*** X4 2.48-1.8-20. MILLE?
V nice when on th gas, v noisy @ cruise
Still to check top of 2nd-3rd

*** X7 2.50-1.8-20
Seems great, no leaning, noise @ cruise
Seems ok at top of 2nd

*** X61 2.46-1.8-20

X5 2.46-1.8-24
Unlikely, due to 24!

Poss. Ideal:
2.50-1.4-20
2.48-1.4-20
2.48-1.6-20
2.50-1.6-20

Having said all that... I’ve worked out that a X27 is the best... I’m waiting to get one to try, but after 3500km track I stand by that diagnosis.

https://www.sip-scootershop.com/en/products/jet+needle+dellorto+x27+_94772700

A) is the initial diameter
This is IDLE to about 1/2 to 2/3 throttle.
Thinner (ie Lower) number, means it’s RICHER
I initially thought 2.46mm would be awesome, it ended up being WAY TOO RICH.

B) is the final diameter
It is the size it the TIP of the needle, ie WOT.
1.8 seemed to be the “best”.
If you are finding it’s leaning out or not enough fuel @ WOT then use a thinner tip.
I found 0.60mm to at least 1.20mm (even 1.40mm, which I thought would be cool) was simply way too rich.
Remember: thinner (ie SMALLER Number/mm) means it’s gonna be RICHER.

C) the length of taper?
This it the “transition” from about 1/2 to 3/4 throttle TO FULL throttle
This is actually a STRAIGHT LINE, even though it should theoretically be a curved transition!
I put one (that I had a double-up of) into a drill, spun it & used sandpaper to try to change the taper, but went too-hard & it was crap... next time I’ll use 1000grit... however I still think (with finesse) it would be a great way to fine-tune.
... if you find it’s LEANING (pinking/pinging) at about 1/2 to 2/3 throttle then use a 24mm taper
Of it’s LEANING (pinking/pinging) at about 2/3rd to 3/4 throttle, then use a 22mm taper (it will add more fuel lower down)
If it sounds sweet, but you want MORE FUEL at FULL REVS or the TOP END (ie 3/4 throttle to WOT), then use 20mm (it dumps way more full when you give it a wellie)

NOTE; hopefully all my thicker/thinner are correct, feel free to change things.

I

hibbert, If the mechanical set up, is not near ok, then no amount of jetting will make it work. Seems like you have tried a lot of combinations already and you will get it running reasonably but the gutless 4th and pinking is not going to get any better.

If jetting alone is to fix the gutless 4th it needs to be weaker and to fix the pinking, richer.

Yours is an old set up but they can be fixed and even tuned more powerful than a new MHR.

I can help you get the jetting right, once its sorted mechanically.

First need to get the cylinder off and set it right. I did have an after thought that you might have one of them old cylinder heads that don't work. Better post a picture of the head too, while its off.

Thank you SubEtherBASS I have charted the X61.

Thanks for hanging in with me Jack. Took a few more solder pressings and came out with maybe a more accurate measure I'm seeing 1.8mm. Still not where you are suggesting.

I removed the head. The streaks that you can see are the solder pressing marks. I was pleased to see I got 6 very good pressings uniformly around the bore. I feel good about the measurement.

This is the packing plate I believe 1.5mm

This is TDC

Bottom Dead Center

engine

Head is not the worst generation. Setting up with this is worth a try.

Barrel is in great shape. A fair amount of port work done in there too. We should check if someone has had a fiddle with the heights.

Can you measure from 2mm inside the port to the cylinder top.
0.00mm accuracy preferred

Exhaust port
Main transfer
Secondary transfer
Centre boost
side boost

Have to keep in mind the up geared primary. Is that 23/64 or more?

No more mucking around... Borrow & Try a different pipe

They often end up having a shortish powerband, mainly rev based.... Different exhausts, completely different results.

I tried taking some measurements but I don't know how good they are. I may need to treat myself to a digital caliper. This is what I came up with:

Exhaust - 33.1mm
Main Transfer(s) 46.1mm
2nd Transfer(s) 47.2mm
Boost 47.3mm

I didn't measure all the boost ports it looked like the center comes in a smidge lower than the outers but could be illusion.

Also this measurements could be a smidge long. I could only fit the caliper into the exhaust port so I used a 0.011" feeler gauge to find the top of the port with the piston and plunge measured the distance.

I don't know the teeth count on the primary my only recollection was that it was 8%.

I hear you, there is an exhaust issue that I was going to raise further along in the project. Thinking about a big box.

Based on these there will be no need to sand the head on glass. This kit is a long way from stock and has been slightly over tuned for your gearing.

Put in a PX150 primary, close the squish and a high rpm expansion and it would scream. As she is now, probably quite impressive in 1st and 2nd. 3rd not so much and 4th forget it

The good news is, to pull your lets say 'long' primary it is just about possible. Will need to put on the thinnest base gasket you have and see how much piston is poking out. Your TDC seemed slightly under before but if you can get to 1.3mm with a thin base gasket, all will be fine.

Measure the poking out piston with your feeler gauges. Not much chance of going over though.

Thinking about dusting off the P222. Have jet packs, silencer stuffing, and cylinder base gaskets 1.0 and 0.80mm. Do I try dropping the cylinder or is the primary needed to make 4th do what it should? May get a Polini box as part of the project or a suggested box for this tune. It's just sitting here neglected.

Pulled the head to get better measurements. Some were good some not better start over. Was able to get a PBT and stroke measure too. Put the dims into the calculator and ran 4 scenario's for different base gaskets. Have no idea what any of if means this is where is sits now.

Stroke 60.33mm
Conrod 110mm
PBT +0.83mm above cylinder deck entered -0.83 in calculator
Squish 1.80mm
Ex 33.25mm 181.15°
Tr 46.65mm 124.59°
2Tr 47.75
BD 28.28°

Not a lot to do to this one

These new numbers are way better than the last set. Really not so bad.

If you can get PBT 0.3mm less to 0.5mm poking out. The raise the exhaust port up 0.75mm. Widen as far as you dare, 50mm arc length would be nice. Then this would be set quite well.

Would expect it to pull taller gearing but would go best with 23/65 and 36 tooth 4th. Worth giving it a go and see if the carb sets up.

Great it deserves to be stretched out again. Pulled the cylinder and found a little surprise a gasket sandwich. It's been so many years I forgot what was down there a 1.5 + 0.25 = 1.75. Also with my failing eyes think the PBT is less than reported think it might be closer to 0.75. My feeler gauges at .030" and .032" seems a P hair more than 30 (.75) and less than 32 (.80).

Raising exhaust port 0.75 to 32.5mm and with a 2.0 base gasket PBT becomes +0.5 should leave 2.05 squish. How does this work?

EX 185.22°
TR 126.21°
BD 29.59°

Exhaust width is 40mm on paper.

All seems as expected but I don't see how you have 2.05mm squish. If the piston is 0.50mm out the top of the cylinder and the head typically has 1.5mm built in. That means squish is 1.00mm with no head gasket. Where are you getting 2.05mm from?

Those old exhaust ports were pretty small. On paper is the same as arc. Lets say that is 42mm. Could be opened out to 50mm. The issue is the cylinder studs. Should be able to get to 46mm easily but more needs a radius as straight would break through into the stud.

Thanks Jack I'm basing the squish on what I measured in 2018 which looks like 1.80mm. If this is correct adding 0.25 more at the base would make the PBT 0.5 as you suggested and moving to a 2.0mm base gasket I think will change squish from 1.80 to 2.05 if the math jives.

Not sure what Hot Rod Al did to the head.

Safe would be to widen exhaust maybe 2-3 mm on the sides? I like the Pinasco shape leaving bottom width alone and taper increase to top?

Still good at 32.5mm for the Exhaust?

Something still not right here. If the piston is 0.5mm out of the bore. The squish is going to be tighter. That head has +0.75 written on it which usually means the amount of squish built in.

Earlier in the post a picture has TDC shown as negative deck.

Typically an old 210 with a 60mm crank and a 1.75mm packer would be slightly negative deck. And this confirms the picture.

the photo I posted showing a negative TDC is WRONG not sure why I did that.

The PBT is 0.75-0.80 above the deck sticking out. This is with 1.75 base packer.

currently
Stroke 60.33
PBT 0.75-0.80
Squish 1.80
Packer 1.75
Exhaust 33.25
Trans 46.65
2nd trans 47.75


TDC feeler resting on deck piston above gauge