Modern Vespa

Just about ready to button this back up.
I am going to go with a .5mm foot spacer (instead of .8mm) and a .5mm head spacer (instead of none).

Timings don't change much E=176.5, T=120.08. Squish goes from 1.19 to 1.4mm, which is more in line with the tech sheet. 1.8mm is probably too much. Will check with degree wheel and solder.

I was also wondering if a 23t clutch cog from a p200 would work with the 68t primary. Reducing revs makes sense but I don't want to change the primary at this point.

Thanks.

For what it's worth, I don't think you need to change anything unless u want to.

You were running on gear oil and petrol.
If you re-seal with a good bond (I use Honda bond because the dealer near me Carries it) I suspect u will have no heat issues at all.

One man's opinion.

Thanks. That got me thinking. Even if the clutch side seal was not leaking air, the mixture would get diluted from so much oil coming in. Plus, as you said, if it can suck oil, it can suck air.

Just caught up on this post and the VMC tech sheets stood out to me. I have a Stella with a VMC Super G 177 kit (with the CAST head), mazzu 57mm crank and Sip road 2.0. Stock spaco 20/20 carb on the LML reed block with the center bar cut out and a "GGR Hot Reed" which is made from Polini carbon reed material. I did not smooth out the intake tract or anything; I just cut the bar out and threw it back together.

My paper said squish should be 1.0mm +-0.1, but with no base gasket at all it was still ~1.25mm. I used the thinnest base gasket it came with and did not think about it again as I did not trust myself to lap the head down.

I wonder if there was an interim update with the kits themselves or if they put the wrong specs in?


I am also running into some temperature issues though. I may make my own thread about it. 130 main, BE5 mixer, 140AC. No filter on the carb. It runs like it is slightly on the rich side; especially right before the powerband kicks in, where it 4-strokes somewhat heavily. I have just ridden around that spot as I got tired of messing with jets. When I went from 160AC to 140 per the guidance of some users here, that deadspot got much worse but I was told 160AC is dangerous to run on any 177 kit as it leans things out too much.

I can cruise at about 53mph on flat ground indefinitely as the CHT goes to about ~330F and stays there. If I try to cruise any faster or if I need to go up any incline it begins to creep up at about +1-2F every 5 sec, and the last time I had a long ride it got up to 357F before I slowed down and let it cool off. This is at about mid throttle so I am wondering if it could be the stock air shroud and flywheel fan design as well? Or the stock throttle slide's cutouts causing it to lean out slightly?

Temperature is way too high for longevity. Crusing at 53mph on this should be under 280F, maybe way under with acceptable rich jetting.

What could it be? 130 main on a 20/20 carb still too lean? My only richer main is a 135 and I have trouble believing that is necessary for stock carb, non port matched case and a basic SIP pipe...

Could it also be that the 23/64 gearing means that in 4th the flywheel/fan is spinning too slowly for adequate cooling?

The main jet on an SI carb is the whole stack. 130 is a big jet at the tip but with a 140AC it's not going to be very rich in the atomiser. For a DR kit your current jetting could be ok. Modern kits need more.
If the speed of the fan is important it's getting too hot.

I have seen a number of tech sheets for the Super G with squish all over the place. The one you posted is the tightest, The tech sheet I have was something like 1.3+/-.1mm but I have seen it listed as high as 1.7mm. My kit worked out to 1.2 with a 60mm crank. I think VMC has been revising there tech sheets a lot.

Jack and I worked on reducing heat with jetting and ended up a lot richer than you are now. (AC100/be3/130's main with 55/100 pilot), but it's possible we were jetting around an air leak.

You sound like you're not too far off in terms of your temps. As for your gearing, I'm not sure how it would effect cooling. Air cooled fans have a maximum rpm beyond which spinning it faster won't cool more. The limitation becomes the cooling shroud being unable to flow more air. It's a trade off between reducing engine speed to the point where it's cooling, but not lugging or spinning it faster to get more air. from the fan. I guess it depends on engine load. I don't know where that point is.

gummy, in addition to all the good advice above, a few things spring to mind...

1) Have you drilled the float passage on your carb? if not, you're not getting the benefit of that 130 main (or the 135)

2) I'm in 100% agreement that your temps are way too high. You should be in the 240-260 range mid-throttle cruising.

3) the richer the air corrector, the harder it will be to get 1/8-1/4 throttle to feel smooth because it interferes with atomizing the fuel. Mix will be correct, it just will tend to feel a little rough. Ray8 has bought some specialized atomizers off SIP (I forget the brand) that he swears by for fixing this sort of problem. In the meantime, have you tried a BE4?

4) You can now get high-flow fan covers for the Vape if you think that will make a difference. If you're making changes at the margins of heat reduction, though, you'll probably get more benefit (or at least a better cost-benefit) from painting the cylinder and head with black hi-temp paint.

5) What's your ignition timing set to? How'd you set and measure it?

6) Have you run a recent pressure test to ensure you're not trying to jet your way around an air leak?

7) What's your cold compression? Higher compression == higher temps

8) As a general rule, I think sustained temps of 320F are about the max safe temp to not materially reduce the life of your parts. People's opinions on maximum "safe" temperature (i.e. not seizing) seem to vary a fair amount, and are heavily dependent on where the CHT is located and what type it is (under plug, screwed into the head, attached to a cylinder stud).

The CHT is also a trailing indicator, so by the time it tells you that you have a problem, you may already be well aware of that fact as you stand on the side of the road cursing.

9) 1.2mm of squish should be fine for your kit. Most modern 177's (and other performance top ends) call for .8-1.2mm, depending on the kit. Assuming you pass the leak test, adding a .25mm head spacer would be the first thing I'd try in your situation to get compression down a little and see if that helps with the temps.

10) What's your gearing? Are you trying to run too far under the power band when cruising? If you're on stock Stella gearing (68/21), 53 MPH should be on the power curve in 4th gear speed with a VMC, so motor buzzing happily away.

1) Yes I did this when I did the 177 kit. I followed FMP's guide.

3) I have only tried BE3, E3, and BE5. Is changing the atomizer similar to raising or lowering the needle on a sidedraft carb? Or changing needle taper?

5) It is set to 18deg BTDC, as per my Super G spec sheet. I found TDC with a piston stopper and I used the fan + timing light to set it. I followed one of FMP's guides with scratches on the case.

6) I don't have a pressure tester but I should do this. I struggled with an airleak at the airbox/reed block/carb and fixed it with permatex 85420. I don't believe I I have any major symptoms of a potential airleak (like very unsteady idle/mix after a pull) besides the general high temps.

7) Don't have a compression tester but I definitely need one.

8) For reference I have a trailtech CHT gauge under the plug.

10) Malossi 23/64 straight cut with a T5 short 4th. It sits just at the start of the pipe/powerband in 4th. To accelerate much past that I need to drop down into 3rd. I understand that this is a bit tall for my setup but I plan to do a MRP intake + PWK + port matching + new pipe this year. I am hoping to push about 18-20hp when all is said and done.

Fan or fan cover?

Fan.

I would imagine that people have tinkered with cooling on Vespas. Aside from having a fan that pushes more air, is a cooling shroud that is either is larger to accommodate more air or a way for more hot air to exit. In the VW type 4 world, some building high performance engines use the Porsche style cooling shroud. The fan is huge, but there is a lot more space between the engine and the cooling shroud.

Also, the 200 cylinder has a lot more mass and thicker walls compared to a 177/187. As many builders seem to able to keep temps under control with 177 builds, I doubt there has been a lot of interest in revamping the cooling system. I have seen the occasional reference to water cooling, but no one seems to be doing it. Probably because it really hasn't been needed.

I am wondering if I should use the metal reed stop for the reed block. The instructions and videos I've seen for Boyeson reeds say that it can be omitted. Not sure if it's a great idea. I have removed the center bar and matched the reed block to the carb box.

I was also wondering if a 23 tooth clutch cog from a P200 would work with the 68 Stella primary .

I'm not sure if omitting the reed stop is a great idea either. I did it anyway. So far, so good.

The 23 tooth cog from the P200 does not fit the 68 tooth primary. DRT sells a 23 tooth cog that does. Not clear why you would want one, though. You will be leaving a lot of max rpms on the table. Best bets are a 21 tooth cog if you have a 35 tooth 4th, or a 22 tooth cog if you have a 36 tooth 4th.

Thank you. I have been running a 22t tooth cog that feels pretty good. I'll stick with that.

On DR177 I was with 22/68 and 35T 4th. Tried 23/68 but not enough power.
On Super G at first was 23/68 and 35T 4th. It screams like mad but not really much acceleration.
Then I go to 23/65 and 36T 4th and absolutely happy with it.

Thanks! I'm glad it worked out. I guess going up to a 23t reduces the revs enough that you would want a short 4th. With the 22t, I haven't noticed the gap between 3rd and 4th. It's revvy, but not screaming at 90 kph either.

Why, oh why an allen head bolt here? And a shitty one at that.

All of their Allen bolts are the absolute lowest quality. I replaced my cylinder head ones already with much better bolts. One of my exhaust ones is stripped but I've got no leak there so I'm not gonna replace it till I need to.

I might have to remove the cylinder to get a clear shot at welding on a nut. Probably replace the bolts with hex head before reinstalling the cylinder. At least it will be leak free.

The fact that VMC consistently ship garbage hardware with their kits is enough to put me off trying them, even if the fundamental engineering is solid.

I was a little disappointed with the casting quality of my Quattrini TV-210. Significant mold seams inside the ports, but quality was good otherwise, so I'll deal.

It's definitely put me off VMC kits. Granted, it was a cheap kit, but the awkward way it bolts together and the cheap fasteners have made it a real chore to get air tight.

i gotta ask. . . did you use anti-seize on the allen bolts for the cylinder?

No. I will this time though.

that would be paramount regardless of quality of bolts/screws. You want it to remain serviceable, you have to treat is as such.

Got the flange bolt out, but of course, the o-rings fell apart. Could I just use sealant? I haven't been able to find replacement o-rings in the US. I have tried ordering generic Viton o-rings after measuring the old ones, but haven't found ones that fit.

Found a source!

https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=368_65_68&products_id=24154

I've had luck in the past hammering a posi-drive bit into the rounded off allen-head screw. Worth a shot next time.

Great find.
I suffered same leak.
Ended up turning the flange on lathe to create a secondary seal at the corner.
Somewhere in the last 5-6 pages of my thread if ur bothered to look.

The hardware is unworkable. Allen heads are shallow and strip…

The o ring seal is a miracle of clearances. Slightest movement of flange and it doesn't seal. Really the week point on these cylinders in my view.
Otherwise has been pretty wonderful.
Have a look at my fix if helpful.

Thanks, I'll have a look. This kit has definitely been difficult to keep sealed.

I had a look at the modification you did to the exhaust flange. On my kit, it's a complete 1-piece stub that bolts onto the cylinder. The groove for the o-ring is set in the cylinder.

I think part of the problem has been that both o-rings have failed and leaks have developed at both points in spite of replacing the original rings and hardware and resealing a number of times. This engine has had solid pressure tests before leaving the bench. It just doesn't stay that way.

I'm wondering if it's possible to omit the o-rings and just use kopper coat or something similar. I have not had this problem before even with old stock heads.

Oh - that's interesting.
Suppose they knew they had an issue.
Little surprised that it's failing given that design (basically put it where I put mine).

The heat of the exhaust is probably eating the O ring - it's getting exposed in some fashion.
Frustrating.

What do others use to seal their exhausts?
Wonder if maybe a copper crush washer of some kind - lit what a spark plug uses - might work.

Is your exhaust hitting the bottom of the scoot in some fashion that is adding to wear through prying and movement?

No, nothing like that. I will just retourque a couple of times once it's sealed and I'm riding it again.

Might try a silicon o-ring. Might withstand the temperature better. Not sure what is supplied but might be lower temp spec.

Thanks, I will give it a try.

Before you try to find the right silicone o-ring -

I'd be tempted to try filling the o-ring groove with silicone so it sits slightly proud, letting that go off for a day. Then fit the stub, using silicone to seal. Wipe off excess, let it go off again before trying the pressure test.

That's a really good idea. I will give it a try.

On my Super G I used original o-ring and copper silicone. Work perfect.

This is almost exactly the instructions for RTV Red (hi-temp). They say tighten the bolts/nuts hand-tight, let it sit for an hour. Then torque to spec and let sit 24 hours before operating.

Interestingly, RTV Copper doesn't call out the hand-tight portion of the process.