Modern Vespa

I guess most people find that the screw in type sensors runs hotter. I would actually expect it to be hotter at the plug.

Reading up a lot on the subject, 360F doesn't sound hot at all for an air cooled engine…close to 400F being the point to back off, but not a big deal if it goes back down once engine load is reduced. This seems to be consistent across VW, Rotax engines, 2t AC dirt bikes, aviation engines and also cited for 2T Vespas. As compared to my bus, the biggest difference is in lubrication…a constant supply of cooled oil, but otherwise, aluminum pistons and heads, cast iron cylinders. Oh yeah, and it won't seize and throw me in the ditch if it overheats. There's that.

So 300F seems quite low and this is the only place I've seen that number mentioned. Gauges on air cooled engines can drive you crazy. Oil temp and pressure are all over the place as well as CHT's…unlike a water cooled engine.

Difference in temps between in head and under plug…Something I've mentioned once or twice.

Here is some practical experience I can share.

I have a 4+ mile run, up hill, in a canyon that always has some windy gusts.
Traffic runs minimally at 60-70 MPH.
I peg mine on 65.
I make this run every morning going to the shop.

It's a great stress test.
Gives me consistent data.

The settings for my carb - optimized on dyno for power - were allowing the in head readings to get into the 390s.
Once when not paying attention, I spiked to 433.
That's probably 50-70 degrees more then under plug - but I should test.
No seizing.

I currently have a rod (jetting) that holds temperatures in the 370s going up that hill. It's slightly too Rich to maximize power/allow full rev out. I will settle somewhere between the two and likely see temps in 380s.

For fun I will try that run measuring from both spots.
Will be interesting to see if my temps read 330-ish under the plug, or if such a long run, heat, soaks, everything, and keep realizes the readings.

Keep in mind, with uphill, wind, side, car, loaded with tools, and 65 mile an hour resistance, this represents really stressful conditions that are hard to re-create, even on in rally.

Thanks! That info is really helpful. After 2 days of downpours, decent weather today, so I will be back at it.

I finally got out for a good long ride today. Sputters up high, sputters down low. But rideable. CHT's briefly hit 330F twice with the screw in sensor, but mostly stayed around 290-300.

I was really pleased. Absolutely no motivation whatsoever for jet diddling. No way, not today. I didn't have the engine cover off once. Just enjoyed the ride.

I needed that.

I'm sure Mr. Gick will be seriously disappointed, but I will be suspending the jetting volume of this epic thread for the next 10 days or so.

I have been hard at work getting the VW bus ready for a trip with my boys to Quebec, New Brunswick and Nova Scotia.

I will be back at the Stella when I return to hopefully finish dialing it in for the late summer and fall season. I left it in a good place with CHT's running a lot cooler during a hard ride with a sensor/gauge combo that would be expected to show hotter temps. A good place to leave it for now.

If it's ok with moderators, I will post some trip reports and pics here in this thread. Non-Vespa content, but maybe relatable in some way. If it's not allowed, that's fine too.

On our way to Nova Scotia.

In my head - I can literally hear the low roar sound of ball bearings sliding rather than rolling as I open and close the VW bus side door, the clunk of it closing, and the feel of the worn smooth beige colored inside door handle.
Enjoy!

Yes! Just like that, but some fresh grease before leaving, so nice and smooth now.

Done for the day.

deeply.

Camping in PEI.

Funny enough I set my temp alarm light to 180 celcius (356 Fahrenheit) as a warning.
Why this temperature, I have no idea. I have the screw in head temp sensor and I can reach the 360 Fahreheit if I push hard up hills.
So far no seize with the BGM and its running ever slightly rich with a darker than ideal plug and very slight splutter through the rev range.

I have the feeling I have also set the temp limit light a little too low, but as everyone knows, You only know the real limit when it seizes 👹

My highest temps were reached during mid range cruising, while pushing it up hills and greater engine loads seemed just normally higher. I will have to test it again at sustained mid range to see if the latest round of jetting and sealing up the head helped.

We made it home from our trip last night. 4 States and 4 provinces in 8 days in a '73 VW Westfalia. It reliably plodded along at a steady 100 kph the whole way without a hitch. It's about all you can reasonably ask from it. Some final highlights and back to Vespas for awhile.

Thanks for humoring my bus trip photos. Vespas and Vdubs are complimentary interests for me. My first Vespa led me to my bus. Wrenching on the bus brought me back to Vespas.

Pouring rain here again, so no jetting adventures. I have a to-do list from Jack of things to try that I will get to.

Trying to get back my mo by redoing the Stella seat;cleaning rusty or broken hardware and replacing the tatty seat cover. Luckily the foam is in perfect shape. Nice little side project to spruce up the bike and add a little more comfort. I was using the 200 seat before but the latch fell apart.

Thought I was getting somewhere, but feels like I'm back to square 1.

I just can't get this thing to run at a decent temp. I have been all over the place with jetting and it still seems to be lean on top even with jetting that should be filthy rich.

The only thing I can think of is that it developed an air leak. If one doesn't turn up with pressure testing, I think I'm going to chalk it up to an unworkable combo, extreme user error or ghosts and call it quits with this engine.

An educated guess…

But piston head looks like typical "too rich at 1/4-1/2 throttle".

The burn pattern is too even.

Usually the pilot and main are too small. But it'll ride ok, and the temps will be within a reasonable window because the mid is doing all the work.

But the temps will be all over the place, which will depend on how you're riding.

Plug is dark with slow riding because it's too rich and the small pilot stops it from stalling. Engine just feeds off the residual rich conditions.

Plug is clean and lean looking at WOT because main is too small and is able to run off the rich mid.

I'm guessing temps drop quite quick at WOT, when you roll off the throttle.

It's been a real puzzle. Jetting has lately been 55/100 pilot, 100 AC, BE3, MJ's from 128-138 (Si26).

I thought I was good with fuel flow after checking the flow rate through the hose, etc. A 138 will splutter clearly rich at WOT in 2nd gear, A 135, fainter splutter, so I thought I had that sorted; 128-132 should be about right. It FEELS good, with 4 stroking confined to 1/8 throttle and below.

The problem is CHT's still getting high with sustained 50-55 mph cruising. The longer, the hotter. Doing a plug chop at these speeds shows a lean plug. When I go up on the main, I feel that additional richness at low throttle, but not really at higher throttle.

Some conflicting info I have seen repeated many times:

- Many have had trouble dialing in an Si carb larger than 20/20 on the stock Stella reed block, but also read 20/20 is too small.

- Airflow with an Si 26 (and 24/24) is too slow with the Stella reed block causing insufficient fueling.

The Si 24 or 26 is workable but not in its bone stock form. I'm not sure how the "reworked" carbs are different.

The stock Stella reed block is too small for a larger displacement engine.

I would consider enlarging the intake and going with a real reed block, but I know nothing about those options. This late in the season, it's just too deep a dive, so that would be more of a winter project.

The last possibility I will look at is that I picked up an air leak. At one point after 10 miles of sustained cruising, the idle hung at 3,000 rpm and took forever to come down. It did this once, but never again.

I'm stuck.

I think you are right to doubt the SI 26.26 (not sure if it was an E or a G) for this build. Do you have an SI 24.24E (not G) autolube in your parts hoard? If so, I would go back to basics by jetting that with an AC160/BE3/MJ135 mainstack and a 55-160 idle jet. If it bogs off the line, go richer on the idle jet. If it bogs at 1/4 -1/2 throttle, go richer on the mixer tube. You already know how to use the presence or absence of splutter at WOT in 2nd to dial in the AC/MJ combo.

I see VMC's instructions call for a B9ES sparkplug. Seems cold to me, but I would trust that. They also call for .9 - 1.1 mm squish and 18 degrees BTDC static timing. Hopefully you are in the ballpark with those.

If you're running a 135 main jet, you'll need to drill the float passage, too, or you'll have fuel starvation issues at extended WOT. I just went through this with the 24/24e on my 210 a few weeks ago.

Thanks.

I do have a 24/24 autolube carb. It's worth a try.

Chandlerman: Are you referring to drilling the float bowl passage out to 2.5mm or something else?

That's exactly what I'm referring to.

Agree with CM you need to drill. Doesn't need to be 2.5mm. If you have a 3/32 bit, that is perfect.

Yes. I've done it before. Just gotta make sure to go all the way through the first time.

Drilled out my 24/24E carb last night. I had tried this carb before but had forgotten to drill out the float bowl, so too lean.

I used a drill bit vice and did it by hand which was much easier. Months ago, I asked FMP about starting jets for my setup. He suggested: IJ=2.7, 160,BE3,132. I will start with 135 or 138.

I'm about an afternoon away from finishing up my 200 rebuild. Last night I pulled out the original engine mounts. It was a bit of a grunt but I got them out. There was quite a bit of vibration when I last rode with this engine so thought it would be a good idea to replace them.

If I'm not getting anywhere with the LML engine, Im going to throw the 200 in and get the last of the good out of riding season.

Recently, I picked up a cheap GoPro type camera. It works quite well. Hoping to take some riding videos during the fall foliage season.

I drilled out my carb as recommended by most, but after drilling I could never dial it in properly. I gave up in the end and ordered a Pinasco VRX-R carb.

Description from Pinasco:
"The Pinasco Carburetor VRX-R 24mm Vespa PX200 / Rally 180cc with auto-lube is based on the Dell'Orto carburetor. Pinasco modified it - the float needle diameter and valve are bigger, the hole between float bowl and jet carrier was bored open (from 1.5mm to 1.8mm).
Fuel supply is improved so the carburetor is perfectly suited for tuned engines."

After fitting the new carb it ran like a dream.
I obviously messed something up when drilling…and I guess its easily done..

I have a feeling that the new out of the box Spaco carbs are kind of crap. The reworked versions are probably better…at the very least in terms of deburring, finishing and quality control.

Eley and I drilled his carb last night and it was just the thing to get his main jet where it needed to be.

I have one of the re-worked SIP carbs on my P200, but it still didn't have the float bowl passage drilled, despite that allegedly being part of the re-work. It also requires a different (larger than stock: 4.4mm) float needle, so order a spare float needle (unless SIP is close by) if you buy one of these carbs.

When I retorqued the cylinder head last night, one of the head bolts was loose. This is the third time I've found it that way. That can't be helping. Twice I have pulled the head and found a deteriorated o-ring.

Time to replace that stud and reseal the cylinder. I'm wondering if I can seal the head with copper coat and skip the o-ring. Wondering also about the 2 paper cylinder foot gaskets. A metal shim might seal better.

Btw, I tried the 24/24 carb with 55/160, AC 160, BE3, 135. Temps went up to 340 after 5 miles of sustained 50-55. Put Jack's jetting in for the ride back: 55/100, 100, BE3, 135. Temps held at 320 or below. The 135 was too rich. The same setup with a 130-132 main ran quite nicely with the 26/26. No complaints. It's just those damn CHT's with sustained cruising.

Sounds like your temps are up because of a cylinder head leak. Jack's jetting is rich enough to offset the leak, but should not be necessary if you solve that problem.

That makes sense. At one point last weekend, the idle hung at 3,000 for a long time before coming down after 15 miles of sustained 50-55. Probably because at this point the engine was really heat soaked making the leak worse.

Studs can stretch, especially at the head end. Running a tap over a handful of studs I have, on some the tap runs loosely over the head threads but more snug on the case side threads.

I'm going to take one more solid run at this engine with the Si carb.

Check/replace cylinder studs and reseal.

Pressure test to ensure winning conditions.

See how it goes.

If I can't get it to run at reasonable temps, I'm gonna call it done with the Si carb and move to a PHBH 30 carb and real reed block. I think it's possible to just bolt it on, but would be better is the intake was optimized.

Either way, I would probably end up spending the last few weeks of riding season tinkering with the carb, which is not how I want to spend it, so a winter project for sure.

If it still runs hot after a good pressure test I will either just ride it within its temp limits or put in my rebuilt 200 engine.

I'm kind of itching to give the 200 a try. I never got to ride it much before it seized and I'm really curious to see how it goes.

Resealed the head yesterday. When I removed it, I didn't see any evidence of a head leak. Was really hoping the wonky stud was causing my CHT issues. I didn't pressure test, but it's otherwise not behaving like it has an air leak. Temps hit 345F after 6-7 miles of sustained 50 mph. Might as well be riding a VBB. I'm done with this engine for this season.

Throwing in my rebuilt 200 in the next couple days. Just got another engine mount to fight in. I will revisit the LML engine at some point when I install a real reed block. I will rework the case a little to get the good out of it.

The 200 just stock?

Bone stock, except for a SIP R2.

Will be pedestrian… fun but pedestrian.

Have so many stock px200 pass by… all needing a good tune. Lol

The 190 is probably quicker. Would be a good city bike as is, but not so much for the open road in its current state.

I went for the best ride yesterday. Perfect fall day. In spite of the unresolved carb issues…it's not gonna blow up or quit so I just rode, got some good video and enjoyed the afternoon.

Pressure tested the 200. There is a slow leak where the exhaust stub screws in. Last year, I resealed the same leak with copper coat and retorquing, but it returned after a few heat cycles. I'm not sure what else I could do to seal it. It's an original cylinder, no defects. Threads were good.

Exhaust paste is best…

Dries to a ceramic coating rather than staying wet. That stuff seals the best.

Copper paste and anti seize is for when you're looking at unscrewing it in the future.

Thanks! I will give it a try.