Modern Vespa

My plug colour is not that bad. I was told it was a little rich which I can live with. I have no flat spots. Idle is rich but I may fit the 55/160 and try that again with the 130 main jet. The bike still lurches from time to time when coming off a WOT run in 4th. I have no idea what is causing this, but I can live with it.

It's not perfect but it may never be. When the time comes to change kit, I will opt for something not as tuneable. Maybe the BGM 187 Pro which is just bolt on.

It's my first Vespa and I wish I had gotten one sooner. I really like it.

With the 60, 58 and 55/160, the bike starts after two kicks from cold. I think the richer idle jets are just too rich. The bike lurches with the 68/160 fitted so I don't think being lean is causing this issue. I would like to lower the squish from 1.4mm to 1.1mm but that will have to wait.

I am off out for a biggish ride in the morning. Can't wait.

The 60/160 has to be rich enough. AC120/BE4/132 is plausible as correct. With a race cylinder the lower throttle has to stay slightly rich and the main jet has to be not rich and closer to optimal.

The 60/160 and 120/BE4/132 seems to be good all round, if a bit rich at idle. WOT in 4th on flat road gave CHT of 155. It was dropping by a degree or so but had to lift off for a roundabout. Surging still happens about a second or two after WOT to no throttle. A quick blip of the throttle sorts it out.

Had a good 50 mile ride today. No issues. Starts two kicks from cold and half a kick when warm. All good.

Awesome, Roody!

Three kicks cold here. Like timework.

Quick tip:
Don't go from WOT to no throttle. Blip it a bit on the way down to clear the main circuit.

Agree. After a WOT run I usually pull the clutch and blip the throttle a few times. This stops any surging. Not sure why but it does. Maybe masking an issue but it works for now. I don't WOT very often.

How many rpm in 4th at 155C? Sounds like it's still slightly rich. Some of the surging will be because the inlet duration and transfer ports are not matched to the kit. With the richness the crankcase will run a bit wet and take a few blips to clear.
Remind me what the gearing is.

Its about 7400 in 4th. Not sure of the gearing. I know it's a 21 tooth clutch. I presume standard gearing.

21 tooth on a EFL stock box. Thought it would be higher.
When trying different main jets now, just look at this rpm in 4th on the same stretch of road each time. The fastest one that holds temperature is correct.

I shall do this tomorrow and report back. What gearing would you recommend and how do I change this?

Thanks.

Good evening. I have deduced that the 132 main is the best jet for my setup. It's ever so slightly rich but does not affect anything that seriously. It still splutters at max revs and when applying slight throttle when already moving.

In 4th gear on a flat section of road, the engine seems to max out at 7500 - 7700 revs and still sounds good. Max temp at this point, after the temp has settled is around 150 degrees C. Always gets warmer when coasting in 4th with temps getting up to about 170 degrees at partial throttle.

I have put another 400 miles on it over the weekend with no issues at all. Still starts from cold with 2-3 kicks and 1 kick when warm.

Thanks.

Mark.

Hello again. So the bike is running well apart from two minor things. The surging after periods of wot and this one... When in 4th gear, say doing around 50 to 60 mph, the engine heats up quite a bit. I am probably around 1/3 to 2/3 throttle. The engine temp got to 176 degrees C. As soon as I WOT the temps come down to around 150 to 155 depending on incline.

I have just done a WOT run for 4 miles on a variable incline / decline dual carriageway. Max engine revs was 7500 with a max speed of 72 mph. Temps hovered between 149 and 156.

Is the temp of 176 safe when using partial throttle in 4th? It does not seem to have a negative effect on the engine. I am just curious. The surging does not happen as soon as I close the throttle. Normally starts to happen a second or two later.

Thanks.

Your cooling at WOT is logical as fuel is the coolant . You're getting too much air prior to the 4th WOT surely.

When I don't want to travel at WOT in 4th, and the temp starts to rise, I blip WOT a few times and it brings down the temp. Not a massive issue as I can control it. I just wanted to know why it heats up a bit. I have no Air leaks as the leak down test is good. Maybe I need a smaller air corrector. I am running a 120 at the moment. Thanks.

Not implying you have air leak but as main jet at wot takes over it's clearly hotter before this stage with AC / mixer combo . Have you tried the ac140 be4 and a 125 jet as base. That will work fine on my dr177 albeit bit ric but a 140 be5 124 is spot on now for me with a 50/120 pilot. It's all very slightly in the rich side but results in nice brown plug and good top speed and general running . I run on the safe side,it's capable of getting a few mph more top end dropping my main but heading into paler spark plug territory. Many of the advice for jetting 170 kits on here often falls with the ac140 be5 and some large MJ . Can't imagine your 190 kit being radically different

Last edited by ferriswolf on Tue, 20 Sep 2022 09:59:52 +0000; edited 2 times

Agree.

To much air doesn't necessarily imply a leak. Your description is, leaner or more air than you need at part throttle and colder to nominal at WOT. Mid range jetting a bit lean? Is there an atomizer richer in that area? Another option would be to look at bottom of slide in carburetor, if it has a notch or cutout in it, putting in a slide in that is flat will richer up part throttle.

The slide has a notch. At work so can't identify the slide.

He's on a be4 I think which is the richest mixer. Are you sure that your mj is correct as you have an ac120 and is it maybe the case your mid range temp is normal and you are drowning the engine at wot hence it cooling dramatically , eg very rich wot. You are judging temperature change from mid which in fact might be the normal range for your rig ???

I am on 120/BE4/132. I think the main is slightly rich but nothing way over the top. I need to know what is the max safe temp my engine can run. Some say 150 C, other say that 200 c is safe.

Have you headed to pinasco website? Find out the temperature tolerances for your cylinder kit?

I cannot find any information. I have emailed them for some info.

What slide in the carb now?

Not sure. Standard one that came with the BGM Fast Flow 24/24. Has a groove in the bottom of it.

Might need a sip slide
https://www.sip-scootershop.com/en/product/throttle-slide-sip-42_84920420
With this slide it will need less main jet too.

I will get one on order. It says it helps the lean mid-range. It appears that is exactly what I have. Thanks again.

£33 delivered. Fuck sake.

Can't think of a way offhand, but if there were a safe way to block the intake on the top of the carb, that feeds air to the slide cutaway, you would essentially have a flat side.

With a filter I taped over the hole on the bottom that feeds that intake.

Hello. I did not realise the slide was fed via another source than the venturi. I will have to take a look now when I am home next. T

Thanks.

The cutaway on the slide you have pulls air through here, from around 1/4 to 3/4 throttle.

Well you learn something new every day. Thanks for that. I suppose that could be blocked off.

Blocking this air hole will reduce the air. Some will still come from the spring plate.

Might try and cover that hole. Although it won't stop all the air, it may reduce it enough to lower my mid range heat issue until my new slide arrives next week.

It won't stop all the air, but neither will a flat slide with an unblocked air port. The slide isn't a seal.

Covering that hole is VERY equivalent to a flat slide, based on tests with several carbs.

BTW it's just a method to see what results with your setup. There are three slide variations SIP currently supplies (more are in the works). In my anecdotal experience, I couldn't get a flat slide to work with the BE4 on a 24 carb. Hoping you have better luck!

What atomiser did you use or what slide? Thanks.

Favorite-to-ride of the three bikes in the garage has your BGM carb, intake and transfer ported BGM 177.
55/160 idle, BE3/160/128mj with this slide and a drilled stock Piaggio filter:

https://www.scooter-center.com/en/throttle-slide-scooter-center-for-dellorto/spaco-si24/24-e/h-vespa-px200-cosa200-cutaway-50-3331591

Not recommending this setup! Too many variables on a particular bike that affect carb tuning (gearing, exhaust, porting..).
"If I were you" I'd get both slides and see which one works best. Save $hipping.

Did you get a reply from Pinasco?
Max CHT on the above is 150-160C, sustained 2/3 throttle uphill. Max CHT on another bike was 370F (actually 410 with a threaded sensor) for an hour or so, also on a BGM kit. I pulled the cylinder afterward to check things. For now that's my safe-enough CHT, but I'm not recommending that either!

Good afternoon. I have fitted the new carb slide from sip. Temps are down a bit at mid throttle by about 10 to 20 degrees. No difference in running apart from tick over needs more turns in on the slide to keep it running. Will tick over be a bit rich now or should the new slide not really affect it? Thanks.

Sounds like the richer slide is doing what it should.
Reconfirm the main jet is still the correct size. After redo the pilot jet. It may now be one size too big.
Pilot jet is fully online by 1/4 throttle and while under about 4000rpm.

Nice one. I will do the main jet second gear tests later. Aim for about 9k with splutter. Then drop the idle l jet a size. See how that goes. Thanks.

Well, well. Long time no post. So since my last post, my Vespa has been running really well. Must have put nearly 2000 miles on it without hiccup. Settled on 58/160 at 2.5 turns and 128 main jet. I still think both the 58/160 and 128 main are slightly rich but I will live with that.

Bring on the Spring and some nice riding weather.......

Good evening all.

I think the clutch unit is almost knackered. The basket is the original and has bad grooving now. Should I stick with the 21 tooth clutch or go higher? It has the standard 68 tooth primary.

Thanks.