Modern Vespa

Thanks! There is no such thing as over engineering, but point taken. My first throttle marks were way off.

I got so frustrated with this engine that I took it out of my Stella and ran the 200 engine I rebuilt. No issues in the same bike and running the 26/26 carb that I had on the 187.

The 187 will go back in the Stella soon once the P200 is done. I will start with opening up the reed block and get some solid data on it.

As for throttle positions. I don't remember exactly, but low throttle (maybe 1/4) cruising. Cruising at 50-55 over flat ground happens at very low throttle. In the hills=more throttle and way lower temps.

Yeah. My bus is one gauge short of requiring a flight engineer. Then there's this thing. More wiring in the homemade autopilot than my whole bus. Scooter is next.

Victorians need to know throttle positioning too.
They just dress and act like they don't.

Damn. I've been doing it all wrong with a piece of tape and a white marker.

After reading through Chandlerman's porting 101 write up, I took a closer look at my spare Stella reed block and carb box.

They look similar to the parts CM worked on where material could be removed to open it up. Mostly, I will remove material where the 2 parts obstruct one another as well as the center bar. It's worth a try. If that doesn't get temps down, I will try a little detuning, but one thing at a time.


The engine will probably end up in the 200 frame for starters since it's sitting right next to it. The 200 engine is a bit boring in comparison. Pretty sure the 187 makes more power than the 200. Gearing makes it zippier.

One warning I'll give you is that those autolube reed blocks are apparently now fairly unobtanium, so I would source a spare before I started going crazy with the Dremel.

I loaned my modded block out to Eley to try out on his Stella for this reason, but I'm happy to send it your way for a test drive if you can wait a bit.

Thank you for the offer. I actually do have a spare in good condition. I'm fairly confident with the dremel as I've used it a ton for detailed metal work.

Gonna stay away from where the flappy edge where the reed seals. And the narrow spots where it seals to the carb box. I hope it ends up making a difference.

Honestly, I doubt it will make a difference.

I've tried a bunch of porting where it's was previously blocked / restricted / overlapped. You'd be surprised at how insignificant it is to flow orifices on these engines…

Can't remember the details of your overheating issues but I'd revisit jetting and ignition.

Qa seemed to have better results with the white largeframe when squish and timing were addressed, reminds me of that…

I will be revisiting everything once I get the engine back in a bike. It's been a puzzle for sure.

Could you point me in the direction of that build please?

Two thoughts...

1) People build and run a motor like yours without issue on the regular, so something is just out of whack. Jetting, squish, port timing, or ignition timing. Not enough to make it seem craptastic, but enough to create heat issues.

2) I'd suspect that just a little de-tuning is what you ultimately are going to need. When I de-tuned my 210, that turned it into an ice cube. It doesn't take much to make a big difference.

I tend to agree. Something simple that I overlooked, but took for granted was correct.

This one…

https://modernvespa.com/forum/topic176530.16

But, CM hit the nail on the head…

Fortunately/unfortunately we're not reinventing the wheel, these kits have been assembled in their thousands, and in a sustained way, in other words, the design works.

I think, a lot of the time we overthink the build, and over compensate/complicate things. And then you end up overlooking the basics (I'm guilty of it too…). It's super forgiving, if we mess things up, they still run. Which gives a false hope of progress…

It's a fairly simple engine design, with basic physics applied. I think that's why so many people can create parts for them.

Thanks. Yes more likely something missed in setting up port timings or setting the ignition timing than reed being too restrictive.

Opened up the reed block. Worth a try.

I figured out why the carb box and reed block were shifting around when trying to mark them even when bolted together. The carb needs to be on there too with the tube nuts to line it all up.

I'm thinking that this might help more than I first thought. Even removing the center bar opens it up a lot.

Next steps will be rechecking the cylinder timings with the degree wheel as well as ignition timing. I'm damn near sure I had those right. Degree wheel was within a degree or two of calculators. When I set up timing (with the degree wheel) they were fairly close to the factory marks. It's worth triple checking though.

I measured my exhaust port timing again with a degree wheel and pointer. If I understand this right, I measure from the piston covering the top of the port through bottom dead center to its original position with the port closed again.

I got 180*…which would be too high.

You don't want to measure the piston covering the port, you want the roof of the port. That is probably where your extra degrees came from. I use the method shown in this pic.

You are going to get many opinions on best method here.
Somewhere in my 100 pages, I show a close up using an endoscope camera to show how easy it is to alter the measure.

My preferred method is using a caliper that the tail is cut off of.
But its essential to get just the very tip of the caliper in the port to measure the roof at the exit.

My view:
All measuring means will give you different results.
That's ok - as long as you can get tight consistency on the chosen method.

It's all relative in the end.
If you find its too peaky, you can of course lower the barrel.
No matter what number you are getting.

BTW - 180 is not particularly aggressive.
I consider it kind of an ideal for every day street riding.
Power bands in the 4500-7000 with a box, or 5000-7500 with a mild pipe.

Where is this crazy heat coming from?!
It will show itself at some point.

FOS method takes some math or a deg table but gives very repeatable results

Obviously I don't know as much about this as Frits (understatement of the decade) but I thought that the radius is basically ignored in the calculation? That you were supposed to go with the the main direction of the duct? As in the red line (wire) in this diagram.

If in his right-hand diagram in your post the edge was sharp then there would be very little wiggle room, with a radius you could get some quite different results, just in the angle you might hold the wire?

The downward angle of the exhaust port should only be 15-25° so the wire bent at a 45 would rest against that radius (assuming you actually have a radius) kind of splitting the difference.

the radius (if you use one) opens the port earlier but slower so splitting the difference is not a bad idea.

The port chamfering is ignored by most in the calculations. Seems like it should matter but it really doesn't make enough directional flow to be of any concern.
Measuring just within the port is considered to be where the port is open.

180 degrees is very much medium. Many tuners believe any less and the baffle wave effect is greatly reduced.

If using a thin bent feeler gauge and a degree wheel. These numbers are good enough as a guide.

I used a .2mm bent feeler gauge. Last season I just eyeballed them as I turned the degree wheel. Got 125* for the transfers. So they are essentially the same numbers.

Not high timings, but still higher than those given in the spec sheet. I'm not sure if I'd get any cooler lowering them.

That leaves squish to play with or the possibility that I set ignition timing incorrectly. Seems like it would be hard to be that far off with timing. The stock type stator doesn't have much of a range of adjustment.

What are you going to do for the reed now with the bar removed?

I'm using Boyeson reeds.

I put in a .5mm head spacer. The squish is now 1.8mm.

Looking like there is gearbox oil in the crankcase.

!

I'm sure you've experienced similar gremlin chasing with the Vdub.
Sometimes, the best solution is to just go through everything - until it shows itself...

If oil can get in - so can air...
You might have your culprit.

Maybe. Funny that it passed the pressure test though…as recently as this past winter. I completely rebuilt this engine the summer before last.

Bus gremlins…Yes, the disappearing camshaft thrust bearing was a real stumper.

So far, neither of the Vespa engines I have rebuilt are gremlin free after 2 years of trying. Gonna have to let it be for awhile.

Gasket failures develop over time as the pressure and heat work on the weak spot. Just like every other aspect of the Vespa motor, those sealing surfaces weren't designed for 8,000 RPM's and 150 PSI of pressure.

Yeah, makes sense to split the case and reseal. Not a hard job. I've done it enough that's it not a big de anymore.

Got over the "say it ain't so's" and split the case. It went pretty quickly. Quite a bit of gear oil around the crank. Possible the clutch side seal was leaking. I will replace it with a blue cortico seal.

Watcha think?

What type of sealant did you use? Gasket seems to be coming away pretty easily.

I think I just lightly greased them. When I put it back together I will use the FMP case sealing video.

When these things were new I think grease was a reasonable answer, who knows how much they have moved over the years? As a minimum use one of the silicone-based sealants, if you want to be sure it will stay put until next rebuild then use Threebond/Hondabond/Yamabond.

Honda bond, Yama bond, … Ginch is spot on.
Will make all the difference.

I suspect it's coming through the circled areas. Looks to be stained there?

This is a known area for oil sucking.
Looks highly suspect from photos.

Thanks. I think that would help. Definitely an oil sucker.

I dealt with this on a friend's Malossi build…

https://youtu.be/REjPG7u6jfo

Surprisingly, it passed the leak down test, but it really does look like the seal was leaking. Would be great though if that turned out to be the problem. Would explain why it would run hot in spite of puke rich jetting.