Hello. I’ve just seen your post. I once thought 6mm off the crank. 8mm off the back of the inlet pad type formula. No it’s a science 1/2 mm off a port and it runs great go another 1/2 mm and it’s ruined. You really need to do a lot of research. You need to measure ports, gaps and degrees of the entire engine before the Mainshaft. Everything is made to an acceptable tolerance. Tuning takes it to the edge. Unless you really know where that edge is you stand a good chance of stepping over.
Get a book on two stroke tuning and work it out. “Tuning Vespas the Norrie Kerr way”. If that doesn’t scare you read a Haynes Manual “ two- stroke Performance Tuning” by A. Graham. Bell. At least Then You’ll know what questions to ask. I’m not trying to put you off. A year ago I was asking exactly the same.
There are many experts here who will gladly answer your questions once you’ve narrowed things down.
Post by scooterbooter on Sept 14, 2019 16:26:15 GMT
Hello there del thanks for your comments and suggestions. All I really wanted to know was how top heavy the revs would be and stuff like that. I did all the sums and that carry on. I've got one of those mazuchelli cranks and felt the inlet was choking it a bit. Tuning books always make my head hurt and my foot itch. How did your tune go? Figures like 8mm scare the life out of me.
It's made a little difference. I had the engine in bits and was going to fit a 60mm stroke Mazz crank and pinasco Magny cors top end.
I was aiming for 180 degrees inlet opening but a situation I was in meant I had to get my scooter back on the road practically overnight. I hadn't opened the transfer ports so the Pinasco barrel was back on the shelf. I rebuilt it with the original crank and 125 top end. I haven't measured the inlet timing with the standard crank in.
what I had done so far. lengthened the inlet port by 8mm towards the back and made the sides of the slot parallel. there was nearly 1mm difference between each end. I blended the carb box to the top of the casing. I left the carb alone as it was a fraction smaller than the carb box.
I did it using hand files and took my time and I did a lot of careful checks with a degree disk. Recently I saw a Mr Freakmoped video where He shows how to do it without a degree disk or as He calls it Voodoo.
The inlet timing is only part of the Whole. Have a look as Sime66 posts on what He did with a DR top end if You want to see the Maths in the real world.
Post by scooterbooter on Sept 15, 2019 10:12:02 GMT
Hello del. Bad luck with not having the time to finish, that's always my downfall short on time. 180° that's massive isn't it. I'm at 120°. Think I'm on about the same measurement. Yeah I flowed the carb box too, rounded that horrible bit of casing of. My mod made a big difference but I think that's cus if suits the duration of the crank's opening. Thanks I will try find that thread but my search bar thing don't work to well.
Imho, Sime66's Dr180 tuning thread ( with a lot of help from Vespaguru aka Jack221,both moved to the modern Vespa forum, by the way ) 😉 , is excellent, tho it goes in to too much detail for some/most? People ( I believe Sime66 may have acknowledged this himself), so that's not me having another dig at him/them 😉, tho maybe I should because I mention the forum they are now on regularly, but the only refer to this forum along the lines of " the previous forum we were on or "the other forum" l😂l.
Imho more people like to see things done on a video, that's why, mista freak moped made his videos. He has more than enough videos to help in tuning vespa engines, how to simply measure and change inlet timing having a few videos on the subject. Here's just one of his video's on the subject 👇
I used to use degree discs and/ or dial gauges, but now find it much easier using my Buzzwangle 😀.
Last Edit: Sept 15, 2019 18:32:17 GMT by mijapxman
Just checked my figures 120°is when mine opens.durrr brain . 180° opening times is not massive mines not far off that.
Yes that’s the same as mine. Thank you for pointing that out. I don't want to confuse anyone. The open time before TDC is done by lengthening the slot in the crankcase towards the back. The closing after TDC is done by the crank web which is already done on the Mazzuchelli one.
thank you Mij for finding the videos. I was too p*shed and tired last night.