sha only runs heavily restricted. wut?

A3 with a35 ported jug, 15.15 sha, estoril. Hits 40 with 62 jet, stock filter with plastic low flow cover. Bogs with higher flow filter, with eveything from 62 to 68 jet. Runs good, clean plug when restricted. How can i fix this? Shouldn't i be able to derestrict, upjet, and go faster?

Re: sha only runs heavily restricted. wut?

If you can not get enough vacuum across the jet then it will not suck the fuel into the airstream. Some restriction is sometimes a goodly thing.

Re: sha only runs heavily restricted. wut?

That makes sense, but i should have decent vacuum, if I'm hitting 40 on a 50cc bike, right? But it is a reed valve cylinder, so maybe at low revs, the reeds still aren't engaging enough to allow for proper vacuum? Any further opinions, thoughts, or confirmations?

Re: sha only runs heavily restricted. wut?

unless you have an airleak, there isn't much else you can do, 42-45 is probably the highest i've ever heard of on a stock cylinder, with terrible gearing that makes your acceleration suck hard

Re: sha only runs heavily restricted. wut?

Upjet moar.

Re: sha only runs heavily restricted. wut?

Upjet MOAR? I'll see if i can get my hands on low 70's. My acceleration is pretty killer. I'm gonna get some stiffer springs for my clutch, too. Even better. Maybe I'll talk some dudes at ghost ride into a 50cc race. so, i doubt this more upjetting will work, ten jets bigger just for a high flow filter sounds ridiculous. I just want to be the very best, the best there ever was.

Re: sha only runs heavily restricted. wut?

Start checking the plug color at 0-1/4 throttle on a heat soaked engine and same at WOT. Lower should be slightly darker then the upper range if possible, if it is lighter then vacuum signal loss is the trouble. You can also go for a slide with more angle at the bottom of the gate if the bog is only below the bottom 1/3-1/2 of throttle.

Re: sha only runs heavily restricted. wut?

Rebel, if his plug is light that would mean signal loss at low rpm is the problem, right?

If so, don't you want less slide cutaway? (according to the PHBG wiki if I remember correctly)

Re: sha only runs heavily restricted. wut?

Yes - explained very goodly in real english here - http://outofcontrolmopeds.blogspot.ca/2012/03/dellorto-sha-boring.html including a goodly picture.

You would want to get a 6108-01 slide which is a flat bottom and use that for tuning... unless the flatty is giving you enough signal that the engine is getting grumbly from too much fuel.

https://www.treatland.tv/dellorto-SHA-slide-p/dellorto-sha-slide-metal.htm

Easiest is to use the flat slide and get a jet in the range of the top end, get her heat soaked and check color. Go up numbers until she 4 strokes at WOT when heat soaked and then come down by 2. Then see if she idles rich and shave an angle in her until it is a goodly colour. Always jet on a heat soaked engine so you can guard against running too lean at temperature.

6108slides124.JPG

Re: sha only runs heavily restricted. wut?

Thanks for all the info! I'll see if i can order the slide sometime this week, i've gotta put in an order to get my girl's maxi back from the dead. (looks like it sat in a leaky barn for 15 years, completely coated in rust)

This looks simple enough, i didn't realize there was so much you could do with SHA's. I was considering upgrading to a 17.5 PHBG for the increase in tunability, but then i'd have to get a new intake and everything else. Even if i fuck this up, it's only a ten dollar part that needs to be replaced. hell, i could even throw this SHA on the maxi if i get that phbg.

Hopefully i can get it modded before ghost ride!

Thanks again!

I'll try to post back after i get some of it done.

Re: sha only runs heavily restricted. wut?

I'm glad you're getting good use out of that cylinder

Re: sha only runs heavily restricted. wut?

me too, thanks dude.

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account