SHA filter/ jet question

hey all,

i have a sha15 and matching intake on my moby 50v build, just installed the airsal 74cc kit and did the usual to ensure compression is within reason.

highest temp I've reached was 380...anyway...

I had a dellorto screen w/o the cover on there with a set screw to keep it from falling out. i just picked up a new cover,screen and clip for the carb.

I know it's more restrictive and i can remove screens and all but i was wondering if all things being equal I can just drop a couple jet sizes (to lean it some) and accomplish the same thing (really not a huge difference but top end speed was a little more mellow).

so, for instance i had a 68 jet in it with the derestricted screen...can i go down to a 66 or 65 with the more restrictive air filter and achieve the same result???

oh another thing...I've always installed the dellorto cover with the vents on the bottom but i've switched them to facing up on the 2 bikes i use dells on...i don't imagine there's much there?


just wondering

Re: SHA filter/ jet question

Yes, you absolutely need less gas when you add a filter, because less air is flowing.

I've found that (in my limited experience with them) SHAs seem to want to have the filter mesh thing and cover on to run right.

Re: SHA filter/ jet question

Matt Madden /

Well I went ahead and threw a 65 jet in…it definitely has a little more pep!

I’ll put my temp gauge on it tomorrow and make sure I’m still good temp wise…it’s supposed to be almost 97 degrees…ugh but a good test for what to expect down the road…

Re: SHA filter/ jet question

I cant keep kitted mobys cool

Re: SHA filter/ jet question

Yes you could go down in jet sizes, but I would opt for removing screens from the filter pack rather than dropping down in jets.

Consider that a sha is a single stage carb with no needle or idle jet to adjust the fuel flow for various throttle positions. It all works off of one jet and slide for air flow.

You can modify your slide to function more like a typical needle as well by cutting out a notch at the bottom or also adjusting the angle of the bottom of the slide.

I also like to remove a few of the screens from the filter pack and insert a piece of fabric or thin foam to help with air restriction.

Just gotta get creative with these carbs. But I am always trying to get as large of jet as possible in my sha carbs. with kits I'm usually in the mid 70's and kits with reeds up into the 80's

Re: SHA filter/ jet question

Matt Madden /

So, a couple observations...even after throwing the the smaller jet it it's kinda holding back. I checked my temps with the smaller jet expecting them to be higher but try as I might I couldn't get them to climb above about 340...even went so far as to remove the screens altogether and just use the plastic cover...anyway, probably some of the top end is suffering because I still have the stock cashew exhaust on it.

As far as keeping the engine cool, that's a good thing but I don't really wanna throw a big pipe on it anyway. For now, I've gone back to a 68 jet and removed all but 2 of the screens out of it...I think I hurt both the top end and the low end responsiveness of the throttle by cutting the fuel flow that much.

btw, I'm at a high altitude so generally my kits perform better in the 68 jet range anyway. My puch has a 14 bing so it's much easier to tune the carb...SHA's are somewhat limited in what they can do...even so, my pug winds out to 50mph when really cranking on it...this moby will probably only hit 40 or so w/o a pipe change.

thx for the input tho' if I discover any crazy improvements i'll let ya know

Re: SHA filter/ jet question

Matt Madden /

Final setting I have is the 65 jet, screen filter with all screens and then the plastic cover.

Seems to give me the best all around performance considering I’m trying to keep temps below 380.

Speed run showed me at 40+, low end is really crisp and temps are within reason


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