Exhaust mod = performance boost

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Well, you know someday I'm going to have one of these then I can speak with great authority instead of just passing along general engine knowledge and diagnostics! :D

Seems strange that the carbs don't have an idle mixture screw...is there maybe one under a cap? Can someone post a big photo of each side of the carb?

Anyhow, let me know if you find an improvement in the top end when you enlarge the main jet.
 
our only mixture adjustment is through moving the pin that goes into the jet.

I can take a pic or two tomorrow. I don't know that I'll drill out the jet, that would probably make it run wayyy rich throughout the entire rpm range. It almost seems I need that "5th injector" push...aka a forced fuel induction at higher rpm....if in fact a lack of fuel is what is causing my engine to cut out at high rpm. With all the research I've done, however, it does seem to mostly be due to the fact that the exhaust isn't allowing the proper tumble/turbulance/pressure/whatever-you-want-to-call-it for the correct burn cycle at that higher rpm.
 
well, i'm gonna try the jet thingy, because i can always back off one notch on the mixture...i think it's gonna be the solution, tho.

Bikeguy Joe: srdavo posted an excellent pictorial on the carb, but i'll be danged if i can find it...

the main needle in slide has 4 slots & a circlip to adjust depth/mixture.

the idle screw merely seats on an angled slot on the slide, in or out for more or less.
 
augi you gonna drill out the jet? I figure at least one of us should? lol
 
yes, i've been flirting with the idea all along, now i just need to find the right drill-bit.

i'm gonna be busy all this week maybe not even get to ride, surely no time to work on it. i'll let you know when i make the leap.
 
Alrighty then..... I DO mean to drill the MAIN JET, not the one the needle goes in! These carbs do have a main jet, right?

I've never seen a carb with no idle mixture adjustment (except for the smallest of two stroke engines- the Cox model plane engines).

Just thought I'd add that.

Also augi, you may want to take the jet with you to home depot or wherever you are going to look for drill bits and find one that is close to the opening in the jet.

I know it's going to be really small, and therefore cheap, so you may want to buy a couple of sizes.

A reminder to those that will try this- remove only the smallest amount of material from the jet, don't use a bit that is so big you actually have to drill it in there, you should be able to just hold the bit with pliers and turn the jet to get the bit to "thread in" and then gently pull it straight out. don't remove any more than that until you try it.

Now, can you buy a replacement jet from your "dealer"? Maybe they have a slightly larger jet in stock? That would save the hassle of finding the right sized bit, and playing the "looks about right" game.

I have done this before BTW, mostly because I'm too cheap to go all the way to the bike shop, find out they don't have the right size in stock, then wait two weeks to pay a rediculous amount for a tiny piece of brass!
 
BTW- if you remove the float bowl and look into the bottom of the carb, is there a bigger jet next to the one near the center one where the needle goes?

That should be your main jet.

I really need to get one of these things....... :???:
 
well, for no pics you're getting it mostly right....
41_59_100_1323_1_1.jpg


(note how too much tilt could in fact cause float-binding & false fuel-level. mixture is adjusted by changing the relative position/height of the needle in relation to the slide. on the other side of the slide is the angled slot that the idle-screw acts on)

yes, the main jet is at the bottom of the "pick-up"...it's gonna be a fairly easy job, i've bored/jetted many a single-barrel/6-cyl chevy in my day.

actually, when you DO get to look at one, you'll be a be a bit impressed i think, pretty good features thru very simplistic engineering.
 
I might bore out my jet just a tad today....I am convinced that my fuel is becoming a restriction...
 
i haven't been able to do it yet, but here's what i've learned about mine: it's running as best it can & it runs great. it responds a bit at topend when i apply a tease of choke, so i'm convinced...

maybe rif has the right drillbit, i could do it this weekend.
 
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