Jetting my 80 650

[yamaharichey]

OK all you jetting experts, I'll try to make this short. 1980 XS650, stock carbs and air filters. Installed custom headers with shorty mufflers and put in 45 pilot jets and 145 main jets. Ran pretty good just a little popping off idle. mufflers too loud so installed
baffles in the shorty mufflers now back fires when its just sitting there idling and when you ride it and go to give it some gas, it just goes baaaaaa and doesn't accelerate, once you get passed that point just off idle into the mid range then it pulls hard and runs great. so my question is now that I put in the baffles should I go back smaller on the pilot jets or do I go bigger. I know some of you will say try it both ways but it is a pain in the butt to keep changing the jets. I live in Utah at 4500 ft. and I hoping somebody has already figured out the right jetting so I don't have to keep messing with it. Thanks so much and I'm sorry that it wasn't so short.

 

[5twins]

Have you uncapped your mix screws and re-set them to somewhere in the 3 to 3.5 turns out range? If not then probably all the re-jetting in the world won't help. As far as your jetting goes though, the pilot sounds about right but the mains are probably much too big. A 137.5 or 140 main should do.

 

[yamaharichey]

Thanks for the reply. I have tried the mix screws all the way from 1, 1.5, 2, 2.5 3, 3.5 and 4. I can't get it to idle good enough to turn the screws while its idling. Its got to be the idle jets because it ran good stock and even with the new headers and 45 pilots until I put the baffles in. mid range and on top it runs fine. So I don't know I'm thinking of going back to the stock jetting and starting over again. whatdaya think?

 

[Newagerocker]

the pilot sounds about right but the mains are probably much too big. A 137.5 or 140 main should do.

Sound advice there. Your mains are too big for running stock intake air filter regardless of baffled or non baffled exhaust.

 

[yamaharichey]

thanks I will go to 137.5 for my altitude here but that's not going to help my bottom end problem is it?

 

[Newagerocker]

Be sure you have the appropriate style pilot jets for your stock BS34 carbs not the BS38 style. See chart, right side.

 

[scabber]

What diameter headers are you running.

 

[CDNTX650]

Be sure you have the appropriate style pilot jets for your stock BS34 carbs not the BS38 style. See chart, right side.

This one here is a good one to check.

 

[yamaharichey]

Headers are 1.5" and I made sure the pilots were the right kind. So when go to give some throttle and just goes baaaaa and doesn't accelerate until I keep pumping the throttle, then when I get passed that first hesitation it goes fine. I have never understood how a stutter compares to a stammer. if it doesn't accelerate just off idle is that sign of too lean or too rich pilot. Thank for all the help guys.

 

[5twins]

I'm not really understanding your terminology or description. I'll try to explain it using slightly different terms and maybe you can relate to it. There are usually two basic types of indicators, one for lean and one for rich conditions. If the bike has a flat spot, falls flat on its face, like you momentarily switched the motor off, that is usually a lean indicator. If the bike stumbles, gurgles, or sputters, that's usually a rich indicator. Those are the two main symptoms but you can get a lean stumble or misfire too. It's similar to the rich sputter but is sharper sounding or pitched.

Playing with your mix screw settings can sometimes show you which type of symptom (lean or rich) you're dealing with. If opening the screws improves things, you're too lean. If closing the screws improves things, you're too rich. Start with both set to 3 turns out and adjust both together in unison by 1/4 turn increments. Work them both out then in (or vice versa) from the 3 turn setting to see which way improves things.

If adjusting your mix screws does nothing then you have other issues. The idle circuit passageways could be plugged or partially plugged, or the o-ring on the mix screws could be bad. Or the float settings may be off.

 

[scabber]

With the 45 pilot you might try turning the mixture screws 1 1/2 left 1 3/4 right. The main jet 135 was what worked for me with a stick pilot. Too much fuel. If the bike ran ok before you changed the head pipes you might not needed a jet change.

 

[scabber]

5twins good explanation sums it up. The big main is the killer.

 

[yamaharichey]

Thanks so much for your help, so what I'm going to do is pull the carbs and replace the boots that are looking old and cracked along with the seals on the butter fly shaft just to make sure I'm not getting an air leak. then go down on the main jets and put the stock pilots back in, then go from there. Does that sound like a plan?

 

[scabber]

I wouldn't change the butter fly seals at this point. Get the jetting sorted and the pilot circuit clean and O-rings in place. Bench sync the carbs and see how it works.

 

[XSLeo]

The carb guide has a section titled "Tuning For Mods" you might try reading it. It has test procedures and what to do with respect to the results you get from the testing.
Leo