Higher RPM's sputter

[Ccanady]

I have a 1981 with stock BS 34's, pamco ignition, xs charge pma with capacitor (kick only), 'Ya mama" pandemonium open exhaust and foam pod air filters.

The bike starts and idles fine. Once I get it into the mid to higher RPM's it begins to sputter and pop and sounds like its drowning out or bogging down. I'm not exactly sure what to do. I've read about people re-jetting their applications but I'm not sure what jets I would need with the setup I have.

Also, the carbs are clean, valves are set and ignition has good voltage and brand new plugs.

Any help would be greatly appreciated!

 

[2BallCane]

Check your diaphragms on your carbs. It could be that the slides are not opening up fast enough or staying open when you crank the throttle, or perhaps your bowl isn't filling fast enough with fuel.

 

[grizld1]

Click the Tech button, find the link to the XS650 Garage USA Carb Guide, and read the section titled "Tuning for Modifications." No point writing all that out again.

 

[RustiePyles]

What do your plugs look like? Could be an advance issue as well. Have you put a timing strobe on it to check the advance rate?

 

[Jan_P]

Charging high ??? ... heating and shorting the stator ??? One or both sides problem ?
shorting Pamco ?

Could try a run with " Everything " Switched on see if any difference

 

[Ccanady]

What do your plugs look like? Could be an advance issue as well. Have you put a timing strobe on it to check the advance rate?

So I'm not 100% sure about my advance. I had to make my own markings and if i remember correctly it was 38 or 40 BTDC for the advance. When I put the strobe on it, it lines up to the advance when i accelerate. But is there something else that I should be checking at this point? If not, then I'd say advance is fine.

 

[ippytattoo]

Who did the mods? Did you purchase the bike with pods and open exhaust? Did it run properly before the mods? If you did the mods and didn't change jetting then it definitely needs to be looked at. If you bought it with the mods already done then you need to verify jets in the carbs and adjust as needed. You said it lines up with the advance mark when you increase revs but what about at idle? Have you verified the tdc mark is correct? The timing marks on a pma are made by the installer and could be subject to discrepancy.

 

[Ccanady]

Who did the mods? Did you purchase the bike with pods and open exhaust? Did it run properly before the mods? If you did the mods and didn't change jetting then it definitely needs to be looked at. If you bought it with the mods already done then you need to verify jets in the carbs and adjust as needed. You said it lines up with the advance mark when you increase revs but what about at idle? Have you verified the tdc mark is correct? The timing marks on a pma are made by the installer and could be subject to discrepancy.

I did all the mods. When I purchased the bike, it had all the stock air filters, exhaust, charging sysytem and points. When I first bought it, it ran find but had low compression (I have since did a top end rebuild on it). It lines up with the advance when I rev it and at idle it lines up correctly with the fire mark. I know the mark is correct.

Where would be the best site to purchase jets? Im not even sure where to being besides just pulling the jets I have and ordering new ones that are plus sizes and playing around with it to see which one runs best.

 

[ippytattoo]

General recommendations for pods on bs34's and open exhaust is 2 up on mains and 1 up on pilots. Stock jetting is listed in the carb guide (132.5 main and 42.5 pilot). I have used jets-r-us when doing my carb tuning and have had good dealings with them. Always use genuine mikuni jets instead of repops.

 

[Ccanady]

General recommendations for pods on bs34's and open exhaust is 2 up on mains and 1 up on pilots. Stock jetting is listed in the carb guide (132.5 main and 42.5 pilot). I have used jets-r-us when doing my carb tuning and have had good dealings with them. Always use genuine mikuni jets instead of repops.

I'm checking it out now! Thank you for the help!

 

[5twins]

Verify the jetting you have now. There's no telling what a P.O. may have done to the bike. Besides the mains and pilots, you can also change the idle circuit air jet. It's a way to fine tune the idle circuit as it doesn't have as big an effect as changing the pilot jet size. One size smaller than stock has worked well for me. It makes the idle circuit just a little richer. I'm up one on the pilot jet size but now I'm a little richer, not as much as another step up on pilot jet size would do.