Sputtering, backfiring, lag in throttle?

Godric

XS650 Enthusiast
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Hey yall, I'm getting the kinks out of my $300 runner, and it seems to be all there, except for the delay I get when I hit the throttle. I'll get it going in 1st and it kinda "blab blab blab VROOOOOOM's". I'll throw the gas to it and it'll go, but it kicks off like a scalded dog after a few seconds. I'm thinking it's a fuel/carb issue, anyone have any thoughts? Also backfiring out of right cylinder. No oil leaks no gas leak, I don't think there's an air leak but I am running the carb mounts that came with it (not rotted, I was told they looked good)
 
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Hey yall, I'm getting the kinks out of my $300 runner, and it seems to be all there, except for the delay I get when I hit the throttle. I'll get it going in 1st and it kinda "blab blab blab VROOOOOOM's". I'll throw the gas to it and it'll go, but it kicks off like a scalded dog after a few seconds. I'm thinking it's a fuel/carb issue, anyone have any thoughts? Also backfiring out of right cylinder. No oil leaks no gas leak, I don't think there's an air leak but I am running the carb mounts that came with it (not rotted, I was told they looked good)

Also, in my case, the lag in the throttle is from my pilot jet being a touch too big. I don't know if yours have ever been changed but that might be something to look at as well.
 
Stock mikunis, recently cleaned. I'm running 54mm pods, and my pilot jets have rubber plugs on them (I live in the mountains,I guess that's why someone did it?)
 
No, that's part of the design, they need to be there. You really have to provide more and better info on your bike. There were no fewer than 5 different carb sets used on these, all set up differently. I'm assuming that since you mentioned the rubber plugs that your bike is an '80 or newer model with BS34 carbs. That carb was the only one with the rubber plugs.

You mentioned 54mm pods. I'm going to assume they are the pleated style K&N copies from MikesXS. A pleated style pod doesn't work well on these CV type carbs, it messes with the slide lift. So, they may be part, or maybe all of your issue. Remove them and take a short test ride to see if your problem goes away.

It's also possible your need to change some carb jets. When you make changes to the bike's air filters and/or exhaust, some carb jet changing is usually required. That is especially true with the BS34 carbs as they came set up from the factory very lean. Pretty much any little change you make will throw them off.
 
No, that's part of the design, they need to be there. You really have to provide more and better info on your bike. There were no fewer than 5 different carb sets used on these, all set up differently. I'm assuming that since you mentioned the rubber plugs that your bike is an '80 or newer model with BS34 carbs. That carb was the only one with the rubber plugs.

You mentioned 54mm pods. I'm going to assume they are the pleated style K&N copies from MikesXS. A pleated style pod doesn't work well on these CV type carbs, it messes with the slide lift. So, they may be part, or maybe all of your issue. Remove them and take a short test ride to see if your problem goes away.

It's also possible your need to change some carb jets. When you make changes to the bike's air filters and/or exhaust, some carb jet changing is usually required. That is especially true with the BS34 carbs as they came set up from the factory very lean. Pretty much any little change you make will throw them off.
Thanks 5twins, I'll take note of all this. Yes they are bs34s, and yes they are pleated k&n copies. If I were to re-jet, what size should I install? Also, should I invest in the foam filters?
 
Kinda sounds like you need to clean them a bit better. It sounds like your idle circuits are still a bit cruddy.
www.amckayltd.com/carbguide.pdf Have you read through this? It's a carb guide written by two of our best carb guys. With input from others.
Follow the steps to tear down, clean, inspect what you have. Write down the numbers on all the brass parts.
When cleaning pay particular attention to the idle circuits. There are tiny passages and port that plug easily. They take some time to get clean.
In there is a section on carb tuning. Titled "Tuning for Mods" This gives you tests to see how the bike responds. Then it gives causes why it didn't respond the way it should. and then how to adjust to fix what's wrong.
It helped me a lot.
On jets you need to know what's in there now. Then you make one change, test, make a change test. repeat as needed to get it right.
Leo
 
Kinda sounds like you need to clean them a bit better. It sounds like your idle circuits are still a bit cruddy.
www.amckayltd.com/carbguide.pdf Have you read through this? It's a carb guide written by two of our best carb guys. With input from others.
Follow the steps to tear down, clean, inspect what you have. Write down the numbers on all the brass parts.
When cleaning pay particular attention to the idle circuits. There are tiny passages and port that plug easily. They take some time to get clean.
In there is a section on carb tuning. Titled "Tuning for Mods" This gives you tests to see how the bike responds. Then it gives causes why it didn't respond the way it should. and then how to adjust to fix what's wrong.
It helped me a lot.
On jets you need to know what's in there now. Then you make one change, test, make a change test. repeat as needed to get it right.
Leo
Super helpful Leo, this shold be just what I need! Tanks a lot!
 
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