650 maxim bacfires

I recently had let my xj sit for a couple of weeks . Started and idled rough it was suggested to use sea foam which helped considerbly with idle . Now it runs great for first 15 minutes then breaks up when trying to accelerate in first and backfires . I have to keep rpm,s high to keep it from stalling. Again only after it seems to warm up almost as if the choke was still on which its not. Any suggestions would be appreciated . Thanks

 

I assume you mixed the seafoam with the gas.
you can ride for 15 min. then the problem starts?
pilot circuit clogging?
may be your slides are sticking,
have you pulled your spark plugs to see if they are fouled?
exhaust pipes all heating up?

it could also be a charging problem check your sitting voltage and charging voltage.

 

I will check thank you!
Yes after it appears to warm up I can keep it running if I keep up rpm's
The plugs appear to be black ( almost like when they run too hot from leaving choke on had the same problem with Yamaha dirt bike cold natured left choke on too much). Plugs are only month old. Cleaned them several days ago did not check them after letting it run again.

 

black would be rich
how high do you keep the rpms?
from
TALKIN' TECH: Various thoughts on various issues
".......The pilot fuel circuit is active from idle up to about 2500-3500 rpms, and at about 3000 rpms the main fuel circuit starts becoming involved, and by 4000+ rpms the main fuel circuit is responsible for about 80%+ of the engine's fuel supply conditions......"

 

Black can be lean too, and backfiring, along with needing to keep the revs up to prevent stalling, suggests that he is indeed lean.

Lets get straight down to brass tacks. It's almost winter. Pull the carbs and give them a thorough cleaning.
http://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/

 

would that be due to misfire/ lack of combustion?

 

Lack of full combustion. The soot is from an incomplete oxidation reaction. That can happen on either side of the ideal ratio.
It could be that he's rich at idle, but has a vacuum leak causing the backfire.

 

Lean conditions can and will cause overheating combustion temps. High temps can burn pistions and damage ring lands. Stop trying to run it like that and pull those carbs and go through them. Crappy fuel and moisture causes the jets to corrode and restrict fuel flow. Take your time and clean every passage and wet set the floats off the bike so when you put them back on its just all adjustments. Good luck and ask many questions if you don't understand. Many of us have cleaned carbs so many times we can do it in our sleep.

 

Thanks to all !
It's great to have a site like this one where you get answers from experienced people !