weird carb problem, pics of plugs inside

[MIKE93SVT]

so i took the baffles out of my exhaust and in turn the bike was running a little lean. so i put 137.5 jets in and back the mixture screw out to 2 3/4 to smooth the idle and get rid of the popping on decel.

well the left cylinder is barely hitting at idle. the right side is loud and burning clean. the left side is very intermitent. bare makes the exhaust tone until you give it some throttle, then it wakes up.


so i replaced the plugs with the same gap (27) and that didn't do anything. i tried to adjust the mixture screw and that didn't change.

i also adjusted the valves and synced the carbs. both pulling about 19 inches of vacum. still no solution. so is something weird with the carb adjustment, or is it a weak spark that needs more voltage?



left side is the darker plug, they have about 20 miles on em

 

[MIKE93SVT]

it also picks up more acceleration around 2,700 rpms with the same amount of throttle. as you give it throttle and the rpms come up, it pulls a little harder like it was given a little more throttle. not sure if that has to do with it

 

[Tz250racer]

I would try to set the air screws at 1-1.5 turns out and see if you notice a better running.Two+ turns out is alot.The motor is not getting enough gas to run right.

 

[MIKE93SVT]

do i have it backwards? thought screwing them out would fatten it up.

forgot, bike is a 78 and the stock setting is 2 1/4 out. so i only went half a turn out more

 

[5twins]

No, you have it right, tz250 is wrong. The BS carbs on these bikes don't have air screws, they have true mixture or fuel regulating screws. Turning them out makes the idle circuit richer.

It sounds like your sync is still off. If not that and you still have points, maybe the left set is oil contaminated and misfiring. Or maybe the float level is off in the left carb and it's running too rich.

 

[MIKE93SVT]

thanks for the info. it all started when I synced the carbs. then I did the valves, so I'll try to sync them again and check the points

 

[ann0yed]

The points could be the culprit; I spent the spring and most of the summer solving a similar problem on my '79 - at idle the right cylinder was missing a lot and no amount of adjustments had any effect. I ended up scrapping the points and installing a Pamco electronic ignition and new coil and also wired the coil to run directly off the battery. Done.

-j

 

[Sundie]

leaking choke bodies.

 

[XSLeo]

Dirt in the idle circuits on the side not running.

 

[remmy1101]

I agree with xsleo just because this happen to me about a week ago. I thought I had everything perfect and clean but somehow the idle vain that runs through the float bowl got clogged again and really messed with me.
One side fired and idled the bike fine the other side would fire when i gave it about half throttle and it sounded like the bike really got up and going (because now 2 cylinders were firing not just one)
I sprayed some starter fluid in the non running side just to confirm it was not a spark issue I suggest you try that then you know thats its a fuel delivery problem.

 

[XSLeo]

One of the first thing to check when a problem crops up is the last thing you worked on.
This is why I think your trouble may be dirt in the idle circuits. The idle circuit feeds the engine up to about 1/4 throttle, then the slide starts to lift and feed fuel from the mid range area. With one carb not running on the idle circuits it won't run until the mid range starts to feed it enough fuel to run, thats why the surge of power at around the 2700 rpm range.
I wouldn't reccomend starting fluid. I woulg use an oil can, the kind with a pump lever, fill with gas, use this to squirt in the engine.
If you can figure out which carb, you can remove the mix screw and use the tube on your carb cleaner to spray in to the hole for the screw and watch to see if cleaner comes out the holes by the throttle plate. Drop the float bowl and clean it out. That should help.
The points are the same way, a bit of crud can effect them too. A heavy white peice of paper, like a business card, with some electrical contact cleaner sprayed on both sides and pulled through the points until the paper comes out clean.