Bad idle backfires on one side

[Ajgamester]

I bought and have been rebuilding a 81 es650 the problem now is I can get my idle quite right and I keep getting misfire randomly on one side. I have cleaned the carb w times and put in new plugs. The odd thing is if I unhook the plug wire on the side that backfires the engine runs the same minus the backfireing. If I unhook the one on the other side instead the engine instantly dies. It starts up real easy with the choke on but keeping the idle in a good range is hard after it was up sometimes when driving the rpm get stuck up high and I have to adjust the idle down until a later time. Any idle on what it could be should be awesome. Im about to try and get a new ignition coil for it and hope that's it is there anyway to check the coil.

 

[Jan_P]

Not knowing what ignition system .But I would ( after thinking it over ) take out the backfiring side.spark plug.
Cap on and grounding plug to the cylinder head.And then observe if there is a spark that looks normal.
It runs more or less on one cylinder only. Now
Depending on Ignition system I would consider shift leads between left and right Cylinders see if the Problem follows so the misfiring changes cylinder.

 

[5twins]

It's probably not the coil. You have just one coil that fires both cylinders. If it was bad, both cylinders would be acting up. But, it could be the plug cap or it's connection to the plug wire on that bad running side. I would, at the very least, redo that connection, but if your plug caps are the originals, I'd suggest replacing them with new NGK 5K ohm caps. If you just want to try and fix what you've got in the mean time, pull the cap off (it "unscrews"), cut about 1/4" off the plug wire to get to some fresh wire, and re-install the cap. To insure a good connection, I like to strip about another 1/8" off the plug wire and fan the strands of the wire out in a radial pattern like so .....

If you are going to re-use the original cap, while it's off, check it. Measure the resistance through it. Stock caps had an oddball rating of something like 8 or 9K ohms. When they go bad, that begins to climb, eventually getting so high it starts choking off the spark. So, if you measure like 10K ohms or more, your cap is going bad and needs to be replaced.

If the plug cap and connection are OK (or you "fix" them), then you probably didn't do a good enough job cleaning out the idle circuit on the carb on that troublesome side. It sounds like you're only running on one cylinder at idle.

 

[BowlingSS]

You could also check the coil connector. Might be a bad connection.

 

[BowlingSS]

Did you sync the carbs?

 

[BowlingSS]

The system should be the TCI ignition If it is stock.

 

[Ajgamester]

Yeah the whole bike is stock and original one owner before me bought it with every feature that came out that year and only used it to get the mail at his farm.

I'm new to tci ignition so I'm at a loss here. I tried sync the carb and can get it to run good then it heats up and the rpm go from 1250 idle to about 3000 at idle the back fire comes and goes but itigjt just stop firing that might be why it stop backfireing. It back fired pounder then a shotgun on start up today scared the crap out of my neighbors.

 

[Ajgamester]

With only one coil do both cylinders fire at the same time? I was wondering if I can swap the plugs side and see if the backfire follows.

 

[5twins]

It's not uncommon to have to clean the carbs several times before you really get them totally clean. In particular, this applies to the idle circuit. There are 4 tiny holes in the main bore around the butterfly plate that let the idle fuel mix into the carb. You have to make sure they're all clear .....

So, you need to remove the pilot jet, spray carb cleaner in it's hole, and blow it through with compressed air, watching for it to come out the 4 little holes. You also must remove the mix screw during this process to do a proper cleaning. Stock, the mix screw is capped over with a metal plug. You have to remove that plug to get the mix screw out and then you can do a proper cleaning. Also, the mix screw has a tiny o-ring on the bottom and that needs to be in good shape for the screw to work right. They usually need to be replaced by now if they're original .....

Here's what the metal cap over the mix screw looks like .....

Like I said, you can't do a proper cleaning of the idle circuit if the mix screw is still installed.

 

[5twins]

Yes, the coil fires both plugs at the same time so you could swap the leads side to side and see if the problem follows. Now, although the pistons in both cylinders rise and fall together, the cylinders are on different strokes. When both pistons come to TDC, one cylinder is at TDC on it's compression stroke while the other is at TDC on it's exhaust stroke. Both cylinders get a spark but only the one at TDC on it's compression stroke fires. The other cylinder gets what is called a "waste spark" because, well, it doesn't do anything and is wasted.

 

[BowlingSS]

Yeah the whole bike is stock and original one owner before me bought it with every feature that came out that year and only used it to get the mail at his farm.

I'm new to tci ignition so I'm at a loss here. I tried sync the carb and can get it to run good then it heats up and the rpm go from 1250 idle to about 3000 at idle the back fire comes and goes but itigjt just stop firing that might be why it stop backfireing. It back fired pounder then a shotgun on start up today scared the crap out of my neighbors.

My 81 did the same thing. I found the TCI unit was bad. Replaced the unit and it started right up.
Good luck.

Perhaps this helps --- not checked if it is for your model

 

[nj1639]

Like stated above, swap the plug leads. If the missfiring goes to the other cylinder then you can eliminate the TCI being a problem. Costs nothing to do, quick and easy.
Little steps one at a time.

 

[Ajgamester]

Tried swapping it and it didn't change pulled out my tci and to my surprise the previous owner ether changed it out with a rebuilt one or rebulilt it himself all the resisters were new. Turns out I was stupid and when I adjusted my mixture screws I turn one the wrong way readjusted them from zero and now it good only backfire a little when choke is on. Thanks for all the help. Been doing a lot to this bike can't wait to get it on the road. Adding before and after pic from the work I've done.

 

[5twins]

The blue headpipes indicate lean running. The stock headpipes are double walled, a pipe within a pipe with an air space in between, specifically to stop them from turning colors like that. If you get them to discolor, you're really running lean.

The mix screws on the BS34s, on a mostly stock machine, like a setting of about 3 to 3.5 turns out. That can be reduced to the mid 2's if you put in bigger jets for mods, but your bike looks pretty stock. Still, it can benefit from some jetting changes. It will run better if you go up one on the mains (132.5 stock to a 135), and you can richen the idle circuit up a little bit by changing the air jet. Stock size is a 135 and you can go down one or two to a 132.5 or 130. This won't make it as rich as changing the pilot jet but doing that is probably a bit much for a mostly stock machine.

 

[RichieB]

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