Backfire through carbs?

I picked up the bike in February. It was not running for 3 years, and the guy told me that it stopped running because of an electrical short. I replaced the harness and the rectifier and got it running. It runs like an old lady.

I am just about positive that the carbs are cleaned and synched but when I go to ride the 1982 KZ750e it has low power. It backfires and spudders at idle and periodically I can hear and see what looks like exhaust smoke fire through the carbs. The needle slide then gets fouled, then stuck, and the bike starts leaking gas. The problem is only on the 1&2 cyl side of the engine. The #1 runs normally beside the in firring and the #2 appears to be running rich at idle from the lack heat coming off the pipes. I have a stock air system with correct filter.

What I am 99% sure of:

Electrical is good - Plugs are gapped and spark is there
No air leaks (plugged up the enviro system) and have serious clams onboth sides of the carbs.
Compression is good

If you think it is a head problem, please be as detailed as possible on how to fix it because I have never gone in there before.

Thanks a lot guys, any ideas would be appreciated

I posted a thread on the engine forum with just about the same title. WIREDGEORGE gavea great list of things to check. Sounds to me like a timing issue, though.

Most owners feel "SURE" that some things on their bike are perfectly fine and it usually turns out to be those things that bite them bwhahaha

I don't know what list I made up but FIRST thing to do is to verify the state of tune for this bike. Have you checked compression? Is it within spec? Have you set valve clearances? I know, I know, this stuff is just fine or someone who sold you the bike told you they did it the day before... BUTTTTTT Have you done this basic maintenance stuff recently and verify it is up to snuff?

Next, what voltage are your coils getting? Are you plugs, wires and caps NEW? Do you have points/condensors or electronic ignition? How was the ignition timing verified?

Once ALL that stuff is known an eliminated from being a problem, then perhaps the carbs should be looked at but I am betting that the problem lies in one of the former of the bike's components.

Post edited by: wiredgeorge, at: 2006/04/19 09:21

Thank you George,

I am becoming a big fan of yours. I have been reading through the archives a lot and you have helped on other problems.

I will check the voltage to the coil asap, I just ordered new plug wires because the old ones appeared to work but the were old. The bike has electronic timing. Is it true that electronic timing does not go off?

I also realized that the idle screws probably do not have washers and o-rings in them, and I remember reading in one of your earlier posts for member Jarek that this could lead to some troubles. Would a lack of o-rings and washers for the idle screw cause a carb backfire?

I do not have access to the tools to check the compression or the valve clearances, yet, but if the o-rings and the new plugs wires do not help, that will be my next step.

Thank you so very much for your time and help!

Ben

Dear KB02,

Thanks for pointing me in the right direction. What ended up bing the troble with your bike? I have electrong timing on my KZ750e3. Can electronic timing go bad? Thanks, Ben

I'm still working on mine. Work, house work and other things have nawing away at my wrenching time. Hopefully I'll have a little time tonight to tincker and get it going.

Get a compression tester from the autoparts store and I am not sure, but on your bike, you have to remove the cams to swap shims so all you need are some feeler gauges with the thinner blades for checking your clearances. IF you start buying stuff to fix problems and don't check the basics, you will likely end up spending a lot more money than you should have. Good luck and feel free to ask any question!