Carb problem

Bought my bike ZN750 last fall after it had sat for a year but had been started occasionally. Always ran a little rough so when i did my top end over i cleaned my carbs. Bike seems to be running better than ever except on start up its hard to get an idle. Full choke seems to flood it unless you rev it up to 4000 rpm (not good lol) and it will hold for a while and then it begins to drop rapidly and stalls. before it would rev high with full choke but always held it. On the higway and around town it runs great, but toinight i started it in the drive way and it took an idle right away(motor was still warm from coming from work). BUT for some reasons I decide to touch the mufflers to see how hot they got. The right was warm and the left was cold so i proceeded to the head pipes.
1-cold
2-warm
3-warm (both evaporate spit lol)
4-hot (seemed hotter than than the others)

Not really familiar with motorcycle carbs that much but just looking for somewhere to start.

Oh more info that may help, when head was taken off for rebuild all intake valves were whiteish except #1 i think could have been 4 lol.

Hi Frank,
The problem may or may not be the carbs. If water (or spit) sizzles right off the exhaust pipe then that cylinder is firing. No sizzle then no fire and it sounds like no fire on #1.
First thing to check would be compression and compression testers are cheap.
Next check for spark and ignition timing. If these are ok then look to the carbs. I'm not familiar with your particular carbs but the problem could be caused by clogged pilot jet. You might need to clean again.
Do you have an inline fuel filter between the gas tank and the carbs ?

You mention that when the head was removed all the valves were whiteish. How do your spark plugs look. Are they also whiteish ? Could indicate an lean condition or air leaks around the rubber boots which connect carbs to cylinders.

compression is fine,spark is fine, tank is clean(no fuel filter though), and yes it was running lean before do to dirty carbs. Think i will just pull them off and clean them again.

Thanks

Add a filter in the line also

Frank, I think JR gave you some great advice.... to test cylinder for firing, use a spray bottle of window cleaner or orange cleaner or water and squirt on the pipes one at a time. The water rolls off means the cylinder isn't firing. If the water vaporizes, it is firing.

FIRST order of business when troubleshooting non-firing cylinders is compression. Even if the bike was recently rebuilt, you may have no compression due to lack of valve clearance. Measure compression to verify THEN if you have a problem, check valve clearances for all cylinders. If you skip this step, you may end up spinning your wheels.

Next is to check electrical... SWAP the #1 and #4 plug wires and recheck cylinder firing but use a spray bottle and not your skin.

Once you have worked through compression and electrical, I would then look at the carbs as a possible issue.

del

ok 1-not a spark problem for sure 2-valves were all checked. now on to the good stuff here are some pics of my plugs but the only one that mattered didn't turn out well so i'll explain. Fired it up tonight cold took idle great all cylinder seemed firing all evapoarted water from spray bottle(all pipes that is). but #1 is still cooler and the plug is whitish hence its running lean. But from my understanding if its running lean on the cyclider shouldn't it be the hottest???? anyway 2,3 & #4 are perfect.


can't seem to post any of my pics

Oh and thanks to everyone that has posted

any idea???

do the pipes get hot if you bring the rpms up?, thinking you may have something going on in the idle circuit,
also have you balanced the carbs?

thinking the same thing. Haven;t been able to drive it lately to get it good and hot so not sure. I'm just gonna clean the #1 carb again and check everything i know its lean so its probably dirty.

Hi Frank,

Been following your post for a while. Not trying to get off topic on you... But...

My brother bought the very same kind of bike this year. 1985 ZN750A Ltd Shaft drive.

We have not been able to find ANY info on this bike.

Do you happen to have an owners manual, parts diagrams, or electrical schematics for this bike?? Any info would be helpful.

Ket