1982 KZ750 4 Cyl Idle and Running Issues

First post, will be a long one. I have an 82 KZ750 H3 4 cylinder. It's mainly a commuter bike, rain or shine. It ran okay but leaked fuel, oil, and ran poorly under 3k RPM's. Took some throttle skills to keep it alive at the lights. Figured I take a few weeks and fix it up. Over the last couple weeks I did the following:

Rebuilt carbs. Disassembled and soaked in carb dip. Used Z1Enterprises carb kits, completely rebuilt. Bench set the float levels to spec in FSM. Carbs were vac sync'd after install. Pilot screws at 2.5 turns out.

Swapped out a few shims to get valve clearances into spec. Timed cam back in using FSM specs. New gasket and plugs.

New tach drive gear housing and seals.

Rebuilt tank petcock.

Changed a ton of seals to stop the oil leaks

New chain and sprockets.

New oil, oil filter, and air filter.]

New fuel lines and vac lines. Replaced all the AIR valve hoses.

Bike has stock exhaust and airbox, all are in place when running.

Bike started right up after reassembling but I am having a heck of a time getting it to run properly. Sadly it runs worse than before the work. The idle is all over the place, will rev up and then almost die off. I tested for intake vacuum leaks with propane and got no rise in engine RPM's. I've checked compression, all 4 just shy of 170, checked the coil resistance, tested out good. Ignition timing is good, coils are getting less than a volt difference from the battery. The mixture screws almost seem to have minimal effect on how it idles. Bike is very weak in the upper RPM's now compared to before.

I'm stumped on this one, all the work was by the book and this is not my first 4 cyl older bike. It seems like a fuel or ignition issue but I can't pinpoint exactly what and I hate to keep throwing $$$ at it without some diagnosis. I have noticed that it runs smoother with the 3rd cylinder plug disconnected, feels like that one is missing occasionally.

I'll gladly post up a video of it running if needed.

Any thoughts? I'm stuck driving the truck or rising the wife's 250 rebel

Sounds like you've done all the right things so far - must be something you haven't thought of or overlooked....? May be a silly suggestion, but are your spark plug leads connected correctly - ie is the timing sequence correct? (thought maybe your symptom of the running improvement with removal of plug lead no3 might be a clue) Good luck!

Someone else suggested a Gunson Colortune for my air fuel mix fine tuning. Google it and watch their youtube videos. I am convinced this should be done on all bikes to improve burn in combustion chamber. I ordered mine yesterday.

You have more experience than I do. This forum has taught me a good chunk of what I know. Following due to similar bike and problems.

Someone else was off by one tooth when they put the cams and timing chain back on, then found it when they rechecked it. Sounds like the same symptoms.

The local bike repair shop owner told me to feel the exhaust when starting from cold, feel order of which pipes get hot first and last. If one stays cool beyond the other 3, it is not firing.

-FNG (Fn new guy)

I triple checked the cam timing when they went back in, plus I think if that was off the roughness would be more consistent and would be present at higher RPM's. Once above 3k, it runs decently. Based on this and the issues I have getting the pilot adjusted, I'm planning on pulling the carbs again and ensuring the pilot passages are clear. Not a big deal but those damn airbox hoses are annoying.

weales wrote: Sounds like you've done all the right things so far - must be something you haven't thought of or overlooked....? May be a silly suggestion, but are your spark plug leads connected correctly - ie is the timing sequence correct? (thought maybe your symptom of the running improvement with removal of plug lead no3 might be a clue) Good luck!

Plugs are hooked up correctly, pulled the caps off too to ensure the wire was securely attached.

jayrodoh wrote: Once above 3k, it runs decently. Based on this and the issues I have getting the pilot adjusted, I'm planning on pulling the carbs again and ensuring the pilot passages are clear. Not a big deal but those damn airbox hoses are annoying.

For $40 you can get new airbox boots from Z1 Enterprises that make it a snap to take carbs off and on. That was my least favorite part of the procedure, and the best $40 I ever spent! Look at this post about cleaning the carbs Patton style to get that pilot circuit. I am going at mine today, the colortune arrived too!

Patton method
www.kzrider.com/forum/3-carburetor/48928...pilot-circuit#489287

Great total steps
www.kzrider.com/forum/3-carburetor/59541...carbs-on-bike#646322

Did you perform a vacuum carb sync? This is critical for a good idle, particularly since you took the carbs apart. And speaking of that, not a fan of aftermarket carb kits since the jets are often of inferior quality to that of the OEM parts. I'd reinstall the OEM jets if they aren't buggered up. Make sure you have that jet cap installed too.

Nessism wrote: Did you perform a vacuum carb sync? This is critical for a good idle, particularly since you took the carbs apart. And speaking of that, not a fan of aftermarket carb kits since the jets are often of inferior quality to that of the OEM parts. I'd reinstall the OEM jets if they aren't buggered up. Make sure you have that jet cap installed too.

Yup, did a vac sync too. The carb kits did not come with any jets, mostly rubber, float needles, and the pilot mixture screw.

The more I think/read about this, I have a feeling it has to be pilot passages in one or more carbs. I can close the pilot mixture screws all the way and it still runs. I have to believe its running off the mains at that point and that the pilot circuit was never in play. I only soaked the carbs when I rebuilt, never cleared the passages per Pattons doc. Found some good info on this forum for these carbs, will be pulling them again tomorrow. I did get the jet cap o rings from Kawasaki so they fit really nice.

FaultedGeologist wrote: For $40 you can get new airbox boots from Z1 Enterprises that make it a snap to take carbs off and on. That was my least favorite part of the procedure, and the best $40 I ever spent! Look at this post about cleaning the carbs Patton style to get that pilot circuit. I am going at mine today, the colortune arrived too!

I saw those, I only have two that are slightly hard so it's not terrible. I'm already $1k into fixing this thing up so trying to buy only what's needed at this point. She's an ugly commuter but is in good mechanical shape. Colortune looks cool, not sure I own enough carbureted to warrant buying one. It's one of those tools I'd buy and then loan out more than I'd use it. :lol:

Woohoo, got it. Cleaned the pilot per Pattons instructions, nothing seem blocked. Decided to check the idle jets under the plugs before I put them back in, plugged up 100%. I even soaked them for an hour in cleaner, no go. Had to use some thin wire to clear out. I've never heard this thing idle so well. Almost embarrassed to admit they were plugged, but leaving it up in case it helps someone else.

jayrodoh... congrats on getting her running smoothly - jumping in here late.

I'm no expert but can strongly say that "dipping" carbs to address a problem is not the way. Best to take it all apart, clean each component individually, visually inspect, blow compressed air through all the passages and REPEAT. After reading many problem posts it typically goes back to this.

OEM jets under 25,000 miles should be good to go if the carbs are sealed during non-use