Runs only when on Full Choke...please help

77 KZ 650 only runs at full choke...I can get it to run without choke at rpm's above 5k but it misses and backfires from beinf to lean I would guess. I have cleaned the carbs pretty well (it wouldnt run at all until I cleaned them) the carbs were pretty bad but they look good now, I cleaned all the jets and everything found under the float bowl, all the fuel lines are flowing properly.

Any ideas? I am getting this bike ready for my wife (as a suprise gift) and I really want to get it ready for spring.

Thank You!


Jim

I too just purchased a 77 KZ650. It would start but any roll on of throttle or taking off the choke would kill it. I have ordered a completed carb kit. I will soak and clean all bras parts for at least 24 hours. I will soak the aluminum bowl and body parts for an hour. The cleaner can etch or damage the AL if left too long. I will replace ALL O-rings, seals, jets and gaskets. I will replace the fuel line too.

Your dilemma begs more questions & answers:
-Have you performed a complete carb rebuild or simply cleaned and replace old O-rings and gaskets?
-Backfiring could be a sign the floats in the bowls are sticking. May require further rebuilding or adjusting.
-Have you checked the carb to cylinder head intakes. They are rubber. They can appear supple. Check for cracks and how they fit on the carbs and cylinder heads. If not fitting well or cracked they should be replaced. Kawasaki dealers can get them for approx $140/set.
-Is the inside of your tank clean. If there is any reddish/pink buildup in there you may need to perform a chemical flush. I know that I need to do this.
-AND, check your fuel petcock and make sure ther is no closgging in that. It may require taking off and cleaning the same time you have your tank cleaned.

You are describing a lean issue which you have already diagnosed. If you have not done a complet rebuild then you need to consider this. The KZ tends to run lean even when in good stock tune. Good luck and post up your further findings. I am still learning on this myself.

I just ordered the rebuild kits from Z1, I cant see anything else wrong, I really spent a long time cleaning everything really well it looks like everything was ultrasonically cleaned now but it was in really bad shape. I did find a float bowl gasket that has a tear causing a small leak and I noticed a couple needles were bent slightly at the tip, but seriously are these carbs that fussy? I just put the main jets in the same amount of turs that it took to take them out will 1/4 to 1/2 a turn cause that much of a lean condition. I have never had to tune the carbs on a bike before so while I have good mechanical knowlege I have no expierence with this bike.

Thanks, and I will post if/how it gets fixed

Jim

You are welcome Jim. I hope this info helps. I am a relative neophite with this bike as well. I do have the pleasure of knowing some that have owned these bikes all the way back to when they were new. My brother owned a 79 KZ650. I could pull a power wheelie in every gear change! :ohmy: I am glad to read you ordered the rebuild kits. I ordred one too but not because of bent needles. The bike I purchase has only 1,746 miles on it. The carb bodies and am sure even the needles are fine. The rubber O-rings and gaskets are what I really want replaced I will replace all parts with the new kit parts because I want to eliminate as many problems as possible. If my intake boots are bad, they will get replaced. The original chain is on my bike but I have a replacement for it. Heck, it still has the original Dunlop Gold Seal tires on it. These things were not meant to last 32 years. Keep me posted. I am thinking of starting a project thread. I want to chronicle the progress. Hope you are as excited about your new old bike as I am. Stay in touch by posting your progress.

If you want to really do it right first do a valve adjustment, make sure you're not dealing with horribly out of spec valves. These shim under bucket valve trains are a bit of a pain in the ass so frequently get neglected. Out of spec valves will mimic symptoms from carbs. After valve adjustment make sure your timing is correct and all ignition parts (plugs, points, condenser, wires) are either new or good. AFTER these steps get to the carbs. A lot of symptoms can lead you to think carbs but actually be valve or ignition based.

Use the rebuild kits in the carbs, make sure all passages are clear, set your float heights (by the wet method, dry bench setting will maybe get you close but not worth it really). Spray carb cleaner on the carb holders and intake boots from the airbox (assuming you're still running the airbox) and make sure you don't have any leaks there. A leak either before or after the carbs will cause all kinds of issues.

plugged pilot circuits this spring there are two constants come spring the grass will eventually turn green again and so won't carb's after improper storage over the winter.

Forrest wrote:

-Backfiring could be a sign the floats in the bowls are sticking. May require further rebuilding or adjusting.

Backfiring can also be caused by improper timing. Might save you some time and effort to take a few minutes and check that as well.

Ok after reading this hondanighthawks.net/carb14.htm I understand what a pilot circut is and how it functions, my 650 should have an jet located tword the engine side of the carb, I am going to wait until the rebuild kits get here tuesday and install everything, paying close attention to the channels between the jets and adjusting the jet screw (I removed and cleaned these but the rubbers are in rough shape and I just put them back in the same amount of turns it took to take em out so I am not too precise)

I have checked and set the timing.

Thanks again

Jim

P.S. notice the blueing on 2 of the pipes, maybe this explains why the last guy melted a hole in 2 of the pistons I bet it has been running lean for awhile now (I swapped in a different engine from a 78)

Great info on the postings here! Looks like you are getting it dialed in. Wish you the best.

for a four stroke to melt 2 pistons it must have been some freakin lean i don't even see that happening with nitrous bikes that have fuel solinoid problems usally if it is that lean with stock type ignitions those cylinders wouldn't fire isee that kind of thing happen in big power two strokes that have crankcase or crank seal leaks but not on 4 strokes

would it be possible to send us some pictures of the jets your trying to adust as there is no adjustment in the pilots or main jets they screw in place and that is it the only possible adjustments would be in an air screw or a fuel screw if so equipped or needle heights, please do your self a big favor and buy a manual and study it closely.

I have a manual but the carb illastrations are pretty poor, if someone has a good exploded illastration that would be very helpful. I belive I am talking about the fuel screw that pokes through the float bowl...but I havent really adjusted them I just removed and cleaned them when i did this I noticed some were slightly bent at the tip and 3 of 4 had a bad o-ring gasket that and a broken gasket on a float bowl and a lot of varnish made me get the rebuild kit.


Jim