TOPIC:

Hello again. 77 kz750 twin. I removed the pods and put on a stock air box and the plug on the left facing from rear of bike is black while the right plug is white, in fact the exhaust pipe started glowing red. This was doing this prior to rebuilding the carbs, I had thought I had found the problem when I noticed a hole in a hose the goes between the carbs the synchronizing hose. that did not help, also when I kill power I get a very loud backfire after engine has stopped running, this is stock electrical. new plugs get discolored within minutes of engine running. I am very new to actually working on bikes, I am assuming I have a air leak still, but I am becoming quite frustrated. Or could timing cause this? I want to know what I need to check next. PS. It has a two into one exhaust.

While I cant answer specifically I do want to say DONT run this bike until you get some good answers. You can burn a valve or a piston with that lean cyclinder (the white one)

you might check to see if you have both cylinders firing
i had the wires crossed on my 900 and only two cylinders were firing. i got the same backfire when i shut her down. rewired the cylinders and she runs great maybe a plug or plug wire. pull one plug wire off or quickly feel the exaust to see if the one opposite to the glowing is hot or warm.

The cylinder with the glowing pipe is sucking air somewhere, most likely a cracked and leaking intake manifold.
On the 750 twins both plugs fire at the same time, so if the timing was off on one cylinder it would be off on the other one also.

Spray some ether/carb cleaner/propane (from a propane torch) between the carb and the head on the side that's glowing while it's running and see if the motor speeds up.

Double check the exhaust connection at the head. Make sure it has a gasket and has a solid connection with no leaks. Air can get sucked in here and lean it out too.

Thanks for the replies. I tried the wd40 idea that I had read in the archives and I did not get any change at all, I sprayed it on and around intake boots, I will try the starting fluid next. I do have a extra pair of used intake boots, Should I use gasket sealer between boots and engine when reinstalling ? So bad valves would not cause this? And also I should mention when engine is warmed up with choke off, bike idles at about 3000 with idle adjustment turned all the way out. And pilot is about 1.5 turned out, I assume this high idle could relate because of a vacuum leak. Once again thanks for the help.

hiebs wrote:

Thanks for the replies. I tried the wd40 idea that I had read in the archives and I did not get any change at all, I sprayed it on and around intake boots, I will try the starting fluid next. I do have a extra pair of used intake boots, Should I use gasket sealer between boots and engine when reinstalling ? So bad valves would not cause this? And also I should mention when engine is warmed up with choke off, bike idles at about 3000 with idle adjustment turned all the way out. And pilot is about 1.5 turned out, I assume this high idle could relate because of a vacuum leak. Once again thanks for the help.

It could be the valves need to be adjusted, do you have a manual to guide you thru this? If not go here and take a look. www.kz400.com It has manual pages you can look at.

When you say 'intake boots' I think of the rubber boots between the carb and airbox. When you say 'intake manifold' I think of the hard rubber connection between the carb and head. It would not hurt to put a light smear of hi-temp sealer between the intake manifolds and head surface, as long as the manifolds are not cracked and leaking.

i would say that because of the high idle you have an air leak for sure. I had a dirtbike that when it was cold, it had a really high idle.....but as soon as it warmed up the air leak closed and it cam back down to normal. The leak was in between the intake manifold and head. I threw a new o ring in there and smeared some high temp permatex in there, and that took care of the problem:silly:

Update, I figured out my running lean problem. There were two main jets in carb, one was wedged in the needle jet holder and the other one in the correct spot. And on the rich cylinder one of the valves were out of spec. Now the old lean cylinder is some what rich. could timing cause it to run to rich? I have not had a chance to sync carbs or time bike yet. I was quite happy how quickly the bike fired up, I had used cream liner on tank and cleaned carb bowls so there was no fuel. Put gas in tank put on choke hit start fired right up on second crank. So close to finally having this bike on the road.

location in signature please