Carburetor problems I think ... - Motorcycle-Journal Forums

alextnecc · 11-04-2006, 07:49 PM

I have a 1987 FZ700 with carbs that I have stripped down and cleaned twice. They are mikuni BDS34 (2KT00) carbs which are factory carbs for this bike, downdraft jobbers with the pilot screw plug still in and untampered.

The original problem was that the bike was not running. I cleaned the carbs and was able to make the bike then run with choke on only. The minute choke was off the bike would die. Needless to say this is symptonmatic of a pilot jet / pilot circuit problem so I stripped the carbs down again and cleaned them again a bit more carefully.

Being sure that the carbs were completely clean. The carbs look spotless now and now they are back on the bike. The bike starts now and acts as if it is loading up and running rich and I cannot set the idle properly.

I checked the float level and it is correct when the bike isnt running. When it is running it gets abou 5-10mm higher float reading on the carbs. I took the bottom of the carb off and key on the bike so the pump kicks and manually press the float up to see if it stops flow. It seems to and it doesn't seem to be getting any seepage past the o-ring on the needle valve testing like this. The bike is not dripping fuel from the overflow when running or not running so I know the bowls arent overflowing to the ground. There is connections between carb 1&2 and 3&4 for the overflows to ground.

When I goose the throttle it seems responsive and the idle doesn't always drop to where it previously was. It seems like the bike is loading up and after idling for a while it wants to die unless I rev it up then it doesn't always and return to idle. I sync'd the carbs manually so I know that they are correct and they look perfect. I setup my vacuum gauges and all four cylinders look perfectly matched.

When I adjust the idle screw the effect doesn't happen instantaneously and a few minutes later after screwing with the throttle the bike is idling at 4-5k. If I repeatedly rev the snot out of the bike it seems to be good. But idle just seems to load up and kill the engine.

I am not sure about this but at one point I didn't have to use choke to start the bike and the engine was cold along with air temp in the garage. I have to make sure that the idle screw is backed all the way out and then screw with the throttle a bit to start the bike when it seems like it is stumbling when starting to get it to run.

The electrical is all good and spark is very strong. I straightened out all those problems already. The plugs that cover the a/f screw are still so they haven't been touched yet. I haven't touched the a/f mix screws because I have no clue about what the baseline setting is for the a/f screw the service manual doesn't spec it for this bike.

I sprayed the carb boots and everywhere that I believe a leak could happen with wd40 and no noticeable change. Not sure what it could be and I was sure to check the diaphrams carefully for holes or leaks and they look great even perfect.

Could this be something related to the engine running rich ? Could it be a float related problem that is making the bike run that rich. When a bike runs rich what symptoms will the bike give (meaning will it load up) ? Is there something else that I should look for ? Could I have a valve issue by chance ? Does anyone know what the baseline setting is for the a/f mix screw on this bike ?

I am pretty good with motorcycle repair and really good with carb rebuilds and cleaning but for some reason this bike is throwing me for a loop. I am pretty aggrivated with it and probably not thinking clearly but any ideas anyone can give would be much appreciated.