1993 Suzuki Katana 600 runs rough and stalls but stops when it gets up to temp?

The hot start problem is noticed in many Suzuki Katana 600.
Symptoms: Runs rough ,Stalls at idle only when hot, won't restart when hot, very inconsistent idle, push starting, ect. When I would push start it the engine seemed very weak when it would start, and acted like it was only running on 2 cylinders.....

I had the carbs off twice to check the choke circuit, choke cable, fuel mixture screws, float level, replaced the spark plugs, ignition coils, and did the whole carb sync'ing with my Motion Pro fluid sticks. It helped, but still had issues only when the engine was hot ( ran like a champ when cold or when below 175F). So pretty much if I'm riding (or idling) and the bike stays under 175F it runs great, but if I'm in traffic or sitting at a light and the engine gets closer to 200F+ forget it...

I spoke with a two different master techs at 2 different Suzuki dealers and 1st tech told me it sounded like a possible vapor lock problem and he'd start with the carbs and hoses. The 2nd tech told me to check the valve adjustment and could have a possible "too tight" clearance, so when the engine heats up the metal expands causing the valves to not completely seat leading to low compression, so on, and so on. So my main goal was to start eliminating possible issues being that the bike is almost 14 years old.

So I started with the valves. All adjusted ok and all within factory specs. I wrote down everything so you guys could see. No problem there.

Next I moved on to the carbs. I completely overhauled the carbs with new needle/seats, gaskets, seals, cleaned, and adjusted float height according to specs @ 7mm, ect. After digging into the carbs I came accross this small carb side fuel filter within the main fuel line. When I pulled the filter it was completely collapsed which would make more sense for a vapor lock problem when the engine heats up and runs inconsistent during idle. The odd part is that this filter is NOT labeled or mentioned anywhere within the Factory Suzuki Service Manual nor in the owners manual within maintenance ect. After doing some more research I found this little filter labeled in the Suzuki microfiche as "FILTER". So after rebuilding the carbs ( which were quite dirty and worn ) I thought to myself this collapsed filter has got to have something to do with all these running issues.

Here are a couple pics of the Factory Manual ( as you can see the FILTER is not labeled in the manual ), along with the old filter and the new filter.

Microfiche with filter SEE # 15

So after installing the new in-line fuel filter, rebuilding the carbs, and checking the valves I knew I had eliminated a few prospects for this problem. After starting the bike it idled great and ran perfect. After warming up though it started to hesitate slightly and progressively got worse as it heated up more. Finally stalled once again after it got up to about 206F and completely refused to re-start. I let it cool down and then once again it started back up.

Next I moved onto the electrical side of things and checked, battery, stator, and regulator to see if all were within "SPECS" of the manual. Regulator and Stator both checked good within the test of the manual. Battery voltage was perfect and battery was brand new anyway. After reading a possible issue with both of these parts I thought I'd better install a "NEW" stator and regulator to again shoot down another potential culprit that could be throwing me off my test results if a good "COLD TEST" would result different from a bad "HOT TEST" on the Stator itself.

Received the new stator and regulator this past weekend from Suzuki and perfomed the install. During the install the plugs, wiring, and hardware all looked good. See picture.

After the install I started up the bike again, but this time it seemed much more consistent at idle even when the engine was cold. I let the bike heat up till it hit 210F. Had a super smooth idle and very strong off idle throttle response compared to before. So once it wamed up I Sync'ed the carbs and I couldn't believe the awesome results of the new stator and regulator.


Lastly, I gotta say the bike runs WAY better now then it has in the last 7 years. Very smooth idle, crisp off idle, and runs awesome all the way to 13,500 RPM @ 100+MPH ( shhh, ooops I mean 75MPH hahaha ) Also now I can actually start the bike cold without any idle-up-choke without stalling or hesitation.

No comments:

Post a Comment