SUZUKI T500 1971, Running hotter on one cylinder

[DENNISTHEMENACE]

Hi

I have been working on a T500 J. The engine has been fully rebuilt before coming to me.
It is running 150 Main Jets, 30 pilot jets, 2.5 slides, Float height 27mm. Timing is spot on, Oil pump set up.
Carb bodys been ultrasonically cleaned all passages clear and checked.

I have gone round in circles. It would not run on right hand cylinder, we swapped carbs and fault moved with carb. In the end we have swapped the slides about and it now runs and rides and ticks over but the right hand cylinder is hotter than left. Also the airscrews seem to make no difference at all!!

I am beginning to think both the air screws are incorrect. Ours have no recess for O ring. Were the 500J different. Any pictures of mixture screws or useful advice appreciated

[karl pa]

Welcome to the forum

Were the 500J different

Yes the early 500s had different carbs from later 500s, they were not vented to atmosphere. The early ones had 150 mains and later ones had 97.5 mains.
It sounds like your one carb may be partially blocked, or has air leak causing a lean condition.

[jabcb]

Check ignition system. Had problems with a plug cap on a GT750 that caused the right cylinder to not run correctly.

Is the battery in good shape & fully charged. Battery & charging problems tend to first manifest mostly on one cylinder.

[karl pa]

It would not run on right hand cylinder, we swapped carbs and fault moved with carb.

I would think it is a carb issue,since it followed when you swapped.

In the end we have swapped the slides about and it now runs

Can I ask what you mean by swapped slides about?
My first thought was one might be lean, but it could be one is too rich,maybe from a heavy float?
Sometimes the mixture screws don't seem to do much at idle, but normally come into play when you have surging at deceleration.

[ConnerVT]

Your have me a bit confused.

The T500 carbs are not identical. They are a mirror image of each other. Swapping the carbs - you installed them so the adjustment screws are now facing inboard, instead of pointing toward the outside of the bike?

The slides are also not interchangeable. One of the most common mistakes people make is installing the left slide in the right carb, and vice versa. As there is a cutout edge on one side, it severely affects performance, to where the engine may not run at all.

My gut tells me your issue may be one of three things (again, common issues when dealing with the T500):

1. Still have a (partially?) blocked air passage. Ultrasonic cleaning alone won't always clear blockage deep in a carb, especially if it has been there awhile. If it can't get wet, the vibrating solution won't break it up. Especially when using a small home unit;
2. Using aftermarket brass. I hate aftermarket kits. I've measured up a number of them, and none match OEM Mikuni parts.
3. Be sure you have the right carbs. Many people may have had their hands on the bike over the past 50 years. The early carbs, which do not have external vents, use a 150 Main Jet. The later carbs, which have an externally vented bowl (overflow hoses) use a 97.5 Main Jet. Don't assume because it is a 1971 model that it still has its original carbs.