Idle Screws - Confused!

Well, I couldn't help myself. I went down to the local shop, and asked if they could help me tune the idle mixture on my Mikuni's for my Maxim X. They told me no, and their procedure for tuning was turn in until misfire, turn out until misfire, and then leave the screw in the middle.

I thought - what the heck, couldn't hurt! I turned in until misfire, and turned out, and out, and out, and the idle went up, but it never misfired! Now I feel stupid, because I lost all of the factory settings. I left all of the carbs on 2.5 turns out, but it is not running like it did before. By the way - the Mikuni screw is on the engine side, and it is a air-fuel mix, so turning in makes it lean.

Sorry for the gripe. Now to my question:

When I turned in all the way on cylinders 1,2, & 3, I never got a clear misfiring sound. When I turned in all the way on 4, the whole bike would bog down and almost die. This is confusing to me. Why would only this one carb do that to the bike? The bike doesn't sound like it is running on three cylinders, although it is rough now that I screwed with it. Maybe I fooled with the settings enough that one of the other cylinders is occassionally misfiring, and it is hard to tell.

Also - my vacuum readings never changed substantially... Is that because of the way the Mikuni's are set up?

 

By the way - I will not be riding the bike until I buy and use the colortune. This sucks, but I deserve the kick in the pants for getting anxious anyway.

 

Richard,

Colourtune is essential for correct tuning on these bikes. It is near impossible to "ear" tune a four carby bike as adjusting the mixture on one carb will not make a noticable difference to engine tone.

However you can get close by pulling the plugs and adjusting to the mixture to match the lean/rich condition of the plugs. Take it for a ride to clean the plugs off and check/adjust again. As you are trying to set the idle circuit you don't need to do the flat out and kill method. Just general riding is suitable for setting idle mixtures.

Still, go the colourtune. :wink:

 

If you have a YICS bike, the cylinders are "sharing" intake at lower speed, and idle. They will draw some fuel/air from other cylinders. This is why you can't get a clearcut misfire. When you screwed the pilots all the way in you did it gently, right? Screwing them in tightly will deform the needle/seat, and make proper tuning difficult. Barring this, I would set them all at 2.5 - 3 turns out (full 360 degree turns), until you get the proper tools to do the job. I would also never go back to that shop. You can tune a single carb by ear, but a bank of 4 (especially with the YICS) is impossible.

BTW 2.5 turns on the pilots is generally accepted as stock setting.
A little more info about your bike would help.

 

You can tune by ear well enough to get the bike rideable sometimes. Had you inserted the YICS tool this method may have worked better. Nothing will set the carbs accurately other than an exhaust gas analizer or the colortune. The idea of turning out until misfire is nuts. It shows that this shop doesn't possess the needed knowledge or equipment.
I really feel bad now that I missed your bike Saturday. Part of it was misscommunication. Gary had brought his 12mm colortune and I didn't know. Of course I found out after you guys announced you had to leave. Let me see if I can work something out with the guys in Dallas. I will PM you when I know something.