Setting mixture screws

[Curtie94]

I have a 1985 GS550ES 4 valve.

It has the 2 barrel style carbs.

I attempted to set the idle mixture using a colortune.

There are 4 mixture screws just like a 4 carb setup. But either way. When using the colortune I adjusted the mixtures richer until the flame changed to a orange blue tinted then went a 1/4 turn leaner. 3 of the 4 cylinders are between 2.75 to 3.5 turns out but cylinder 4 is at 1.5 turns out.

Any ideas why 1 cylinder would act so different? Carbs are clean I tore them down and ultrasonic cleaned them, then blew all orifices out with carb clean and shop air. I did check and try a different mixture screw in cylinder 4. Compression is 150psi across the board.

The only other thing I could think of is the pilot jet. I even swapped plug wires.

But I dont think the color tune is the best on these carbs. I would think 2 to 2.5 turns out would have been sufficiant. The color didn't change as much as I think it should. It went from blue for about 2 turns to orange.

Is there any reason for 1 cylinder to run richer?

 

[Steve]

If you haven't THOROUGHLY and COMPLETELY cleaned the carbs by dipping them in carb cleaner overnight and replacing all the o-rings, you are wasting your time trying to adjust them.

That being said, there are differences sometimes. On my son's 650, three of the screws worked well between 2.5 and 2.75 turns out, the fourth one had to be almost 4 turns. That one is far enough out to maybe hint at a different-size pilot jet, but I never tear them apart to verify.

I'm surprised that you actually got to see a color change. Many of us have tried that on the CV-style carbs and have only seen the flame die out when it was too lean, but never changed color.

.

 

[Guest]

Any ideas why 1 cylinder would act so different? Carbs are clean I tore them down and ultrasonic cleaned them, then blew all orifices out with carb clean and shop air.

He said he tore them down and ultrasonically cleaned them. Ultrasonic tanks kick azz. I don't use my dip cans unless the carbs have been sitting for a decade filled with varnish. Sounds like he did a thorough job.

My guess is the one carbs jet may be flowing, but it may not be fully open like the other three. It could have been the jet from the #1 carb which is the one that always gums up the most. I like to run a wire through all the jets so I can feel the same resistance or lack of. I like these sets as it gives me many sizes and some of them are wounded like guitar strings that allow you to open up the blockage easier like a file.

 

[Curtie94]

I actually use the carb dip tanks in my ulrtasonic cleaner. It works real well. I guess I will need to remove the bowl and see about removing that pilot jet and cleaning it again, but would't a partially plugged jet cause me to turn the mixture screw put more?

Because on cyl 1 the mixture screw is at 1.5 turns and if I go to 1 3/4 turns the flame changes to orange.

I will remove the carbs again and just double check the pilot screws make sure they are clean.

Unless there is something else?

 

[JTGS850GL]

I actually use the carb dip tanks in my ulrtasonic cleaner. It works real well. I guess I will need to remove the bowl and see about removing that pilot jet and cleaning it again, but would't a partially plugged jet cause me to turn the mixture screw put more?

Because on cyl 1 the mixture screw is at 1.5 turns and if I go to 1 3/4 turns the flame changes to orange.

I will remove the carbs again and just double check the pilot screws make sure they are clean.

Unless there is something else?

I wouldn't waste your time unless you're prepared to do a complete teardown, poke and dip. The passages in the pilot and enrichment circuits are very small and are the most prone to getting clogged. None of those passages can be cleaned without complete disassembly.

 

[Curtie94]

Carbs are spotless I did dissemble and dunk them using carb dunk tank solution in my ultrasonic cleaner. I cleaned them a few weeks ago.

I found that a previous owner changed the pilots from 37.5 to 40. But I noticed that the pilots had a k on them that looked like a keihin logo. So I took pilots from a spare carb rack I had off a parts bike and cleaned and installed them. The pilots I removed where actually longer then the correct mikuni jets.

Started the bike and it idles smooth. I set the mixtures after letting the bike warm up and got them all set using the gunson. They are all between 2 and 2.75 turns out now and the bike falls right back to idle after blipping the throttle.

The keihin jets must have the same thread but not the same flow rate or taper where it meets the carb.