Air mixture, idle

[MadHatch]

hey guys,

I have two mikuni carbs, and I can only find one screw that controls anything. It looks to be the air mixture screw. It's in the right carb towards the back (on the air filter side of the carb).

I've read to tighten it and loosen two turns. But when I loosen two turns, my idle ends up being overboard once the bike warms up. I'm also confused on how I have two carbs and only one of them has a mixture screw and not the other. Because they are not stock carbs, I'm a bit lost and new to carbs. I know this is simple, but I just don't know why the idle is going nuts. If I really loosen the screw, the idle will be better, but the bike will overheat it seems.

Are these signs pointing to a air leak in on the the seals? Or is there another screw or adjustment I should make?

Thanks everyone

 

[weekendrider]

A picture of what you have will help us, help you.
In the mean time read this. It may help. Oh and quit turning things till you know what is what.
Not trying to be mean or cruel. Trying to save you from yourself.

 

[MadHatch]

I guess the best start is to show these photos of the carbs. I've been doing tons of research on it all, but I can't specifically find these carbs. Can anyone help identify these?

 

[5twins]

I doubt you did much research. Those are aftermarket VM slide carbs, about the most common aftermarket carbs used on these bikes, and they have been for the past 30+ years.

I think you've got them mounted on the wrong cylinders. There's a spring-loaded idle speed adjustment screw sticking straight out the side. I don't see it on either carb so I'm betting it's on the inner side of each one. Swap them side to side and these screws will be on the outside so you can easily access them. The little brass screw that angles down into the side by the air filter is the air mixture screw. There should be one on the other carb in the same spot. You'll have to look between the carbs to see it. This adjusts the amount of air delivered to your idle circuit.

 

[MadHatch]

Awesome. Thank you.

Yeah the guy before me had them mounted this way, and I didn't know if that was correct or wrong or what. I'll switch them, and now I'll have a starting point to diagnose my issues. New to all this, and just trying to learn. Appreciate the help!

 

[MadHatch]

ok, i have switched the carbs so the spring loaded idle screws are both facing outwards.

I turns the air screw all the way in, delicately, and then turned it out two turns.

I'm finding several issues, The bike may start, but will cut if i don't have the throttle open. My spark plugs are burnt, and the pods are backfiring. these are all symptoms of running lean, correct?

But once I richen the air mixture screw, it doesn't seem to make much of a difference.

Could this be a jetting issue?

Thank you in advance. Want her running while there is good weather.

 

[Tomterrific]

The most common problem with old bikes is the pilot/idle jet plugging with varnish (dryed fuel). You can try this simple trick if they have not set long. Remove the mixture adjusting screw and stick the little red tube from a can of spray carb cleaner in the hole. Give a blast of the carb cleaner to melt the varnish. Give a few more after giving the cleaner time to work. Wear eye protection because the spray will turn and blast out.

 

[grizld1]

If you read the VM section of the XS650 Garage USA Carb Guide (click the Tech button and follow the menus to the link), follow the instructions, and check all of your jetting against the recommended baseline, I'll be happy to help with any remaining issues. Your "ton of research" evidently missed it.

 

[weekendrider]

He was linked to it(the carb guide) in post #2.

 

[grizld1]

Yep, you gave OP the link, but it doesn't look like he took the trouble to read it, or if he did read it he figured it was too much trouble to use it. My memory is getting weak but maybe you can remember just how it went--you know, that thing about horses and water?

 

[TwoManyXS1Bs]

You can break a horse, but you can't break water???

 

[buzzword]

Yep, you gave OP the link, but it doesn't look like he took the trouble to read it, or if he did read it he figured it was too much trouble to use it. My memory is getting weak but maybe you can remember just how it went--you know, that thing about horses and water?

so many assumptions. the energy you put into this grouchy post may have been better suited being helpful beyond "hey i threw the manual at him, not my fault he can't figure it out!"

everyone starts somewhere, and so did you.

 

[grizld1]

No, Bubba, I didn't "throw a manual at him," I wrote the sonofabitch, and I get real tired of people who think it's less effort for me to write it again for them individually than it is for them to read it in the first place. I saw no questions about material in the manual; if I had, they'd have been answered, but there wasn't a thing to indicate it had even been looked at. Bottom line: if you're going to do it yourself, then start by doing some looking; don't expect to be spoon fed, and don't think that information only signifies if it's addressed to you personally. BTW, if you think I'm crusty, you should have turned a wrench in that somewhere I started.