'82 XS650 engine revs out of control

[victor1082]

just got my '82 xs650 running the other day but as soon as it starts up the engine revs way up and I shut it down with the key. I went and got new gaskets for where the carb meet the head. Tightened up everything and still having the issue.

[XS Rod]

Stock Carbs?
Check Idle settings?

[headcase]

Ignition advance springs too weak? Zoomiezoomie.

[grizld1]

Unless it's a non-US model or has had breaker point ignition retrofitted, there aren't going to be any advance springs in the ignition.

That replacing gaskets didn't solve the problem does not mean there isn't an intake leak. If the mounts have been overtightened at some point in the past the flanges on the mounts may have warped, so that firm contact is achieved only under the screws. Overtightening can also extrude the screw holes so that flanges on the head need to be flattened with a file wrapped with 220 or 320 grit paper. Leaks can also occur at the ends of the throttle shafts. For some odd reason Yamaha did not include the seals in the 1980 and forward XS650 parts lists, but they are identical to earlier seals, and the good news is they're current parts. The bad news is that changing them is a touchy job. Mounts may also be leaking at the vacuum barbs, and the vacuum line to the petcocks could have a leak.

Back the idle down with the throttle stop and spray carb cleaner at possible problem points, waiting a few seconds for the engine to respond. When you hit a leak rpm's will either rise or fall.

[victor1082]

I'm new to working on motorcycles so bare with me while I try to explain what's going on. I'm running the bike off of a fuel bottle not the gas tank. I have 2 1/4 hoses coming out of each carb the hoses coming out the Bottom of carbs just dangles and drops fuel I assume they are some sort of overflow the other hoses I have connected together with a barbed t the top of the T isn't connected to anything or plugged its open. When I start the bike it immediately revs out control without touching the throttle and I nuts it down for fear I'm going to damage it. It acts as though the throttle is wide open on it. Ill post some pics of what I'm dealing with the bike is set up alittle different then stock.

Attachments:

[grizld1]

Alright, we're getting down to it now. Those are not the original carburetors. They're Mikuni VM series aftermarket carbs. If you do a few searches you'll find what you need to know about baseline jetting for them; you've probably inherited the problems of a PO who didn't know what he was doing. You'd be very well advised to buy a copy of the Sudco Mikuni tuning manual and read the VM section of the Carb Guide at www.xs650temp.proboards.com ; you'll need to register and sign in there to get access to it. Sorry, but I wrote that thing once have been writing it a piece at a time since, and that's getting pretty old.

That intake--is that some kind of joke? It's way overlength, and that close radius bend is going to undo whatever benefit is intended by attempting to gain a "ram" effect from turning the carbs around. At low speed and idle you'll have fuel condensing out of the mixture before it ever reaches the combustion chamber, so forget about achieving reasonable idle speed with that setup.

[victor1082]

Thanks for the info ill look into it. I got the bike with very little info been trying to figure it out as I go.

[grizld1]

Victor, you absolutely need to lose those overlength turned-around intakes. I can't tell which VM carbs you have. Pull one off and measure the ID of the spigot with a good caliper, then order a pair of Michael Morse's Hi-Vo mounts from www.650central.com . Get some decent K&N air filters while you're at it. All those gravel strainers will do is get your cylinders torn up.

[victor1082]

Alright I pulled the stupid ram horns off have the carbs on my workbench I don't know how to distinguish what model they are there are no numbers on it I can see.

[weekendrider]

Victor1082 if you are in the dark, as you attest, start with steps. The first one being to follow grizld1's advice for reading material. The carb guide he listed is free and immediately available.
For whatever reason you have piqued his interest and you are getting valuable advice for the price of a little
effort. But to continue this education you will have to read, think and do what he says otherwise you will lose his interest. If you hang with it he will help and you can have best "badass" noisemaker in the neighborhood.
He already answered part of the "which carbs are these?" question in his second post and told you how to determine the rest.

I know the season is getting late and you are wanting to feel life in your new toy but there is no quicker way than this advice. You can waste a lot of time with helter skelter questions to arrive at the same destination.

[victor1082]

I understand I'm going to read that manual and do what griz said and go from there. I'm not worried about getting it on the road anytime soon I just want to get it done right.

[XS Rod]

I believe the term is coalesce

[richard]

Wow! now that's not something you see every day. Reminds me of the time I saw where a guy put XS650 head on backwards trying to accomplish the same thing. I never did hear how it turned out. I don't think I've ever seen a "J" tube between the Carb and intake port. You have to give the PO an E for effort, not so much for physics or thermodynamics , but it is creative.

[grizld1]

You're very generous, Richard. I give the PO's effort a "W" (for wasted). A truly creative individual takes the trouble to find out how to work with the intended medium. That's very much not the case here.

[XS Rod]

gotta agree with Griz... looks like something out of those old Big Daddy Ed Roth Rat-Fink comics...
Griz... you gotta agree... it was an eye popper and did/will give us something to chat about.
Wonder how many offers he got for them... hope mine was the highest... kidding... really...