VM34s, ran like a dream for two years now, shit!

right ok, Ive posted on this before a few months ago and only got links to the tuning guide. I don't need the tuning guide, I've a dozen copies of it and frankly it aint helping.

So i bought some VM34s a few years ago, swapped out needle, needle jet, main, and idle, dumped the air jet. This baby was bullet proof, pulled hard, ran smooth, easy start AKA I would have rode it across country any day, was my daily rider. 185 main, 25 idle, needle set in middle clip, needle and needle jet... i forget but god damn it worked!


This spring i start it up and holy christ the smoke!!! Terrible terrible smoke. Ive had the carbs apart a dozen times, cleaned every obvious passageway, fooled around with float height, dropped the needle, raised the needle. Shes running insanely rich, as in 3/4 of a sporty tank in 25 minutes rich. At anything under a 1/2 to 3/4 throttle she sputters like its bogging down, just drowning in fuel. Ive done cam chain, valve, and ignition adjustments, even swapped out the coils and condenser to be sure it wasnt a ignition issue. So the issue here isnt ignition or valves, done that, its not jetting, the jest were correct last year, and its not fuel as I've run a tank of fuel from every station in town, no result.

Ive cleaned the needle valves well with a swab and carb cleaner, there is no noticable debris or varnish sitting in there.

plugs show sooty sooty black

When the bike is first started there is a few seconds of clean running then smoke starts coming out bad, at this time bubbles are seen rising up through the fuel lines. Is it possible that the needle valves or more worryingly the needle valve seats are worn out after only a couple years? is there any way to correct this, can i cut a new seat into the body? Am I barking up the wrong tree? Im at my wits end here.

No oil on the plugs? Got compression? No new noises? Floats floating or are they full of gas? Carbs fully clean? I wouldn't change the jetting. Something changed.It was runnin great before so don't change anything, just keep looking for the demon that got in your motor and get it out.

B4 you futzed with the carbs, did you check all ignition possibilities?

Sounds like one of your chokes is stuck on.

hotdog said:

Sounds like one of your chokes is stuck on.

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If your high fuel consumption is not riding the bike but at rest then thats the big clue. I would expect the garage to stink of petrol. The other suggested faults would result in poor performance and so you'd get the high consumtion using high revs and wide throttle openings just to get along the road. If its using that level of fuel at rest I would suggest extreme richeness or flooding.

Working logically through it. Something has suddenly changed.

Yeah, it could be the choke (enricher) is stuck on.

OR

If one of your floats has sprung a leak it will fill with gas. If this happens it will be less bouyant and so will not float high enough to shut off the petrol flow so one of your float bowls will have a high fuel level resulting in flooding and very rich mixture. It seems very unlikely that both would go at the same time (so one side would be rich and not the other). However, there are tubes connecting carbs together, so are the carb bowls linked in this way? If so, high level in one would result in a high level in the other. (But it could be that the tube is to enrich the other carb from the enricher on one side.) My old RD350 had this system.

The other possibilty is that the valve is not shutting off properly again resulting in very high fuel levels. Again unlikely that this would hapen to both valves but if linked as I describe both sides would flood.

Hope this helps.

Let us know.

Dave

It's unlikely a sunk float with those later plastic floats, however, a leaking/stuck float valve could be an issue. But it would have to be both of them. Both cylinders are fouled, correct?

jetmechmarty said:

It's unlikely a sunk float with those later plastic floats, however, a leaking/stuck float valve could be an issue. But it would have to be both of them. Both cylinders are fouled, correct?

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Cheers Marty, I was imagining holed brass floats. There's an o-ring on the needle valve isn't there? Perhaps this has perished, split, fallen out. Sounds like the culprit. (This is all logic as I've not had carb problems .... yet but would feel confident to tackle them.)

There is a SOLVED thread here: http://www.xs650.com/forum/showthread.php?t=1262

oh yeah 145psi on both jugs, plugs fouled, the carbs are not linked, they are VM34s. Enricherners are closed on both carbs. I do wonder if perhaps the problem lies there because oddly there is little difference between open/closed plungers. I went through my ignition first before messing much with the carbs. How can these two carbs, operating totally independently of each other start puking gas like this?

Im gonna go pull the chock plunger off on and see if there is anything blocking it, but i would be amazed if there was as Ive blown air through the circuit and closing the plunger has stopped it.

no o ring on the needle valve....... hmmm

i honestly cant remember seeing one on these carbs, but, would/could it have totally disintegrated? Ill check but im pretty sure there is no groove for one.

Does this help?

not in the slightest, thats a CV carb, Im running VMs, Thanks though. I just went out and started it with the hose disconnected from the fuel tank. Ran just like it has, smoking black, until the fuel level got too low, it rev'd up then died. So maby its NOT the float level, nor the needle valve. hmmmmmmmm

Well you learn something every day.

I thought the o-ring was something the point of the needle pressed up against but there apear to be two types of valve body - screw in and push fit. The push fit has an o-ring around it.

Both are shown here - http://www.mikesxs.net/products-35.html#products

I guess if the pointed end of the valve doesn't seal against the internal surface (shutting off fuel flow) (and there's no muck) then (I guess) it's worn out and needs replacing. It doesn't seem logical for this to happen on both carbs at the same time. So, if they're not linked, my money is now on the chokes (enrichener).

ProSimex said:

not in the slightest, thats a CV carb, Im running VMs, Thanks though. I just went out and started it with the hose disconnected from the fuel tank. Ran just like it has, smoking black, until the fuel level got too low, it rev'd up then died. So maby its NOT the float level, nor the needle valve. hmmmmmmmm

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I'd say this adds evidence for level being too high. Disconnecting the fuel supply means the fuel is run down to the correct level (and then it revs up) but then when the level gets too low, it dies. In the thread posted above a similar test is done (something about disconnecting the vacuum barbs??? but I think this is just shutting off the fuel supply... my fuel taps are manual, thank god.)

Off to bed ... one in the morning here.

Dave

I wonder if your needle valve is worn. That would make it less pointy and could cause mroe fuel to come through. But im not sure man

It has to be something that happened as the bike just sat.

1. Pull bowls off
2. Check your float heights are correct & needles are free, needles can get stuck/gummed open from sitting
3. Check your floats are not holed as suggested (if older brass type)
4. Blow out your pilots with compressed air - they will be gummed up from sitting all winter
5. Clean out your choke plungers as they too could possibly be gummed up
6. Drain your bowls next time

I believe hotdog is on too something here! It's gotta be something gummed up from sitting

I would look at the ignition again . Cracks in the boots on the coil ,stuff like that . Sometimes weak ignition seems more like a carb problem .

CRAZYBEN said:

I believe hotdog is on too something here! It's gotta be something gummed up from sitting

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Absolutely agree now I've had some sleep.

"When the bike is first started there is a few seconds of clean running then smoke starts coming out bad, at this time bubbles are seen rising up through the fuel lines."

Got to be fuel.

"Is it possible that the needle valves or more worryingly the needle valve seats are worn out after only a couple years? is there any way to correct this, can i cut a new seat into the body?"
Yes, but they were OK before you put the bike away. See link supplied (above) to Mikes XS to see that these parts are replaceable. Pull out the needle valve and its seat and clean them up.

Do the same with your choke (enrichener). It's gummed up. I'm sure. You say it doesn't push down as far as you remember.

needles are free, and seats are clean. I've swaped coils and condenser, float level is a crap shoot as I the one guide I have shows the carb reversed from float arm ie doesn't look the same as mine. I've a good machinists ruler here to measure with. I've read on the old xs650 forum that float arm should be parallel with the carb body. if there is a better way to measure let me know. plastic floats so I no pinholes or dented floats.