Running great on three cyclinders, Help!!!

[slip]

I am almost ready to give up on this old bike. I got this bike a month ago, and haven't been able to ride yet, with waiting for the parts and all to come in and trying to get this thing to run right. I don't mind wrenching, but this is ridiculous.

Today I took the VM29's off, and bench synced them, I didn't do this after cleaning and rebuilding them. I put new plugs in to get a baseline. I backed the air screws out 1 1/2 turns at the suggestion of a fellow member. Took her out for a blast, nah, she is still not running right. Took all of the plugs out, and they all looked clean, except for number 3, sooted all up. Actually, is it me or does the number 4 plug look too clean, like the metal didn't get hot??? So herein lies my problem. Running to rich on number 3, and not sure about 4. Just for giggles, I did a compression test on this cyclinder again. Still got right up to 150psi, so I am pretty sure rings and valves are ok. I am perplexed. Could the K&N pod possibly be bad, or do I have a circuit in number 3 carb that is not working correctly. I dipped these carbs and blew them out, but anything is possible. Here is a pic of the sparkplugs. I swear, I am about ready to sell this, and get a bandit. But if this thing was running good, I bet it would be a blast. I got it looking pretty good, polished the pipe, the fender, the engine covers with that Blue Job. Rebuilt the forks, and calipers. Cleaned the crud from the front wheel/rotors, painted the calipers and rotors. I have invested some time in this bike. I just wish I could get to run right. Ok, I am through with my rant.

 

[slip]

I just thought of something. I replaced the intake o-rings, maybe 3 or 4 is not positioned correctly. I'll check. Off with the carbs yet again.

 

[tkent02]

Your petcock is probably leaking fuel down the vacuum line into carburetor #3. The diaphrams get old and hard, develop small pinholes or whatever. Fuel then flows unregulated straight into the cylinder. There should be no fuel in this vacuum line.

Pull the vacuum line off the petcock and plug it, put the petcock on prime, put in a clean plug and see what happens.

If this lets it run right get a new petcock, $40-$60 and you are good to go until the next time the bike sits another 20 years or so.

You do have spark on all four, right?

 

[TheCafeKid]

one and two look a little lean, but its hard to tell in pictures on the forum here, cause my monitor may make them look lighter...but 3 is definately fouled, (duh) and 4 doesnt even look like its fired...

 

[Ludeykrus]

Ditto, one and two look a bit leanish, three's coked, and four has definitely not been firing. No signs of heat at all. Is it easy to get running?! Fire it up and pull the #4 ignition lead off the spark plug and see if it makes a difference in engine speed.

 

[slip]

I re-bench synced the carbs, as I didn't think that I did it right the first time, and still # 3 is running rich. I am getting good spark to both 3 and 4. And when I pull the plug cap from both 3 or 4 while running, it makes a difference. I am completely at loss. The only thing I can think of, is maybe the float needle valve came out of # 3 when I was putting the carbs back together. Very frustrating to say the least.

 

[TheCafeKid]

Is 4 wet with gas when you pull the plug?? If its not wet, its not getting fuel, because it certainly hasnt fired (the plug may have but the chamber has not) you CERTAIN the pilot circuit is clean? How did you clean the carbs?

 

[mac65]

From my experience make sure choke plunger is going all the way down and petcock vacume has to run to #3 and plug the others not looped to each other my 750 was doing the same thing exactly also check petcock as previosly posted good luck and dont give up yet but that is how igot mine on the cheap took nearly nothing to fix with some help from the gsers onhere

 

[slip]

Is 4 wet with gas when you pull the plug?? If its not wet, its not getting fuel, because it certainly hasnt fired (the plug may have but the chamber has not) you CERTAIN the pilot circuit is clean? How did you clean the carbs?

No, not really???

To clean the carbs, I took all of the jets out, and dipped them in carb dip. After letting them sit in the dip for a 1/2 hour, took them out and submerged them in a soapy water solution and rinsed them. I then blew them out with compressed air.

 

[tkent02]

Half an hour in the dip isn't long enough unless they were spotless already. Did you remove the fuel and air screws? Did you clear all the tiny passages in the carb body and in the floatbowl with spray carb cleaner?

 

[slip]

From my experience make sure choke plunger is going all the way down and petcock vacume has to run to #3 and plug the others not looped to each other my 750 was doing the same thing exactly also check petcock as previosly posted good luck and dont give up yet but that is how igot mine on the cheap took nearly nothing to fix with some help from the gsers onhere

The petcock is hooked up to a vacuum hose that goes to a tap on the # 2 carb intake. There is nothing hooked up to # 2 and # 3 ports. I thought these are for venting.

 

[slip]

Half an hour in the dip isn't long enough unless they were spotless already. Did you remove the fuel and air screws? Did you clear all the tiny passages in the carb body and in the floatbowl with spray carb cleaner?

No, I didn't use the spray carb cleaner. Maybe I should do this, huh.

 

[Guest]

Half an hour in the dip isn't long enough unless they were spotless already. Did you remove the fuel and air screws? Did you clear all the tiny passages in the carb body and in the floatbowl with spray carb cleaner?

+1 on that - you need to let them sit in the dip at least overnight. I typically let my carb bodies sit for 24 hrs in the dip, then use about 2 cans of carb spray each through all the passages, then compressed air through all the passages.

 

[TheCafeKid]

Well, what you SHOULD do is completely disassemble them again, and soak EACH BODY AND BOWL for AT LEAST 24 hours....Yes, im not kidding.. i know the instructions say 30 minutes, but thats simply not going to work on gas that has varnished up and sat for god knows how long... I promise you if you take the time to do it correctly and right, you will be SOOOO happy when you get them back on the bike and it fires right up...

 

[slip]

Ok, what do I have to lose. I have had the carbs off so many times that it really doesn't matter anymore. I could do it in my sleep. I am waiting on a part, caliper piston dust boot, so I don't have front brakes anyways. Oh and I have discovered such an easy way of installing these, I will have to take pictures and post them for all to see. I tried the paper clip method and got no where.

 

[Don-lo]

You are correct, 29mm smoothbores do not have a vacuum takeoff on #3 carb for the petcock. Those 2 vents need to be open.

Is the pipe on #4 heating up when you run it?

Have you tried swapping parts from 3 to another carb? Separating the carbs again is ridiculous. You can flush out those passages with gumout and air and verify they are flowing. Concentrate on the precision surfaces, using fine copper wire strands to verify they are open.

Odd things to look for:

- Different slide cutout number
- Different needle number
- Different/internally corroded needle jet tube
- Bad choke plunger
- missing plug in carb body
- damaged fuel screw/port

If you see nothing, swap all the components in the bowls, #3 to #4, see what happens

also, swap #2 and #3 plug wires, please

 

[slip]

You are correct, 29mm smoothbores do not have a vacuum takeoff on #3 carb for the petcock. Those 2 vents need to be open.

Is the pipe on #4 heating up when you run it?

Have you tried swapping parts from 3 to another carb? Separating the carbs again is ridiculous. You can flush out those passages with gumout and air and verify they are flowing. Concentrate on the precision surfaces, using fine copper wire strands to verify they are open.

Odd things to look for:

- Different slide cutout number
- Different needle number
- Different/internally corroded needle jet tube
- Bad choke plunger
- missing plug in carb body
- damaged fuel screw/port

If you see nothing, swap all the components in the bowls, #3 to #4, see what happens

also, swap #2 and #3 plug wires, please

Great suggestions, I will do this when I get home. I feel like I am close, so hopefully I am.

 

[slip]

Well I am a bit embarrassed. The problem with #4 was that the main jet was completely clogged. And the number 3 float height was off by about 10mm! The bike is running like a scalded cat now. Only thing is I could not fully appreciate it without any front brakes, can't wait for that caliper boot to get here. No calipers on the front! It is finally running decent!! It is not perfect, as number 3 is still running just a tad rich. But nothing some fine tuning can't fix. I am still perplexed with 3 though, as I thought for sure the float height would have cured it. Can I adjust this out with the pilot screw???? Thanks for all of the help here, and being most patient with some of the dumb questions.