Author Topic: white smoke?!?!??!? (Read 7035 times)

oldk6guy · « **on:** July 15, 2013, 05:52:44 PM »

So...just bought a bike. I'm getting it ready to ride. I adjusted the valves, set the points, new spark plugs. It was running but really rough. Missing and sputtering. Decided to rebuild the carbs. So, I did that. She runs much, MUCH better. Only now I have a white smoke coming from cylinder 3. It may have been present before the bike just was barely running so idk. Any ideas what this might be? I have yet to sync the carbs but none of the other cylinders are smoking. Bike is 76 cb750k. 4to 4 drag pipes and air horns on the carbs. I rebuilt the carbs w 110 mains and I'm on the 4th from the top needle position. Would really like to get this bike on the road tomorrow.

Greggo · « **Reply #1 on:** July 15, 2013, 05:53:57 PM »

Put a few miles on it and do a compression test.

bjatwood · « **Reply #2 on:** July 15, 2013, 05:59:08 PM »

Oil and gas mixing together and getting burnt out the exahust pipe. Could be from the rings not sealing well on that cylinder.. Run it a bit, it will either get better or much worse.

nevernoluck · « **Reply #3 on:** July 15, 2013, 06:07:14 PM »

My bike done it directly after I adjusted valves, went away after one ride, it's been a few weeks with no more smoke until yesterday I came inside to get my helmet and left it choked on high idle, it was smoking white out of three and four, took it off choke never saw it again. Just my .02, might be bad might not

oldk6guy · « **Reply #4 on:** July 15, 2013, 06:15:03 PM »

It only has 22000 original miles on it. The guy I bought it from owned it for 7ish years and never even registered it. He didn't ride it very much.

scottly · « **Reply #5 on:** July 15, 2013, 07:31:32 PM »

Quote from: oldk6guy on July 15, 2013, 05:52:44 PM

So...just bought a bike. I'm getting it ready to ride. I adjusted the valves, set the points, new spark plugs. It was running but really rough. Missing and sputtering. Decided to rebuild the carbs. So, I did that. She runs much, MUCH better. Only now I have a white smoke coming from cylinder 3.

Is the #3 exhaust pipe sizzling hot? How does the new plug look?

seanbarney41 · « **Reply #6 on:** July 15, 2013, 08:24:39 PM »

any bike I've ever had that sat around for a while smoked pretty good when first warmed up...it might stop smoking, it might not. Quite often I think it is just residue burning out of the exhaust pipe. If there is a mouse nest in there, you will smell it.

oldk6guy · « **Reply #7 on:** July 15, 2013, 08:29:25 PM »

This isn't the first start. It ran when I bought it. Just not well. I've ridden it. The smoke is either new or just more noticeable since the tune up and carb rebuild.

seanbarney41 · « **Reply #8 on:** July 15, 2013, 08:34:23 PM »

yes, but did you fully warm it up when it was still running poorly?

oldk6guy · « **Reply #9 on:** July 15, 2013, 09:50:06 PM »

Yup. And like I said the smoke may have been there before the tune up. Just not as noticeable. It almost seems like #3 is barely firing....I'm really stumped.

scottly · « **Reply #10 on:** July 15, 2013, 09:55:24 PM »

Quote from: scottly on July 15, 2013, 07:31:32 PM

Quote from: oldk6guy on July 15, 2013, 05:52:44 PM
So...just bought a bike. I'm getting it ready to ride. I adjusted the valves, set the points, new spark plugs. It was running but really rough. Missing and sputtering. Decided to rebuild the carbs. So, I did that. She runs much, MUCH better. Only now I have a white smoke coming from cylinder 3.
Is the #3 exhaust pipe sizzling hot? How does the new plug look?

oldk6guy · « **Reply #11 on:** July 16, 2013, 07:06:14 AM »

the tip of the plug is black and wet. But its just the tip. im wondering if i didnt have it screwed in all the way. im a bit nervous about tightening it down on this old bike. i cant seem to find the right compression tester to do a compression check. i have a nice snap-on one with 4 different attachments and none are small enough. i also went through autozone rent a tool and theirs didnt have the right size either....

oldk6guy · « **Reply #12 on:** July 16, 2013, 07:10:29 AM »

Can't seem to find a way to upload from my "smart" phone.

nevernoluck · « **Reply #13 on:** July 16, 2013, 07:13:24 AM »

If you have photobucket upload to there if not you can hook it to an attachment but need to resize it first

oldk6guy · « **Reply #14 on:** July 16, 2013, 09:11:57 AM »

put the plug back in and made sure it was tightened down this time. there is only smoke and back firing when its warmed up but its still only coming from cylinder 3.

And to Whoever asked if that pipe was hotter than the rest...yes! it is way hotter than the rest. i played with the air mixture screw, turned it out half turn made no difference so i turned it back.

dohcdelsol93 · « **Reply #15 on:** July 16, 2013, 10:51:18 AM »

I'd do a compression test. If its within 25% of the others you probably have a lean running condition from that cylinder.

oldk6guy · « **Reply #16 on:** July 16, 2013, 11:00:09 AM »

Quote from: oldk6guy on July 16, 2013, 07:06:14 AM

the tip of the plug is black and wet. But its just the tip. im wondering if i didnt have it screwed in all the way. im a bit nervous about tightening it down on this old bike. i cant seem to find the right compression tester to do a compression check. i have a nice snap-on one with 4 different attachments and none are small enough. i also went through autozone rent a tool and theirs didnt have the right size either....

.........

oldk6guy · « **Reply #17 on:** July 16, 2013, 04:29:11 PM »

Any idea where I could get a compression tester that's small enough for a motorcycle? Cheap. I'm probably only going to use it once.

nivlac · « **Reply #18 on:** July 16, 2013, 06:51:39 PM »

I bought a cheapo from Harbor Freight, and used it on my kz1100.

Tactical · « **Reply #19 on:** July 16, 2013, 07:15:35 PM »

Mine did that when I bought it too. Turned out to be the valve guide seals. Oil was seeping past them and burning off in the exhaust. Replaced the seals, no more smoke.

scottly · « **Reply #20 on:** July 16, 2013, 07:58:04 PM »

Quote from: oldk6guy on July 16, 2013, 07:06:14 AM

the tip of the plug is black and wet.

Black and wet indicates a rich mixture from that carb; you stated the problem started after the carb rebuild, so that is the first place you should look, IMHO. Check the fuel level in the float bowl with the "clear tube method" to verify it is not too high. Also, use a new plug in that cylinder, or at the least "burn the black off" with a propane torch before running the motor the next time. BTW, back-fires can be caused by both too lean and too rich conditions. They have different sounds: too lean has a very sharp pop, while too rich has more of a haw-whoomp sound, if that makes any sense?

oldk6guy · « **Reply #21 on:** July 16, 2013, 08:40:38 PM »

And this is why I'm confused. The black, wet plug would indicate a rich condition. However the backfire is sharp. And I just rebuilt the carbs w 110 mains which from what I'm told isn't big enough gor straight pipes and open air horns. I should be running at least 120 mains. With 110's and my setup I SHOULD be lean. And then the wet , black plug...

scottly · « **Reply #22 on:** July 16, 2013, 09:02:58 PM »

If you have the same jets in all four carbs, but the problem is only on one carb, check the fuel level on that carb.

oldk6guy · « **Reply #23 on:** July 16, 2013, 09:11:07 PM »

Will do. I shall google this "clear tube method". Thanx.

70CB750 · « **Reply #24 on:** July 17, 2013, 04:15:20 AM »

Quote from: oldk6guy on July 16, 2013, 04:29:11 PM

Any idea where I could get a compression tester that's small enough for a motorcycle? Cheap. I'm probably only going to use it once.

Your local Autozone may have it as tool rental, that's what I use. You pay full price with credit card and have 90 days to return it for refund.

Scottly, looking at your location I realized I was in your home turf the first week in July - we camped at Dead Horse Ranch for three nights - and went to Jerome and Sedona and tourist places like that. Nice country, loved the far views and open space.

surveywaters · « **Reply #25 on:** July 17, 2013, 04:53:19 AM »

Quote from: nivlac on July 16, 2013, 06:51:39 PM

I bought a cheapo from Harbor Freight, and used it on my kz1100.

+1 on the Harbor Freight compression tester. I bought it just for the attachment only to find that it's the same gauge I paid twice as much for at the auto shop.

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Author Topic: white smoke?!?!??!? (Read 7035 times)