Author Topic: smoke coming out of the air side of carbs while syncing. (Read 3447 times)

asom · « **on:** April 22, 2010, 11:44:54 AM »

I've been working on this for days now. I attempted to sync my carbs and now it won't run when I throttle up. I took the carb of and cupped the boots...no air leak. put the carbs on and cupped the intake...no leaks, but I noticed that puffs of smoke coming out of the carb. Is this normal or could it be a sign as to what my problem is?

thanks as always
Scott

jkot55 · « **Reply #1 on:** April 22, 2010, 11:58:07 AM »

I would think that if you have exhaust coming back through the carbs it would be difficult to gat proper vacuum for syncing them up. I am no expert but just sync'd mine up as a first timer but there has never been any smoke emitting from the carbs.

asom · « **Reply #2 on:** April 22, 2010, 12:19:27 PM »

Also, you have a fuel/air mix not a fuel/air/smoke mix...

cb550fcafe · « **Reply #3 on:** April 22, 2010, 12:26:36 PM »

Back up to what was wrong that led you to synching carbs. That may shed some light.

If you have adjusted trying to sync and gotten way far from normal, a bench sync with the drill bit method may be a place to restart.

A severly misadjusted, poorly running engine can puff and pop back through the intake. Now an engine with severe amounts of smoke from intake side indicates more serious problems.

asom · « **Reply #4 on:** April 22, 2010, 12:34:15 PM »

the reason I started syning is the bike was only firing on cylenders 3 and 4, wouldn't idle and required choke to even run. The carbs had been removed at least four times by the previous owner trying to fix the problem. I broke the carbs down and cleaned them. got the bike running on all 4 but the idle and choke problem still stayed. I synced the carbs and got the idle down to 1000 rpms and fixed the choke issue also, but now I can't throttle the bike. Everyone told me I had an air leak so I took them off to check for suction with my hand...no leaks, but when I started it with the airbox off I noticed the smoke.

cb550fcafe · « **Reply #5 on:** April 22, 2010, 12:52:24 PM »

Can't throttle bike, do you mean it doesn't rev, it backfires, stalls?

Carb sync should be done after ignition system is perfectly tuned, after a valve adjustment is done and after cam chain has been adjusted. Reason is the carb sync depends on all these items being right. If you sync, then tune the valves, points, the sync will be way off.

Alot of carburetor problems aren't really carb problems. Make sure you have the basics covered first.

asom · « **Reply #6 on:** April 22, 2010, 12:58:14 PM »

bike stalls when I throttle. Haven't done any of the other things you mentioned. Can you give me a list and order? I've never owned a bike and I'm at a lose. Any help would be great.

cb550fcafe · « **Reply #7 on:** April 22, 2010, 01:19:08 PM »

At the top of this forum SOHC/4 Bikes, download the service manual, I think its for a CB500, but its pretty much the same for what you need right now.

Adjust the point gap then timing, adjust the valves cold engine I mean cold, let it sit overnight before you do it then adjust cam chain tension. Install nice clean good spark plugs gapped properly. Then clean out petcock filter. Then do carb sync.

asom · « **Reply #8 on:** April 22, 2010, 01:26:35 PM »

I have the Honda service manual for the 78cb750. I'll see what I can do.

thanks

cb550fcafe · « **Reply #9 on:** April 22, 2010, 01:35:39 PM »

Well, its not the same as the 550 & could get you trouble. I would use the free manual from this site. It too is a factory manual, things will match up better.

asom · « **Reply #10 on:** April 22, 2010, 01:38:29 PM »

my bike is a 78 cb750f

cb550fcafe · « **Reply #11 on:** April 22, 2010, 01:42:17 PM »

Wow, what was I thinking? I guess I expect everyone to have a 550, lol. It is my favorite you know.

Yea you'll be good with that, just do the adjustments in that order, should get you going in the right direction.

asom · « **Reply #12 on:** April 22, 2010, 01:59:58 PM »

any special tools needed? Don't know how to adjust timing.

cb550fcafe · « **Reply #13 on:** April 22, 2010, 02:07:45 PM »

Nothing really special, feeler gauges, regular hand tools, timing can bet set with a test light. You'll find it in the manual, if not in yours, its in the 500/550 one I keep trying to get you to read.

A real carb sync tool in my opinion is a must. At a minimun 4 vacuum gauges. But in a situation where you have no way to sync with a tool/gauge, the drill bit method will get you close enough to run.

asom · « **Reply #14 on:** April 22, 2010, 02:38:53 PM »

I have plenty of hand tools, I'll get a timing light and feelers, and I actually have vacuum guages. Thanks.

Old75_ratafe · « **Reply #15 on:** April 23, 2010, 12:02:25 AM »

Quick question are you syncing/tuning with the air box off and then putting it back on??? That would mess with idle. Also I had a similar issue on mine just on my #4 carb and it was my floats sticking I had to have the choke at about 1/4 open for it to run ok (even when hot) and even then after awhile #4 would load up and foul the plug.

Nikkisixx · « **Reply #16 on:** April 23, 2010, 07:07:14 AM »

Asom,
Sent you a PM. If you want some on site help or would like to borrow tools let me know.
John

cb550fcafe · « **Reply #17 on:** April 23, 2010, 08:03:14 AM »

John, that is awesome you would offer to help someone like that!!!! Thats why I love this place, so much knowledge and cool people willing to help a fellow SOHC4 member. I kinda wish the rest of the world was this way. I can sense good karma headed your way.

asom · « **Reply #18 on:** April 23, 2010, 08:15:18 AM »

thanks John. sent you a pm.

no I'm syncing with the box on. I took it off to check for air leaks. my floats are showing no signs of sticking when the bowls are off.

thanks again for all the advice.

Rosinante · « **Reply #19 on:** April 23, 2010, 09:46:20 AM »

Is this "smoke" happening with the engine running, or with the engine off? When you turn the engine off, of course there may be an intake valve opened and allowing some smoke to rise through the carbs and out. But if you're talking about the "smoke" that appears at the mouths of carburetors while running, this is a normal phenomenon. I believe it is fuel/air mist, rather than smoke. It seems to come up and out of carburetors while the engine is running. Probably has to do with air reversions due to brief, positive pressure in the intake plenum. At least, this is the case with cars. A "halo" of fog appears at the mouths of carburetors, commonly.

asom · « **Reply #20 on:** April 23, 2010, 10:10:55 AM »

It's when the engine is no longer running. If I move the throttle smoke puffs out. Could be a mist of gas and air I dunno.

Nikkisixx · « **Reply #21 on:** April 23, 2010, 11:46:30 AM »

Quote from: cb550fcafe on April 23, 2010, 08:03:14 AM

John, that is awesome you would offer to help someone like that!!!! That's why I love this place, so much knowledge and cool people willing to help a fellow SOHC4 member. I kinda wish the rest of the world was this way. I can sense good karma headed your way.

LOL, my motives are not completely altruistic: I like having people to ride with! If Asom's bike doesn't run, that's one less amigo on the road

Besides, that's how we roll down South, and on the SOHC forum

Rosinante · « **Reply #22 on:** April 23, 2010, 01:18:27 PM »

Quote from: asom on April 23, 2010, 10:10:55 AM

Could be a mist of gas and air I dunno.

Yes. I'll bet your bike has an accelerator pump.

asom · « **Reply #23 on:** April 23, 2010, 06:56:02 PM »

looking forward to meeting up with Nikkisix tomorrow for a once over on the Bushwhacker. If things go well we'll be riding down the road before the afternoon is over.

fingers crossed

Thanks folks...

Old75_ratafe · « **Reply #24 on:** April 24, 2010, 12:35:01 AM »

Quote from: asom on April 23, 2010, 08:15:18 AM

thanks John. sent you a pm.

no I'm syncing with the box on. I took it off to check for air leaks. my floats are showing no signs of sticking when the bowls are off.

thanks again for all the advice.

the floats are fine but how is the little rubber part that attaches to it and stops the fuel. My issue wasn't the floats themselfs it was that they were not sealing and stopping the flow of gas.

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Author Topic: smoke coming out of the air side of carbs while syncing. (Read 3447 times)