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Issues with Cylinder 3, Vaccum leak?

  • Thread starter Thread starter mortation
  • Start date Start date
M

mortation

Guest
Sorry for the double post I put the original in the wrong forum :

I am having an issue with Cylinder 3. It doesnt get as hot as the other 3 and I get some sputter/backfire out of my right pipe.

Seems to run OK when the bike has been on the road for 15+ minutes but still sputters on sharp deceleration. I am thinking it is probably not related to coils, the problem doesnt appear move when I change the coil wire.

Valve gapping is write. Dont think it would be a timing issue. Has good compression so not likely a valve issue.

So I am thinking it may be a vaccum leak some place in the carb, a T perhaps? The boots and clamps are all new on both sides so they are not leaking. New air filter too.

Any thoughts or suggestions? I was thinking about cranking up the Fuel/Air screw just on #3 but I bet that will just hose my plug :P
 
#3 carb still needs some cleaning ? To test try swapping # 2&3 plug wires. If # 3 is still cold It is still the carb. If #2 is now cold It is ign
 
SqDancerLynn1 said:
#3 carb still needs some cleaning ? To test try swapping # 2&3 plug wires. If # 3 is still cold It is still the carb. If #2 is now cold It is ign
Click to expand...

Yea I did that. 3 Still stays colder. I pulled 3 apart again last time and rechecked it and recleaned the guts. I swapped the diaphrams with another carb too. The only thing I didnt do is seperate the carbs again which is why I think its an issue with a cross connect. But f it was wouldnt #4 have issues too?
 
Probably a dud plug on #3... easy way to find out is simply swap the plug with another cylinder. If the problem moves, you've nailed it.
 
There's no vacuum present at any of the carb interconnecting points.

You could split hairs and argue that if a vent line were plugged, those two carb bowls wouldn't be at exactly atmospheric (they could be slightly less), but for all practical purposes there's no vacuum there.
 
tfb said:
Probably a dud plug on #3... easy way to find out is simply swap the plug with another cylinder. If the problem moves, you've nailed it.
Click to expand...

It was a new plug, but I changed it out for another new plug. No better.
 
smagnusen said:
have you done a carb sync yet?
Click to expand...

Nooooo been a little weary of messing with the new manometer. Never done it before lol. Perhaps sunday. But a slightly off sync wouldnt cause backfiring/sputtering would it? I did a bench sync when I put them together so they couldnt be that far off. And #3 is the one without the adjusters anyway isnt it?

Perhaps a morgan color tune... But I dont have one of those.
 
Betcha it's a vacuum leak on #3. If it was just sync you probably wouldn't have backfiring. Check the boots/o-rings/clamps. As Robert said, there's no vacuum between the carbs.
 
t3rmin said:
Betcha it's a vacuum leak on #3. If it was just sync you probably wouldn't have backfiring. Check the boots/o-rings/clamps. As Robert said, there's no vacuum between the carbs.
Click to expand...

I replace the boots and clamps on both sides, Guess I will have to tear the carb apart again and see if I can see an issue this time. 3rd times a charm right? :)
 
Checked for exhaust leaks?

*shrug* Maybe it is sync... Sync can absolutely make a pipe cool at idle. Had it happen to me several times.
 
t3rmin said:
Checked for exhaust leaks?

*shrug* Maybe it is sync... Sync can absolutely make a pipe cool at idle. Had it happen to me several times.
Click to expand...

Cool yes but backfire? Dunno.

After the rebuild my Fuel T is easily rotated. perhaps it has an air leak? But then I would have a gas leak too and I dont...

Exhaust leak. Hmm I dont see exhaust coming out of any place weird. I guess changing the gaskets wouldnt be to bad of an idea. I am sure they are old and crappy anyway.

I think Sunday I am gonna pull the carbs off and check my boots again and look em over. Really cant think of anything. Other than back firing at idle or on decel it runs great lol.
 
And the answer is......


I AM AN A$$H0LE!!!

I had the #2 L boot on #3 and vice versa! Dont think that screwed up much other than the fact the airbox side boot didnt seat right on carb three and was letting AIR IN!

So I swapped em.

Then 2 & 3 were sputtering (Only a little on deceleration, pipes were all equally hot now) So everything is locked down properly on both sides of the boots. Double and tripple checked. I turned my mixture screw out to 2.5 and was in the process of using the manometer to sync my carbs when I had to call it a day cause its late and the neighbors will bitch :P

All of the cylinders were WAY out of sync. They were good when I killed it but I wanna redo the sync in the morning and make sure it is all golder. Then take it for a test drive and see how she runs :)

One QUESTION!

The Motion pro instructions say the manometer tubes should all be even. But the Clymer manual using the suzuki tool say that 2&3 should be lower than 1&4. Anyone know which is right or is tool specific? The clymer manual also mentions calibrating the manometer which isnt possible on the unit I have.
 
If you have stock exhaust (with crossover) and stock airbox, middle two cyls should be and inch or so lower.
 
t3rmin said:
If you have stock exhaust (with crossover) and stock airbox, middle two cyls should be and inch or so lower.
Click to expand...

I have a stock airbox but not stock exhaust. It is some after market 4 to 2....
 
Carb Sync for 4-1 and 4-2

Carb Sync for 4-1 and 4-2

From my understanding

4-1 : all carb same level
4-2 w/ crossover between 2&3 : 4&1 at same level, 2&3 at same but lower
4-2 w/o crossover : same level

hope this is correct
 
I have a 4 - 2 no crossover. I did it both ways and I am still getting popping out of both pipes. I must have ruined the engine side boots by having 2 & 3 backwards :( Oh well it runs and it runs good. Just pops at high RPMS or rapid decel.
 
Boots

Boots

I don't think you ruined the boots and I don't think they're leaking (based upon all that's been said and done).
 
The #3 carb is the control carb. There isnt a synch adjustment for that carb.
The 850 started as an 8 valve, VM carb'd engine. When other models went to the 16 valve head and CV carbs, the 850 remained an 8 valve design. If you have VM carbs, the fuel petcock vacuum nipple/connection is on the left side of the #3 carb. If you have CV carbs, the petcock vacuum nipple is on the front of the #2 carb. If connections are wrong, you will have loss of vacuum on the incorrectly plumbed cylinder.
Might want to check the connections.

Just a thought though.

Earl

mortation said:
Nooooo been a little weary of messing with the new manometer. Never done it before lol. Perhaps sunday. But a slightly off sync wouldnt cause backfiring/sputtering would it? I did a bench sync when I put them together so they couldnt be that far off. And #3 is the one without the adjusters anyway isnt it?

Perhaps a morgan color tune... But I dont have one of those.
Click to expand...
 
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