Issues with Cylinder 3, Vaccum leak?

[anikmankar]

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

[chef1366]

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

That's right.\\/

[mortation]

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.

[chuckycheese]

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).

[earlfor]

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

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.

[mortation]

I have CV carbs and everything is connected right. I am gonna ride it for a while and see how it makes out. Right now it only sputters a little at high RPMS other than that everything is fine. All pipes are equally hot, everthing is connected right, synced as best I know how.

[earlfor]

OK then, I think doing a precise vacuum synch will solve the problem. Manual synch's are really not meant for anything more than getting the engine to a point it will run so you can do the actual synch. The problem you are having could be caused by the #3 slide being out of position by as little as fraction of a mm in position. you would not even be able to see that small amount when doing a bench/setup synch.

Earl

I have CV carbs and everything is connected right. I am gonna ride it for a while and see how it makes out. Right now it only sputters a little at high RPMS other than that everything is fine. All pipes are equally hot, everthing is connected right, synced as best I know how.

[mortation]

OK then, I think doing a precise vacuum synch will solve the problem. Manual synch's are really not meant for anything more than getting the engine to a point it will run so you can do the actual synch. The problem you are having could be caused by the #3 slide being out of position by as little as fraction of a mm in position. you would not even be able to see that small amount when doing a bench/setup synch.

Earl

Well after swapping the engine side boots on 2 & 3 cause I had them wrong it is popping out of both exhaust pipes at high RPMS off the throttle. If I stay on the throttle there is no popping. So I must still have a small leak some place right?

Grr this is frustrating

[N56629]

I've had the same problem. It used to be #3 and has now moved to #1 so it's not a leak in the boot because nothing has changed.

[mortation]

I've had the same problem. It used to be #3 and has now moved to #1 so it's not a leak in the boot because nothing has changed.

1 & 3 use the same coil. Your issue may be coil related.

Mine was a leak. It now runs the same temp as the other pipes now that I fixed the bunched up boot. But I think I screwed up my sink ports by tightening the screw to much and shewing up the rubber around the hole. I am gonna do one more sweeping replacement of boots, Orings, sync screws and gaskets. If it still pops after that I will be replacing the exhaust gaskets and chain tensioner cause it sthere :P If it still pops I am gonna go get my hammer....

[N56629]

I would think that if it were a coil the problem would be at all speeds. Besides, I replaced the factory coils with accel. I would say boots but I haven't made any changes there. I am thinking about replacing the boot orings just so that they get removed and inspected. Even though I've just cleaned the carbs I'm thinking the pilot circuit might be the culprit because I've never removed the sealed screws. I think that might explain the low speed fuel starvation on #1. I know I have spark because I can see it and the plug is not wet.

[mortation]

I am REALLY about to loose my $h1t. This bike is driving me NUTS. I put an old boot on #2 with a new O ring and new sync screw and it is still popping. Maybe #1 is making it pop? I don't know but I am starting to get a little frustrated here.

#3 has started to be cooler again while idling.

I am about ready to smash this thing with a 50 lb sledge hammer!

I can buy all new engine side boots (Again), O rings (Again), exhaust gaskets, Coils, Wires, Plugs (AGAIN!) I am sure somewhere around $500 total and then I may still end up in the same boat.

ARGH!

[N56629]

I'm still thinking pilot circuit. One thing I noticed is that I couldn't possibly do a carb sync when the engine is cold. The vacuum on my #1 cylinder is way high. Once it warms up and is getting gas like the other three the vacuum is very close to the same.

Anyone know when the main jet takes over and the pilot no longer delivers any fuel? I'm thinking between 1500 and 1800 rpm.

[mortation]

Well I will see where I stand next week. I ordered 4 new boots with gaskets, 4 new O rings, 4 new exhaust gaskets, and a new tensioner gasket (Hey its in the same area and it was only $3!). If it still pops after that I am gonna track down a color tune and do my mixture exact. Then re-sync. And if it still pops I guess I will have no choice but to replace the exhaust. Than still popping I will rejet. Then still popping its for sale :P

[anikmankar]

Popping = Lean

no other reason....unplug one plug at a time and replace back while the bike is running. Check if the popping stops when the plug is removed ...if it does you know the problem is in that cylinder area. then you can go deeper...may have to increase the idle so the bike does not go off.


make sure you have rubber gloves or something when you do it.