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Backfire from carbs

  • Thread starter Thread starter lordnv
  • Start date Start date
L

lordnv

Guest
Hey all,

I just changed the manifold boots on my 1980 GS850 and that fixed the idle issue I was having earlier. However, I have a new problem. When I started the bike it initially was high idling and having 'pops' coming out of the back side of the carbs, meaning the side toward the air filters. It would happen in each carb at different times. I thought it might be too lean and so I riched it out with the knob underneath the carbs. That made the pops decrease in number big time as the RPM went down. However, as soon as I hit the gas at all the pops increase coming out of the back of the carbs. I hear it and you can see a little fine mist or smoke when that happens.

Just so you know, before I changed out the boots this was not happening at all.

Does anyone have any advice or thoughts? I'd really appreciate it...

THANKS!
 
Air leak big time. Welcome to my world. I am still trying to sort the mess out after changing my boots :P Any way did you put the new O ring in when you put the boots on? Did you try spraying them with carb cleaner or starter fluid to see if the RPMS pick up??
 
The knob under the carbs doesn't "rich" them out. It is simply an idle adjustment. It's a screw that puts more or less pressure on the throttle linkage.
 
Have you done a valve adjustment? How's the compression. Could be an air leak or a valve that's not sealing.
 
had same problem

had same problem

had the same problem after i i did a full clean up...

I used 2 gadgets ...

Guage Balance : Got the balance correct. if you have 4-1 / 4-2 (without cross over) exhaust then all same level, 4-2 withcross over - then middle 2 should lower

Colourtine : Checked the color on each cylinder to get the color from yellow to bunsen blue...stop there...repeat the same to all cylinders. Make sure the guage is still on when doing this. balance again if requried.

pop's are due to lean conditions, do you still have the same problem if the filter is still on ?

check the balance screw nuts and the washers there---they too tend to leak causing a lean mix

Check if any of the pilot jets are blocked...
 
Still not working

Still not working

Hey Guys,
Thanks for the advice. I've tried everything I can think of to fix my vacuum leak without any success. I've installed new O-rings in the manifold boots, greased them, tightened them down with new bolts and washers, tightened the sync port bolts, and tightened the clamps between the carbs and the boots as tight as possible. Still, I have this backfire from my carbs. It happens from all cylinders and it comes back out of the air filters. Assuming I still had a leak I sprayed some carb cleaner around the boots and as expected had a rise in RPMs. I'm at my wits end trying to figure out how to get rid of this leak. Any thoughts?
 
Did you adjust the idle mixture yet? My '81 550 had a hanging idle because the mixture screws were too lean.

The carbs come with covers over the screws that needs to be removed if they are still in place. The photo below shows the location of the screw.

007_AIR%20SCREW%20LOCATION.jpg
 
I've tried that, but I still have this stinkin air leak problem. I'll continue to fiddle with the air mixture screws and see if that at least gets rid of the pops.

THANKS!
 
Mr. lordnv,

Have you sealed up your airbox? You'll need to install sticky-backed HVAC type weatherstripping on both side covers of your airbox (don't forget to clean up any old stuff still stuck on) and on top of the air filter cage. These bikes are particularly particular about air leaks anywhere in the intake system. Forgive me if I state the redundantly obvious.

Thank you for your indulgence,

BassCliff
 
My bike has pods on it, which it also did before I changed the manifold boots. It has been rejetted for the pods. I notice a rise in RPMs when I spray carb cleaner around the boots, and it actually happens when I spray around any of the boots, either on the left or the right. I have changed the boots, O-rings, bolts, washers, clamps, etc. I can't think of anything else that would be causing a leak. I wouldn't have any problem with the leak or would have even noticed it if I didn't have these 'pops' coming back from the pods. Strange thing is that before I changed the manifold boots I had none of this 'popping' going on. Running too lean? Probably. But the leak? Not so sure why or how.
 
Do the manifolds have to be installed in an order for this model?
Are you positive they are the correct manifolds? What part number(s) came with them?
If correct part number and any manifold can go wherever you want, are you sure the carbs "popped" into the manifolds fully?
Did the manifold o-rings fit correctly into their groove or did you have any problems at all?
 
Guys

I have taken the whole setup apart and reassembled it a couple times. I put the o-rings in place with grease to make sure they line up and don't move during installation. The boots are asymmetic, and so I have the L on the left and the R on the right. The carbs actually fit really well into the boots with a satisfying 'pop.' I thought the OEM clamps I got didn't feel very tight and so I put screw-drive pip clamps on it to hold it better. I just compared my part numbers to those on the online references, and they match I'm not sure what else to try. Now I fiddled with the air mixture screws and the dumb thing won't start at all! AAHHHHH!!!!
 
Well, I don't know. If spraying around any/all manifolds raises the rpm, it's obvious you've missed something/done the same thing to each manifold.
Since you say you're positive the new manifolds are the correct ones and mounted in correct order, only other things I can think of is how much you tightened them and the possibility the o-rings are not positioned correctly. Whatever it is, each manifold probably has the same problem.
Correct torque is about 6 ft/lb. Grease helps the o-rings last but too much could cause an installation problem that you may have missed?
 
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