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Bike runs bad at low rpms popping and backfiring

  • Thread starter Thread starter Speedy7722
  • Start date Start date
S

Speedy7722

Guest
Hello,

My dad recently bought a great shaped 1982 gs850gl

The owner said it ran fine when he parked it in 2009, so we got it home the first day and put fresh gas in it and tried to fire it up but realized we werent getting fuel from the tank. Unkowing that it had a vaccum petcock we took it apart and ran compressed air through it and I believe we blew out part of the diaphram, haha because now in the "On" position fuel runs out of the peetcock.

So with fuel now running we put some seafoam in it and pulled it down the road and managed to get it firing on one cyclinder. So I decided to pull the carbs and do a cleaning. I open them up to a sight of alot of yellow whitish dust from the dried gas. So after cleaning them and not having much success I went ahead and bought a rebuild kit and rebuilt all of the carbs and reset the float heights.

So now the bikes fires up and with adjusting on the air/mix screws and the idle screw it idles and revs. I put the airbox on and sprayed carb cleaner around and it did not seem to have any leaks.

Now on to the problems. The bike starts up and runs without choke now but it seems to have excessive amounts of backfiring and popping through the carbs. and I believe it only fires on 3 cylinders up until maybe 6 or 7 grand? (I have no idea for sure since the tach is not working at the moment) then its like hitting the powerband on a 2-smoke, the bike just seems to take off and everything is revving and running in sync, then you let off and its pops and backfires like crazy and wants to almost bog out wiithout feathering the throttle. The engline also seems to run awfully hot for the little time it is rode.

Me and dad have been slowly marking off the possibilities. Got the carbs cleaned spotless, rebuilt, and float heights set. There doesnt seem to be any vaccum leaks but it could still be a possibility. I assume the electronic timing advance or whatever couldnt be screwed up?

Only possibilities I can think of would be valves need checked or since both undersides of the mufflers have a like 1in diameter hole rusted through probably 3in from the tip that could be causing it to somehow run lean?

Any suggestions are appreciated.

Thanks for your help,
Josh
 
First off and most importantly..CLAMP OFF THE FUEL LINE WHEN NOT RUNNING!!! Use hemostats if youn haqve some. Youm cant let fuel be able to set under gravitational forces and not risk it slowly leaking into the crankcase and ruining the oil.

Secondly, how did you "clean the carbs'? full tear down and dipped for 24 hrs per carb body? New orings in the carbs AND the intake manifolds? ( carb holders to some ).Have you adjusted the valves and checked the timing yet?

Heres the order..

1..clean carbs by dipping ecah one for 24 hrs in the Berrymans.
2..adjust the valves while the carbs are in the dip.
3..once its running right on all 4, then sync the carbs and set the timing.
4..this bike should have CV carbs with just the 1 needle on the top of the throat close to the head..that should be about 2 to 21/2 out as a baseline setting.
5..be very gentle when setting the mixture screw..on top..go in very softly till it bottoms out. Once you feel it stop then thats it..do not force it further. Make a mark on the rim of the hole the needle goes in and turn the screw out the specified amount.
6..replace the intake manifold orings and be sure the grroves are cleaned well as well as the mating surface on the head.
7..PM Robertbarr here on the forum for the carb oring kit or visit his website...cycleorings.com. There isnt any need for "rebuild kits" for carbs unless there are broken or bent needles.
8.. set the circlips on the jet needles in the CENTER groove..this is the factory default setting ( unless you have modified exhaust thats not of stock configuration.
9..install either a new petcock or maybe a pingle fuel tap. If you go with anythingb that IS NOT vacuum operated, then you will need to cap the vacuum port nipple on carb 3 that would otherwise go to the OEM petcocks small nipple.
 
Also, the plug caps simply screw onto the wires. Unscrew them and clip about 1/4 inch off the wires and refresh the connections...be sure the plugs arent fouled. Carb cleaner wont tell the story really as far as air leaks around the carb intake manifolds go..use starter fluid..if it gets sucked in youll hear the RPMs change. In any case, do ALL the maintenance and adjusting and youll be more ready to troubleshoot properly. Trouble shooting an out of maintenance bike is like pizzing in a fan and wondering why your boots are getting wet.
 
The reason I rebuilt the carbs was because the passage plugs were shot and almost dissolved so we just went ahead and bought rebuild kits for new bowl gasket and what not. The plugs are all getting good spark and are not fouled. The mix screws are set 2 turns out from bottom and the slide needles are in there original positions.

oh and the vacuum port on the 3rd carb is capped also.
 
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Thats good...but did you replace the rubber plugs withn new ones? What was the cleaning process? If it was just some carb spray and some compressed air up the passages then your chasing your tail till you fully disassemble and soak them. Poke every hole in the pilot jets and needle jets clean with a small wire. also be aware there is a VERY tiny hole in the rounded end of the pilot jet. That has to be poked out very carefull with a real fine wire...gently twist the jet aginst the wire and avoiud breaking the wire off in the hole. I have an old wood handle wire brush that is specifrically used as donor wires for cleaning the holes.
 
Yes the plugs were replaced. Cleaning the carbs I dissasembled them the first time and cleaned all the jets and passages and yes I used wire from a wire brush. Then after getting the rebuild kit I replaced all the jets, plugs, etc. Then I dissasembled the carbs again and checked to see that everything was clean when I set the float heights.
 
I mentioined that Tom....it will most likely run fine where its at now...once he tears the carbs all the way down and does them right. However I agree he should do the valves before he syncs the carbs and does any further fine tuning.
 
No I have not adjusted the valves yet. I was going to try that next. I believe I read that the valves should have 0.001 - 0.003 in clearance? I have never checked valves before so I am slightly hesitant to jump in there.
 
Specicifcally answer this question..Did you or did you not fully disassemble them and do the Berrymans dip for each carb body for a 24 cycle...if the answer is NO, then there is your mistake..trying to short cut it. You can either doit as we are saying or just keep whats going on. Sorry to be so blunt and adiment about it but thats just the bare bones. no BS truth my man.
 
No chuck hahn, I have not had the carbs dipped. Honestly, I did not see the need if they were totally dissasembled, and all jets, passage plugs, etc replaced.
 
Heres the need...you saw all that scale and grunge in the bowls...well there are really tiny passages all through the carb bodies and that same crap is stuck and jammed in there..no amount of carb spray or air will clear the passages 100%..they MUST be chemically dipped so the stuff can be dissolved and dislodged from the passages ...so that carb spray and air can effectively flush the passages.. You have them open only a tiny fraction of what the bike requires and your getting the symptoms your getting. Keep any new orings that came with the rebuild kits and get the opring kit from Robert if you dont have all the required orings. DO NOT put any rubber or plastic parts in the dip. Get to Walmart or the local auto place and get the dip and redo them and your symptoms will vanish.
 
Alright, thats what I was afraid of. By taking off the valve/cam covers will there be any gaskets that need replaced?
 
Ok I will buy some carb dip tonight. Will the petcock not running off vacuum have any effect on things? it seems like it doesn't effect the amount of fuel getting to the carbs.
 
Speedy7722 said:
Alright, thats what I was afraid of. By taking off the valve/cam covers will there be any gaskets that need replaced?
Click to expand...

Probably the valve cover will need to be replaced, if it hasn't been removed lately it's likely to be stuck.
 
The only effect the petcock will have is that there needs to be a way to shut it off when the bike is not running..Ever so slowly, gravity will draw fuel downward and if it gets past the carb bowls it has to go somewhere. That somewhere is that it seeps down into the crankcase and fills the oil with gas. Then what you have is watery oil that will not lubricate and protect the engines internal parts and youll fry that engine as fast as eggs in the skillet. Like i said, pinch it off with some hemos or some small needle nose vice grips till you cann get a working setup.
 
If it were me...since it has obviously already been sitting like this..I would drain the oil, get the fuel line pinched off and put new oil in before i even think of restarting the bike..better spend 25 bucks on new oil than gamble on frying the engine.
 
Ok I went out and pulled the carbs and attempted to remove the valve cover put it is stuck pretty good. Any tricks for removing it like heating or beating? haha, and to use carb dip do I need to totally dissasemble everything in the carbs that i can and should I remove each one from the rack or can I leave them attached?

I just changed the oil the other day and even the old oil looked pretty good and was not "watery". So do you think after I install an on/off fuel valve I should change the oil again?

Thanks for your help everybody.
 
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