HELP! 1980 GS850G Starts, but stumbles-Pops-won't rev??

[Darin Jordan]

Hi Gang,

Well... in the beginning, I purchased this 1980 GS850, knowing it had a problem running. $400.00, it was a good deal.

The bike started, and idled with the choke on, but the idle was rough, and it would spit and pop back through the carbs a little.

I rebuilt the carbs, rebuilt the Petcock, cleaned out the fuel tank, etc. Spark plugs look good, wires are attached to the correct plug, and everything generally looks fine.

Put it all back together, and it runs EXACTLY the same way. When you try to give it gas, it stumbles and bogs and spits back through the carbs. Almost acts like the cam timing is off or like a distributor that isn't timed right. But that's my "if this were a car" diagnosis, so I could use some guidance.

One thing I did notice is that the clamps that hold the carbs into the rubber intake manifolds clamp down ALL the way, and are still loose, so I suppose it could be sucking air past these. Is this a common/known issue?

Otherwise, HELP? Can you please give me an idea of the things to check from this point? I'd really like to NOT have to just guess.

I can take a video of the bike running so you can see/here what is happening, if you think that would help.

Would love to get this bike running.

Thanks!

 

[Ranger]

Video it up.

Sounds like it could be an airleak or maybe its running too rich.

Pull a plug after it does this and look at the color. Spray some WD40 around the carbs and intake boots with the bike running and see if the rpms change.

 

[Big T]

When you say you "rebuilt" the carbs, what did you do?

What shape are the intake boots in?

Did you replace all the O rings?

Got the airbox on and sealed?

Read the BassCliff site?

 

[Darin Jordan]

When you say you "rebuilt" the carbs, what did you do?

What shape are the intake boots in?

Did you replace all the O rings?

Got the airbox on and sealed?

Read the BassCliff site?

Carbs taken apart, cleaned well, all new rubber and gaskets. Needle and seats and floats looked/worked fine, so reused those. All passages were cleaned. Everything was carefully reassembled.

Airbox isn't currently installed, I'm using K&N Pod filters.

I'm reading through the BassCliff site now...

The story from the previous owner was that he took the bike for a ride one day and it ran fine. He parked it and didn't ride it again for about 3-months. When he tried to start it then, it acted like I described. It's still actiing that way after the work I described.

Any more leads would be greatly appreciated.

 

[Darin Jordan]

Video it up.

Sounds like it could be an airleak or maybe its running too rich.

Pull a plug after it does this and look at the color. Spray some WD40 around the carbs and intake boots with the bike running and see if the rpms change.

The plugs appear normal, with a little bit of richness around the outide (I've been running it on the choke), but light brown tips. They look normal.

I put brand new intake clamps on the boots, but even fully tightened down, they spin freely, so I suspect you may be right about the intakes. They appear to be soft and flexible still, but the clamps don't tighten on them at all. Sounds like this is a common issue???

 

[Ranger]

Try the things I mentioned and get the video up. Story he told you makes no sense, there has to be something else.

Not sure about the clamps spinning around being a common issue, it shouldnt be an issue at all since they are clamps afterall but I have all new ones $3 each.

You'll know for sure with the WD40 test if its sucking air in before the carbs.

 

[almarconi]

Pod filters will almost certainly require rejetting the carburetors. I'd try to find an airbox and get rid of the pods. When you rebuild the carbs, did you make a note of the jet sizes that are currently installed? More than likely, jets are stock and you are lean because of the pods.

 

[Darin Jordan]

Pod filters will almost certainly require rejetting the carburetors. I'd try to find an airbox and get rid of the pods. When you rebuild the carbs, did you make a note of the jet sizes that are currently installed? More than likely, jets are stock and you are lean because of the pods.

Main jets were upsized by the previous owner when he installed the Kerker pipe. They are 117.5s (stock are 115, if I recall correctly)

I'll look for leaks and see what I find.

As for the clamps on the intakes... they are brand new, factory parts, and when bottomed out, they still spin freely, which makes me suspect that the intakes have shrunk down or dried out sufficiently to not allow a good seal.

 

[Ranger]

Main jets were upsized by the previous owner when he installed the Kerker pipe. They are 117.5s (stock are 115, if I recall correctly)

I'll look for leaks and see what I find.

As for the clamps on the intakes... they are brand new, factory parts, and when bottomed out, they still spin freely, which makes me suspect that the intakes have shrunk down or dried out sufficiently to not allow a good seal.

You're not lean, so I wouldn't worry about jet sizes. Its not a fuel problem so it seems but it cant be eliminated for sure until you test for air leaks. I have a hard time believing that the intake boots shrunk although possible because the carbs would be pressing against the boots which would be pressing against the clamps, its more than likely they could be the wrong sized clamps.

 

[Mop Bucket]

I had to reorder clamps since the ones I ordered were the wrong size. I had my bike running ok until I noticed the air box clamp wasn't tightened down. I had to readjust everything to get it running ok. I had similar issue where it would only run with choke and hitting the gas killed it. Check for leaks.

 

[Darin Jordan]

OK, so I just ordered new O-Rings for the intakes and some stainless socket head bolts (from http://www.cycleorings.com/). Ordered the complete o-ring kit for the carbs as well, just in case I need to do that to (I never did take all the carbs off the rack and replace the O-rings in the t-fittings)

I'll see what I can do to get some clamps that will tighten down all the way to make sure there aren't any leaks there.

I'll be very happy if this is simply an airleak problem. I'll check it out tomorrow....

Anyone have any suggestions on where I can get some quality clamps, since the factory replacements don't seem to fit??

 

[Ranger]

OK, so I just ordered new O-Rings for the intakes and some stainless socket head bolts (from http://www.cycleorings.com/). Ordered the complete o-ring kit for the carbs as well, just in case I need to do that to (I never did take all the carbs off the rack and replace the O-rings in the t-fittings)

I'll see what I can do to get some clamps that will tighten down all the way to make sure there aren't any leaks there.

I'll be very happy if this is simply an airleak problem. I'll check it out tomorrow....

Anyone have any suggestions on where I can get some quality clamps, since the factory replacements don't seem to fit??

Edit: Dont look thru that link if you saw it. I looked and they dont list your bike. Find the part # then look it up.
http://www.bikebandit.com/search-products?q=Intake+clamps&ch=0&sc=0&v=0&n=4294967169

 

[almarconi]

You're not lean, so I wouldn't worry about jet sizes.

Pods and a kerker pipe, only 1 size up on the main jet and he's not lean...very interesting observation

 

[Ranger]

Pods and a kerker pipe, only 1 size up on the main jet and he's not lean...very interesting observation

He'd be showing it off idle even with a possible air leak. His plug color is fine but thats with an assumed airleak which leans the mixture out even more. I'd be more interested in how his needle is than the size of the jet so for the time being it seems he's not lean, which is why I made that observation as to not worry about the jets because it is unlikely the cause of the problem especially since it supposedly ran fine before.

 

[BassCliff]

Hi,

With pipe and pods you'll need to go up at least three sizes on the main jets, probably one size on the pilot jets, shim the needles, and adjust as necessary. Plug chops will tell you definitively. Clean the carbs properly. You'll find the procedure here on the GSR homepage and there's a copy on my website. Read your "mega-welcome" and go through the maintenance lists. Most of that stuff really is mandatory for a good running bike. Keep us informed.

The PO says it ran fine.


Thank you for your indulgence,

BassCliff

 

[Guest]

Pods and a kerker pipe, only 1 size up on the main jet and he's not lean...very interesting observation

I agree

 

[Guest]

He'd be showing it off idle even with a possible air leak. His plug color is fine but thats with an assumed airleak which leans the mixture out even more. I'd be more interested in how his needle is than the size of the jet so for the time being it seems he's not lean, which is why I made that observation as to not worry about the jets because it is unlikely the cause of the problem especially since it supposedly ran fine before.

But he's been running it with the choke/inrichener on

 

[Ranger]

But he's been running it with the choke/inrichener on

Good call, didn't realize that. But still for the time being.... he's not lean

I still doubt thats the cause of his problem. Personally I'd been running stock mains with raised needles and cracked headers at the flange and running lean but completely rideable.

 

[850 Combat]

especially since it supposedly ran fine before.

Goodness knows no seller said that before.

He has to run it with the choke on. I believe his plug reads were with the choke on.

 

[Darin Jordan]

Goodness knows no seller said that before.

He has to run it with the choke on. I believe his plug reads were with the choke on.

Thanks for the input guys... Just for clarity, the seller is my best friend, who is going through a divorce and was just thinning things out... He really was riding this thing daily, and it ran fine, just as I described. He has no reason to lie to me, and never has. He's also a professional mechanic and owns a business building/maintaining racecars, so he knows his stuff.

Anyhow, I took off the intakes last night and I doubt the o-rings were even making contact with the mounting surface any longer... they are HARD and flat and recessed up. I'll shoot some pics today and post.

I have two stubborn screws to remove, so I'll work on that today, then get everything cleaned up and see where I am.

As for the clamps, I ordered them from BikeBandit (seems I should just have a conveyor belt from their door to mine lately!), and they are "SGP" part number 09402-52306 (Bandit part number 09402-52306-11384348-109) They are suppose to be for a 1980 GS850GT. Mine is an 850G... Perhaps that's the issue with their size??

As for jetting... I would think that main jets wouldn't be the issue at idle or just off idle, but perhaps I'm wrong. One would think it would run at some level and just lean out up through the power band. The main circuit should even be in play that low in the range, but again, I could be mistaken. I've raced sports cars for years, so I know all about how to tune Webers (48IDA, 32/36, etc), as well as making Quadrajets work, so I'm not a complete newbie to this... just to the Bike end of things...

I will eliminate the possibility of the intake tract leaking and get things back together and continue trouble-shooting from there, if necessary. Hopefully I can get it running, then we'll work on jetting, and likely making the investment into a balancer for the carbs...