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Engine Dies at 1/2 Throttle

  • Thread starter Thread starter Uruka
  • Start date Start date
U

Uruka

Guest
I have an '82 GS650GL which will start with no problems and has descent throttle response, but at half throttle or over the engine dies. I've rebuilt my carbs according to tutorial posted here, but I suspect there is still something not right with them. Can anybody give me any clues as to what may be wrong with the bike?
 
Uruka said:
I have an '82 GS650GL which will start with no problems and has descent throttle response, but at half throttle or over the engine dies. I've rebuilt my carbs according to tutorial posted here, but I suspect there is still something not right with them. Can anybody give me any clues as to what may be wrong with the bike?
Click to expand...

Did you take the needle jets out and clean them and the bore they sit in???
 
Yea, I completely disassembled the carbs and cleaned all the jets.

I know it's not the petcock causing the trouble, because I'm running fuel straight from a can to the carbs. But it seems to be starved of fuel, so that would indicate a carb problem usually.:-k
 
Uruka said:
Yea, I completely disassembled the carbs and cleaned all the jets.

I know it's not the petcock causing the trouble, because I'm running fuel straight from a can to the carbs. But it seems to be starved of fuel, so that would indicate a carb problem usually.:-k
Click to expand...

Not the float needle valve, but the passages in the needle jet itself was cleaned?

There is a lot of differing terminology used around here.

How bout the rest of bike, all stock in good shape? Airbox, etc?

Has it always done this or just started?
 
I bench synced the carbs before I re-installed them. The bike was not running when I bought it, I stripped it down to the frame and rebuilt it. It has no airbox.

I was able to actually ride it several months ago, maybe for about 50 miles but the carbs started acting up and I could no longer start it. Even when it was ridable it would stall out at half throttle, which made my first freeway run very exciting.

I cleaned and rebuilt the carbs a few weeks ago, just installed a new battery, and it fires right up and idles nicely.
 
Not sure it's your problem, however, I suspect it is......you need the airbox. I'm sure someone that understands this better will explain why. But my uneducated recomendation is to find one somewhere and put it in.:)
 
Larry D said:
Not sure it's your problem, however, I suspect it is......you need the airbox. I'm sure someone that understands this better will explain why. But my uneducated recomendation is to find one somewhere and put it in.:)
Click to expand...


Or, if you know what the jetting is that's in it, see if it's stock or not. If it's been jetted to run without the airbox, there may be other problems.

What did the insides of the carbs look like when you tore into them? Dirty? Not too bad? Obviously the problem was there when you got the bike, not because of something you did, or didn't do. Dying at half throttle is bad, as you well know.
 
I was having similar issues with my bike if you look up jetting questions under this forum. I re jetted myn and its running great lots more power.
 
rudy said:
Or, if you know what the jetting is that's in it, see if it's stock or not. If it's been jetted to run without the airbox, there may be other problems.

What did the insides of the carbs look like when you tore into them? Dirty? Not too bad? Obviously the problem was there when you got the bike, not because of something you did, or didn't do. Dying at half throttle is bad, as you well know.
Click to expand...

The bike had the air box when I bought it, but it was missing the filter element and the cover, so I'm pretty sure the carbs are still in the stock configuration. The carbs were very dirty, lots of gunk, partially solidified gas, really bad. The bike was out of commission for so long that the DMV no longer had a record of it. The odometer was at 38k, so the engine is pretty sound.

I believe the reason the last owner bike gave up on it was because of an electrical problem. Some of the wires in the harness appeared to be burnt and many were shorted or disconnected. I rewired the bike for just the basics. Ignition, starter, head lamp, tail lamp, brake lamp. I tested the coil and the ICU and they checked out OK.

I put some fuel in it and ran it about an hour ago. I adjusted the air screws and it seemed to help some. Looking inside the carbs when I apply throttle, the pistons rise, but not all at exact the same rate. They vibrate a lot and look as though they are bouncing slightly. Are the pistons supposed to move smoothly? Could it be bad diaphragms?
 
I have the exact same model and it would do the same thing when I first got it. When you re-built the carbs did you replace all the O-rings? The first time I cleaned mine I didn't replace them and it didn't fix the problem. The second time I replaced all o-rings and also the o-rings in the rubber intakes themselves and now it runs like a champ. There is a guy on here that sells the o-ring kits for you bike. Do a search to find his name.(I can't remember his name)
 
I don't think I replaced all the o-rings. The kit I bought came with new float valves, float valve seat, the o-ring for the valve seat, float bowl gasket, and various other o-rings. I couldn't figure out where the other o-rings were supposed to go so I set them aside. I did put new o-rings behind the intakes, I actually bought new intakes as well.

Could you tell me where these extra o-rings might go?
 
Someone else will have to address your wiring configuration. It sounds that you have enough to make her run right though.

I do know that the bike will never run properly without the airbox. Or re-jetting sans airbox.......So you (and anyone) have two options here.

#1. Get the airbox with the proper filter and cover. Shouldn't be to hard, you just must be patient and search ebay often. Probably need new rubber boots, clamps. Basically go stock.

#2. Get some pods and install them. And re-jet the carbs. This can prove difficult to get them tuned in correctly. However, many here report fantastic results and wouldn't do it any other way.

The choice is yours.:)


And get your o-rings here.......http://www.cycleorings.com/
 
Last edited:
Thanks everybody, I think I have something to go on now. I'll get the pods and rejet, I developed a grudge against the stock airbox when I first removed it. I'll install the new o-rings, I know that I am missing some on the air screws. Hopefully that will get it functional.
 
Good Luck to you ! There's a few "left coast" members that you could look up. Perhaps they'll give you a hand.

And keep reading and using the search feature here. There's many, many posts on re-jetting. Keep working on her, you'll be rewarded when she's running like a top.:)
 
re-jet

re-jet

Uruka said:
Thanks everybody, I think I have something to go on now. I'll get the pods and rejet, I developed a grudge against the stock airbox when I first removed it. I'll install the new o-rings, I know that I am missing some on the air screws. Hopefully that will get it functional.
Click to expand...

Others have probably given you enough to go on, but here's my take. You are getting too much air and at 1/2 to full throttle the mixture is going too lean.

That's because it's jetted to have the somewhat restricted air flow of a normal air filter. When you took the stock box off you changed that. Add the pods if you want, but you will have to add a stage II jet kit, or if you have changed from stock exhaust you'll have to go with a stage III. There is a ton of information out there about carb jetting. Read up and then go out and test your bike to get the proper jets. Since they are about $5 each it's not very expensive to change them, but can get to be a lot if you keep getting it wrong. Try this to get started:

http://www.factorypro.com/tech/carbtun.html

It's hard to imagine how much a little change in air flow can affect the carb performance. If your pipes have a significant air leak it will make a difference. You can try to cover the carb intakes...wrap a shop towel or something around the pods for a quick, very rough estimate, of what changing the air flow does to the carbs.

good luck.
 
Does your bike have a mechanical advance? Check and see if it's froze up.
Did you adjust the valve clearance?
What are your compression numbers.
The slides should rise evenly which makes me think you are not pulling the same vacuum through all the cylinders. (compression)
I would also check the diaphrams on the slides and also make sure the slides slide smoothly in their bores.
 
Uruka said:
... It has no airbox.
Click to expand...
I suspect that this is your problem. :-\\\

The CV carbs need at least some resistance ahead of them to develop enough vacuum to lift the slides. Either a stock airbox/filter or a set of pod filters. For a quick check, take a shop rag, fold it in half, drape it over the carb intakes. Secure the rag to the two outer carbs with hose clamps or tie-wraps, making sure it's taut over the inner carbs. Now check your throttle response. This setup is even good enough for a ride around the block, but it's not good enough for jetting checks.

.
 
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