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850L stumbling carbs

  • Thread starter Thread starter Anonymous
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Anonymous

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The carbs were rebuilt I think 2 years ago but there is a major flat spot. When cruising along and giving it just a little more throttle it stumbles and doesn't want to speed up. BUT when you twist a little more throttle it takes off like a wild aminal. Alot of popping through the exhaust when decelerating. Valves sound a little noisy. Will check clearances. I haven't synched the carbs yet either. Any other suggestions? When I really turn it on it runs without a miss. Starts super easy. Very strong acceleration- I think this bike would outrun my 1100GK.

Don't know who or when header was installed. Original airbox. Unknown jets, etc. in carb. Just boughtthe bike today. KNow very little history.
 
Re: 850L stumbling carbs

five string said:
The carbs were rebuilt I think 2 years ago but there is a major flat spot. When cruising along and giving it just a little more throttle it stumbles and doesn't want to speed up. BUT when you twist a little more throttle it takes off like a wild aminal. Alot of popping through the exhaust when decelerating. Valves sound a little noisy. Will check clearances. I haven't synched the carbs yet either. Any other suggestions? When I really turn it on it runs without a miss. Starts super easy. Very strong acceleration- I think this bike would outrun my 1100GK.

Don't know who or when header was installed. Original airbox. Unknown jets, etc. in carb. Just boughtthe bike today. KNow very little history.
Click to expand...
Can anybody give me some ideas what is going on here? Thanks.
 
At what throttle position are you having the problem? It sounds like there is some crap in the pilot jet to me, but without some more specific data it's impossible to troubleshoot.
 
more info

more info

Thanks for helping out, tbarnby.

The flat spot comes at ? throttle. Around ? throttle it will rev right on up. It's the throttle position you are most frequently in when traveling down a flat piece of road and giving just enough throttle to maintain speed. It acts just like the bike is running out of gas until you twist throttle back another ? turn to get it to accelerate.

Some more checking today revealed spark plugs that are very white- starving for fuel, right?

I took the carbs off today and opened them up and cleaned all the parts off. New kits were installed within the last 1? years. There was a very small amount of silt in the bowls. Jets were not clogged. I checked the air mixture screws-all were at 2? turns. That's where I put them when reassembling.

I am installing an inline gas filter and a new shutoff valve (the vacuum petcock is shot).

My airbox was missing the foam gasket that seals the filter against the inside of the box. I made one of those.

Tomorrow I will install the carbs and try it out. I have a synch gauge so I will do that, too.

What else should I check?
 
I noticed that your GS is equiped with a four-into-one exhaust. If the carbs have not or badly been rejetted after installing this pipe, it would explain the flat spot.
Perhaps you should check if the original jets are still installed. If yes, you've got some rejetting to do.
 
rejetting

rejetting

Jojo the main jets have a number 115 stamped on them. I have no idea what original jets are. I am not versed in the art of rejetting so any help would be appreciated. Here's what I've done to the bike so far:

sealed the air filter to the inside of the original airbox- a foam gasket was missing

checked to make sure advance weights were free behind breaker plate

disassembled/cleaned carbs

installed inline fuel filter

synched carbs

checked valve clearances

cleaned all electrical connections for a good ground

cleaned fuel petcock screen

cleaned/gapped spark plugs

It does seem to be running better but I still have the flat spot at about ? throttle. It is more pronounced after the bike is up to full temperature.


SO where do I start in this rejetting thing?

thanks
 
Due to emission regulations, US types had different carb setups than the European bikes.
Don't know what the jet sizes are for US models. Perhaps anyone else knows?
 
BTW:

Found this in the 'old' Q&A section. Might be interesting to look for the answer there.

QUESTION: Jet sizes needed - 1983 GS750E

Jet sizes need for K & N Mod - 1983 GS750 I'm looking for correct jet sizing (and any other carb settings) for a 1983 GS750 with K & N pods. The bike still has the stock exhaust system and Mikuni BS32SS carbs. Settings with the addition of a four-into-one exhaust would be greatly appreciated too. Cheers.

RIDER: Stewart Schmidt

REPLY: Sandra Whitney
Sudco International in So. Cal has been very helpful with information for GS's with both smoothbores and CV carbs. They answer their e-mail promptly. Just give them all the pertinent information (make, model, year and modifications).

Sudco International <sudco@sudco.com>
 
Try raising your needle 1 notch. If you dont have adjustable needles try shimming them with some very fine washers about the same size as the one that holds the spring in the diaphram.
 
I'm having the exact same problems with my GS, except it's with slightly less throtte application. The popping when decelearation, too. Last year, it wasnt' such a problem, but this year it is. From my experience it sounds and feels lean. I believe mine is because the carbs need an overhaul. My friend thinks it may be the needles, too. Maybe the springs are crap.
 
lean

lean

It is definitely a lean condition on mine, too. If I turn the choke on while it is stumbling the engine will smooth out quite a bit. I have tried adjusting the air adjustment screws on top of the carbs. It made no difference in the rpm range where I am having trouble. Next I will try shimming the needles like Jay suggested. If that doesn't work I will be looking for jets. I'll post with the results.
 
shimming needles

shimming needles

Well, I tried putting small washers under the needle to no avail. I only used 1 washer on each carb but it made no difference in my problem. I believe it made midrange rpm a little 'wetter'.

Next I am going to take the carbs back off and recheck float height. I will also record my jet sizes while in there.

I am certain it is a carb problem. The bike runs wonderful once I get above the stumble. When I finally get this ironed out I will have quite a ride. It is already fun riding it the way it is now. The exhaust sound is very pleasing with the 4-1 pipe on it. I don't think there's any baffle at all.
 
850l stumbling

850l stumbling

i noticed this topic was over 1 year old and am wondering what remedy was finally used to fix the problem. my 850l is having the same problem. any help appreciated.
 
I just stumbled onto this topic and was reading to see if it got fixed.
Considering what the owner said he checked or repaired, I wanted to ask if he had a higher idle, ONCE WARMED UP. An intake leak in the o-ring(s)/rubber manifolds would cause similar lean problems, most noticable at steady speed, along with the high idle.
Since the original poster is gone, I suppose I can ask you instead? :)
 
gs850 stumbling

gs850 stumbling

my idle is ok and dosent increase when warm. i blew gas from a propane torch (un-lit of cource) around my intake boots yesterday and nothing happened. i wasn't able to get the torch gas all the way around the boots as it was too tight. i'll probably do the same for the boots at the airbox side today. mine stumbles/flutters off idle to about 4000 rpm, and dosen't happen during a ride but happens when i start the bike after sitting for 2 hours or overnight. sometimes it dosen't happen. i posted more details yesterday as a new topic. no responses yet. if you're interested you can find my post under my name (fr555) or topic name(engine misses). thanks
 
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