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too lean in the low rpms?

  • Thread starter Thread starter Rein
  • Start date Start date
R

Rein

Guest
Hey guys, I recently encountered a problem after cleaning and rebuilding the carbs, and finally getting the bike running.

Once it's warm, the bike will hesitate from idle to about 3000 rpms, at half to wide open throttle, it might even bog out and die if you give it a quick twist. However, once it hits 3000, it has great response. However, go moderately on the throttle, and it'll rev evenly. Seems like it's too lean? The pilot jets were dipped and used a compressor to blow out the jets.

New intake o rings already, intake boots are pliable and new. Valve clearances still need to be done. Stock airbox. Could it just be a valve issue?

Bike is an '81 gs650l
 
Dipping the pilot jets is a good start, but you really need to go back and dip the whole carb.

Actually, you need to disassemble the carb down to the bare body and just dip the body and the jets. Do NOT dip any non-metallic parts as they will not last in the dip. A guide showing how to do it is in the Garage section on the home page of this forum. I will save you the effort of looking for it and just give you this link to the CV Carb Cleaning Series. You will need a can of Berryman's Carb Cleaning Dip and a new set of o-rings for the carbs. The o-rings are available from www.cycleorings.com. The owner of that little establishment is a member of this forum.

Is the bike new to you or do you know its history? How long has it been since the bike ran well? Is this a new problem or has it been doing it for a while? I ask this because, if you don't know the history of the bike or if it's been sitting for a while, the tiny passages inside the carbs are likely plugged up. Only a good cleaning will clean them out. When you read the directions on the can of Berryman's, ignore the time part. They recommend dipping for 15 to 30 minutes. For badly gummed-up carbs, 15 to 30 hours is what it takes. When you take the parts out of the dip, rinse them in warm water (I use the kitchen sink :eek:), then spray carb cleaner through all the passages to flush out any crud, then blow them out with compressed air. Re-assemble the carbs with your new o-rings that will have arrived by the time you are done dipping all the parts.

To help with your low-speed stumbles, make sure your float heights are set correctly. Specs call for 22.4 mm from the gasket seating flange to the bottom of the step on the float. You also need to open up the mixture adjustment screws a bit past the factory settings for good operation. Factory settings are typically about 1 to 1 1/4 turns out, the carbs work MUCH BETTER if they are set between 2 and 3 turns out from lightly seated. Here is a picture that will help you see where to measure the floats:
IMG_2161.jpg


.
 
What do you have your air/fuel mix screws set at.... should run them at approx 2 to 2 and a half full turns. (720-900 degrees)
 
Steve said:
Dipping the pilot jets is a good start, but you really need to go back and dip the whole carb.

Actually, you need to disassemble the carb down to the bare body and just dip the body and the jets. Do NOT dip any non-metallic parts as they will not last in the dip. A guide showing how to do it is in the Garage section on the home page of this forum. I will save you the effort of looking for it and just give you this link to the CV Carb Cleaning Series. You will need a can of Berryman's Carb Cleaning Dip and a new set of o-rings for the carbs. The o-rings are available from www.cycleorings.com. The owner of that little establishment is a member of this forum.

Is the bike new to you or do you know its history? How long has it been since the bike ran well? Is this a new problem or has it been doing it for a while? I ask this because, if you don't know the history of the bike or if it's been sitting for a while, the tiny passages inside the carbs are likely plugged up. Only a good cleaning will clean them out. When you read the directions on the can of Berryman's, ignore the time part. They recommend dipping for 15 to 30 minutes. For badly gummed-up carbs, 15 to 30 hours is what it takes. When you take the parts out of the dip, rinse them in warm water (I use the kitchen sink :eek:), then spray carb cleaner through all the passages to flush out any crud, then blow them out with compressed air. Re-assemble the carbs with your new o-rings that will have arrived by the time you are done dipping all the parts.

To help with your low-speed stumbles, make sure your float heights are set correctly. Specs call for 22.4 mm from the gasket seating flange to the bottom of the step on the float. You also need to open up the mixture adjustment screws a bit past the factory settings for good operation. Factory settings are typically about 1 to 1 1/4 turns out, the carbs work MUCH BETTER if they are set between 2 and 3 turns out from lightly seated. Here is a picture that will help you see where to measure the floats:
IMG_2161.jpg


.
Click to expand...


Done ALL of that, which is what I meant by cleaning and rebuilding. (not to mention new floats, needle valves, and shiny new allen bolts.) New o-rings, plenty of time in the carb cleaner, and like I said, blew air through all the passages to get the gunk out.

I can ride the bike, and it runs and idles, save for the the problem I mentioned earlier. If you twist the throttle quickly it'll bog slightly, then it pulls hard. If you go gradually on it, then it revs evenly.

mix screws were the problem, one was over tightened, so I had to replace with one I got from a set of carbs I got for parts. Thanks guys!
 
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