Carb float bowl problem?

[Anonymous]

Hello Guys, I have a 1980 GS750 with about 49,000k on it. The problem I am having seems like a starvation problem, I will be going at about 3-4 thousand rpm, doesnt matter what gear, and it starts to surge. If I open up the throttle wide then the power seems to slowly come on. When I come to a hill I need to open up the throttle as I dont have hardly any power just cruising along. When I open the throttle it takes a little while for the power to kick in, it sort of slowly comes on. Also if I let the throttle off completely when I am slowing down it will stall. It also backfires when decelerating.

I have checked the petcock, it seems ok. I get lots of gas flow when I open the vacuum. I checked this by taking the hose off carb #3, and turned the bike over. Lots of gas came out into the bottle I had on the end of the hose.

Here is one other thing, if the bike hasnt run for a day or so, I have to take the seat off and spray gas into the carb opening in the air box.

I am thinking this could be the float in the bowls not floating anymore. If this is the case, is it an expensive fix, or hard to do?

Opinions?

Thanks guys. :wink:

 

[earlfor]

Jamie
You didnt say what color the plugs are and what they look like.
That should tell you where you are with mixtures. From your description, it sounds like you are running on the lean side.

Earl

 

[earlfor]

Also, wasnt 1980 the first year for CV carbs?...and if so, is the airscrew the only adjustment you have on the carbs?

Earl

 

[Anonymous]

Hey Jamie, I have the exact same problem on my 81 GS550L. starts off ok. Extreme bogging between 3000 & 5000 RPM, and lots of power after 5000. I have to completely open her up to get her to go from 3000 to 5000 rpm. I personally don't think it's the air mixture. Mine is the same no matter where my air screws are set. I now have them at 2.0 turn out. #3 spark plug was fouling. I took them off again today and #3 floats were about 2mm to high, also the o-rings on the needle seat were bad. We should work together to figure this out. Please let me know if you find out anything. Do you think your carbs need to be balanced?

 

[Anonymous]

I was having the same trouble at the begining of the season, I did a THOROUGH carb cleaning, follow the instructions on the homepage or
http://www.thegsresources.com/gs_carbrebuild.htm
My problem seemed to go away after that.
There was also a guy on e-bay selling o--ring kits for the mikuni's, they work very well. I can give him you e-mail if your interested.
good luck,

 

[Anonymous]

carb problem

carb problem

Hi Jamie

I would start with a thorough cleaning as described in this web site.It's really quite easy . Good luck

 

[Anonymous]

Thanks

Thanks

Thanks guys, I will just try cleaning the carbs out like you both mentioned.

Just FYI Earl, my spark plugs are a medium nut brown, no soot, or wetness at all.

I just spoke with my local MC mechanic, he noted that there is an aftermarket four into one pipe on the bike and figured that the carb needles will need to be adjusted to make it more rich. I guess that makes sense, but I am thinking that those pipes have been on there for a while. I am sure the person that put the pipes on would have re jetted the carbs.


Thanks Jamie

 

[earlfor]

Re: Thanks

Re: Thanks

I wouldnt count on the person that installed the aftermarket pipes being knowledgable enough to know anything about jetting. There are a lot of people that buy a pipe because they like the way it looks cosmetically and havent a clue mechanically.

Earl

I just spoke with my local MC mechanic, he noted that there is an aftermarket four into one pipe on the bike and figured that the carb needles will need to be adjusted to make it more rich. I guess that makes sense, but I am thinking that those pipes have been on there for a while. I am sure the person that put the pipes on would have re jetted the carbs.


Thanks Jamie

 

[Anonymous]

That is true Earl. Thanks, what would you suggest? Should I move the needle up or down? Also do you know if there is a tutorial on carb rebuild for my 1980 750?

Thanks

 

[Jay B]

With after market pipes you might want to move the needle up but usually dont aftermarket pipes call for re jetting. That might be the better wayn to go AFTER cleaning the carbs.

About the carb tutorial. Follow the one listed. I bet you have BS 32 SS on your bike. While the pictures arn't exactly like your carbs they are close enough that you can us it to clean your carbs to perfection.

 

[earlfor]

Jamie, I think the 750 carbs changed from the slide type (1979) to the CV type in 1980. The carb pages on GS are enough to clean either type. The proceedure is the same, just the parts sequence will be a little different. They all have pilot, midrange and main jets and needles, so just keep the parts from each carb segregated for that carb in disassembly and re assembly. Disassemble one and reassemble it before going on to the next if you are unsure about how to proceed. That way when youre just starting and least sure, you will have three others that are assembled correctly to refer to. From your previous brief description of what is happening, my inclination is that you are running lean. That would mean you would move the needles up. Meaning there will be a shorter length of needle extending from the slide.

Earl

That is true Earl. Thanks, what would you suggest? Should I move the needle up or down? Also do you know if there is a tutorial on carb rebuild for my 1980 750?

Thanks