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gs450 carb problem driving me nuts!

  • Thread starter Thread starter Red
  • Start date Start date
R

Red

Guest
:confused:
Since completing my 1981 gs450s restoration two years ago there is one problem I haven't been able to resolve, the bike runs with one cylinder running lean and the other rich, the following is what I have to done to try to rectify this now protracted and irritating problem;

- Stripped & cleaned all channels, replaced jets, pipes you name it, it was done!
- Replaced air box & cylinder head rubber boots.
- Balanced carbs
- checked resistance on both coils
- Had igniter box tested
- Tripple checked valve clearance
- Tried various pilot & main jets
- Fitted new plugs & caps
Probably loads more that I can't think of at this moment in time!

So, after exhausting my options to fix this problem I decided to buy a 83 - 86 gs450 carb on e-bay and try my luck with a slightly newer/improved carb.
This newer carb was again stripped, cleaned, new needle jets etc.
Once fitted on the bike when I tried to start the bike the right cylinder just fired up with I think fuel starvation, the left cylinder would not fire up at all. On investigation there was no fuel getting to the left cylinder and a limited amount getting to the right cylinder. Both float bowls had fuel in them.
The 'attached' drawing is the newer carb I fitted with no fuel getting through.
Can anyone HELP! :(
 
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Did you have the carb bodies ultrasonic cleaned? Because even if you pulled the jets, the passages inside the carb body may be plugged.
 
gs450 carb problem

gs450 carb problem

Not sure what u mean by 'ultrasonic' but after soaking for few hours I used compressed air to clear passage ways. What is the correct oprocedure for cleaning carbs?
 
gs450 carb problem

gs450 carb problem

The carbs checkout as being balanced if that's what u m?ean.
 
No, I mean does the engine have compression on both cylinders?
Did you ever check the compression?
 
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gs450 carb problem

gs450 carb problem

To tell you the truth, no I never did because the cylinders were honed and new rings were fitted.
 
if you application has a fuel crossover tube, make sure your "new" carb doesnt have a blocked off passage. The reason Im saying this is because I replaced a messed-up carb on my 1100, and got a cold cylinder because the replacement carb I put in the #3 position, came from either the #1 or 4 so it had a blank hole. I carefully drilled it out and no probs. Just a shot in the dark.
 
gs450 carb problem

gs450 carb problem

Thanks for that Snicreps5, my carbs are an original pairing. I've ordered a compression tester on e-bay, my next move will depend on the results!
 
You asked earlier about the correct procedure for cleaning carbs... the right way is to make sure they are absolutely thoroughly clean internally and that every single passage is completely clear of any fuel varnish. One little bit of varnish in the pilot circuit for example will definitely give you bad results.

The best way is an over night soak in proper carb cleaner. I chose to simmer mine in Yamalube carb cleaner but that is not the safest or most recommended method but it did let me get both done in a couple of hours rather than over night.

This was followed by a rinse in water after they had cooled down followed by compressed air through all passages, a spray through all passages with an aerosol carb cleaner, and finally one more go with compressed air through all passages.

I did this process for the carb bodies, float bowls, and all jets.

You should also replace all internal rubber O rings to be sure they're in good condition.
 
gs450 carb problem

gs450 carb problem

Thanks Pete, for some reason carb dips are difficult to buy in the u.k. But there is a solution were I work called Kem Safe, might use that.
Changing the subject slightly, can u do a compression test without the carbs fitted?
 
Carb dip's getting hard to find here too, and Yamalube seems to be the only one I've found so far.

Testing compression requires holding the throttle wide open, so carbs off should be the same as that :)
 
gs450 carb driving me nuts!

gs450 carb driving me nuts!

tkent02 said:
No, I mean does the engine have compression on both cylinders?
Did you ever check the compression?
Click to expand...

Just checked the compression on both cylinders and both were 142-144 psi (tested with a cold engine). PHEW! Something less to think about I suppose.
Does anyone know if the compression readings go up or down with a warm engine?
Spark is good, so its back to the carbs I guess.
 
gs450 carb problem driving me nuts! - "Finally Solved"

gs450 carb problem driving me nuts! - "Finally Solved"

Well I got there in the end!
Turns out the carb problem was caused by a 'pin hole' in the petcock diaphragm. I never suspected a faulty petcock as it did not leak when the fuel pipe was removed. Small amounts of fuel (gas) trickled through the hole in the diaphragm down through the vacumm inlet pipe on the carb resulting in that cylinder running rich when the bike was running.
So if there are any gs bikes out there running rich on one cylinder, before you do what I did and check every f%*ing thing you could possibly think of (except the petcock diaphragm), check if the carb running rich is the carb with the smaller petcock pipe attached to it, a possible tell tale sign is when you pull the smaller petcock pipe off the the carb watch for a tiny dribble of fuel coming out the pipe.

Thanks for all the input everyone gave!
 
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