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GS1000 backfires when at full throttle.

  • Thread starter Thread starter Trinnypig
  • Start date Start date
T

Trinnypig

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I am finishing up a carb rebuild and have everything back together. it is idling nice between 1000-1200 rpm. and runs good at normal stop and go but when i give it full throttle it boggs down and backfires. I feel i still need a little adjustment in the mixture screws. i turned them out about 2.5 turns. it feel to be running a little rich. i will adjust them a little later today anyone have any similar problem?
 
.........but when i give it full throttle it boggs down and backfires. "

Mixture screws aren't your problem as they have handed fuel delivery off to main circuit. Must be too lean on mains- what have you got for filter/intake setup? Did you note main jet sizes when you were cleaning carbs?
 
I bought the bike with the moxi pods on it. i don't have the air box. I know its not going to run perfect, but I'm not picky. if i can just ride it without it stalling or whatever without damaging the engine, then i don't care. i did wrap a clean rag around each one to help with slowing the air flow. I didn't make note of the main jet size.
 
if anything its running rich. my spark plugs come out black. any suggestions on what i can do?
 
change you jets and adjust your carbs

which carbs do you have?
 
Remember your first post?
"....
I have a '81 gs1000 that I just got. I can run the engine but it is rough and sluggish. The exhaust from number one is cold. 2,3 are hot and 4 is warm after 20-30 seconds of running. I have changed..."

you need to know what your jets sizes are and go from there
 
It has Mikuni Carbs. Is there more than one kind for this year?

This back fire thing is only new since i rebuilt the carbs. I do know my pilot jet is a 30. I don't have time right now to tear the entire thing apart to check the size of the main jet. when i do find the size how will i know to go from there. what are the sizes and if i go bigger won't that richen the mix?
 
To begin with, your pilot jets should be 40's. Until they are, all bets are off.
 
Trinnypig said:
It has Mikuni Carbs. Is there more than one kind for this year?

This back fire thing is only new since i rebuilt the carbs. I do know my pilot jet is a 30. I don't have time right now to tear the entire thing apart to check the size of the main jet. when i do find the size how will i know to go from there. what are the sizes and if i go bigger won't that richen the mix?
Click to expand...

Since you haven't specified the year or model

78_79 have VM carbs
80 And newer have bs carbs
 
Holy ****! I have found my problem. I was looking through a guide on rebuilding carbs to see if i missed something. I must have skipped over it or just not notice what i needed to do but the o-ring under the rubber boot that attaches to the engine block was not checked. I figured if they were old and cracked it would prevent a good vacuum seal for the carbs, so i pulled the first one off to check the condition, and sure enough, some dumb ass did not bother to replace them. There was nothing there!! 5 minutes of cursing all the way to the hardware store i found a perfect fit and $2 worth of o-rings i replaced them and started the bike. a minor adjustment to the throttle and it is now purring like a kitten. It revs smooth quick up and quick down as well. Before i would rev it and it would go up somewhat fast but takes about 5 seconds to calm down. It drives like a dream now. when i took it for a spin it throttles up nice and has great power, full throttle has a tiny bit of popping but it is minor and i can live with it. Thanks to all that helped. I think everyone needs to remember that a bike needs good vacuum to work good.
 
If you want to keep riding and living with the popping, that's your choice, but those hardware store o-rings you got are likely plain old buna rubber- these won't last long with the high temp of cylinder head (300 plus)- you need viton o-rings or plan on replacing the buna ones regularly.
 
Sounds like what my bike is doing. 1985 GS450L I bought it last year with only , 8,000 miles on it and it was clean! I bought it from the dealer who had serviced it since it was new by prepping it each fall. It was in perfect working order when I got it. The one exception is it would only run to 90 mph when I got it and I know it should do a 100 but I chalked that up to the age of the bike and my 210 lbs. About 5,000 miles and a few months later it began to pop and backfire when I tried to go faster than 75 or if I gave it full throttle. I have used sea foam in gas and really don't think it is the carbs. Also since I bought it if I let it idle unattended the throttle will race once the engine is warm.
I have done carb rebuild on previous bike (Honda CX500), soaking carbs in ultrasonic cleaner. I had a book and help from someone who has done several. It was a real pain and then and it turned out to be a stator problem, not even the carbs. I don't want to do one again if that was not needed. I think it may be the O-rings under the rubber boot.
 
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