GS1000 backfires when at full throttle.

[Guest]

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?

[tom203]

.........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?

[Trinnypig]

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.

[tom203]

Don't count on previous owner to have upped mains to compensate for pods! Best to be sure ,as running lean can lead to hot engine, burnt valves and other unpleasant stuff .
Did you get this memo about common issues?

http://members.dslextreme.com/users/bikecliff/images/GSR_Greeting.html

[Trinnypig]

if anything its running rich. my spark plugs come out black. any suggestions on what i can do?

[Big T]

change you jets and adjust your carbs

which carbs do you have?

[tom203]

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

[Rob S.]

I know its not going to run perfect, but I'm not picky.

Why can't it run perfect?

[mrbill5491]

Why can't it run perfect?

There is no such thing as "perfect" but just damn near.

[Trinnypig]

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?

[GSX1000E]

To begin with, your pilot jets should be 40's. Until they are, all bets are off.

[Big T]

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?

Since you haven't specified the year or model

78_79 have VM carbs
80 And newer have bs carbs

[Trinnypig]

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.

[tom203]

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.

[lbracy]

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.