Frustration ....

[bcallender]

Hello All:

1981 GS 850 G

Background:
Rebuilt carbs (cleaned 4X), floats set to spec etc, new boots (intake and airbox),new o-rings, new fuel and vaccum lines, valves adjusted, compression within specs, new plugs, new air filter, airbox gaskets replaced, carbs bench and vaccum synched ....

Problem:
Bike starts well when cold without using choke and will idle @ 1000 rpm. When warm still idles @ 1000 rpm, but is lazy upon acceleration ... seems to be down on power (but this is my first gs ... so) Seems to starve for fuel after a few miles when petcock is set in run but is fine when set @ reserve.

Thanks in advance for any suggestions.

[Agemax]

have you tried stripping the petcock? there is a filter inside the tank and there may be a partial blockage in the run position

[snowgoose]

Hello All:

Problem:
Bike starts well when cold without using choke and will idle @ 1000 rpm. When warm still idles @ 1000 rpm, but is lazy upon acceleration ... seems to be down on power (but this is my first gs ... so) Seems to starve for fuel after a few miles when petcock is set in run but is fine when set @ reserve.

Thanks in advance for any suggestions.

Starting when cold without choke suggests to rich to me, hav you checked colour of plugs? I would check this first?

If all good then, as stated, good idea to bypass petcock anyway to rule out starvation.

Then if all good I'd return to needle and main jets

[OhioEric]

i reworked my petcock last night...not all that complicated or difficult. (just gassy)
What i know for sure--- is that the bike wont run right if thats not working properly.

[flyingace]

Hello All:

1981 GS 850 G

Background:
Rebuilt carbs (cleaned 4X), floats set to spec etc, new boots (intake and airbox),new o-rings, new fuel and vaccum lines, valves adjusted, compression within specs, new plugs, new air filter, airbox gaskets replaced, carbs bench and vaccum synched ....

Problem:
Bike starts well when cold without using choke and will idle @ 1000 rpm. When warm still idles @ 1000 rpm, but is lazy upon acceleration ... seems to be down on power (but this is my first gs ... so) Seems to starve for fuel after a few miles when petcock is set in run but is fine when set @ reserve.

Thanks in advance for any suggestions.

If the bike runs fine on reserve, you've pretty much eliminated everything below the petcock. You've also eliminated the petcock vacuum valve since (I believe) it operates on reserve as well. I don't know what could be left other than some blockage in the 'run' stem of the petcock. The only other thing I can think of is an inline fuel filter that is marginaly plugged such that the increased pressure of reserve pushes just enough more gas thru to run OK.

[82Shafty]

When it's all warmed up, pull your air filter out of the box, re-install cover and go ride.

If it runs better then you are too rich. Check jet #'s against stock to start with.

What is your float height currently set at? I believe some would say that if all your jets are not molested and are indeed stock # jets, then to raise the float height from the 22.4 to 23.4mm.

[Nessism]

No disrespect but cleaning carbs 4x indicates you did not follow the procedure properly - shouldn't take more than one time.

Did you ungang the carbs, remove all the various bits and soak the carbs in carb dip per the CV carb rebuild series? That said, I agree with the others that the petcock could be causing the problem.

[robertbarr]

You're on the right track; examine your petcock filter screen. I had a similar problem with an '82 850, and I finally just gutted the screen altogether, and that solved the problem.

On mine, the engine would actually stall at speed if the tank was below about 2/3 full.

[GQROD]

Hello All:

1981 GS 850 G

Background:
Rebuilt carbs (cleaned 4X), floats set to spec etc, new boots (intake and airbox),new o-rings, new fuel and vaccum lines, valves adjusted, compression within specs, new plugs, new air filter, airbox gaskets replaced, carbs bench and vaccum synched ....

Problem:
Bike starts well when cold without using choke and will idle @ 1000 rpm. When warm still idles @ 1000 rpm, but is lazy upon acceleration ... seems to be down on power (but this is my first gs ... so) Seems to starve for fuel after a few miles when petcock is set in run but is fine when set @ reserve.

Thanks in advance for any suggestions.

1-Not to sound offensive but i did this, make sure you have more than 1 gallon of fuel in the tank otherwise you may forget and it will run out of fuel in the run position yet still have fuel in reserve and you may forget to turn the lever to reserve, silly i know but it happened to me.

2-Test petcock by putting fuel line into a plastic cup and the other end connected to the tank. Put lever in prime you should see fuel coming out a little. This means prime position works.

3-Do same thing as above but put lever in Run and suck on the vacuum line this opens the valve, you should see alot of fuel coming out. If not make sure you have enough fuel in the tank. Or the screen on the petcock is blocked with rust or varnish.

4-Do same as abouve put lever in Reserve and same result as #3 applies.

5-Start doing plug chops at different rpms, read your plugs by the color this will tell you where the problem is and what exactly the problem is meaning wether it's running rich or lean. then you can start adjusting your mix screws/needles in order to get the correct mixture.

6-Finally it may be that although everything you have doen on the rebuild is correct if the bike is old and has a lot of miles or has been sitting you may just have to go higher or lower on your jet sizes in order to get it to run well. Last thing to check is your choke adjustment just in case it is not seating correctly, and especially your vent tube hoses just in case they are kinked.

Hope this long winded explanation gets you in the right direction.

[bcallender]

No disrespect but cleaning carbs 4x indicates you did not follow the procedure properly - shouldn't take more than one time.

Did you ungang the carbs, remove all the various bits and soak the carbs in carb dip per the CV carb rebuild series? That said, I agree with the others that the petcock could be causing the problem.

None taken .... Sorry I was unclear ... I cleaned all 4 carbs 1 time .... not 4 times for all.

[Steve]

1-Not to sound offensive but i did this, make sure you have more than 1 gallon of fuel in the tank otherwise you may forget and it will run out of fuel in the run position yet still have fuel in reserve and you may forget to turn the lever to reserve, silly i know but it happened to me.

2-Test petcock by putting fuel line into a plastic cup and the other end connected to the tank. Put lever in prime you should see fuel coming out a little. This means prime position works.

3-Do same thing as above but put lever in Run and suck on the vacuum line this opens the valve, you should see alot of fuel coming out. If not make sure you have enough fuel in the tank. Or the screen on the petcock is blocked with rust or varnish.

4-Do same as abouve put lever in Reserve and same result as #3 applies.

5-Start doing plug chops at different rpms, read your plugs by the color this will tell you where the problem is and what exactly the problem is meaning wether it's running rich or lean. then you can start adjusting your mix screws/needles in order to get the correct mixture.

6-Finally it may be that although everything you have doen on the rebuild is correct if the bike is old and has a lot of miles or has been sitting you may just have to go higher or lower on your jet sizes in order to get it to run well. Last thing to check is your choke adjustment just in case it is not seating correctly, and especially your vent tube hoses just in case they are kinked.

Hope this long winded explanation gets you in the right direction.

1 - Good

2 - Good, but be careful with the plastic cup. Some of them will get eaten up by gasoline.

3 - Good

4 - Good

5 - Not good. Plug chops are done at different throttle openings, not engine speeds.
Easiest way to judge throttle opening is to use tape and a marker, like in the following photo.

6 - Good

[GQROD]

1 - Good

2 - Good, but be careful with the plastic cup. Some of them will get eaten up by gasoline.

3 - Good

4 - Good

5 - Not good. Plug chops are done at different throttle openings, not engine speeds.
Easiest way to judge throttle opening is to use tape and a marker, like in the following photo.

6 - Good

You are right about that on point of number 5, i should have corrected that.

On point number 2 you can cut a plastic milk jug in half a clear one is what i used, not the colored ones i have not used those so i don't know if they will stand up to the gasoline.

[jwhelan65]

frustration

Same prob with my 82 GS 1100E......carbs completely rebuilt, new petcock.....Not sure if this is related but I had a wiggle lose wire on my regulator...secured it and it went away for awhile now its back...don't have a clue???

[Go Mifune]

So far all that you have mentioned is fuel related stuff but how is your timing and ignition system?

[bcallender]

So far all that you have mentioned is fuel related stuff but how is your timing and ignition system?

Coils are new stock units, new plugs and timing is set to spec.