GS1000G - it's the carbs again ...

[LA_Mike]

Hi all - I guess I need somebody to show me the light !

I purchased a 1980 GS1000G a month back and it drove only acceptable.
Very slow from the start and mid-range and good above 6000 rpm.
Since the air filter box was filled with little black foam pieces and the air filter
did not fit tight as well as the rubber boots I thought it sucks air on the side and the carbs are stuffed with foam pieces.
To remedy "it all" i bought 4 pod uni foam filters 54 mm, a K&N jet kit and a V&H 4-in-1 Megaphone.
I took the carbs apart and they did not look bad inside. Cleaned the pilots
which are 47.5 I think and replaced the main jets with 175's from the jet kit.
The instructions said to also insert some pin air jets on the intake side of the carbs (outer ring) which I did. Oiled and installed the foam pods and put on the 4-in-1.
Now I have acceptable start and midrange but no power after 5500 rpm.
Basically the GS feels like a V-twin now. Two observation I made during my repairs.
1. The diaphragms are intact (no holes) but pretty hardened out.
2. When "reving" the engine from idle the resonse is not exactly quick and
especially on the downslide when letting go of the throttle it takes many seconds to get back to idle.

I'm kind of lost here - I thought it sounds like fuel starvation but with the
biggest main jet supplied I find it hard to believe.
Any suggestions would be welcome. Thanks.

Oh, I forgot to mention I also replaced the spark plugs with new iridium plugs.


Mike

[earlfor]

Sounds like your pilot passageways are still clogged. If you cleaned the passages with a can of spray carb cleaner, you could have saved yourself the trouble. Its useless for cleaning carbs. Great for dissolving "O" rings and plastic parts though. The only reliable way to clean carbs is complete disassembly and soaking.

Rpm faltering above 5500 rpm leads me to think its flooding. Main jets are too big. I doubt you would need anything bigger than about a #140 main.
A friend of mine has a 1000 with pods and pipe and is using #130 mains.

Earl

[LA_Mike]

Carbs still not good ?

Earl

You might have a point here. I did open the carbs and removed the pilots,
blew then out with some carb cleaner and pressured air. All the little holes
seem to look OK. I replaced the main jets so I thought everything should be fine. Maybe some of the passages to the jets could still be clogged.
On the other hand off-the-line performance to about 5500 rpm is OK it just kind of shuts off after that which it didn't before my mods ...
Maybe I will try smaller main jets and see what happens. I just don't want to lean-out an old bike and overheat it ...
How to you recognize when you clutch starts slipping. Can that be something that will only kick-in in the upper rpm's ?

Mike

[earlfor]

Re: Carbs still not good ?

Usually, if the clutch is worn or adjusted too tightly, not allowing complete engagement, you will get slip with higher throttle application. It takes a lot of miles to wear out a clutch. I would check adjustment first. That may be all that is wrong. I have found that a leaking petcock and resultant gas in the crankcase oil will cause a clutch to slip even though the clutch linings may not be worn. Changing oil multiple times (at least for me) had no effect on improving a slipping clutch that resulted from gas absorption into the lining. If the bike is losing power above 5K rpm, I would be somewhat surprised if clutch slip is a lining problem if milage isnt too high and there has been no gas in the crankcase oil.

I would try a set of mikuni #130 jets and install new plugs to get an accurate read for the test rides. I know my 1150 with derestricted intakes goes rich on anything over #130 mains and the head on the 1000 does not have the flow the 1150 head does. My feeling is that while you can pod and pipe a 1000 to run with bigger jets, I dont see any point from a power and efficiency view since the head does not flow enough air volume to efficiently use the bigger jets.

I dont know how a mikuni #130 equates to a dyna #175 though.

The normal sequence when rejetting is to size the main jet first, then work down to midrange and finally pilots.



Earl

Earl

You might have a point here. I did open the carbs and removed the pilots,
blew then out with some carb cleaner and pressured air. All the little holes
seem to look OK. I replaced the main jets so I thought everything should be fine. Maybe some of the passages to the jets could still be clogged.
On the other hand off-the-line performance to about 5500 rpm is OK it just kind of shuts off after that which it didn't before my mods ...
Maybe I will try smaller main jets and see what happens. I just don't want to lean-out an old bike and overheat it ...
How to you recognize when you clutch starts slipping. Can that be something that will only kick-in in the upper rpm's ?

Mike

[Guy]

I've got 125 mikuni main jets with a four into one on the bored out (1085cc) GS1000, and it runs on the rich side. 170 mains sound way too rich. Are the plugs sooty?