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Best "how to" to shim the needles on my carbs... links!

  • Thread starter Thread starter legaleli
  • Start date Start date
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legaleli

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I just bought my second GS and it is arriving this Friday. It is a 1979 GS850 with 16K and is pristine. Much of the work has been done by the person whom I purchased it from:

ie - new battery, rebuilt all brake master cylinders and brake calipers, new brake pads, rebuilt carburettors, new Metzler tires and tubes, new air filter, new fork seals, new tapered conical steering neck bearings, adjusted valve settings, new oil and oil filter, new valve cover gasket, clutch cover gasket, generator cover gasket.

The guy I purchased it from wrote this to me:

"As with most bikes of this era, the carburation is set very lean from the factory. The bike runs very nicely once it's fully warmed up, but will sputter and fart unless you use full choke or until it reaches full operating temperature. If it were mine, over the winter I would have a knowledgeable mechanic raise (shim) the needles, increase the size of the idle and secondary jets and fully lube the choke cable to alleviate this problem once and for all. This isn't that difficult a job, but I would still leave it to a professional whose work you trust."

I don't want someone else to do this work - I want ME to do this work. I am comfortable with the CV carbs on my current bike but I know little or nothing about the ones on this bike - that said Bikecliff's site has some good information.

But I am wondering if there is a "how to" to shim the needles on my VM Carbs... :D

Note: I did do a search but came up with stuff like this which helps... but doesn't show me how...
 
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Hi,

Sorry I don't have pictures, but here are a couple of pretty good explanations.

Shimming The Needle

It will become glaringly obvious once you get your slides and needles out of the top of the carbs.

Thank you for your indulgence,

BassCliff
 
Just saw this as I'm going out the door.
I'll try to help later if I can. But generally, I see no good reason why the jet needle positions would need changing.
 
is it just me or does that make it seem like the shims go on top of the needle, in stead of under?
 
I won't argue that factory jetting is a bit on the lean side for your bike but it shouldn't be so lean that you need to make jet needle adjustments. Maybe some minor pilot circuit adjustments but that should be it. Only if you're in higher elevations for most of your riding would adjustments to the jet needle and main jet be helpful and you still wouldn't have to richen it much.
I'm not exactly sure what "sputtering and farting" until it's warmed up means but the typical 30 year old bike isn't going to run clean and idle smoothly when it's still cold. But it shouldn't run badly either. Without hearing the bike run for myself it's hard to say if there's really any problem.
You said the carbs were rebuilt but I wonder what was done. Maybe everything's in good order and maybe not. Now if the carbs are truly clean, floats adjusted correctly, inner o-rings fresh, all jetting stock, fresh manifold o-rings, synched decently, and the bike is in otherwise good tune, but it still seems the jetting is lean, then I'd try some basic pilot circuit adjustments and test. If it's possible the carbs haven't been synched correctly or the air screws or pilot fuel screws set correctly then don't blame the jet needles for any problems. If the sputtering is happening at less than 1/4 throttle then the jet needles have nothing to do with it.
If you feel it's necessary, first try some simple screw adjustments. Be sure the side air screws and pilot fuel screws (underneath) move freely. Mark their current settings and lightly seat them all while noting how far out each is adjusted. This way you can set them back if you like. The side air screws need to be adjusted using the highest rpm method. Set them all initially to 1 1/2 turns and once FULLY warmed up you can fine tune them. Start at any carb, set the idle to 1,000 rpm's by using the idle adjuster knob. Slowly turn an air screw in either direction until you hear the rpm's reach maximum. Then lower the rpm's to the base idle of 1,000 by using the idle adjuster knob. Repeat to all carbs and the air screws are done.
If you feel the pilot fuel screws should be richer then turn them out to richen. They are generally 3/4 to 1 turn out from the factory. They are sensitive to adjustment so you may need just an additional 1/4 turn or so.
Ride the bike around town a few miles at minimal to 1/5 throttle positions and then check the plug coloring. If the plugs are too light/white and the bike seems lean (surging/hesitating) then try richer pilot fuel screw adjustments.
I really doubt the jet needles need richening. Their e-clips should be in the factory set 3rd position from the top. If you still wanted to play with them then you would need some jetting spacers to place under the e-clips because raising the needles just 1 position richer is a significant change. Jetting spacers for your carbs are approx' .022" thick and represent a 1/2 position change. I think even that would be too rich for a stock bike that may need just a little added richness to compensate for higher elevations/colder climates. Something closer to .032 would seem better to me (1/4 position change). To get to the needles and adjust them you need correct fitting tools and some finger dexterity. Be sure all parts go back in exact order. In the case above, you would place the e-clip in the 4th groove from the top and then place the spacer directly on top the e-clip. This would be 1/4 position richer. I've never bothered with an adjustment of less than 1/2 position but if we're trying to be perfect then you might want to. But again, 1/2 position I feel would be too much for a stock bike.
After adjusting the jet needles you must re-synch the carbs too.
 
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boogerboy72 said:
is it just me or does that make it seem like the shims go on top of the needle, in stead of under?
Click to expand...
Well, they do go near the top of the needle, but it's below the very top.
They will actually sit on top of the clip.

On the CV carbs, there is a thicker nylon spacer on top of the clip and a thin metal one below it.
To "shim" the needle, you remove the nylon spacer and replace it with a stack of shims that is thinner than the nylon spacer.

On the VM carbs (like his '79 850 will have), the needles have multiple grooves. Simply moving the clip will move the needle.
Remember that the needle is spring-loaded UP, so moving the clip to a lower notch will raise the needle.

.
 
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Congratulations, sounds like you have found a very good 850.

Not trying to be contradictory, but the stock '79 850 needles were clipped in the second position. This usually would be quite lean, but the stock needle shape allows this without causing undue leanness. The stock needles are 5DL36-2

Keith is correct when he says that small shimming adjustments are required to get the ideal needle position. I experimented with VM 29 needles too (5DL31) but found they were slightly too fat right through the mid range rpm.

My 850 is now 900cc and 10.5-1 CR. I've settled on a 0.016" shim positioned on top of the #3 clip position. This makes the needle O.024" higher than the stock position. As a guide, I was happy with the performance of the stock needle position before I modified the engine.
 
Thanks for the correction 49er. I thought the '79 850 used the same needle position as the '79 1000 since they use the same jet needle.
I guess the 850 requires a little less fuel.
legaleli, you would then place the e-clip in the 3rd position from the top and place the appropriate spacer directly on top.
 
KEITH KRAUSE said:
Thanks for the correction 49er. I thought the '79 850 used the same needle position as the '79 1000 since they use the same jet needle.
I guess the 850 requires a little less fuel.
legaleli, you would then place the e-clip in the 3rd position from the top and place the appropriate spacer directly on top.
Click to expand...

WOW! Ask a good question get great answers. :D

The way all this sounds to me I should start with adjusting the carbs and richening the mixture (if it needs it), after which if it is necessary (or fun and it might improve some performance) shim the needles.

The shimming of the needles will require some basic knowledge, a few washer/spacers to spec, a digital camera, and this forum. :D:D

The best part about me having asked this question at this point is knowing that when I start this project I won't have to worry too much about getting it right - I have you wonderful people. :D:D:D

I will post pictures of my bike when she arrives on Friday!
 
KEITH KRAUSE said:
Just saw this as I'm going out the door.
I'll try to help later if I can. But generally, I see no good reason why the jet needle positions would need changing.
Click to expand...

Tried shimming mine and switching positions, found it didnt work so well for me. Worked better stcok (for me at least):D
 
My 850 is stock and I get similar cold starts but within approx. 3 mins it runs very well. I don't think I need to shim any needles as once it is warmed up it runs nice! I believe my shims are in the same spot as 49er states. I chalk it up to her being somewhat cold blooded.

I have notice over the last 2 yrs and 5,500k miles that the cold start up seems to be a little worse so I'm thinking I probably need to clean me carbs and its time for a valve adjustment. The cold start up is worse if i don't ride the bike for 1-2weeks.

That's my experience with the 850 anyway.
 
You guys both back up what I said. I really doubt Eli needs to adjust his jet needles on a stock bike, unless someone has moved them in the past.
Minor pilot fuel screw adjustments should be all, if that. If the bike is kept in reasonable tune then it should be fine.
 
KEITH KRAUSE said:
You guys both back up what I said. I really doubt Eli needs to adjust his jet needles on a stock bike, unless someone has moved them in the past.
Minor pilot fuel screw adjustments should be all, if that. If the bike is kept in reasonable tune then it should be fine.
Click to expand...

True Keith. And I have found the same as tas850G reports.

In winter months, mine pops on one pot at full to 1/2 choke from start up, but soon smooths out after a minute or so of running. It's always done so and hasn't improved after thorough carb cleaning sessions. There is some wear on the rubber seats where the choke plungers seat, so I guess that may have some influence on the cleanness of the cold running circuits.

As well as mine is tuned, it does run worse at startup, after a prolonged break, say 2 -4 weeks.

Mine's still cold blooded enough to need some choke for restarting when the engine is allowed to sit for more than 2 hours in moderate ambient air temps.
 
I totally agree with both you guys. Unless there were changes by the PO there should be no need to raise/lower the needles to get it running better.
 
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