VM 26 needle shimming 1979 GS 1000

[jknappsax]

All the posts I've found on shimming the needles refers to CV carbs, so I'd like to ask for opinions. I'm just about to finish tweaking my VM 26s. With pods and header, the carbs have DJ kits, with the DJ adjustable needles. I have the clips set on the third position from the bottom, and when checking with a Colortune, the midrange is pretty rich, whereas the idle is good, as well as to about 1/3 throttle . I'm thinking of just going up one clip; does anyone think I might need to shim as well, essentially moving up 1/2 a half-clip. Any opinions welcome. Thanks.

[hampshirehog]

Are you checking with the Colortune correctly or just blipping the throttle? You need to hold the throttle steady for a few seconds at 1/2 to 3/4 open to test the needle circuit.

[Steve]

I agree, but checking at 1/2 to 3/4 throttle is basically impossible, without putting the bike under load. You need to do this on the road or on a dyno.

Also not sure just how durable the Colortune is to extended useage. I know there is no problem with short-term use to check idle mixtures, don't know about "road trips".

.

[jknappsax]

The Colortune manual say NOT to use them under load. The bike definitely runs rich when transferring from the pilot to the main jet/jet needle. I guess I'll move the clips up one notch. I was just wondering if folks thought I would need to be in the 1/2 clip (with washers).

[hampshirehog]

The bike definitely runs rich when transferring from the pilot to the main jet/jet needle.

That is precisely how it is meant to run. If it didn't show an orange flame as you twisted the throttle the engine would stall.

You can use the Colortune to test the needle position and main jet (they are '2 different things') - remove 3 plug caps, stick the bike in gear and rev the thing with your foot on the rear barke. You have to keep the throttle position steady and in the right position (1/2 to 3/4 WOT) for, say 5 seconds. You have to keep the bike cool when doing this (obviously) and it helps if you are either double jointed or have a mate who can help.

I have never had to use a 1/2 position on VM carbs - it's always one or the other full position.

I think the 'don't use under load' thing means don't go for a ride with the Colortune plug fitted.

[TheCafeKid]

Yeah your different circuits aren't going to be real accurate without a load on it, however I'd think they'd be more reliable than CV carbs since they're mechanicals. You controll the flow with your hand rather than waiting on vac to lift the slides which would surely change under load.

I still wouldn't count on what you're seeing though.
You can shim it to the half, washer above the clip.
But only if you feel like it needs it. What does the bike tell you, both in feel and sound? Raspy and dry, it's lean... Sloggy, wet, too rich. Don't use just your eyes.

[KEITH KRAUSE]

Can't comment on the Clortune as I've always tested any jetting circuit on the road.
I'm familiar with your model and the DJ kit. Not sure exactly what pods and pipe you have but I'll share my experience when running quality pods such as K&N and V&H pipes.
Most often the 138 main is best.
My '79 GS1000 w/DJ stage 3 kit/V&H/K&N's has the jet needle e-clips in the 4th position from the top, BUT, with the DJ jetting spacer placed directly on top the e-clips. That's position "3 1/2". Most 1000's I've jetted ran best like this. I've found position 3 was always lean unless there was something about the pod/pipe combo that wasn't flowing well or the bike had some other issue that caused poor combustion/richness. Position 3 from the top has always resulted in obvious surging and white or nearly white plugs after testing a few times at solid 1/3 to 1/2 throttle position.
My bike and a couple of friends bikes ran a little rich when we tried position 4 so position 3 1/2 worked better. That was many years ago and nothing has changed.
Just my suggestion. Be sure you also synch the carbs well. Be sure the air screws are adjusted correctly for highest rpm. I also suggest removing the two floatbowl vent lines so the bowls can breath their best and to avoid fuel starvation in some conditions such as freeway/crosswind conditions.