that #*&!@ choke plunger

[superawesome]

In general my bike (1978 GS1000EC) runs well, but I had moments in the past where the exhaust pipe of #3 stayed cold, but before I found out why it was back to normal again. So nothing I could really get hold of, more an idea of "something" not being right.
Few days ago I used the Colortune to set the carbs (after installing Dyna S ignition and coils), when I saw cylinder #3 not firing. Just a little spark, nothing more. Colortune manual pointed towards choke, so I had a closer look. Carbs are stock VM26. I found the choke plunger on #3 did not go all the way back in when turning off the choke, staying maybe 1-2mm higher than the others (barely to see). I used a screwdriver to push it all the way in (see pic) - et voila, stable idle. After moving it up and down a few times, it seems to go in all the way now without getting stuck. Wonder what that is, carbs have been ultrasonic cleaned last year...

Also I don't think the plunger should be lubed, right? (It would have said so in BassCliff's carb rebuild tutorial I guess)



Just wanted to share in case anybody else has a similar situation.

Best
Juergen

 

[Guest]

sometimes those brass shafts wear or bend ever so slightly. I've had to swap the odd one out for one that moved freely. On occasion I've see the part that connects to it not be properly lined up with it so it binds when moved up or down.

 

[Nessism]

To fix the problem you need to remove the plunger and clean out the passage and polish the plunger. Some gray scotchbrite will do the trick. Be sure to clean out any grit before reinstalling the plunger.

 

[superawesome]

Thanks, I'll make sure to plan that for the next maintenance.
Are these assemblies still available? I did not find them on the parts fiche for the 1978 GS1000...

 

[Steve]

Note that the forks that lift the plungers are not symmetrical.

The one on #3 might be reversed from the others.

.

 

[superawesome]

I checked that, and the forks are all the same way.
Also it seems that the forks only lift them and keep the plungers up, but they are supposed to slide in by themselves. At least on mine the forks don't push them all the way in.

 

[KEITH KRAUSE]

I've found on these carbs that the "fork" mentioned must be carefully installed. It must be positioned just right as you tighten the Philips screws tip into the choke shaft's V groove. Tight, but be careful to not over tighten. Then double check the choke plunger movement and compare all 4 for uniformity and positive closing. I dab on just a bit of white lithium grease to the brass plunger shaft.

 

[chuck hahn]

To expound on Steves response, the lifters have tear drop shaped ends that engage the plastic drum on the chokes. If you look at them youll see that one rounded side is bigger than the other one. The bigger lobe goes down..as in towards the carb body. This pushes the plungers fully seated when the choke is released.

 

[1978GS750E]

The VM carb rebuild tutorial says that the choke plunger forks should be placed with the "indention" on the screw end pointing down??? That's the way I have always put them on??? Hope that is right.

 

[KEITH KRAUSE]

To expound on Steves response, the lifters have tear drop shaped ends that engage the plastic drum on the chokes. If you look at them youll see that one rounded side is bigger than the other one. The bigger lobe goes down..as in towards the carb body. This pushes the plungers fully seated when the choke is released.

Looking at his photo, the lifter is installed correctly and he said they're all installed the same way.

 

[superawesome]

I did follow that tutorial as well as I put the carbs together, so the little indention is down.
I need to double check on the bike, but to me it seemed, the forks do not fully push the plunger down, but expect it to slide by itself, at least the last mm. I did play with the philips screw's tension (as Keith mentioned), and it seems to work when a little less tight. Maybe overtightening is not a good idea here (and not necessary anyway when using loctite on it).

 

[KEITH KRAUSE]

It's not just being careful how you tighten the Philips screws, it's also how you hold/position the fork as it's tightened. If you just let the fork lay there as you tighten the screw, the fork can end up being a tad higher or lower than you want. This can lead to one or more forks not completely pushing the plunger down and the 4 plungers not operating as uniformly as possible.
Also, my '79 has a choke cable. Correct cable slack is important. With your '78, a thumb lever operated choke, you have to be sure the choke mechanism allows the plungers to fully close. As with my cable choke, there must be a tad bit of slack before the choke actually starts raising the plungers.