VM29 carbs help

[razooki]

Well I finally started the bike up after some engine work. The good news is that it started without much effort. The bad news is that it's not running right. I tried setting the idle using the RPM method and it worked OK - it held the idle at about 1100. However, when I give it some gas it revs but it does not come back to idle. the cables are new and lubed and I triple checked to make sure they are not the problem.
Any suggestions with respect to tuning would be greatly appreciated.

 

[Guest]

Which bike?
Sounds like an intake leak.

 

[razooki]

GS850. I thought of that and I took a spray bottle and sprayed around the intake boots while at idle and when I was revving it. It did not make a difference at all.

 

[SqDancerLynn1]

Did you rebuild the air box ??

 

[razooki]

Did you rebuild the air box ??

No airbox. It has pod filters. At least it's not blowing smoke after I lapped the valves and changed the valve seals. I also set the valve clearances. I started with the screws 2 turns out on all 4 carbs and adjusted to highest idle individually. After adjusting each carb I played with the idle adjuster to get it back to about 1100 and moved on to the next carb. The intake boots are new.

 

[Spyderman]

Well I finally started the bike up after some engine work. The good news is that it started without much effort. The bad news is that it's not running right. I tried setting the idle using the RPM method and it worked OK - it held the idle at about 1100. However, when I give it some gas it revs but it does not come back to idle. the cables are new and lubed and I triple checked to make sure they are not the problem.
Any suggestions with respect to tuning would be greatly appreciated.

what size are the pilot jets ?
what size are the main jets ?
what is the clip position on the needle ?
and what is the throttle cut away 1.5 ? 2.0 ? ( this can be found stamped on the inside of the throttle valve where you unscrew the cap to get to the needle to change the clip position)

 

[razooki]

what size are the pilot jets ?
what size are the main jets ?
what is the clip position on the needle ?
and what is the throttle cut away 1.5 ? 2.0 ? ( this can be found stamped on the inside of the throttle valve where you unscrew the cap to get to the needle to change the clip position)

112.5 and 261 are the only numbers I remember from the last time I looked. As for the cut away and the needle clip position - no clue, I never took the carbs apart. They were dipped and cleaned by the PO and I only gave them a cursory check when they were off the bike.

 

[Nessism]

It's good to dream.

 

[Guest]

Mines a 79 and has two throttle cables. Not sure about the 80 models. But if you don't have the cables adjust properly at the carb the throttle won't come back properly.

 

[49er]

Mines a 79 and has two throttle cables. Not sure about the 80 models. But if you don't have the cables adjust properly at the carb the throttle won't come back properly.

Good point. The VM29's should also be fitted with twin cables. It can be a safety issue should icing occur in colder riding conditions.

Talking about dreaming, are you sure that the PO was leveling with you. I would suspect that the carbs haven't been cleaned properly, or the pilots are too lean for the pods. This will cause the idle to hang up. Your mains are probably in the ball park at 112.5. Suggested needles for the 29's are 5DL31. The 26's use 5DL36.

 

[Spyderman]

for you and those carbs
pilot jets 22.5 or 25
needle clip position third from the top
main jets 112.5 or 115

that should be a good starting point
if you feel like calling me to talk about this shoot me a PM and i'll give you a call anytime after 2pm Mntn time

 

[razooki]

for you and those carbs
pilot jets 22.5 or 25
needle clip position third from the top
main jets 112.5 or 115

Took them apart tonight the and needle clip position was on second from top. I dropped them down to third from top and I used this method to bench sync them gleaned from another post on this forum.

Well then, here's something to play around with and learn. The VM bench synch.
FULLY CLOSED POSITION first ('78/79 GS1000): Take the tops off the carbs. Throttle return spring INSTALLED. Be sure the throttle valve arms and throttle pulley are torqued to the throttle shaft and the throttle shaft stopper plate is tightened.
Turn the idle adjuster knob to make a good clearance between its tip and the throttle pulley. Above each slide is the slotted adjuster screw and its holding nut. Loosen the holding nuts. Hold the carbs with the ENGINE side facing you. Look at the small nick at the bottom of the slide. When done, you want these to all look as close to uniform as possible. On the 1000, you can start with any carb. Turn the slotted screw to fully close or seat, the throttle valve. Don't tighten it down. Just seat the valve. When you see the valve stop dropping, stop turning the screw. You'll find that the screws are very sensitive. It does take decent eye sight and a careful hand. Once the valve is fully closed, hold the adjuster screw STILL and tighten the holder nut to 3.5 ft/lb. NO MORE. Repeat to the others. When done, the small nicks should look uniform.
Now the FULLY OPEN POSITION: There's a slotted screw under spring tension mounted on the carb bracket. When you open the throttle fully, the pulley will stop when it hits this screw. Turn the carbs so the FILTER side is facing you. Raise the valves by pushing up the throttle pulley until it stops and hold it. Look up and inside the bore. Note the bottom of each valve. The bottom of all the valves must be between .5mm and 1mm above the top of the intake chamber. Turn the slotted screw in to decrease the gap, out to increase. It usually only takes a 1/2 turn or so, if needed.
Now turn up the idle adjuster knob enough so the bike will idle when you do the vacuum tool synch.
A good bench synch will make the vacuum synch easier/quicker.
Use two fans. Stop if you think the motor's getting too hot. Remember to adjust the side air screws by using the highest rpm method before the synch. This is to be done on a warmed up engine. The ignition timing, tappet clearances, and throttle cable slack must be correct too. Clean and oil those K&N's with K&N filter oil and mount.
Note the initial vacuum levels at start up. I synch at about 3,000 rpm's. Don't rev the bike suddenly or you'll suck up mercury. Easy on the throttle. Adjust the higher level(s) to match the lower levels. Don't over tighten the adjuster screws. Get the levels as close as possible. If you can get them so the difference between the highest and lowest level is about 1/2", that's good. Double check all adjustments by slowly opening/closing the valves. It takes practice. You can do it.
Any questions, let me know.

 

[rudy]

VMs are VERY easy to work with. Easy to clean, easy to rebuild, easy to set/sync. I'm running a K&N filter on my 1000 in the stock airbox, 4-1 Kerker with a Yosh can. Still running a touch rich with stock jets and needles. Always has, even with OEM filter. This bike has always been in the Kitchener area, so not jetted for anywhere else. Original jets. Runs VERY nicely, but pops a little when it's cold (below 6) out. I should probably have a look at the idle mix though.

Keep working at it, you'll find the problem.

 

[razooki]

I have a question regarding the method I mentioned above. Do the slides have to close all the way? Because I tried and I could not get them to close all the way.

 

[Guest]

if you are doing a bench synch they shouldn't be closed all the way. A fraction up from the top(small wire or small drill bit, what ever works roughly a few mm's), the main thing is that they are all the same. This just gets you close, a vacuum synch gets them bang on, you just need them close enough to start the bike. I'm trying to remember but I do think they will close all the way or close to it if you wanted them to but you DON'T want them to be left in that position.

 

[Guest]

They don't close all the way. You want them all closed as far as they will go. If you go too far with one, it will start lifting the other three. They all have to be as even as possible. There is also a stop screw adjustment in the back where the cables attach that adjusts for fully opened

 

[KEITH KRAUSE]

They don't close all the way. You want them all closed as far as they will go. If you go too far with one, it will start lifting the other three. They all have to be as even as possible. There is also a stop screw adjustment in the back where the cables attach that adjusts for fully opened

Correct. Close them carefully as far as they'll go, and no more.

 

[razooki]

Well thanks to everyone!! I re adjusted the slides using a very thin guitar string as a guide and I also moved the needles to the middle position (third from the top as per Spyderman) and..... it started right up and holds an idle beautifully!! I've also adjusted the cables some more so now the throttle is nice and crisp. I was so tempted to take it around the block without the headlight installed and everything but I thought better of it.
Again, thank you everyone. There is light at the end of the tunnel yet.

 

[Spyderman]

cool glad you got it sorted out to the point where it runs
now comes the fun part getting the jetting done correctly

 

[KEITH KRAUSE]

Test the jet needle performance at 1/3 to 1/2 throttle position. At those positions you're running on the jet needle with no significant overlap effect from the pilot or main circuits. Chop off and read the plugs. Do what the plugs/performance say.
You'll get your most accurate reads if you vacuum synch the carbs first and set the air screws for best idle but a decent bench synch/screw adjustments will be good enough for testing.
If you do find the jet needles need another adjustment then you must re-synch.