VM29 running RICH! History included

[petersenj20]

78 GS1000C. I have done the whole Basscliff rebuild. Soaked carbs. Rebuilt with new O-rings. I had it running pretty well about a month ago for two days until the #2 and #3 floats weren't shutting off fuel, smooth ride became popping and crackling. When I returned, the #2 and #4 carbs were dripping fuel from the air side.

Was down for a month waiting to get new floats. Replaced two floats. Repaired broken float hinge post. Bench sinc'd the carbs according to Paul Musser's rebuild guide.(I had not done this step the first time around so is the only new carb adjustment).

Now the popping and cracking are still there, all 4 plugs are black and sooty. 1 or 2 maybe but all 4? I have peered into the carbs and confirmed floats are shutting off fuel. How could it be running so rich at this point? I thought maye too large jets, but it ran smooth for those two days and the plugs weren't sooty.

 

[almarconi]

Float height and service fuel level. Did you check these values?

 

[petersenj20]

Yes. I checked the new floats and had already checked the other two with the rebuild.

Float levels may have changed on the new ones but not the old floats.

 

[sharpy]

Yes. I checked the new floats and had already checked the other two with the rebuild.

Float levels may have changed on the new ones but not the old floats.

Why would the float level changed between old and new? Are all the flaots brass and have no pins holes in them?

 

[hampshirehog]

Choke plungers not shutting off properly?

 

[petersenj20]

Why would the float level changed between old and new? Are all the flaots brass and have no pins holes in them?

The two old floats are brass and heights are adjusted. The new floats are plastic and I adjusted them. However, I was unsure wether height is adjusted to needle close, or to include compressing the spring inside the needle. I believe I measured with the spring compressed.

 

[hampshirehog]

Float height is adjusted to the tab just touching the needle - you'll have waaay to much fuel in the chanber if you adjusted to compressed needle and it'll drip out through the gasket (which was never intended to hold fuel back - just 'slop' as you accelerate / decelerate).

 

[woodman]

Just turn them upside down and measure them that way. Dont push down on the float

 

[sharpy]

Why plastic floats? Im sure u can get the brass ones from Z1 enterprises and are you sure EXACTLY that the plastic ones are the same. Also you can have the carbs one there side so the float needle is just touching the needle. These are rare/expensive carbs so utmost care is warranted

 

[petersenj20]

I'm going to re-adj the floats then. There is a lot of play in the plunger so would make sense.is getting too much. Why do these have plungers anyyway? Everything else I have ever worked on were solid.

Z1 industries did not have any floats for them. I checked. Got from my local shop. I have never read these are rare carbs, but I also have not seen the exact same carbs in any tutorials or any pics. The thing that really threw me off on the bench sinc is the two adjusting screws on the bell crank. Just an observation.

I did have a look at the Mikuni manual on Basscliff's site which does have the exploded view. That's how I knew they were VM29's.This manual is not a repair manual, reall just a parts list.

I will report back my results.

 

[almarconi]

Even if you set the float height with a float height gauge, you should still check the level of fuel in the bowls. Most manuals have a spec for service fuel level. The measurement is usually taken, with the bike on the center stand at idle. I can tell you from experience that no matter how close you get them with a gauge, the wet method is more accurate. It only takes a tiny movement of the float tang to change the fuel level. It usually takes me a couple of hours during the rebuild process to set the fuel levels in each bowl but it is worth it.

 

[petersenj20]

Even if you set the float height with a float height gauge, you should still check the level of fuel in the bowls. Most manuals have a spec for service fuel level. The measurement is usually taken, with the bike on the center stand at idle. I can tell you from experience that no matter how close you get them with a gauge, the wet method is more accurate. It only takes a tiny movement of the float tang to change the fuel level. It usually takes me a couple of hours during the rebuild process to set the fuel levels in each bowl but it is worth it.

Someone mentioned Service fuel level before. I have no idea how to determine the level of fuel inside a closed bowl. Please explain this process. EDIT: A little searching and I learned I have to use a clear tube attached to the bottom of the float bowl to act as a manometer type set-up. END EDIT
I do understand a need for this as the buoyancy of a given float could be more or less, effecting how much fuel is allowed in.

I have adjusted the floats. Both new floats were inaccurate due to the improper needle spring compression. The two brass floats each had the pontoons at different levels so needed twisting and adjusting.

The heavy loading up of fuel has now gone, thank you all, and has returned to how it rode back when. However, I still think it is running a bit rich and am waiting for it to cool to check the state of the plugs after a short ride.

This is my starting point. I have been reading about the plug chops and why each are done differently to pinpoint a circuit. The bike has pods and a big, un-muffled 4-in-1 open exhaust pipe and I suspect the person that did all that, may have gotten a little excessive on the jetting.

 

[petersenj20]

The plugs are still quite sooty and the motor is deffinitely getting too much fuel. I have been reading about checking the wet fuel level. I have the float bowls with the large drain plug so will be harder to screw a tube into it. I found a fitting made just for this on ebay but is $20 with shipping. Too much for my blood. I'll try to make one once I find out the screw diameter and thread pitch.

 

[Guest]

Does it rev smoothly through the 5-7,000rpm range up to red line?

 

[petersenj20]

Rare mikuni's indeed.

Rare mikuni's indeed.

I have now adjusted the service fuel level. I determined the float bowl drain plug thread size is 5/8" x 24 TPI. Ace doesn't carry this size as a bolt. I found it as a:

Male Adapter
15
5/8" x 24 THD for Female Aerator 2
(Its a kitchen sink faucet male aerator adapter)

These carbs seem to be in limeted qty's. They had a large drain plug so the jets could be easily removed for re-jetting at the track (No need to remove the float bowl)
​

The small side of the adapter is what I need. I JB Gas tank Weld'ed a 1/8" barb that has a taper thread and I got a 10 x ? nut to thread the barb into. Attach a plastic ice maker line to it and a manometer is born. $7 plus materials on hand (JBweld and ice maker line). Sorry...crappy cell phone camera.

I painstakingly adjusted all four floats to 5mm from the carb/bowl deck, aligning the manometer tube exactly 20mm from the intake side of the carb (The fuel rail casting on the outer carbs does not go all the way through since they are outer carbs - The center of the fuel rail turned out to be the center point of the manometer) utilizing an eyeball calibrated "General" dial indicator dead accurate to the .010 degree.

"Note: When checking the fuel level place the machine on a center stand. The fuel level gauge pipe makes sure to locate at about 20mm (0.08 in) off the rear end of the float chamber." - excerpt taken from an '80 model Suzuki GS1000 service manual.

I still haven't found an actual, '78 GS1000 service manual with Mikuni VM29 carbs to tell proper ways to adjust them or what the "stock Mikuni" jets were. If you have this carb, disregard all the tutorials about air screw and fuel screw cause it only has one. I don't know which it actually is at this point because I apparently am a retard. I surmise from parts list's that the '78 was the only year stock with Mikuni VM29 carbs. Why else would they all sell parts for it? Everything other than parts houses say the Mikuni VM29 was an aftermarket add-on for the period.
​

Guess what. On 4 flooding cylinders, the floats were set too low on two carbs and too high on one carb. The third carb was dead on. Yet all 4 plugs are black and sooty. After I leveled all the carbs I went for a ride. The good news is I made it home and didn't need a tow. The bad news is I think I have eliminated the carb problems, save needle notch adjustments and jet changes. WOW.

By the way...It is has an unknown 4into1 pipe with no baffle and is loud as all get-out (Ask me about my homemade muffler), pods, and 112.5 jets - I know because I checked when I had the carbs apart for the 1200'th time. Correct me if I'm wrong, but doesn't adding all these free flowing aftermarket parts usually make a bike run lean?

I have bought 4 new spark plugs and ordered 4 new plug wire boots. If it turns out to be a weak secondary electrical system, I will ride it directly into a creek.
​

 

[almarconi]

So even though you adjusted the float height to spec, the fuel levels were different in 3 out of 4 bowls. I figured as much. Glad you got it sorted out.

 

[petersenj20]

After I leveled all the carbs I went for a ride. The good news is I made it home and didn't need a tow. The bad news is I think I have eliminated the carb problems, save needle notch adjustments and jet changes. WOW.

After re-reading my post here, it didn't really reflect what happeed on my ride. It popped and cracked worse than the first time. I have the electrical parts ordered and I'm going to leave it alone for a day or two.

 

[Spyderman]

I painstakingly adjusted all four floats to 5mm from the carb/bowl deck, aligning the manometer tube exactly 20mm from the intake side of the carb (The fuel rail casting on the outer carbs does not go all the way through since they are outer carbs - The center of the fuel rail turned out to be the center point of the manometer) utilizing an eyeball calibrated "General" dial indicator dead accurate to the .010 degree.

"Note: When checking the fuel level place the machine on a center stand. The fuel level gauge pipe makes sure to locate at about 20mm (0.08 in) off the rear end of the float chamber." - excerpt taken from an '80 model Suzuki GS1000 service manual.​

good so now you know that the float level is right it's time to start jetting

I still haven't found an actual, '78 GS1000 service manual with Mikuni VM29 carbs to tell proper ways to adjust them or what the "stock Mikuni" jets were. If you have this carb, disregard all the tutorials about air screw and fuel screw cause it only has one. I don't know which it actually is at this point because I apparently am a retard. I surmise from parts list's that the '78 was the only year stock with Mikuni VM29 carbs. Why else would they all sell parts for it? Everything other than parts houses say the Mikuni VM29 was an aftermarket add-on for the period.

you won't find a service manual with ball bark settings for these carbs because they were a go fast add on made by Mikuni for the GS1000 and 750 the factory mikuni carbs that came on the 750 and the 1000's were VM 26's and were a very different animal to the 29 smoothbores
​

Guess what. On 4 flooding cylinders, the floats were set too low on two carbs and too high on one carb. The third carb was dead on. Yet all 4 plugs are black and sooty. After I leveled all the carbs I went for a ride. The good news is I made it home and didn't need a tow. The bad news is I think I have eliminated the carb problems, save needle notch adjustments and jet changes. WOW.

your problem is defiantly in your carbs and not anywhere else
at a 1000 ft ALT or there abouts
you should start with these settings
pilot jet
22.5 or 25 (start with the 22.5)
pilot air screw
2-2.5 turns out (fine tune each one for highest idle RPM )
pilot air jet
.9
jet needle
P3 (right in the middle )
Main jet
115 (117.5 may be needed)

here is a note for you the jet needle on the 29's is very aggressive on the taper compared to the stock needles in the 26's so it is possible that you will still be rich on the needle and may need to raise the clip to P4(second from the top) jetting is a very fussy thing to do and it takes time
start with the setting i gave you as i ran my 1000 at this ALT with good results. remember though that once you have them set as i have suggested then ride it and see how it feels do some plug chops and see what the plugs tell you
be sure to only make one change at a time after your initial ride so you can see what that change has done for you and what the plugs are telling you
it will take some time but is worth it in the long run

By the way...It is has an unknown 4into1 pipe with no baffle and is loud as all get-out (Ask me about my homemade muffler), pods, and 112.5 jets - I know because I checked when I had the carbs apart for the 1200'th time. Correct me if I'm wrong, but doesn't adding all these free flowing aftermarket parts usually make a bike run lean?

it would be good for you to tell us what jets you have in them and what the needle clip position is and not just the main jet the more info you give the better we can help you to get it running the way you want it

I have bought 4 new spark plugs and ordered 4 new plug wire boots. If it turns out to be a weak secondary electrical system, I will ride it directly into a creek.

i am more than 90% sure that your problem is in your carbs and jetting and not in the electrical so there will be no need to ride it into a creek
​

 

[petersenj20]

Thanks for the encouraging info Spyderman.

I have the plug ends on order because these ones are worthless. I needed them regardless.

When you say "pilot air jet .9" - Is that what the Mikuni manual calls a "BS30/97 air jet"?
I could not figure out how to remove this on any of the carbs. Maybe a special screwdriver? They were dipped and I sprayed with carb cleaner, but I can't figure out how to remove them to see what size they are or be able to change them.

I am not sure what notch the needles are in. When I was cleaning I noticed them but don't remember where they were so will have to confirm that along with the size of the others.

 

[KEITH KRAUSE]

Float height is adjusted to the tab just touching the needle - you'll have waaay to much fuel in the chanber if you adjusted to compressed needle and it'll drip out through the gasket (which was never intended to hold fuel back - just 'slop' as you accelerate / decelerate).

Just contacting the float valve is correct, but incorrectly adjusting the level to include spring compression would require the float tab to be bent upward and this would result in a too low fuel level in the bowl.