VM29 running RICH! History included

[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.

[KEITH KRAUSE]

The 29's are considered the best carb for the 1000 with basic mods. Strictly an aftermarket carb. Vance and Hines used to sell them "pre-jetted" for the 1000. Their jetting was at least very close if not spot on. I tried to get the old jetting records from VH headquarters out here but got nowhere. I'm sure the info exists but how to get it I don't know.
One major issue is the throttle valve cut-away size. There are 2 sizes used for the Suzuki. Some say the 1.5 works best while others say the 2.0 is better. The wrong choice will make the bike run poorly while transitioning from the pilot circuit to the jet needle.
Try going back to the basics. Once you install the new plug leads and are sure the voltage is good at the coils (primary) and plug caps (secondary), spark is a good/bluish at all cylinders, correct heat range plugs are being used and gapped correctly, advance timing set, valve clearances adjusted, filters PROPERLY oiled, carbs cleaned/new o-rings and floats set as you've done, new manifold o-rings and manifolds inspected...then focus on the carbs.
A good vacuum synch is important for accurately testing the jetting but a careful bench synch can get you by until you know the jetting is in the ballpark. If vacuum levels are too far apart then you don't know which cylinder plug read to trust. Each time you disturb the jet needles you must re-synch the throttle valves.
As basic tuning, the side air screws must be adjusted using the highest rpm method first before testing (done on a fully warmed up motor). If the bike is running poorly and has sooty plugs then this adjustment will be compromised but still attempt to set them for now. I don't own these carbs and can only SUGGEST you set the side air screws to 1 1/2 turns out if you have trouble finding the highest rpm. If equipped with pilot fuel screws to assist the pilot jet, then set them to approx' 1 turn out from lightly seated. If others here KNOW better starting points then please say so.
I can only assume the correct air jets are already installed.
If these carbs have 2 float bowl vent lines then I suggest removing the vent lines and leaving the ports open to allow maximum bowl venting and to avoid fuel starvation in windy conditions.
Try testing the main jet by warming up fully first then going to a safe place to do some high speed testing at FULL throttle. Take a run of 1/2 to 1 mile, then repeat the run and chop off by quickly closing the throttle/pulling in the clutch and turning off the key. Coast to a stop with clutch in and check the plugs. The reads should tell you what to do with the mains as no other jetting circuit is being used at full throttle. If taking the reads away from the house then take a rag along to help with the hot plugs. A piece of hose that fits snugly over the plug end will help you avoid burns when removing/installing. Be careful of cross-threading when installing with a hose.
Tell us what the plugs look like and the performance you noticed.
Once the mains are done we can test for the jet needle e-clip position by testing at 1/3 throttle to no more than 1/2 throttle.
Then the pilot circuit can be done.
Final synch using a vacuum tool will be necessary.

[Spyderman]

keith i do own a set of these carbs and they are on my 78
you are one of the handfull of carb gurus her at the GSR and always give very good advice
however the 29 do not have the fuel mixture screw for the pilot circuit
that is why i suggested the settings that i did for him
as for the throttle valve cutaways for a 78 1000 i would go with a 2.0 as i have both 1.5 and 2.0 and the 2.0 work best

again keith i suggested what i did for him to start with because i have had good success with those settings on mine at his ALT so it should be a good ballpark for him to start with and go from there with the plug chops

petersenj20
that is the correct part for your air jet it will unscrew it has a slot cut into it so you can unscrew it and reomve it for cleaning and size conformation

[petersenj20]

I received the plug tips and got one step hotter plugs, per the service manual B7ES NGK. I also adjusted the air screws to two turns out. When I cranked, It fired right up and sounded good. Big time black smoke from the exhaust though. I went for a short ride and was doing well for about a mile and a half when it started the same crap again. I limped it home. Plugs were clean and a bit wet.

I fiddled with the air screws and wound up at 1/2 turn out. Went for a ride. Same story. Good and then bad. This time though, I realized, if I flipped the choke on, it would move under protest. Flip it off, and wanted to die. Limped home. Could it be starving now?

I flipped the fuel cock to prime. Went for a good ride this time. I put about 30 miles on it in and out of the neighborhood. Have to get tags before I can start doing plug chops. It is now back to where I started way back when, which is to say I believe it is still running rich, because I get a bit of popping and hesitation at transitions.

I am not totally certain on the function of the choke. I think that by applying it, I was enriching the fuel and able to run. How would it be starving for fuel, yet reading black on the plugs? Maybe when I got the floats set properly, I uncovered another problem of not getting enough fuel through the petcock.

I am waiting for it to cool down to have a look at the plugs. I understand looking at the plugs at that point, doesn't really prove much, but it is a start until the chops. I'm going to try to ride it a bit this weekend and see how it does. I am mostly curious which notch the needles are in and will start there next week.

[Spyderman]

I received the plug tips and got one step hotter plugs, per the service manual B7ES NGK. I also adjusted the air screws to two turns out. When I cranked, It fired right up and sounded good. Big time black smoke from the exhaust though. I went for a short ride and was doing well for about a mile and a half when it started the same crap again. I limped it home. Plugs were clean and a bit wet.

I fiddled with the air screws and wound up at 1/2 turn out. Went for a ride. Same story. Good and then bad. This time though, I realized, if I flipped the choke on, it would move under protest. Flip it off, and wanted to die. Limped home. Could it be starving now?

I flipped the fuel cock to prime. Went for a good ride this time. I put about 30 miles on it in and out of the neighborhood. Have to get tags before I can start doing plug chops. It is now back to where I started way back when, which is to say I believe it is still running rich, because I get a bit of popping and hesitation at transitions.

I am not totally certain on the function of the choke. I think that by applying it, I was enriching the fuel and able to run. How would it be starving for fuel, yet reading black on the plugs? Maybe when I got the floats set properly, I uncovered another problem of not getting enough fuel through the petcock.

I am waiting for it to cool down to have a look at the plugs. I understand looking at the plugs at that point, doesn't really prove much, but it is a start until the chops. I'm going to try to ride it a bit this weekend and see how it does. I am mostly curious which notch the needles are in and will start there next week.

you have a few conflicting things there
most of the time hesitation and popping is from being lean

it is possible to be rich and starved for fuel if for some reason you have a fuel flow problem check your gas cap vent to be sure it is working and not clogged

you do know that the 29MM smoothbores do not have a vacuum feed from the #3 carb to the petcock so if you leave the petcock in the ON or RES position then you will not have fuel flow to the carbs
with the 29's you have to run in prime for the bike to function properly
also make sure that you check the petcock to be sure it doesn't leak in the on or Res position because if it does the 29's have no floatbowl overflow tube the excess gas that leaks from the petcock will run through the carbs and right into the engine and thin you oil out and this is not good for your bottom end at all

also you need to take the carbs off again and find out what size pilot jets you have
they are recessed in a smaller hole to the side of the main jet the # is stamped on the side (20 22.5 25 ETC) and most likely you will need to turn the pilot air screws that are on the side of the carbs back out to 2 turns

the function of the choke is to enrichen the fuel mixture for cold starting

i hope that i have helped you and given you a path to go on let me know if i can help you further i will be watching for your reply as to how you are making out

[petersenj20]

you do know that the 29MM smoothbores do not have a vacuum feed from the #3 carb to the petcock so if you leave the petcock in the ON or RES position then you will not have fuel flow to the carbs
with the 29's you have to run in prime for the bike to function properly
also make sure that you check the petcock to be sure it doesn't leak in the on or Res position because if it does the 29's have no floatbowl overflow tube the excess gas that leaks from the petcock will run through the carbs and right into the engine and thin you oil out and this is not good for your bottom end at all

No I did not know that. Actually, I just went and looked and my petcock does not have a vacuum outlet. I never realized the ON position would be a problem. I still wonder why they don't just have an off position. I did however place a $3 shutoff valve in the fuel line because it never stops dripping. These do have an overflow tube in the #2 and #4 carb but when the floats were bad, it did dump fuel into the throats and dripped out the filters.

also you need to take the carbs off again and find out what size pilot jets you have
they are recessed in a smaller hole to the side of the main jet the # is stamped on the side (20 22.5 25 ETC) and most likely you will need to turn the pilot air screws that are on the side of the carbs back out to 2 turns

I will do that at the same time I check the needles.

i hope that i have helped you and given you a path to go on let me know if i can help you further i will be watching for your reply as to how you are making out

This has been valuable information. It makes me think of when I was "rodding" as a teenager how we all bought the hot add'ons because they were hot, and didn't really know how to tune them. I much appreciate understanding a little bit more about these add-on carbs. I bet all the motorcycle shops that have gone by the wayside knew how to lay hands on these things. Maybe I will when its all done.

[Spyderman]

the 2 tubes the you think are over flow tubes are not
they are tubes for venting the floatbowls to atmosphere so that the floats will work properly if you look you will see that they are connected to 2 T's inbetween the #1 & #2 and #3 & #4 carbs
do not plug them and be sure to have the hoses no more than a foot long so that the ends do not get obstructed at all

in order to see the vacuum line port you need to lift the tank it is on the back of the petcock and faces the front of the bike and is smaller than the fuel line outlet it should be there if you have a stock petcock
a shut off valve is a very good idea i also have installed one on my bike

if your petcock has a RES ON and PRIME position then it is stock and will have a vacuum line port on the back

if you have had the carbs dripping fuel then it is a very good idea to drain the oil and replace the filter and give it fresh oil i would bet that if you took off your oil filler cap on the clutch cover that you will get a good smell of gas and if you do then you have gas in your oil and need to change the oil and filter right away

it would also be good if you could post a picture of your carbs with the pod filter removed so that it can be confirmed that you actually have 29MM smoothbores just incase for some reason you don't but i do suspect that you do infact have them

[petersenj20]

the 2 tubes the you think are over flow tubes are not
they are tubes for venting the floatbowls to atmosphere so that the floats will work properly

No wonder the fuel came from the carb throat.

if you have had the carbs dripping fuel then it is a very good idea to drain the oil and replace the filter and give it fresh oil i would bet that if you took off your oil filler cap on the clutch cover that you will get a good smell of gas and if you do then you have gas in your oil and need to change the oil and filter right away

Did the oil and filter earlier this week.

it would also be good if you could post a picture of your carbs with the pod filter removed so that it can be confirmed that you actually have 29MM smoothbores just incase for some reason you don't but i do suspect that you do infact have them

I am certain that's what they are. I kept getting frustrated why all the tutorials did not look the same. When I saw the Mikuni tuning manual it all made sense. Here is a pic anyway Notice the sexy NGK white lettering on the black spark plug boots.

[Spyderman]

yup most defiantly smoothbores

so now for you to set the petcock to prime and go for a ride and see what the plugs tell you and then you can start to tune them in
and we at the GSR will help you when you need it
nifty new plug caps

[Spyderman]

so how did you make out ?????

[tkent02]

Are you interested in an absolutely problem free set of VM26 carburetors that are working perfectly on my GS1000E engine?