A few questions on VM29 carbs

[robinjo]

Bike is running on all four now and how!

When I checked the spark plug on that cylinder it wasn't soaking wet but was kinda black and shiny instead of light brown, I changed it out with another used one I had and no change, picked up a new one at the shop today and it instantly ran. I kinda gave up hope it could something that easy.

Vacuum port system is working well too.

 

[Hoomgar]

Bike is running on all four now and how!

When I checked the spark plug on that cylinder it wasn't soaking wet but was kinda black and shiny instead of light brown, I changed it out with another used one I had and no change, picked up a new one at the shop today and it instantly ran. I kinda gave up hope it could something that easy.

Vacuum port system is working well too.

Rock on! 8)

 

[KEITH KRAUSE]

Rock, not sure why #2 is leaner than the others. I assume the reads were at least uniform in the past? What could you have done between now and then to change #2?
As for the accel' pump, I have very little experience with these. But because it's surrounded in fuel, I would say that it could only create a rich condition in #2, or, by not working correctly, a momentary lean condition at all 4 carbs. It only operates at the initial throttle opening as you said. It just gives a quick shot of fuel. It wouldn't cause a constant lean running condition.
Not sure what to suggest at this point except to install the new manifolds and be sure their o-rings are the correct size and lubed with hi-temp grease and torqued to about 6 ft/lb. Double check the vacuum synch. I'm sure you've adjusted the floats and all other things are checked the best you know. Let us know and maybe we can go down a list of all possible causes of 1 carb/cylinder running lean?

 

[first timer]

ok i am reserecting this thread cause it is now my turn.

i have been tring to tune my 29's

this is what i have,

79 gs1000 stock

4 into 1 yosh header and can
carbs were synced merc stixs

vm29 (A7 the sudco kawaski specific carbs)

1.5 cutaways
25 pilots
117.5 mains
not sure about air jet

ok here is my deal the bike seems to run either real rich or real lean, the rich is probly cause of the 1.5 cutaways

so would it hurt if i went down to some 20 pilots
to compansate for the more mix from the cutaway?

also what should be the float height setting? i read in this post that it was 22.3mm is that for sure?


also forgot to add my air screws are set at about 1/2 to 1 turns and as i adjust them the engine rpms don't really change so i have been ending up adjusting them a little bit ride the bike then pull the plugs and readjust acordingly

-ryan
-ryan

 

[KEITH KRAUSE]

Not enough info. I just saw this on my way out for the day.
Gotta have full, 1/3 and minimum throttle opening reads to decide.
Your info just seems to be about the pilot circuit/lower speed area.
Can't say how the richer cut-away will factor in. The cut-away is the transition between the pilot circuit and the jet needle circuit. Fine line in between, but can cause trouble for sure. I don't know if a smaller pilot jet will help. Need more time to think about this one and I gotta go.
The way I jet, I need those throttle reads above and any other symptoms you see at that time. Such as any black exhaust, rough idle....

 

[first timer]

well it's goign to be hard for to get those reads since i am right in the middle of chicago, the bike just seems kinda grumpy through the first two circuts, i think it is just going to take time cause i think every thing is getting reseated right now which will throw the sync, i also am suspicios of my points and timing, i reset it but am still leary about it. so i am goign to see about all that, put the 20 pilot jets in and see what that does and i'll report back

-ryan

 

[KEITH KRAUSE]

Yeah. The timing and spark quality have to be correct before the synch or re-jetting.
I don't know the correct float level. I've seen it at a website but can't remember the site name. I know if you just search under "29 smoothbores", you'll find the info. I think Sudco's website will help? You have to set that right first.
I assume you removed the floatbowl vent lines?
I don't know any other way to test each circuit without running the bike at each throttle position. Without a Dyno, you're just guessing.
I'm not sure what's going on with your air screw adjustments, but a "rule of thumb" method is to try to make a pilot jet choice that works with a "normal" air screw adjustment range. Generally, this bike should have its air screws set somewhere between 1 1/4 and 1 3/4 turns out, at least that's what I've read. I'm by no means an expert on these carbs.
And of course, the richer cut-away really complicates things.
With your testing limitations and info provided so far, I suppose I might try setting the air screws to about 1 1/2 and keeping them there while I run the bike at minimal throttle for a few miles and chop off. Go ahead and leave the 25's in there for this test. See what the plugs say and note performance. If rich and you've done your best to stay off the needle circuit, then try the 20's if that's what you have. Don't touch the air screws with either test. Any plug color/performance change can then be attributed to the pilot jet size. By going two steps apart (25's to 20's) you should see some change you can work with. This might simplify things??
I don't think you'll run lean (at least with the 25's) so I won't make any suggestion about that.
This procedure isn't normal for me, I always seem to have luck using the highest rpm method to set the air screws, but I'm just trying to come up with something to get you in the right direction.
I'll be gone all day tomorrow, so good luck on it.
Again, I'd set the floats and timing, etc, first. Then test/adjust the jetting.

 

[jeff.saunders]

23mm is the correct float height.

The jetting seems very unbalanced. Very rich pilot jet, very rich pilot air screw setting, rich slide cutaway, very lean main jet.

Did you buy the carbs and just change the main jet? How did you arrive at the current jetting?

I would suggest coming down at least one, possible two sized on pilot jet.

I suspect you'll need to go up on the main jet one or two sizes too.

Where is the needle set? Is it still in the middle slot?

 

[first timer]

Hey Jeff, these carbs came on the bike it was a non runner when i got it. the carbs are basically jetted for the kawasaki kz650, 900 and 1000 according to sudco's referace chart. the only thing diffrent that my carbs are set with is a smaller main jet (117.5 instead of a 120 like sudco speced)

the settings as speced by sudco for the gs 750 and 1000 are #115 mains, .9 air jets, 25 pilots, 5dl31-3rd needle (which is where i have my needle) 0.6 needle jet, and 2.0 throttle valve.

So it seems my delema is that i have richer throttle valves then i need, is there any way to compensate for this, like using smaller pilots?

on a side note i may know where to find some 1.5 throttle valves for 35 bucks a pop is it worth it?

Hey Rock speak up how has the bike been working? what was your final conclustion?

-ryan

 

[jeff.saunders]

There are a few people on this site running with 29mm carbs - there seems to be a fair discussion on the 1.5 versus 2.0 slide cutaway.

The carbs setup for GS's had 2.0 slides - but this seems to cause some poor low-end performance.

I have plenty of sets of good used 2.0 slides - most people seem to go with 1.5's - so if you need any, just contact me.

First I would try smaller pilots - but I'm curious to hear from anyone else running a setup like yours to confirm my thoughts.

 

[first timer]

thanks for the offer i will diffently keep you in mind, like i said earlier i think i need to play around with it more, there are several other factors that i need to be sure of that aren't causing problems before i drasticly start swaping things around.

-ryan

 

[robinjo]

Ah back in the old topic!:-D

I replaced the #25 pilot jets for 17.5 and put the screws 1 and 1/2 turns out but didn't run well, bad idle and choppy when cruising at 30 mph. Warmed her up good and used the Colortune, I ended up with 2 screws completely closed and the other two under a half turn out to get a perfect burn.

So it seems they are too lean, I will try some #20's but I will need to order them. Also replaced the #120 mains with 116 ones and they are close, I may have it on the Dyno tomorrow to check if I find the time.

Also replaced the old points ignition with a Dyna S ignition and replaced the float needle assemblies because they had a bit of a ridge on then.

 

[first timer]

Ah back in the old topic!:-D

I replaced the #25 pilot jets for 17.5 and put the screws 1 and 1/2 turns out but didn't run well, bad idle and choppy when cruising at 30 mph. Warmed her up good and used the Colortune, I ended up with 2 screws completely closed and the other two under a half turn out to get a perfect burn.

So it seems they are too lean, I will try some #20's but I will need to order them. Also replaced the #120 mains with 116 ones and they are close, I may have it on the Dyno tomorrow to check if I find the time.

Also replaced the old points ignition with a Dyna S ignition and replaced the float needle assemblies because they had a bit of a ridge on then.

hey robinjo

please get that hog on a dyno, for your referance i am running #20 pilot jets (down from #25) 117.5 mains, and 1.5 cutaways, it seems like it is kinda working for me, i still need to work out the bugs i was only able to ride the bike for about 30 miles and it seemed happy, 2 months back but i was running open carbs with no filters and was getting a back fire out the carbs once in a while. i now have k&n's so as soon as the weather gets better and i get the body back from the painter i will do some more fooling around with the carbs to see what i get. and put some miles on it too. if it helps i am running yosh can and yosh 4-1 and have a dyna 3 installed
keep me posted in what you find out.

-ryan

 

[robinjo]

Well I've had the bike on the Dyno yesterday and it seems I did pretty good! \\/ We did several runs which produced between 74.5 and 76 HP at the wheel, ,max torque about 70 Nm. A/F ratio was measured seperatley and was good, slightly rich on the topend but thats not a bad thing with these old aircooled bikes. And I have the feeling the engine is being restricted somewhat by the quiet-ish 4-1 pipe, I have plans for a good performance pipe so we will see how that turns out then, I could well screw the whole thing up again.

 

[first timer]

if you have everything settled now could you please post the setting and internals you have in your carbs, as well any engine mods like hot cams and bigger pistons or a port job.

thanks,

-ryan

 

[robinjo]

if you have everything settled now could you please post the setting and internals you have in your carbs, as well any engine mods like hot cams and bigger pistons or a port job.

thanks,

-ryan

This is for Mikuni VM29 carburettors:

Needles 5DL31 middle position, no shims on top or bottom

17,5 idle jet, #20 could be better, these are too small to put the screws at the usual range of turns out.

116 main jet

Throttle slide cut-away 2.0

Float height 22.5 mm

Seperate oval K&N filters.

4-1 exhaust but not straight through.

Synchronised them to within an inch of their life.

Otherwise stock as far as I know but haven't had it open yet.

Dyno operator found it a bit overgeared causing it to lose power in the higher gears, it topped out at 230 real km/h (144 mph) on the Dyno. I'm going to try a two tooth larger rear sprocket, standard is 42 right? Already ordered a Tommaselli quick-action throttle grip.:-D

 

[first timer]

thanks for the info, i'll see if i can get it working for me, i am basiclly in the same boat you are the only diffrence is i have 1.5 cutaways, i may end up going to a 17.5 pilot jet then to lean it out a tad but we'll see i first need to get some miles on it, and it's good to know i'll have about 80 at the wheel when working right.


p.s. you got any pics, i would like to know what the "light weight version" is
thanks
-ryan

 

[robinjo]

thanks for the info, i'll see if i can get it working for me, i am basiclly in the same boat you are the only diffrence is i have 1.5 cutaways, i may end up going to a 17.5 pilot jet then to lean it out a tad but we'll see i first need to get some miles on it, and it's good to know i'll have about 80 at the wheel when working right.


p.s. you got any pics, i would like to know what the "light weight version" is
thanks
-ryan

Do you wanna swap pilot jets with me? please?

The bike's not ready yet but here's a preview. Not all the parts are fitted, not even all the stickers...

 

[first timer]

i wouldn't mind swappin pilot jets but there is a little problem with some water between us that would make it cost more to ship then to buy new ones.

bike is looking good make sure to show me when she is all done.

-ryan

 

[robinjo]

i wouldn't mind swappin pilot jets but there is a little problem with some water between us that would make it cost more to ship then to buy new ones.

bike is looking good make sure to show me when she is all done.

-ryan

Four pilot jets including enveloppe weigh seven grams, this will cost me less the $1 to ship priority.:-D 20-50 grams is getting close to $2, also priority. The price for four new ones is ten dollars excl. shipping.

I will be sure to show the bike when it's finished.