A few questions on VM29 carbs

[Guest]

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

Wow, great thread! No since starting a new one!:-D I was going to ask if my carbs were in the ballpark for my mods. I wish Rock would post his final results, but it sounds like with the bikes in this thread that none were very modified, except for maybe pipe and pods, and they all needed leaning out from what the last version of the 29's came with. My bike will be:

'78 GS1000 with Weisco 1085 kit
K&N pods
Ported intake and exhaust with new stock valves, new springs, etc.
Performance cams (nothing too wild)
Performance 4 into 1
VM29's with the following:
120 mains
.9 air jets
25 pilot jet
5DL31-3 jet needle
0.6 needle jet
1.5 throttle valve

IF I read all this right, it sounds like my carbs may be suited for my mods, agree?
I was thrown for a loop by Rock talking about an excellerator pump on his 29's? I didn't know you could get them that way. I've never seen a diargram showing them that way. Could he have 28's?

 

[KEITH KRAUSE]

Very unfortunate that people just disappear.
It's their bike and they're doing the actual work but some of us put in a lot of time and thought trying to help too. At some point the efforts should pay off and this helps others down the road.
If communication stops, we all lose.
I try to understand. Jetting can be tough and jetting over the internet even tougher.

 

[Guest]

Very unfortunate that people just disappear.
It's their bike and they're doing the actual work but some of us put in a lot of time and thought trying to help too. At some point the efforts should pay off and this helps others down the road.
If communication stops, we all lose.
I try to understand. Jetting can be tough and jetting over the internet even tougher.

So.... whad'ya think, Keith? Put these carbs back together the way they are set up? I've got fresh orings, needle valves, and those funky little paper gaskets ready to go. I was surprised to find that these carbs don't have many orings, and no pilot screws underneath. I guess they are all that way?

 

[KEITH KRAUSE]

So.... whad'ya think, Keith? Put these carbs back together the way they are set up? I've got fresh orings, needle valves, and those funky little paper gaskets ready to go. I was surprised to find that these carbs don't have many orings, and no pilot screws underneath. I guess they are all that way?

No pilot fuel screws for the 29's.
I don't have enough experience with the smoothbores to say what initial jetting is best. What you said seems like a good starting point to me...most of it. The correct cutaways have always been an issue. I've always thought the 1.5 works but others disagree. There are so many jet needle/needle jet combo's, let alone e-clip position. I think your main jet choice is OK. I think your pilot jet choice is too large, but others may disagree there too.
Test at various throttle positions and see what the plugs/peformance say. I'll try to help any way I can.

 

[Guest]

Thanks, Keith. It will be awhile before she's all back together and ready to run. The crank is coming out this weekend for welding, then all the other stuff! I'll keep you posted.

 

[Rock]

Dredging up the old thread. Well first I would like to thank Keith for all the help and advice as well as others that helped.

I have gone through and replaced ALL the gaskets and o-rings in the carbs and boots as well. I thought my boots looked good until I took them off and flexed them. Wow, one was cracked pretty bad and was only visible by bending them and although they looked great while mounted though and one would think they were in excellent condition as they were not hard either. A learning experience for sure.

I am back to the original jets that I started with and the info Keith gave me about adjusting the carb helped tremendously once all was in order with the carbs. I also installed a new Vance & Hines exhaust. The bike is running super now and the mix screws are all set between 1 3/4 to 2 turns. My compression is 165 on all cylinders, but I think my valve seals are in bad shape and also feel they may have been giving me bad readings at low chop tests? It is going through a bit oil and with the compression readings I can only assume the 30 year old seals are responsible for it. I guess that is for another thread.

Sorry I did not relay my results long ago but I was ill for over a year or so and just did not work on the bike or even go for a ride but a few times in the last two seasons. Any how, I'm back on it again and having fun. Thanks again.

 

[KEITH KRAUSE]

Welcome back. Glad you're feeling better.
I'm glad the bike is running better. I quickly re-read some of this thread and many parts are hard to make sense of, such as how after assumed identical 1/3 throttle chops, the plugs went from "clean white" to black with just 1 position change to the jet needle, things like that.
These 29's are by far the hardest carbs to jet, based on info I've read. Many times the posted "correct" final jetting of others doesn't even help. Owners come up with final jetting that contradicts what others say works, though they have very similar mods.
These carbs, like other carbs, have so many jets you can change that the combo's are almost infinite. What makes these 29's more difficult is that they are aftermarket carbs and can come to you with any number of jet needle, needle jet, slide, etc, changes. They may also come with some abuse or parts wear you may or may not be aware of. Most owners usually just have to deal with main, jet needle position, and pilot jet changes. But with these, the needle jets, air jets, cut-aways may have to be changed too. It appears these carbs come in 3 "preferred" set ups/stages of jetting too. One for stock/close to stock bikes, and 2 other stages for specific mods. Even the 3 different cut-aways are recommended best for a specific brand/engine, Suzuki, Kawa, Honda... I know if you do find the right jetting, these carbs are perfect for the 1000. Many years ago, Vance and Hines used to "pre-jet" these carbs and send them to you for your specific bike and mods. They reportedly had it down perfect, at least according to Motorcyclist magazine. I tried calling and e-mailing V&H long ago at their main office/headquarters but they say they didn't keep any old records of what was proven to work. Kind of hard to believe really but that's what I was told.