VM29SS carbs

[Nik]

Hi all!

I need your help!

I am getting my last MOT on an 85 slabby soon. I have a 1216 for it, but I will fit a 748 for the MOT. I will use the original VM29SS carbs, but I do not have an airbox for it, but have to run individual K&N filters. I haven't run 750s in my bikes for ages and I am senile. Any suggestions on main jet size? It doesn't have to be perfect, just good enough for the MOT (emissions are not checked). Any help is appreciated!

 

Edited Monday at 10:16 AM by Nik
Typo

[Nik]

Nobody with a suggestion on jetting? 

[Dezza]

As long as it runs wouldn't that suffice? Even so the last mot I had the tester didn't even bother to start the bike.

[Oilyspanner]

If it struggles to run, going up 4 sizes on the mains and one up on the pilots should be close enough to run. Lifting the needle one notch should help too. 

[Nik]

Thanks guys. Sorry if I was unclear. I haven't fittted the carbs yet, so I have no idea how it runs. I need a ballpark jet to begin with, so I get it as close as possible to decent from the beginning. 

97.5 are the original main jets, for use with airbox and original exhaust. I have to use K&N filters though (and an original exhaust from a 1990 GSX-R 750), and just like some suggestion on what main jets to try. I doubt that the exhaust makes much of a difference, but the airbox will have a bigger impact. 

Edited Wednesday at 06:20 AM by Nik

[Upshotknothole]

Sorry, no idea on the jet size for those early VMs. Check the Dynojet website for the jet kit for your setup, the instructions will be a PDF on the bottom of the page for the jet kit, that'll have the Dynojet size mains listed. Next do a search online for a Dynojet to Keihin to Mikuni jet size conversion chart, that'll give you a ball park idea of what size Mikuni main jets to run. Probably won't run very well with stock needles, but should hopefully get you close enough that you can start it.

[Nik]

2 hours ago, Upshotknothole said:

Check the Dynojet website for the jet kit for your setup, the instructions will be a PDF on the bottom of the page for the jet kit, that'll have the Dynojet size mains listed. 

Good idea. I checked, and unfortunately Dynojet only shows jet kits for the vacuum carbs that were used in the U.S. 

Edited Wednesday at 08:29 PM by Nik

[Upshotknothole]

7 minutes ago, Nik said:

Good idea. I checked, and unfortunately Dynojet only shows jet kits for the vacuum carbs that were used in the U.S. 

Damn, but not surprised as they're an American company.

I looked up my 750M with great big BST38s. Stock was 127.5, and I believe I'm running running 150s with dual pods and full exhaust. If you can get the jets local for not too much, I'd try something in the 110-115 range. Larger carbs and more free flowing setup than yours and it's a 22.25 jump. Thinking smaller carbs and more restrictive exhaust, going up by 15 will maybe be close enough to go from. Unfortunately we never got those carbs here in the states, so I don't have any experience tuning them.