VM34's in a 400??

So my stock carbs arent working for me on the 400. Just can't get them jetted right, and non-stock jet sizes are virtually impossible to find for the bloody things.

So... I have a set of mikuni round slide 34's sitting in my garage. Was going to use one for a single carb conversion, but figure if I can just run them both, I'd be better off.

I know 34's are a bit big for a 400, but I know it's "possible" cause I have seen a video of a 400 with it done. My question, how should I jet it? Theyre off of a snowmobile so the stock jets are 150 and 45. what size jets would you all recommend?

I am currently running kn style intake and open headers.

Thoughts??

Some other performance work would bring out the best it that sort of set up. A compression increase if you get some bigger cams, and some port work on the head. Otherwise, Why? It would be over fueled. While I'm sure you could get it to run, it would perform better with just 1 if the rest is more or less stock.
Buy a set of drills in a Numbered "Wire Gauge" for adjusting the jets you have now, if you can't buy replacements. Go slow 1 step at a time.

The other issue is I often see snowmobile carbs as needing different fuel valves when used on bikes. Not sure why, but maybe gravity fed versus fuel pump?

loudhvx wrote: The other issue is I often see snowmobile carbs as needing different fuel valves when used on bikes. Not sure why, but maybe gravity fed versus fuel pump?

That would be correct. The Sleds use smaller Float Valves.

Damn. Was hoping for a "easier" solution.

I tried drilling out the stock jets but the next size up from wtock on the primary main took it from lean to rich. Guess I'll just have to go back to stock on the primary mains and live with it being a little lean.

A true "Wire gauge set will go up in small increments, or look at these tapered reamers.
www.stahlwille-online.de/pictures/all/11085_fot_022.jpg
I've been using these for a good 25 years. Yea I'm old.

Motor Head wrote: A true "Wire gauge set will go up in small increments, or look at these tapered reamers.
www.stahlwille-online.de/pictures/all/11085_fot_022.jpg
I've been using these for a good 25 years. Yea I'm old.

Hm okay. I know they were numbered but not sure if they were "wire gauge". I have to research those.

Unfortunately stock mains for these stupid carbs are $13 each so it's sort of a expensive trial and error process. Which is why I was hoping the mikunis would work. Cheaper and more readily available jets.

Well 1 set is small,#61-80, Blue Point DB120B: buy1.snapon.com/catalog/item.asp?search=...napon-store&tool=all
looks like the current version. Also available cheaper elsewhere.
Then buy1.snapon.com/catalog/item.asp?search=...napon-store&tool=all is the the set that keeps going larger. So if you had these and the reamers, you can make any size you want. just be very careful to make things the same when dealing with multiple carbs, or you will get imbalance.
There is an actual flow rate, not just size that is made into jets from factories, no matter who made them. but drilling carefully has been a way that carb tuners have used for, well ever.

loudhvx wrote: The other issue is I often see snowmobile carbs as needing different fuel valves when used on bikes. Not sure why, but maybe gravity fed versus fuel pump?

Alright so I think I am going to go with the 2-1 manifold and just use one of these carbs.

Can you give me more info on this "fuel valve" swap? Is it hard to switch out? Is it expensive?

I don't think the valve swap is hard or expensive, but I don't know for sure. I've always thought it was just a new fuel valve and needle. So it would probably be in the $20 range at most. Check with Dennis Kirk, I think they may have some details on valves to get.

The only other thing to make sure of, is sometimes carbs designed to work in pairs will have linkages or adjustments on one carb to control both carbs. In that case one or both carbs can't stand alone without some mods to the choke or throttle.

I love seeing the 2-into-1 mods on the twins, though, so I hope it works out.

loudhvx wrote: I don't think the valve swap is hard or expensive, but I don't know for sure. I've always thought it was just a new fuel valve and needle. So it would probably be in the $20 range at most. Check with Dennis Kirk, I think they may have some details on valves to get.

The only other thing to make sure of, is sometimes carbs designed to work in pairs will have linkages or adjustments on one carb to control both carbs. In that case one or both carbs can't stand alone without some mods to the choke or throttle.

I love seeing the 2-into-1 mods on the twins, though, so I hope it works out.

They did have a 1-2 throttle cable and a 1-2 choke cable when they were on the sled. So I will be purchasing a single pull throttle cable, and a new choke plunger. Other than that they are independent.

It looks like the valves come in a few sizes. So I'll just have to research what size I need.