Dual Carbs vs. Single Carbs

[Rocky]

What is the process of changing from a single carb setup to a dual carb setup. What I am asking is what type of parts do you need to change it. Is it advisable to go from a single carb setup to a dual carb. I have located a replacement engine that has dual carbs on it, but my old engine has a single setup on it,could you just take the whole assy., away from the rotary valve and replace the dual setup with the stock single. If I wanted to keep the new dual setup that is on the motor what changes would I need.

[Technical Support]

Re: Dual Carbs vs. Single Carbs

You need the whole intake assembly. Rotary valve cover, intake manifold and dual carb rack. It's not worth it, only a few HP.

[Rocky]

Re: Dual Carbs vs. Single Carbs

Can I just take the dual carbs off of the engine and put my single carb setup on the other engine or is their some other difference with the engine.

[frankey01]

Re: Dual Carbs vs. Single Carbs

Rocky you need to tak eoff the rotary valve cove rall the way up to the carbs if you have the stuff already ie the dual setup then it is worth doing but if you are needing to buy any stuff just take your rotary and install it with the single carb setup and intake manifold and such you will be okay.

[Shiprekd]

Re: Dual Carbs vs. Single Carbs

Forgive my ignorance on this but....

Wouldn't going to dual be troublesome from a vaccuum/pulse standpoint anyway? It's obviously a minimal gain in hp, but isn't there a difference in the single & dual carb cranks? (lip/seal) - SBT even has an option you have to check for single or dual carb on their cranks.

[frankey01]

Re: Dual Carbs vs. Single Carbs

the cranks are the same.

[Shiprekd]

Re: Dual Carbs vs. Single Carbs

There must be a difference in the seals then. I've read somewhere there is a difference. check this out:

http://www.sbtontheweb.com/Merchant2...gory_Code=20-1

There's a question you have to select what you have, single or dual carbs.

[Technical Support]

Re: Dual Carbs vs. Single Carbs

LOL no, sorry - that's my mistake...type-o. I'll remove that :) That should have only been on the engine page! The cranks are the same.

[Bill O'Neal2]

Re: Dual Carbs vs. Single Carbs

There is a difference between a single carb engine crankshaft and a dual carb engine crankshaft.
A dual carb crankshaft has a labyrinth sleeve and a single carb crank doesn't.

The labyrinth sleeve works as a case stuffer, lowering the CC's of volume in the rear haft of the engine cases to more equalize the volume to what the front half of the crankcases have in crankcase volume. Volume is empty space not taken up by bearings and rods. The raises the crankcase pressures in the rear half of the motor.

I doubt anyone could really tell the difference in engine performance wether they had one or not.

[Technical Support]

Re: Dual Carbs vs. Single Carbs

We've never heard that, and the microfiche and OEM samples we had don't show it. Regardless, we only have and use one, as do every other manufacturer that we know of.

[Shiprekd]

Re: Dual Carbs vs. Single Carbs

I wish I could find the article that talked about the cranks being different. The original post is what sparked my question. If I can hunt it down, I'll post the url to it.

[Bill O'Neal2]

Re: Dual Carbs vs. Single Carbs

Sea Doo Parts manual #219-800-007 , page A6, #28 Labyrinth sleeve.

SP 5806 -
SPX 5807 +
SPI 5808 -

Which means the SPX dual carb model 5807 is the only crankashft on this parts page that uses a laybrinth sleeve.

The SP and the SPI are both single carb motors.

Look on the back of any dual carb crankshaft and you will see an aluminum labyrinth sleeve taking up the space between the rear bearings.

[Technical Support]

Re: Dual Carbs vs. Single Carbs

You're right Bill, I read the microfiche incorrectly. All three skis use the same picture, but I didn't look at the chart enough to see they had three separate collumns for the different models.

[Shiprekd]

Re: Dual Carbs vs. Single Carbs

<-- wonders how many calls SBT will take for SPX dual carb cranks now.. LOL

[Bill O'Neal2]

Re: Dual Carbs vs. Single Carbs

Like I said, you wouldn't notice the difference.