Single Needle Carbs

[J Solinger]

I was chewing on the idea of making a carborator for my .12 size boat engines. My question is: for the purpose of boat racing is a low speed needle worth putting in?

I have an older OPS 45 engine and it doesn't have a low speed needle. It works fine. What marine engines come with single needle carbs now days?

 

[carlnoki]

most all the CMB's and MAC engines have the one (1) needle carbs now a days. the low speed needle just realy isnt needed much anymore.

CARL

 

[aamick1971]

k&b also has a single needle ,and they work fine like that but that all i run is k&b's

 

[Ron Olson]

Get hold of Kevin (isitbrokeyet?) Bulifant, he's cut down several Nova Rossi .21 carbs for me. They've added about a good 5 MPH to my boats! The stock carbs are restricted to 5.5mm by ROAR, IFMAR, etc., we have no restrictions.

 

[J Solinger]

The stock carb bore on my Pixy is 6.35mm. I have an OS carb here from a .21 engine with a bore of 9mm. Thats a realy big step. Will that work ok? I'm a little conserned about the air speed in the venturie being to slow.

 

[EatMyShortsRacing]

I would say 9mm is too big for a .12

9mm diameter = 63.25 mm2

6.35mm diameter = 31.67 mm2

so the 6.35 is basically half the area of the 9mm carb.... stands to reason the 6.35 should be suited to the .12 as the 9mm is suited to the .21

EMS Racing I was a constipated mathematician but I worked it out with a pencil...

 

[gil sonsino]

On my truck equipped with an Irvine 15 I 'm using a 4e os carb(9mm) with a reduction to 8mm and it runs great. I believe this bore can work in a .12 boat once it works at full throthle.

Gill

 

[Eric Perez]

On my truck equipped with an Irvine 15 I 'm using a 4e os carb(9mm) with a reduction  to 8mm and it runs great. I believe this bore can  work in a .12 boat once it works at full throthle.Gill

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I've had wierd leaning out problems on .12 with big mouth carbs. I ended inserting a piece of brass tubing on the pipe to help increase back-pressure and fuel-tank pressure, this seems to help the engine get fuel when at WOT. Too many factors to attribute to an engine that leans out too much at WOT, but that's my story and I'm sticking with it.

 

[anthony_marquart]

On my Fantom racing equiped FF.12, if the low end needle isn't in far enough the engine floods every time I bring it in. Then I have to take out the plug and blow it out to start it again. ,... other than that,... never used one.

 

[Ron Olson]

Those Fantom carbs can be a pain in the rear. A lot of them got out of the factory with bent low-speed needles. I'm selling my Fantom .12's so I have a carb that Kevin did for me. It did make a big difference on that motor, no more of the problems that goes with the stock carb.

 

[anthony_marquart]

What are you going to do with that carb Ron? Use it in a different engine? (or sell it to me cheap?)

What engine are you going to go with? I'm thining Pixy or 5 port Sirio for my sport 12 hydro.

Those Fantom carbs can be a pain in the rear. A lot of them got out of the factory with bent low-speed needles. I'm selling my Fantom .12's so I have a carb that Kevin did for me. It did make a big difference on that motor, no more of the problems that goes with the stock carb.

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[Saugling]

Since last year I use 6.5mm carbs on my .12 / .15 engines...noticeable more power than the 5.5mm stock carb B)