300/440/550 Motor is not drawing fuel out of the carb

suva

suva

57
Location
Just south of the Citadel, Idaho
My buddy got a '92 440sx with a 550 top end and a bunch of bolt ons for $60 the other day. The carb is pumping fuel (fuel comes out the return when cranking), if you hold your hand over the carb it will suck fuel into the venturi, but won't run if it isn't choked. He had a 44bn on it, and I bolted on one of my 44sbns and it did the same thing. I noticed the intake manifold opening is smaller, probably for a 38mm. Could that cause it to not suck fuel into the motor?
 
Motorheads5

Motorheads5

Livin the generation gap
Location
ketchikan alaska
If it doesn't have enough Venturi vacumm then the carb will want choke to run, Soak the old paper flame arrestor in the bildge and then put it on.

Do you have a fuel pill in the return line.
 
Last edited:
S

Super Dee

Location
Mount Albert, Ontario
ger87410 said:
Well, go do that, then post the results. That could be your problem.

I think a leak in the bottom end will do the same.
Click to expand...

Definitely look for a bottom end leak or some time of a leak in the intake system. Sounds like it's running too lean (need the choke to run). Likely because of an air leak.

Compression has to be pretty low for it not to run. My buddy's 1990 piston port 550 ran reliably for 3 years at 90psi compression per cylinder.
 
motoman96

motoman96

Banned
Location
Lodi Cali
all 440's were piston port motors, i think you have low comp or an air leak as well. 440's also dont require a restrictor since they have no rev-limiter.
 
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