roughneck793

I Just bought a K&B 3.5 inboard with a red carb. Engine starts and runs like a raped ape, only it wont shut off when close the carb and evan if i cover it with my finger. What could be the problem. I also have a boat with a solid drive shaft, can i run a flex shaft and strut or will it destroy orignal tube in the hull. ooh yeah, can u cut a flex shaft to size or do you have to order the size you need? Thanks Roughneck793

Dan S

hello,

is this while running on the bench?

have you tried to see if it will shut off when in the water (prop under load)?

also the carb doesn't have a low speed needle, instead it has a small hole on the top of the carb, make sure you cover that hole aswell and make sure that the hole is facing up and not down.

one more thing, when closing the carb ensure the barrel does not rotate to much (it will start opening at the bottom) since you can rotate the barrel all the way on this carb.

Dan.

scardina

My Feedback: (3)

yes, flex shafts can be cut. usually you order them longer than you need, cut them to length, and silver solder the end.

roughneck793

I Just Got the engine in the mail toay, so it was a bench test. I See the hole on the carb and it was on the bottom. I'll Flip the carb and give it another try.

Dan S

another good way to shut it off on the bench is cover the pipe.

Dan.

scardina

My Feedback: (3)

yeah covering the exhaust is how i prefer to shut my truck down. my truck has a plastic pipe though, so it doesnt get too hot. DONT do it with yer finger, the boat pipes seem to get A LOT hotter than car and truck pipes do. du-bro makes something called the "kwik stop" which is essentially a plastic cone, and i think losi sells a tuner screwdriver with a rubber cone on the back.

other than that, you could shut it down by pinching off the fuel line with a hemostat, although i dont care for that method because it runs the engine lean and could do damage, ESPECIALLY out of the water without load on it.

roughneck793

My Main concern is if it does this in the water it could be fatal for the hull

Ron Olson

My Feedback: (1)

OK, the Red carb is really too big for the 3.5 as it was made for the 7.5's. You have to run it slobbering rich at idle as it will clear out under load and at speed.
What you're probably running into is that the engine is lean and that's keeping it running oddly enough. A fatter needle will bring the idle down.
A better carb would be either the Black or Gold.

laoniu

GOOD�

Sean Bowf

I would check the carb and other mating areas, and make sure you have a decent seal. I know nothing about K&B engines, but normally, if an engine keeps running if you put your thumb over the carb, that means it is sucking air from some other place. So if it is NOT the little hole Ron mentioned, then you probably have an air leak some place.

Sean

roughneck793

I tried to read up on this engine and i though that carb was ment for the 7.5 but the guy i bought it from said it was the orignal. Everything on this boat including the hull came off ebay. Guess i'll have to try to find a carb ,Although It ran really really well good on the bench, smooth idle and and fast respose to throttle

roughneck793

Scratch that, no carbs on ebay today

Ron Olson

My Feedback: (1)

I find that hard to believe but hey, it's his story.
The K&B carbs on the 3.5 and 7.5 engines are interchangable as they both have the same bore in the carb flange on the block. The rpoblem is that the bore in the carb is too large to get it to run decently.
That's one old engine that you have there, it's a wonder that it runs at all. I'm estimating it at being late `70's to early `80's. The previous version used an exhaust throttle with the venturi laying on its side up by the flywheel. That's why the housing is so long and the flywheel is made like that.

roughneck793

Wow, didn't think i was that old, starts right up and runs strong on bench, Bought it off ebay along with strut, rudder, flex shaft, radio, battery, charger, prop (although its to large prather 220) fuel tanks, glow starter, 12v starte,r 2 extra glow plugs, eng mount for 91 bucks . Might as well try to get some us out of it. Got the hull for 99 cents from a different seller.

Dan S

when a boat engine is running strong, crisp and fast response on the bench means that its too lean and will more than likely die in the water.

needs to be rich on the bench and most of the time bleeping the throttle just enough to keep it clear.

Dan.

roughneck793

Needle was 4 turns out

moparbarn

i don't think it's that old, ron. appears to have the thick/double bubble combustion chamber head on it. that started with 13 mm crankshafts. older versions would have the thin head, with the single bubble chamber.

ob nut

My Feedback: (1)

The red/purple carbs come with a small air bleed hole that allows better idleing. Cover this hole with a piece of tape. I've used RX tape after cleaning the carb up. Once the barrel closes, motor will shut off shortly afterward.

roughneck793

Thanks, ill give it a try, I/m almost ready to take it for its maden voyage.