Engines trouble

[wmortenson]

It's a kohler carb but bored. Yes it's a new engine. 16 hp. I do run a return line. Not sure on the pressure because I don't have the fuel regulator on yet. 18 hp cam and runs on gas.

[wmortenson]

This is also the first open rpm motor I've had.

[dvogtvpe]

you gotta be careful how much fuel psi you run or its going to cause problems. who built the carb?

[J-Mech]

Originally Posted by dvogtvpe

is this a new engine or has it been run with no problems in the past?
whenever I have issues with a motor I start with the basics. check your timing, make sure spark is good, check your valve lash. I would change the float level back to level with the carb tipped upside down unless you run a return line back to the tank. how much fuel PSI are you running? gas? alky? is this a SA cam? .330 lift. is it a flat top design or a typical profile? is this a 16?

Ok, I've been a mechanic for years. Not sure why you would run a return line back to the tank on a motor with a carb. Or where you would put it. I've built diesel engines for pulling tractors, but never a small tractor puller. I'm not following the logic. I'm just curious.

[dvogtvpe]

there's a couple different ways of doing it, the most common is to solder a fitting into the float bowl as hi as you can. then run a line back to the top of the tank, has to be a gradual gravity return or it does no good. helps regulate the fuel along with the float. there are times when the float bowl can get sucked dry under load but spew fuel during idle. adding a return lets you run a bit more fuel psi and prevents the float from sticking . keeps fuel from running out the vents or delivering fuel under pressure up the emulsion tube into the venturi. We started doing this back in the early 80's . currently we don't use it on the 1.200 carbs but on the 56mm S&S super D alky carbs We will add a return line or they tend to run over out the vents. years ago we tried taking the float out and tried to just use the return to regulate the fuel. that never panned out very well. Kohler float bowls are very small. and the amount of fuel through the needle and seat is limited even after you drill them out. its difficult to get 80% nitro through them. in a way its just another tuning tool. you can add a restrictor in the return line if you want. just depends on what you are trying to do.

[J-Mech]

Ok, that makes sense. Will the little motors really "out run" a low pressure auto fuel pump, like what you can install to feed a BIG carb? The pressure is low on them, and I wouldn't think that they would let you run out of fuel.... After all, I've used them to feed a 460 Ford with a 4BBL Holley.

[austin8214]

How low pressure are you talking about? I think most guys running pumps on a cub only run about 4 PSI.

[dvogtvpe]

3 - 5 PSI is pretty common . running alky or nitro its possible. more common years ago. there was no Midwest Super Cub, Lacota, Nichols ect. no internet . Vogel and Brandt were about the only ones who sold stuff . it wasn't cheap. you pretty much had to figure it out yourself or find another hobby. When We first developed the S&S Super D for the MVP engines with Midwest we had allot of trouble with sucking the bowl level down. it would uncover the air bleeds when we put a load on it. Eventually we made an external site tube on the side of the carb to verify the actual level. When you guys purchase a part sometimes you have no idea how much went into making it work. I know the Super D had about 4 good days on the dyno and when we finished , the motor was pretty well wore out. there was over 40 runs on it. now imagine trying to figure this out years ago before dynos , you try allot of stuff. some works, some don't, some mask the real issue. Julians started going back to returns on the bigger V twin engines. a kohler float bowl couldn't fill a shot glass. the other thing I forgot to mention that we used returns for. keeping the fuel pump from bypassing. a typical Holley will start bypassing when a preset PSI is hit. the return keeps that from happening also.