cmb67 purplehead

[Allen Burns]

I have a question on the settup of this motor. I am totally lost. I have run piccos forever and have never had this much problem getting them to run right.

I have this motor in a outrigger with a abc h31 prop. The pipe is at 11 inches from the plug to the weld on the pipe. (cmb pipe). My proplem is that when I set the needle at 2 turns out the motor runs OK for a half lap, then dies. If I richen it up a 1/4 turn it won't come up on the pipe. If I lean it at all it dies as soon as I give it more than half throttle. Have tried different plugs (McCoy 9, K&B,) Fuel is 50% O'donnell.

I just can't figure this one out. Would run my picco still, but I am afraid to hurt it and not be able to get parts.

Any help would be great.

Allen

 

[Propjockey]

Are you using a pressurized fuel tank? If so, are you sure it's getting enough pressure. I know that the carb draws the fuel, but a steady pressure to the tank (read 'check valve') could make your needle friendlier.

 

[Hammerhead]

I agree with Propjockey. Sounds like you have a leaky pressure system, or a dirty needle valve.

Hammer

 

[[email protected]]

Allen,

These motors are starved for fuel. Take out the original brass tubes from your tank. Drill the holes larger and add the next size brass tubing into it. This will help prevent what's happening to you since it sounds like your motor is leaning it self out.

 

[Ozzy]

Allen

Witch CMB 67 engine are you using CAM or Evo and witch pipe are you using ???

 

[PHIL THOMAS]

replace the fuel lines with a larger size the Cmb and Mac engines will starve for fuel on standard size lines. I went thru this with a mono setup for picco but the Mac would do just as you described.. PHIL T

 

[Dougster]

Allen,

Do you run dual or single tanks. If dual, are you using 2 cross over tubes? With the two tanks, I have found this is all you need with the thirstyist CMB 67's or 90's while using standard tubing with pressure. If you use large tubing, as suggested previously, make SURE that all tubing and fitings are the same inside diameter, or else you will find yourself forever lost on your setup. The symtoms (sp) you have expressed, sound like you are still to lean with a lack of enough load. Do you use a flow meter? If so, what does it flow? Anyway, good luck. Doug

 

[TimD]

Allen,

Are you using the "big belly"CMB pipe?

If so try it at 11 3/8 centre of case to weld as well as the fuel line stuff!

Tim.

 

[PHIL THOMAS]

Doug you wrote: make SURE that all tubing and fitings are the same inside diameter, or else you will find yourself forever lost on your setup.

What leads you to this idea? Can you explain why this is so, i hadnt thougt about keeping all lines the same. PHIL

 

[Dougster]

Phil,

Sure. For example, you don't want to mix a med fuel line in with your large lines... it's a volumn thing...don't ask me for a scientific explanation....just don't mix the two. I've seen the result and it just doesn't work. Doug

 

[Mark]

The inside diameter should be kept the same all the way along the lines because if you use a nipple for example that has a slightly smaller inside diameter than the fuel line you might as well run smaller fuel line.

It's all about surface area of a circle which equals

pi X radius squared = 3.142 X radius squared (thats if you don't have the pi button on your calculator.

The flow through the line will only flow as much as the smallest orifice in the series of fittings and hoses.

Hope this helps a little.

 

[Allen Burns]

Thanks for all of the advise. Hope to try running my rigger this weekend (weather permitting) and try all of your ideas.

I have been told that the cmb's like alot of heat. Is this true? I was told to reduce the water flow to the head by pinching off most of the flow.

Allen