'68 9.5hp slow speed problem

[fcryon]

I can't figure this one out. My motor has good compression, I've replaced points and condensers, the coils are strong, and I just disassembled the carburator, soaked it in carb cleaner, and rebuilt it. She fired up on the second pull. The strange thing is that it runs great WOT but sputters and stalls at slow speed/idle, unless I pull the choke out. With the choke engaged at low speed/idle it is smooth as silk. I've been all up and down the low speed rich/lean adjustments at 1/8 turn increments, and get the same thing. Anyone have any ideas as to what I'm missing?<br /><br />Thanks

 

[Paul Moir]

Re: '68 9.5hp slow speed problem

fcryon - If adjusting the rich/lean knob doesn't do anything, the only reason can be that the low speed circuit is somehow clogged.<br />When you disassembled the carb for cleaning, did you remove the core plug at the end of the low speed valve, at a right angle to it? That should give you a direct look at the idle oriface.

 

[R.Johnson]

Re: '68 9.5hp slow speed problem

Did you set the throttle pick-up point at the magneto plate? Sounds like throttle could be opening way to early.

 

[fcryon]

Re: '68 9.5hp slow speed problem

Yes, I did Paul. Everything seemed to be clean before I put the news plugs in. One thing that I haven't done yet is to replace the gas lines. I was wondering last night if an air leak in the line might not cause this problem.

 

[fcryon]

Re: '68 9.5hp slow speed problem

R.Johnson - I played around with that also, without any significant change. When I first started the motor the butterfly valve was completely closed at the low end so I tried to adjust it open alittle with the same results. I'm baffled.

 

[Paul Moir]

Re: '68 9.5hp slow speed problem

If it were an air leak in the fuel line, air would cease to leak into the line when you pumped the primer bulb due to the positive pressure you would put on the system. Worth giving it a try to rule that out.<br />To adjust the throttle opening properly, the carburetor's butterfly should just begin to open when the carb's pickup centers on the mark(s) on the cam attached to the magneto plate.<br />Exaggerate your carb butterfly's movement somehow.

 

[fcryon]

Re: '68 9.5hp slow speed problem

R.Johnson - I played around with that also, without any significant change. When I first started the motor the butterfly valve was completely closed at the low end so I tried to adjust it open alittle with the same results. I'm baffled.

 

[fcryon]

Re: '68 9.5hp slow speed problem

Paul, I think that I'll give that a try before tearing the carb apart again. Most of the gas line is before the fuel pump so maybe I'm getting a combination of fuel and air. Just thinking out loud.

 

[Paul Moir]

Re: '68 9.5hp slow speed problem

Pumping the primer bulb will also pressurize the pump and carb line (further), so it should rule out air leaks there too.

 

[fcryon]

Re: '68 9.5hp slow speed problem

I guess I'll start by replacing the fuel lines anyway. Who knows how old they are but I'm sure they're overdue. I assume that it's a good idea to put an inline fuel filter in also, as you can't see the carb bowl. Thanks for the feedback.