Won't idle.

[ranger 1,750]

10 hours ago, Tuneup said:

Sounds to me like your weak fuel pump suggestion has merit. try a gravity feed to see if the problem goes away (after you check the float height).

I would certainly try a gravity feed, although if the pump delivery was weak at low rpm, you would expect, when returned to idle, the engine would run for a while  until the float bowl emptied, and not cut out straight away? Does “Black Horse” have a primer bulb fitted? If so does the engine keep running if you “pump” it? Perhaps the pump has a build up of “Gunge”, like Mark, (meadowfield), found in his carburettor? Any build up would, I imagine, reduce the volume of the pumping chamber, and therefore the amount of fuel delivered, especially at lower rpm’s.

Doug.

 

Edited May 11, 2021 by ranger

[ohiofarmer 3,276]

getting out the popcorn on this detective story

[Stormin 9,981]

  It's not the Black Horse Doug. That's fit and healthy. It's the C-125.

  I can get it to run continually 1575 - 1600rpm. Below that it keeps running before dying down.  Now it does have a primer bulb and yes, if I pump it the engine will pick up again. I did that yesterday. So it is a fuel delivery problem.

  This morning I fitted another carb, tried two spare pumps and changed the inline filter it has on. No change. Threw the towel in and cleared off for the afternoon.

  Tomorrow, if my presence is not required elsewhere, I'll check the fuel tap filter and blow through the fuel line. I'd replace the pipe but I've non that size on the shelf. I'll get some when I can.

  I've a couple of spare fuel tanks so I might try gravity feed as well.

 

Edited May 11, 2021 by Stormin

[squonk 41,155]

nORMSTER, I ASSume you have also tinkered with the idle mixture screw as well as the speed setting? Every once in a while my C-160 idle will drop and stall out. A couple of tweaks on both screws sem to get it right again

[Stormin 9,981]

I have indeed mIKe.  Twiddled and twiddled and twiddled. Now at the best I can get.

[Stormin 9,981]

  Today I drained the fuel tank and removed the tap. There's no filter on the tap and the tank was spotless inside. Blew through the fuel lines and nothing but fuel came out.

  I also tried gravity feed. Made not one iota of difference.

  So the only thing I can think of now, as the exhaust valve clearance was rather close, the valve seat may be a little burnt. Maybe come winter I'll give it a valve job. Apart from refusing to idle properly it's doing it's job.

  I've adjusted the main jet screw and that part I'm happy with. Never had this much hassle when I was tuning Triumph twin motorcycle engines for racing.

[Gregor 4,846]

Leak down tester. Anywhere from $30 on up.

[Stormin 9,981]

Thanks for the suggestion, but for one use onIy I can't justify the cost.

[squonk 41,155]

nORM, anyway of putting a video here on what's happenen? 

[Stormin 9,981]

I suppose so, but not soon. Off over to Scotland tomorrow and possibly at the farm Friday. I see at the weekend.