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Pinto compression test issues


Davo

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2 minutes ago, IanS said:

The primary progression channel should (35) have a petrol/air mixture in itwhen the throttle butterfly is nearly closed.

This is sucked through by the vaccume under the butterfly.

The diagram shows this as white air bubbles in black petrol.

So yes check the calibrated bush.

So in my nativity, I always assumed that the idle mixture control (34) adjusted the fuel that got mixed with the air... but according to that diagram, it controls how much pre mixed enters the manifold- correct? My gut feeling is, there is no fuel mixture going down that channel. 

 

In fairness, I haven't removed that bush yet to check it. Is  there a special way to remove it?

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As you say It sounds like you are not getting fuel in the idle circuit. I suggest you remove the idle jet and make sure it is clear, they are quite small. If you screw the idle needle right in and can squirt carb cleaner with a tube or air line into where the idle jet seats, it will blow any muck back into the float chamber. If I remember correctly those bushes a quite small and pressed in, you would wreck them trying to remove them. I suspect it’s just dirt somewhere, have you got a fuel filter in the system?

 

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11 hours ago, Peter Bell said:

As you say It sounds like you are not getting fuel in the idle circuit. I suggest you remove the idle jet and make sure it is clear, they are quite small. If you screw the idle needle right in and can squirt carb cleaner with a tube or air line into where the idle jet seats, it will blow any muck back into the float chamber. If I remember correctly those bushes a quite small and pressed in, you would wreck them trying to remove them. I suspect it’s just dirt somewhere, have you got a fuel filter in the system?

 

Thanks Peter. A change of sparks today made a massive difference although I suspect they will get fouled pretty quickly again. 
 

it was running much smoother and I’d almost be happy with it, except I can’t wind that idle screw far enough back as described without the engine dying. I’m convinced it’s running on  those progression holes rather than the idle. 
 

I guess I might get to the bottom of this if I got a meter to understand if it dies lean or rich. Any expensive dial though! 

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  • 3 weeks later...

I would go back to basics and take out the jets and clean them with carb cleaner and jet brushes, I’ve just done this with some bike carbs and you’ll be surprised at the amount of fine dirt that comes out.

I have a very small pot with a lid and spray enough carb cleaner in it so I can immerse a jet, soak that for a little while then take it out and use jet cleaner brushes (some are just twisted wire) and push through every hole, I also have some canned air but a compressor would be better just don’t blow the jet out of your hand.

check all the cast in air and fuel runs in the carb body.

once you’ve done this you should at least have a base to start with.

have you checked air leaks around the throttle plate shaft?

can you help idle by using the throttle stop?

some people drill the throttle plate to allow a little more idle air, I’m not proposing you do this just pointing out that there are ways to make carbs work

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