Tillotson Carb Question

[kevinrude]

I am working on a 1947 7.5HP Scott-Atwater-made Firestone and have narrowed down my problems to the carb. Each cylinder has 80 psi of compression. The motor fires when I spray starting fluid into the carb which, I think, means the reed plate is OK and the motor is timed properly. The carb bowl fills fine. I have cleaned the carb and all orifices.

I think the problem is with parts 465-611 (Idle tube) and 462-612 (idle tube gasket) in the diagram below. The tube has a hole in the bottom and the fuel travels up it to two lateral holes just beneath the screw threading. There are holes on either side of the channel into which the idle tube screws that, I believe, are supposed to line up with the lateral holes in the tube. I assume that one of the gasket’s jobs is to stop the tube from being screwed down below the level of the holes in the carb such that the holes in the channel line up with the holes in the tube. The original gasket was disintegrated and I have been trying to make a new one.

I tried using both of the gasket materials that I have (cork and blue). The cork one fell apart and plugged up the holes in the carb channel while the blue material was forced down into the carb body. So, all of this is a long way of asking: what can I use to make the idle tube gasket? I have scored the top of the screw head so that I can line up the holes in the idle tube with the holes in the sides of the channel. Any other hints on how to line these up?

As always, thanks!

[dave-bernard]

THAT "GASKET " is copper washer. on all the tillitson carbs I have worked on and they usually don’t fall out.

[RICHARD A. WHITE]

Is this starting fluid you use have some sort of lubrication?????

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[david-bartlett]

If there is a channel where the fuel can travel around the jet, then alignment should not be an issue.

Some of the Wallbro carbs have jets that are drilled through in place and need to be left alone because you can never get them back in correctly.

Are the holes you are referring to drilled through the threads?

[frankr]

I’ve repaired lots of those carburetors and I would be extremely surprised to now learn that the holes have to line up. I’ve probably seen some with the gasket missing also. About the worst thing that would happen if that tube wasn’t doing its job is it might not idle properly. It certainly wouldn’t keep it from starting and running at higher than idle speed. Are you aware that the slow speed needle works backwards? But that also would only affect slow idle.

[kevinrude]

quote betty ann bernardd:

THAT “GASKET ” is copper washer. on all the tillitson carbs I have worked on and they usually don’t fall out.

This is interesting. I DO have a copper washer. However, I also have this sentence in my Scott-Atwater manual pertaining to AJ carbs: ‘In removing and replacing the idle tube, be careful not to damage the small fiber gasket.’ Thanks.

[kevinrude]

quote FrankR:

I’ve repaired lots of those carburetors and I would be extremely surprised to now learn that the holes have to line up.

That’s good to know. I guess I will install with just the copper washer and see what happens. Thanks.

[kevinrude]

quote david bartlett:

If there is a channel where the fuel can travel around the jet, then alignment should not be an issue.

Some of the Wallbro carbs have jets that are drilled through in place and need to be left alone because you can never get them back in correctly.

Are the holes you are referring to drilled through the threads?

Yep, the holes are in the threads. There is a channel for the fuel to travel around for about 1/4 of the circumference. But, like Frank says, alignment shouldn’t be an issue. Thanks.

[kevinrude]

quote kevinrude:

quote betty ann bernardd:

THAT “GASKET ” is copper washer. on all the tillitson carbs I have worked on and they usually don’t fall out.

This is interesting. I DO have a copper washer. However, I also have this sentence in my Scott-Atwater manual pertaining to AJ carbs: ‘In removing and replacing the idle tube, be careful not to damage the small fiber gasket.’ Thanks.

All right, well, apparently I do NOT have a copper washer. The one that was sitting on my parts table does not fit so I guess it came from some other project. Is there any chance I can just screw in the idle tube without any kind of gasket?

[kevinrude]

OK, I managed to pick up a parts motor locally on the cheap. It had the above mentioned copper washer. I installed the idle tube with the copper washer, motor doesn’t start. I swapped out the carbs, still doesn’t start. I swapped out the reed plate and valves, still doesn’t start.

So, I am out of ideas at this point. Again, motor is timed correctly, has plenty of spark (as evidenced by the motor firing right up using starter fluid) and compression. The darn gas just isn’t getting from the carb to the engine!! I know this because when I shut off the fuel line, the needle protruding through the top of the carb does not go down (which would indicate gas leaving the carb).

What am I missing? Any other ideas?

As always, thanks!

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