1920 Harley Model F

[TechNoir]

Looking at the cam strip and wheel closer I was sure that they could be contributing to the issues. The wheel is not exactly round and so resembled a very mild cam as it turned and the cam strip did not have uniform wear on it either. The movement of the needle from fully closed to fully open is very small and so even small variances in the cam and wheel seemed to me that they could affect the rocker adversely and in turn the needle.

So I ordered some 0.025" stainless steel shim stock to make the cam strip and milled it to the correct width. (the existing cam strip turned out to be copper but stainless is a good replacement because it wont corrode)

Then I needed to remove the old cam strip. Cotton has previously stated that this is difficult so I approached it carefully. I held the cam assembly in a small Engineers clamp which in turn I held in the vice. I sharpened a very small cold chisel, the blade is only about 3/16" wide, and I carefully used it to loosen the peened over metal that holds the cam in position. Without much trouble at all the cam strip freed up and I was able to slide it out.


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John

[TechNoir]

Hi folks and Happy Christmas to all.

For various reasons too long to explain here I have only recently got back to sorting this bike out, suffice it to say that I have been preoccupied with other issues.

Since the last installement I retraced my steps with regard to the air side of things to make sure all was well. The carb had previously been bored out by someone else and I carefully measured it and found it to be approx 0.0005" out of round. Also, following some comments about air leaks elsewhere, I had some small doubts about my new shaft with the seperate washer.

So I made another new shaft, this time as one piece. I have also honed the bore to make it round, it is now good to within 0.0001" and I then made another new disc and then fitted everything. Again.

With the carb refitted this made no difference whatsoever.

However at this point I was now certain that they are not the problem so at least that is progress in that they are now ruled out.

My attention then turned to the cam mechanism.

For those reading this who are not familiar with these Schebler carbs here are some pictures showing the cam mechanism.


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Previously I was commencing with the low speed cam adjustment screw in roughly the middle of the adjustment and making quarter turn adjustments. However even with the cam adjustment screw wound out as far as it would go, the carb was only slightly less bad. I haven't said "better" because it was still bad, just less bad.


John

[T. Cotten]

Thanks Cotton.

You can stop thanking me for leading you in circles now, John!

...Cotten
PS: I didn't do it on purpose.

[TechNoir]

Thanks Cotton.

[T. Cotten]

... By the time it gets to me it will be about $75 with shipping and taxes...

*GASP!*

Let's make sure it will fit with an HX first!

.....Cotten
PS: Sure enough, as I now see on the bench, the bowl of an HX is closer to the manifold flanges.

[Steve Swan]

John, i just sent you email.

[TechNoir]

Thanks Steve for that clarification on parts, my book only goes up to '21.

Checking CD's website they list one for $22. By the time it gets to me it will be about $75 with shipping and taxes. I will speak to them tomorrow.

John

[Steve Swan]

oops.... thanks for catching that, Cotten!

[T. Cotten]

My notes now show it is a DLX support, Folks,...

But it still aught'a fit!

(Or something like it.)

...Cotten
PS: Or get a bowlnut with a stud, and "farmer" a bracket down to the cases, somehow.

[Steve Swan]

as always, following this conversation to learn what i can, otherwise i'll stay out. looking at my 22-26 factory parts book on the carb support, the book calls for pm 1110-25 "manifold support" to fit "1925-26 twins (fits earlier models)"...... (i would suggest perhaps the pre-25 models did not have this support, but by 1925 the factory realized it was not a good idea to have the carb unsupported, hence the factory's mention, "fits earlier models").

Comp.D sells pn 1110-25 - https://www.competitiondist.com/prod...-61-74-1110-25

[TechNoir]

Thanks for the picture, interesting. There is nothing like that in the parts book so I assume its an aftermarket part.

First thing tomorrow I will have a quick game of darts.

John

[T. Cotten]

I don't know if this one is "correct", John,...

But something like it would seem prudent.

(Sorry I forgot who to credit, but Tommo gets credit for the tensioning routine.)

If you take the airhorn and act like you are throwing it hard like a dart, the valve itself should make a snapping noise.

....Cotten

[TechNoir]

Cotton, the roller does roll so I wont worry about it.

PS: Two questions: How did you tension your airvalve? (please link me back to it if already discussed...)

Previously I took some advice from this guy

Tensioning the airvalve spring corrects for variances. Following Tommo's advice, I "weigh" the tension as shown in the attachment.
Most original springs read either an even 3 oz or 5 oz, with the adjusting screw in the middle of its travel.
This assumes, of course, that the mass of the carrier assembly resembles the original.

...Cotten

That was back in post #115 of this saga so over 200 posts ago.

However, I have been playing around with it to see if the bike starts any better with it tensioned more or less than the mid point. I forget where it is at the moment. Could that have a significant impact on tickover?

And have you a carburetor support? It might not be the immediate problem, but...

In a word.... No.

It might be a part that I am missing. I will look through the parts book.


John


P.S. I looked in the parts list and couldn't find a carburetor support. Was is a later part or possible a mod?

[T. Cotten]

John!

Yours has a typical roller track with nice and sharp knurl marks; The knurl on your lift wheel has either eroded, or it was a different wheel that made the track.
If the wheel turns through the entire arc of the cam, I wouldn't worry about it.

If the needle closes enough to pass the 'suck test', burnishing can only cause a problem.
(Looking at diagrams again, the nozzle is not in line with the needle, which travels in an arc to boot. so wear would be a scallop into the seat. It would have to pass air before it would be worth messing with.)

...Cotten
PS: Two questions: How did you tension your airvalve? (please link me back to it if already discussed...)

And have you a carburetor support? It might not be the immediate problem, but...

[TechNoir]

Cotton, once again thanks for all of your input on this issue.

I checked the float height which was correct. Now that you have confirmed that your floats have been compensated for the density difference between the materials I can rule that out.

I used a fine stone to lightly dress the tip of the needle. I didn't take much off at all, just really polished it.

What I haven't done yet is burnish the needle into the spray nozzle. I feel that this might be the next thing to do?

I reassembled the carb and then checked the closed position by sucking on the stem, then I replaced it.

The bike is no better. I did struggle to start it at first. The best position at the moment seems to be about 2 1/2 turns out. I tried various positions, varying each time by 1/4 turn. Below 1 1/2 turns it struggles to start, ditto 5 turns out.

Then I tried adjusting the cam but no matter where I had it the bike displayed the same behavior. It runs way too fast over 25% throttle and stalls below that. I had had a belly full of it today so tomorrow I will take it off the bike and note the cam positions as per Cottons advice above.

I didn't take any pictures of the cam today but found one that I had taken before I replaced the disc.





You can see a rough strip where the roller has been running (although it doesn't seem that bad with the naked eye) the roller is quite rough too.

Would you recommend replacing the roller? Is it brass o steel? Looking at the pitting I would guess steel but I can remove a bit of plating to see whats underneath.

Looking at the area to the left of the roller it seems the cam strip is be held by the edge of the track that has been peened over. I guess that to replace it you have to grind the peen off and then peen over in a different place when the new one is in place.

However, I will try polishing it first.


Today I left the right hand tank off. This gives me access to the carb a bit better and also I can actually see the throttle position.





John