1920 Harley Model F

[T. Cotten]

Let's keep it simple, John!

You want the needle to close upon the seat before the knob bottoms out.
And you want the stop on the cam to hit the raised block on the body when the disc is full open.
(With my spliced replacement shaft method, I can often use the cam's original pinning holes.)

Worn cam strips can be filed and stoned; Replacement is *tedious*.

Please note the modern float material is less dense (more buoyant) than cork, so it is proportionately smaller, to achieve the same fuel level.

Beware also, Folks, the exclusive material is now unobtainium. The manufacturer does not reply.
(So I can no longer offer replacements for my early productions that might swell like a ducky, and I am guarding my remaining inventory jealously.)

....Cotten

[TechNoir]

I'd be much more concerned with the cam than the needle angle, John.

...Cotten

Hi Cotton, thanks for the steer. I did spend some time pondering this issue since my last post (and before reading your latest post). It seems to me that I need to get the disc and cam to be coordinated so that air and fuel is increased in unison. No surprises there.

But how much fuel? Obviously the ideal stoichiometric Air Fuel Ratio is 14.7:1 for non ethanol fuel and a bit less, say 14.0:1, for E10 and 13.8:1 for E15, I am not about to hire a dyno or rig up an AFR meter in the header pipe but the size of the "spray nozzle" plays an important part. If the nozzle is not easily replaceable (which seems to be the case) then the only variables are the needle position in relation to throttle disc and also the taper on the point. If the needle is clear of the nozzle at less than full disc opening then whilst more fuel will flow at wider throttle openings due to the increased vacuum will it be enough at full throttle? Will it be too much? I obviously don't know so my musings regarding needle characteristics were in relation to spray nozzle size and its relationship (as the needle moves) to throttle position.

At the moment I have one needle which isnt getting modified other than a light stoning so it is a moot point. I will check everything and reassemble the carb and see where it takes me.

John

PS, Another observation, the original cork float has a greater density than the excellent Cotton floats. Therefore shouldn't the setting be fuel level height rather than float height because the float height relative to fuel height is different between cork and "Cotton" floats?

[T. Cotten]

I'd be much more concerned with the cam than the needle angle, John.

...Cotten

[TechNoir]

Wow, John!

You've got a dyno?

....Cotten

I wish I did have one.

However that doesn't mean that I cant screw around to see if anything makes a noticeable difference.

John

[T. Cotten]

...I might make some needles with varying point angles to see what varying the angle does...

Wow, John!

You've got a dyno?

....Cotten

[TechNoir]

Thanks Cotton. I wont mess too much with the original parts. I might make some needles with varying point angles to see what varying the angle does.

John

[T. Cotten]

Wish I had answers, John!

But I never lap brass or bronze any more. Burnish maybe..
(Please note the diagrams do not show the needle perfectly in line with the nozzle; It doesn't operate shut anyway.)

....Cotten
PS: The hole drilled in the bottom of the flusher is unique;
And the bowlstem threads extend more than the usual 3/4" below the flange for the cork?

[TechNoir]

Hello Cotton, thanks for the reply.

I did wonder if the factory had different needles and used the grooves to identify them?

Do you happen to know if the angle of the point makes a difference? Is 30 (ish) degrees OK? Would a longer point give a finer flow control?

I had seen the advice about the spray nozzle (I had forgotten they called it that) but wondered if guidance had changed since 1928. If you believe that I shouldn't touch it then I will leave it alone. Do you know if the size of the jet makes a difference?

I assume that if when I suck on the needle it doesn't seal fully and if stoning doesn't cure it then would you lap the needle to the jet?

John

P.S. Thinking about the length of the point, should it be the same length as the length of movement of the needle when the throttle is opened?

[T. Cotten]

The two grooves mystify me too, John!

(I've encountered several.)

I'd just stone the needle point in the lathe. (I came up with 30° , but it probably doesn't matter, particularly if your nozzle seat has "mated" to it.)
And don't blow through it when inspecting for the needle closure; Suck.

Page 40 of the Service Station manual says its 'not adviseable' to mess with the soldered 'spray nozzle', and those that crossed my benches damaged from removal were Hell.

Are you missing an airvalve spring?
(Fickauprototypes@cs.com makes *some* sizes, and the flusher spring, too.)

....Cotten

[TechNoir]

With the Mikuni carb the bike ran OK. If it had been the Schebler I would have said great but I am pretty sure the 30mm Mikuni is a bit big for the bike and with a smaller one it would run better. However It enabled me to get the timing right. The mid point between the two advanced and retarded positions where it started to noticeably run badly was 0.370" BTDC which is very close to 3/8" so that's where it is set. I was expecting it to be a bit more advanced than this so I checked it twice (because I am a glutton for punishment).

So with the timing established my attention now turns back to the Schebler.




I have stripped it and here are my observations.:

In 1988 when the previous re-builder "fixed" the bike he wrote this in his build report:

"After cleaning out, found to be worn on butterfly spindle, also distorted & worn butterfly valve. Replacement spindle fabricated & carb body re-bored to suit, replacement butterfly made up. Spindle is now modified to take a screw retained butterfly (rather than old soldered in type). New air balance valve & spindle assembly made up & seating machined to suit. Replacement high speed air flap made up also spindle for the same. All other parts cleaned up & re-shaped or replaced as required. Main body components blasted to remove verdigris prior to plating with other parts."

The carb bore currently.measures 1 1/8" which would suggest that the guy bored it out by 1/8".

The last sentence says that the carb was "blasted" and then plated.

The inside of the bore is plated and is not perfectly round. Its not far off but would benefit from honing. I did manage to get the throttle disc to be a pretty good fit. Its not perfect but I don't think it can be contributing much, if anything, to the behavior displayed by the carb. The disc and shaft move smoothly with no binding and no play. From what I can tell the "air" side of the equation is OK.

So what about fuel?

The rocker arm moves fine on the cam.

I set the float height to 19/32" which is what seems to be the setting for 1" model "H" carbs. This was using one of Cottons floats and not the cork one.

I assume the needle is the one that was in the carb the last time it was on the road. I have taken measurements and apart from the length, which is obviously OK because it cuts off air when you blow up the hole from the other end, the other feature that seems to control when and how much fuel is sucked up is the point angle.




The included angle of the point is about 32 degrees from my basic measurements.




Also, what are the two grooves further up the needle for?


The last feature which influences fuel is of course the jet. The cross sectional drawings that I have seen seem to show this as a seperate item.





The entire assembly on my bike has been plated so its hard to see how its held. I assume its soldered or brazed, I will file a bit of plating off to check.








Its obviously very hard to check its condition whilst in the carb.

I would assume that they are not available new?

My thoughts are these:

Needle. Would a longer point help? I wouldn't touch the "original" one but it would be relatively simple to make new ones with varying lengths and/or points.

Jet. Is it replaceable? Is it worth doing? Can the existing one be refurbed? Can I make a new one? The first measurement before doing anything else would be to measure the aperture, can anyone provide any guidance on the jet size?

All hecklers welcome.


John

[TechNoir]

So the workshop is tidy (ish).

The twistgrip and broom handle was really just a proof of concept. I already had the cable made for the twistgrip and Mkuni so it was a quick job to use the already made up cable to see if the Mikuni did the job.

It did so after I had tidied up I had a rummage in my box of cables and levers and dug out an alternative throttle and made up a new cable. This is what it ended up as. This proved quite useful as i could hold the throttle at whatever revs I wanted without having to leave my hand on it.





Then, once the motor was warm, I was able to find the best timing position which, as I had guessed is a bit less advanced than I currently have maximum advanced set at.

I marked it with some tape. I tried a fine sharpie marker but a pencil line proved best.





At this point (earlier today) Mrs Technoir reminded me that I had some other (non bike related) jobs to attend to so I left things to cool down and tomorrow after work I will measure the optimum timing and reset it. Again.

Then it will be back to the Schebler.


John

[T. Cotten]

Cotton, how did you know what the inside of my workshop looks like?

I don't, John,...

The pic captured us outside.

Stone tools are timeless...

....Cotten

[TechNoir]

Cotton, how did you know what the inside of my workshop looks like?

[T. Cotten]

You are of course correct, fresh copper should be soft although I am not certain how much work hardening will be introduced by the machining process.

John

Spare the hammer, John!

....Cotten

[TechNoir]

Shouldn't the fresh copper already be quite soft, John?

Best not to interject any more variables than necessary..

(PEEK would too, of course!)

....Cotten

You are of course correct, fresh copper should be soft although I am not certain how much work hardening will be introduced by the machining process.

John