schebler model H tips and advice!

[Matthew N. Olse]

TOMMO and anybody else,

I need input, advice and help on rebuilding a model H carb for my cannonball sears. I am really new at this, and need all of the help that I can get. What should I look out for ? ARe these carbs impossible to tune? Would it be advantageous to put one of the ported racing sleeves on the end of the carb to gain extra adjustment? Thanks for your input and advice!
best,
Matt Olsen

[Chris Haynes]

Matt,
Here is a little information. These are pdf files so you can read the whole booklet. Click on the booklet you want to see then Click on "Download document in original format" under the picture of the cover.
http://vintageamericanmotorcycles.co...r+information/

[Matthew N. Olse]

Thanks for the tip chris, that is good info!
I talked to my foundry today and they are shipping me an order early next week. Your new shift gate should be in there, I will call you when it shows up.
best,
Matt Olsen

[Tom Lovejoy]

Hey Matt, you might also try Johnny Eagles. He could walk you right through it, alot of guys told me not to run my model H. The newer carbs are better for riding, thats what I was told. But mine seems to be doing the job pretty good. Alittle more of the antique flavor I think, for my 25 Scout - of course, your Sear's does not need that. Cant wait to see more progress on your Sear's.

[T. Cotten]

Matt!

I haven't figured out the "ported racing sleeves" either.

Or much else about the H Model, as I only see them on the bench.
The airvalve must be like a constantly variable choke, kind of like using your hand over a carb to keep a motor running.

I guess that's critical when there's no venturi!

So for top speed, the later big H's had a thumbtab straight to "atmosphere", by-passing the airvalve completely.

How then, could hanging something off the airhorn add any advantage?

Did these machines have a lot of reversion out the carb?

....Cotten

[Tommo]

Matt
Hi there, I'm not sure how I can briefly put down 50 years of playing with these carbs but I'll try and get the major things down here and will have to hope it makes sense.

1, The throttle shaft and butterfly must be in good order with all signs of any butterfly chatter marks removed from the carb body. I hone the venturi, removing as little parent metal as possible, to remove the chatter marks and then make a butterfly to suit whatever the venturi size ends up at. Remember that there are 3 different angles on the butterfly, 12, 13 and 14 degree, so make sure you get the right one for the carb you're working on.
I convert the butterfly attachment to the throttle shaft to screws instead of soldering and this makes it a lot easier to centralise the butterfly in the venturi when you're finished.

2, The Air Horn. Get rid of the leather washer and make up one using a modern plastic, Cotton will say use PEEK, and recut the seat in the air horn and then turn a seat on your new plastic one to suit the one in the air horn.
Why replace the leather one? In the old days the bikes were used daily and the leather stayed damp and pliable but when we use these old girls today they may sit weeks or months between outings and the leather drys up and distorts and won't seat properly which leads to erratic idling and part of the Model H's bad reputation.
The carrier that the air valve washer mounts on and the shaft that it moves along wear very quickly so new ones of those will have to be made and it is very important that the carrier moves freely on the shaft but that it does not have too much clearance as this will only lead to an excessive air leak that you are trying to eliminate.
The knob with the pin sticking out of it that you use to tension the air valve spring for starting is screwed onto the shaft then has the end peened over. To remove the knob hold the shaft in a lathe chuck and put a piece of flat steel between the pin and the shaft and gently screw the knob further onto the shaft. Don't use too much force as you may loosen the pin but I generally have no trouble and then just turn the peened end off the shaft and screw the knob off. You now have an original knob you can use on your new shaft.

3, Cam follower and Cam track assembly. It is most important that the cam follower roller is nice and free and follows the cam track without any binding what-so-ever. If the roller has siezed and worn a flat on itself it will have to be replaced. If it has worn a groove in the cam track you generally can get over this problem by making the new roller as wide as possible as this allows the top and bottom edges of the roller to bridge the track worn by the seized roller. Just make sure the roller stays on the cam track and doesn't foul anything else.

4, Float bowl, If you recut the fuel needle valve seat do it very gently because if you drop the seat too far you may end up having to make a special needle so you can get your float at the right setting. I custom fit all the new needles we make by varying the distance between the ball and the needle seat.

In general if the carb is set up right you will not need to worry about opening the extra air trapdoor unless you are hard out with nothing left and then you get that extra surge of power by opening the trapdoor and in effect giving the machine the equilivant of a dragsters high speed lean-out.
Altitude change will probably more concern but I imagine that if you set the bike up in South Dakota you will only have to lean it out a bit for sea level running and you will know what your higher altitude settings are.

That's probably all as clear as mud but if I need to expand on any of it just ask and I'll do my best.

I'd love to be doing this run with you guys but health prevents it, I just wish everyone a successfull and safe journey, enjoy the experience and if I can be of any further help just ask.

By the way Matt I do have some Model H carbs that are overhauled and ready to go if that is any help

[Tommo]

I should have added that there is quite a few jigs and special tooling needed to accurately do a lot of the operations described above and whether or not it is worthwhile to make jigs and tooling to do a one-off job is up to you.
Depending on the condition of the carb being overhauled we spend somewhere between 40 -60 hours on each overhaul.

[Matthew N. Olse]

Peter/ Tomo,
Thanks for the very in depth response. It helped me out and probably helped some other people out as well. I sent you a pm regarding the spare carb you mentioned in your previous post. Please check it out and have a great day.
best,
Matt Olsen

[T. Cotten]

Tommo and All!

PEEK is my current choice for airvalve material only because I have a surplus;
Teflon would be a great deal softer, but I know so little about the operation of the airvalve that I cannot guess if that is an advantage, or not.

Matt's early 1" H has no airvalve seal, nor even a bevel for a seat on the airhorn casting.
Instead, the brass disc that would later support a leather is the seal, seating flush upon the airhorn. There is no room upon the bushing to add a leather, yet the disc had loosened.

Does the airvalve "chatter" during operation?
If so, how violently does the valve slam against the seat?
(That's the reversion question again.... as there will be only 3.5oz of tension from the spring, as Tommo has prescribed.)

Thanks again,

...Cotten

[Tommo]

Cotton,
That's a very early air horn, looks like it might even be early Henderson, and in such a venture as this it is in my opinion not the best choice.
The reason I say this is that style of air horn is not easily adjustable whereas the later style can be adjusted on the move and I think that might be desireable for this event.
I've sent you an e-mail and will wait until I've received a response from you before going any further.

[Tommo]

I better expand on one major thing here.
With that air horn unless you use a Henderson shutter style choke device you have no way of enriching the mixture for starting.
In saying this I'm presuming that on the other end of the air horn, that we can't see, the valve carrier rod is screwed into the air horn and doesn't have a knob that can be pulled out to load the air valve spring.
Am I correct Cotton?

[T. Cotten]

Sorry to get back to this so late!

Tommo,
It has the usual knob, although it has only has two positions for the pre-load (off and on; no intermediate notch in the adjusting nut), and the pin in the knob was shorter than usual.

I have absolutely no experience with the operation of H models, and don't even know which side the bowl valve should be mounted.

....Cotten

[Tommo]

Cotton,
For starting you have the ability to load the spring so that won't be an issue.
I've never held in my hand one of those type air valves so I'm not too sure about their exact make-up.
When you pull the knob out is there 3 holes set in a triangle shape that the pin can sit in or is it just a flat surface?
The reason I ask this is that most or the early air valves I've seen have the 3 holes and each of them is a different depth.
The different depth of each hole allows you to richen the mixture by varying degrees so the deepest hole only loads the spring a little bit and therefore only richens the mixture a small ammount. The other 2 because they are each a bit shallower richen the mixture to greater degrees.
The later air valves have as well as the pin the ability to rotate the centre carrier and thus load and unload the spring tension of the air valve on the move. While the later air valve may not be period correct (First appeared about 1917) I feel for this escapade it would be the best choice as it gives you the ability to adjust the mixture on the run.
If I'm correct with the air valve you've got you will have stop, remove the valve assembly from the carb and manually adjust the nut that retains the spring on the end the stem if you want to vary the air valve spring tension. This is not the most simple of things to do on the side of the road and the chance of losing one or more of the small pieces involved would be quite high.
As far as bowl placement goes, viewed form the top, Harley has the fuel outlet at about 7 o'clock, Excelsior somewhere between 3 and 4, Indian Scout between 8 and 9 and my Dayton with a Spacke has it at about 4.
Hope this helps.

[T. Cotten]

Tommo!

This one has only a slot detente in the side of the carrier adjusting nut.
Most that I have encountered have a double-slot, with a portion that allows an intermediate tension, as shown in the rugged example below.
The '28 Service Station Manual notes that there was a variety of this part.
One with holes in the carrier adjusting nut hasn't crossed my benches yet...

With a fresh Fickau Prototypes spring, this one dialed in to your suggested 3.5 oz tension with great sensitivity, as a half-turn of the spring retainer nut produced a noticeable difference. And of course, I set it at the middle of the carrier adjusting nut's travel, which matched others at close to fourteen turns.
That's a lot of adjustability!

The friction spring for the adjusting nut snubber came out in pieces, and the replacement was not as stiff.
Are the adjusting nuts prone to moving on their own?

...Cotten

[Tommo]

Cotton,
After carefully reading your last couple of posts again I take it that you do have the adjustable type air horn (I can't see the mouth of the air horn in the pictures you posted) and that it only has one position for loading tension onto the air valve spring.
If that is so I would have to say that I have never seen one like that and that is not saying they didn't exist, just that I've never seen one.
The only problem I can see Matt having is at start-up, usually it's two kicks with the spring fully loaded to prime the engine and then by putting the choke onto one of the notches that lessens the spring tension you start your bike. Once the motor warms up the choke knob is returned fully home into the normal running position. I've never had one that will start successfully in the fully loaded position.
As it is you don't have the ability to vary the spring tension between the full choke and the normal running position which could make things interesting at cold start times.
As to the differing pin lengths on the choke knob, the bigger the carb the longer the pin.
When we built a rig to pull a vacuum on air valves we overhauled we found that the bigger the dia of the air valve disc the more we had to load the spring to achieve constant opening pressures across the varying sizes of air valves.
There's a hell of a lot more to this than is possible to post quickly here and the variables that occur in Model H carbs are a minefield for those that don't fully understand them.
Hope this helps.