View Full Version : schebler model H tips and advice!

Matthew N. Olse
03-17-2010, 01:35 PM
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!
Matt Olsen

Chris Haynes
03-17-2010, 02:46 PM
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.

Matthew N. Olse
03-18-2010, 09:24 PM
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.
Matt Olsen

Tom Lovejoy
03-22-2010, 12:40 AM
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
04-02-2010, 03:29 PM

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?


04-02-2010, 08:59 PM
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

04-03-2010, 04:35 AM
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
04-04-2010, 10:57 PM
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.
Matt Olsen

T. Cotten
04-05-2010, 08:44 AM
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,


04-05-2010, 05:50 PM
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.

04-05-2010, 05:59 PM
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
04-26-2010, 08:29 AM
Sorry to get back to this so late!

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.


04-26-2010, 04:25 PM
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
04-26-2010, 05:59 PM

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?


04-27-2010, 05:43 PM
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.

T. Cotten
04-28-2010, 09:25 AM

Not only am I entering a minefield, I'm blind and wearing lead snowshoes.

One aspect that always worries me is vacuum leaks.
How were these early manifold threads sealed?
Was there a gland nut to lock the carb upright?


06-07-2010, 09:45 PM
Tommo- in your post of 4 3 you point out the 3 different angles on the butterfly. What angle does that refer to? Is it the edge of the disc relative to the face? What is the affect of mixing these up? I am using the same one I unsoldered from the shaft, but am cutious.

Also- the low speed screw. I'm rebuilding a HX 181. It did not have a low speed screw when I obtained the body. I bought both a repro and a NOS, both are the same length, and both are too short to seat against the notch by the throttle shaft by almost 1/4". I have reviewed different literature for the H and can't see when/if the screw was changed. Any advice in this area? I assume for idle the screw tip needs to be able to close the notch nearly fully? I can extend the tip, but would buy the longer if it is really out there.

Also, when the float valve ball is secured by the nut, should it have up and down play, or be like a heim ball joint- meaning pivot but not play?

Final question- when the bowl nut is on, there are few threads left for the hot air intake. How many threads are typically exposed below the bowlnut?


06-08-2010, 04:01 AM
The degree angle is the edge of the butterfly relative to the bore of the carb.
On 1 inch and smaller bore Model H carbs it can be either an 8 or 9 degree angle on the edge of the butterfly depending on the model.
The 1 1/8 to 1 3/16 bore carbs are usually 12 degrees and all the bigger bore ones 13 or 14 degrees once again depending on the model.
When fitting a butterfly to a Model H you require the butterfly to stop turning in the carb bore at EXACTLY the same time as the throttle stop on the cam track hits the stop on the carb body.
At no time ever, should you be able to rotate the butterfly through 360 degrees.
The butterfly when closed should fill the carb bore totally and be in the centre of the idle speed screw when at rest against the throttle stop.
I gave up trying to solder butterflys back in years ago and have for many years made replacement throttle shafts with screw holes and mount the butterfly using 2 #5 32 tpi screws. This method makes it so much easier to centralise the butterfly in the carb bore.
If there are butterfly chatter marks in the bore of the carb you will have all sorts of trouble in getting the carb to perform if you don't remove them

Your idle speed screw should be 31/32 of an inch long when measured from the underside of the hex head to the end of the screw.
It sounds like you have a 13/16 of an inch long idle screw that is for the smaller bore Model H's

The ball pivot for the float needle should have a very small amount of up and down movement. I can't tell you exactly how much as when I assemble them experience tells me if it's right or if it's too much. The needle should be free from any binding and wobble around freely. I always check this while the arm is out of the bowl.

Normally there's somewhere between 3/16 to 1/4 of an inch spare thread protruding below the bowl nut.
The bowl nut for a carb with an air horn fitted is 7/32 thick where-as those that were not intended to have one fitted had a thicker nut at 9/32 thick. An 1/8 of an inch makes a lot of difference in this instance.

Finally before anyone asks NO! I'm not doing any more carbs. Alan Travis caught me at a weak moment and I've done one for him to use on his bike in the Cannonball but that is the last, finish, no more, so please don't ask as my reply may offend you.

T. Cotten
06-08-2010, 07:20 AM

I have no problem custom-cutting the different angles for the outside of the butterfly discs, as I made mandrels for most of them (attached). But to hand-file the angles to the idle screw is quite a chore!

Have you any information as to those different angles, and tips or tricks as to how to cut them?

We all greatly appreciate the experience that you pass on to us!


06-09-2010, 10:35 PM
THANKS Tommo and Cotten for your guidance!

One last question- could you measure a bowl for the larger bore HX 181- for the height- the dimension that would set the threads of the stem showing. My bowl is 1.95" and is stamped DL4 on the gas inlet below the float pivot pin. Is this an H bowl? It did come with the lever and float valve with the ball....There are only a few threads showing beneath the nut. Although my nut is thicker, I made it from a Linkert bowl nut by turning off the bulge to keep just the nut, I can cut it down further.

06-10-2010, 12:19 AM
So long as the butterfly is a good fit in the bore the angle on the relief that the idle screw protrudes into is not too critical as when you adjust your idle speed the end of the screw has plenty of clearance. You do need to try and keep the clearance between the top shank of the screw and the top of the notch to a minimum. Around about 2 to 3 thou.
We always use a full circle butterfly and not the style with the flat top and stuffing washer as it is a lot easier to get a full seal and then have better idle speed control because you are only worrying about the space around the idle speed screw.
As far as cutting the relief we have made jigs that hold them so we can cut them in the mill. The only trouble with this is that you need a seperate jig for each of the main butterfly sizes and customers have trouble understanding just how much time and money is outlayed to be able to do the job properly. Because we screw mount the butterfly these two holes are critical to the whole operation as they are our datum points for all our machining operations and all our jigs are made to suit these two holes

You have a Deluxe bowl which if I'm right should measure 1 15/16 high
The Model H bowl is 1 13/16 high.
The best way to tell the difference is to look at the bowl side on and you'll see that on the Deluxe bowl the surface above the needle valve that the small cap screws down onto is above the surface of the main bowl by about an 1/8 of an inch.
The model H bowl is flush right across both surfaces and the Model H bowl is straight sided at the top where-as the Deluxe curves in slightly at the top.
I only have a very basic digital camera and it doesn't take very clear close-up photos so I'm not able to post pictures that might explain things better.
Sorry about that.

T. Cotten
06-10-2010, 07:35 AM

Attached is a comparison of the two styles, with the larger version shown on a patinated HX181.
I do not even know which side of the carb the bowlvalve belongs!
The 'horseshoe' float seems to allow it to be anywhere.

And Tommo!
I use the two screw holes to index as well, as that it the only way my bevel mandrels can work... And of course I can then use DLX choke butterfly discs, or most often Linkert throttle discs for blanks. If you can find a 'macro' mode on your camera (usually a little flower comes up on the control display), I would really appreciate a clue as to your approach to the relief jigs.

The examples that I have encountered with no 'stuffing washer' had the shaft retained by a lip of the body casting rolled over it on top. How do you prevent upward movement and wear into the bore without the domed washer?

Again, many thanks!


T. Cotten
06-22-2010, 03:01 PM
It has been brought to my attention that Type "A" DeLuXe models used the same bowl as the 1 1/4" HX models!

The '28 Service Station Manual pictures seem to confirm this, as well as the examples on my benches.


Tom Lovejoy
06-23-2010, 01:09 AM
Thanks for sharing this info guys, good stuff to know and learn.

06-24-2010, 12:51 PM
Sometimes you find a carb that has been in the bottom of the rain barrel for years all the steel bolts are rusted to the point where you can't get them out. Here is how I get them out. Battey acid, drill a hole in the bolt as big as you can, then put the carb in acid for a week or more. All you have to do is run a tap in the hole and you are good to go.
One more good trick is freezing brass. If you have tryed to heat and bent brass you know it don't work but if you freeze it, it will bent like butter. Have fixed many parts with these tricks. Levers and carb ears are easy.
I has taken me years to learn these tricks, try it.

T. Cotten
06-24-2010, 01:49 PM
Sometimes you find a carb that has been in the bottom of the rain barrel for years all the steel bolts are rusted to the point where you can't get them out. Here is how I get them out. Battey acid, drill a hole in the bolt as big as you can, then put the carb in acid for a week or more. All you have to do is run a tap in the hole and you are good to go.
One more good trick is freezing brass. If you have tryed to heat and bent brass you know it don't work but if you freeze it, it will bent like butter. Have fixed many parts with these tricks. Levers and carb ears are easy.
I has taken me years to learn these tricks, try it.

Wow, acid is a little rough on Miss Patina, isn't it?

I absolutely agree that heat is verboten when bending brass and bronze.

Attached is my hi-tech approach to bent H airhorns.

PS: Anyone needing a spare billiard ball, I've got freebies.
(But the 8s are all spoken for....)

23JDCA 808
06-25-2010, 08:59 AM
. . . If you have tryed to heat and bent brass you know it don't work but if you freeze it, it will bent like butter. . . . .
Brass and bronze can contain air bubbles, which explode if you heat it with a torch. ...bill

Tom Lovejoy
06-28-2010, 12:13 AM
Right on Cotten and Marsh, I never heard of either method and my airhorn is bent. Thanks again for sharing .