Marvel Schiebler carb

I've been fighting a battle with the carb for my Oliver 1550, If I remember correctly, it's a TSX 903? It runs good above 1000 rpm, but having a time getting it to idle right. I have taken it apart and cleaned it twice , the second time it was working great, would idle smoothly about 700 rpm, I could idle along in 6th gear at 500 rpm and push the throttle ahead and it would accellerate smoothly. Then it took a fit and wouldn't idle. I took it apart and I could see a speck blocking one of the jets in the bottom of the bowl. Cleaned it out and soaked it for a couple of hours in a gallon of Napa carb cleaner and put it back together. Runs great above 1000rpm, below 1000rpm, it lopes and sputters and wants to die. I have to choke it to start it even when warm. I ran a wire thru all of the holes in the body. There is tiny hole in the bowl that I can squirt carb cleaner thru but it seems like the hole doesn't go straight thru, the wire bottoms out. I even ran a small drill bit into it by hand and it stops like it's a dead end. I have another similar carb and the hole in it is the same way. I have an old crock pot in the shop, I think I cooked a carb in vinegar a year or so ago to clean it, That is the next step unless there is something better to use. The operators manual says idle speed is 450 rpm, I've never been able to get it that low. The carb was pretty dirty inside when I started all of this, I think it had set a lot before I got it, I scraped a lot of rusty crud out of the bowl. What next???? Thanks, Chris

Two things I'd first put an in line filter in the gas line to catch those small specks of rust that will pass thru the sediment bowl.2nd check for intake leaks,my 1550 and my 66 were doing similar to your 1550.Apparently the intake will warp on the Olivers, the 1550 was hardly noticeable but the 66 which kept running worse and worse had clearly warped upwards.Good used replacement manifolds fixed both of them they will now idle right down and accelerate smoothly.Also when installing the manifolds tighten the bolts first that apply pressure to the intake ports to make sure they square up to the head.

my experience has been that if crud is getting in it is coming from the tank or lines . NAPA and others sell a fuel filter that is designed for gravity based systems. I would use one of these in the line just prior to the carb. Clean everything first including drain and rinse the tank through the outlet hole, not with the fitting in the hole. Idle passages are very small, and fine particles can plug, and replug them. Also make sure your manifold in not cracked or loose on the block. A vacuum leak can create the same symptoms. Jim

Good thoughts. like minds on this. Jim

Chris,
Crock pot and vinegar is a good idea, but to answer your question, the only thing I know of that would be better is to let it sit in a heated sonic cleaner for a couple hours. Use either full strength vinegar of dilute it with water, depending on how bad it is.
Good luck
Todd

If the manifold is warped why not have it milled to straighten it out rather than change it.

Jani. put it in the best of terms. Good morning Chris .CM

If it is cast iron, I boil them in lye water until the water stays clear. Sometimes have to change solution 3 times. I had one recently that I thought I had all passages clear with tip cleaners & brake cleaner, but it would not idel. I cooked it & let it sit overnight, then boiled it again next morning. Solution was dirty so I boiled it again & again. Now it idels down just fine.

It does sound too lean if you have to choke it hot. Look for vacuum leaks, if a siamese manifold possibly it is burned through internally.

You say it won't idle down to 400, does it die or will it just not go down even with the idle stop backed off?

If it won't idle without dying, that can be low compression, or idle circuit failure. Idle circuit failure is caused from clogged passages or the bowl gasket not sealing where the fuel is drawn up. Also be sure the throttle plate will close light tight with the stop screw backed off. If not the plate may be in backwards or not centered.

Look up a fuel circuit diagram online for that carb, you can trace the idle circuit and get a better idea of the flow, mixing, and adjustment function. Remember, you are adjusting air bleed, not fuel flow. Backing the screw out leans it. The idle screw will have no effect above about 500 RPM.

I started it and sprayed starting fluid around the intake manifold and no change in rpm, so no leaks there. I took the carb off and apart to cook it. It is a TSX 903.

The wire is in the hole that the wire wont go through. I figured since I was cooking, I might as well do the carburetor for the 88 also, so I took it apart too. Its aTSX374. Where the wire is sticking out, I dont think theres a jet in the hole,on the 903 there was a jet in this hole. Am I missing a jet??

Are the two little holes in the bottom of the carb that feed the jet open?

I don't think I've worked on that exact model of Marvel Schebler, but
many of them have a stepped down hole in the passages, so drilling
them is not a good idea. You checked it by hand, that probably didn't hurt.

I think you're on the right track with boiling/cleaning it for a period.
Vinegar works, but takes time. Same with commercial carb cleaners.
I just finished a TSX-580 today that was full of red RTV. What a mess.

The idle circuit is normally in play below ~500 RPM, so if it won't
run below 1000, I'd try pulling the choke out a bit at those lower
speeds and see if that will smooth it out or make it worse.
That may point us in the right direction.

Lopes at idle is usually lean, in my experience, so I think you may
be looking at a good tank and line cleaning to keep the carb clean too.

Here are so very good pictures of those carbs. Hint:hit and hold ctrl & the + at the same time, and hold, it will blow up the page,same thing with the - and it will shrink.
Untitled URL Link

Again, I'm not familiar with that particular model TSX, but, on other
Marvel Schebler carbs, that hole in your second picture would be
the Economizer jet. Some had them, some did not. Some had them
as an option, so they had threads, others weren't even threaded.

(quoted from post at 19:35:26 07/21/21) Here are so very good pictures of those carbs. Hint:hit and hold ctrl & the + at the same time, and hold, it will blow up the page,same thing with the - and it will shrink.
Untitled URL Link

Click to expand...

nteresting! That is a ton of my photos, notes, drawings annotated, all put together with others. No credit given. But I did it to help all & any way it is distributed is actually good.