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Marvel Schebler Carb Problems

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Matt the Brat

12-18-2006 11:07:57

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I have a '42 Cletrac, the carb has been rebuilt, it idles and revs great, until the gov calls for power, the unt has no power and tend to starve fo fuel. I have found that if i crack the bowl drain open the machine pulls/pushes with the best of them and no fuel leaks out of the bowl until I shut the machine off. This is just a band-aid, does anyone have the answers to fix this. Thanks, Matt the Brat

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Bob

12-18-2006 20:38:17

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

If this is a typical MS carb, the float bowl vents to the air horn though the open area SURROUNDING the venturi.

If the venturi is not the correct one for the carb, damaged, installed wrong, or the gasket surrounding the venturi is damaged, all sorts of weird problems can occur 'cause the mild vacuum in the air horn and float bowl gets opened up to the HIGH manifold vacuum.

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Mike Van

12-19-2006 02:15:44

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Re: Marvel Schebler Carb Problems in reply to Bob, 12-18-2006 20:38:17

And that venturi wants to be big end up - don't ask how i learned that.

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JerryMT

12-18-2006 12:52:57

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

If you can run with the bowl drain open, there must be something wrong with the fuel delivery system. With the bowl drain open the fuel should pour out of the fuel bowl like a cow peein' on a flat rock! Check the sediment bowl filter and the inlet in the tank and then make sure that your line from the tank to the carb can deliver fuel, no kinks or blockages. It doesn't take much fuel to rev an unloaded engine and when you're under load you need a much higher fuel rate which your fuel delivery system isn't providing.

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Gerald J.

12-18-2006 11:54:52

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

Did you clean the screen on the back of the inlet adapter? I've seen much younger ones plug solid (not pass 60 psi air). When almost plugged it will sure starve an engine.

Could it be that the drain plug sticks into the float chamber enough to hold the float up so it can't drop and open the needle valve all the way and so restricts fuel for full throttle running?

Most carburetors have two mixture adjustments, idle and power and for the intermediate range the only adjustment is a finesse of the float level. Seems like that might be possible.

Has it carbon or copper wires? Magnetos are especially critical to needing copper or iron wires, no carbon wires? Do the plugs have resistors, same problem?

It may be simply that the no load adjustment for the high speed jet is a bit on the lean side and for power it needs to be opened up a bit. Then it will run a bit rich no load at speed and may even soot up the stack, but it shouldn't be so rich as to foul plugs or put out visible black smoke. I know my MF-135 pulls the plow best when full rich.

Gerald J.

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12-18-2006 12:03:30

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Re: Marvel Schebler Carb Problems in reply to Gerald J., 12-18-2006 11:54:52

Yes
No- hardware on the outside (shut-off valve)
Float level has been checked, any more it will flow out of the carb.
iron wires-new
plugs - no resitors
Jets are on the rich side
Thanks

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Greg_Ky

12-18-2006 11:41:24

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

Bowl vent plugged?

En richen the high speed needle?

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12-18-2006 12:05:55

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Re: Marvel Schebler Carb Problems in reply to Greg_Ky, 12-18-2006 11:41:24

Bowl vent?? is this the stone filter on the bottom of the bowl next to the drain?? How do I clean if neccesary?? Specs for doing so?
Thanks,
Matt the Brat

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Joe (Wa)

12-18-2006 11:27:17

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

The fuel tank cap vent may be plugged or has been replaced with a non-vented cap. Test run with the cap off.

Joe

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12-18-2006 11:30:29

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Re: Marvel Schebler Carb Problems in reply to Joe (Wa), 12-18-2006 11:27:17

I have drilled a hole in the cap --no difference

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repy

12-18-2006 11:21:27

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

I have checked that with carb cleaner and starting fluid, Checked the timing, new points and condenser, new wires and plugs. Still scraching my head.
Matt the Brat

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RustyFarmall

12-18-2006 11:26:40

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Re: Marvel Schebler Carb Problems in reply to repy, 12-18-2006 11:21:27

How about the actual ignition coil?

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12-18-2006 11:32:22

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Re: Marvel Schebler Carb Problems in reply to RustyFarmall, 12-18-2006 11:26:40

Mag ignition, All seems to work great.

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RustyFarmall

12-18-2006 11:38:10

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Re: Marvel Schebler Carb Problems in reply to Reply, 12-18-2006 11:32:22

What color is the spark, bright blue? or kind of a dirty yellow?

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12-18-2006 12:07:33

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Re: Marvel Schebler Carb Problems in reply to RustyFarmall, 12-18-2006 11:38:10

The spark is bright blue.

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RustyFarmall

12-18-2006 11:18:45

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

Opening the fuel bowl drain even just a little should let the fuel run out even when running so I'm a bit confused on that one, but maybe cracking that drain is allowing more air to come in? That tells me that maybe the air cleaner is dirty and restricted? Maybe the choke is hanging up and not opening completely? If indeed it is starving for fuel, then you need to check the carb float level, the inlet screen in the carb, the sediment bowl under the tank, and maybe even the possibility of dirt and crud in the tank. Also, a weak ignition system can cause the same symptoms.

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12-18-2006 11:28:39

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Re: Marvel Schebler Carb Problems in reply to RustyFarmall, 12-18-2006 11:18:45

With or without air cleaner hooked up it runs the same, cleaned the tank, new sediment bowl, choke is fine, ignition systems has a good spark, carb float level has been adjusted.

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old

12-18-2006 12:14:30

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Re: Marvel Schebler Carb Problems in reply to Reply, 12-18-2006 11:28:39

Heres some thing to try. If it works doing this then the bowl vent in the carb is clogged. Pull the main jet adjustment screw out. If it keeps running then you need to open up the carb again and clean out all passages becuse the bolw vent passage is clogged and you can't get enough gas to the engine because it causes a vacuum in the carb bowl. BTDT

Hobby farm

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Will- Tx.-Mn.

12-18-2006 11:12:22

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Re: Marvel Schebler Carb Problems in reply to Matt the Brat, 12-18-2006 11:07:57

Matt:

Perhaps your intake may be leaking

just a thought

~Will

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