Monojet carb problems

[pseigmund]

Hi All,

I am having some problems with my Rochester monojet on a stock 292 in a 1970 3/4 ton with a 4-speed tranny. The problem is that I pull the choke(manual choke) shut and it starts fine but after it starts to warm up, it will die if I don't keep the choke almost closed. I can pump the gas to keep it going if I do open the choke but then I get some backfiring. It will also stall when I try to put it in gear and take off. It seems that it is starved for gas. I have a new fuel pump and checked all the lines. I get good gas coming out of the line near the carb when I crank the engine. I just double checked the float level and needle valve. There must be some other problem with the carb that is making me have to keep the choke closed. I put a carb kit in it a few weeks ago so it has a new accelerator pump, etc.

Any ideas?

Thanks, Pete

[68gmsee]

It does sound like it's not getting the gas it needs. When you did the carb kit did you use carb clean on all the orifices and used compressed air to blow them out?

I've done a few rebuilds on my mono carbs and they're simple enough to do, but you need to make sure that you clean them out real good.

Also, make sure you don't have any vacuum leaks, broken or cracked hoses, or bad gasket on the carb base.

One more thing, when you check the fuel pump don't assume that if gas comes out your supply is good. Use a plastic container and make sure it has a good strong pulse of gas. A weak pulse indicates a fuel restriction somewhere.

[blakeaz33]

I had a problem very similar to what you're describing with the same carb on my 250 - rebuilt it did everything I could think of would idle but as soon as I would take off it would die. My problem I finally discovered was the fuel filter in the carb base where the fuel line attaches had come apart and was creating the fuel starving problem - went and got a new filter installed it drove fine for an hour or so and then same problem. Checked the new filter and it had come apart and the element was clogging fuel flow again. Not sure if I had the wrong part, too firm of a spring, it was not installed backwards. I got tired of screwing with it and removed it and added an inline filter and have had no issues for the last 5000 miles.

[pseigmund]

Thanks for the replys. I did get rid of the small 'in line' filter and have an after market filter between the tank and the pump and the pump and the carb. When I disconnected the fuel line and cranked the engine, the gas was coming out with good pressure and lots of it. So I am thinking it has to be something in the carb. There is a small spring and ball bearing that came with the carb kit that I didn't replace (left the old ones in). These were held in by a small metal bar that I couldn't get out easily. What I probably need is a good diagram of the gas flow once it leaves the float bowl. Maybe take it apart and clean it again. I did use carb cleaner and compressed air the first time.

Any ideas on where is get a diagram of the gas flow. I have the diagram that came with the carb kit?

Thanks again.

[68gmsee]

Not sure where I got this one, but it may help you:

[pseigmund]

Thanks for the diagram. I am going to try and take the carb apart tonight or tomorrow. I am thinking it is possible one of the holes in the throttle base are plugged or I am sucking air in somewhere hence the need to choke it to compensate.

Thanks again.

[Martin64]

Does anyone know the baseline mixture screw setting? I just put the above diagramed carb on my truck.

[68gmsee]

Originally Posted by Martin64

Does anyone know the baseline mixture screw setting? I just put the above diagramed carb on my truck.

Every engine is going to be different but here is how I've done mine.

Preliminary: I turned the screw lightly all the way in and then back out app 2 turns. I use a vacuum gauge and attach it to one of the lower vacuum inlets or manifold vacuum. I crank the engine and adjust for the recommended idle speed and then refine the idle air screw adjustment for max vacuum.

I check the timing to make sure it's correct and then go back and recheck the idle rpm and idle air screw adjustment for max vacuum again.

[Wrenchbender Ret]

There are 2 different gaskets that go between the throttle body & the fuel bowl. Both generally come with a kit. Make sure you have the right one & it is in correctly. Did you set the metering rod like the instructions says? This adjustment is critical. You can raise the adjustment a little if it is running lean. Other then those you must have a vacuum leak somewhere.