I'm still having a bear of a time getting my 351M up and running after swapping it in place of my 460.

It starts okay, but won't stay running. I took a closer look by the carb, and it looks like the front pump diaphram area is leaking. When I manually activate the throttle (engine off) it shoots out some gas whenever I return it to the resting position.

I really, really, really don't want to rebuild the carb. Last time I did that was on my 460, and I f'ed everything up pretty bad (dropped a washer down the intake unknowingly).

If I -am- going to take the time to do this, are there better jets I should use than what came from the factory?


This is a stock 2150 carb on a 1977 351M in a 1979 F150. The engine ran fine when it was in the donor truck about two months ago.

 

Put some tape or foam rubber in the throttle bores. Take the top of the carb off and check the inside for junk. Blow some carb cleaner in all the little holes. Check the spring on the power valve. The accel pump diaphragm can be changed without removing the carb. Just unbolt it from the front of the carb and change the diaphragm. If you want to inspect the power valve you have to pull the carb and turn it upside down.

Good luck.

 

AMiller320,

If the carb shoots gas out the accelerator pump cover on the front when the throttle closes, the pump diaphragm is bad.

You can get the accelerator pump diaphragm alone and replace it like willd suggested, however, it's a lot easier to work on the carb if you take it off the engine.

I have some info on this URL about how to improve the performance of a stock M-block (351M/400), including changing the carb jets:

http://home.earthlink.net/~bubbaf250/perf/perf02.html

 

Thanks, guys.

I think that I'll go ahead and just do the full rebuild. Consider it conquering my fears, I guess...

Bubba -- I've read your page a few times over in the past. I know how to change the jets, but I was wondering if there is one particular jet number that always works better than stock, ya' know?

Oh, one other thing -- while cruising Napa's site online, they have about 10 different rebuild kits for the various iterations of the 2150 carb. Are they all actually different? Is it recommended to bring the carb in the the store when I get a new kit? Or are they all pretty much the same?

Thanks again!

Andy>>

 

Andy,

There is no one particular jet number that always works better than stock, and there is no one particular jet number that is stock. Different jet sizes were used in different carb calibrations, depending on the vehicle and engine application, and the emissions controls and compliance requirements.

Carb rebuild kits are usually designed to work with several different carb variations, so if the catalog has 10 different kits, they are intended to cover 40 or 50 different carb calibrations.

The power valve is the main part in the rebuild kit that is specific to a particular calibration. Other than that, the main differences will be the gaskets (number and shapes). The instruction sheets are usually the same in all the kits made by a particular manufacturer, and they cover most every possible variation.

To get the right kit, you need the carb ID number. If you don't have the carb's ID tag, you can look for the correct application (i.e., engine and vehicle type) in the rebuild kit catalog to narrow it down.

I also have a list of OEM carb calibrations and ID codes for '77-'82 truck M-blocks on my web site at this URL:

http://home.earthlink.net/~bubbaf250/parts/parts06.html

 

Take the carb in with you and the I.D. tag if it's still there. As for the rebuild. Luckily I think this is about the simplest carb ever invented, just lay the parts out on a big table like they come out. Then put the new pieces in where the old ones were and re-assemble it. When you replace the power valve check to see if there are any numbers stamped on it like the holley's have. Usually these indicate the vacuum point at which the valve opens. If so, they should be relatively close to each other.

Have fun.

 

 

Thanks for the help, everyone. The carb doesn't have an ID tag on it, and I don't know for sure what year the motor is or what exactly it came out of. I got it from a guy who got it from a guy who... you know the story.

I'll rebuild it with the kit I have, paying special attention to the jet numbers and any stamped numbers on the power valve. I'm planning to take it apart tonight, then I'll let it soak overnight.

Bubba - I was going to take advice from your site and look for a carb from an '82 Mustang, but I decided that I should just stick with what I have for now. If I continue to mess with (read: break) the truck more, I'll change that later.

Andy>>

 

One more point about selecting a carb rebuild kit.

Regardless of the carb ID tag, I would look for a rebuild kit appropriate for the vehicle you intend to use the carb on, not necessarily the original application or the original carb calibration. For example, if you're using the carb on a 351M truck engine, rebuild it as a 351M "truck" carb, not as a "car" carb, even if that's where it came from. Vice versa if you're using the carb on a car engine.

Fortunately, you can get main jets and power valves separately, and tweak the performance by changing those parts without buying a rebuild kit.

BTW: If you're going to work on a carb that's been sealed up for a while, be very careful with the gasket between the main body and the top (air horn) so you don't damage it. If you damage that gasket, then you'll have to buy a rebuild kit to replace it.