Rochester 2-Barrel M2MC Carburetor Jan 15, 2011

Taking on the project of resurrecting a Rochester M2MC 2-Barrel carburetor for a vehicle a friend will be using in a demolition derby in February. The M2MC was brought forth as an economy oriented carburetor intended for smaller displacement engines in the late '70's - actually only a few years! GM kinda cheated on this project by using the front half (primaries) of a Quadrajet carburetor. The primaries on a Quadrajet are very tiny, meaning high air velocity, in conjunction with a metering rod system and triple venturi design assure top fuel efficiency. It comes at the expense the engine, especially the V8 offerings, would be a little restricted in the higher RPM ranges. In all honesty, the public had all but given up on 'performance' during that period. This particular example appears to have suffered from a little water getting into it while it was sitting off of a car a while ago. It will be cleaned before assemble with new gaskets, then adjusted after it is reassembled.

Category:

Autos & Vehicles

Tags:

• Rochester carburetor
• Rochester 2-barrel
• carburetor apart in pieces
• servicing a carburetor
• Rochester M2MC
• 2-barrel carburetor
• spikedpunk

[327pd]

2 easy mods that will improve that carbs performance are to drill out the idle mixture screw holes to .090" then set the idle mixture screws about 4 turns out from fully seated. Also drill out the accelerator pump discharge holes located underneath the airhorn to .028" Lastly, remove the float needle/seat assembly and drill out the seat to .130" and set the float level at 1/4" down from the top of the float chamber measuring the float at the toe end.

[spikedpunk]

@327pd Thank you very much for the advice. It is much appreciated. I will apply these things if time permits at this point. The modifications you present make very much sense to increase fuel flow.

[327pd]

To add some performance for a demolition derby car, you can modifiy the accelerator pump discharge holes ,the idle mixture screw holes,the needle/seat assembly and several other passageways on that dualjet taking it to a mild performance 2 barrel carb. As it is just like a qjet it can benefit from some of the same performance mods. Don't forget to check the throttle shaft for excessive play as this can cause poor idling and stalling(not good for a derby car) Good Luck!!

[spikedpunk]

@327pd Thanks very much for the tips. I will look into this. My modification 'skills' on Q-Jets has been jets/metering rods on the primaries, and metering rods on the secondaries, I will look up and see about the mods you mentioned, but will take it easy, for like you said, stalling is a no-no on a derby car! The mileage seems low on the carb in question, for the throttle shaft has barely perceptible play in it, in fact I would almost say nil.

[monarch1957]

I used to have a 82 Olds Brougham with a 267 V8.

[spikedpunk]

@monarch1957 Now that must have been a car that needed a little patience to get up to speed!

[spikedpunk]

Thanks for the kudos and confidence in the work I am contributing to this. My role in the project of the derby car is but a tiny one. The Q-Jets and related spinoffs are pretty decent units, doing a very capable job of metering fuel if only understood a little.

[Radiowild]

Never saw one apart before. Your'e right it's a 2 barrel Q-jet. I'm sure the "bumper" car will run like snot when you get it back together! I've always liked the Q-jets! RW