The Stovebolt Site Forums The Shop Area Engine Shop Trying to squeeze a few more MPG

The vehicle; 1963 Grumman Kurbmaster with a 292 and Rochester B carb.

Carb just rebuilt by me, no unusual wear noted, and runs much - much smoother....but... 8.3 mpg.

Timing is spot on.

Before the carb rebuild and now, the engine seems to like a "touch" of choke when running, even after getting to full operating temps.

The poor little 292 is busting its butt pushing the Grumman, no doubt!

Question is, did the Big Bolt 292 Rochester Bs get different jets than standard truck models? I have no idea whether this carb is original to the machine.

Seems like this one wants a bit more fuel, and as odd as it may seem,I think efficiency may improve by replacing that "touch" of choke with a jetting adjustment.

Any ideas on jetting and sources for jets would be appreciated!

Before you go making changes to the carb, try this: With it running at usual driving rpm, 2500 or whatever it is at most, pull a vacuum line. Yes, create a vacuum leak. Watch the rpms, listen to the engine. If speed decreases, the mixture is now too lean and needs enrichment, more jet. If engine speed increases, you have too much fuel already, as additional air allows greater rpm with by burning that fuel better.

Having said that, I've found B's to be very rich from the factory. I've worked with mine to get it dialed in, it is now jetted down to about 2/3 what the original jet was. Do not do this without the engine telling you it wants it however. I was not able to find jets available to buy, so I soldered mine up and drilled it smaller. You can buy drills to do this at your local hardware store, meant for cleaning torch tips.

Devin

Sounds like a plan!
Just trying to reach 10mpg {or better, if I stumble into it!}

You can lower the float a bit, that will lean it down, same for raising it to richen it up. Try turning the timing up, listen for pinging on long hills or hard pulls. They run best with at a slight ping at light throttle, but goes away at heavy throttle.

From what I read, 292's are hard on gas. I don't understand why this engine would be different from any other, but it seems everyone that has the same problem.

And to answer you question about the carb, yes 292's use a bigger bore carb then the 250's did. I don't know anymore then that, but if you go to your local parts house and buy a rebuild, you may still get a 250 carb. It seems they combined them all in to one to keep stock down.

Joe

About 20 years ago there was a UPS maintenance shop here. Their cars were similar to yours except that they used 300 Ford I6. The guys said that 10 mpg was always their goal, but 8 mpg was realistic. I have an Isuzu NPR Diesel that only gets 10.

I have a 63 C20 with a 292. I replaced the Model B with a Monojet. I think the Monojet is a bit more tune-able. The best I could get was about 10 mpg on a good day. I put in an overdrive and the mileage went up to 14 mpg.

Larry