392 fuel starving

[Michael Caffrey]

I have a rebuilt 392 with a Quadrajet carb which runs great except that... when under a high rpm load it starts to starve for fuel. It has exceptional power at lower rpm and will cruise nicely in OD unless you push the pedal down and it will begin cutting out. I have replaced the fuel pump three times, (two different mechanical pumps and one electric), changed the fuel filter twice, changed the fuel line, tried each of the four gas tanks, increased the size of the carb jets to #73, tried a different distributor (now have a HEI), changed the timing and nothing helps. It is driving me crazy. I would appreciate any input you guys out there can offer! I don't dare go out of town with it the way it is .

Originally Posted by Michael Caffrey

I have a rebuilt 392 with a Quadrajet carb which runs great except that... when under a high rpm load it starts to starve for fuel. It has exceptional power at lower rpm and will cruise nicely in OD unless you push the pedal down and it will begin cutting out. I have replaced the fuel pump three times, (two different mechanical pumps and one electric), changed the fuel filter twice, changed the fuel line, tried each of the four gas tanks, increased the size of the carb jets to #73, tried a different distributor (now have a HEI), changed the timing and nothing helps. It is driving me crazy. I would appreciate any input you guys out there can offer! I don't dare go out of town with it the way it is .

Michael,

I suspect the secondaries are not providing enough fuel. I am not a Q-jet expert yet but I will become one. (I have one that's going on my 345 this summer). You might want to consider buying Doug Roe's book on these carbs. It is considered the bible on Q-jets. It's called "Rochester Carburetors" and it's published by HP books. It is available from a number of places but I got one from www.buy.com for around $13. It's about $19 retail.

Also you might want to take a look at Scott H's web site: http://home.mchsi.com/~s2doc/. Click on carb tips.

Sorry I can't help more at this time.

[jordandoc]

Originally Posted by Michael Caffrey

I have a rebuilt 392 with a Quadrajet carb which runs great except that... when under a high rpm load it starts to starve for fuel. It has exceptional power at lower rpm and will cruise nicely in OD unless you push the pedal down and it will begin cutting out. I have replaced the fuel pump three times, (two different mechanical pumps and one electric), changed the fuel filter twice, changed the fuel line, tried each of the four gas tanks, increased the size of the carb jets to #73, tried a different distributor (now have a HEI), changed the timing and nothing helps. It is driving me crazy. I would appreciate any input you guys out there can offer! I don't dare go out of town with it the way it is .

Mike, you say you replaced the fuel filter twice!!! You don't say WHICH filter as there is, in addition to the inline filter, a fuel filter in the front of the carb. Did you look at that one? It's small and fits inside the carb fuel inlet. Also, check your float level, it may be low.

Dan

[Jay Tabor]

if its an almost instant fuel starvation when into secondaries, its the carb, not fuel filters or pumps.
secondary needles and jets arent right, maybe the needles they arent lifting up out of the jets.

[Michael Caffrey]

John,
Thanks for the info. I think that makes sense. Can you tell me how to adjust the secondary jets. I understand that there is an adjustment but I have never done one. If you can teach me over the web site, i would really appreciate learning this one from you!
Mike C.

Originally Posted by Michael Caffrey

John,
Thanks for the info. I think that makes sense. Can you tell me how to adjust the secondary jets. I understand that there is an adjustment but I have never done one. If you can teach me over the web site, i would really appreciate learning this one from you!
Mike C.

Mike,

Actually you can't adjust the secondary (or primary jets for that matter) in a Q-jet. You can change the primary jets, the primary rods and the secondary rods. You can't change the secondary jets only the rods.

Frankly, Mike, spend the $13 and buy Doug Roe's book. Especially if you are going to open up that Q-jet yourself. Go to www.buy.com order the book and a CD you like and you get free shipping if the order is over $25. You can't beat that deal with a club! You will be doing yourself a favor.

BTW, secondary rods not only vary in size (diameter) but in taper and the length of the taper too. And the rod hangers come in different ratios too.

You should be able to get more fuel to the secondaires by installing smaller secondary rods. But to do that you have to determine what size is in there now and where to look for this info on the rod and how to interpret the combinations of letter on these rods. There are charts in the book explaining how to understand these rods along with lots of other good stuff.

[Michael Caffrey]

Doug,
Thanks for the info and advice on the book as well as the web site on Q jets. I will order the book and see what I can find out. Since the secondary metering rods are so easy to change I can play around with this one easily.
BYW, yes I also changed (removed) the little ceramic filter inside the carb in my attempts. As everyone has said, it is not a fuel flow problem.
Thanks again,
Mike C.

Originally Posted by Michael Caffrey

BTW, yes I also changed (removed) the little ceramic filter inside the carb in my attempts. As everyone has said, it is not a fuel flow problem.
Thanks again,
Mike C.

Mike, thats good! Virtually no one uses that filter in the carb anymore. Too often the threads in the carb body would get stripped when tightening it and ruin a carb body. I do recommend you use at least two inline fuel filters though, one before the fuel pump and one after.

Since I got a really bad load of gas a year ago that clogged two fuel filter, my fuel pump and my carb too, I now run three filters. Two before and one after. They sure are a lot cheaper than replacing a fuel pump and rebuilding the carb. BTDT. I use the NAPA #3032. They are metal andwont melt or get frayed by an errant belt either. I know a guy that used a plastic filter and a frayed belt wore a hole in it and started a fire under the hood of a really great looking 72 SII.

Not a lot of folks here run Q-jets yet but it seems like more folks are going that way. I have one that is going on this spring/summer.

There is more in Doug Roe's book than you probably want to know but it's there if you want to learn. You do need the charts on secondary rods though.