Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
SECONDARY FUEL CUTOFF UNDER LOAD
THEDODGEBOYS:
OK, here goes. I have a part #1757280 quad that is giving me a fit! This carb was rebuilt back in the spring by a very good Mopar, yes Mopar engine builder that happens to like to use Quads just as I do. The carb performed just like it should up until a few weeks ago.
It starts great, idles great, and runs great on the primary side. The issue comes in on the secondary. When you get after it, the secondaries open and it takes off great, no bog or anything, then it lays over, and begins to backfire and pop thru the carb. I have tried the carb on 2 different vehicles and it does the same thing.
Well last nite, I got up in the engine bay and wanted to see if fuel was coming out og the tubes in the secondary. I went from 2500 rpm to WOT and everything was correct for 1-1.5 seconds, the front and rear throttle plates open and the rear air door began to open, then when the air door was all the way open, the fuel stopped coming out of the tubes. It is like someone turned off a switch.
Like I said, this all took place in 1-2 seconds. Any ideas?
This is on a mild 360 Mopar.
THEDODGEBOYS:
Dodge 360/ 10.5 compression/ J heads w/ 2.02/1.60 valves/ LD340 intake/ .454/.470 hyd cam
Carb specs .110 needle/seat, 74 primary jet/ G hanger w/ DA rods, fuel pressure set at 7psi, fuel level in bowl is 1/8" from the top.
omaha:
Hey, welcome to the forum! I also like the mopars. I have an '80 dodge powerwagon that I am in the process of building a 318 for right now. (replacing a slant six). Yes it will have a Q-jet. Also, on the back burner is the 67 Barracuda project. This too will get a Q-jet [much to the dismay of some of my "Mopar" buddies.]
Yes, I also am a big fan of the Pontiac powered cars and some oldsmobiles. If I had a VW bug it too would probably have a Q-jet or maybe a Dual-jet. {I like the old air-cooled bugs}
Anyway, as far as the problem is concerened, it sounds like the carb IS running out of fuel. These carbs like alot of fuel but at a low pressure. Things like small fuel lines, clogged fuel filters and incorrect float setttings can cause the symptom that you have. Usually, a 1/8 float level would be too little but not always. Usually 1/4 is the common setting if you dont know where to set it. So, my best guess would be the filter in the carb fuel inlet fitting or possible something to do with the needle and seat. You shoud always use one of Cliff's needle and seats 'cause they are better able to withstand the "new fuels" with the alchohol. Since you have tried this carb on other vehicles, seems to rule out fuel pressure probs.
I dont think it is the float (although I think the setting is too small). It would cause a different problem
than what you are experiencing. Merry christmas and enjoy the holidays!!
THEDODGEBOYS:
Thanks for you insight. What I was referring to concerning the fuel level and float was that the fuel level in the bowl is only a 1/8" from the top, hence the float level is set very high. I have not had any gurgling issues or spillage. I am affraid to set it any higher.
I have a high flow .145 needle/seat assembly that I am gonna install tonight, as well as trimming 1/4" off of the plastic baffle that sets over the float to increase bowl capacity.
On the left of the float is another cavity with a cylindrical black plastic piece that contains fuel as well. I have always been told that this is to keep the fuel from sloshing around. Is this true? Or, can it be removed?
I have read on here guys talking about some of Cliff's carb recipes. Where do I find these?
Thanks, Allen
Cliff Ruggles:
Waste of time to trim the splash guard to increase fuel bowl capacity.
In any application, the fuel delivery to the bowl must keep it full at all times.
You either have insufficient fuel delivery, or the fuel inlet seat it too small, or both. Run the larger fuel inlet seat first, and if the bowl still goes dry, increase fuel delivery to the seat.....Cliff
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