305 QJet Secondaries Not Working

At least thats what I think is happening, I am a fuel injection guy, love TPI engines and love tuning them.

1985 LWB Chevy Silverado with a 305 Qjet (M4MED ?)

Bought this truck at auction while back and it sat for about a year because I was pretty ill. I finally got around to fixing everything, back window, tires, muffler and a bunch of other stuff. Have not changed oil or plugs or anything yet.

I put some gas into the carb and fill up the tank and she starts right up after a few attempts. Engine has some miles on it, I think its the original engine and it does not smoke.

It does not have the power to smoke the tires, but it does take off, somewhat. The primaries seem to been working great, there is good off idle acceleration, but its only part throttle acceleration.

When I floor it, it feels as if it wants to accelerate, it feels as if the timing is trying to advance and there is only that nice part throttle. The secondaries dont seem to be doing much, if anything. I do not hear that classic WAAHHHH of the secondaries opening up and bringing the engine to life.

Every once in awhile, they seem to open up partially and allow lukewarm transition but it feels like it chokes and stops accelerating and then starts up again intermitently.

I was dinkering with the linkages and there seems to be a secondary lockout thingy near the choke and it seems to keep the secondaries from opening. Opening the throttle all the way and looking inside, those secondaries were not coming open.

I sprayed intake cleaner on the shaft sticking out the body of the carb and inside the doors and they seem to be opening now. They were definitely stuck. Having said that, the lockout is still keeping them from opening.

I asked my Camaro buddies and they all seem to switch to Holley or other carbs that are easier to mess with. I am thinking of just cutting off that lockout thing and figuring out if its fuel or something else thats keeping the engine from going WOT.

Any ideas?


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Ideas? Yeah, first ignore those who say to swap the carb. The Qjet is by far the most sophisticated 4bbl ever made. Unfortunately the complexity means that those without patience won't take the time to learn how to tune it properly.

Second, the lockout is designed to hold the secondaries closed until the choke opens fully. This is to prevent a bog when the engine is cold. Either the choke coil needs to be adjusted or the linkage rod needs to be adjusted. Either is a simple operation. Get Doug Roe's Qjet book and lean how these things work.

howdy there, well the q jet is actually the most fuel efficient and is actually larger CFM than the other models. i agree with Joe totally.

it is E4ME if its the original one with the electric fuel mix solenoid and such parts. if the solenoid doesnt make rapid audible clicking noises with the ignition on, then its not operating/controlling


the truck will be not geared very well in the axle

this is where i would start, is by putting at least a 3.42 rear axle under it from another truck in which are somewhat common if you hunt around enough.

these trucks in the '80s were almost always the horrible 2.73 and 3.07 ratio in which is far from a performance ratio and prevents the engine from using good RPM when taking off.

the '80's stuff were built for fuel economy rather than performance.

the truck will wake up alot with a good axle ratio in it.

you will find this out if you actually go for a deeper ratio axle.

the secondary AV's can be adjusted to open sooner by lightening the adjustment screw on the pass side there is a screw up underneath where the shaft end is. so it will open sooner
make sure the secondaries throttle shaft is turning and opening the blades, if not then the Av's cant open regardless of how far you open the throttle and try to make the AV's open. there is a lockout function on the secondary throttle shaft. check this lock out link,
it is on the pass side and ties into the choke linkage parts mounted to the float bowl part of the carb where the choke housing attaches.




good luck!

First of all, this Qjet runs extremely smooth, I would not put on a junk carb (unless it was an Edelbrock) because it runs so well.

It has an electric choke and it does have an M/C solenoid. I cannot figure out if this is a computer controlled carb or not. It seems that it has a M/C solenoid that does not tick when you put the key on run, my dad's camaro does that so I know what that sounds like.

When I turn the key to ignition on and mess with the connector it clicks once and then stops. Its either not getting a proper signal or the solenoid is getting stuck.

I noted there is no ECM fuse or wires going to the ECM fuse at the fuse panel but it is marked there. Also, there is a four pin connector that is just hanging there at the back or the passenger side head?

I have heard of problems of that secondary lockout, and my buddy gave me the CC QJet he had on his 84 camaro. Looking at it, I figured out that there is linkage that keeps the secondaries from coming on until the choke is all the way open, and then it hits the lockout when you press the gas to let the secondaries open.

I sprayed intake cleaner all over the linkages, AV doors, shafts, springs, you name it, they were gunked up. This also helped the truck idle lower than it had been before.

Then I carefully removed the electric choke and backed the main bolt out just enough to remove the stupid lockout without messing with any of the other linkages. Carefully put the electric choke back together and ran it.

It started to wake up after mashing the throttle several times. Sometimes it would get up and go and sometimes not. It feels like its definitely timing or fuel related.

The gears are part of it, they feel like my 2.73 camaro before I swapped it for a 3.27 posi rear.

I am going to swap out the fuel filter to see if its clogged with year old gunk.

Carb:




Truck:




Thanks for your help guys, I'll keep you posted

PS: If anyone has a 15" X 8" Progressive wheel like the ones in the picture, let me know, it is an orphan and I would like to reunite it with its 3 brothers.

I changed the fuel filter today, that was the easiest thing I have ever done on a car.

The problem has been upgraded to a bog, I let the engine warm up before I drove it and went to go get some gas.

I press the pedal fully and it has no balls at all. Once it gets moving the engine starts to rev like its got some life. At the second gear transition it bogs bad. This is with a full tank of gas, so it should have plenty gas available.

Would the non functioning M/C solenoid have that much effect on the A/F ratio?

I know u my have already put new gas in but just in case are you running on that year old gas ?

It was empty when I bought it at auction. I put a few gallons in and ran it until it ran out of gas and it just conked.

Then I put some gas in recently and did the same thing, and filled it up with gas right before I started driving it around. Its had about 3 good tankfulls of gas run through it now.

I was looking at the carb and some pictures of other carbs and it does not have a front vacuum break.

I dont think its an E4ME, it seems to be an M4MED

I read this post from http://www.automotiveforums.com/t190250.html

"The carb is a M4MED... it does not have a mixture control solenoid. It has a
solenoid to control the accelerator pump discharge volume. When the engine is below 170 degrees (cold) the pump provides a full shot. When the engine is hot, the pump discharge volume is one-half.

I have the GM Factory Shop Manual which describes the carburetor in detail. It is not a California emissions vehicle..... definitely has the M4MED carb.... no mixture solenoid."

Then on Thirdgen.org:


Quote:
Originally Posted by blackandgoldl69
" 'It stumbles when you slam it from a dead stop when driving but if you ease into it for a second the slam it it will light the tires up and take off.'

Classic description of what happens when the accelerator pump linkage gets sloppy and out of adjustment. When it gets loose, it will give the pump shot too late after the throttle has been cracked open, and probably too little of a shot too. This is why it will bog - its leaning out badly when you snap the throttle open. Check the accelerator pump linkage, I'll bet it feels somewhat loose and sloppy. Tighten it up and I bet your problem is solved. All you need to do is just adjust all the slack out of it. Easy. "

I think I am getting close, just got to figure out what the hell this all means.