It's got a problem where it bogs down and has no power once the secondaries open at WOT in 2nd and 3rd. It's fine in first, where it has the most torque multiplication. With the primaries it's fine and acts normal, but once it opens the secondaries, it just revs down/engine brakes like the throttle is closed until I back off the throttle and let the secondaries close.


I've already cleaned the fuel filter, it's got a serviceable inline filter and have removed the in-carb filter. Didn't help. Flow into the filter does look a little low at idle, but it runs normal until about 3500 where the secondaries open.


Could it be a clogged jet in the secondary side, or maybe a restricted line in before the filter? Thanks

 

What carburetor are we talking about here?

 

Electronic quadrajet, factory equipment on a stock 305.

 

4bbl carb? - could be a few things and they arent particularly easy to find without taking the carb apart.

Common - air doors opening too early causing a bog - if you havent touched them then chances are this isnt it, google how to adjust them if you want to.

Pump could be on its way out.

Less common but still common- theres 2 tubes that feed the secondaries on the secondary side of the metering rods. Occasionally these things rattle loose as theyre sort of pressed/banged into the housing. if they do that they they sit flush on the bottom of the casting and dribble tiny amounts of fuel as opposed to letting it run freely into the secondaries. Not enough fuel means not enough power and therefore not enough demand for air to keep to doors open. if you have 1 dropped out which is quite possible they will still open for a bit, if both of them have dropped then you dont have a snowballs chance in hell of getting those secondaries to open.

sadly that last one requires a disassembly, some epoxy and a rebuild kit. a few hours of your time and probably $40 bucks for the kit will do it.

Happy Hunting

 

FYI - im rebuilding a quad now that has this exact problem

 

OK, are you getting any black smoke out the exhaust when this happens? If so that would suggest a too rich condition. If not, it's probably running too lean; you running a mechanical pump or an electrical? I'd suggest hooking up a fuel pressure gauge with a long enough hose to watch it while driving to see if it's not getting enough fuel pressure during wide open throttle.

 

I should also add that I built a pretty hot small block 350 many years ago that would run the fuel bowl on a quadrajet dry before getting through the quarter mile; swapped to a Holley and problem solved.

 

Nope, don't think I have any black smoke. I usually look forward while accelerating but I don't recall ever noticing it. Revving at idle enough to open them doesn't produce black smoke. It does have slightly richer metering rods and a richer chip in the ecu but no black smoke. The timing is advanced a bit for the richer mix.


It has the original pump as far as I know, so that's not unlikely to be it. As I said before, it's working properly in first gear at WOT since that's less load, so it's gotta be something related to the amount of fuel it can deliver, not the doors not opening. I've also taken the metering rods out and sprayed a little carb cleaner down their holes, but that didn't help much either.


The motor is completely stock minus a double roller timing chain, so it shouldn't be able to overwhelm the float bowl's capacity and the system's ability to fill it.

 

i dont think ive ever seen the doors open revving at idle, i thought they only opened when the car was under decent load

 

Yep, they can open with the car in park as long as there is enough air flow, but opening too soon would cause a very noticeable bog with out any black smoke.

 

and like i said, if there isnt enough fuel/power and therefore vacuum the doors wont open.

Fuel can get blocked in a few places

Tank strainer (or in tank pump), inline filter, in carb filter (the little paper spring one), accellerator pump dying (carb rebuild time), float malfunction, Metering rods too far in, secondary feed tubes


Start from the back of the car then work your way to the front

 

just a thought, push down on the doors and make sure that the cam is pulling up the metering rods. is there any excess wear on it?

 

99.999% of the time, this symptom is caused by poor fuel delivery.

The other .001% of the time, it's caused by not enough fuel being delivered to the carb.

What it happening is, when the car sits there idling or cruising at very light load, the engine's fuel demands are low, and the fuel system (pump, filters, lines, etc.) can send enough fuel to the carb to keep everything going. But then when load increases (WOT) and RPM increases and the fuel demands of the engine go to some MULTIPLE of what they were before, the fuel bowl in the carb simply gets drained dry, because the engine is taking it out faster than the fuel system can keep it refilled. It's not about "gear"; rather, it's about the TIME that the load has existed for. In a given car with this problem it might take 10 seconds (top of 3rd gear or some such), 4 seconds (middle of 2nd), or some other LENGTH OF TIME for the carb to just basically run out of gas.

The ACTUAL PROBLEM is almost always one or more of these. Start with the easy one, which is, the little one in the fuel inlet nut of the carb. Work your way up to the harder ones to get to.

I would add to that list, the pickup in the tank being filled with the crusties that accumulate from fuel drying out. If the car has EVER sat for more than a couple of years, and had fuel in the tank during that time, the solution may be to take the pickup out and rod it out with a coat hanger or something.

Another really obscure cause is, if somebody has hacked the smog pump off the car and removed the bracket (pass side of the engine down low), and put a bolt into the upper one of the 2 holes to prevent the oil leak as it is essential to do, then if that bolt is too long, it may be preventing the fuel pump rod from moving freely. The eccentric on the cam pushes the rod down which creates the "suck" stroke of the pump, then the pump's internal return spring must BOTH "blow" the gas up to the carb, AND push the rod back up into the block. If that bolt hits the rod then then the pump might only be able to complete a VERY short stroke before the spring simply can't move the rod any further against the friction.

The problem IS NOT the carb itself, with the possible but extremely unlikely exception of trash stuck in the needle valve. Leave the carb alone and work on the fuel system FIRST.

 

Have you always had this problem or did it just start? Zed-028 is correct, with the engine off, check your top air doors on the secondaries by pressing down on the rear of them, make sure the cam works and they move smoothly, I cant tell you how many times they will get stuck in the closed position, this test only works with the engine off, it its running you cant open them due to a vacuum diaphragm that will be holding the doors shut. you can also adjust the spring tension, very easy but also easy to mess up as ZED-028 said as well. after these small checks let us know how everything checks out!