Been chasing this problem with no success. car cruises okay but when I press down to GO it results in a sudden hard bog that only resolves when I let off the gas. I replaced accelerator pump seal and checked secondary adjustment on my Q Jet assuming that was the culprit but that has not solved the problem. Timing is correct, fuel pump, fuel filter and plugs have been replaced, points look okay. Any ideas where to look next.

 

Take a look at the mechanical advance. Make sure it's free and not stuck.

 

checked that as well as rotor and cap condition. all looks good. Mechanical advance free and moving.

 

First off, I had my carb seviced by Lars so I know there wasnt any underling problems with it I had to deal with, so getting him to rebuild yours is a good idea if it hasnt been touched in years
Luckily I put in an Air/fuel meter in my 68 for this reason and it told me my bog was lean. If you creep up on WOT does it bog?. Mine wouldnt bog if I pressed the throttle to the floor over a second or 2 but if I just slammed it to the floor it would bog , then take off. My problem was the secondary air vavle was slamming open. There is an allen set screw and a flat head adjustment screw on the passenger side that controls how fast the flap can open. You can try that. I'll try and find the post that talks about it........ here it is.


borrowed from Ricks Garage over at the HAMB jalopyjounal
"With the engine warmed up and the choke open, idling, take off the air cleaner and push on the secondary air valve. It should open with some resistance then snap closed. If it opens easily it needs to be adjusted. Shut off the engine. Under the right side of the air valve arm is an allen head screw and a small screw driver slot. Holding the screw driver in place slowly back off the allen screw, tighten 1/4 turn (to start) on the screwdriver (you will feel tension), hold it in place and tighten the allen screw. Drive it....reset as necessary...9 times out of 10 it is too loose...There are other things that can be done to a quad to make it run strong."
https://www.jalopyjournal.com/forum/...t-help.810151/ post number 11

 

I had the same thing, and rebuilt the carb and still had it, finally solved it
went thru the timing and followed LARS papers and all fixed

 

Had my q jet rebuilt about 6 months ago and it was operating fine. then it started to develop a bog situation. I was advised by those in the know that it could be my accelerator pump seal so i replaced that (the old was fine) and I also adjusted the secondary secondary air valve as well, no change. I dont really stomp the pedal all I have to do in press part way to suddenly accelerate and it bogs. It still bogs when I creep up on it but its not as forceful a reaction. If I accelerate gradually its usually okay but I have noticed if i get up to the 3000 rpm range it starts to stumble a bit at times but not always. I know most information seems to indicate fuel related or timing issues. since I have checked out everything I can think of on that end I am wondering if its not something else mechanically related Valves or something?

 

Where can I check out Lars papers?

 

Sounds like you've done the most logical items, so next I would suspect a fuel supply problem.

how is the float level? Maybe it's high enough for primaries but too low to supply the secondaries.
fuel pump delivering enough fuel? Filter plugged?
something along those lines maybe.

 

which engine 327 or 427?
from a just closed position how much of an additional turn did you adjust the secondary air valve screw?
with the engine off looking down the primaries when you open the throttle fast and slow do you get a good shot of gasoline?
do you have the vertical arm from the carb linkage in the hole in the accelerator pump arm closest to the body of the carburetor?

 

checked the output of the fuel pump, replaced the fuel filter, checked for restricted fuel lines. i also have an external fuel pump attached which Ive kicked on during the bog to assure enough fuel/pressure is reaching the carb but no luck. Dont know how to check the float level with out tearing the carb apart. Often its suggested that something such timing or something else was set wrong but I always figure if it was working OK prior and suddenly it starts having an issue then something has changed to cause the problem not a pre existing setting.

 

Email Lars at V8fastcars@msn.com with a description of your problem and he will email you the appropriate papers.

Here's a photo of the adjustment of the air valve that Rescue Rogers mentioned.

 

327 Is my motor, I have adjusted the secondary air valve 3 times just to be sure. twice with 3/4 turn in from when the flap just closes then another time added an extra 1/4 turn in to see if it made any difference which it did not. Good shot of fuel is seen on the primaries , The vertical arm is attached to the accelerator pump lever.

 

Is your choke operating freely, and can you get the secondaries to open with the engine off and hot by moving the throttle. I'm wondering if the choke pulloff isnt pulling far enough or the secondaries is being held shut by the little open prevention lever at the bottom.

 

I'll have to give that a look.