i have a 1971 buick skylark with the orginal 350-4 and a 4bb q-jet that has been rebuilt. the only problem im having is . well the darn thing wont stop black smoking @ full throttle. whats the deal? i leaned it out and im talking really leaned out to where i have to idle it up or else it stalls. i think its turned out 2 1/4 turns. any ideas on how i can help this problem?
I'm pretty much clueless on these things, but have you checked the choke? I had one that wouldn't open, causing black smoke, but only at idle.
ive checked the choke b4 and even disconnected it to see if it would stop black smoking and it didnt change a thing. and at idle there is no smoke. only when i floor it and the 4's open up does it black smoke
Since you mentioned that the unit had been recently rebuilt, is it possible that the metering rods for the secondaries were omitted? One other thing to consider; if the little sail plate on the air horn was not reinstalled, the secondary air valves will pull fuel directly from the float bowl when they open. This plate was installed on almost every Qjet after 1969, and actually prevented the secondary air valve opening, (actually, the leading edge) which is adjacent to the float bowl vent, from drawing fuel from the vent directly. I have actually seen this phenomena occur on a chassis dyno, and am aware of this plate's effectiveness. If your carb had one, and it was omitted, or if it is missing and could have one, I suggest checking for it. It is a plate, mounted on the air horn directly in front of the secondary air valves, using the two screws retaining the air horn. Let me know... Ray
By the way, since it is a full throttle problem, playing with your mixture screws will have absolutely no effect on it at all. Your mixture screws only affect your mixture at idle.
Actually, plugged jets will result in the same thing as a defective metering rod hanger cam, little or no fuel delivery at WOT. This will not result in black smoke, but a lean mixture. Did you check for the sail panel on these carbs as I suggested? Ray
Yes Ray I agree of course, about 15 minutes after I posted that I thought "wait a minute Mike everything you said was right EXCEPT the plugged jet part, WTF?" but I was already in bed by then. I guess that's what's called a brain cramp, I hoped no body would catch it but I guess there's no fooling you Buick guys :error: :laugh:
i might have found the problem BUT im not sure hey i was working on my carb the other day and i notice that when i floored it. the upper butterflys to let air in was not opening. am i missing some linkage? i also noticed on some pics that all of the skylarks of my mine had 2 plastic vacuum "things" that went on the carb. it looks like im missing 1 and i need to know what the part is called so i can replace it and give that a try. thanks for the help guys
Many people are unaware that the Q jet is a "demand" system, where the secondary throttles are mechanical, opening with the driver's foot. The secondary air valves, however, operate on demand, where the engine rpm and load open the valves. They may or may not open when the throttle is opened in Park or neutral. Depending on the set-up, there may be one or two vacuum diaphragms controlling the opening rate, depending on the vintage of the application. You can usually tell when they open on the road, making a unique sound like they intend to ingest the entire world, including the vehicle in front, and the hood. Make sure that the air valves are free to open, and that the metering rod hanger moves with the valves as well. Let me know... Ray
my qjet hey ray, i figured it all out. i had a carb spacer on it and the 4's were opening a lot sooner and sucking in. now that the spacer is off, it just seemed different. the carb is fine and im not having any more problems.i ditched the carb spacer bcuz my MPG really took a huge dump with it on lol. do you know a website that sells tbi. efi or any kind of fuel injection system for the 350 buick? thanks
To all, Unfortunately, spacers do some strange things. Also, bear in mind that since fuel is heavier than air, manifolding is a science, not magic. Any time changes are made, they should be made one at a time, noting the results. Spacers are typically magic, and do not always do what we expect. They are intended to make changes to fuel delivery, including distribution, reduction of reversion, etc and their usage is, to some degree, magic since we cannot predict the outcome, regardless of the research done in advance. I am pleased about the solution. I will do some research on the injection concept and get back to you. Ray
Ray, put me in line to receive that info too...I'm prepped to do a 4bbl intake swap on my 71J but waiting on linkage for the secondaries. Depending on the availability of a TPI for us Buickers, I may go that route. Wayne S
