At a wall with my Q-Jet

I suggest first plugging the vacuum advance off completely, and check for the surge. That eliminates the vacuum advance over-advancing the timing. Is the engine performance smooth at idle? 17" is low for a stock engine, and I suggext confirming the vacuum at idle. What happens off-idle besides the surge? Does the vacuum come up? Are all eight firing? If not, which are not? Knowing which are not, if so will help. Let's keep it simple and focused. Ray

 

Ray, I blocked off the advance completely and the issue was still around. After taking another vacuum reading, with everything hooked in as before, nothing blocked off it pulls about 20"....must not have been fully warmed up as I thought before. I'll hook the gauge up and drive it tomorrow and take note of the vacuum readings. As far as things firing on all 8, I have checked everything and the car is getting good spark, even when the thing started running like crap. I have noticed that the gasket between the throttle plate and the body is wet after the car has been run, do you think the main wells could be leaking after the car warms up which is causing the problem?

Thanks again everyone for all of the replies, I will not be beaten by this thing.

 

Ross I had the same problem with my Riv , I ended up putting a glass filter between the carb and the fuel pump and as the car warmed up during city driving I could see it fill with air get it out on the exspressway for a few minutes and it would clear up , ended up running braided hose from pump to tank that cured it I'm not sure if this helps , but I think putting in the clear fuel filter may answer some questions

 

there is also a rubber fuel line connection around the passengers door/fender area in the main fuel line that may need to be replaced if your tank connections were bad also. i would check the entire run also for dents and other damage. good luck

 

Thanks, I have one hanging around somewhere I'll throw it in and see what happens.

 

well, after putting a length of clear hose to the carb and running the car until the issue reared it's ugly head I noticed some bubbles in the line. I only noticed the bubbles after I shut the car off and started to wiggle the line from the pump to the carb. They started off really small then got bigger. So it looks like I have some rubber line replacement ahead of me.

 

Doubled up main body to airhorn gaskets and still seeing fuel leaking indicates there is enough warpage between the parts that they aren't effectively sealed up.

It will help to flatten the airhorn, and upwarp the main body, but a good effective seal between those parts is required.

The surging at light part throttle indicates a lean condition, since you've covered the potential of too much timing.

There is no need for a such a quick advance curve, but it's probably not causing the problems.

From what I've seen here, light springs will often allow some timing to come in at idle speed, and the engine rpm's drop considerably when a load is placed on the engine.

Blocking off the heat crossovers on a stock engine is a complete waste of time, and only causes long warm-ups, and the choke isn't going to work (divorced or hot air). The parts eventually heat soak anyhow, and a slightly richer calibration will be required as the fuel will not atomize as well on it's way to the cylinders.

Get rid of any and all rubber fuel line on the pressure side of the fuel pump. It soaks up heat, and a good way to burn your car to the ground if a hose develops a leak. If you MUST use rubber hose, make sure the steel lines have a "bump" in them so the hoses don't pull off of them.

We sell 1/4" thick gaskets to go between the carb and intake, they make great spacers and insulators as well, but I don't think that this is your problem......Cliff

 

I second Cliff's contentions all the way. IF the issues are not caused by timing advances, they can be determined simply. Disconnect the vacuum advance and plug the hose. Next, retard the intial timing some 6 deg, and drive the car. I suspect, as Cliff does, that the issues stem from lean mixtures, either from vacuum leaks or lean calibrations. It is likley that the carb has a mixture of calibration parts, or is from an incompatible application. If the engine will carry itself through first gear at WOT, the issue is not one of fuel starvation in the bowl. The fuel flow off-idle is not sufficient to drain the bowl, but if it was, the empty bowl would be proof. I suspect the bubbles are the result of this crap we call fuel and the underhood temps caused by heat soaking. Something to check here is power piston movement, as Q-jets are infamous for sticking power pistons. I have fixed my share of sticking power pistons, not only during overhauls, but also during simple open carb surgery.
First, determine the cause of the problem using very simple checks, then, after determining the cause, address it directly. All of the guys writing in have no direct contact with your vehicle. Though all writing in want to help you solve the problem, they cannot offer any more than recommendations, and suggestions. I have no problem offering advise regarding testing, solutions, and answers, but without test results, we are all shooting in the dark. If the bowl is nearly full when the surging begins, it is either vacuum leaks or calibration. I hope this helps, but please realize that it frustrates us as much as it does you when we cannot help. I know it frustrates me. Ray

 

Thanks Ray. I'm gonna be busy the next few days so I won't be getting much work done with it for a bit but I'll keep you guys posted. Again, thanks for all of the advice.:beers2:

 

Throw a new coil in it for grins and see what happens. Also, if the dwell is off, you will get the same issues. Very rarely will a carb problem cause a buck/stutter/surge unless there is gas pouring out of it all over the engine(bad). There are virtually no moving parts in a carb besides the throttle plates, the float, and the accelerator pump. Maybe if the carb is starving for fuel, but that is not the carbs fault. I would take a serious look at your ignition system. If the problem occurs after the engine is warm, light to medium load, 3rd gear cruise, I would want to bet on an ignition system fault. Check your distributor for side-to-side movement...there should be none, and any that is there will throw dwell way off(provided you are running a point distributor). A bad capacitor(condensor) can cause issues too.

 

Twice You've Said That The Carb Gasket Between The Body And Throttle Plate Was Wet. Try This... Remove Carb And Remove Throttle Plate From Body. There Are Two Metal Caps That Are Peened Over. They Like To Leak And Will Add More Gas Especially At Idle When Vacuum Is Highest. If It Has'nt Been Done Already, Mix Some Two Part Epoxy And Completely Cover Them. Be Careful Not To Add So Much Epoxy That The Body Will Not Fit Back On The Base. This Is A Common Q-jet Concern. Rebuild Kits Give You A Little Black Sponge To Put In That Well. Once Epoxy Is Applied Leave The Sponge Out. Use New Gasket When Reassemling.

 

Here is a picture of what it looks like with the proper epoxy fix.
http://www.v8buick.com/attachment.php?attachmentid=150683&d=1254617123


John

 

I hate to create issues in the forum, but I beg to differ with those thinking that the Qjet has few moving parts. The most critical, and the most troublesome part in the carb is the one overlooked by Buick Rat. That is the power piston. Due to issues with its exposure to manifold vacuum, This component tends to stick, causing metering rod issues in the jets. If the power piston sticks, engine load will not affect metering rod position and movement, causing the very issues encountered by this individual. I have fixed too many of these very problems in GM dealerships with power piston repair. As a matter of fact, GM had its share of tech bulletins describing the very issues discussed here. Heads up guys. BTW, power piston issues can frequently be determined with the air cleaner off, and the engine off. Using a chemical can straw, carefully attempt to move the power piston in its bore, feeling its performance. If it sticks, it needs to be addressed regardless of its contribution to the problem addressed by the original poster. Good luck... Ray

 

Ray, you are definitely correct about the power piston. The point of my post was to get him to try looking elsewhere for any other issues. Many people condemn carbs first, and usually it turns out to be something different. Yes, I also know there are metering rods that move and spring adjustments, but in my experience, those are rarer issues than ignition problems. Only when I have verified that everything else is good and in spec will I look at the carb as a possible culprit.

 

I see where you guys are coming from, having not too much experience with these things aside from a few rebuilds, all of this information is useful in my book. I'll go through and recheck some things with the ignition and what not to make sure there are no issues there and see if anything improves. Thanks again.:beer

 

The suggestions regarding the metering issues result from my assumption that ignition issues have already been addressed. From a troubleshooting standpoint, ignition issues far outstrip fuel and carb issues. My sexpeience indicates that there are some 5-8 as many ignition issues to carb issues. MOST of the time they are spark plug wire issues, as the required voltage to fire a plug under a load rise very quickly as the trans upshifts. Though they are more prevalent in the late model vehicles due to aggressive trans programming, my experience indicates that ignition issues far outweigh carb issues. You might try listening at the exhaust for intermittent misses, especially under a slight load. This can be done, for example, setting the choke or high idlecam on the carb and having someone put the trans in gear, holding the brake. You can then, if a miss is encountered, pull one plug wire off at a time. If the intermittent miss becomes a steady one, with no other intermittent miss present, you can assume that that wire may have issues. Or, since they are relatively inexpensive, simply install a fresh set of plugs and wires, carefully observing the firing order. If you have doubts, check a manual, or I can. From a spark plug standpoint, point ignitions were relatively intolerant of fouled plugs, and even the slightest unsuspecting spot on a plug created a miss. That spot could have been caused by a choke issue, or a flooding issue; either way, replacement was frequently the only solution.
My concern here is that we are throwing parts at a problem, and the more work we do, the higher the chance of something either being over-looked or created. These issues are why I always had an ignition scope, allowing me to observe the activity in the engine, including the plugs.
In conclusion, I agree with the concept that ignition issues far out-weigh fuel when sourcing problems. In that light, plugs and wires might be a good place to start, especially with winter, with its cold and wet weather issues approaching.
With respect to that, an easy and quick troubleshooting tip for checking wire issues was to allow the engine to idle in park, and using a spray bottle filled with water, spray around the cap and wires, all the way to the cylinder head, looking for the tell-tale miss, or even a few cool sparks. Ray

 

Well, I pulled the cap and rotor off to inspect some things on the distributor and while I was fiddling around with things noticed that the breaker plate had more play than I remember, moves up and down a little bit and side to side more than before. On top of that I noticed that if I bump the motor over enough to just get one of the lobes to the point where it would open the points and rotate the shaft by hand a bit it doesn't open the points but rather moves the breaker plate and the points don't open (I remember doing this before and it would open the points no problem without moving the whole breaker plate). If I hold the plate so it doesnt move the points do open but barely. There is spark at the plugs so I'm a little confused how this is possible if the points aren't opening. Any ideas on what to tackle next? New breaker plate maybe?

 

Finally got it working. Turns out the points were way out of whack. Got them adjusted properly and the thing never missed a beat. Thanks again for all of your input, I'm no ace mechanic and appreciate all the help.:beers2:

 

Have you solved your Q-jet problem . I was cleaning my garage and came across my Q-jet it was rebuilt 3 or 4 years ago by the carb shop in west allis my brother was using it last summer , he told me it works great no problems , I'm not trying to sell it I'm just asking if you would like to try it to see if it solves your problem , I live in Greenfield not to far to drive.