OK, put a 4 bbl carb on my 68 skylark. Ran, but real rough after the install. The quadrajet is a number correct for the year. I read all the hints and stuff I could find. Found the timing to be off by 3 degrees. Corrected it. Found the dwell off by 5 degree's. Corrected it. Car runs like crap. Jump on the pedal, and it bogs down, gets better if you hold the pedal down and rpms build up. Ignition system seems to be fine. It was launching hard but idling like junk, so I decided the carb was out of tune. Started trying to tune it. Now it launches and bogs, if you go soft on the peddle it goes better but bogs down when you go past half throttle. Checked for vacuum leak, found one and fixed it. Still runs like crap. I have 15lbs of vacuum at idle and it roars up to 25 when you get in it. Car can be tuned to run nice with the aircleaner off, but put it back on and everything goes to hell. I have to restart the whole tuning process to get it back right. I am out of idea's. The 4mv Carb wants 4 turns out from all the way in on the idle screws to run correct, 4 and a quarter is even better, but once I put the air cleaner back on, it all goes to hell. Any suggestions? The air filter is new, and I have removed the vacuum lines on the air cleaner from the equation. The butterfly in the air cleaner is wide open. BTW it smells rich once I take it around the block trying to jump on it.
I put a spacer on it to get it away from the carb, as the air cleaner is a newer variety. Don't think it is too close, as the spacer takes the air cleaner 1/2 inch away from the top of the carb.
Well, if it were me. I would start by trying a different air cleaner top with more room over the center of the carb.. 1/2 inch doesn't seem like enough, just to test that equation... and tune it with vacuum gauge to the highest steady vacuum on the dial...
Was the carb recently rebuilt? Could be a faulty accelerator pump. Specifically the neoprene plunger. Some of the older kits have pump plungers that will swell when they come into contact with today gas with ethanol added. That may create your bog.
OK, thanks for the tips. Found that the spacer was hitting a rod on the choke, causing the secondaries to not open. Fixed that. Retimed using my ear instead of a light, timed it to where I got the highest idle, highest vacuum and runs and starts real smooth. I hade to buy an aftermarket timing cover, which came with an aftermarket timing scale, so I do not trust it. When I put the timing to zero using the marks, the engine will not run worth a darn. Hard idle, no vacuum (less than 15lbs). After doing all that I took the car out, it accelerates better, but still bogs down under hard acceleration. Going to recheck the dwell tomorrow. Would improper dwell cause this?
Sounds like your secondary air valve is possibly opening too soon. Check the spring tension. Somewhere around here is a chart, but I'm too lazy to look. I've had a long 3 weeks at work, missing some sleep.
Four turns out of the idle mix screws is a bit much. You may have another vacuum leak somewhere leaning out your mix. When you have it warm & idling, try holding your hand over the choke flap on the primary barrels. If the idle smooths out & RPMs go up, then you're running too lean. Check your rod/jet size on the primary metering, and increase the area by 10% (larger jets and/or smaller rods). Some carbs also have the hot-idle compensator in the back, and if that's opening too soon it will also lean out your mix. Did your Q-jet get new bushings on the primary throttle shaft? If not, you could have a bad vacuum leak there. Spray carb cleaner on the throttle linkage while the engine is at idle, and see if you get an RPM increase. If so, no amount of tuning will fix that leak. You'll need to take the carb off and install the bushing fix. I learned this, myself, after trying tons of different things to no avail.
I bought the carb from Holley as a rebuild. Gonna try that as My dwell is still 30 degrees and the car runs awsome cold or hot under mild throttle kick, and starts choking at full throttle. Maybe it is the fact that no kickdown cable is hooked up? Drives well enough I am driving it to the car show in Salina Kansas this weekend, but will be easy on the throttle. Still looking for the grommets and peddle to go with a kickdown cable. Another member opened my eyes to the fact that in 68 the kickdown is connected to the pedal. Mine is currently not connected.
I've had bad luck with Holley re-manufactured Q-Jets. When I had a fresh block put in my 1980 G20 Chevy Van 10 years ago, the carb which the engine builder selected was a brand-new Holley Q-Jet, and it never ran right. Idled like crap and bogged down all the time. Eventually, it got junked & replaced last year when it failed smog and the shop replaced it with another no-name factory brand. It also runs badly, but not as bad as the Holley. I still need to keep my van smog-compliant out here in CA, otherwise I'd slap on my own correct Q-Jet. Smog tests are all run on a dyno out here, and they are really trying hard to fail older vehicles like mine.
I do not have to worry about the inspections here. What I am currently thinking is it might be ignition related. I need a double pulley on my alternator, and it squeals real bad when I start up. Upon close inspection, I found I had the same problem as another member, where my belt is slipping because it is too wide for the pulley. I do not have time to fix it before the show, but am wondering if maybe the belt slips under heavy acceleration and I do not hear it because the quad makes a real loud noise. (which I like by the way, a real loud WAAAAAAAA) and maybe the points are not getting enough electricity? My dwell was still 30 degree's and that is not the problem. Currently have the car car running at 2 3/4 turn out on both carb screws, will see how it keeps up on the highway tommorrow. Gets to 55 real quick if I do not lay 100% into the throttle. Also, the fuel pump is the correct one for a 2bbl. Is it different for a 4 bbl? Question keep coming to mind and I am trying to chase them down. I am gonna say bad carb is last resort. Has a one year warranty, so I have some time before I return it and say send me another one.
