I recently scored a well used bone stock 1976 800 CFM Quadrajet (#17056240) on E-bay. Pulled my first mistake (a 600 CFM Holley!) and slapped the 800 on my stock 69 Electra as shipped. Runs well on the primary side at idle and around town, but under load at 3000 + RPM or WOT at 50 + MPH it stutters and bogs. Think I need to rebuild at least. Can anyone recommend any jet, metering rod, or power piston (???) changes that will get me a bit more UMMPH out of this carb? I can't imagine this carb being originally built in 1976 for the kind of performance which they intended in the 69 430, but who knows. Also interested in any other relatively easy mod's I can (or need to) do to this carb while it's apart that will help. Motor is stock for now, but will soon have a mild cam, fresh heads, and duals. Thanks!
I think a 76 carb is going to be lean especially on the secondary side. I would first try replacing the secondary rods with something alot richer. That may in fact solve your problem since it seems like the carb runs OK on the primary side, but falters when the secondary barells come on. Changing the secondary rods is easy, and worth a shot before pulling the carb apart. I have BG rods in my 800. Take a look at which ones are in your carb now. Bet you they are really thick tipped. BTW, 1975 and up carbs beginning with the numbers 170----- have primary metering rods that are .080" shorter than previous year carbs with numbers 70---- You cannot interchange the two.
The secondaries could be lean, pull out the secondary metering rods they should taper down to a fine tip, if they stay fat to the bottom then they should be replaced with a thinner rod, they are interchangable on all Q-jets (unlike the primaries as Larry pointed out). If they are already the thin metering rods then your fuel pump may not be able to keep up. Q-jets have a very small fuel bowl and very easy to run them out of fuel. The Holley has double the fuel capacity and could cover a weak fuel pump. You can tee in a fuel pressure gauge while driving it should maintain at least 3 pounds during a wide open run. I don't think the carb needs any mods on a mild engine like yours except for tuning the secondary opening spring.
Thanks for the responses. I'll be getting into the guts of the carb probably next week. I've noticed intermittent variations in how the motor runs as I've driven more with the new carb and I suspect some minor leaks in vacuum and possibly fuel to be one of the causes. Looks like both primary and secondary choke pull offs are solid and functioning but I think it needs a refurbishment on the gaskets and a good cleaning. I can look further into changing the secondary metering rods and spring once I get that done.
Something to note on the carb is the condition of the cam driving the secondary metering rods. These carbs tend to eat this plastic camm creating a situation where the air valves open, but the metering rods do not move. Try this: with the engine not running, open the secondary air valves, noting the movement of the metering rods. If they move very little, or not at all, the cam will require replacement.
Well I finally had the carb rebuilt by a local carb only shop. He did a great job. Ended up with a new primary choke pull off, new float level, and 71 jets, 45 rods, DL code - using the specs from 69 GS 4-speed if I remember correctly. I already forgot how to read what he put on the receipt but I get great idle and have converted (for now) to a hot air choke with retrofitted manifold pick up tube which seems to work well. I STILL have the bog/stutter problem at wide open throttle under load 3000 RPM's. I've checked the inline fuel filter and have a brand new filter in the carb housing. I'm convinced it's a fuel delivery problem. Is there an easy effective way to check the state of the lines between the gas tank and fuel pump? How about the fuel pump itself? At idle and revving the motor at stand still the glass inline fuel filter stays full of gas, but I'm not sure about under load. Which direction should I go with my troubleshooting? Am I missing something? Also, I understood from reading here that Buick vacuum advance ALWAYS connects to full manifold vacuum at the carb as opposed to ported or timed vacuum. The carb shop admitted little experience with Buicks but believed it to be the other way around. Any further help appreciated.
Most cars 70 and up connect distributor vacuum advance to ported or timed vacuum, including Buick. Some late 60's used full manifold vacuum. It's really a personal preference here, some guys will tell you full manifold vacuum is the way to go, others feel their car just runs better with ported. I like full manifold vacuum, a cammed V8 loves the extra advance at idle, and off idle. Either way, you won't have vacuum advance at wide open throttle, as the vacuum will drop towards 0 with the engine under heavy load at wide throttle openings. That brings me to my next question. Have you optimized your mechanical advance? Do you know what your total timing is, and at what RPM it's all in at? This can make such a difference. You wouldn't believe. Try reading this thread. http://www.v8buick.com/showthread.php?t=58598&highlight=total+advance
