nsimmons

cars a mild 350, with a summit 1103 cam, non cc qjet rebuilt. Ive got about 200 miles on the engine so far and it cruises and drives great. Main and secondaries are working properly, but the stupid thing wont idle down after its been driven any distance (even a block).

choke and fast idle (2000rpm) are working properly, comes off fast idle when gas is pressed, chocke plate open. it idles pretty smooth at 800-850 rpm, 14 degrees advanced, mixture 2 turns out, 15" vacuum, distrib on ported vacuum.

I can play with it all day while in the driveway and the idle always comes back down immediatley, but when i drive it and let off it will hover around 1500, then slowly (after a couple minutes) come down to 1200-1000 and will sometimes, rarely drops back to 800. If i kill the car and fire it back up the idles fine.

Im having a hard time tuning the idle, it seems to need a lot of timing to smooth out, if not i have to crack the throttle blades which kicks in the vacuum advance, and if the rpms get much above 900 the mechanical advance comes on. Its a nasty circle.

Im also having trouble holding a stable idle when the cooling fan kicks on, the idle drops 300-400rpm. If i want it to idle at 800rpm when the fan kicks on i need to set it around 1200. Alternator is new.

It did infact fail emissions today with 4x too many idle hydrocarbons, but the other 4 tests were very clean

nsimmons

nevermind i think i fixed it..one of the boosters was dripping at idle, after fiddling with the mixture for 1/2 hour it seems to be ok now..

Apeiron

If it was dripping from the booster you may have a stuck float or dirty needle and seat. Playing with the mixture screws may have masked the problem, but probably didn't fix it.

nsimmons

i should of added i closed the throttle blades a fair amount while playing with the mixture. The float and needle should be fine since i just put them in a couple weeks ago.

I followed every idle tuning article ive come across and adjusted it for the highest rpm/vacuum possible, while reseting the idle back to 800. After maybe 5 adjustments i ended up backing the idle out about 3 turns. The rpms are holding pretty stable at 800, 15" vacuum, but it does smell too rich now, without the booster dripping (before it was a tad rich).

Im going to wire up an o2 sensor i have and see if i can get it to idle around 400mv, but it threw another alternator belt so im done tweaking till morning.

I never did find the belt, thats 2 in a week, doesnt like 6krpms i guess.

Apeiron

I wouldn't bother trying to use an O2 sensor to set the idle mixture. If you're tossing belts you might have a pulley alignment problem.

nsimmons

well after i tossed the first belt i checked and the alt pull was 3/8" too far foward. The cars a botch job by the previous owner. I trimmed the bracket and triple checked the alignment, everything is straight and looked fine. Im going to get 2 belts with teeth on the top, as ive read they are more resistant to beng tossed, and re route so the water pump has a backup belt. Plus my pair of nylons as a third backup until i can do a serpentine conversion in september.

Anyway back to the carb, the idle is really all i need to tune. The carb is performing better than i expected under all other conditions.

Do you have any suggestions for the idle mixture. Im much more used to tuning efi, hence the 02 sensor idea.

Apeiron

A vacuum gauge works pretty good, tune for maximum vacuum at minimum throttle opening at your desired idle speed.

Lordco has Dayco Top Cog belts, but they're probably not going to help if you have an underlying alignment problem.

nsimmons

thanks..i'll hit lordo tommorow..crappy tire doesnt carry them

Apeiron

Lordco is one of the things I miss about BC, there were some pretty good guys in the Kamloops and Kelowna stores. The guys at Mopac here are better than at the coast though, so I guess it evens out.

nsimmons

picked up a couple of top cogs from lordco today, 6000rpms 3 times and it held..hopefully.

but then the slave cylinder blew out so its dead again. I knew i should of just replaced it in the first place.