I am helping a friend wake up a 235 chevy 6 that has 2 rochester 1bbls & split exhaust....don't know what cam is in it. I can get the truck to start if I prime it with ether or fuel...it will run OK but doesn't want to idle. I ckd the float lvl & that the carbs wern't gunked up, put good eth free fuel in it. I have changed the gastank, all the metal & rubber lines. the truck was done 15 years ago, driven for a while & parked outside for 8-10yrs ideas? I don't know much about these carbs, let alone 2.... I am guessing that the fuel pump may be making it hard to start, my bros nailhead did that & a fuel pump cured it.... I just hate throwing parts @ something thanks kevin
Two preliminary guestions...is at least one of the chokes operative, and is there heat on the bottom of the intake?
Maybe you could make up a SAFE gravity feed fuel system. See if keeps running. If it does then you may have the pump figured out.
no cables hooked up to the choke(s), tried closing them a bit b4 starting, no change.... heat under the intake? ummm it's an offy intake w/fenton split manifolds... it doesn't have any heat tube fm manifold to carb like my 65 riv does.... owner said it 'used' to start up cold just fine.....
did you clean the varnish out of the carbs 8-10 year old gas can sure do a number on the needle valuve and cause the float not to work right just a thought
I know what's wrong...almost guaranteed. Typical with the old Chevy sixes with Rochester 2-barrel carbs. Three things: The sealing surface at the base of the carb has a really REALLY narrow cross-section in places, and can easily cause a vacuum leak at the base of the carb. Check by spraying a little carb cleaner around there while the engine is running. If there's a vacuum leak, the engine will change rpms for a couple of seconds. Also: Both the phenolic spacer and the gasket have to be in good condition and in the proper orientation. There's a notch on both that has to line up with the tiny hole (about 1/16" diameter) in the bottom of the base of the carb. This hole is the source for the vacuum signal that allows the idle circuit to work properly. Also: The idle circuit vacuum hole (the tiny hole I referred to) goes way up into the body of the carb. If it's clogged, there'll be no vacuum there, and the engine won't idle. Take a piece of small wire and push it up in there to dislodge any crap, and spray some carb cleaner in there too. Then blow it out with compressed air. Do this 2 or 3 times to make sure you got it clean. I imagine that you may have tried to adjusted the fuel mixture screws to compensate for the bad idle...and now they're adjusted too rich. If you've done that, then once you fix the vacuum leak and/or the clogged idle circuit vacuum hole, be sure to check the plugs to make sure they're not all black and fuzzy, (fouled) and either clean them well or replace 'em. Then re-adjust the mixture screws. Chances are she'll now idle nicely. Good luck.
Btw... There are a couple other typical places that can cause a vacuum leak at the carb. If the carb has an automatic choke, (big round black thing on the side) there's a threaded fitting on the inlet meant for warm air intake to warm the choke and shut it off after the engine warms up. If there's no line on it, or at least something there to plug it, that'll be a vacuum leak. Or if the black plastic cover for the choke is missing or cracked, then it'll leak vacuum too. Or if the line is there but has a pin hole or a crack or the fittings aren't tight...vacuum leak. Again...check for leaks with the carb cleaner.
thanks for the info, but it has 2 rochester 1bbls.... I'll file the 2jet info for when I put on my 4 deuce offy manifold on a 331 chebby I replaced the fuel pump, re-cleaned the carbs & bead blasted & filed the plugs... it runs now but still doesn't really like to idle... one thing that I did notice is that there is no real way to adjust the idle speed...maybe a piece of linkage is missing fm the carbs(no suprise there, lots of stuff is cobbed on this rig)....?
2 carbs lowers the vacuum so then there is enough to work the power valve inside the carb. Find a weaker spring or cut one coil off the power valve spring to compensate for the low vacuum.
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