Carb not delivering fuel on front rotor
12-15-08, 04:32 PM
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Carb not delivering fuel on front rotor
Hey I have a 1982 rx7 gsl. Engine ran fine with another carb, just hard to start. I'm installing a 79 carb that I rebuilt from a junk yard. Ok the problems im having are its idling at 2000 rpms. Its not delivering fuel into the front rotor unless I rev it up a little. Also, this morning when I went to work on it again the engine was flooded. I wanted to run what I'm planning to do by a couple of people. I think the high idle is the butterfly valves sticking. The fuel not delivering is a low float or a clogged valve, and the flooding is probably a slow leak from the bottom gasket. Any other suggestions? Thanks appreciate it.
Chris
Chris
12-15-08, 05:58 PM
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"Low" (leaky) float will cause a flood (needle stays open, bowl gets too full) as will a stuck-open needle, bad float adjustment, or binding float/needle.
I don't think there's any way the bottom gasket can cause a flood; it doesn't restrain fuel. Vacuum leaks, yes; flood, unlikely.
No fuel to front is probably a clogged primary jet, or a stuck-closed needle. I'd bet on the jet; sounds like you're only getting front-rotor fuel when the secondaries open up.
High idle could be sticky butterflies, misadjusted linkages or throttle cable too tight, stuck throttle opener or hot-start assist, or bad base idle screw adjustment, or a couple other things.
79 S and 82 GSL carbs have some differences between them, as do manual- and auto-intended carbs.
I don't think there's any way the bottom gasket can cause a flood; it doesn't restrain fuel. Vacuum leaks, yes; flood, unlikely.
No fuel to front is probably a clogged primary jet, or a stuck-closed needle. I'd bet on the jet; sounds like you're only getting front-rotor fuel when the secondaries open up.
High idle could be sticky butterflies, misadjusted linkages or throttle cable too tight, stuck throttle opener or hot-start assist, or bad base idle screw adjustment, or a couple other things.
79 S and 82 GSL carbs have some differences between them, as do manual- and auto-intended carbs.
12-16-08, 02:24 PM
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High idle is most likely due to a vacuum leak, unless your throttle cable to too tight.
Lack of fuel to the front is most likely a clogged something or other. If a can of Seafoam through the tank doesn't clear it up, you'll probably have to rebuild the carb.
Lack of fuel to the front is most likely a clogged something or other. If a can of Seafoam through the tank doesn't clear it up, you'll probably have to rebuild the carb.
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12-17-08, 07:39 AM
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Your idle trouble may be attributed to trying to use a 79 carb on an 82 manifold. (Keep the spacer/heatshield with the carb.) This is not to say there aren't other reasons for your high idle, but since you've rebuilt it a few times, I would check out the spacer deally. Air horn assemblies are interchangeable, so long as emissions crap has been properly removed & blocked. So if you want to check to see if it's the floats & delivery section or the main body being clogged somewhere, swap it out with a known good one. If none of those combos work, it could be the throttle body (butterfly valves) binding.
Flooding like that is either stuck floats like everyone says, or your Float Bowl Solenoid is stuck or unplugged. Funny lil' bastard can confuse the hell out of people because it causes flooding after shut-off, and it can cause a vapor-lock no fuel situation at high fuel demand.
You say you have no fuel going to a rotor at part throttle, but you see it when you manually operate the carb to full throttle?
That's less likely a float level issue if you've rebuilt it, though I would certainly check the level, but it would have to be not binding, and just set really, really low, with very little drop set.
I think you may have dirt in your primary front emulsion tube. Emulsion tube blockages can be tricky because if there is a partial blockage above the midpoint of the booster venturi, it will simulate a smaller air bleed, which will mean more fuel at lower air velocity. But if there is a blockage down near the fuel level (fuel varnish, debris...) then it's constricting the fuel flow. But then, if there's debris only all the way at the bottom of it, it will behave fine.
For probing & cleaning such jets, I use the clippings from new guitar & bass strings, with some of the outside winding removed. Drill bits that are small enough in diameter are rarely long enough to reach the bottom of emulsion tubes and transition air bleed jets.
But if you have the other carb, the easiest thing would be just to swap out the jets.
A trick for getting the idle to calm down is to replace the primary idle step jets (the outer most jets under the airhorn at the primary edge of the carb) with the .60 secondary idle step jets from another carb. The primary idle step jets range from 1.5mm to 1.9 mm, but all the 79-85 Nikkis have .60mm secondary idle step jets. -They are the nickel plated jets.
This is a band-aid fix that can help you track down trouble, and in some cases even seem to fix the symptoms entirely, but there's still something wrong somewhere. It won't harm anything to leave them in, though when you do finally discover whatever the problem is, it's likely you won't have control enough using the screw to optimize your idle mixture with the .60s in place.
Good luck.
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