C3 rpm drop
07-31-2016, 12:18 AM
#1
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C3 rpm drop
Sorry guys, I'm re editing my post for better info.....
......my c3 is no longer cfi, switched over to an edelbrock 600cfi carb, & computer is no longer hooked up.........
Have another question for you guys, my small block 350, carb, has a comp cam with a 520 lift, all I know about it, the guy who built the engine keeps giving me a part number that comes up for a 396, idk, anyway, the vette idles at about 1000rpm, but when you drop it into reverse or drive it drops to about 250-300rpm, kid was over tonight & said its cause I have a stock converter, but if I install a stall converter I'll tear up my 700r4 trans, is this true about the tearing up the trans & the reason why the rpm drops off so much, I have checked for vacuum leaks, none, I have tried vac advance hooked up both ways, vacuum, & it does the same, stumped again
......my c3 is no longer cfi, switched over to an edelbrock 600cfi carb, & computer is no longer hooked up.........
Have another question for you guys, my small block 350, carb, has a comp cam with a 520 lift, all I know about it, the guy who built the engine keeps giving me a part number that comes up for a 396, idk, anyway, the vette idles at about 1000rpm, but when you drop it into reverse or drive it drops to about 250-300rpm, kid was over tonight & said its cause I have a stock converter, but if I install a stall converter I'll tear up my 700r4 trans, is this true about the tearing up the trans & the reason why the rpm drops off so much, I have checked for vacuum leaks, none, I have tried vac advance hooked up both ways, vacuum, & it does the same, stumped again
Last edited by Dano1982; 07-31-2016 at 09:04 AM. Reason: Not enough info
07-31-2016, 07:55 AM
#2
Drifting
yes, Big cam motors, not that .520 is lift s all that big,..do idle better with a higher stall converter... and if you still have the original 700r4 from 82 with the smaller input shaft, yes they are notoriously weak transmissions.. But, dropping from 1000 rpm down to 300rpm in gear is unusual . try increasing your initial timing to 12-14* and use ported vacuum source
07-31-2016, 08:52 AM
#3
Zen Vet Master Level VII
Double check your coolant sensor at the front of the engine. This gizmo tells the ECM that your engine is cool/warm/hot so it adjusts the idle accordingly. Yours may be faulty or going bad. They are in stock and pretty cheap at most parts stores. It will be different than the original so you will have to splice the wires (careful not to cross).
Bump up the timing to (at least) 12. Your engine will like it.
Our engines are super vacuum quirky so your Cam creates a variable... do you have a vacuum gauge with readings you can share? You need to be between 17-20ish AT IDLE.
07-31-2016, 09:00 AM
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I have a couple of things to consider as I had similar problems with my 82...
Double check your coolant sensor at the front of the engine. This gizmo tells the ECM that your engine is cool/warm/hot so it adjusts the idle accordingly. Yours may be faulty or going bad. They are in stock and pretty cheap at most parts stores. It will be different than the original so you will have to splice the wires (careful not to cross).
Bump up the timing to (at least) 12. Your engine will like it.
Our engines are super vacuum quirky so your Cam creates a variable... do you have a vacuum gauge with readings you can share? You need to be between 17-20ish AT IDLE.
Double check your coolant sensor at the front of the engine. This gizmo tells the ECM that your engine is cool/warm/hot so it adjusts the idle accordingly. Yours may be faulty or going bad. They are in stock and pretty cheap at most parts stores. It will be different than the original so you will have to splice the wires (careful not to cross).
Bump up the timing to (at least) 12. Your engine will like it.
Our engines are super vacuum quirky so your Cam creates a variable... do you have a vacuum gauge with readings you can share? You need to be between 17-20ish AT IDLE.
I'm no longer a cfi set up, I've converted over to carb setup, also pretty much I'm all mechical so no coolant sensor & I've disconnected my computer which also I'm wondering about the transmission converter lock up which I think the computer controlled, I don't understand the lockup part so if its locked up or not & if thats going to affect all this? Also the carb is edelbrock 600cfm electric choke, its new but that's no guarantee, if the secondary butterflies are not closing completely, as your noticing I'm not a mechanic, I know how to do somethings but don't understand a lot & why it works but I'm not a complete moron lol
07-31-2016, 09:41 AM
#5
Drifting
Your torque converter lock-up has no effect on idle. It only locks in 4th gear , and your carb secondaries are not your issue....you have a ported connection on the carb, use it for vac advance, increase initial timing to 12*-14* ..
08-01-2016, 06:38 AM
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Ok, I'll check it again but I'm pretty sure I've already got my timing at 14* & I've tried both vacuum ports on my carb for vac advance, 1 question about initial timing, what rpm do u want it at when u set ur timing, I can only find info for total timing
08-01-2016, 06:56 AM
#7
Drifting
set idle to 900 rpm in PARK.. adjust initial timing to 14* @ 900RPM with vacuum advance disconnected .. Use Vacuum Gauge and adjust idle mixture screws on carb to get highest vacuum reading at idle .reconnect vac adv
08-01-2016, 11:26 AM
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Thanks, I appreciate it, I was thinking 750 or so but I wasn't sure, thanks again
08-01-2016, 06:28 PM
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Drifting
08-01-2016, 08:32 PM
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Well no luck my man, got it timed & no changed, even got the Ole lady out to have her put it in gear & tried turning the distributor both ways, still doing it, pretty much only like 3 or 4 vacuum lines going to motor, plugged them off 1 by one to make sure I don't have a vacuum leak I'm not getting to, still no change, really stuck now ugh......
08-02-2016, 09:09 PM
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Well no luck my man, got it timed & no changed, even got the Ole lady out to have her put it in gear & tried turning the distributor both ways, still doing it, pretty much only like 3 or 4 vacuum lines going to motor, plugged them off 1 by one to make sure I don't have a vacuum leak I'm not getting to, still no change, really stuck now ugh......