434 SBC idle problem
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Re: 434 SBC idle problem
more initial timing. I run 20 and did same thing with idle mixtures set at highest vac. 1/4 turn richer all round fixed mine
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Re: 434 SBC idle problem
Yeah, I don't think 16* is going to cut it, buddy. If you don't want to lock it out, see how it behaves with the initial cranked up to 25* (don't load the engine up like that because your total will be off the charts) and let the fans cycle. That should help give you a better starting point.
Shawn
Shawn
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Re: 434 SBC idle problem
Maybe I'm not clear, the engine is running great at idle right now. When the fan comes on it seems to cause a short or something else with the ignition system, because, it starts to die out. I increase the idle with the idle screw (front butterfly) to keep it running while the fan is on, but when the fan turns off the idle goes back up. So I am chasing a electrical problem. Yes if I lock it out the idle will go down when the fan comes on. I have set the distributor. at 36 deg. and same thing. So is it alternator, electric fan or MSD box?
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Re: 434 SBC idle problem
I see. I've had some with "just" barely enough initial advance for the cam and the smallest amount of load would send it into the downward spiral so that's where my thinking was.
Are those fans run through relays with direct battery access?
Shawn
Are those fans run through relays with direct battery access?
Shawn
Live in such a way that those who know you but don't know God will come to know God because they know you.
Re: 434 SBC idle problem
Lock out the mechanical advance, set the timing to 36 degrees or so to start, and get something to pull some timing out (MSD programmable or similar) when you're cranking the engine. Or just leave the ignition switch off when cranking the engine and then turn the switch on when you get it whizzing over. Everyone on here is telling you correctly about that.
Re: 434 SBC idle problem
rickyracer wrote:OK guys I have got a new issue I set the rockers @ 20 thous I changed the mechanical advance springs (med and Heavy) bypassed the timing retard. It idles good until it warms up and the electric fan turns on, that is when the idle drops. I than screw in the idle set screw, when the fan turns off the idle goes up again. I am wondering if the voltage to the MSD 6AL can be the problem? Just so you know the timing is set at 16 and 34 all in, and stays at 16 until about 1800, my idle is at 1100 mostly.
Alternator? Perhaps it is exactly what you think....
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Re: 434 SBC idle problem
408 Nova wrote:Lock out the mechanical advance, set the timing to 36 degrees or so to start, and get something to pull some timing out (MSD programmable or similar) when you're cranking the engine. Or just leave the ignition switch off when cranking the engine and then turn the switch on when you get it whizzing over. Everyone on here is telling you correctly about that.
I have a MSD 3 step retard with 10 to 20 degree start retard. I have set the idle at 36 degrees at idle 1000 rpm and when the electric fan comes on it dies just the same. When I run it at 18 degrees at idle or 12, 14, 16, or any idle degrees (When the electric fan comes on the degrees do not change (timing light in hand) the thing starts to die. I quickly grab the throttle and bring up the idle at that point I have to raise the idle screw to keep it running but still at no more than 1100 RPM's. After the engine cools from the fan and the fan turns itself off the engine starts to race, at that point I unscrew the idle screw to get it back to 1000 - 1100 idle. The only time the mechanical advance kicks in is when the fan turns off, because it revs to 2200 RPM's.
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Re: 434 SBC idle problem
I'd be interested in what the voltage at the coil and the box does when the fans kick on. Do you have everything grounded well?
Shawn
Shawn
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Re: 434 SBC idle problem
If not a voltage problem it's the extra load from the alt. when the fan comes on that's pulling it down.
Try richening the idle some or a lot.
Try richening the idle some or a lot.
Jim
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Re: 434 SBC idle problem
you might try going up to around a .075 or .076 idle air bleed ,,, I think I would ditch a 950 for that motor ,, and get a good 850 ( HP1000 now ) or a 1050
how many turns out are the idle mix screws ?
how many turns out are the idle mix screws ?
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Re: 434 SBC idle problem
swatson454 wrote:I'd be interested in what the voltage at the coil and the box does when the fans kick on. Do you have everything grounded well?
Shawn
I added a extra ground to the block directly. Battery in the back.
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Re: 434 SBC idle problem
77cruiser wrote:If not a voltage problem it's the extra load from the alt. when the fan comes on that's pulling it down.
Try richening the idle some or a lot.
Ya did that. They like the 1.5 out.
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Re: 434 SBC idle problem
levisnteeshirt wrote:you might try going up to around a .075 or .076 idle air bleed ,,, I think I would ditch a 950 for that motor ,, and get a good 850 ( HP1000 now ) or a 1050
how many turns out are the idle mix screws ?
Yes I got a 850 Mighty Demon that I know runs richer and better then this P.O.S. Holley 950 (NEW). I have used the Demon also same thing. It must be a short or something I was just seeing if anybody ever had this problem. The MSD box should not change voltage when the fan comes on, it is just a signal. The coil should also be constant voltage. I will change the alternator for a check tonight first. The idle mix screws are at 1.5 turns out I adjusted them in and out but went back to 1.5 turns out in the end.
Re: 434 SBC idle problem
as said mine done same thing idled fine but when elec fans kick in the alternator load caused idle to drop 200rpm at best idle to die to a stall at worst. opened idle mix screws out a bit then opened idle screws to raise idle back up to cover what the rich mixture dropped it.
now idle drops a little with fans but not as bad & idle is more stable
now idle drops a little with fans but not as bad & idle is more stable
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Re: 434 SBC idle problem
I changed the Alternator no change then I changed the Carb over to the Mighty demon 850 I am running at about 36 degrees at Idle getting dark same however the mighty demon is responding better.