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| New Modification https://slantsix.org/forum/viewtopic.php?t=44607 |
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| Author: | 63dartdude [ Tue Apr 19, 2011 4:38 am ] |
| Post subject: | New Modification |
I just swapped out the Dutra split system for headers, with an Offy quad intake manifold. I also put a 500 cfm 2 barrel Holley on there, since the Offy info said it was built for a 400cfm as a minimum. I turn on the car, and the engines surges a little. The rpms go up, and then down, up and down. If I try to give it gas, it just cuts out. Is this a vacuum leak? I have found a couple areas that appeared to be leaking, but think I have them fixed. And at this point, can't picture any vacuum leaks. Where do I go from here? I know the timing is set right on. |
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| Author: | wjajr [ Tue Apr 19, 2011 5:08 am ] |
| Post subject: | |
You may have two things happening that are exacerbating each other. A vacuum leak causing a higher idle rpm, may be high enough to cause mechanical advance to kick in; bringing up timing from its static set point. Once timing is advanced a degree or two, it causes rpm to increase. The up and down rpm most likely is caused by light spring in distributor trying to pull back governor weight, and vacuum leak causing it to stretch. This fluttering of timing is not uncommon on stock distributor equipped engine running performance modifications. A stock distributor will start to advance timing at as low as 800 to 900 rpm. Get any vacuum leaks sealed up. Reduce curb idle to 650 rpm using idle mixture screws, and close the throttle plate a little by backing off its set screw or idle adjustment screw to get them out of the transmission circuit. Use a vacuum gage to dial in highest vacuum at recommended idle rpm. If you have an after market camshaft you will need to re-curve the distributor to comply with cam’s higher idle rpm requirements, and possibly address torque converter stall rpm. First; do the no cost carburetor idle circuit tuning, and vacuum leak abatements. |
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| Author: | 63dartdude [ Tue Apr 19, 2011 5:47 am ] |
| Post subject: | |
I should have also stated, I just added the recurved dizzy as well, to add for this added performance. I don't have a vacuum gauge. |
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| Author: | DusterIdiot [ Tue Apr 19, 2011 6:33 am ] |
| Post subject: | Not the case... |
Quote: The up and down rpm most likely is caused by light spring in distributor trying to pull back governor weight, and vacuum leak causing it to stretch.
I did his recurve and he does not have a light spring in the pair for this dizzy. I think you are right on about the vacc. leak and this is probably exacerbating the situation with mech and vacc advance occuring at 2000 rpm (which is essentially the bottom end of the cruise rpm). Vacc Gauge is a must for any tuning.-D.Idiot |
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| Author: | LUCKY13 [ Tue Apr 19, 2011 10:43 am ] |
| Post subject: | |
If it cuts out when you try to give it gas I would think there is a bigger problem somewhere than any timing curve issues. First I would find out if the ignintion is breaking down, if you just changed the dizzy it could be possible there is a problem not detected with it before. If its a points dizzy check the points a condenser, it may be that you got a bad set, have a bad condenser, or have a wiring grounding out when the advance plate moves. This could also be a carb problem, check the float level, and then the power valve for leaking. What size jets are in this carb? A vacume leak or timing advance jumping around could cause a unstable idle, but it probably would not cause it not to rev, or take gas. Maybe the dizzy cap got cracked during the swap. Or is it possibe the coil wires where taken loose and then installed backwards ( points wire going to + side of coil instead of - side)? Have you pulled the spark plugs to see if they show a extreme lean or rich condition? If you hold the choke half way closed does it help? Is the choke opening up all the way? Jess |
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| Author: | 63dartdude [ Tue Apr 19, 2011 12:59 pm ] |
| Post subject: | |
Well, I think I found the problem. Checking the tightness of the intake and headers studs, I found that the lower stud on the number 1 cylinder was just spinning, and wasn't tight. Now I have to figure out how to replace that stud, and make it tight again. As it just turns and turns, and of course, will leak water if not tight at all. |
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| Author: | 63dartdude [ Tue Apr 19, 2011 1:12 pm ] |
| Post subject: | |
Just did a search. I guess helicoil is the answer for me. |
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