Do you know anyone in your area that has the same set up only bone stock that you could check the vacuum difference in their engine between Park and Drive for a comparison of the drop in hg? Maybe someone on the Forum here could do that too. I suspect there is a difference but I also think that with an enough bigger cam that difference is going to be greater and some adjustment in the idle circuit and idle speed is going to be necessary assuming all other systems (timing, ignition, etc.) are in proper adjustment.
Rough idle in gear
- Thread starter mugsy
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mach1 mark
Well-known member
I just thought I would post some results: I took the carb completely apart, cleaned it (polished it also), put in a new power valve of 4.5, and a new "squirter", # 37 , the stock "squirter" was a 28. The power valve before changing it was 6.5 and this was to much fuel at ideal (explains that gas smell). The new squirter really gets the car going, no more feathering the pedal and holding my breath when pulling out in traffic.
Although making these changes did improve the performance of the car, the "in gear stumble" was still happening. Harte3 was correct, I changed to ported vacuum and it worked like a charm (thank you Harte3). I had to set the timing at 23-25 BTDC. 22 was to low, the car would quit in gear, and 30 was to high. So as Goldilocks would say "that was just right". The car is at 1000 rpms in park and now only drops down to 600 rpms when in gear.
I'm still having a little stumble, but I can sit in traffic without the car smelling like gas and having to put it in nuetral at every light.
I hope this helps Mugsy, I am going to play with the throttle plates a little and see what happens, I'll keep you informed. Are you having any better luck, and if so what did you do?
Although making these changes did improve the performance of the car, the "in gear stumble" was still happening. Harte3 was correct, I changed to ported vacuum and it worked like a charm (thank you Harte3). I had to set the timing at 23-25 BTDC. 22 was to low, the car would quit in gear, and 30 was to high. So as Goldilocks would say "that was just right". The car is at 1000 rpms in park and now only drops down to 600 rpms when in gear.
I'm still having a little stumble, but I can sit in traffic without the car smelling like gas and having to put it in nuetral at every light.
I hope this helps Mugsy, I am going to play with the throttle plates a little and see what happens, I'll keep you informed. Are you having any better luck, and if so what did you do?
To see if that helps , if that works well enough , recurving your dist may be all you need , But You may need to change the Torque converter to a higher stall Unit, the bigger cam has more overlap and is causing a lower Vacuum reading , which will reduce the signal to the carb , the engine will make Less torque at Idle with a larger cam , on a stick car its not as much of a problen since there is no load on the motor in neutral, but in gear with an automatic there is , A higher stall speeed converter is looser will alow less drag at idle, and will also allow the motor to flash ( rev ) quicker giving much better performance and aceleration, All parts need to work in sync , and a cam change alone without taking in to account its total effects will result in what you have here.
Mugsy, the 260 comp cam already is advanced at the factory. You should degree that cam as received since there is a 4 degree advance already built into the camshaft. Degree the intake at 106 degrees. The only correction needed would be to correct keyway errors if necessary.
That camshaft is really mild.
You need to put full manifold vacuum to the vacuum advance with your deal.
The distributor should have at least 12 distributor degrees of centrifigul advance @ 2500-2800 rpms to put that into crankshaft degrees 12 X 2 = 24 + 14 initial = 38 degrees total advance + the vacuum advance @ idle.
If you still have a rough idle after that let us know.
If that cam is the comp 260 degrees & 212 degrees @ .050 you should be able to use the stock converter. However going to a looser converter will really perk up your initial acceration & help your idle.
That camshaft is a weak performer, the better camshaft would be classic inlines 264.
Fix your distributor first. Also check the harmonic balanced to see if the ring with the timing marks has not spun on the hub, that will really screw up you setting the proper timing. Bill
That camshaft is really mild.
You need to put full manifold vacuum to the vacuum advance with your deal.
The distributor should have at least 12 distributor degrees of centrifigul advance @ 2500-2800 rpms to put that into crankshaft degrees 12 X 2 = 24 + 14 initial = 38 degrees total advance + the vacuum advance @ idle.
If you still have a rough idle after that let us know.
If that cam is the comp 260 degrees & 212 degrees @ .050 you should be able to use the stock converter. However going to a looser converter will really perk up your initial acceration & help your idle.
That camshaft is a weak performer, the better camshaft would be classic inlines 264.
Fix your distributor first. Also check the harmonic balanced to see if the ring with the timing marks has not spun on the hub, that will really screw up you setting the proper timing. Bill
The front pulley/balancer was rebuilt and I did use my dial indicator to find TDC. The mark on the damper is dead nuts on to the TDC mark on the timing cover. I can say the timing mark is spot on, no questions.
As for timing the cam, that was a different story. It had the regular hydraulic lifter and not a solid, and tried to use that. I tried to degree in the cam and never got it right. I kept getting weird numbers like the cam lobes were 20 degrees further apart, the intake centerlines were way off, etc. I had the dial indicator (with mag base) set on the block deck, a lifter and push rod on the cam and then used the dial indicator to steady the pushrod (the motor came with adjustable rocker arms so the top end of the pushrod is cupped). I just figured it was my technique that was bad and not the cam....
I took the week off between Christmas and New Years as vacation, so I'll try some of your sugestions.
Thanks guys!
Mugsy 8)
As for timing the cam, that was a different story. It had the regular hydraulic lifter and not a solid, and tried to use that. I tried to degree in the cam and never got it right. I kept getting weird numbers like the cam lobes were 20 degrees further apart, the intake centerlines were way off, etc. I had the dial indicator (with mag base) set on the block deck, a lifter and push rod on the cam and then used the dial indicator to steady the pushrod (the motor came with adjustable rocker arms so the top end of the pushrod is cupped). I just figured it was my technique that was bad and not the cam....
I took the week off between Christmas and New Years as vacation, so I'll try some of your sugestions.
Thanks guys!
Mugsy 8)
