Author Topic: Poor Idle  (Read 3522 times)

Offline 78GMCMH

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Poor Idle
« on: December 04, 2009, 09:03:43 AM »
Hello, I'm having problems getting my new motor to idle. 72 cadillac 500, .020 over,,507ci. 9-1cr,, comp RV torque cam,, .540 lift, duration intake 233,ex 235,,,,lobe seperation 112. Factory Ex. manifolds. Edelbrock 2115..This is for my GMC motorhome. Its sitting in my shop in the frame, hooked up to the transmission,differential,radiator. Hooked up a temporary contol panel with a throttle that can be locked into place. Also installed an oil pressure gage,water temp, fuel pressure and AFR. Fired up ok and ran for 20 min. at 1800 to 2200 rpms. Small problem with glowing ex. pipes but thats what happens when you leave out the idle air screws. in trying to set the idle I had costant problems with flooding. 1/2" of gas ontop of the butterflys. Had 8.5 lbs with a factory pump. Switched to a .125 needle and seat. Installed a regulator and gage,,,4.5 to 5lbs. Factory manual calls for 8 degrees but it won't hardly idle. have to crank on the idle screw and opon the primarys some.  8-10 inches of vacume. very rough. more advance,,,12 or 14 degrees lets me back of on the idle screws,,,12 to 13inches of vac.,,,,, still idles rough. 700 rpms.Responds to bliping the throttle and it takes alot of sudden throttle quickly to raise the APT. Sprayed ether and carb cleaner around the manifold and carb looking fo a leak. Nothing. IR temp gun shows all cyl. head passages the same temp.,,320 range. Made a smoke feeder out of a paint pressure pot and injected it into the manifold to see if I had a large leak in the valley. Never came out of the rocker covers. 165 to 175lbs. compression. Rmoving one wire at a time makes it idle rougher,,None make" zero" diffrence. It idles better rich,{screws out 5-8 turns} 12.5 AFR on gage. Idle air screws will change AFR to 14/1 but it idles worse. Removing the plugs after warmup and idling, very wet. Checked zero mark on crank hub twice,,and came shaft using the "intake centerline" method. After warm and idling I removed the carb twice and found fuel around the well plugs. Tested for leakes,,none found. Filled bowl with penatrating oil ,,overnite,,no leakes.
             Idle tubes  .037
             Idle channel restrictions  .046 loose,no go .052
             upper air bleeds   .070
             Lower air bleeds .055
             Idle screw holes  .059
             Idle bypass air  .108
             Main air bleeds  .052
             Jets  73
            Rods  54 V
            Carb# 17080212
                            14444 GPW
   Carb is off of a 1984 P30 cassis motorhome.,, used a kit from you. Hpe I didn't miss anything, help.,,,,,,,P. Leavitt.
         

Offline 78GMCMH

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Re: Poor Idle
« Reply #1 on: December 04, 2009, 10:05:27 AM »
   Hello again; also, i blocked the crossover. In order to eliminate ignition problems, found an HEI off a 77 425, swapped out the Pertronix, no change in idle quality,, thanks,,PL

Offline 78GMCMH

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Re: Poor Idle
« Reply #2 on: December 05, 2009, 07:47:17 AM »
OK, I think I know where my vacume went,,,,,wrong cam. I thought I orderd an RV torque grind.
Heres what I got,,,,,,
    Duration @ .050     In. 233    Ex. 236
    lobe sep.          112
    lift   .540  .537   I think this explanes why I have a rough Idle and little vac. and also why it likes so much advance. Looking for a new cam now,,,this is HOTTER than comp cams hotest,,,more later,,,PL

Offline omaha

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Re: Poor Idle
« Reply #3 on: December 05, 2009, 07:02:05 PM »
yes that is a big cam. especially for a motor home. I would think 210-220  @ .050 would be more apprpriate. Maybe about .450-.460 lift. Lobe center @ 112 LSA ok though

Offline Cliff Ruggles

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Re: Poor Idle
« Reply #4 on: December 06, 2009, 05:22:29 AM »
I agree, pretty big cam for a towing application, even at 500cid.  You'd need up near 11 to 1 compression to smooth it out. 

I run a 236/245/112 in the 455 that powers my Ventura, at 11 to 1 compression.  It idles OK, vacuum is around 13", but it would not be suiteable for towing at low rpm's.

About 10 degrees smaller duration, on a 112 or even a 114 LSA will really smooth out the big Caddy engine......Cliff

Offline 77cruiser

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Re: Poor Idle
« Reply #5 on: December 06, 2009, 08:31:17 AM »
Like Cliff said big for towing. Did you degree the cam?
Jim