Vacuum advance still far too aggressive after crane adj unit

crazypete · 01-11-2003, 10:28 AM

I know I posted on this before, but I wanna throw this out to the community before I finally decide to scrap the system and cap it off. I could use that extra 1-2 mpg, even though I'm getting 20 mpg with a carb and 3.73's (I have no idea either!)

I'm using an 85 mustang distributor with a holley 670 street avenger. I get 20 hg's vacuum at idle (1100 rpms, but same happens at 800 rpms), I'm not running egr or air pump and I have no spacers or anything else in the way. Based on how smooth it runs, I do not have a vacuum leak. Running base timing for now : 10 deg. Yes, I am using the spark advance port on the carb =) . Mixture guage shows stoich + 1 bar.

Originally, what was happening is that, with the light aimed at the timing marks, I would connect the vacuum advance at IDLE and see the marks shoot off to somewhere under the motor and it would run like crap and backfire immediatley when I touch the throttle lever by hand. Holley said it misdrilled it's spark ports on some of the avengers and they sent me a tested unit under warranty.

Ok, now, at idle, no problem. I hook it up and see no change. Cool, I think. I reach over and blip the throttle. BANG!! BANG!!! I can feel the backfire go up into the carb. I see the timing marks jump way up to just past 40. Darn it.

Ok, I get the crane cams adjustable cannister and allen wrench it all the way out. Same behaviour. I allen wrench it all the way in. Same behaviour. This is so annoying! What is going on with this silly car?

PKRWUD · 01-11-2003, 11:12 AM

Put your vacuum gauge on the spark port and see how it applies vacuum. It should gradually go up as the throttle opens. If it suddenly pegs as soon as you touch the throttle, then the carb is bad.

Post your results.

crazypete · 01-11-2003, 11:52 AM

Here's what I see (guage to spark port):

0 hg's at dead idle (800 rpm)
2 hg's the second I touch throttle at all
rises very quickly but smoothly (not a spike but almost) to 16 hg's at 2300 when stomped
5 hg at 1800
10hg at 2000
15 hg at 2200

Hope this helps

Thanks for your quick reply man

PKRWUD · 01-11-2003, 10:29 PM

Heh, I don't know about quick, I worked a long day today.

Anyway, that sounds perfect. If there is no difference in the amount of advance regardless of where the advance can is adjusted, than it is what is bad. Get your hands on a hand vacuum pump, and attach it to the advance can, and slowly apply vacuum. How does it react? It should gradually advance.

crazypete · 01-13-2003, 12:54 PM

Ok, I did the test. I did not have the vacuum pump as mentioned, so I used the amazing patented "suck on the hose" trick. I removed the distributor cap and sucked on the vacuum canister hose and I saw the plate move a decent amount. I then cranked the canister all the way in the other direction and I sucked till I was blue in the face but could not achieve any movement in the plate. I guess the canister works too. Excited, I blipped the throttle a few times with mostly success and 1 backfire. What the heck, I thought and threw it in gear and tried taxiing it around the driveway. The second there was any load on the engine, it started missing wildly and then popped and died. I think I'm doing something else wrong. I have 66/70 jets, 95 powervalve and the long yellow spring for the secondaries and this works royally otherwise, I drove 120 miles yesterday, driving smooth and wild and no complaints. Based on the plugs, it's running a bit on the lean side if anything (but not by much, operating temps are a bit below halfway on the temp guage).
I dont think those mixture sensors are worth much of anything.

01-11-2003, 10:28 AM	#1
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	Vacuum advance still far too aggressive after crane adj unit I know I posted on this before, but I wanna throw this out to the community before I finally decide to scrap the system and cap it off. I could use that extra 1-2 mpg, even though I'm getting 20 mpg with a carb and 3.73's (I have no idea either!) I'm using an 85 mustang distributor with a holley 670 street avenger. I get 20 hg's vacuum at idle (1100 rpms, but same happens at 800 rpms), I'm not running egr or air pump and I have no spacers or anything else in the way. Based on how smooth it runs, I do not have a vacuum leak. Running base timing for now : 10 deg. Yes, I am using the spark advance port on the carb =) . Mixture guage shows stoich + 1 bar. Originally, what was happening is that, with the light aimed at the timing marks, I would connect the vacuum advance at IDLE and see the marks shoot off to somewhere under the motor and it would run like crap and backfire immediatley when I touch the throttle lever by hand. Holley said it misdrilled it's spark ports on some of the avengers and they sent me a tested unit under warranty. Ok, now, at idle, no problem. I hook it up and see no change. Cool, I think. I reach over and blip the throttle. BANG!! BANG!!! I can feel the backfire go up into the carb. I see the timing marks jump way up to just past 40. Darn it. Ok, I get the crane cams adjustable cannister and allen wrench it all the way out. Same behaviour. I allen wrench it all the way in. Same behaviour. This is so annoying! What is going on with this silly car? __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

01-11-2003, 11:12 AM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Put your vacuum gauge on the spark port and see how it applies vacuum. It should gradually go up as the throttle opens. If it suddenly pegs as soon as you touch the throttle, then the carb is bad. Post your results. __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

01-11-2003, 11:52 AM	#3
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	Here's what I see (guage to spark port): 0 hg's at dead idle (800 rpm) 2 hg's the second I touch throttle at all rises very quickly but smoothly (not a spike but almost) to 16 hg's at 2300 when stomped 5 hg at 1800 10hg at 2000 15 hg at 2200 Hope this helps Thanks for your quick reply man __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

01-11-2003, 10:29 PM	#4
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Heh, I don't know about quick, I worked a long day today. Anyway, that sounds perfect. If there is no difference in the amount of advance regardless of where the advance can is adjusted, than it is what is bad. Get your hands on a hand vacuum pump, and attach it to the advance can, and slowly apply vacuum. How does it react? It should gradually advance. __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

01-13-2003, 12:54 PM	#5
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	Ok, I did the test. I did not have the vacuum pump as mentioned, so I used the amazing patented "suck on the hose" trick. I removed the distributor cap and sucked on the vacuum canister hose and I saw the plate move a decent amount. I then cranked the canister all the way in the other direction and I sucked till I was blue in the face but could not achieve any movement in the plate. I guess the canister works too. Excited, I blipped the throttle a few times with mostly success and 1 backfire. What the heck, I thought and threw it in gear and tried taxiing it around the driveway. The second there was any load on the engine, it started missing wildly and then popped and died. I think I'm doing something else wrong. I have 66/70 jets, 95 powervalve and the long yellow spring for the secondaries and this works royally otherwise, I drove 120 miles yesterday, driving smooth and wild and no complaints. Based on the plugs, it's running a bit on the lean side if anything (but not by much, operating temps are a bit below halfway on the temp guage). I dont think those mixture sensors are worth much of anything. __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

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