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Re: Holley Cruising Lean Out: Stumped...
Camaro Firebird Camaro Firebird Discussions (alt.autos.camaro.firebird)
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Re: Holley Cruising Lean Out: Stumped... -
02-17-2007
, 07:22 PM
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Where is your distributer vacuum connected to? I accidentally (read stupidly) connected the vacuum advance to manifold vacuum rather than the carb pre butterfly outlet. It killed the engine response like yours. Have you checked your ignition timing at idle (about 8 degrees) then up to 3000 rpm to see what the advance is doing - should be about 30 deg total advance or so? My rule in troubleshooting - if it looks like a carb problem: check the ignition system. If it looks like an ignition problem: check the carb. Works 90% of the time. You never said if you have a HEI distributer or points. If it's points check the gap. James Drinkwater wrote: Hi Guys, Got a Holley 650 double-pumper on "Dad's hotrod" with some probs tuning. Upon depression of the throttle, my fuel/air ratio gauge shows that the mixture goes way lean and the engine goes into lean misfire and dropped power. Eventually it richens back up as the RPMs slowly increase. Not talking about the accelerator pump, just giving it a little more gas while driving. Bought the carb from my machinist in the original box in like-new (visually) condition. Here's what's new and ruled out: high-volume fuel pump, fuel filter, fuel regulator and pressure gauge, float needles & seats, jets (just to be sure), 6.5" power valve (like the original). both squirters appear to pump fine but the problem occurs when you slowly roll into the throttle and it happens really quick (very throttle sensitive). It's a moderate, street performance SB Chevy that makes about 10.5" vacuum at idle. I know the PV should move up to 8.5" but rolling into heavy acceleration (vacuum below PV opening point) doesn't overcome the lean condition either. Two last things are that idle mixture is pretty un-responsive to idle mixture screws, even when idle speed is as low as the engine will reliably rev. Second, main jets were very, very rich at stock 67's (primary) and still a tad on the rich side with 65's. Dirty passage somewhere? Higher vacuum power valve needed and drill the PVCR's? I'm a little stumped. Best Regards, Drink '87 TransAm (No computer controls) Holley 650cfm double-pumper Victor Jr. single plane 186 heads, fully ported with 2.02 valves 218/228 roller cam 1.6 magnum rockers 10:1 KB pistons Mallory Comp9000 distributor Hooker SuperComp headers 3.73 gears -- Eugene Blanchard http://www.catsasskustoms.com Parts, Performance, Passion News for Motorheads |
#2
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I'm not a Holly expert. I've worked on a few quadrajets. Here's some general troubleshooting suggestions/comments: Your idle circuit is not working right. You've stated that it is unresponsive to the idle mixture screws. |
working. What he was saying is that adjusting the idle screws has no
effect on the lean response under very light acceleration. He did say at
one one point: "I can turn in the idle mixture screws a 1/2 turn or more
until it makes a difference and the revs drop off hard"
So it looks like the idle circuit is working it just doesn't have any
effect on the problem of the mixture going lean under light load, which
is normal.
-jim
Quote:
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Are the tips of the screws sharp or dull? If you screw in an idle mixture screw in too far it can dull the point. Are they the correct ones for length? Some screws are shorter than others. Maybe you have the wrong length ones. I know that there is a difference in length for emission vs non emission idle screws. Could be that the main jets were rich to compensate for the idle circuit is not working... You may have to open up the carb to find out why the idle circuit is not working. BTW what model Holley is it? Could it be one made specifically for racing? James Drinkwater wrote: Thanks for the reply, Steve. But, I considered the accelerator shot and that can't be it. Let me describe the situation better. Interstate cruise is the most obvious. So, there I am on the interstate cruising along at about 60mph. The engine's revving and the mixture's doin' alright. If I press a little on the accelerator smoothly to get up to 65 or 70, it goes way lean and holds in a lean condition until I get up to the desired speed and ease out of the throttle a tad to hold it. I'm not "kickin' it" to need the pump shot or so heavy that the vacuum drops enough that I'd need the Power Valve; just a little more throttle. If I do continue to roll into the throttle for heavier acceleration, it don't see the PV overcome the lean condition. Perplexing, huh? Drink "Steve Austin" <saustin4 (AT) twcny (DOT) rr.com> wrote in message news:45d79695$0$28119$4c368faf (AT) roadrunner (DOT) com... James Drinkwater wrote: Hi Guys, Got a Holley 650 double-pumper on "Dad's hotrod" with some probs tuning. Upon depression of the throttle, my fuel/air ratio gauge shows that the mixture goes way lean and the engine goes into lean misfire and dropped power. Eventually it richens back up as the RPMs slowly increase. Not talking about the accelerator pump, just giving it a little more gas while driving. Bought the carb from my machinist in the original box in like-new (visually) condition. Here's what's new and ruled out: high-volume fuel pump, fuel filter, fuel regulator and pressure gauge, float needles & seats, jets (just to be sure), 6.5" power valve (like the original). both squirters appear to pump fine but the problem occurs when you slowly roll into the throttle and it happens really quick (very throttle sensitive). It's a moderate, street performance SB Chevy that makes about 10.5" vacuum at idle. I know the PV should move up to 8.5" but rolling into heavy acceleration (vacuum below PV opening point) doesn't overcome the lean condition either. Two last things are that idle mixture is pretty un-responsive to idle mixture screws, even when idle speed is as low as the engine will reliably rev. Second, main jets were very, very rich at stock 67's (primary) and still a tad on the rich side with 65's. Dirty passage somewhere? Higher vacuum power valve needed and drill the PVCR's? I'm a little stumped. Best Regards, Drink '87 TransAm (No computer controls) Holley 650cfm double-pumper Victor Jr. single plane 186 heads, fully ported with 2.02 valves 218/228 roller cam 1.6 magnum rockers 10:1 KB pistons Mallory Comp9000 distributor Hooker SuperComp headers 3.73 gears Maybe you aren't talking about the accelerator pump, but you should be looking at it. -- Eugene Blanchard http://www.catsasskustoms.com Parts, Performance, Passion News for Motorheads |
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#3
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| Eugene Blanchard wrote: I'm not a Holly expert. I've worked on a few quadrajets. Here's some general troubleshooting suggestions/comments: Your idle circuit is not working right. You've stated that it is unresponsive to the idle mixture screws. I'm not positive - but I don't think he meant the idle screws were not working. What he was saying is that adjusting the idle screws has no effect on the lean response under very light acceleration. He did say at one one point: "I can turn in the idle mixture screws a 1/2 turn or more until it makes a difference and the revs drop off hard" So it looks like the idle circuit is working it just doesn't have any effect on the problem of the mixture going lean under light load, which is normal. -jim Are the tips of the screws sharp or dull? If you screw in an idle mixture screw in too far it can dull the point. Are they the correct ones for length? Some screws are shorter than others. Maybe you have the wrong length ones. I know that there is a difference in length for emission vs non emission idle screws. Could be that the main jets were rich to compensate for the idle circuit is not working... You may have to open up the carb to find out why the idle circuit is not working. BTW what model Holley is it? Could it be one made specifically for racing? James Drinkwater wrote: Thanks for the reply, Steve. But, I considered the accelerator shot and that can't be it. Let me describe the situation better. Interstate cruise is the most obvious. So, there I am on the interstate cruising along at about 60mph. The engine's revving and the mixture's doin' alright. If I press a little on the accelerator smoothly to get up to 65 or 70, it goes way lean and holds in a lean condition until I get up to the desired speed and ease out of the throttle a tad to hold it. I'm not "kickin' it" to need the pump shot or so heavy that the vacuum drops enough that I'd need the Power Valve; just a little more throttle. If I do continue to roll into the throttle for heavier acceleration, it don't see the PV overcome the lean condition. Perplexing, huh? Drink "Steve Austin" <saustin4 (AT) twcny (DOT) rr.com> wrote in message news:45d79695$0$28119$4c368faf (AT) roadrunner (DOT) com... James Drinkwater wrote: Hi Guys, Got a Holley 650 double-pumper on "Dad's hotrod" with some probs tuning. Upon depression of the throttle, my fuel/air ratio gauge shows that the mixture goes way lean and the engine goes into lean misfire and dropped power. Eventually it richens back up as the RPMs slowly increase. Not talking about the accelerator pump, just giving it a little more gas while driving. Bought the carb from my machinist in the original box in like-new (visually) condition. Here's what's new and ruled out: high-volume fuel pump, fuel filter, fuel regulator and pressure gauge, float needles & seats, jets (just to be sure), 6.5" power valve (like the original). both squirters appear to pump fine but the problem occurs when you slowly roll into the throttle and it happens really quick (very throttle sensitive). It's a moderate, street performance SB Chevy that makes about 10.5" vacuum at idle. I know the PV should move up to 8.5" but rolling into heavy acceleration (vacuum below PV opening point) doesn't overcome the lean condition either. Two last things are that idle mixture is pretty un-responsive to idle mixture screws, even when idle speed is as low as the engine will reliably rev. Second, main jets were very, very rich at stock 67's (primary) and still a tad on the rich side with 65's. Dirty passage somewhere? Higher vacuum power valve needed and drill the PVCR's? I'm a little stumped. Best Regards, Drink '87 TransAm (No computer controls) Holley 650cfm double-pumper Victor Jr. single plane 186 heads, fully ported with 2.02 valves 218/228 roller cam 1.6 magnum rockers 10:1 KB pistons Mallory Comp9000 distributor Hooker SuperComp headers 3.73 gears Maybe you aren't talking about the accelerator pump, but you should be looking at it. -- Eugene Blanchard http://www.catsasskustoms.com Parts, Performance, Passion News for Motorheads ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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