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Old 07-07-2008, 02:57 PM
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Help Needed Adjusting Holley DP

I need some help adjusting a 700cfm Holley DP on a 400 SBC

it's too rich, I think. the choke is not on the carb, and it fires right up. the car can set in the garage a week, and with 1 pump and turn the key, it's running. with the idle down around 800RPM it sounds/is loading up. I have the secondary linkage off the carb just to slow my 16yr old boy down a little. when you get on it, this 400 is strong ! with no bogging or sputtering, it gets right with it. we drove the car with the secondary linkage on the carb and it gets with the program. (thats why I decided to pull it just to slow it down a little) but my son said the other nite he was driving around town and when he let off it in 3rd gear he could see a glowing under the car. (from the headers back to the rearend it has 3" exhaust with 14" round race mufflers, then it turns down at the rearend)
glowing like unburnt raw gas igniting.

how do I adjust this DP correctly ? how do I lean this out some ? or what do you recommend I do ? is there a pic somewere that shows the carb and witch screw is witch ? I'm no Holley or no carb man.


in a 74 Camaro we put together for my son we put a 400SBC and a M21 4 speed with 342 geared posi. I didn't build the engine so not sure on cam specs. what I know, 400SBC (prob bored .30) forged pistons and #187 camel hump heads, I was told compression is in the high 10s maybe low 11s. it has a weiand dual plane alum intake with a 700cfm Holley DP carb, headers ect. it runs cool, like 180 degrees and seems to run real good. it has good throttle response. you can tell it has a healthy Hyd flat tappet cam in it. the engine and tranny was in a 73 Z28 a buddie bought. the 400 was built just B4 my buddie bought the car, maybe 500 or a 1000 mi on it, maybe less. the Holley DP was on the 400SBC, my buddie finnished the 73 Z28 and put a 502 Ram Jet BBC in it with a temec 5 speed and 35 spline moser detroit locker in a ford 9" housing. so I bought the 400SBC & M21 4 speed.







thanks






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Last edited by Mustangsaly; 07-07-2008 at 03:10 PM.
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Old 07-07-2008, 06:06 PM
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if the headers glow the timing is way too retarded!
Advance your timing for best idle .
then using a vacum gauge adjust the idle mixture screws for highest vacum.
also sounds like you might have a blown power valve in the carb.
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Old 07-07-2008, 09:17 PM
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I was not around the car, but as far as I know the headers were not glowing. we will re time it. whats your recommended timing setting ? the glow under the car was unburnt gas burning out the end of the exhaust tips like a flame thrower. the carb was near new as the engine, (so I don't now what the carb went through be for I got it) but we never had any back firing at all.







thanks
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Old 07-08-2008, 07:11 AM
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no one can help me ? maybe I didn't explain my problem very well ? if I didn't, please ask any questions you have. so you can help me.






thanks
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Old 07-08-2008, 07:32 AM
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Set your timing to 36 btdc at around 3500 with vac advance unhooked to start with.Reconnect vac advance. Then set your idle to the desired speed, turn the idle adjustment screws to see if they affect idle.If so with a tach hooked up (dwell tach would be best for better resolution)adjust mixture screws 1 at a time to get highest idle speed then turn that screw in till rpm drops by 50 rpm. Repeat with other side.Do it again you have now set the carb to best lean idle .If this doesn't solve it let us know we will get it straightened out for ya.
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Old 07-08-2008, 09:34 AM
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thanks !

I knew it seemed a little rich, plus it starting with no choke after setting and not running a week or 2 between starts with a 1/2 a pump. and when the idle was around 800rpms it sounds tough with a mean lope witch my son loves, but at 800rpms it loads up in a couple minutes. but if you rap it up a little bit it clears up. and when you rap it up to clear it out, I don't see it smoke. it runs good in town and on the HWY. he just told me of the un burnt fuel burning like a small flame thrower, when hes cruising down main street in 3rd gear (witch hes prob turning it fairly hard in 3rd being cool) and lets off the throttle.

me taking the secondary linkage off doesn't effect any thing but the secondaries not opening correct ? my son doesn't know the linkage is off

this 400 4 speed gets with the program quick ! it's scary fast and can get away from ya real quick. it's a real quick raper ! and it has lots of torque and power. I know it will or can get over on my 16yr old son quick. as my 20yr old daughter (his sister) was with him when we were gone one weekend, and he had the Camaro out. and stopped in the center of the HWY and warmed the tires up with the line lock on, and when he let the line lock off she said it was side ways into 3rd gear of course he loved it, and it scared the crap outa her.............
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Old 07-08-2008, 09:58 AM
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That lopey cam is sucking the mixture right out into the exhaust.

I suggest that you will need a operable vacuum advance,
and it will probably need to be hooked to manifold vacuum to you get a lot of advance at idle to help burn the slow burning richer/overlap mixture at idle.

Check out Performance Distributor's website for insights into distributor curve timing and vacuum advance for lopey engines. They have been doing distributors since 1974.
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Old 07-08-2008, 04:11 PM
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thanks I will look into that also !

I read where the loopy idle cams don't run well. but this sounds mean and is a strong solid runner. when my son 1st drove it had the secondary linkage on the carb. I told him after we timed it and pulled the secondary linkage and drove it, we needed to recheck the timing. he said NO you guys aren't doing nothing ! cause after you timed it the 1st time, it don't have as much as it had but he did not know we pulled the secondary linkage. hes sense forgot. we are running high octane gas, 91 & 93 octane. this 400 has a new HEI distributor recurved by a local speed shop and has accel super coil with taylor 8.5mm wires, this was done when the engine was built.





thanks
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Old 07-09-2008, 09:06 AM
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You need to look at the spark plugs and see if it little dark in color.
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Old 07-09-2008, 09:45 AM
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don't touch the carb till you know the timing is atleast in the correct base and centrifugal timing ballpark for your cam duration....

a crude but simple way to get a first rough idea of what your particular cam's duration is....
is to read the Hg at idle with a vacuum gauge....
click on each of the graphs on this link and it tells you the idle Hg at what rpms for that cams duration,
http://www.compcams.com/Technical/DynoSheets/

from what you have posted so far, at 800rpms the Hg is likely only 5-8....
a carb can't make a "atomized" mix at all without about 10Hg minimum at idle piston speed
note on those charts, idle rpms has to go up to make more Hg as the cams get bigger...or you will foul the plugs

once you do know the camshaft's duration ballpark by measuring the Hg, (250/260/280/etc)....
then you can use the info in this article to set up the correct ballpark base and centrifugal and vacuum timing values..... http://www.gnetworks.com/v4files/bar...ithimages.pdfk

because you don't know the specifics of the motor build, (CR/cam timing/etc) I recommend you set the centrifugal at 34* max WOT......
for some detonation insurance....
especially due to it's your (young?) son driving the car

Last edited by red65mustang; 07-09-2008 at 10:14 AM.
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Old 07-09-2008, 12:33 PM
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Quote:
Originally Posted by red65mustang
don't touch the carb till you know the timing is atleast in the correct base and centrifugal timing ballpark for your cam duration....

a crude but simple way to get a first rough idea of what your particular cam's duration is....
is to read the Hg at idle with a vacuum gauge....
click on each of the graphs on this link and it tells you the idle Hg at what rpms for that cams duration,
http://www.compcams.com/Technical/DynoSheets/

from what you have posted so far, at 800rpms the Hg is likely only 5-8....
a carb can't make a "atomized" mix at all without about 10Hg minimum at idle piston speed
note on those charts, idle rpms has to go up to make more Hg as the cams get bigger...or you will foul the plugs

once you do know the camshaft's duration ballpark by measuring the Hg, (250/260/280/etc)....
then you can use the info in this article to set up the correct ballpark base and centrifugal and vacuum timing values..... http://www.gnetworks.com/v4files/bar...ithimages.pdfk

because you don't know the specifics of the motor build, (CR/cam timing/etc) I recommend you set the centrifugal at 34* max WOT......
for some detonation insurance....
especially due to it's your (young?) son driving the car

yes my 16yr old son is driving it, I haven't been in it in 2 + months. I know it's low on vacume for the power brakes. I noticed that as soon as we drove it the 1st time. I will read these later today and we will play with it.

thank you
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Old 07-09-2008, 01:52 PM
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Sounds to me like you are looking for an adjustment for the right foot on that 16 year old...
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Old 07-09-2008, 06:39 PM
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the power brakes booster has a one way check valve.....

if you blip the throttle just once so that the Hg does go to 15+ the vacuum is stored in the booster....

if the low idle Hg is affecting the brakes you need to check for a vacuum leak or faulty check valve....

a good booster check valve will hold the vacuum overnight....
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Old 07-09-2008, 07:31 PM
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Quote:
Originally Posted by 65smallblock
Sounds to me like you are looking for an adjustment for the right foot on that 16 year old...

well you hit the nail on the head ! really I knew the 400 was too Hot for a 16yr old when I bought it. I almost swaped set of vortec heads I have in place of the #187s double humps that are on the 400 now, I had planed the head swap B4 the engine swap. but I held back, and put the 062 vortecs on the shelf. the 400 and all the goodies seemed like a good idea, (a big list of performance parts were installed with the 400) till my buddie and I took the Camaro out the 1st time but I keep thinking how I enjoyed my 1st car that was way over powered, (a 67 GTO 389 4 speed and a 411 12 bolt), and my buddie that sold me the 400 and helped me drop it in, had a over powered 1st car (68 Camaro 396 th 400 12 bolt.

looking back the tired stock 350 I pulled out would of been plenty

did I tell you he got his drivers license at 9am and at 7pm the cops were knocking on my front door ? they wanted to with him up for wreckless driving for 50+ ft of 2 black marks in front of the quick shop. I said 50ft now way ! they wrote him up for careless driving. Ooh I measured the marks, they were 64+ ft long



yup I did it this time, he my last out of 4 children. 3 girls and one boy ...................

Last edited by Mustangsaly; 07-09-2008 at 10:02 PM.
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Old 07-10-2008, 01:36 PM
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Quote:
Originally Posted by red65mustang
don't touch the carb till you know the timing is atleast in the correct base and centrifugal timing ballpark for your cam duration....

a crude but simple way to get a first rough idea of what your particular cam's duration is....
is to read the Hg at idle with a vacuum gauge....
click on each of the graphs on this link and it tells you the idle Hg at what rpms for that cams duration,
http://www.compcams.com/Technical/DynoSheets/

from what you have posted so far, at 800rpms the Hg is likely only 5-8....
a carb can't make a "atomized" mix at all without about 10Hg minimum at idle piston speed
note on those charts, idle rpms has to go up to make more Hg as the cams get bigger...or you will foul the plugs

once you do know the camshaft's duration ballpark by measuring the Hg, (250/260/280/etc)....
then you can use the info in this article to set up the correct ballpark base and centrifugal and vacuum timing values..... http://www.gnetworks.com/v4files/bar...ithimages.pdfk

because you don't know the specifics of the motor build, (CR/cam timing/etc) I recommend you set the centrifugal at 34* max WOT......
for some detonation insurance....
especially due to it's your (young?) son driving the car




Red65Mustang




this link don't work
http://www.gnetworks.com/v4files/ba...withimages.pdfk
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