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Old 11-30-2004, 07:46   #1 (permalink)
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confused 351W Assistance plz....

Here's my setup - 78 Cougar XR7, newer (3 yo) 351W, mostly stock at time of install.

So far, I've installed the following:

750 holley
Edelbrock performer intake
brand new cap,rotor,plugs, wires
all new vacuum lines except the one going to the dash for the heater controls

Now, the questions I have are:
1. What is the correct spark plug gap for this engine? Dont have the emissions label anymore.... I set it to .040, but I'm wondering if that's too small....
2. What is the correct ignition timing for this mild of an engine?
3. After warm up, my oil pressure starts to drop (even on a new change) to about 20-30, unless I am on the throttle. Is this a problem?


The issue I'm having is this. At 6 degrees ATDC timing, the engine will stumble under load. It idles fine, and if I throttle up gradually, it seems to like it, but if I slam the throttle down (without opening up the secondaries on the Holley) about 1/2 way, the engine bogs; almost seems like a "miss". I've read in all different places all sorts of different timings, and would like to know that at least this part is correct. I'm kind of sick of trial and error on this engine; now that I've got it idling without missing, I'd like to get it running good.

Also, could an incorrect idle fuel mixture be throwing this all off too? I'm not too sure how to adjust carbs, and the Holley book I have is worthless for a backyard mechanic like myself. Maybe someone can give me some pointers...

I know the carb is a bit much for the car too. Call me inexperienced.....
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Old 11-30-2004, 07:54   #2 (permalink)
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Re: 351W Assistance plz....

6 degrees ATDC (After Top Dead Center) shouldn't that be BTDC - Before?
If you have the ignition set after TDC it will run but will run like crap and have very little power.
An incorrect idle mixture can cause it to idle rough too but won't affect it off idle.
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Old 11-30-2004, 08:18   #3 (permalink)
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Re: 351W Assistance plz....

In thinking about it, I think the engine spins clockwise (looking at engine from front of car), so it would be BTDC.

The stumbling worries me though.... I really really really don't want to have to pull off the heads.... Was thinking that the low oil pressure after warm up at idle might have something to do with the head gaskets or possibly even worn cylinder walls.. but it doesn't have that many miles on it......
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Old 12-01-2004, 00:52   #4 (permalink)
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Re: 351W Assistance plz....

check the adjustment of the primary accel pump lever, should have no slack at idle position. Is the pump diaphragm ok?. Is there a accel pump cam fitted (don't laugh seen too many missing). Is the cam fitted in the correct pos for your engine. is the power valve recieving vacuum, pull the carb and check the ball and spring which is backfire protection is not stuck shut.
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Old 12-01-2004, 09:40   #5 (permalink)
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Re: 351W Assistance plz....

I think the adjustment is fine - where is that cam located at? Also, the backfire protection - is that off the jets or where? I may just tear the carb off to see what's going on.

A year ago I had an issue where the float valve actually had a piece of "metal" stuck in it, looked like part of a round seal (washer looking, but thin)... had to remove that from the center of the float seat, since it was keeping the float wide open....???

Any other assistance (spark plug gap, timing setting for a stock engine, possibly even RPM range to time to) would help greatly, since I don't have the original emissions label.....

Thanks in advance..
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Old 12-01-2004, 23:14   #6 (permalink)
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Re: 351W Assistance plz....

040" is heaps, especially if you are running a stock style ignition with an oil filled cannister style coil.

You should be able to have it running on at least 10 deg BTDC at idle with the vac advance disconected. Run the vac advance off a timed source, your holley book should tell you. Otherwise it's the vac port in the front metering block.

20-30psi at idle is OK but not great, provided you have a minimum of 10psi/1000rpm (i.e 5000rpm=50psi). Try stick in a thicker grade of oil, you said it starts after warm up something like a 25/70 weight multigrade oil.

Take the air cleaner off, look down the choke horn and slightly turn the throttle, if the accelerator pump is right you should instantly see fuel come out of the pump shooters.

Is the carby a 3310 750 (4160 series) or one of those crappy spread jobbies?
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Old 12-02-2004, 06:38   #7 (permalink)
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Re: 351W Assistance plz....

I've currently got the ignition set to 6, I'll have to try 10... Also need to go spend about 10$ on a tach, since I'm doing the timing rpm's more or less by ear of what sounds right (with a timing light, of course, but should probably be sure it is 600-800rpm for sure)

I'm pretty sure the accel pump is working fine. No play; not at home though, so can't check on the fuel flow, but I'd lay money it's there.

I keep looking at other carbs and wonder if the carb is just too darn big for the fact that it's a stock engine. I would have hoped the fellows at Jegs would have steered me in the right direction, but they just sold me this carb without blinking.... I really don't want to sink another 200$ into a 600/650, but we'll see.

The oil pressure rises quickly off-idle, starting at 20 after warm up and ending up in the 40-60 range, depending on RPM, so I'm guessing if I throw a higher weight oil in it, the pressure will stay up (using 5w30 now, getting cold here in ohio!) I had a problem in a Z28 where the oil pressure was dropping, but it was leaking near the filter, and since I redid the intake and the valve covers, there's no oil on the ground now.

I was thinking of getting a better ignition system to see if that would help as well - maybe a higher-powered coil, and stepping up the gap on the plugs to .050.... Anything I can do to "tinker" with this and get it to stop the hesitation would be awesome, since all the work I've done so far has seemed to assist the crappy idle it's had in the past.

BTW, the advance is coming off of the master fuel bowl (the FRONT of the carb, right?). The passenger vacuum runs to a block off (used to be hooked up to the air cleaner pre-heater, but I don't have a hose) and the rear passenger vacuum off the carb goes to PCV. This is a correct set-up, right? When timing the engine, the advance jumps pretty good even at idle, so I'm not totally sure if I've got those two lines correct in the front/front passenger....

I'll have to dig the holley book up, but the last time I tried to read it, it went WAY over my head. Guess I'll need to find someone who knows carbs in and out, since I'm still a relative noob at it.
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Old 12-03-2004, 03:34   #8 (permalink)
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Re: 351W Assistance plz....

In the aussie GT falcons, Windsors had 80 pound oil gauges in them, Clevelands had 100 pound guages. Windsor's don't make as much oil pressure, my rebuilt windsor has 35-40 at idle and about 60 when on song. Fitting a high volume oil pump did sfa aswell.
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Old 12-03-2004, 21:04   #9 (permalink)
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Re: 351W Assistance plz....

If the carby is a 750 Vac sec model with list no.3310 then its OK for your application. I have run a 650dp on a 265 six cylinder before.

Don't screw around upgrading the ignition untill you know how to tune the Holley properly.

Get a tach and find out what the timing is doing at various revs with and without the vac advance hooked up.

Also get a manifold vaccum reading at idle in gear (auto) and at steady cruise. This is important for correctly sizing the PV!!
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Old 12-03-2004, 21:10   #10 (permalink)
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Re: 351W Assistance plz....

Quote:
Originally Posted by karnal351w
BTW, the advance is coming off of the master fuel bowl (the FRONT of the carb, right?). The passenger vacuum runs to a block off (used to be hooked up to the air cleaner pre-heater, but I don't have a hose) and the rear passenger vacuum off the carb goes to PCV. This is a correct set-up, right? When timing the engine, the advance jumps pretty good even at idle, so I'm not totally sure if I've got those two lines correct in the front/front passenger....
What model carby is it first??
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