Help?! Engine Tuning Trouble - Vintage Mustang Forums
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post #1 of 24 (permalink) Old 04-01-2018, 07:50 PM Thread Starter
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Confused Help?! Engine Tuning Trouble

I have a 1968 mustang with a 1969 302 in it. I am having trouble tuning it to run properly. I bought the car with lots of modifications already done to the engine and have taken the top half of the engine completely apart and back together to try to fix the problems but they are still there. I have tried tuning the carb with different jets and rods, and adjusting the timing but the car still struggles to go especially at low RPMs and some dead spots in the throttle. I doesn't really seem to have the power it should have. I tuned the carb with a vacuum gauge and got to a max of 11-12 at 1000 RPM which i think is the correct idle for the cam i have but i do not know for certain what cam i have in there. I am wondering if i should open the engine up again and check the cam and bring it back to stock as this will be a fun street car when done. Distributor curve maxed at ~3000 RPM initial timing at ~15 degrees i have thrown some money at it to fix it but i don't wont to spend any more until i know what the issue is.
Any wise engine sages that can help me out?
Engine mods are:
MSD pro billet distributor with 6AL box
Edelbrock Performer cylinder heads,
Edelbrock Performer RPM Air Gap intake manifold,
1406 Edelbrock 600 CFM carburetor,
Possibly Edelbrock Performer RPM Camshaft ??
engine pistons, rods and crank and all stock as far as i can tell.
all attached to a T56 magnum transmission with a ford 9 housing 3.25 gears

PS: while taking the heads apart i noticed quite a bit of gunk on the top and bottom of the valves
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post #2 of 24 (permalink) Old 04-01-2018, 09:10 PM
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Describe junk. Iím not a Edelbrock carb guy, but several here are. Sounds like you might be a little rich though. Need to know your cam specs that determine where you should be on vacuum. When you say max timing, what is it? Any smoke out the exhaust? If so, what color?

Regards,
Patrick
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post #3 of 24 (permalink) Old 04-01-2018, 09:26 PM
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Take a look at the lifters and the cam lobes through the holes in the lifter valley. (Pull lifters out one at a time for examination) Look for signs of the cam being wiped due to lack of proper lubrication (ZDDP)

If cam and lifters are ok, degree the cam to see what it is. Decide if that cam works for your intended purpose.

If so, check the timing set to see if the crank and cam gears are lined up properly and the timing chain slack is within spec.

Next check to see if the preload on the lifters is within spec.

Check the plugs for signs of fouling and double check gap

At that point the distributor and carburetor should come into the mix.

If the carb hasn't been gone through (rebuilt) in the recent past, rebuild it and make sure the fuel filter is new as well.
If there is lots of junk in the float bowls, the gas tank and fuel lines are suspect, clean or replace as needed.
Check the distributor and vacuum advance for proper and full function

Hopefully your issue(s) are somewhere in this list. In any event. let us know when you sort it out.

Good Luck

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post #4 of 24 (permalink) Old 04-01-2018, 10:24 PM
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An inexpensive vacuum gauge can tell you a lot about the condition of the engine. Most mechanics have forgotten their vacuum gauge thinking the computer will tell them what's wrong.

http://www.onallcylinders.com/2016/0...auge-readings/
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post #5 of 24 (permalink) Old 04-02-2018, 12:49 AM Thread Starter
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Originally Posted by patrickstapler View Post
Describe junk. Iím not a Edelbrock carb guy, but several here are. Sounds like you might be a little rich though. Need to know your cam specs that determine where you should be on vacuum. When you say max timing, what is it? Any smoke out the exhaust? If so, what color?

Performance Camshafts Cam Card Locator - Edelbrock, LLC. Here is the cam card of the cam i think it might be, i checked the exhaust and intake opening and closing degrees and they match if that means anything to confirm its identity. The timing i am talking about is the initial timing and the point at which the total advance occurs in terms of RPM. The initial timing is 15 and the total is 33 at ~3000 RPM. as for smoke i haven't really payed attention but it think white if any. the junk on the valves is black oily shmoo on top of carbon buildup
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post #6 of 24 (permalink) Old 04-02-2018, 12:59 AM Thread Starter
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Originally Posted by awhtx View Post
An inexpensive vacuum gauge can tell you a lot about the condition of the engine. Most mechanics have forgotten their vacuum gauge thinking the computer will tell them what's wrong.

http://www.onallcylinders.com/2016/0...auge-readings/
I have been using a vacuum gauge and it reads quite steady at 10-11 hg ~1000RPM (idle) The quick throttle test works well, it goes down to low vacuum and then up high and back to 11.

Last edited by falldowngoboom; 04-02-2018 at 01:02 AM. Reason: quoting
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post #7 of 24 (permalink) Old 04-02-2018, 03:51 AM
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That RPM cam is little bit too much for street cruising, it does not work very well on lower rpm like under 2000. Vacuum reading is correct for that cam, i had same on '66. Timing on my setup was 18 on idle and 37 at 3000rpm. I changed to roller cam and car worked much better, duration 220 .50 and .544 lift. I would suggest to get that RPM cam out and change it something that has less duration.

Mustang HT 289/302 4-speed 1966
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post #8 of 24 (permalink) Old 04-02-2018, 06:35 AM
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The issue the OP is describing wouldn’t be caused by that cam, unless it has a wiped lobe. The streetability of it has no bearing on this issue, so don’t just go to throwing parts at it. JeffTepper gave great advice on where to start. awhtx apparently didn’t even read your post.
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post #9 of 24 (permalink) Old 04-02-2018, 12:41 PM
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I think you know why it was for sale
So it runs OK mostly but is gutless?
Eddy carbs have a rep around here of being plug and play, nearly foolproof.
I dont know that combo but street warriors often dont build for the big picture. It may only be good while spun up, like it needs to live above 2K rpm. Cruising around does it have consistant pep above 2500rpm?
Does the dizzy have a vac advance? If so loosen it up. I think you might want more total but more important is the rate and increments of the progression that you should be able to see with a light.
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post #10 of 24 (permalink) Old 04-02-2018, 01:20 PM
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How about a compression check? It's cheap and easy and will at least rule that out if the numbers are good.

BTW - I have the Eddy RPM cam in my 351W daily driver and it's just fine (=fun!) for the street.
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post #11 of 24 (permalink) Old 04-02-2018, 02:03 PM
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Have you tried setting your initial timing to 10-12 see how it runs? Are you running a vacuum advance? A wideband AF guage will tell you right away where your at at part throttle, etc and makes it very easy to tell what your changes are doing to the car.

I have had this one since 2016 works great:
AEM (30-4110) UEGO Air/Fuel Ratio Gauge https://www.amazon.com/dp/B00N3VGPYS/

Not as advanced as the ones that let you collect data and import it to your computer but good enough for tuning.

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1965 Mustang Fastback 302 | Letter Cam | AFR165 | RPM Air Gap | CSU Carbs 750 | Novi 1200SL (7-8psi)
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post #12 of 24 (permalink) Old 04-02-2018, 02:05 PM
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Sound suspiciously like a 302 I had once that wore down three cam lobes. I was bound and determined it was something else (I don't remember why) but it passed all the basic tests. Even measured decent compression. I didn't give in until I finally broke down and measured the cam lift at the suspect cylinders.
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post #13 of 24 (permalink) Old 04-02-2018, 04:44 PM
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Youíre getting some good advice here. Donít know if this helps or hurts, but the single greatest tuning I ever did to my car was to junk the Edelbrock carb and put a Holley on it. Car ran great with the stock heads and cam, but I could never get it to run right after adding heads and cam until the Holley.

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post #14 of 24 (permalink) Old 04-02-2018, 06:43 PM
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Worn engine with "speed parts" added?
There is some mismatch to the parts that are on the engine, but
it's not damning.
The vacuum reading seems really low to me...... 7" less in mercury
for 6 degrees more cam than I have. Sum-ting not right there.
Look closely at the cam lobes.

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post #15 of 24 (permalink) Old 04-02-2018, 08:07 PM Thread Starter
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Thanks for all the great feedback guys. As excited as I am to open the top end of the engine for a 4th time, I am hoping that it is the cam and I can replace it and be done with it and drive around. I have done a compression test already as Rorin67 mentioned I should do; the cold numbers are 125psi average with no outliers. I read that the air velocity inside the intake runners is very important with large cams, could the Edelbrock performer rpm air gap intake be too big for my engine? As to changing the carb I am hesitant because I am no carb expert and even without using a Holley I know they are inherently more difficult to tune right because there are just so many more adjustments to be made... and mess up. Anyway thanks again for all the replies guys, ill try messing with the timing again and if that doesn't work then Johnny 5 disassemble!
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