I have a 1969 mustang with a 302 in it. I built the engine last year with a comp cams extreme energy 268 camshaft. It has 268 duration with a 509 lift on the intake and a 280 duration with a 512 lift . I put ported cylinder heads with 1.94 intake valves and 1.60 exhaust valves.
It has an edelbrock performer intake with holley 670 street avenger. The car runs really good when first started and driven around for 20 minutes. The temp gauge gets up to about H and stays there, doesnt get any higher, unless in heavy traffic. After about 10 minutes it usually gets up to H and runs and drives fine. i thibnk that i put a 190 thermosat in but not 100% sure. After about 30min of driving, the car begins to have a qiet popping coming from the exhuast on deceleration, also a slight loss in power. It also runs like it isnt firing on a cylinder. I then take it home let it sit over night, and in the morning it runs fine until about 30 minutes pass. The weird thing is that it will run for about 20 minutes at H and nothing happens, it runs great, but then suddenly out of no where it starts acting up. This leads me to belive that maybe it isnt heat, and maybe its something else such as fule mixture. I also forgot to state that i have a mallory igntion box with a magnetic breakerless distributor. Do you think that maybe the timing is off a little or the fuel mixture is not right. I adjusted both the timing asnd fuel mixture using a vacumm gauge trying to achieve maximum vacumm. I also have a 1969 cougar that runs hot and it never has this problem. Any sugestion would be appreiciated!
thanks alot
Matt

 

humm i have never heard of this. Shut it off if it starts overheating the worst thing to do is ruin an engin like that. my only gues is that you are a little to lean, check your plugs and tell me what they look like.

 

Vapor lock????

 

Check your oil and see if there is any trace of water. If it does this when the engine is hot and expanding, something may be cracked.

 

hey, thanks for the replies.
I checked the oil and no trace of water or coolant. There is no sign of smoke from the tailpipes when i get on it and it is hot. As far as the plugs go, the are very clean, no soot. the insulator is all white but has a very light tan tint to it. The mark on the grounding strap is below the arch, so i am wondering if the car has too much timing. There is also no ring around the top of the insualtor and if i recall that means that it is running a little lean. I currently have the idle screws out 1 and 3/4 turn. I installed 63 jets in the primary and 65 in the secondary becasue with the standard 65's in the front and 68's in the back, it ran too rich when only 1/2 out. Now with the 63's i have it out 1 and 3/4 turn. Any suggestions would be helpful. I started building the car last year on the 16th birthday and just recently turned 17, so i got my license and have actually been able to drive it. It has come a long way though. My twin brother and I had to strip the car down to a bare shell, install new troque boxes, frame rails and pretty much everything else. the car had been sitting for 15 years out in the elements so it was really rough. We just painted the body hotrod black after replacing the quarters and every other panel on the car, and just finished the interior. I have hundred of pictures of the entire build and will eventually get them posted.
thanks Matt

 

Here is one of the spark plugs

[IMG]local://upfiles/32960/056760E3DE6E4B188DAD9E617C7BBDDC.jpg[/IMG]

 

Check the gap. Looks a little to far open, unless you are running a full out electronic ignition. Should be in the 0.034-37 range.

 

vapor lock would be my first guess, also, you should really think about getting a real temp gauge

 

Hi Matt,

sounds like you've built a real nice car.
I agree with your assesment on the plug reading, I'm also wondering if your PCV is plumbed into one of the runners instead of the the plenum chamber. As you've all ready learned reading plugs on unleaded gas is a bit tricky. Good to see you are reading the G.E. The burble on decel versus looking at your plug leads me to believe you are pretty close on jetting, but might need a change depending on what you do with timing. Normally a burble like that on decel means a little rich, but with the high temp and good breathing you could be drawing a bit of fresh mixture through into the exhaust when you close the butterflies.
I also agree with getting a good temp gauge, and I'd suggest a 180* thermostat. Running it a bit cooler will help all the way around.
What have you done as far as curving your advance? How close are you to pinging under load, and at a mid throttle-light load condition?

Look forward to seeing some pictures.

 

Hello,
As for the spark plug gap, it is at .035, and i am running a full electronic ignition system. As for the PCV i have it running from the vavle cover right to the port on the carb that it is suppose to go to. I did however dent up the baffle to clear the roller rockers. The baffle is touching the PCV the goes into the valve cover. Do you think i should pull out the dipstick to see if that helps get some of that pressure out. I first noticed the problem about a week ago, and throught that i was running too lean because i was only out 1 full turn, so i bumped it up to 1 and 1/2 turns. I do believe that made it slightly better. As for the timing, i havent noticed pinging under loads or going up hills. I am very familiar with the pinging noise because my 69 cougar used to ping under acceleration until we intalled a timing control that gave us 7 degrees both ways. I have one to install in the mustang but havent gotten to it. the exhaust is two super 40 series flowmasters that dump out under the car, no H pipe. I have to say that i only really notice that popping coming from the passenger side.

Here are some pictures of the car. The one of the engine compartment was taking in the winter, therefore the new ingition system isnt shown
http://69stangnj.tripod.com/mustang

thanks alot
Matt