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Discussion in 'Engine and Drivetrain/Mechanical' started by RagTop, Jun 8, 2017.
It's a 625cfm Road Demon 4V.
You said your tach just came back to life? If it's a stock tach, it is in the ignition circuit- the path is from ignition switch terminal C, THROUGH the tach, through the resistor wire, and to the coil. The tach could be your problem; you may want to bypass it to test. Look at the attached pdf
The tach is an after market cheapie that is installed on the steering column. After further experience it looks like it has not recovered. I decided to change out the old Flamethrower on the outside chance that the old one was breaking down in the heat, and I discovered that the bolt hole in the GT40P cylinder head was stripped. Couldn't get the damn thing to tighten again. That took some drilling and a helicoil kit to remount my ignition coil. I'm pleased to announce that the coil bolt now runs in the hole but the new coil did not clear up my miss. It did push it back up to 4K rpm (if you believe the tach) where I started this whole thing six months ago. I'm afraid Horseplay might be right and I'll have to install a new Ignitor, but this process of elimination is getting kind of annoying if it doesn't cure the problem. Maybe I'll run a compression check tomorrow and look at the condition of the new plugs and wires while I think about other measures. A new rotor and cap perhaps?
take the tach out of the equation n see what happens.
Dizzy cap n rotor are inexpensive items to replace.
I agree eliminate the tach, I've experienced chafed wires with my first 69 would occasionally kill the car. Took awhile to track down but once found it had no more issues.
OK, I'm convinced! I'm heading to the garage with my 3/8" ignition wrench as I write this. I'll let you know how it comes out or if I strip anything.
The miss is there with and without the tach connected. I just replaced the distributor cap and rotor and the miss seems to have gotten a little worse at 3K rpm and up. This must be a fuel problem. It's hard to find anyone who can work on a car with a carb anymore.
I will work on it
Look at the breaker plate in the dist for worn bushings or sticking/restrictive movement.
From your description of your problem it may not be carb related.
I'm taking the car to a known professional Mustang expert a week from today. I had been avoiding that because his shop is an hour's drive from my home, but I suckered a buddy into driving over and bringing me back while I leave the Mustang until the problem is solved. I was talking to the mechanic last night at a cruise in, and he was opining that the distributor could be my problem. The disti that is in the car is a '68 J code unit that was custom curved to my needs back about 12 years ago. My original stock F code disti was pretty much worn out in '05 when I rebuilt the engine. I sent it to a specialist to be rebuilt and he offered me the J code unit that he had on his shelf in exchange. At the time I jumped at the offer. Maybe the springs are shot or the weights are sticky after 50K miles of driving. I hope that's the problem rather than some deeper engine mechanical issue. He said he'd run a compression test on the engine as well in case I might have a burned valve or weak valve spring. I'm just sorry that I pissed away $442 with my local mechanic because I wanted to believe he could find and fix the problem. I'll let you guys know what the on-deck hitter comes up with after his time at the plate.
BTW, the overdrive pulley on my water pump seems to have completely cured my problems with overheating in hot weather. I was sitting waiting for a green arrow last evening in 99* ambient and the temp gauge never really moved. And I'm running without a shroud. Finally one problem solved!
Got my pulley n going to do some wrenching to get it installed today.
What better way to spend Independence weekend than wrenchin'
So, did you go with the polished finish or the anodized black finish?
polished finish. I need to countersink the 4 bolt holes to get clearances squared away with the electric fan and other goodies....
So, once more into the breech. My Mustang is now with the doctor, a guy in my Mustang club who is pretty much the expert in all things Mustang and '69 Mustangs in particular. He pulled the plugs that I had installed about six months back and found that the gaps were all around .048. Because my heads are GT40Ps and they use the smaller long reach plug, I had used them right out of the box. He cranked them down to .035. He also ran a compression test and found that six of the eight cylinders showed 152 - 155 lbs. The rear two on the passenger side were 145 and 147 respectively. Certainly within acceptable range of variation, but the plugs coming out of those two cylinders were "blistered" per his description. He said it could be a sign of moisture in the cylinders. We both started thinking head gaskets, but my radiator is never down and there's no milkshake in the crankcase. He test drove the car with the re-gapped plugs and decided to have a look at my carb. It is a 625 cfm Road Demon and, I believe, uses the same jets as a Holley. He felt the car was showing signs of running too lean and was starving out at high speed under load. He removed the #74 jets that came in the Demon and replaced them with #76. The high speed miss began to disappear, only showing up at around 75 mph (or 3,700 rpm). He went up to #78 jets and he said he can get it all the way up to 90 mph before there is any sign of stumbling. He is installing #79 jets, replaced the safety valve (the little goody that blows out on Holleys all the time on backfires), and generally cleaned up the Demon. He's going to run another compression check and replace the plugs with new ones. He also mentioned that he was very surprised at the way my little pastel yellow gramma convertible pulled in low end acceleration, and said that he was hoping that the larger jets wouldn't erode that low end pop too severely. The jury is still out on why those two rear cylinders were slightly lower in compression than the rest. I'm taking the car to Hot August Nights in Reno, NV, which is 100 miles of up hill from where I live, and then I'll have another look at those two rear plugs when I return.
Great to hear things are clearing up!
So, I can now wind the car out to over 5,500 rpm without the slightest hesitation (except for my guts), and it seems to perform even better than it did pre-miss with the new jets and power valve, which is slightly larger than the power valve that was in the Demon stock. I'm super happy with the way the car performs now. Lots of smoke off the line and it chirps second under heavy acceleration. I saw the mechanic last night at a Sierra Mustang Club meeting and he told me again how impressed he was with my little 302 convertible's performance. Maybe, when the folks at car shows ask me if it's a Boss 302, I'll answer "yes" in the future or tell them it's a rare HiPo 302.
GAWD! The miss has returned! The car makes some lifter noise when it first fires up and the mechanic is thinking that the lifters may have become weakened over time (53K miles since rebuild) allowing the valves to float at high RPM. I dunno. He says he noticed the cold start lifter noise and, upon examination, found it was emanating from several cylinders. I had recently switched up to Kendall 20W50 which seemed to make the lifter noise worse. I just went back down to Castrol High Mileage 10W40 synthetic blend and the lifter noise has quieted a little. He wants to replace the lifters and pushrods as the cheapest top end mechanical fix, but I'm now wondering if there isn't another reason that remains undiagnosed. When we assembled the engine way back ten years ago or so I remember that the pushrods that the vendor had provided with the heads and roller rockers were too short and I had to use the pushrods that had come out of the engine, which only had around 13K miles on them. One of those "I want to get it running today" decisions. I never figured out why the vendor would have provided short pushrods, but maybe the use of the existing pieces is now biting me in the ass.
So, it's beginning to look a lot like Christmas and my Mustang has been in the hands of this "Mustang expert" for about three weeks. He switched the lifters that I had in the car to anti-pump up types, cleaned up everything he could find and then discovered that the engine mounts that he had just replaced in October were torn again. He replaced the engine mounts and the tranny mount, just to be on the cautious side, and fired up my baby. He says it runs great but the engine sounds like a sewing machine from all the lifter noise. We were discussing the reason why the noise would be increased and I suggested that either the pushrods were of an incorrect length or the rockers were improperly adjusted. His response was that the rockers (Motorsport roller rockers) were basically the stud type that don't really allow for adjustment(?) and the pushrods were identical in length to the ones that were in the car. That led me to ask about the height of the lifters, but he said they were the same as the Federal Mogul ones I had in the engine. He's back to working on it now. BTW, he suggested using a chain to prevent the engine from tearing motor mounts. When I asked him where he was going to connect it he said on the ground stud on the right side. I reminded him that the engine will torque to that side, so a chain or strap there would just go slack when the engine torqued and it wouldn't offer any protection for the engine mounts. Now he tells me he can't decide where to attach a cable on the left side. This is a mildly built 302, not some fire breathing 428. I can't believe it suddenly started ripping motor mounts for no reason. I'm losing my faith in this guy.
Yeah. Mustang expert...not. Hell, sounds like not much of an expert at anything to be honest. Anti pump-up lifters are noisy. Can be very much on the level of old solid lifter set-ups. Pretty common knowledge anyone who has ever built engines should know. A non-stroked 302 built like yours will not destroy stock mounts. Certainly not as quickly as it seems those failed. Likely a cheaply made part more than anything else.
Press in stud mounted rockers are all non-adjustable, to my knowledge. Tighten the nut until it seats and you're done. Correct length pushrods are very critical in that type of arrangement, obviously. Stock length should be correct unless he installed something other than stock ratio arms. I'm betting it is nothing more than the noise those lifters will make. I would yank 'em in favor of stock type. You're not gaining anything by using them other than noise. If you have installed threaded rocker studs than the rockers should be of a type that are adjustable. Not real tricky to adjust just tighten down until the rocker binds the pushrod (can't spin with your fingers) and give it another half-turn or so. Just make sure the valve is fully closed when tightening each arm. Easy peasy.
FWIW, some roller rockers are just plain noisy. Whether you have pressed-in studs, or not, will not define whether you have an adjustable valvetrain...that will be determined by the stud type. Early "non-rail type" rockers (prior to change level 11) had adjustable pre-load. Later, "rail type" rockers were non-adjustable, as are later pedestal mounts. "Rail and non-rail" type VALVES are also different lengths as the retainers and keepers are placed further down on the stem to allow the "rails" on the rockers to center the valve tip. Running "rail type" rocker arms on "non-rail type" valves can make a helluva racket as the rails will be constantly whacking the retainer.... watch what happens when a keeper finally pops out!!!