Rebuilt 200 w/spark knock

[Anonymous]

I am new to this site but it really appears to be just what I am in need of.

I recently completed a total stock restoration of my 64 1/2 Mustang coupe including a total stock rebuild of the original 170, only aftermarket piece being Pertronix electronic conversion of stock distributor. Everything worked like a champ.

Make a long story short, a good friend of mine approached me and asked me if I would help him do a ground up resto on his 68 Mustang coupe. We rebuilt his original 200" 6, punched it .030 over, and installed a Hooker 6/2 header with 2 1/2 " dual exhaust and again, the Pertronix conversion. Carb and distributor were replaced with reman. units from local parts store. So far, so good, right? Well, now it seems that no matter what I do as far as initial, total timing, We have a slight intermittent ping under light to moderate throttle. The only way I seem to be able to "time" it out is to back off my initial to about -2, at which point the engine idles and performs about as well as my Farmall B tractor. I did repair a small crack in the intake right behind the carb. I have 20" man. vacuum and do not seem to have an intake leak. At this point I am beginning to think that the install of the header is creating a lean condition or, possibly even worse that the crack in my intake extended into the "roof" of the middle two exhaust ports and is causing my problem. It has me truly stumped. I have been working on Mustangs and other Fords for years and have run into some wierd stuff, but this one is starting to get the best of me. Thank you in advance to anyone who may be able to point me in the right direction.

Thank You,

Phil

 

[JackFish]

There has been some discussion lately about reman carbs, especially with regard to spark control valve. I don't know if this is related to your situation as I am running a later setup, but perhaps you need the carb with valve, and didn't get one at the parts counter.

 

[addo]

Do you know what your compression ratio is? Also, is the cam dialled in? One fellow here found his replacement cam was 11 crank degrees off. I would also check the fuel pressure between carb and pump, and the float level. Final note would be to verify TDC on the balancer.

Regards, Adam.

 

[Anonymous]

as far as the carb, we originally received a Holley style reman from the auto parts store. The float level and several other adjustments were way off, so we replaced it with the autolite 1 barrel, which appears to have the spark control valve in it. As far as valve timing, fuel pressure, balancer mark accuracy, that has all been checked. I pretty much think I've checked all the usual `possible causes of timing inaccuracies/spark knock and that's why I am wondering if the problem could be related to the header and/or crack in intake runner or combination of both. As far as compression ratio, I did the math myself and by increasing the bore by .030 while retaining the stock size combustion chamber, it comes out to about 9.2/1. I certainly wouldn't think that would be an issue, even with today's rather substandard fuels. I was considering installing an inline vacuum check spark control valve in my distributor line, like the ones Ford put in some of their mid 70's cars when they were having a lot of problems with spark knock. I was really hoping that maybe someone out there had experienced a similiar crack in the intake runner right behind the carb and may have experienced similiar symptoms.