Hey!
I have a 1970 f100 with a 302 in it. I recently installed headers and dual exhaust, and found that when I am slowing down or especially if i let her roll down a hill I can hear a popping from the engine. It dosnt backfire while idling, but if I rev the engine and let off immedietly I get the popping and a bit of whiteish smoke. At idle the engine has a bit of a lope, which I found odd because it is totally stock, and if your hit the gas really hard it revs up to about 2000,2500 rpm then bogs momentarily, loses a bit of rpm and then revs up again. I have just installed a k+n airfilter as well to ensure the engine is not starved of air. The timing is set exactly at 6 degrees btc. I also conducted a vacuume test to only to find it is perfectly normal and a compression test to find the higest and lowest readings within the proper tolerance. THe engine has 95500 miles on it and does burn some oil but It isnt too bad. On the highway i can even get 16 miles per gallon (at 3000 rpm/70miles mph) which is pretty decent. (imperial gallon) I recently had a two barral carb off a 79 LTD rebuilt and installed. I did this before installing the headers, so I was thinking the bog could be due to and improperly adjusted carb. If you have ANY suggestions let me know.
Scott:confused: :confused:

 

Did you get glasspacks? Mine crackle everytime I let of the gas. Stock rebuilt 351 with stock exhaust manifolds performer intake and edelbrock 600 carb, so basically a stock motor. Then again mine doesn't bog as you described maybe there is some need of carb adjustment as you mentioned. Is the crackle from the tail pipe or your carb if it is carb then yeah I do believe it is lean. Good luck hope you figure it out

 

Air infiltartion somewhere in exhaust system, but if you hadn't already checked for it , I'd first say a vacumn leak, you may have disconnected a hose or fitting you did not re-connect. We used to pull our vacum wiper hoses off to make our glasspacks backfire (yep, windshield wipers used to be vacumn operated-made it a real joy passing another vehicle in the rain!)

 

Could also be an exhaust leak allowing air in the pipes.

 

Well now you all have me thinking. I figured my exhaust crackled because of the glass packs but now you all have me thinking air leak however, I installed my vacuum gauge at the carb and it read fine or at least it did when I tuned the carb so maybe if anything it is the exhaust manifold. Any thoughts

 

Thanks for all your replys, I will check the exhaust system for leaks, I never considered that possibility because I had the whole exhaust system professionally installed. I am running headers so I will check and see if they need to be retorqued again. I am running boss turbo mufflers, not glasspacks so I dont think that is the problem. Would a vacuume leak in the carb be causing these problems? Does anyone know what size a cam these engines ran stock? (1970 302, in a f100). Thanks again

Scott

 

Do a good visual on your exhaust system, paying attention to each joint. If the "slit" on a connection leaves a tiny hole exposed, there could be your culprit. A dab of silicone seal will solve that, but let it dry overnight before you start the car. Also stick your head up under yoir hood while its idling and listen for a hiss. Hoses break all the time, one little slit could be the problem, and hoses are cheap. I looked and looked and couldn't find a leak on our Buisck, but the garage found it in a minute...it was a hose under a hose behind a hose...had jut worn and cracked at the nipple. I'm convinced you have an air or vacumn leak unless your carb is WAY lean.