You all are certain to get a good laugh outa this one - I'm relatively new to American iron most of my cars having been sports cars,small trucks or hot rod aircooled VW'S of which i still have a sand rail but thats another story for another day.I have a 70' F-250 camper special 3/4 ton - I have no idea what kinda mileage its got - any who it came with a nice set of stainless albeit old and crusty merged collector headers those i've retained somewhere along the line someone tossed a 390 4 barrel iron manifold on it and a 750 Edelbrock carb - got it rebuilt but it still ran like ****..Everyone was telling me thats way too much carb so i got a 600cfm Motorcraft on there and it seems to like that very much along with the Edelbrock aluminum manifold i'd put on to match the 750.Have also installed an MSD billet disto with the 6A box - very nice - Alright heres the fun part i was trying to find TDC on # 1 had the plug out and was bumping it with a starter button and had a tweaker straight blade screwdriver in the plug hole i left it there turned the engine over heard a sharp ping and the screwdriver shot outa there bounced off the underside of the hood and landed in the garage - it must've gotten caught under i'm assuming the exhaust valve for # 1 the piston came up and bam snapped the tip off it which fell back down inside the chamber - You have NO idea the relief i felt in being able to fish that little ******* outa there with a slim magnet.Several months later and the truck runs very good really - I did a compression test on it last weekend,145 in 5 cyl's,`140 in 2,& 135 in the last one which was NOT the one with the snapped screwdriver incident.Now when its running at idle sounds and runs great - when its warmed up - gas it and as soon as you let off it will pop/ mild backfire out the exhaust.Now if you give it a LITTLE gas and just hold it steady there it will continue to pop not all the time but pretty consistently.I've got my hand on the door and i can feel it firing the plugs and its not an ignition miss - its got new platinum plugs and taylor 8mm wires along with the disto,coil,ignition box - The compression is great for a 42 year old motor which i'm sure has never been apart with who knows what kinda mileage - My question is if it was a damaged valve and or seat would'nt it be reflected in the compression reading? and a popping like that in the exhaust is one indicator of a bad valve/seat is it not?

 

firedup, Do you have a balance pipe connecting the exhaust between the headers and mufflers,if not have a muffler shop install one, also make sure that the #7&#8 plug wires are seperated as much as possible. Try to route them on oppsite sides of the looms on the valve covers. Goood Luck , Kenny Nunez

 

Check the timing chain and gears.

 

You know i had thought this as well - as it seems to run the best when set/tuned by ear which ends up being about 10 degrees advanced beyond the 8 specified so its at about 18 now -

 

whew...that could be too much timing.
do you know what slot the distributor weights are using?

if you're in the 13L slot (26 degrees mechanical advance), and then you add the 18 initial...that puts you at 44 degrees advance, which is above the 38 degrees total that you should be using. even worse if you're in a 15L slot...

plus- how on earth do you get that thing started with 18 degrees initial?

tuning the initial timing by ear is dangerous if you don't know what's happening under the cap.

 

Absolutely RW - If - everything was right on but if the timing chain has stretched along with worn teeth on the gears - In trying to remember how i initially timed it i know it was static timing in a sense in that i made sure i was at TDC for # 1 then advanced to 8 BTDC dropped the disto in with my best alignment of the rotor pointing towards # on the cap - it fired up - so i fiddled with the disto tuning by ear and it ran alright,would fire-up relatively easily run like crap when its cold but it still does that anyway i've thought possibly with the headers eliminating the stock preheater off the stock exhaust manifold not a big deal - Anyway when i drug the timing light out it was actually quite a bit more advanced - as i brought it up closer to 8 it started to crap out so i again adjusted until it smoothed out which appears to be in the neighborhood of 18 deg. with this popping in the exhaust other than that it runs great i have'nt driven it as its not current on registration and the tires are pretty soft - Now if everything was in GOOD condition which i'm finding out basically by trial and error as theres no telling how many actual miles are on it - I think the oil and filter were changed fairly regularly as theres almost no sludge in the valve covers or any real buildup anywhere on the valve train but i don't think it had much maintenance beyond that i found a lot of crap in the filter bowl off the fuel pump -and theres a long term buildup of an oil leak combined with dirt over quite a bit of the general area under the engine and trans - Now if the chain had stretched a tad not enough to seriously throw everything off but just a little - as it is 42 years old i'm reasonably sure all the internals are original so it is a definate possibility.As far as which weights are currently installed i know the instructions has them listed i just went with how MSD shipped it to me - I provided Summit with the particulars concerning the engine which is basically stock and thats how it came.Once it warms up you can blip the throttle and it revs up nicely sounds very healthy i'm amazed but as soon as you let off it will pop out the exhaust just once - I've done this inside the cab with my hand on the door to see if i can feel an ignition miss or any roughness and theres none i've leaned against the side on the fender doing the same thing and i can't feel a miss - If it was that far advanced i'd think you'd have a ping and it does'nt at all and i'm not shy with the loud pedal - not insane - but i do enjoy hot rodding and performance - I'd thought with the screwdriver incident i'd f---ed up a seat or an exhaust valve but i've got good compression and that cyl. is not the low one which from 145 to 135 being the low one is still not bad - So i've leaned towards a slightly stretched chain - but like i say its a learning curve for me..

 

I have the same problem with the poping thing. I even put on hooker headers with dual glass packs, thought would solve the problem, but nope still happens.

 

gotcha- i missed the part about the MSD distributor.

maybe a sticky exhaust valve? that wouldn't have shown up in the compression test. like you said, though- the stretched timing chain muddies the water.

 

It seems like the logical conclusion,with the timing chain - in the case of a sticky valve how would you remedy it? How would you determine which one it was or could you? Yeah the MSD disto is a nice piece of work but you've also got to use their ignition box with it so by the time you're done you looking at the better part of 5 benjamins but i'd much rather have strict mechanical advance - I'm sure and the thoughts already been creepin' in that while i've got the timing cover off to slip in a mild cam and lifters - would'nt you? at least toss it around?

 

Yep i'm not sure who this set is made by but they are crusty stainless and they've got merged collectors so who ever they would'nt have been cheap even back in the day.It is a camper special 250 with a saddle tank which i've eliminated which neccessitated the use of you guessed it dual glass packs coming out on the passenger side - i plan to redo it from the collectors back and use some magnaflow muffs 1 down each side.Have you done the timing chain? where are you timing it at? Does it run well if you've got it at 8 BTDC? -

 

just a note, a balance pipe, cross pipe or H pipe is useless unless you take the time to find the hottest points on each side of your exhaust & install the cross pipe at those two points, otherwise your just wasting your money

 

Thanks for the advice - its not something i was considering i believe the problems elsewhere.Another individual i'm assuming had a stock exhaust system installed a set of headers thinking it would cure the same problem i've got - and it did'nt he still has it.I am going to reconfigure the exhaust after the collectors as originally with the saddle tank they had to run both pipes down the passenger side leaving the only muffler that would fit being glasspacks i've eliminated the 2nd tank so i'm going to run down each side with some magnaflow mufflers which i would do anyway - I was'nt thinking of a balance pipe -

 

How does missing the part about the disto affect your thought?

 

To be honest i dont know where the timing is set at. My grand father recently set it. (He worked at ford and delivered it to the first owner).
I dont know what BTDC is..

 

BTDC before top dead center ie: advanced - do you ever check it with a timing light?