Alright guys,been lurking here but I need some help.I got a 1987 F250 460 with a C6.Stock about as far as I know.Bought it about a month and a half ago,just got it on the road a few days ago.(Drive home when I bought it was umm,interesting...) Anyways after rebuilding the brake system and front end I changed the fuel filter on the carb (stock holley 4 barrel) changed plugs,wires,cap,rotor,ignition coil and ignition control module?Little silver box...So what she's doing is in park and neutral Idles great and I can rev all I want.In gear,Idles fine but with a slight miss every now and then that seems to get worse the hotter it gets.Biggest problem though is in gear I get horrible backfires from the exhaust if I floor it while driving or even at half throttle from a stand still.Seems to be under load is when the problem occurs.Any and all advice and suggestions are appreciated,she's gonna be my new daily so I need to get these things figured out before I go and sell my little B3000. (Not much to look at but man oh man a reliable SOB even at 265*** miles)

Edit:Forgot to mention,not sure if it's related or not but when the motors hot if I stop say at a store to get a soda,come back out sometimes when I start it the motor almost acts seized.The starter sounds like it turns 1/4 turn real slow and stop,but then it will pick up and start and run just fine.Starter is brand new too.

 

on the hot starting, start with checking the timing, battery cables and ends. terminals too. make sure the firing order is good. you might want to start reading up on holley carbs too. that or make friends with someone that knows them.

 

When you say "backfire" my first thought is ignition. But wait. Are we talking backfire like a firecracker out the exhaust or like a spitback through the carburetor?

Exhaust side is unburned gas out the exhaust. Intake is a different issue.

 

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It's backfiring out the exhaust not the carb.I definitely need to find a buddy whose good with carbs can't argue there,believe it for not this is the first carbed motor I've ever had.Built a few mild 302's one in my first truck and one in the LTD I had but both were EFI so as simple as carbs may be,this is all a learning experience for me.

 

holleys need specific knowledge to work with them. i had to learn a lot back in the days. for sure if it sat for a while there could be problems with the gaskets and the dreaded power valve. if you rebuild it get a anti-backfire valve for it. its a special made screw with a floating ball in it to help prevent from putting a hole in the power valve diaphragm.

 

Chances are the dia.is bad, after replacing any bad stuff,set idle,put truck level,{with running} remove 1 float sight screw at a time,gas should just come out a little,the adj. screw is in top with a lock nut,set your mixture screws to start with to 1 1/2- 2 1/2 turns out finale adj. from there.Holleys are easy to work on,dont let anyone fool you.

 

Sorry it's taken so long to get back to you guys,been working 16 hour days with no days off until atleast next Monday so it's been crazy.Well quick update,had a MASSIVE boom from the carb this morning,guessing a wicked backfire for whatever reason.Well it blew out the float bowl gasket on the front bowl and I don't even know what else just POURS gas with the ignition on.I went ahead and ordered a carb from national carburetors this afternoon so I can have a fresh start there....now we play the waiting game...

Edit:Noobie question here...where are the mixture screws on the carb?

 

there are 2 idle mixture screws on each side of the metering block. gently turn them in till they stop or seat, then back them out turn or so and start from there. they affect the idle mixture. usually the more you back them out the richer it gets. but on some its backwards.

 

Backfiring is generally considered only through the carb. in the pipe it is after-fire. Not to get caught up in semantics, it just makes it easier to help. Backfire is usually ignition too advanced, after-fire is generally ignition timing too retarded. Big question is, did it do it before the new parts, if not, I'd start working backwards, undoing the tuneup until the symptoms stopped. It really sounds like a misplaced ignition wire pair, double check the plug wires against firing order.

 

Alright I know it's been awhile,busy busy sorry guys.The new carb came in yesterday I threw it on there fired her up and went for a drive.Seems to me all the issues I was having are gone now so I guess it was all carb related.Just wanted to let everyone know it was resolved and thank you all for the input it's appreciated.

 

Did you mean after-burner? Didn't think so. This post is the epitome of FOS. What is this based on anyway?