Exhaust backfiring

[Mv7fd]

We set it at 12 initial then took an Alan wrench stuck It in the vacuum advance and adjusted it that way to give me the overall 36 we changed the springs as well

[geezer#99]

Now I got it!
But that's not how you adjust for all in timing.
All in is with the vac pot plugged off.
Adjusted with modifying the slot in the dizzy, plus different springs.

[Mv7fd]

well finally figured it out i should have done this from the start. it has a bad cam lobe..... cylinder number one intake valve doesn't hardly open. so now i guess i'm looking for suggestions on cams and i'm also thinking about replacing the intake. i'm looking for something that is street able nothing high power. or should i just go ahead and buy a crate motor. this is the second cam this truck has messed up

[geezer#99]

You likely messed up the second cam cause you didn't do a complete tear down and motor flush, if it's the same motor. And it'll happen again.
If you're gonna do it right you mights well look for a crate replacement.

[Mv7fd]

The first cam went bad in 1985 that's about 7 years before I was even born

[rich weyand]

The 350/260hp base crate engine is strong, reliable, and cheap. Around $1500 and free shipping from JEGS and Summit.

You can cam it up in various ways, or cam up your existing motor in various ways.

You could google my last name and one or more of these Comp cams numbers to find a lot of data on various forums on the 12-300-4, 12-234-2, 12-235-2, 12-238-2 cams.

You want a dual-plane manifold. I like the Edelbrock 2601 air-gap manifold, but you need to use the thermostatic air cleaner with that or cold-weather performance will positively suck. Again, google my last name and 350 and induction.

[Mv7fd]

If I were to put a new motor in it do you think i'll be able to achieve 14 mpg right now with the bad cam and things adjusted wrong I'm at like 9.5

[rich weyand]

A C-10 you should be able to get 14 at 60 mph depending a bit on tires and axle ratio. Stick shift helps too if you have that. Maybe 15 then.

For a K-10 it's probably more like 12.

[Dead Parrot]

My 75 C10 with the 350/260hp crate motor, TH350, 3.42 rear end and stock size tires gets about 12.5 @ 70mph, a bit over 14 @60, and about 10 @ 70mph when towing a 16' boat. Using a performer manifold and a edelbrock 1405 carb. No emissions other then PVC system. Using a stock but not original to the vehicle air cleaner housing. Made no changes to the internals of the motor.

[Mv7fd]

So my plan is to go with a crate motor I wanna buy one that's got the intake and carb with it too that way it's all set up. What's good to buy that's a 350 and I'm going to use this as a daily driver

[dfrank]

Originally Posted by Mv7fd

So my plan is to go with a crate motor I wanna buy one that's got the intake and carb with it too that way it's all set up. What's good to buy that's a 350 and I'm going to use this as a daily driver

I would go with this gm performance products 35HO turn key crate motor then. http://www.speedwaymotors.com/GM-Per...AHYaAgUg8P8HAQ

Stay away from blueprint engines. They use a cheap chinese cast bottom end.

[gchemist]

I didn't read all the thread. What year is the block? If it has nylon timing gears, they are starting to crack or have broken off. It's only the matter of time before the gear has teeth stripped off. A failed nylon gear is how my old 305 finally blew up by breaking the cam when the gears stripped.

[Mv7fd]

well guys my truck is finally back together i ended up having to pull the cam out and replace it that was causing the pop one lobe was totally round and i also had a bad lifter so i put new cam lifters rockers and push rods got everything back together and it ran better but had an idle problem no matter what i adjusted it to it wouldn't stay right so i found out that the EGR was leaking so i got a delete plate and also replaced the carb base gasket because that was leaking as well. fired the truck back up and still had problems so i was on the hunt for a vacuum leak again. the vacuum advance canister had a air leak and the back side of the intake manifold was leaking so i picked up a performer intake for 50 bucks and a buddy gave me an older rebuilt holley 600 cfm carb for free and i also replaced the distributor and wires this time and i fired it up all is great now. i'm getting 6.5 mpg which sucks but it sure runs good

[rich weyand]

OK, so now you have to tune that carb....

[Mv7fd]

carb is tuned thats the thing if i lean it out even just a hair it'll die

[Mv7fd]

it has awesome response great power no bogging down just likes gas

[rich weyand]

Lean it out where? At idle? What about the other circuits?

[Mv7fd]

if anything i might have to have my vacuum advance limited because i'm running like 10 degrees before TDC and overall 35 or 36 then you add the vacuum advance and there is a lot

[Mv7fd]

At an idle

[Mv7fd]

I don't figure i'll get that good of mpg its a k20 with 4.11's and a 4 speed with granny gear

[rich weyand]

Originally Posted by Mv7fd

if anything i might have to have my vacuum advance limited because i'm running like 10 degrees before TDC and overall 35 or 36 then you add the vacuum advance and there is a lot

No, those are the correct numbers. At rpm and high vacuum, you should be running about 50* BTDC. That's all fine.

[rich weyand]

Originally Posted by Mv7fd

I don't figure i'll get that good of mpg its a k20 with 4.11's and a 4 speed with granny gear

You should be getting 9-10 mpg in town, and 11-12 on the highway.

You are running way too rich on the cruise circuit, and probably on the power circuit as well. Secondaries always run rich, but those are engaged too seldom to kill mileage like that.

A good A/FR meter is $300. That will tell you exactly what your mixture is running everywhere, and allow you to tune the carb to save a lot of gas money.

[Mv7fd]

I'll give that a try it doesn't smell like it runs rich at an idle or anything and it runs pretty good. I filled it up yesterday so this will be the first tank since I fixed everything let's hope it goes good

[rich weyand]

I have the earlier version of this unit, and it works great. I got my mixture (and mileage) dialed in to the numbers. Leaning it out also increased performance, because the extra (unused) gas displaces air molecules that the engine could use.
http://www.summitracing.com/parts/ngk-96604

[Mv7fd]

I can't lean the idle mixtures screws out at all it will kill it as soon as I barely move it