The Stovebolt Site Forums The Shop Area Engine Shop 250 engine trouble after upgrading ignition

Ok, I got all excited when I found out I wouldn't have to swap engines just to get to an automatic tranny! I dedided to update the '67 250 with a new carb (old one was beyond rebuild) and went with HEI ignition...neither of which I haven't done before, only it was on v8 engines.

Symptoms before the upgrade:
slight miss felt/heard at idle.
strong acceleration albeit with some smoke from the pipe!
recently gasoline started dripping from the bushings around the throttle-plate shaft.

List of parts changed: (from autozone)
Holley reman rochester OE carb.
AC r44xls plugs
HEI distributor
cap, rotor, coil, coil cover, plug wires

Symptoms after the 'upgrade'!
HARD ERRATIC miss at idle
severe lack of power on acceleration
when carb is tuned to produce no smoke at idle, the engine bogs when you go to wide open throttle.
when carb is tuned to where the truck DOES smoke some at idle, it doesn't bog nearly as bad.

Timing is currently set at 4 degrees BTDC ('67 specs) When set to specs of engine with HEI, idle is even rougher.

I know I probably should have changed the carb first and verified running condition before proceeding. My thought was 'why take the time to tune the carb, when it'll probably need re-tuned after putting new plugs and hotter ignition?'

I'd like to hear some veteran opinions on whether there's issues with the current setup, or if it's possible that there are engine issues that just manifest bolder with a better fuel/spark system.

True mileage of vehicle unknown. Odometer shows 66k. Truck was owned by county from '67 to '83 when my grandfather bought it for a ranch truck. Something I'm wondering about is possibility of burned valves/worn seats. With being a 'leaded gas' engine, I don't recall my grandfather ever using any type of lead substitute. I've never had an engine with burned valves or bad seats, so I don't know what kind of symptoms that produces.

(will be banging head against wall...once again considering sbc conversion)

First make shure the plug wires are on the right plugs. Did you check the gap on the plugs? sometimes one can get mashed shut in shipping. Did you disconnect the vacuum advance hose when setting the timing? The original "slight miss at idle" could be a burnt valve but would be no worse after these changes. A compression check would verify it. Be shure the gasket under the carb. has a passage for the vacuum to reach the hole in the bottom of the carb. Only about half the rebuilt carbs. we buy are good. Try these things & post what happens . Some other bolters will have some more sugestions.

A few things come to mind, check the fireing order of the plugs and check for correct gasket under the carburater! The HEI should make it idle better no matter what the engine condition is, internal problems won't become worse with better ignition. Double check the plugs, make sure you didn't crack the insulation putting one in or bump the gap closed.

I like to set the timing where it idles the best with out the vacuum advance hooked up. Lock it down, hook up the advance to full vacuum and adjust the idle speed at the carburater. With the low compression and better fuels now, you can get away with more timing then the factory settings. You may find the mechanical advance of the new HEI is a lot differnt from your points set up. The timing at idle is not nearly as important as the timing at cruize speeds so I set the timing at high rpm (approx. 2500 rpm or where the full mechanical advance is in) at 34*. I don't know where the idle timing is set, I never check it there because it doesn't matter that much.
Once you are happy with the timing, move on to the carburater. It sounds like the jetting is wrong or the gasket under it is blocking the vacuum ports. Check the gasket first, make sure the open port lines up with the slotted gasket. Next, pull the top off and check the jet size and rod part number and compare to the old unit you pulled off. Check float level and float drop measurement. These are all simple to do and will help verify all is right for your application. The idle mixture screw is for idle only! It should be set for maximum rpm/vacuum at idle. Set the idle speed using the throttle lever set screw, then set the idle mixture screw ( start at two turns out from fully closed), alternating between the two till the correct speed is set, somewhere around 650 to 700 rpm. A very slight hesitation can be overcome using the idle screw, but only a very slight one. Just a touch on the rich side, say half a turn out from ideal idle speed, anymore then that and you are waisting fuel and fouling plugs.

Yours just sounds like its jetted to lean, check out the two and let us know what you find. A vacuum leak can also cause a bog and now power. Joe

You don't make things easy.

Gasoline at throttle plate, needle and seat not shutting fuel off completely ie float level set too high.

The smoke from the engine is black indicating burning to rich (float level) or whitish blue, indicating burning oil. Don't adjust carb by the smoke. Adjust carb for idle mixture, which may not be possible if float is not set correctly.

HEI distributors are excellent distributors and recommended. Unfortunately HEI distributors are setup for smog compliance, which means generally not having the advance of your original distributor therefore lack of power on acceleration.

Engine mileage could be anything considering the age of the truck. Doing a compression check will give you an idea of condition the top end of the motors is in.

First straighten out the carb.

Larry

I'm almost positive that engine should take r44(gasket-type) or an r44t(taper seat) in an AC plug. the xls means an extra long seat IIRC. maybe a piston has closed up the gap. I added HEI to a 64 230 & it idled smmother & gave excellent fuel mileage,,,brian