The Stovebolt Site Forums The Shop Area Engine Shop 250 timing or fuel problem?

Hey all,

I will throw this one out there for comment, mostly because I gave up for now. I have a '70 Chev 1/2t 250. It started and ran ok. It did have a suttle miss that was hardly noticable at hiway speed. Driving it home it died, seemed like gas problem. I kept it going and it would keep dying. I got home by driving in 2nd at higher rpm. I did rebuild the Roch MV carb, plugs, points, wires. Tappet cover gaskets leaked bad, so new, so dist was out. On the truck the timing sticker says 0 btdc with manual trans at 700 rpm. The truck won't seem to run at that spec. It seems to need way more adv. to run. The vac adv. and mech adv. appear to work when I bring rpm up and check with timing light. It will start and idle perfect. Go down the road and it misses and has no power. I adj. the timing by ear and ran down the road, it never seemed quite right. The light says base timing is at 15 or more degrees, on the 0 the spec says. The truck ran down the road and died, starter of cours quit. Towed it home and cooled it off, then starter worked, but would not start. Retard timeing and once again it idled fine. I don't know if I am fighting more that one problem or if I am the problem. Do these 250's have nylon gears for timing? I checked the crank to cyl 1 tdc and it looked good. Throw me a bone someone...

Thanks.

Stock cam gear is fiber and the only time I had one fail it was absolute - running one second, and dead the next, with zero rotation on the distributor.

My balancer had slipped giving me a lot higher baseline timing number than spec. Maybe yours is too but that isn't why it dies.

Probably vaccum - cheap insurance to replace the vacuum advance and other hoses. That would explain the variance at idle vs. speed, and the works well one minute and not the next kindof symptoms.

Possibly electrical - double check all the connections are tight. I've had a loose coil wire cause a car to run fine at idle and flip out at high RPMs, or vice versa.

-Boyo

Check the points. The adjustment may have slipped or the rubbing block may have wore down with no grease on it. The dist. bushings may be worn out. An HEI conversion works wonders for these. Know may be a good time.

Last night I checked the dwell, about 23 deg., spec says more like 30. Timed it by vacuum, inital timing was 27 deg., that is what is weird. Then the starter quit again, so will have to replace before we start in again. I might be leaning toward coil or distributor. One time it missed with the timing light on it and the strobe went black during the miss.

Fix the dwell.
Check to make sure the balancer outer ring hasn't slipped. Very common, as chuckthetruck mentioned.
Don't expect that starter to crank it over if it really is at 27 degrees.

>I might be leaning toward coil or distributor.<
The dwell is off and the timing is off. Isn't that enough of a problem?

The dwell is now close, 28-29 degrees. The gap is at the minimum recommended .016. The truck starts good and idles all day long. Why the timing marks are goofy, I can't figure out. The starter is just old, it is not cranking hard. Would a new HEI distributor drop in? It sure looks like a tight fit against the tappet covers. I will road test tonight and see how it runs.

Yes a HEI will drop in if its from a 6 cyl. 292 or 250. It sounds to me like its a fuel problem. Ignition problems don't normally care if you run the engine faster, they eather work or they don't! HEI will be a big inprovement over the points, I replaced a brand new points dist. with HEI and was really suprized at how much better it ran. Set the timing where it idles best and test drive. My '73 manual wants them at 6 degrees advanced, I run mine around 8 degrees.

Yours sounds like a fuel delivery problem. Crap in the tank plugging the pickup tube, or a fuel line sucking air. When it dies, get out and look down the carburator and see if it has fuel. Also take note of the engine temp. If its running lean, it will be hotter! A vacuum leak will do the same thing, check around the intake mounting bolts with a hose and listen for a leak. Joe

>>Why the timing marks are goofy, I can't figure out.<<

Your posts don't indicate that you've checked the balancer outer ring. If it's loose, it will eventually come off.
I had one fly off and disappear at about 65mph. I had another fall off onto the ground when I started the engine.

Richard,

It appears tight. The cylinder number 1 and TDC do line up correctly with the 0 on the marks and pully. I must be doing something wrong, but I have not banged by head on it yet. If the inital timing was truly 30 degrees BTDC, the truck should not even start. I will give it some time, maybe it is self healing....

Brad

Be shure the vacuum advance hose is disconnected when you are setting the initial timeing.

Rapper1,

I just replaced my points system with HEI and noticed that the crankshaft pulley had two marks on it (the ones you use to figure the timing). They were both at opposite sids of the pulley. Could you have this also and be lining up the wrong mark? (Thus being 180 deg rather than 0?) Also, I believe that the timing should be 4 deg BTDC.

For adjusting the fuel/air mixture, my manual said to turn it all the way right towards the seat.

Then back the screw out 3 turns.

And then turn it IN a 1/4 turn or until it runs smoothly.

Should idle for a standard be something like 500-700 RPM?

Haha, these old motors. Sometimes you can spend hours in that hot sun playing with their timing and carb adjusts.

True, then the next day it will all be different! I have a hand heald exhaust analyzer so I can play with the mixture screws all day long, its fun trying to get it just right! Joe