combustion problems - HELP

[cobra_2_76]

I have a problem I just can't figure out. I'm getting fuel to and though the carb, floats ok, 66 primary jets, 68 in secondary. Idle screws about 1 turn out. I'm getting spark to the cap and plugs, verified MSD box works fine. No fuel filter obstructions.

But it won't run. I can get it started once and awhile if I turn the dist to about 30 degrees advanced, but if I return it back towards 10 degrees it dies, and becomes harder to start. It also appears to be harder to start when warm.

This engine ran really nice up to about two weeks ago when I noticed a slight miss or something when driving it at 60 mph, just barely noticeable. Mechanic who was checking my drive shaft balance didn't notice any problems. Over the next week it progressively got worse... until it wouldn't start unless I started advancing the distributor as noted above.

Originally I thought I had a broken coil wire to the horseshoe connector, so I replaced it with a new one. Didn't solve the problem.

Replaced the plugs, cap and rotor, just in case something was amiss there but again no difference.

Any suggestions......one thought I had was whether the carb is passing too much fuel, maybe a cracked carb body? Crack worsend over couple weeks? Would that explain why it might run 30 degrees advanced? (advance gives the engine time to burn the fuel but at 10 degrees floods out?)

I'm open to any ideas

Other particulars:
9.0 compression
351W heads
Blueprinted Duraspark by Accel
MSD 6AL box
Mild cam
about 8,000 miles on engine
does not burn oil or consume fluids
17 inches vaccum
Edelbrock Performer manifold
Holley 600 4150
Holley mechanical fuel pump

 

[D.Hearne]

Sounds like it may have jumped time. Pull the distributor cap, then with a breaker bar and 15/16 socket, turn the crank slowly and watch the rotor, it should turn in time with the crank. If you can turn the crank a quarter turn or more, your timing chain is way too loose. It could have also sheared the roll pin that secures the distributor gear to the shaft.

 

[cobra_2_76]

I have spun the engine with the cap off to verify good smooth movement. The Ford Motorsport chain has about 4,000 miles on it, so it's doubtful it's slipped, but will make a note to check.

I'm not running a roller cam, so theoretically the gear should be good, but has been a consideration as well. Probably should pull the distributor to check.

keep the ideas coming!

 

[skywalker]

Jumped time sounds likely to me. I had an old pick-up truck I had do that to me. The timing chain on it was old and it jumped a couple teeth...wouldn't crank to save a life. In your case it probably isn't the chain, it's probably the gear. I'd pull your front cover and have a look.

 

[D.Hearne]

You might also check to see the voltage getting to the coil is sufficient. Even though there may be a spark at the plugs, it may be too weak to fire the mixture. Have you verified that the carb isn't passing too much fuel ? A stuck float, vapor lock, too much fuel pressure, and probably a few other reasons could be the cause with a too rich mixture, as for a cracked part in the carb, that's always possible, but not a likely scenario. I've never had a Holley that was so bad that fuel could get thru to the throats to cause a too rich condition. Check the power valve too to see if it's not blown.

 

[cobra_2_76]

Let's see plug in coil wire while triggering MSD sounds like bug zapper....I'm comfortable the coil and box work.

I agree about the carb, I was thinking back 20 years ago when my Ford carb cracked at the float bowl.

Float levels are perfect....power valve is probably bad due to the multiple backfires trying to just get a hit on the engine...have two more waiting to be sacrificed!!

Timing gear is a Ford Racing version with about 2,000 miles. It better not be stretched. I'm wondering if maybe the drift pin might have pulled out of the cam. Torqued bolt would keep the cam turning and with the pin in the fuel eccentric would keep the carb fed.

Comments??

 

[D.Hearne]

Never seen the pin come out of a cam that easily. The big thick flat washer normally retains the pin, you DID use that washer under the bolt? I'd change the power valve first, then work from there.

 

[WORTH]

well if the float level stays good i dought you have a crack in the carb. Could be the distributor gear slipped as D.hearn mentioned. IS it possible you got some **** gas?

 

[cobra_2_76]

I wouldn't bet my life on it, but almost positive I did. Hard to forget a washer that thick. Your scaring me a little, because if I didn't forget it my hopes for a final solution and one of relatively low cost may have gone out the window.

Dave

 

[cobra_2_76]

Now that you mention that cam washer.....I'm going to pull that distributor one more time and take a real close look at the gear pin. Hate to pull the timing cover to find that the gear pin has sheared and is slowly rotating around the shaft.

I did notice last night that the valve timing in realation to the distributor is WAY off, almost one cylinder in the distributor.

 

[cobra_2_76]

Turns out distributor gear is ok. Tapped the retaining pin out and looks fine.

Now I'm wondering if I sheared or bent the dowel pin. I was reminded that it did feel loose in the cam when I put the new chain on a couple years ago. Hopefully didn't mess the cam up, and will just need a new pin....

Dave

 

[cobra_2_76]

Bad news....nothing wrong in timing chain area. Cam pin intack and properly aligned. AAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHH

I guess I'll put it back together, re-check all parts of the distributor, lube it up. Recheck MSD box is working, re-align the distributor to #1, and re-check the carb.

Thanks for all the ideas.
Dave

 

[WORTH]

I'd do a compression check just to be sure before you go any farther.

 

[cobra_2_76]

Short answer it runs!!! Seems the coil was not dead,
worked but just barely enough to hide its
problems....here's what transpired.

Well went back to the drawing board and started over
with the spark. Re-checked the magnetic trigger on
the box and got a good spark with a plug in the coil
wire.

Next decided to check the wires from the MSD box to
the distributor. Stuck two tabs into the female side
of the Duraspark distributor connection and used a
screwdriver to make the trigger jump. Again fantastic
spark with a plug in the coil wire.

Next put the coil wire on the cap, aligned the rotor
with a plug terminal, pulled that wire off at the head
and installed a spare plug. Then ran the screwdriver
over the terminals again to trigger the plug.....hit
six times THEN it started discharging in the MSD box
not at the plug. OOOOOO, shades of a bad box?

Tried several times with same results. Re-checked
cap, no cracks.

Friday morning called MSD and discussed findings. Of
course electricity finds the closest ground, so
concensus was box was ok. Said to check coil. Now
the instructions say if the ignition FAILS to replace
the coil and if it still doesn't work return the box
for service. They gave me the ohm spec's for the
primary and secondary windings.

My ohm meter on my Craftsman diagnostic box failed so
Friday I take an eary lunch to Radio Shack and they
don't carry one in those ranges, darn. Off to my
favorite parts store and get one there. (Should know
better and stay with a sure thing.)

Take off early from work, (one of the few benefits of
being salaried!) Get home and check the ohms.

Supposed to be .7 for primary and 4.7K for secondary.
The coil registers 1.2 primary and 4.3k secondary

Hummmm, call MSD back and they say the coil is bad.

OK, off to Summit, three and a half hours later return
with the coil. Ohms match, install and still won't
run. ****.

This morning go back out and recheck - notice no fuel
in carb. Hummm, I know I re-tightened the cam
eccentric bolt, but no fuel. Try some gas in the carb
anyway, doesn't run. Oh well, I'll get back to it
when I get the eccentric tightened. Get started
tearing the power steering off AGAIN, when I notice my
vice grips hanging under the car. Darn forgot to hook
up the fuel lines to the pump. Hooked it up, turned
over the car to fill the bowls and IT STARTS!!!!

Seems the thing was slowly failing....who would have
guessed. Because it was not generating a strong enough
charge it wouldn't jump the gap in the distributor and
grounded in the MSD box. I guess if I had followed
the MSD instructions I would have saved a lot of
frustration, but darn it was still generating a spark.


OH well it runs great and I'm out of my gloomy
cloud!!!! Summer may be good afterall!!

 

[D.Hearne]

Well I was partly right about the spark not being strong enough Glad you've finally fixed it.

 

[cobra_2_76]

Yes you did and I missed it by focusing on your accurate carb comments. I had an autolite quadrajet, which cracked a bowl causing my 72 Mustang to run like crap.

Dave