Up Date On My Timing Problem, Its Half Way Fixed

[bigd65]

ok i used a dial back and i did find out what my total is or about, i really couldnt tell with this lite, i will redo when i get a timing tape. well it is about 32* at 3000 rpms with 12 initial. when the engine is cold it dont have any spark knock, not even when the passing gear releases and goes into 4th gear and the load gets harder. the problem is when it is warmed up and driving around then i get into it, it has the spark knock. it dont get hot, the temp gauge is below the 180* mark and yes that is about correct, because i even put a mechanical one into it and read the same thing. i am taking a wild stab here but i am thinking maybe the way i have the fuel line ran maybe is heating the fuel ? it is clamped to the front valve cover bolt (center bolt covers) and the area that is clamped is a steel section of the line. does this sound like it could be heating the fuel up, it looks good this way but it sure can go if that is the problem. i have been working alot lately so i have not had a chance to move it, but was wondering, do yall think that where the line is can be heating the fuel. BTW it is hooked with a steel clamp but rubber coated and its not really think rubber. if that is the problem then i need some better ideas how to run this fuel line.

[SCOTI]

Why not just hook up a 'temporary' section of rubber fuel line. You can route it far away from heat sources. Don't remove your current set-up, just bypass it & see if the situation improves. If it doesn't, you haven't done alot of extra effort in vain, if it works you will @ least be able to drive it w/o worry while refiguring the route.

[swervin ervin]

Jeff,

I'm starting to believe your problem is a lean running engine. This will cause spark knock for sure. What you just posted is a pretty good indicator to me. I think I would start looking at the WOT part of the carb circuit.

On another note, is it a coincedence that most of the time I see foks having trouble with spark knock, they are also running a Edelbrock 1406 (square bore) type carb.

I find it strange how everyone is always having trouble tuning these things, either lean or rich.

Not talking about you Jeff, but then these same folks are always dissing Q-jets, calling them Q-junks. I agree, a Q-jet ain't pretty and chrome, but it works flawlessly for me.

[bigd65]

I am starting to wish that i would have spent the money on the Q-jet.

but do you think it could be possible that the motor is heating the fuel before it gets to the carb. the fuel line is attached by a clamp to the valve cover, as i said i have ben working alot and have not had a chance to move it yet, but will tomarrow. i think i am also going to put the .101 jets in the secondaries and see what that does.

[swervin ervin]

Jeff,

anythings possible, but I don't feel this is your problem, not this time of year anyway. If it was hot like in the summer it would be more possible.

Unless you have something wrong internally, like carbon buildup or some hot spots on the pistons, there is no way you should be spark knocking with the mods you've performed to it.

Something is just not right here. I am real inclined to feel like it's running real lean in the power circuit. When you say it don't do it when the choke is on tells me it's at least partially fuel related. I don't know jack about the 1406 type carbs so I'm no help in tuning it. Now if you had a Q-jet, this would be a different story.

It's a fact if it runs lean at anytime it will make it a ton easier to detonate. Reason it does it at cruise or part throttle is because this is when you have the most timing. If it runs lean, it will overheat the chambers, because fuel acts as a coolant. This then in effect causes hot spots on any carbon buildup on the piston tops or in the combustion chambers, and you have spark knock. Spark knock is really called detonation or pre-ignition, or early lighting of the fuel charge to put it in simple terms. What is happening is the fuel lights too soon and and is trying to push the piston down on the upstroke in a sense. As you can see, this will kill a piston if left unchecked.

So if you increase the fuel in the range it is knocking in, it will help to cool the hot spots. One thing you can try is some top engine cleaner. This will help remove any built up carbon. I have also heard of people using piston stops to degree in cams. These things are threaded like spark plugs. They will rotate the engine to make contact with the stop and do it too hard. This leave a nick in the piston top and you guessed, a place for a hot spot.

I wish you good luck with moving the fuel line, but don't be too disapointed when it don't do anything.

[bigd65]

well mike i really appreciate your ideas/help on this. i guess just abck to the drwing board.

about 1 year ago i had pulled the heads when i it was heating up and there was no carbon on the valves, pistons, no where (late found out it was the flex fan) now with the 4 core rad. and the electric fans it rus below the 180 mark. the way i drive i doubt that the carbon is built up. i to am thinking about the secondaries to lean. i think i am going to try one step heavier metering rod spring. i dont know what else it could be, everything else inside the distributor looks fine, the weights , the springs everything, nothing looks worn.

ONE MORE QUESTION, do all HEI have the 20* built in advance or are there other models that might have more or less centrifical advance built in.

[86-C10-V6]

This may sound a little off base but the 700r4 will not lock the torgue converter when the engine is cold and it makes it just about impossible to "lug" the engine and make it spark knock.
Once the engine is warm the TCC will lock and "lugging" will cause spark knock.
This is usually caused by lean fuel mixture at high vacuum levels.
I know my engine is not a 350 but this is what mine does all the time, no spark knock when cold, but spark knocks under part throtle when warm.
Just a thought, you could temporarily disable the TCC to see if the spark knock goes away.
Good Luck

[swervin ervin]

Originally posted by bigd65
ONE MORE QUESTION, do all HEI have the 20* built in advance or are there other models that might have more or less centrifical advance built in.

Yes, all stock HEI's will have 20 degrees of crankshaft advance built in. Only way it will change is if the weight pins are worn, or the holes in the weights are worn. Then it won't be much, maybe a degree or two. My old distributor had 21 degrees.

Have you found out how much mechanical advance you have yet? If you are using a dial back light, it's easy to do. Once it's running, and the vacuum advance is disconnected/plugged, point the light at the timing mark and dial the knob to where it lines up with the zero. This will be the amount of initial advance you have. Make a note of it. Then rev it up until it quits advancing. Turn the knob again to line it up with zero. The amount on the dial now is your total mechanical advance, initial and centrifugal total. Subtract the initial amount and the result will be your total centrifugal advance. Should be real close to 20 degrees if everything is in good shape.

I'm at a loss of what to tell you. Work on the secondary side of the carb to see if you can get it to quit. Did you get the cruise range to stop knocking?