The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 12-11-2002, 06:38 PM   #1
bigd65
Registered User
 
bigd65's Avatar
 
Join Date: Mar 2000
Location: Clute, TX.
Posts: 1,935
Up Date On My Timing Problem, Its Half Way Fixed

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.
__________________
2004 Silverado Crewcab
1972 Chevy Monte Carlo
2017 Chevy Tahoe
bigd65 is offline   Reply With Quote
Old 12-11-2002, 07:16 PM   #2
SCOTI
Registered User
 
SCOTI's Avatar
 
Join Date: Apr 2001
Location: DALLAS,TX
Posts: 22,066
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.
__________________
67SWB-B.B.RetroRod
64SWB-Recycle
89CCDually-Driver/Tow Truck
99CCSWB Driver
All Fleetsides
@rattlecankustoms in IG

Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive.
It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar.....

Cubic inches is like Indiana Jones with a cheap pistol.
SCOTI is offline   Reply With Quote
Old 12-11-2002, 10:02 PM   #3
swervin ervin
You get what you pay for
 
swervin ervin's Avatar
 
Join Date: Dec 1999
Location: Cherryville, NC
Posts: 4,798
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.
__________________
Mike

1985 Chevy C-10
swervin ervin is offline   Reply With Quote
Old 12-12-2002, 10:17 PM   #4
bigd65
Registered User
 
bigd65's Avatar
 
Join Date: Mar 2000
Location: Clute, TX.
Posts: 1,935
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.
__________________
2004 Silverado Crewcab
1972 Chevy Monte Carlo
2017 Chevy Tahoe
bigd65 is offline   Reply With Quote
Old 12-13-2002, 12:17 AM   #5
swervin ervin
You get what you pay for
 
swervin ervin's Avatar
 
Join Date: Dec 1999
Location: Cherryville, NC
Posts: 4,798
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.
__________________
Mike

1985 Chevy C-10
swervin ervin is offline   Reply With Quote
Old 12-13-2002, 09:59 AM   #6
bigd65
Registered User
 
bigd65's Avatar
 
Join Date: Mar 2000
Location: Clute, TX.
Posts: 1,935
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.
__________________
2004 Silverado Crewcab
1972 Chevy Monte Carlo
2017 Chevy Tahoe
bigd65 is offline   Reply With Quote
Old 12-13-2002, 10:49 AM   #7
86-C10-V6
Shadetree Mechanic
 
86-C10-V6's Avatar
 
Join Date: Oct 2002
Location: Youngsville, NC
Posts: 100
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
__________________
Dave M. (Hacksaw)
86 C10 Scottsdale LWB, 4.3L, Edelbrock 1904, K&N, 700R4, 3.08 Auburn Performance
89 GMC S-15 Extended Cab 4x4, 4.3L, FI
98 K1500 Xcab, 5.7L, 3.43 Gov-Lok
86-C10-V6 is offline   Reply With Quote
Old 12-13-2002, 11:10 AM   #8
swervin ervin
You get what you pay for
 
swervin ervin's Avatar
 
Join Date: Dec 1999
Location: Cherryville, NC
Posts: 4,798
Quote:
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?
swervin ervin is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 11:22 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com