still having spark knock issues.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
still having spark knock issues.
heres where im at...
69 350/300hp 10.25:1
fresh tank of 93
checked the dwell, it was a little low at 26, set it to 30.
knocked off 3* of advance.
ran half a bottle of seafoam down the carb, and half in the gas tank.
i checked the distributer for play with the dwell meter., there was very very little. it shook back and forth a little inside the 30 the line, but never went out side of it.
im getting knock through all the gears when im heavy on the gas, from about 2000rpm and up.
69 350/300hp 10.25:1
fresh tank of 93
checked the dwell, it was a little low at 26, set it to 30.
knocked off 3* of advance.
ran half a bottle of seafoam down the carb, and half in the gas tank.
i checked the distributer for play with the dwell meter., there was very very little. it shook back and forth a little inside the 30 the line, but never went out side of it.
im getting knock through all the gears when im heavy on the gas, from about 2000rpm and up.
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
Continue to retard timing in 2* incriments then test drive to see if you are still experiencing detnotation (spark knock) when the engine is under load.
Last edited by Oldguard 7; Oct 4, 2009 at 06:12 PM.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Too high of heat range on the spark plugs could also promote detonation. Or carbon in the cylinders. Your seafoam should have taken care of that. (water would do it too and it's cheaper)
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
ive got colder plugs in it right now, 43s. ive been running these plugs for about 4 years now.
the cars been running good for the last 2 years now. i havnt touched the ignition in that time, but within the last 2 weeks, its started knocking.
the cars been running good for the last 2 years now. i havnt touched the ignition in that time, but within the last 2 weeks, its started knocking.
Racer
Joined: Dec 2004
Posts: 410
Likes: 0
From: Wichita Kansas
Then something changed. My guess is the timing sliped or the distributer has someting wrong with it. Are you using the stock unit with points?
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Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
I would check your vac adv can and see if it still holds vacuum. It could be on it's way out, causing your pinging/knocking
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Try a colder thermostat.
A vacuum adv adds adv at idle or cruise with large amounts of intake vacuum - no adv at WOT. If it was inop it would not add any adv so disconnecting it won't tell anything even if its stuff in the adv position (never heard of).
Things that increase the chance of pre-ignition:
-low octane fuel
-hotter combustion chambers, carbon build up, hotter plugs
-hotter coolant water temps
-hotter intake air temps
-yes too much adv
It sounds like u testing all the right things and my guess is your dist has deteriorated but u should find out by reducing total adv a little each time.
Heck some guys here have reported there dist adv plate frozen from corrosion.
Good luck,
cardo0
Things that increase the chance of pre-ignition:
-low octane fuel
-hotter combustion chambers, carbon build up, hotter plugs
-hotter coolant water temps
-hotter intake air temps
-yes too much adv
It sounds like u testing all the right things and my guess is your dist has deteriorated but u should find out by reducing total adv a little each time.
Heck some guys here have reported there dist adv plate frozen from corrosion.Good luck,
cardo0
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 39
From: Fremont CA
Back when I worked in gas stations, if you over ordered fuel it couldn't go back on the tanker truck, perhaps you filled up at a station who filled it's premium tank with regular fuel in a overorder situation? I would back-off the timing and buy some race gas or octane additive and see how the next tank performs. Your 350 has iron heads and high compression, I would probably install some stiffer mechanical advance springs in the distributor to delay the timing advance. This is easliy done by removing the rotor and changing the springs underneath. Try to find a quality kit as many are Chinese made JUNK now a days. Here is a link to Summit: http://www.summitracing.com/parts/AC...2/?image=large
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
i thought i had bad gas my self, but i topped off from a different station with 93 octane.
delaying the advance curve has come to mind, but the only problem is, its ran with this current curve for the last 2 years with out issue. its just with in the last 2 weeks ive started knocking.
delaying the advance curve has come to mind, but the only problem is, its ran with this current curve for the last 2 years with out issue. its just with in the last 2 weeks ive started knocking.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 39
From: Fremont CA
Gasoline formulas change from Summer to Winter blends but, if the detonation is really severe, you could have a distributor or fuel mixture issue. Try adjusting your idle mixture by hooking up a vacuum guage at the headlamp vacuum port and setting mixture screws for highest vacuum reading at idle (while leaning out mixture from rich setting) then turning mixture screws 1/8-1/4 towards rich from this reading (shoud stay relativley the same.) Possibility that your distributor advance weight is sticking or a spring broke, you should look under ignition rotor and test movement of mechanical advance weights/springs. Maybe vacuum advance can is going bad? Process of elimination is what is required here, the penalty we pay for driving good looking older Vettes
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
i thought i had bad gas my self, but i topped off from a different station with 93 octane.
delaying the advance curve has come to mind, but the only problem is, its ran with this current curve for the last 2 years with out issue. its just with in the last 2 weeks ive started knocking.
delaying the advance curve has come to mind, but the only problem is, its ran with this current curve for the last 2 years with out issue. its just with in the last 2 weeks ive started knocking.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
its spark knock, im 100% sure of it. id get some audio of it, but my cars so loud in the cabin, you would never hear it.
anyways, i unhooked the vac advance this afternoon and capped of the vac line. it eliminated 90% of the spark knock. theres still some there, but very briefly and under heavy loads. seems to only be in 2nd/3rd gear now.
bit of interesting info i found out after unhooking the vac advance, my car will idle all day long at 450-500rpms. im at 650-700 normally, but i may have to knock it down a hair.
anyways, i unhooked the vac advance this afternoon and capped of the vac line. it eliminated 90% of the spark knock. theres still some there, but very briefly and under heavy loads. seems to only be in 2nd/3rd gear now.
bit of interesting info i found out after unhooking the vac advance, my car will idle all day long at 450-500rpms. im at 650-700 normally, but i may have to knock it down a hair.
Melting Slicks
Joined: Sep 2003
Posts: 3,050
Likes: 2
From: Orange Ct
If the idle drops when you remove the vac advance, it is connected to full engine vacuum. Try it with the line connected to the ported vac advance on the carb. A different vac can or an adjustable unit may help also.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
i moved the vac location but i havnt taken it for a drive yet.
what i did do was pull the distributer apart. looked a little dry in there, so im going to regrease it tomorrow. i cleaned up all the old grease this evening.
the springs look good and feel strong, the points look good but i did clean up the contacts on them a bit. and the weights looked good and were moving freely.
im going to put it all back together tomorrow and take it for a drive if its not raining.
if it still knocks... well, keep retarding the timing down. if that doesnt do it, ill dump 3-4 gallons of 110 in.
what i did do was pull the distributer apart. looked a little dry in there, so im going to regrease it tomorrow. i cleaned up all the old grease this evening.
the springs look good and feel strong, the points look good but i did clean up the contacts on them a bit. and the weights looked good and were moving freely.
im going to put it all back together tomorrow and take it for a drive if its not raining.
if it still knocks... well, keep retarding the timing down. if that doesnt do it, ill dump 3-4 gallons of 110 in.
