a little clattering.

[scrappyk5]

i just bought a 1976 vette. it runs great , except when i am going down the highway at about65-70 , just cruising and i decide to kick it up a bit. well when i do this i give it bout 1/4 more throttle and the valves will clatter
a little then clear out.
anyone have any idea's ?
i am running mid grade octane about 89. should i go 93 octane and see if that clears it?.
or maybe the timing is a tad too advanced ?

 

[Emmettology 101]

I'd check the timing and also try the fuel.. Is the engine bone stock or has it been opened up?

 

[scrappyk5]

well it idles smooth , cant tell if it has a cam.
its a 350 with a edelbrock " performer" manifold and
a holly 600 carb.
it doesnt do it if i take off real fast , just seems to do it when i am cruising steady and i put pressure on the pedal. it starts right up so i am thinking i will try a tank of high octane ( if my wallet can handle it /forums/images/graemlins/eek.gif ).
see if that fixes it.
but i will tell ya that thing is freaking fast. lol ,
well faster than a 5700 lb k5 with a 305 and 35's. /forums/images/graemlins/rotfl.gif

 

[Emmettology 101]

Ya try the fuel and check the timing. A 76's compression shouldn't be too high since that was around the time they were hiking gas prices and looking more towards fuel economy.....

My 89 3/4 has a 383 that starts fine and idles fine, but pings badly due to the compression being too high. /forums/images/graemlins/frown.gif So I need to retard the timing. That helps some.

 

[diesel4me]

What your hearing is probably spark knock,not valves clattering--you need to check the timing,if its too far advanced it will ping,from what you are describing it sounds like its worst when the vaccuum advance kicks in--check the weights under the distributor rotor and make sure they arent stuck in the advanced posistion--you should be able to twist the rotor and it should snap back under spring tension--I've seen a lot of them stuck,and needed to be sprayed with WD-40 or penetrating oil to free them up(I'm talking about the factory GM HEI,not any aftermarket distributors).You can buy an adjustible vacuum advance from crane cams,to limit the amount of advance it will get,and how soon,also there are advance curve kits by Mr.Gasket that have different springs and weights to change the rate of advance.But you might just need your timing re-set,and some higher octane fuel--try that first--carbon build up on your pistons encourages spark knock too. /forums/images/graemlins/crazy.gif

 

[scrappyk5]

cool , thanks diesel.
i am going to check timing and change octane.
this thing didnt get much driving around the last couple years cause the p/o only drove around the bock and back and forth to stores. it probably has the build up on the pistons too. still runs great though. /forums/images/graemlins/peace.gif