Ron 75 L48

I am getting valve knock at cruising (50,60, 70) speed when I accelerate. Do need to retard the timing or advance it to fix this problem? Thanks in advance. :)

Ron

cardo0

Ron I have heard a car backfire/pop on acceleration when timing retarted too much - intentionaly to pass smog. They say a car will get detonation with too much advance but I can't really comfirm this. I used to have a high compression GTO and on a hot day I thought I could hear what sounded like lifter noise - but faint. They say preignition/detonation will put holes in your pistons fast. I bought a MSD knock detector but have not installed it yet. Only about $100 if your really worried. :smash:
Okay to answer the question: retard timing should reduce predetonation.

Older Than Dirt

Could be your vacuum advance is too much. Total timing with VA hooked up should be around 52, I think? If it's too high, buy an adjustable unit.

Fevre

:iagree: Check where you are with just your initial and mech adv, should be about 36 at about 2800 rpm's, if this checks out try driving it without the vac adv hooked up to see if that cures it, if so then you need to reduce the amount of vac adv in order to retain your performance.

Ron 75 L48

Thanks for the inputs guys. I will try to check this out tomorrow if I get the chance.

Ron

marshrat99

Is this a new problem? If so, think about what you've last changed such as the timing you mentioned or if you've adjusted your valves, etc. If you've not changed anything in a while, you might have a little carbon starting to build up which is increasing your compression ratio. :smash:

Ron 75 L48

I swapped out the carb. I went from a Holly (kept boiling the fuel after shutdown) to an edlebrock.

Ron

cardo0

Hey Ron this is really good info on carbs. Now this will help diagnose a lean condition. Just hope this makes into the archives. :thumbs:

Ron 75 L48

This whole carb thing has been a pain. I had the engine rebuilt. Swapped out the cam and put in an COMP XE 268, new pistons, had the heads ported, took out the cat and put in true duals and we are guessing it should put out a little above 300hp. However, I can't seem to get the carb issue straigtened out. I'm wondering if the engine knock isn't really coming from the carb not being tuned right. :confused: Anyone have any ideas on this one?

Thanks,
Ron

1SGRET

:lurk:

bigvette1

Like others said, check the timing. Set the base at about 8-9 degrees to start. Get or borrow a dial back to zero timing light. Diconnect and plug the vacuum advance. Check timing for base, and what total is for mechanical and at what RPM. You shold have no more than 34-35 degrees total. When you add vacuum advance you can go up to the numbers you have. Check it out.

The Edelbrock carb should be ok, but if your timing it good, then it may be too lean on WOT or high speeds. Look in the instruction book and see what rods and/or jets to change to go richer at cruise and WOT.

The other thing is wha temps are you running. Too hot can cause detoniation.

Ron 75 L48

Thanks Bigvette. I am running at about 185 for the temp.

What RPM should I be checking this?

Thanks,
Ron

cardo0

Well if yu can't find the time to install an Air/Fuel ratio gauge and O2 sensor, I think yu owe yurself an hour of dyno time. At least to nail that carb (after correcting timing). :yesnod:

Ron 75 L48

Believe it or not I called a dyno shop today to see about getting it set like it should. Of course the only one I could get in touch with today wanted 200 bucks for an hour on the dyno and do the tune. Gotta think about that one.

bigvette1

Just the timing at normal idle speed of say 600-700. If you think there is something off like it just does not idle fairly decent at 8-10 degrees or is way off, (make sure the dial back to zero tiing light is at zero) maybe you need to check to make sure the timing of TDC and zero are correct.

Take the dist. cap off. Mark where the #1 wire is on the cap and make a mark.

Pull the #1 spark plug, put your finger tip in the hole and crank the engine over slowly until you feel air pushing your finger away.

Look at the balancer and see if the TDC mark on the balancer is lining up.

Bump the engine until the rotor on the dist. gets to where the #1 wire mark is. With the #1 piston on TDC, the timing marks should line up with zero on the pointer and the dist. rotro should be on the #1 plug position. This is just to check tos see if the balancer has slipped and/or someone put the dist. in the engine 1 tooth off. This will really screw up the timing.

Good luck.