stevo1988

I had another post in here about my engine pinging at part throttle, before playing with the timing i thought the carb was running too lean so i added rods to make the mixture 2 stages rich in cruise mode. As it was still cold outside it seemed that the richer mix for a short amount of time was able to stop the engine from pinging at approx 2000rpm on light throttle. Then finally we started to get spring weather! with the warmer weather im happy that i no longer need to use my choke! but the pinging had come back, not very noticeable but its back! at the same time as before.

So now i am going to play with the distributors mechanical advance. I bought a curve kit from Accel # 31041, 31042. It comes with new weights and center-plate, bushings and 3 sets of springs (red, blue and white) red is lightest and white is heaviest.

My HEI hasnt really been touched and it used to run the 305 originally in my car. Its made in 1985 so Im not sure which bushings to use but it should be self explanatory. All i have ever changed to this dist. is the cap and rotor and plug wires.

I am trying to figure out my curve, it seems that the springs are very light and open too quickly and causing detonation at 2000rpm but the timing appears to be all in around 3000rpm, if i go heavier springs my timing increases more gradually but keeps increasing past 3000rpm. It appears i have abour 24 degrees of total mechanical timing and to have it all in by 3000rpm i need 16-18 degreees of total. Now I have seen people weld up one of the slots in the bottom plate to limit total advance but are there better ways?

I didnt think my motor was so far from stock that it doesnt like the stock ignition timing. My specs are maybe a tad bit better than a 350HO crate motor, maybe I could find the timing specs for a 350HO???

kevinkpk

At 3000 rpm I'd suggest you'd better be around at least 25-30 deg btdc. If you are at 18, I'd suggest go with mid wieght, wieghts. Or spring change.

kevinkpk

Set your timing - for more performance!

stevo1988

I pulled the cap and rotor off last night and i removed the springs but they were pretty heavy springs, they seemed about as heavy as the heaviest springs from the kit. So i put the 2 heavy springs in and took it for a ride and i still get the same problem. Once the rain clears up and we get a sunny day ill climb under the car and apply the timing tape to see what is going on
could it be possible that i may not be advancing enough??? would i get a pingy sound from that??

stevo1988

drove my car to the gas station down the road to get some gas. it has been down pouring here for 3 days now. last night i drove in very big puddles and water was getting everywhere. Today after getting gas my car wouldnt start. I quickly killed the battery trying to start my car. This gas station is close to home and it is also a mechanics garage. the mechanic today tried to help me by charging my battery but it wouldnt take a charge, also he told me that my plug wires are not any good. Could a bad battery and plug wires be the cause of all my problems? after many different spring swaps i have noticed that not much is changing in the pingy problem i am getting. The mechanic believes that my timing marks are not correct and that i may be running initial advance much too far and hence why i could not resolve my problem. I have noticed in the past week or so that my engine has been missing and very hard time starting and the smell of unburned gas occurs during regular driving.

kevinkpk

If your timing at idle is to advanced, then starting will act like a weak battery when turning over. Set the vacuum advance at idle (700 rpms) at 8-10 deg. Again, at 3000 rpms the timing should be close to or at 30 deg. The spings you have I'd use mid weight to acheive that, abeit it will be trial and error.

stevo1988

OK so my timing is set to 10* at idle, I got it to climb to 36* by around 3500rpm and it doesnt seem to advance any more after that. Right now i have vacuum advance unhooked and plugged. It took 1 heavy and 1 medium spring to achieve the timing curve and im happy with it.

I took it for a ride and sure enough the knocking happens again. It happens in 1st and 2nd gear at around 2100rpm while holding speed and pulling about 11 inHg of vacuum or during light acceleration in that rpm-range. When i give it more gas it goes away.

I discovered in the edelbrock manual that i changed the rods and jets in favor of a richer "Cruise-Mode" but with the vacuum i am pulling should i be moving toward richer "Power-Mode" instead? The knocking happens when the fast idle is on after the engine warms up and sitting in Park. With the engine warm the fast idle sits at about 1200rpm.

If i swap the secondary jets (0.095") with the primaries (0.098") and use a 70x37 rod i should be 4% richer Cruise-Mode and 4% richer Power-Mode

kevinkpk

I'd suggest a compression test. That is WAY low even at idle.

stevo1988

I had the compression test done today actually it came out at 150psi on all cylinders. That is my idle vacuum while in gear. In park/neutral i get 16 inHg
I have a vacuum gauge in the car as well and the needle holds steady all the time

When i sit in park my vacuum at 700 rpm is about 16 inches, when i put it in gear it idles at 11 inches, while cruising (not accelerating not coasting, just holding speed) i pull 11 inches
i am sure this is due to the cam i have and the amount of valve lift created

The cam is single pattern flat-tappet 218* duration @0.050", 0.483" valve lift (w/1.6 rockers), 0.302" lobe lift, 110* LSA, 106* intake centerline

Intake Opens 28* BTDC
Intake Closes 60* ABDC

Exhaust Opens 20* ATDC
Exhaust Closes 68* BBDC

EDIT----------------------
Ive been doing some homework, it seems for my engine i should be at 36-38* total by 3500 RPM, my initial timing should be 10-12* at 600-800 RPM, all of this i have. It seems to me that the heaviest springs in my kit are not the heavist out there. My distributor allows 26* of advance but somewhere around 1300 RPM when the mechanical advance begins to kick in, something in the geometry of center plate and weights must be causing a quick jump instead of a smooth advancement. I am at the moment using the stock center plate and weights with the 2 heaviest springs in my kit. Maybe the weights are sticking a little, or maybe i should try the weights from the kit? i'll have to measure its weight. lighter weights = slower advance and heavy weights = quicker advance??

kevinkpk

Your vacuum is still low. 16 at 600 rpm I can buy, but 11 inches is way low. Even with a stock cam lift/duration it is low. The distributor is fly wieghts, and speeder spring, simple mechanical govenor. The faster it turns the wieghts have to overcome the spring resistance. So, the heavier the wieghts + speed the more advance.
I should add your kit probably wwill have recommended springs/weights to use. On another note, this is a 305.