Would like to get rid of pinging

[itsa68]

Hi roadster guys and gals.

Hopefully I can get some suggestions.
To run a little leaner, I've changed over my needles on my non-smog 1600 to m39's. This seems to make it ping under 2000 rpm when I put the pedal to the floor.
Its almost as if the vacuum advance really kicks in to make it ping up until it reaches 2000 revs.
I turned down the timing to 15 degs but it still doesnt seem to get the ping out, but the tank full gets about 190-200+ miles like it used a few years ago.

The mileage was about 150 per tank when using the original m43 needles at 16 deg and each carb leaned out as much as possible to keep running on 2 cyl at 600 rpm. The tailpipe megaphone was alway black carbon , but the plugs usually were dark tan/light brown.

Is there anything else that I can adjust or check to to get the ping out
(time for new carbs?)

Ray B.

[spl310]

Have you recurved the distributor or installed a recurved unit? You could be pushing too much advance.

[itsa68]

Sid:
I wish that was the case, but the dizzy is at the stock pre-smog curve and the the points plate seems to pull smoothly when I manually pull a vacuum, or move it by hand.
I might have a weak spark thou. The coil seemed a little too hot when at idle.
Going to get one this evening and change it out tomorro to see what happens.

Ray B.

[twinight]

did you check for play in the distrbutor?
Mine was pinging so bad I had to run premium gas all the time. Turned out it was vertical play in the distributor shaft.

[SLOroadster]

Premium gas is what correctly tuned roadsters run on. Every one I have seen try using 87 octaine just pinged all the time. Bad news. I just hope mine will run on premium without pinging. I am a little worried about that.

Will

[itsa68]

Distributor checks out and has minimal lobe backlash/end play.
The timing and points dwell are spot on.

I replaced the coil and coil high tension wire and the pinging was reduced but did not completely go away.
lt still slightly pings at around 1200-1600 rpm when pulling away from a stop if I'm using a little more gas than granny speed, and then it allows me to accelerate towards redline without pinging.
If I continue running up thru the gears to highway speed with a normal to heavy foot, the ping does not re-appear, but I'm now always pulling ahead of traffic.

When I'm doing a constant 2300-2500 rpm cruise in 2nd or 3rd and then suddenly accelerate, a slight momentary ping occurs and then engine quickly catchs ups and then does not ping to redline.

Because I never had this problem when running the original M43 needles in the carbs (or 87 octane), I'm suspecting that the M39's are a little leaner on the bottom end, thus the pinging.

First thing I'm going to try is to run a tank of higher octane @ $4/gal.
If nothing improves, I will build some new high tension wires to replace the old ones.
After failing that, the M43 needles will be loaded back in and I will run the 87 octane @$3.25/gal without ping but get lousy gas milage which started this whole exercise.

New Ztherapy or oem carbs and electronic dizzy might be the next things I consider acquiring over the winter months when the car is put away, but in the meantime I would like to sort this out and be blasting around pingless like I used to.

Ray B.

[spl310]

Ray,

Before you go that route, contact Keith Williams in Vegas. He has an alternate needle from a British SU that he claims is superior. It may be worth the $30 or so to give them a shot.

Sid

[hport]

Ray,

If you haven't already done this, try disconnecting the vacuum advance hose from the dist, and drive as you would normally. Does it still ping ? If not, look into adjusting the vacuum advance, so it doesn't increase timing as much. You will still have full advance at full throttle and high speed.
If it still pings, you are looking at a lean condition in the cylinders, which is not good for the valves and pistons ( increased cylinder temperatures) You are correct with regards to needle size and fuel delivery, the factory does a pretty good job of sizing for overall drivability. The trade off of mileage vs drivability ?? It's a roadster, go fast, top down and enjoy !


JC

[itsa68]

I'll give the suggestions a whirl and see what happens.

I just remembered that I had also changed the carb oil dampening pistons, so I guess that I should measure them to make sure they are not smaller than the ones I removed.
Correct me if I'm wrong, but if the dampening pistons are a couple of thou smaller, the carbs would not dampen as good on acceleration , lean out the and maybe cause pinging.

Thanks
Ray B.

[twinight]

Correct me if I'm wrong, but if the dampening pistons are a couple of thou smaller, the carbs would not dampen as good on acceleration , lean out the and maybe cause pinging.

If the piston and dome are mismatched, you may not get enough piston lift and cause a lean condition because the needle position is lower than it should be. (recent thread on datsun-roadsters@autox.team.net)

Having too thin of dampening fluid in the pistons could also cause an inital lean condition as you accelerate.

Check to see if the vaccum advance is connected to the carb throat(ideal) rather than the intake manifold.

Mine runs fine w/ 87 octane and only pings slightly when starting uphill from a stop. Only when slipping the clutch though. If I'm rolling, even at idle speed, it doesn't ping.