Just got my motor back together and its pinging pretty bad. I have a set of Delta heads decked 0.030" with a set of forged rods and pistons on a big block. Stock timing. Autolite APP 3923 gapped at 0.030". AFR at WOT is around 13. I have tried 93, 93 with octane boost, and 93/100LL(AV) 50/50. Still pinging. Compression is 191 in both cylinders. Has anyone seen this? I cant figure out how to make it go away.

Put a little more fuel to it

Could also run a colder plug

What carb are u using? Also the 13.1 afr is the average. U prob have 1 cyl even leaner than 13.1

Cooler plug and more fuel like Will C said.

Its a 40 mm apt smart carb. Similar to the Lectron. I have also tried at 12 AFR with same results. What plug and gap wound you suggest?

The 3923 is already a cooler plug.

Sent from my SM-T710 using Tapatalk

What about timing? I put a light on it and its firing when the magnet is right of center of the coil. Would retarding timing help any?

How much compression on each cylinder?

Sent from my SAMSUNG-SM-G891A using Tapatalk

191, first post.

Sent from my SM-T710 using Tapatalk

When i check timing i make my own tdc mark. It would be nice to know your exact timing and cam timing just to know your not chasing something weird. You would think the pingging would have gotten lighter with the higher oct. how do the plugs look after a run? Any sighns of detonating on plugs?

Okay ill have to find out what actual timing is with light and known TDC. What is stock Non CDI timing supposed to be? 23* What really sucks is I'm headed to work tomorrow and all this will sit for two weeks. Thanks for the all the ideas. I ll update with progress in two weeks.

191. That ping may be the time bomb ticking.

Man 191 isnt bad. I know of a MB running real good at 220 with no problems. My non cdi was at 23* stock

I've managed 80 some odd hours on 91 or 93 octane without a ping at 215

Sent from my SAMSUNG-SM-G891A using Tapatalk

I wouldn't think that would be the issue..

Are you positive it's predetonation you are hearing? I'd be putting a new set of plugs in it, running it, reading them and checking for signs of the detonation and going from there. Verify that's what it's doing first. Easiest thing to do would be to go another step colder on the plug but that will impact other ways the engine acts. Cold starts get a little less fun the colder you go.

You sure it's not an exhaust flange gasket leaking and making that funny puffing noise lol?


Sent from my iPhone using Tapatalk

its definitely detonation. I haven't run it much in detonation. I have maybe an hour on it since the build. Plugs look normal from what I can tell. Its had 2 sets of plugs in it so far. I changed when I raise the AFR from 12 to 13.

What cam are you running? If it is a low duration cam with a good bit of timing advance he has a REALLY early intake closing point. That would be a lot of effective compression, and it will build more cyl pressure with RPM.

180 isn't bad psi.
Also it got worse from 12 AFR to 13 AFR correct? Cause that is taking out fuel.

It's a Nick Peltier. I couldn't tell you the specs. I told him what I wanted out of it and he sent me a cam. It's hard to tell if it got worse or better with the AFR change. When I changed from 12 to 13 I also mixed 50/50 93 and 100ll. I would say it got better but probably just from the higher octane. I had the flywheel broached for non cdi coils and I'm really leaning towards a timing problem. I won't be able to find out for sure for another 2 weeks unfortunately.

Whoop there it is, need to check actual timing when u get home

You should call Reikens racing and get a set of timing keys #1-10. Tell them its for a briggs Raptor engine as they dont know what fits a bigblock. At least when u get back u will have the keys already waiting

5hp flathead

10/4 Keys on order.

you need to affix a degree wheel onto your flywheel and set TDC for each cylinder. then see when each cyl sparks. I want to say stock is around 21-22* btdc. Its been a while.

I have a dial indicator and will check both cylinders with the degree wheel. Got the keys ordered now 13 days to go.

u can tdc a piston with a dial indicator and deg wheel. Measure from .050 before tdc to .050 after tdc. Then divide the difference by 2, add that to bottom number or subtract from top number to get te exact tdc degree. Same as centerline on a cam lobe

When i re read that i sound like a smartass. I apologize

Awww, that's sweet.

Yep. Your right.... BUT the Piston is .050 in the hole at TDC so that number is WRONG lol. DO I sound like a smartass?

Lol; .050 is irrelevant. U can use .030 or .060 whatever as long as u use the same number btdc and atdc. Im gonna have to do a video

I did the advance timing key #3 & 4 seemed too much for a CDI motor. #2 seems good but had to raise needle in mikuni too bottom groove to rich it up some? Guess work I am doing, I know how to use a cresent hammer without scraping my knuckles. But in all it seemed to me better out the hole and a couple hundred rpms on the top side. yes it "pinged" with the 3 & 4. But the experts know the finer details.

Its almost friday! Yup its a pretty good day

Lol, i was thinking of calling u this past weekend. One day i wanna see your neck of the river