HarleyTechTalk

My old Twin Cam occasionally does that, but it's carb'd, cammed, aftermarket ignition, ThunderHeader, etc., so not unusual. Sounds like a gunshot, just part of the fun!
Kind of unusual with efi. Maybe a way to capture the event with a Power vision or other tuner hooked up when it happens, looking for an unusual ignition or fueling event?

What exhaust mods if any? Any kind of tune in it?
When it started doing this, had any mods been done shortly before it started? Any work at all before it started? Or just bone stock, no work on anything, even as unrelated as brakes or clutch adjustment?
Just trying to determine when it started happening if anything had been changed, minor and unrelated as it may seem.

started when it was all stock. Still doing it with V&H slip-ons. Have also a Powervision. Tried about 4 different tunes. Even re-installed the stock original tune. Today, I re checked the seals on the intake ans related components that can be an issue with air leaks. Everything is good.

Have the exhaust gaskets been changed?

I just changed those earlier this year because I had to take the exhaust off to put it the Mueller clutch slave cylinder. And there isn't an exhaust leak.

How are you checking the checking the seals? I use a spray can of brake cleaner.

Just a "shot" in the dark where you're having trouble nailing this down, but what if you removed the PV and tried it when cold without? I'm not saying put a thousand miles on...just give 'er a rip to rule the PV out.

Mind you I'm not familiar with the PV at all. I have an OEM brain with a Bean tune so I may be suggesting something ridiculous.

Any updates? 

Quote from: truckrglenn on June 11, 2024, 12:42:15 AMHow are you checking the checking the seals? I use a spray can of brake cleaner.

Checking 2 ways. I have a propane set-up that I originally used on cars ans trucks. Works really good. I also spray test with 2 different types. 1 that is flammable and 1 that isn't.

OK !!!!! This is good but,... really sucks. I've been chasing this over a year! Had a buddy come over to give me some support observation. (he's also a very good wrench).
 While I was demonstrating my issue for him, he was VERY intrigued. I has him put his hand on the intake while pushing the start button. He felt the percussion of the "POP".
 So fast forward.  After about 10 - 15 of these, ears and hands all over the place, he says,"I think this is happening in the exhaust"! ?? The weird part is we both could feel the POP in the intake !
 Doesn't make sense. During this session, I had the throttle body off so I could look in the intake to see if there was a "flash" or not. No flash.
 Now this is a much better feeling knowing it's not in the intake.
But, can someone tell me if they know when the ECM tells the coil to fire the plug? I am assuming it is as soon as I hit the start button.  I read that it was when the crank reached 50 RPM. But I think whoever wrote that might not be correct.
     Messing around with the tune a little, it only did it 3 times all last weekend. But when it doesn't "pop", it turns over a few revolutions before it fires normally. Runs fine, no decel pop, good power.
  Yes the ex. gaskets are new and not leaking.   

What exhaust system are you running?

Now I have a V&H Power duals and the 400's. But this happened with the stock header on. So really no difference. Tried 3 sets of mufflers.

Sticky valve?

Quote from: sbeamer on June 22, 2024, 11:08:15 AMNow I have a V&H Power duals and the 400's. But this happened with the stock header on. So really no difference. Tried 3 sets of mufflers.

The ecm wont fire the motor till about the second revolution or about 250 rpm i think . i would do a cold comp test and then a hot one . also try disconnecting the compression release valves . good luck

Just wondering, what results would disconnecting the ACR's do in this case?

Stock engine when cold, little to any difference unless your battery is weak. Hot would be a different story if compression is up (likely hang itself on the C-stroke).