Metallic rattle under hard acceleration
Road Captain
Joined: Apr 2010
Posts: 688
Likes: 350
From: Central Utah
Take a look at your plugs as they can tell a story.
Pre detonation, lugging, different tune etc. I dunno, but I brought my carbureted FLHT from CA to Utah four years ago and never had an ignition related problem. Not sayin this is or isnt your issue, but you can check it out in 30 minutes in your own garage. I Did run premium fuel and plugs always looked light tan. Were at 5,354 elev. and the interstate is 80mph down here and its always a kick to jump on it when youve got the acceleration lane all to yourself.
Pre detonation, lugging, different tune etc. I dunno, but I brought my carbureted FLHT from CA to Utah four years ago and never had an ignition related problem. Not sayin this is or isnt your issue, but you can check it out in 30 minutes in your own garage. I Did run premium fuel and plugs always looked light tan. Were at 5,354 elev. and the interstate is 80mph down here and its always a kick to jump on it when youve got the acceleration lane all to yourself.
Last edited by Mr. Mike; May 27, 2026 at 07:26 PM.
Tourer
Joined: Jul 2021
Posts: 387
Likes: 254
From: Florida
Detonation (pinging)=hole in piston=big bucks. Have a mechanic take it for a ride he will tell you in a minute if it's detonating. Common causes are lean, high compression, low octane gas , improperly timed ignition.
Seasoned HDF Member
Joined: Oct 2012
Posts: 11,226
Likes: 3,049
From: St.Louis Mo.
Carbon on top of the pistons are a big cause also. Sucking hot ,oily air from the breathers back into the engine will cause it too.
You could try spraying water into the intake while keeping the rpm's up to clean the engine up. WARNING go slowly with this. Put some RedLine fuel treatment in it too.
Look at the plugs, they will give you a clue what is happening. While the plugs are out get a camera and take a look at the top of the pistons to see how much carbon is on top of them. Good Luck !
You could try spraying water into the intake while keeping the rpm's up to clean the engine up. WARNING go slowly with this. Put some RedLine fuel treatment in it too.
Look at the plugs, they will give you a clue what is happening. While the plugs are out get a camera and take a look at the top of the pistons to see how much carbon is on top of them. Good Luck !
Tourer
Joined: Feb 2022
Posts: 293
Likes: 207
From: California
Does it rattle in neutral at that rpm? I would check the exhaust heat shields first.
Your bike 100% needs a tune regardless.
I ran with that setup (air cleaner & slip-on's) and a stock tune for quite a while. Too long, honestly. In the summer I was getting detonation on long uphill highway sections when it was hot, and the rear cylinder would shut down in city traffic all the time. It had decel pop like crazy. I don't have plans to upgrade the motor beyond OEM, so I found a deal on a Vance & Hines FP4 and it worked fine. The app & bluetooth connection is terrible, but the tune is installed and it runs great.
Your bike 100% needs a tune regardless.
I ran with that setup (air cleaner & slip-on's) and a stock tune for quite a while. Too long, honestly. In the summer I was getting detonation on long uphill highway sections when it was hot, and the rear cylinder would shut down in city traffic all the time. It had decel pop like crazy. I don't have plans to upgrade the motor beyond OEM, so I found a deal on a Vance & Hines FP4 and it worked fine. The app & bluetooth connection is terrible, but the tune is installed and it runs great.
Stellar HDF Member
Joined: Jan 2017
Posts: 2,678
Likes: 2,081
From: Massachusetts
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Thread Starter
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Advanced
Joined: Feb 2022
Posts: 95
Likes: 20
From: OR
I'm gonna get the tune but do I need to get a power vision or would the dealers screaming eagle tune suffice? I've heard since it's epa compliant it's still on the lean side. I'm fine with the way it runs now I just don't want to hurt the engine if it's pinging.
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Joined: Feb 2022
Posts: 95
Likes: 20
From: OR
I actually don't know. I haven't even looked at them since I got the bike last year. I misplaced a lot of my tools in the move and I'm not sure if I even have a spark plug socket anymore so I'll have to get a new one. They're probably old as hell though so I should just get new ones. If I take it to the dealer for a screaming eagle tune I can have them throw on stock plugs. Or should I be getting a different brand?