SoCal Jet Boats

Tech Talk => Engine Mechanical / Electrical => Topic started by: Hddaddy on July 07, 2013, 02:37:43 PM

Title: Backfire at 4K and higher???
Post by: Hddaddy on July 07, 2013, 02:37:43 PM: Having an issue with backfire and misfiring at 4k rpm and higher... Runs great from idle to 4k.... 454 indmar..... New plugs, fuel pump, cap and coil.... Any suggestions???
Title: Re: Backfire at 4K and higher???
Post by: GT Jets on July 07, 2013, 03:06:03 PM: Quote from: Hddaddy on July 07, 2013, 02:37:43 PM
Having an issue with backfire and misfiring at 4k rpm and higher... Runs great from idle to 4k.... 454 indmar..... New plugs, fuel pump, cap and coil.... Any suggestions???

Carburetor, sounds a lot like a lean pop..

Floats too low?

How much fuel pressure?

Restricted pick up?

What do you have for ignition? Electronic?

Could also be something more serious like a valve hanging up, but sort of wanted to start simple and cheap first.
Title: Re: Backfire at 4K and higher???
Post by: Hddaddy on July 07, 2013, 08:08:11 PM: HEI for ignition... Fuel bowls seem to be full.... Motor is enclosed...Under no load seems to run just fine...
Title: Re: Backfire at 4K and higher???
Post by: IRRebel on July 07, 2013, 08:17:08 PM: Quote from: GT Jets on July 07, 2013, 03:06:03 PM
Carburetor, sounds a lot like a lean pop..

Floats too low?

How much fuel pressure?

Restricted pick up?

What do you have for ignition? Electronic?

Exactly where I'd be looking. More leaning towards the "lean" condition, extremely lean, to be honest.

Ray

Could also be something more serious like a valve hanging up, but sort of wanted to start simple and cheap first.
Title: Re: Backfire at 4K and higher???
Post by: Hddaddy on July 07, 2013, 09:27:16 PM: Running a 750 cfm quick fuel carb. What's the best way to adjust? Boat has ran fine since I bought it in 2007.
Title: Re: Backfire at 4K and higher???
Post by: GT Jets on July 07, 2013, 09:31:57 PM: Quote from: Hddaddy on July 07, 2013, 09:27:16 PM
Running a 750 cfm quick fuel carb. What's the best way to adjust? Boat has ran fine since I bought it in 2007.

If it has been running fine since '07, you will not be able to adjust it out.... Something is either failing or fouled.... Just my $.02
Title: Re: Backfire at 4K and higher???
Post by: 5oclocksomewhere on July 07, 2013, 09:36:21 PM: Your cam is starting to go flat.. I just had the same problem with my bbc and had to put a new motoring it. I probably could've got away with cam and lifters but I decided to up the ponys a while bunch.

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