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-   -   Help - Backfiring Issue on Blown 454 (https://www.offshoreonly.com/forums/general-q/136507-help-backfiring-issue-blown-454-a.html)

Shallow Minded 08-05-2006 09:59 PM
Re: Help - Backfiring Issue on Blown 454
 
Well, took the boat out today with the new coil and damn it, same thing happened. Although it did seem to run for a longer time before the first "sneeze", something is still not right. I'm thinking it's electrical in nature. Going to check wires, cap & rotor.

Anything else I'm missing? This intermittent stuff sucks!

GOODT 08-05-2006 10:20 PM
Re: Help - Backfiring Issue on Blown 454
 
I think everyone here thought you already checked the cap and rotor ....( should of been one of the first things to check )...


ussually after 30min running can be filter or coil


what carbs, did you ck carb filter ???

LS1 MOLESTER 08-05-2006 10:21 PM
Re: Help - Backfiring Issue on Blown 454
 
Originally Posted by Shallow Minded
Hey guys,
I'm running a 454 .30 over with a roots-style B&M 174, about 5 lbs of boost. The boat has ran fine all summer (3rd summer on it) until the last couple of trips out.

It will run normal for the first 20 minutes or so (cold) and then it develops a backfire, sputter and just sounds terrible. I lose power and hate to even idle it. The previous trip, I was on vacation and stuck miles from home so I let it cool down and ran it again. I had no problems the rest of the weekend. Today, similiar situation... hit a sandbar and let it cool down. It then ran fine for the first 20 minutes back to the dock before the backfire started again.

I changed the plugs last time and they looked normal. It seems to happen mainly under load and it will usually idle fine. A couple of thoughts below...

Bad gas - it would do it all the time, right? Plus, I burned most of the tank on my vacation.

Weak valve spring - it would happen all the time?

"Chunk" of carbon build-up inside the cylinder head that once it gets hot enough "glows" and actually causes a misfire?

I'm lost on this one... I'd really appeciate any ideas. Thanks in advance. :mad:

SM
On cars a backfire is typically caused by too much fuel.. maybe you're running rich?
Maybe lean it out a tad.

GOODT 08-05-2006 10:25 PM
Re: Help - Backfiring Issue on Blown 454
 
Originally Posted by LS1 MOLESTER
On cars a backfire is typically caused by too much fuel.. maybe you're running rich?
Maybe lean it out a tad.

no offence but did yo miss the after 20 min part

or are you suggesting choke sticking

LS1 MOLESTER 08-05-2006 11:51 PM
Re: Help - Backfiring Issue on Blown 454
 
Originally Posted by GOODT
no offence but did yo miss the after 20 min part

or are you suggesting choke sticking
no offense taken.

too much fuel.
it ain't gettin' burnt.
simply too much or lack of spark. thats my uneducated opinion.

M

Shallow Minded 08-06-2006 09:16 AM
Re: Help - Backfiring Issue on Blown 454
 
Originally Posted by GOODT
I think everyone here thought you already checked the cap and rotor ....( should of been one of the first things to check )...


ussually after 30min running can be filter or coil


what carbs, did you ck carb filter ???
Sorry, should have probably mentioned that. Going to check cap & rotor, plug wires now. Got to looking and everything (including single Holley 850) was purchased in Jan '04 to give you an idea of age. Probably 150 hours on the set-up.

Dumb question, but you lost me on the carb filter part...?

It doesn't appear to be running rich, if anything, I'd rather add a little more flow to it.

Thanks guys for the quick response, this thing is keeping me up at night. :mad:

Cool Trips 08-06-2006 10:11 AM
Re: Help - Backfiring Issue on Blown 454
 
I had the same thing happen on a 525sc which is basically a 454 with a 177 blower on it. The fuel pump was going bad and it would start to back fire when it was starving for fuel. Its kinda the same principal as a torch set. When you turn off the gas before the oxygen you get a pop :D Do you have a fuel pressure guage?

Shallow Minded 08-06-2006 11:19 AM
Re: Help - Backfiring Issue on Blown 454
 
Yep, I'm measuring fuel pressure right at the carb and it stays rock solid at about 7 PSI.

But my carb does seem to have a large dead-spot / hesitation in it, like the secondaries are slow to open up or something. I wonder if this could have something to do with it.

GOODT 08-06-2006 11:34 AM
Re: Help - Backfiring Issue on Blown 454
 
did you check the filters in the carb itself

Cool Trips 08-06-2006 12:01 PM
Re: Help - Backfiring Issue on Blown 454
 
Originally Posted by Shallow Minded
Yep, I'm measuring fuel pressure right at the carb and it stays rock solid at about 7 PSI.

But my carb does seem to have a large dead-spot / hesitation in it, like the secondaries are slow to open up or something. I wonder if this could have something to do with it.
Watch your pressure as you bring up the RPM's If you have a restriction in the supply or if the pump is bad you will see the pressure drop once you loose the volume of fuel in the system. If it stays then you know your good to the carb. I think GOODT is refering to the stone filter on the carb where the fuel line goes in.


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