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270 crusader random backfire

H

hook_line_sinker

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"I have a 31 twin 270 crusader

"I have a 31 twin 270 crusader engine silverton.
the engine I am inquiring was replaced with a rebuilt unit 4 years ago. (counter rotation) This past season I started to have random back fire while under load over 1500 RPM. Back off the throtle, and ok power up and it returns.
The odd thing that puzzels me is if I warm the engine to normal operating temp. Then let it sit for a while and the run the boat it will be fine. If i just warm to normal temp then go pop-pop, at randoms times.
I also found that if I run the boat and it backfires, stop drift for a while, fish or make a few moves, then start off again most times it will be fine. I checked wires, all seems to be fine as well as new plugs and cap. Any Ideas?"
 
Are you sure it is backfiring

Are you sure it is backfiring or is it misfiring? Does the distributor have points and condenser?
 
"The Dist. is a Mallory withou

"The Dist. is a Mallory without vacuum advance, this has me stumped because of the intermittent acing up, I can have two or three trips without incident. Then have trouble right away the next time out, but like I said if I drift for a while or re-set a few times at idle speed, I car run back to the marina at 3000 3200 rpm without incident.
the problem will start when I first accelerate, over 1500 then backfire & bog down, if I try accelerate, if I back off the backfire stops, try to run it back up it comes back.
The shut it down & the next time no problem.
I thought of a valve but I don't think it would be so intermittent?"
 
"Ayuh,....... Just a Guess....

"Ayuh,....... Just a Guess.......

Have you checked the Fuel Filters lately,..??

Could be trash causes a Lean condition,+ backfiring......"
 
"When this first happened I ch

"When this first happened I chsnged both carb filters, and the water fuel seperator filters.
Thougt it might be a water issue in the fuel, seen a lot of that around this area, (NJ)
I use the star brite enzyme additive each fuel fill, to prevent seperation with the ethenol fuel. My next move is in the spring fit up is to do a complete valve adjustment. Only thing left I can think of is just one hanging from time to time."
 
"Guys,
What's you take o

"Guys,
What's you take on the if i let it sit after warm up and then warm again in te slip, I can run all day without incident. Or when I stop a few times to fish then have no problem. Something seems to expand or clear, and the issue is gone."
 
"Harold,

We had a similiar

"Harold,

We had a similiar problem this past summer on the port engine that turned out to be a bad cap and rotor. Went NUTS trying to find it since those were replaced in March but went bad 25-30 hours later in June"
 
"Harold, it is not clear to me

"Harold, it is not clear to me where the pop pop noise is coming from. Is it popping at the carburetor or the exhaust? This piece of information should help in analyzing the problem. My experiences this summer with both my 454s was popping out both ends. As the result of help from participants in this forum I was able to get to the root cause.

The exhaust popping was caused by misfiring due to fouled plugs. Fouled plugs among other things can cause misfiring. Other things include bad spark wires or distributor cap cracked or dirty (carbon tracks). The carburetor popping, which I will call backfiring was caused by a dirty carburetor resulting in irregular mixture, sometimes lean and sometimes rich. Other causes could be dirty filter, water in gasoline or insufficient gasoline flow to the carburetor.

I had the port carburetor rebuilt, changed the plugs in both engines and got rid of all the bad gasoline that was fouling the carb.

The engines are running fine now.

Chuck"
 
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