Hesitation problem under load 454 Magnum, I need some idea's
 

Hi,

I have 21' Eliminator with a 454 Magnum carb, with CMI headers turning a 28" bravo.

The problem I'm having is while getting on plane it hesitates, coughs/sputters and once going runs fine.

It did "pop" once at half throttle 3500 RPM while going around 50 MPH

I DID change the fuel filer/water seperater (no change, in previous years that got rid of the problem)

I DID try another coil, no change.

I did just have the carb fully rebuilt including new accelerator pump.

I took the plugs out, and found two that have a hairline crack on the lenght of the plug (not good)

Will replace the entire set this weekend, but wondering what would cause the plugs to crack?

One person also suggested to change the rotor, cap and the (not sure if this is what it is called) the pick up coil that the disk below the rotor goes through to trigger the spark.

Also, currently have NGK plugs, and Champion were suggested.

Appreciate your input in advance

Thanks!

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Check your timing

cracked spark plugs , it will fix youre prob , changing the plugs ill bet !

check the float level....and stay with the ngk's or ac....

Cracked spark plugs
 

I went round and round with this one. Finally found that the gil type exhaust and I'm sure other exhaust systems cause the spark plug socket to put the plug in a bind when tightening them causing them to brake. I have had to grind the socket down to a smaller diameter so it would not hit.

You didn't say if you changed the plugs when you had the carb rebuilt. I just assumed you did.

I have the CMI Headers, the plugs seem to go in well.

I didn't change the plugs with the rebuilt carb. Will be doing them this weekend.

richen the idle air bleed screws, it may be a little lean on the bottom, causing the popping, also change the plugs.
Larry

It seems like everyone is on the same page with this one. The broken plugs. This will def. cause poor running conditions. I would also continue with your tune-up, and change cap and rotor. Also check your floats and fuel pressure.

Does anyone know what would cause the plugs to break?

They have been in the boat for a few years, and I assume they were not cracked when they were put in.

I've never seen a plug have the length crack.


Thanks for all the input, I'm feeling that I'll be boating this weekend!!

P.S. How do I check the fuel pressure? And what should I set the timing at?