suggestions on possible air leak???

[jahollis2]

I have a 1993 48 hp evinrude that when i throttle it up it will start surging!. I can get the boat on plane and sometimes even go a decent distance before it will start surging??? I can knock it out of gear then start again, sometime it wont do it again and sometimes it will???? It cranks fine, have to choke it b/c its cold natured but it will idle alright. Im under the impression its an air leak somewhere on the engine? Ive tried swapping hoses and tanks and its still doing it? Air leak or dirty carbs??? Any suggestions on likely places to look?

[bayoumonster]

Your problem may be a coil not producing enough spark under load. Usually an air leak or fuel pump will give pretty consistent problems, which is not what you describe. You might even check your spark plug wires and see if one of them is arcing somewhere under the cowl and shorting out.

[jahollis2]

Ok. Never thought of that. How would a coil not produce a steady spark under a load periodically??? Ill check the wires for arcing but how would i check the coil???

[bayoumonster]

Ok. Never thought of that. How would a coil not produce a steady spark under a load periodically??? Ill check the wires for arcing but how would i check the coil???

When the current passes through the coil the wires heat a little---the more current, the more heat. If there's a crack anywhere in the coil that opens up due to heat expansion.......

A timing light and a partner would be one way to see if you're getting a breakdown on spark at higher speeds. Just hook the timing light up as normal and check that the light is lighting up consistently for each spark plug. If not, you have ignition problems. Switch coils and see if the problem follows the coil. If so, replace the coil. If not, you may need a pro to locate the problem, since powerpacks, stators, and timer bases (if your motor has one) can be expensive. Coils usually aren't that bad.
A fouled spark plug could even cause the problem you describe.

[shermanator]

Archerguy1 is back on the forum he's the one to ask, he's been spot on on the advise he's given on here and gives it for free cant beat that...

[Archerguy1]

An air leak on an engine is constant and will not change, if this problem comes and goes as you describe I would pretty much rule out an air leak, I would look more at ignition, coil breaking down as mentioned and you could remove the front of the air box, back motor in the ramp, hook up timing light then put motor in gear and shove throtle wide open, should turn motor around 3500 under a heavy load, shine timing light down each carb throat to see fuel flowing into the motor, they shoud be steady with out any lack of fuel. If you belive that somethine is arching, do the same to the motor around 9 pm with the cowling off