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43 mercruser down on power

G

gavo

New member
"i have a 4.3 mercruser alpha

"i have a 4.3 mercruser alpha one,runs perfect for the first 30,40 mins up at 5000rpm then it will drop in power and only sit at about 1500rpm to 2000rpm ?it will backfire if i try and give it some.if i turn it off and let it sit for 20,30 mins its ok and its the same all over again.no overheating,my guess is something to do with fuel ?any ideas please"
 
"Ummm! Sounds a little like ov

"Ummm! Sounds a little like overheating anyway. 5000 is above the recommended rpm range - how long does it run if you keep it at not over 4500?
No age given, but things like reduced water flow, hot vs cold compression, valves' condition are swimming in my mind.

How about a few more details?"
 
"it will run a bit longer if r

"it will run a bit longer if ran at say 4000/4500 but your only talking maybe another 15/20 mins. its about 9 years old,temp sits around 150 never higher(if gage is working)i have done the plugs and leads,filters,oil change ?"
 
"The 4.3 is a great engine and

"The 4.3 is a great engine and usually runs like a champ.

If your temps and pressures are all OK, you may have dirty/wet gas or filter, or something is overheating in the ignition area.
The coil would be a prime suspect.

An engine needs:
-unrestricted air mixed with the correct amount of fuel
-compression
-spark at the right time
-unrestricted exhaust

Usually checking these things will lead you to the culprit.

Rod"
 
"Inspect the optic sensor insi

"Inspect the optic sensor inside the dist. cap; if rusty replace it. Check the cap and rotor for corrosion, carbon tracking and hairline cracks that expand from heat.

Your ignition module could be dying from age and heat. Get a can of "COLD SHOT" from an electronics store. It is used to test thermal problems in circuits. As soon as it starts acting up, spray the module to chill it. If the problem goes away, buy a new one."
 
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