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2002 5L Merc , Maxum 31ft twin screw

D

dawdys

New member
My 2002 5L Merc has a popping sound at approx 3k RPM , I have has the coil, pugs , cables , water pump and computer changed or swapped with the starboard motor.
Timing has been done as well along with adjustments to airflow to the Carb. When adjusting the timing the backfiring happens at a lower RPM. Fuel is good and is new .
The vacuum hose squeals and pushes out air??
Any thoughts on why this is happening
 
where is the backfire coming from?
Carb or exhaust? Very important.

If its backfiring thru carb it could be a bad cam lobe or loose rocker arm or bent pushrod...

Does engine go beyond 3000 rpm?

Carbed engines dont have a computer, its called a timing module for better clarity.
Have you looked under distributor cap?
Do you know what ignition is on your engine? (Thunderbolt or different type)?
 
vacuum usually originates from the intake manifold....not the crankcase....

High pitched "squealing" often originate at vacuum leaks.

If you "popping" is periodic, do a compression test to assess the top end's condition...
 
kghost said:
where is the backfire coming from?
Carb or exhaust? Very important.

If its backfiring thru carb it could be a bad cam lobe or loose rocker arm or bent pushrod...

Does engine go beyond 3000 rpm?

Carbed engines dont have a computer, its called a timing module for better clarity.
Have you looked under distributor cap?
Do you know what ignition is on your engine? (Thunderbolt or different type)?
Click to expand...
Its coming from the carb. The engine goes beyond 3000 rpm without a load. When in neutral the engine can rev over 4500 RPM . The crankcase vacuum seems like it is drawing to much air. The ignition coil was also replaced.
 
I'd suggest we get an engine serial number to resolve the configuration uncertainties....TBI units and Carbs are very similar to an untrained eye...
 
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