1984 Mercruiser 470 No Top End

[Swanny87]

How is it going everyone? I have a Mercruiser 470 170hp. I've had the Carb rebuilt last year and tuned by a local shop. It was running really rough and figured it out to be the vent line to the fuel tank was clogged. This year, I've replaced the cap, rotor, condesor, wires plugs and the new vent line. I ran it in the driveway with the muffs and it runs fine. I finally got a nice day off to put it in the water and the low end seems fine. a little tuning of the idle. But when i would throttle up, whether gently going to full throttle or smashing it to full, it has no top end. Had it last year and I'm confused now. What would you guys suggest for me to try? The only thing left that I can think of is rebuilding the motor and I really dont have the time nor the money to mess with that. I'm going to start looking for information on how the carb should be tuned and set.

 

[mfkadz]

Seeing s you have been in the distributor I'm guessing either the timing is off or the advance is not working properly.

mike

 

[Swanny87]

What do you mean by Advance? Never heard that term before for motors.

 

[Eric 3.7LX Alpha 1]

The timing changes as rpm's change. Under the points there is a plate, under that plate are 2 springs and weights. As they spin faster, they change timing. There is a chart in the Service manual with what the advance should be at various RPM's. You need an advanced timing light to check it. If the springs and weights are rusty they can't move= no advance.

It could also be wrong gear ratio in the drive. If the drive has ever been changed, it may have the wrong gears in it which could effect how the engine performs.

There are other possible causes also. What are you getting for RPM's at WOT?

 

[Eric 3.7LX Alpha 1]

Recommended timing at idle was lowered in a TSB also not sure if you are aware

 

[wrestling coach]

Is your choke opening fully when operating temp is reached?

 

[Swanny87]

The engine was able to get up out of idle last year no problem. But I was having issues with it not getting fuel because of the vent line having a blockage. I will look into the timing to see where it is now and should be. It is just odd because last year it had issues with idle and this year is the complete opposite. Thanks for all the input and as soon as I have decent weather when I'm off work, I'll run it again to see if it's the timing.
Thanks again.

 

[Swanny87]

And the choke is operating as designed. I cleaned out the flame resonator, or what ever the flame resist thing is called on top, in case that's an issue as well.