1975 175 Mercruiser tuning and running issues

[Nucknoilerfan]

I've inherited a 17.5' 1975 Campion with a 175 mercruiser 302 motor. The motor has a Holley 2bbl carb and the points ignition has been replaced with electronic ignition. The boat has hardly been used for the last 5 years so I knew that it would require a little work. Imagine that, a boat that needs some work .

The motor fires quite easily and will run with enough throttle to maintain a rpm of about 1800 but as soon as I throttle back even slightly she stalls. I even let it run for about two or three minutes before trying to reduce the throttle to allow the choke to open. When it's running it seems to run fairly smooth. After it stalls it requires me to give it quite a bit of throttle to refire which seems odd. The float level seems set properly and I haven't played with idle adjustments or fuel mixture screws.

I've rebuilt the carb, new plugs, new fuel, new fuel filter and new fuel pump. The fuel tank and all lines are new as well. And all testing has been out of the water with a garden hose attached.

What should I be looking for next to get this boat out on the water for summertime fun with the kids. I'm fairly mechanical but I'm no marine mechanic and the wife doesn't want me spending a whole bunch of money.

 

[Bondo]

Re: 1975 175 Mercruiser tuning and running issues

I've rebuilt the carb,

Ayuh,.... Explain how ya did it,..??

At this point, I'd say the effort Failed....

You replaced everything,....
Is the fuel system delivering Good flow to the Carb,..??

 

[Nucknoilerfan]

Re: 1975 175 Mercruiser tuning and running issues

Yes, there is good fuel flow to the carb and the accelerator pump gives a good healthy spray. As far as the rebuild goes I guess that it was more of a good cleaning and replacing of the power valve. All ports were cleaned with carb cleaner. I didn't buy a carb kit because I was reluctant to spend $170 on the kit.

Could my problem be related to a vacuum leak. Possibly the gasket between the carb and the intake manifold?

 

[Nucknoilerfan]

Re: 1975 175 Mercruiser tuning and running issues

And how could I tell if I did have a vacuum leak?

 

[mkast]

Re: 1975 175 Mercruiser tuning and running issues

And how could I tell if I did have a vacuum leak?

Some people use starting fluid to check for vacuum leaks, flammable, use precautions.
Some people use an unlit propane torch, again, possible hazard.
I would question the quality of the carburetor rebuild.

 

[Nucknoilerfan]

Re: 1975 175 Mercruiser tuning and running issues

Would I be better off to go and buy the carb kit and replace all the components in the kit? What makes a good carburetor rebuild? It seems simple enough but maybe there is more to it then I can see.

 

[mkast]

Re: 1975 175 Mercruiser tuning and running issues

What makes a good carburetor rebuild? It seems simple enough but maybe there is more to it then I can see.

Noticed you didn't use a kit on the first attempt, you can't rebuild a carburetor without one.
What maintenance manual are you using?
Does the carburetor still have the tag with the identification number on it?
Use that number to buy the rebuild kit online, should cost less than the marina.

 

[Nucknoilerfan]

Re: 1975 175 Mercruiser tuning and running issues

Finally solved my problem with fueling issues. I did buy a carb kit and replaced all the parts from the kit. After reinstalling the carb I still suffered some runability issues. I again removed the carb and this time instead of just shooting cleaner through all the passages I soaked the the parts in carb cleaner and then blew everything out with compressed air. Reinstalled the carb and reset all the settings and now the motor runs perfectly. Thanks for all your guys help.