1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

Hello,

I am working on a 1987 Mercruiser 165 inline four cylinder that won't start. I checked compression and had pretty close to 220 across the board. I installed new plugs, points/condensor, cap and rotor as described in the manual. I can see spark on all cylinders with spark testers, and if I spray staring fluid directly into the spark plug holes it will "pop".

The problem is: when I open the throttle lever all the way and look down the carb the intake manifold is full of gas, but everytime I pull the plugs they are just as dry as they were out of the box. If I have an assistant "pump" the throttle lever I can see nice streams of fuel spraying down the carb.

Any ideas how I could have so much gas in the intake manifold and not get the plugs wet? I did take the oil fill cap off and watch to see that the valves on cyl #1 were opening and closing.

Also, I was told this boat ran fine two years ago when put away for the winter.

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

Sounds way too high for compression.

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

If the valves are working correctly and you are getting gas and fire, and the timing is close enough for combustion, Well you have covered all the bases on a combustion motor. That compression is very high though. I would guess that there is infarct something going on with the valves.

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

The main problem that i noticed is that even though I'm getting lots of fuel in the intake manifold it doesn't seem to be making it into the cylinders. I found a little insulation where the exhaust comes out the prop and wondered if an animal had plugged the exhaust up. then I had someone crank the engine over and I could feel some air coming out so I didn't think too much of it.

I'm pretty mechanically inclined, but I've never run into a situation where the manifold fills with gas but the cylinders/plugs stay dry. When I crank the engine over without the plugs installed I feel strong bursts of air coming out, but it's dry, no mist or smell of gas.

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

My guess is something plugged up your manifold ( I KILL ALL MICE AND CHIPMUNKS ON SIGHT!!!) Your reasoning is correct. Before you force all that crap into the chambers, you might want to take a closer look at whats going on.

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

definately something goin on there i would pull the valve cover off and take a look at the rocker arms and such seems like intake valve arn't opening.

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

Thank you for the advice so far.... The boat is over a half an hour away from my house so if you have any more ideas for me to check please let me know so I can check everything in one day!

I could see the valves opening and closing for the first cylinder by looking through the oil fill cap, but I will pull the valve cover for a closer look. Is there an easier way to check the manifolds for blockages than pulling them off?

Other than valve issues or blocked manifolds can anyone think of any other reason fuel wouldn't get from the intake manifold to the cylinders?

Even if the exhaust manifold is plugged, when I crank the engine over without the plugs wouldn't fuel still get sucked into the cylinders and blown out the spark plug holes?

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

Check timing, choke? Rather than starting fluid, you could try a little gas through each of the plug holes. The compression does sound high, but I suspect that it is a measuring problem.

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

the dreaded 165 mcm....check timing mark on balancer.....oops,the stator cover...actually they were good engines,torquey and full of spunk but ruff on timing components......timing chain/gear was iffy......hope it helps

Re: 1987 Mercruiser 165 intake manifold full of gas, but plugs are still dry?

It has been several weeks since the last post - have you found the problem yet? If not, what you have described is a blocked exhaust. In answer to your question, no, with the plugs out there would be no vacuum and no flow from the carb into the cylinders. If the exhaust is plugged or the exhaust valves aren't opening (don't think that could happen to all the cylinders since the intakes and exhausts are on the same cam shaft) then nothing more than leakage will get into the cylinders therefore no gas.

Really wish this post would've been concluded with a fix or not. Reads just like my issue