18xd complications... Any advice?

[jeridday]

I have a 1984 Mercury 18xd (electric start) that I recently purchased from a coworker. The only work the previous owner did on it was a carb kit. He told me the only way he could get it to crank and run was with the trottle open.
I cleaned the carb, changed the plugs, and ran some new fuel through it. I went ahead and checked the compression. While turning it over with the starter, both cylinders were reading near 150psi.
I began to crank it over using the starter. It would fire up for a split second every now and then but die. I eventually opened the throttle near wide open and it fired and ran. After it fired up I released the throttle and it ran for approximately 15 seconds at a high rpm. I shut it off when I saw that it wasn't reving down to idle.
Since then, the started solenoid went bad (I have one ordered). So I have been using the pull chord to try to start it.
I tested the compression again using the pull chord. The top cylinder read near 140psi and the bottom read around 120psi after 5 pulls.
Now, still using the pull chord, the motor will fire up and die on the first pull. If I keep pulling the chord it will not fire again. If I give it a minute or so, and pull the chord again, it will fire and die again.
I have pulled the plugs several times after the motor fired up. The top plug is consistantly dry, and the bottom plug is consistantly wet.
I pulled the ignition coils and plug wires off of my 25xd, which runs great, and put them on the 18. Both plugs appear to be making sufficient spark on the 18.

I'm definitely not a marine technician. I have determined that, since the top spark plug is dry, and the bottom spark plug is wet after the motor fires, I am lead to beleive that the top cylinder firing and the bottom cylinder is not.

If anyone has had similar issues and found a remedy, please fill me in. Any information or comments that might help me will be greatly appreciated. Thanks in advance,

Jerid

 

[green4themoney]

Re: 18xd complications... Any advice?

hmmmmmm just a bit of a guss here... but if your carburater is fine and evrything is open and your fuel lines are ok and everything thing is sealed up to the intake, and you are sure of thos... the only other thing i can think of is your reed valves are sticking (the valves that seal the crankcase and let in the fuel/ air mixture) ... its rare but ive seen this happen b4 and they were giving the same problems you are describing and you have a 20 psi difference between cylinders which id get looked at.... its more of a problem to have a variation in PSI between cylinders then have lower PSI in both cylinders and them reading generally around the same numbers

 

[jeridday]

Re: 18xd complications... Any advice?

Thanks for the reply. I wondered that myself due to the compression difference. Fun work to come I suppose...

 

[jeridday]

Re: 18xd complications... And a resolution!

Re: 18xd complications... And a resolution!

Green4themoney,

After pulling the reed valve assembly off the motor, it was very evident what the issue was...

The reed valve block seal was shot. And by shot, I mean, the bottom half of it was completely deteriorated. On top of that, the sticky rubber residue left behind was inside the engine block. This explains why there was a compression difference on the bottom cylinder.

I Cleaned the gunk off of the inner surfice of the block, dissasemble the reed valve system and cleaned the parts. The reed valves were in good condition...

The local marine shop had the gaskets and seal in stock. I put it all back together and she cranked and ran smooth on the first pull. Never felt better. A very simple job with great results.

 

[Lewis]

Re: 18xd complications... Any advice?

OK, I don't know if you've been following, but I have been running a parallel thread about an 18XD. My best guess is that my problem is a fuel-flow problem. I've ordered a carb kit, but reed valve problems are in the back of my mind. How hard was it to get to the reed valve assembly off? And how did you get to it?
Lewis

 

[jeridday]

Re: 18xd complications... Any advice?

Lewis,

It is a very simple task. If you have the carb off, you have half of the work complete.

There is a plate behind the carb gasket which has two vaccum hoses connected to the bottom of it. The plate is held on by three screws. Take the screws out and the assembly will follow. If you want to look at a schematic, go to ishopmarine.com. Click on "parts list", then "Mercury", find your hp and model, then "cylinder block and covers".

The bottom of the schematic is the reed valve system.

When you take it apart you will be able to see if you need to replace anything. There are two gaskets and one seal. Refer to the schematic for part numbers.

Its such a simple task. You will see. If you have the carb off, go ahead and inspect the reed valve system. Make sure the reeds are in good condition and mount flush to the reed valve block. You can take the assembly apart if necessary and clean it. Good luck.

Jerid

 

[Lewis]

Re: 18xd complications... Any advice?

Thanks! Doesn't sound too bad; I was afraid I might have to pull the power head.
Lewis

 

[green4themoney]

Re: 18xd complications... Any advice?

sweet deal budday... now if i could just get my electrical problems sorted out