70 Horse 3 Cylinder won't open up...

[Max57]

I have a 70 horsepower three cylinder Mercury that I've managed to make run reasonably well at low speeds but it seems to only run at 1/2 throttle when opened up. The boat was given to me for my birthday by my dad. I've replaced the stator, the fuel lines, the vacuum line, the sediment bowl, the plugs, had the carbs cleaned, readjusted the floats, replaced the plug wires - everything I could think of. Could the jet setting on the carb cause this? What could be the cause???

 

[Yepblaze]

Re: 70 Horse 3 Cylinder won't open up...

Do the fuel pump if you haven't allready. Get the kit with the check valves included if so equipped.

 

[Max57]

Re: 70 Horse 3 Cylinder won't open up...

Thanks. I will try that. It seems to idle fine, run smoothly and revs up fine in neutral. As soon as I take off in gear it seems unable to throttle up. Thanks again for your help...

 

[snapperbait]

Re: 70 Horse 3 Cylinder won't open up...

Max.... Did you run a compression test before you started replacing parts? I hope so... Timing advancing and linkage operating ok?

 

[Trent]

Re: 70 Horse 3 Cylinder won't open up...

What year model?

 

[Max57]

Re: 70 Horse 3 Cylinder won't open up...

I don't know what year the engine is. I stuck my thumb over the plug holes while rotating the flywheel to ensure compression (yeah, I know but it was a cheap trick). The engine was running before so I took for granted that the timing was correct... <br />The linkage appears to be ok...

 

[SeaHorse]

Re: 70 Horse 3 Cylinder won't open up...

1) Make sure the throttle is opening all the way. Take off the plastic cover over the carbs (8 screws) and look at the butterflys with the throttle open. If not, adjust cable, be sure control handle can go all the way forward.<br />2) Adjust carb idle screws (front of carbs) somewhat rich. Turn in then open 2 full turns, 720 degrees. Test.

 

[Max57]

Re: 70 Horse 3 Cylinder won't open up...

I've checked to ensure that the butterfly opens fully in the carbs. The adjustment on the face of the carb was set to 1 1/4 turns each, but I can certainly try setting them to 2. Thanks...

 

[AndyL]

Re: 70 Horse 3 Cylinder won't open up...

I had one of those engines and it intermittently suffered from power loss. Finally traced it to leaking needle seat that occassionally would throw its hand in and flood one of the carbs. I only found it by running with the cowl and the carb covers off. This is not advisable I have since learned as it will cause the motor to run lean and may burn a piston but it eventually sourced the problem that was there for two years.If you can see neat fuel pouring in then that too may be your problem.

 

[Max57]

Re: 70 Horse 3 Cylinder won't open up...

What is it that you call "neat" fuel? I've run it with the carbs visible and noticed a small puddle of fuel lying in the top carb. Would this be the case? Would I then simply replace the needle valves? It is a 1983 vintage...

 

[AndyL]

Re: 70 Horse 3 Cylinder won't open up...

Just my opinion, but if you can see a small puddle of fuel sitting in the carb throat then I would suggest that the seat is leaking. As the cost of this part is relatively small I would suggest renewing it otherwise the engine will run over-rich and could be symptomatic of your power loss.. With the amount of air being dragged through the carb any spilt fuel would quickly evaporate unless it is being replenished by a leaky seal.<br />Well worth a try.<br /><br />Good luck

 

[Max57]

Re: 70 Horse 3 Cylinder won't open up...

Thanks Andy. I will give it a try - when I saw the fuel lying there I was suspicious of it. Thanks once again to all who have tried to help...

 

[Max57]

Re: 70 Horse 3 Cylinder won't open up...

It turns out in the end that a reed valve was gone inside the engine.<br />I've scrapped the motor.<br />Thanks for your help everyone...