still puzzled , 1976 merc 850

[surfin bob]

I had posted issues with engine shutting off when put into gear in the water . racerone replyed and sudjested checking compression , plug spark and bad fuel . compression is 149 on all 4 when cold with no bleed down , spark is strong , fuel was drained and replaced with premium and seafoam . oil mixed as well . On land with ears on runs good , goes into forward and reverse no problem , been out twice and cant get off the dock , now i have lost reverse in the water , but have it on land , still goes Bam and shuts off in forward , adjusted idle down to 1000 on land to no avail , the guy i bought it from put a used lower unit on last year . possible issues in lower unit ? Thanks for veiwing , and for replys .

 

[Chris1956]

Re: still puzzled , 1976 merc 850

If you put it in gear and immediately give it throttle, does it stay running?

On many a Merc, when the carbs are dirty or misadjusted, we would have the cold start lever up to keep her ideling, and then push the cold start lever down, drop her into gear and give her some throttle, in a quick, smooth motion, to keep her running. Takes a bit of practice. Does that work for you?

 

[Kitimat_DoubleEagle]

Re: still puzzled , 1976 merc 850

I have a 75 850 and had the EXACT same issues when I purchased my boat last summer. You can't set your idle adjustments on the muffs. I did the same as you and when I hit the lake it would want to stall as soon as I put it in gear or when I put it into neutral comeing out of gear. Made docking smoothly a real pain.
My solution was to take my boat to the boat launch in the evening when it was deserted, back it in on the trailer until the lower unit was submerged and then set my mixture screws and idle stop with the boat still on the trailer. When you're on the muffs you don't have the load of the water on the prop. Do you get everything set correctly you need to do it under load. Once I did it this way it worked great! Only issues i had after this was my mixture screws would back out after a few hours of high rpm operation and then I'd have to reset them. Rebuilding the carbs this spring and hopefully will remedy that issue.

Also I found it was pretty much impossible to get the idle set to the factory specs which is like 650rpms if i recall. I ended up with an idle just around 950 and the previous owner showed me a trick which is to hit the choke button and when the rpms drop shift FIRMLY into gear. These motors are not meant to shift softly. At the end of last season I lost my reverse as well. I had trailered approx 150kms of gravel road to our remote camp and went to launch the boat, started fine, and went to put into gear and didn't seem to engage, not thinking I forced it farther and it engaged very harsh shaking the motor violently. After that it reverse no longer worked. What happened is the clamp that holds the cable in place under the engine cowl and had popped up from the rough road I had trailered down. this had allowed the shift cable to come lose causing the engine to throttle up prior to engaging the reverse gear. When it did engage at high rpm it stripped the 'clutch dog'. This part is expensive through the dealer, however i watched ebay over the winter and scored a new old stock part for 25$ shipped. I currently have my lower unit apart in the garage waiting for new seal and waterpump to replace the clutch dog and reassemble!

Hope that helps!

Check your wiring as well... mine is not in great shape so I am considering installing a new internal engine harness from outboardparts.com as this can cause weak spark at low RPM which may affect the ability to have the idle set at proper RPMS.

Also look up the mercury Lync and synch... this is the procedure you want to do at the boat launch with the boat on the trailer.
Best of luck, when they run they run good! My 850 pushes my 17ft double eagle very nicely! approx 40mph on flat water with just the driver in the boat.