Lower Cowl Removal on 1973 Merc 850

[utah_aviator]

Hello Everyone - I'm wondering if anyone can tell me how the lower cowl is removed on my 1973 Merc 850 (85 HP, Inline 4) as there is no access to the lowest spark plug (for compression tests) and it's also impossible to rejet the lower carburetor while it's in place. I'm hoping that there is some sort of easy "trick" to drop it down low enough to service the lowest engine components.

 

[emckelvy]

Re: Lower Cowl Removal on 1973 Merc 850

Howdy, the only way you're going to get the lower cowling off (without cutting it in two) is to pull the powerhead. A bit drastic for taking compression checks!!

There's a few of ways to get compression on the lower cyl are a special compression gage which is short enough to be able to get to the bottom cyl, such as this one:

http://www.oldmercs.com/91-29287.jpg

This gage, P/N 91-29287, is available from the Merc Dlr for $36.29;

or, unbolt the rear cowling supports either at the upper section, or the lower bolts which secure the support to the cowl; this will usually allow the cowling to drop enough to be able to thread a flexible compression tester hose into the spark plug hole.

Note that you'd need a tester that didn't have a lot of lengthy adapters at the end that screws in; just a short fitting clamped right to the hose. Some are made that way, you just have to find the right one.

The special Merc gage is probably the easiest solution and not that much more than a good-quality automotive type. Plus it's useable on just about any inline Merc, nice if you're going to work on a few!

Regarding rejetting, it would be a lot easier to pull the bottom carb rather than pulling the powerhead to gain access.

Another way is to make a special carb jet tool out of a 1/4" drive screwdriver bit; grind the bit such that it'll fit into the hole and engage the main jet fully. Use a 1/4" combination wrench and this "main jet tool" to loosen the jet. After the jet's been fully unscrewed from the carb, it may or may not come right out with the bit. If it stays in the carb, you can use a bent fine piece of wire to "catch" the main jet and pull it out.

The biggest hazard in this method is if the jet goes sideways and you can't get it out; worst-case scenario is you'd have to pull the carb.

When you're installing the jet, place it on the bit and you should be able to guide it straight in. Or guide it in on a suitable wire (or use a chunk of plastic toothpick which will stick into the main jet hole but pull free once you've threaded the main jet in).

Note you'll probably have to loosen or remove the front cowling support to gain better access to the carb, but still a lot easier than pulling the powerhead!

Anyway, HTH & G'luck...............ed

PS what behooves you to rejet in the first place, change in altitude or..............?

 

[utah_aviator]

Re: Lower Cowl Removal on 1973 Merc 850

Thanks for the insight Ed. I thought that if I unbolted the front and rear cowling supports that it might drop the lower cowl down low enough to get at a few lower things.

I think I'll be picking up the mercury gauge; thanks for the link.

As far as rejetting goes, I bought my boat back in Iowa and brought it back to my home up in the mountains of Utah (4,500' MSL) so she's a little rich.

Thanks again for your reply! --Dave

PS - I'm not going to pull the powerhead!