Merc Classic 50 RPM surge

[Jibbi]

Hi all,

Just found the site, and seems to be a gold mine of knowledge on here, so I hope (and I'm sure) someone can point me in the right direction. Thanks in advance for any help.

I've got a '88 Mercury Classic Fifty (45HP). Just yesterday it started surging at lower RPMS, and was hard to tell if anything was happening at higher range, but it ran pretty good at ~4000 rpms. It has run great this whole year with no problems whatsoever. Tried new gas but that didn't help.

Any suggestion are, as is obvious, much welcomed and appreciated.

Oh yeah, I've purchased the manual, but have to wait on that.

 

[tashasdaddy]

Re: Merc Classic 50 RPM surge

if it's only turning 4000 at wot, something is wrong, either wrong prop. surging can be from dirty carb or link n sinc. fuel pump going.

 

[Jibbi]

Re: Merc Classic 50 RPM surge

Nah, 4K isn't WOT. I just didn't want to push it without knowing what is going on. Then again, I don't really ever run it past 4500 rpm. What is max rpm for this motor?

Anyway, thanks for responding. I'll be doing the fuel pump as I understand it to be a quick & cheap fix. What is linc n sync?

 

[redjmp]

Re: Merc Classic 50 RPM surge

The method to test a 2 stroke outboard is as follows.
Run motor until warm. Pull and visually inspect plugs. Are they all warm indicating they are firing or are any cold?
They should have a nice even brownish tinge to them. If any looks different, then you have a problem in that cylinder. Blackish soot is too rich too much oil, cold and wet with clean gas means not firing, dry means no or not enough gas, metallic deposits mean you have overheated and melted your pistons.
Next you need to do a compression check. Should be at least 100 lbs and at worst within 10% of each other. 125 or higher is better.
Spark test is next. You can get a cheap spark tester at any auto store.
Verify good spark under load by installing clean plugs and running at cruising speed for 10 minutes or so. If problem persists try pumping ball. Visually inspect plugs again.
After you have verified good compression, good spark under load and good gas, check your link and sinc.
Look in the FAQ for how to do this.

 

[Jibbi]

Re: Merc Classic 50 RPM surge

Thanks for the info. I'll run this series of checks and hopefully discover my issue. Also, Can someone let me know what is the WOT rpms for this motor?

Thanks,

 

[G_Lipe]

Re: Merc Classic 50 RPM surge

i have the same exact motor and mine runs about 5500 wot without any issue

also check the fuel lines mine did as you described and it had a kinked fuel line right below the filter after the pump