Noob !!!!!

[VStarod]

HELLO !!!! Well, let me start off by saying that I have been lurking here for 2 weeks and I'm astonished by how much information is posted here. NOW, let me tell you where I'm at ... I just recently purchased a '79 Mark Twain bowrider with what appears to be a '77 Merc 115 outboard. Let me add that I am very knowledgeable on car and motorcycle engines, but this darn 2 stroke is kinda confusing, but I'll get it. Nevertheless, she seems to run like a champ, although, at WOT I'm only hitting 4500 RPM and about 35 MPH, just curious if this is normal and what other nightmares can I expect ... this is my first boat ... thanks

Rod

 

[verado7]

Re: Noob !!!!!

alot of thing come into play such as propellor pitch - trim - loaded weight etc.

but first easiest thing to check is remove each spark plug wire 1 at a time while she's running with some insulated pliers and see if you have a cylinder not firing - the one that isn't firing will have no effect on the engine . then check compression . can the last owner verify that it hit max rpm's before he sold it ? did he run it with less load ( PEOPLE ,GEAR ETC. ) than you are ?

 

[CharlieB]

Re: Noob !!!!!

Same troubleshooting procedure as any other motor, compression test, spark test, fuel supply.

Compression over 100 and within 10% each other

Spark hot blue arc of at least 1/2 inch

Check fuel pump output, diaphragm not leaking into engine, supply hoses in good shape, and not sucking air into the system, no restrictions in the tank pick-up or vent.

Clean carbs, float height correct, sync, timing per manual

Adjust idle mixture IN gear IN the water then fatten mixture till ALL traces of hesitation are gone on acceleration, same as you do your weedwacker.

If the motor RPM under load to under 3000 then DVA test ignition again as high speed windings output may be low, causing a 'governing' effect. If high side ignition checks out O.K. then use a couple of the on-line prop catalogs to look into pitch recommendations for your boat/motor combination.