Rods at my OMC 90 HP engine

[mrbarth]

Hi all,<br /><br />since my engine (90 HP OMC 1991) now starts reliable (thanks to your help), I would like it to run smoothly. While the Seloc manual helps in details, I can't find a picture or description of these 3 "rods" on my motor. They are connected via the cables to the control box of course, but what do I regulate here. <br /><br />

<br /><br />From the board I understood that idle speed (mine is quite high) is set somewhere at the carb "slow speed" needle (I'll have to find that as well)<br /><br />Sorry for these propably stupid questions, but I would by books and manuals if I new which ones would explain those basics)<br />Thanks again

 

[funpilot]

Re: Rods at my OMC 90 HP engine

Nice picture.<br /><br />I'll take a stab at your question, and then let the really smart guys fill in the holes I'm about to leave.<br /><br />On an outboard engine, you can adjust the throttle plate position relative to the belcrank position (the ammount of air coming into the carb) and the point at which the Wide Open Throttle (WOT) throttle plate position occurs. The second adjustment you can make is the spark advance at idle and at WOT. This is important because too much advance can cause your pistons to melt due to excessive heat.<br /><br />You adjust spark advance to get as much burning of fuel/air mix as possible to propel the piston down. The faster the piston is moving (higher RPM) the sooner you have to start the burning (spark advance). You actually set up the engine to fire the spark plugs BEFORE top dead center is reached on the piston. You then check these adjustments by reading a timing flash that goes off at the same time the spark plug fires. A typical spark advance for an outboard engine running at 5000 rpm is about 28 degrees. Now that I think about it, that is largely governed by physics, so it would be fairly typical.<br /><br />Some of the linkages also relate to the amount of throttle allowed in reverse VS. forward.<br /><br />I hope this helps.<br /><br />fp

 

[mrbarth]

Re: Rods at my OMC 90 HP engine

Thank you FunPilot,<br /><br />the spark advance and the physics sound familiar to my experience with car engines, and they are there checked with some kind of stroboscop light attached to the distributor/interrupter (if thats the right word) and was set to fire before top dead center although I forgot that this was changing with RPMs.<br />(but makes sense of course). So I assume the upper rod, as it goes below the flywheel is that one.<br /><br />I still ahve to found out the other ones,<br />The middle one is changing rpms, if I play with it.

 

[funpilot]

Re: Rods at my OMC 90 HP engine

The middle one looks like your idle stop screw... which would advance your engine's timing at idle... not change your low idle throttle plate opening. Some motors run with the butterflys closed at idle because they have the proper amount of opening built in. You also then adjust the low idle mixture screws on the carbs to give best idle. Usually you screw them in gently to bottom them out. Then back them out one and a half turns. Let the engine run and change them 1/8 turn one at a time, letting the engine idle between settings for a minute. You are looking for the highest/smoothest idle speed.<br /><br />Most people are checking spark advance with an inductive timing light. It simply clamps onto the wire (no holes or wire removal) going to spark plug number one. Then they aim it at the little pointer on the engine and read the spark advance on the flywheel.<br /><br />Of course, you know to do all of this with a water supply attached, or with the boat in the water... and never run your boat motor on muffs at WOT.<br /><br />fp

 

[R.Johnson]

Re: Rods at my OMC 90 HP engine

Rod at top of photo is spark advance Rod,shortening rod advances timing, lenghten to retard, The timing is 28 degrees +, or - 1 degree BTDC. Second rod down is the idle stop screw, this will adjust idle speed only. 3rd. rod down with the thumb wheel is the idle pick-up timing rod, timing is 4 degrees +, or - 1 degree, at BTDC, this is the point where the carbs just start to crack open. There are no idle adjustment screws on these carbs. The small bolt with jam nut at very bottom of the photo is the full throttle stop screw. This stops the carb throttle plates at full open, and prevents undo strain on the throttle plate linkage. Keep in mind, you have to start at the very beginning when doing the sync. & link on this engine. This is one case where the proper manual is a must. Any mis-adjustment will have an adverse effect on how the engine runs. Proper adjustment is a must for peak performance, and engine longevity

 

[mrbarth]

Re: Rods at my OMC 90 HP engine

Thanks a lot guys for the info and identification.<br /><br />funpilot, I also searched for the idle adjustment on the carbs, because due to my Seloc manual I thought there must be one. I'll get me an "inductive timing light" to check on the advance. (And as I have the Seloc manual, I know not to run it dry or above idle on muffs,. I think 1/4 of the book is full with this paragraph)<br /><br />R.Johnson, thanks again for the help. As said I'm reading this manual for days now and getting on. Just several things are missing, maybe I should get another one. Thanks for the identification of the rods, that will help a lot.

 

[xikxak]

Re: Rods at my OMC 90 HP engine

boatsrfun,as a newbie to outboards myself the main thing I learned is My first seloc manual will be my last.I found at least two major errors pertaining to my motor(78 rude 140) and it drives me crazy. get the oem manual.(and post here) Good luck.

 

[mrbarth]

Re: Rods at my OMC 90 HP engine

Thanks davexx<br />I searched thru the board an came up with a Ken Cook<br />website. The manuals for my motor are here:<br />Question:<br />which one do I need ( ALL ?????=<br /><br />434248 Parts Catalog $20.00<br />434339 Owners Manual $20.00<br />507943 Service Manual Set $112.13<br />507943 Service Manual Set $112.13<br />507949 Service Manual- $40.00<br /><br />seem like some money

 

[Solittle]

Re: Rods at my OMC 90 HP engine

Here is where I got mine - - Oh I recommend the parts & service manuals - little need for the owners manual if you have been around outboards.<br /><br /> http://www.theoutboardwizard.bizhosting.com/parts_service_and_owners_manuals.html

 

[mrbarth]

Re: Rods at my OMC 90 HP engine

Thank you captain,<br /><br />sent an e-mail and asked for details.

 

[mrbarth]

Re: Rods at my OMC 90 HP engine

OBJ, just so I spend my wifes money correctly <br /><br />It's the service manual for 40 $ you recommend

 

[OBJ]

Re: Rods at my OMC 90 HP engine

I think it may be a little confusing when they say "Service Manual Set". This is all the service manuals for a given year. Someone not familiar with them may think it's the Service Manual, Parts Manual and Ops Manual as a set.<br /><br />Like SoLittle said, Operators Manual aren't really a must since most of what's in the Ops Manual is in the Service Manual.