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Newbie outboard questions.

2123 Views 18 Replies 10 Participants Last post by  lordbater
my boats have always been of a 4stroke I/O configuration. We have recently obtained a twin outboard rig and I'm hoping yall can anser a few 2stroke outboard related questions for me..

I know some of these questions are particular to each model engine, but maybe some general information would help. The engines are '90 Force 120's

The tachometers have a 5200rpm redline on them. The engines feel real comfortable running [email protected]~35mph in 1" seas.. Is this too fast to run Outboards for an extended period?

I've heard good things and bad things about oil injection systems. Our boat currently does not have one, is it worth upgrading?

What voltage should these engines charge at? Currently at running speeds they charge around 16volts. This seems a little high to me, but both engines do it.

Should I be able to put the boat on a plain with one engine? I did some testing with each engine and am unable to plain out with only one. It will bog down around 3500rpm.

Is there anything wrong with using a single engine when trolling at slow speeds or working my way around a weed line? Am I losing fuel economy doing this?

Besides an extra set of plugs & some extra oil, is there anything else I should add to my outboard toolkit?


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That is a good RPM range for outboards. The charging depends on the brand and generator/alternator on the motor, they will vary. Trolling with a single engine is good but make sure to offset the hours from trip to trip. Oil injection is nice but stick without it and mix your own untill you get new motors. Keep life simple on yourself. It is unfortunate that you cant plane on one engine, that is kinda the purpose of having the twins, being able to cruise in if something happens to one engine. But oh well, cruise it in. Better than drifting. Best bet for RPMs and amp charges is look it up online.
Welcome to the world of TCW-3. As far as upgrading to oil injection, I would recommend the K.I.S.S. approach. You never have to worry if your oil injector is working or whether you will run out of oil if you already have it mixed with the gas before you leave the dock. Its probably not worth the investment to upgrade if what you have works. As far as just running one engine while trolling or hanging out, I do it all the time and have not had a problem. You most likely will not be able to get on plane with just 1 engine though. Its not uncommon at all to bog down before you can get up on plane.
Buck, All the boats I have been on with twins can plane with one engine, granted they are all mostly overpowered newer models. *shrug* personal preference
For your tool kit, you might also want to include extra fuel filters.
i can say that from my expierience the force 120's don't last very long in salt water. on my buddies boat he is on his second power head, and he can't keep the thing from rusting uncontrolbly. if it were me and could afford it i would start looking at upgrading the motors just b/c of the problems w/ them. i also have one on my fish n' ski fresh water boat that one hasn't had any problems but then again it doesn't get used that much and very rarely in salt water

Personally I don't run twin engines much over 4K, I rarely push mine over 4200rpm.

IMO the average loaded fishing rig will not plane on one motor.

I too feel your voltage is high. I would put a voltmeter on your batteries to see if your gauges are reading right. I think Force engines were made by Mercury who have the strongest charging systems in newer engines, but 16v's seem too high. If it is your going to start cooking those batteries at 16v's, which is bad!
High Voltage

I have twin '87 200 yamahas and the voltage creeps up to around 15.5 - 16 volts. Keeping something on, e.g. running lights, drops the voltage back down to ~14 while cruising.

This boat will plane on one engine. A previous boat required dropping the trim tabs all the way down and point into the sea, it would slowly get on plane.

On the advice of several that have fished far longer than me, I pre-mix my fuel.
I'm with Capt C, I have a friend in Costa rica that runs outboards day in and day out, He recommends no more than 4000 rpms unless it is to get you out of a bad situation. That also burns less fuel.
My 31 won't even think of planing on one motor. I think it is also a good way to spin a hub, or screw up the other motor.

I usually run my boat at 3800 and not much more than 4200. It pushes the boat plenty fast, and the fuel burn is much better.
Thanks for all the responses. The voltage was verified with the volt meter on the gps, the factory voltage gauge and my trusty portable volt meter.
Even if it will plane on one, IMO its a very bad idea to do that except in an absolute emergency. The single will be grossly over proped for the load and the thrust will be applied in a less effecient manner because it will be offset on the hull. Throw in some swells, a long ride home, and the hull constantly trying to fall off plane, and you have a great receipe to blow an engine.

If you want to be able to run home on one on plane, drop the pitch of your props by 4 inches or so. Of course, that kills your criuse and top end when both engines are running. Alternatively, be prepared to swap out props on the water.
I agree w/ Ernest, I broke a crankshaft on my port motor weekend before last, It didnt matter if I was running 3000rpms or 3800, I still only was able to make 7kts. I opted for for the 3000rpms, because I didnt want to overload the only good motor I have.
Well 16 volts is way too much but you must understand most voltmeters are rated at approx 15% accurate. The best suggestion was to take a voltmeter and check the voltage at the batteries. If it is really 16 volts you will cook all the water out and destroy your batteries. Most outboards(two stroke that is) are designed to max out at about 5 to 5500 rpm you can cruise at 4500 all day it shouldnt hurt them. Some people overprop their motors and in reality hurt the engines . This causes thkem to lug or run loaded all the time they should be able to breathe and not run too loaded. Most twins set up right will not get up on top and run. The good thing the motor will keep you moving and going towards shore. Calm seas

Well, I'm certain that my motors are putting out ~16 volts at higher RPM's. I've measured it with 1 unreliable instrument (tipped me off to a potential problem) and 2 more reliable instruments.. AND I agree that 16v it is not good. I'm really surprised that both motors show this characteristic.. The battery, ignition, and charging systems are completely isolated from each other. .Does anyone have a recommendation for an outboard mechanic in the Houston (preferably close to Sugar Land) area that specializes in electrical problems?
Do they still make these engines? Call and ask a certified mechanic.
no, they do not still make them, but there are several shops that work on them..
and from what I understand parts are not too dificult to get ahold of..
Bater, I had a similar problem a couple of years ago. It wasnt a constant 16v, but it would fluxuate up to 17v or more. After checking the voltage regulators, we discovered that one of the battery connections was loose. after we tightened it all back up, the problem went away. Hope that helps.
yes, I have another problem which I'm not sure if i've solved or not, and it may very well be related. Let my TRY to describe it.

Each cylinder has its own coil, there are two other coil looking things, that I think are pre-coils. one of these has burned a wire twice. From what I can tell, it looks like all coils/pre-coils have been replaced at some point or another. All connections were crimped with ring terminals, most were in horribly condition. So... I've since cleaned and soldered all connections and am hopeful that it will correct my wire burning problem, and my possible overcharging problem..

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