1974 25 hp Johnson: More Questions

[JohnAB]

First off I want to say thanks to all who have helped so far. Your help is truley appreciated.<br /><br />Okay I fixed my armature plate wiggle and adjusted the points and checked at 1000 rpm with timing light and everything lined up, hooked up a Tiny Tach, raised the motor on the transom and rejetted the carb from a 72 down to a 68 as I am at approximately 3000' ASL (couldn't get a 69 so went with a 68). Prop is a 10x9 3 blade aluminum.<br /><br />Took the boat out, a 14 foot Springbok aluminum fishing boat (mid 70's vintage) with me, the oldest kid and a full fuel tank. Probaly 550 lbs total weight in boat ( I am pleasantly plump so to speak).<br /><br />At WOT the Tiny Tach showed I was only revving 2300. Now to me that seems awful low for the sound of the motor and how fast we were going. I forgot my GPS, but I would estimate we were in the high 20's in mph. This seems awful fast for only revving 2300 rpm. The Tiny Tach I was shipped is supposed to be a TT226R-1C and is classified as the model for a 2 cylinder engine firing every 180 degrees of the engine crankshaft. I was wondering if anyone has experience with these tachs and should I bedoubling the RPM readout? Wrapped the red wire around the bottom sparkplug wire. When I am in gear under load in the water and have the throttle at the link and sinc marks, the tach shows I am revving about 450 rpm. Does that sound about right?<br /><br />Also, should I rejet back to the 72 jet? Motor seems to run fine but wondering if I am pushing it by using the 68 jet size.<br /><br />Also should I look at dropping down in prop pitch as I am higher in elevation?<br /><br />Apologize for the long post but wanted to get most of my concerns addressed in the one post.<br /><br />Thanks.

 

[rickdb1boat]

Re: 1974 25 hp Johnson: More Questions

How many times did you wrap the wire? Should be 3 times, I believe...

 

[JohnAB]

Re: 1974 25 hp Johnson: More Questions

I think it is wrapped 5 times around the wire. Instructions said 4. Would this cause the expected reading error?

 

[rickdb1boat]

Re: 1974 25 hp Johnson: More Questions

MAybe this will answer some questions about the tiny Tach...<br /><br /><br />. What is the up date time? 2.5 sec <br />2. How do you hook it up? You have two wires at the engine, the red wire wraps 4 times around the plug wire and the white wire with a lug to put under a bolt head for ground. <br />3 How is the tach powered? An A3 volt lithium battery is used. <br />4. How long does the battery last? The battery should last 5 years, it is not replaceable, becauses it is potted into the case. <br />5. How many models are there? There are 3 main models: 1C, looks for 2 pulses/rev; 2C looks for 1 pulse/rev & 4C, looks for 1 pulse/2revs. <br />6. Will the Tiny Tach work on multi-cylinder engines? Yes, in most cases. Sometimes a filter is needed to cut out electronic noise from the other cylinders. We call this an X and it can be used on all three models. <br />7. Do you make a resetable model for resetting the hours? Yes, it is called an R, instead of an NR. So if you wanted a 2C that is resetable you would ask for a 2CR and if you wanted a filter it would be a 2CRX. <br />8. Why does my 2C tach read double on my two cylinder engine? It can be one of two reasons, It can be picking up the other cylinder signal or your engine fires each plug 2 times/rev. NOTE: Some single cylinder engines do this also.

 

[rickdb1boat]

Re: 1974 25 hp Johnson: More Questions

If anything,5 wraps should give you a higher reading. I'd call them and ask them what's up and give them your motor model.<br /><br />1-630-920-1300

 

[ob15]

Re: 1974 25 hp Johnson: More Questions

Maybe it should be wrapped around both plug wires. That would double your rpms. I'd give them a call. I dont' think the number of wraps matter (as long as it 3 or more). I have one & it's should be wrapped around both wires but don't remember the model number right off hand.

 

[JohnAB]

Re: 1974 25 hp Johnson: More Questions

Okay determined the problem with the tach. Took the boat for a spin again this time with the GPS.<br /><br />Speed reading was just a tad under 22 mph so my previous estimate was a bit high.<br /><br />The Tiny Tach I was supposed to get and was billed for was a 1C meant for 2 cylinder 2 strokes. <br /><br />What I got and hooked up is a 2C, meant for a single cylinder 2 stroke so my readings are cut in half I would assume. So I am revving at WOT at 4700 rpm. I will call the distributor tomorrow over the mix up. <br /><br />So if I am only at 4700 rpm and the operating range is 5000-6000 rpm for the engine, then I should look at dropping a prop pitch size. Before doing this I will put back in the larger main jet, the 72, and then retry the boat under load.