1994 120 V-4 Johnson info.....Crash course for new guy

[musky1]

Hello all, I am looking for some basic info on my "new to me" fishing rig. The motor, a '94 Johnson 120 V-4, model J120TLARK, Ser.# G 035055573 is a big step up from my 25 tiller Yamaha....... First question, what WOT RPMs should I be expecting? I am currently @5750 and catching about 53 mph on the GPS. I was told at one time this setup did nearly 65..... is that realistic and do I need to be looking for a problem? Boat is a 217F Stratos w/ a 13 1/2 x 22 Raker prop. Am I correct in understanding that this motor is sometimes referred to as a "looper"? If so, can anyone give me a brief rundown of loop charging? And last, for now, what service manual should I be looking at? I see products from Johnson, Clymer and Seloc. What's best here? Thanks in advance for your consideration and help.<br /><br />/mike

 

[Scuda11]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

I can only help with the manual part, but if I were to do it again, I think I would get the OMC one, and I prob still will. I have the SELOC, which is ok, but can be a little confusing and covers too many different engines. I will yield to the experts on the other questions.

 

[Walker]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

I help as much as I can. The 120 is a looper and it is 122 ci displacement, if I remember right, almost 200 more cc's displacement than the 90degree crossflows. And more ci's mean more torque. That 120 is a beast. Recommended RPM is 5000 to 6000. Best service manual is OMC hands down.<br />Mine covers 120 thru 300 and has every thing you need to know plus more. My manual is OMC part number 500612.

 

[Solittle]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

Great motor.

 

[musky1]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

Thanks for some quick answers, guys. I have already solved a few problems just by mousing through previous posts. Had to pump out nearly a full tank of prem. petrol to replace it with the proper 87 octane....... that alone cost me 250-300 rpm and a set of fouled plugs. A visit to Ken Cook's Theoretical Performance Calculator reveals that I could, in a perfect world see near 65 mph @ 5750rpm. I am presently addressing a spun prop problem, any chance this might be a contributing factor to less than ideal performance? It's only really let loose a couple of times and then kind of locked back up. I'm wondering if there might be sustained slight slippage at higher speeds........<br />OMC manual is ordered tonight!<br /><br />/mike

 

[jimmbo]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

That doesn't sound like a spun prop hub, more like you had the prop ventilating(sucking air) a bit.

 

[G DANE]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

If your motor runs well at iddle and through the rpm range, I dont think it suffers from any technical problems at all, it performs too well for that. It may very well need a decarb threatment, especially if its on a fishing rig, they all do some slow rpm, now and then. Decarbing once a year is a good idea anyway, keeps your motor in shape. You can get OEM products for it at your dealer, just follow instructions on the can. If your are heading for top speed, its may be neccesary to look at the propeller - shape and type, and the motor/boat setup, hight on transom and trim. Do a little search on setup or X dimension here and you will meet words of wisdom. I dont think you have problems though.

 

[jimmbo]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

Your RAKER is a good prop It is about 20 yrs old but still holds up well against newer designs. It does well when it is partialy out of the water, so feel free to raise the engine an inch or two higher.

 

[Daniel Beckman]

Re: 1994 120 V-4 Johnson info.....Crash course for new guy

Place a nosecone (pics up the water)on that engine and get a power lift and you will get the max out of that beast.