Low RPM on '62 40HP Johnson

[Namcali]

I recently purchased this:<br /><br />TT226NR-1C Model for single or twin cylinder engines with a spark firing every 180 degrees of the engine crankshaft. <br /><br />Installed, the max rpm I get would be 1950 while the boat is running at 25MHP (max)<br /><br />The manual said this engine can get up to 4500rpm. What's wrong here? is that the right model of tinytach that I bought or I have to multiply it by two?<br /><br />Thanks,<br /><br />Nam

 

[Paul Moir]

Re: Low RPM on '62 40HP Johnson

Shoot, that's the wrong one. You want the 2C one.<br /><br />Try wrapping the pickup around both spark plug wires (if it's long enough) and see if you can't get it to pickup both. That would fix the 1/2 problem.

 

[Namcali]

Re: Low RPM on '62 40HP Johnson

Paul:<br /><br />Yeah, I think I can wrap the pickup wire on both of them...that would be no problem. Will try it this afternoon when I get home. If not, for now, I think multiply the number by 2, would be accurate?<br /><br />Thanks,<br /><br />Nam

 

[Paul Moir]

Re: Low RPM on '62 40HP Johnson

Yes, precisely. If I understand what they used to pickup correctly, the direction of the wrap may be important.<br /><br />Sounds like the RPMS are a little past the low end of the range (4000-5000 rpms for that engine).<br /><br />How does the compression look? If I'm not mistaken, those 40hp engines can also stand a lot jacking up on the transom for good results. Keep an eye on the water discharge though at idle and at WOT.<br /><br />Any idea what pitch the prop is? Part number stamped into it somewhere?

 

[daveswaves]

Re: Low RPM on '62 40HP Johnson

Hi Paul, my experience is that it is tough to jack these engines up. OK if water conditions are perfect but the old prop design has a hard time holding on to the water in rough water or hard turns, a doell fin helps. The prop, if original is a 10 3/8 x 13 1/8. I had mine tuned up at the prop shop and tweaked to 14P, works well and turns at 4300 rpm, also does 25 mph at that rpm. Nam, you may not be getting full carb opening at max throttle. Also, if this engine has not been run much it is probably gummed up, check with your local marina for a decarb treatment (additive). Other posts on this board re de carbing. Enjoy your classic 40

 

[Namcali]

Re: Low RPM on '62 40HP Johnson

Hi Paul and Daves,<br /><br />Gosh, I couldn't wait to get home from work today. Here the story goes:<br /><br />I own this boat for about 1.5 years now. It's been always running whenever I want to. I had no idea what year the engine was until I found this community (iboats.com)<br /><br />I even appreciate it more when I found out how old it is. When I first acquired the boat, 7Mph was its max. Last month, I completely rebuilt the lower unit (electric shift) since I detected slippage. It gets max around 24Mph ever since.<br /><br />Tested compression today for the first time, Cyl. 1 = 95Psi, Cyl. 2 = 90Psi. This engine has never been de-carb since I owned it. Champion J4C plugs...they look good.<br /><br />I have 3 props. came with it: 10.5x13 what does this mean? <br /><br />At full throttle, I get 1950x2=3900rpm. What to do to increase this?<br /><br />Daves: you are exactly right about the performance in rough water or turn. During those conditions, I sometimes get about 8-10mph. When I pass that area, the speed automatically increases up to 24MHP, why is that?<br /><br />BTW, what is doell fin?<br /><br />Sorry with all naive questions. Thanks all for the help. I've learned a lot so far.<br /><br />Nam

 

[Namcali]

Re: Low RPM on '62 40HP Johnson

BTW, thanks Paul, I wrapped the pickup wire of the tinytach around two plug wires, it works...<br /><br />I also noticed yesterday while running in a trash can, idle rpm fluctuates between 700-800 rpm. It eventually dies in about 5 minutes of running; however, it starts right up. Where to start from here? rebuid the carb.?<br /><br />Thanks,<br /><br />Nam

 

[Paul Moir]

Re: Low RPM on '62 40HP Johnson

Dave, thanks for the input. I'm really not very familiar with setting up these 40hp engines. Older ones have a really long leg.<br /><br />Good to hear that the tiny tach fix worked!<br /><br />When your running the engine in a trash can, unless their's enough wind to carry it off the engine will choke a bit on it's exhaust. It creates the same symptoms you're talking about.<br /><br />But if that's not the problem, then start by pumping the primer bulb and seeing if that doesn't even it out. I'm thinking you may be getting a little air with your gas.<br /><br />If that doesn't help, try adjusting the idle mix control a bit, or tightening the packing nut on it. How many turns out from fully seated is the idle control at?<br /><br />As far as the WOT RPMS being low, there's all sorts of reasons for that. Starting with your prop, which is 10.5" in diameter and is 13" pitch. If veiwed as a screw, the pitch is how far forward the prop would travel when turned 1 revolution. Of course, there's always a little slip in water:<br />13" x 12:21 gear ratio x 3900 RPM = 29000 inches/m<br />= 27.5 MPH.<br />So, 25/27.5 = about 9% slip at WOT. Or 13% at 24 MPH max. Those slip number tells us that the boat is good and suggests it's light, as those are good numbers. <br /><br />Which suggests to me that there might be some tuning up of the engine you can do to improve things. First on order should be that decarb, to see if we can't pick up the compression a bit. Older engines like yours really seem to appreciate it, as often a ring is hung up in it's land from excessive carbon or coke. Give each cylinder a good soaking!<br /><br />Next is to look over the linkages like Dave suggested, making sure your opening up all the way to WOT. If it hasn't been done in a very long time, removing the flywheel and regapping the points is probably in order.<br /><br />Third, try pumping the primer bulb while running at WOT. We want to make sure you haven't got a fuel starvation issue, or a air leak somewhere.<br /><br />The fourth thing you'll want to do is check your mixture at WOT. With a reasonably new set of plugs in the engine, run at full throttle for a couple minutes. Then as quickly as you can, shut down the engine. At this point, remove the spark plugs and examine the insulators on the firing end. Tan, and no difference between them is what we want. Tell us what they look like and we can go from there. Remember when installing the spark plugs back into the hot engine, not to fully torque them until it cools down.<br /><br />Tell us what you find!<br /><br />EDIT: A Doel Fin is a foil attached to the antiventilation (cavitation) plate to improve takeoff by aiding the boat to get up on plane. To my understanding, properly installed they do not touch the water at full throttle, so they do not affect you there (ie, greater drag).<br />

 

[Namcali]

Re: Low RPM on '62 40HP Johnson

Wow! now that I know the meaning of prop's number. Will keep this in mind.<br /><br />For the idling problem, I think it's fuel starvation. I noticed the fuel pump is leaking when the pressure on the fuel tank is transfered over once I plug in the fuel line. The leak comes from the fuel pump's gasket (the large one with 4 bolts) While the engine is running, I did not see the leak however.<br /><br />I've just ordered the factory service manual for $40. So I will be looking into point setting and mixture screw when I get the correct manual.<br /><br />The engine will be de-carb this weekend as I am getting a few cans of seafoam deep-creep on the way home from work today.<br /><br />So far, I found this: "As far as the WOT RPMS being low, there's all sorts of reasons for that. Starting with your prop, which is 10.5" in diameter and is 13" pitch. If veiwed as a screw, the pitch is how far forward the prop would travel when turned 1 revolution. Of course, there's always a little slip in water:<br />13" x 12:21 gear ratio x 3900 RPM = 29000 inches/m<br />= 27.5 MPH.<br />So, 25/27.5 = about 9% slip at WOT. Or 13% at 24 MPH max. Those slip number tells us that the boat is good and suggests it's light, as those are good numbers." is one of the most interesting I've leaned. with electrical engr. background, this is completely new to me.<br /><br />Thanks Paul and everyone once again...this community rocks!<br /><br />Will share my findings after this weekend.<br /><br />Nam

 

[Namcali]

Re: Low RPM on '62 40HP Johnson

Update:<br /><br />I finally decarbed the engine yesterday. It turns out to be a disaster!<br /><br />Saturday afternoon, I ran the engine in a trash can. It was really hard to start but it finally fires up, did the first part of the decarb process (spray into the carburator until it chocked out and died).<br /><br />Then I removed the plugs, filled up with sea foam, let it sit until Sunday's noon.<br /><br />Took it out to the river (it was a little cold) dropped in water, after a few aptempts, it started. Put in gear, max RPM was 900. Could not go higher than that.<br /><br />Went out about 1000 ft in the river, the engine died. Could not be started anymore. All attempts drained out the battery. We stucked in the water!<br /><br />My friend & I tighted a rope, we walked along the river bank on the rock, pulled the boat to the dock after nearly 1.5 hours navigating through the rough terrain.<br /><br />While in the river, I removed the plugs, they were dried so I think there was no fuel.<br /><br />Took it home, put in a tank, charged the battery, after a few attempts to start, she fired up and ran great with the exception that idle ran a little rough and dies out after 5 mins or so.<br /><br />Checked compression, it's now 95PSI for all two cylinders.<br /><br />In short, yesterday was the first day it died on water. In general, it's really hard to start when cold. However, when it's hot, it starts right up even with a pull. <br /><br />Sorry for such a long post. Any suggestion on dealing with this problem? Thanks,<br /><br />Nam

 

[Mark42]

Re: Low RPM on '62 40HP Johnson

Nam,<br /><br />Congrats on your 40hp! I have a '93 model (remote controls) from a rebuilder. It took two attempts to get the throttle linkage set up right because I didn't read the manual correctly the first time. My OMC manual lists a number of steps to adjust linkage, and when I did it the second time carefully following the procedure, it worked and ran beautifully. <br /><br />My boat weighs in around 600lbs, but with motor, fuel, gear and two passengers it is around 1400. I turn 5000 rpm even at full throttle doing 29 mph on smooth water with a 12.5 x 15 prop. Hope this is info is of use. Keep in mind that your 40hp is rated output at the crankshaft, and mine is rated at the propeller, so the new 40 is actually a little more powerful. But close enough I think to be fair performance reference. <br /><br />Can you post some pics of your boat/motor?<br /><br />Good luck!<br /><br />Mark.

 

[Namcali]

Re: Low RPM on '62 40HP Johnson

Hello everyone,<br /><br />Finally it's boating season again. I've been busy with a new job and away from home. But I will get back to my motor next week as soon as I receive the 379777 fuel pump repair kit and 439074 for the Carb. I think it's gonna be great.<br /><br />Will let you know how it goes.<br /><br />Cheers,<br /><br />Nam

 

[CATransplant]

Re: Low RPM on '62 40HP Johnson

"Next is to look over the linkages like Dave suggested, making sure your opening up all the way to WOT. If it hasn't been done in a very long time, removing the flywheel and regapping the points is probably in order."<br />-------------------------------------------<br /><br />Paul, If I'm not mistaken, you needn't remove the flywheel on that 40 to set the point gap. If it's the same as my '58 35hp, there's an inspection hole in the flywheel, covered with a plate, that lets you access the points for adjustment.<br /><br />All being said, his motor's doing pretty well, I think. Maybe a little low on the RPM, and it could easily be that the throttle's not completely opening, as was suggested. Mine was that way before I lubed the cable.<br /><br />Easy to check, though, without the engine running. Just put it in forward, then push the throttle control to the stop and look down the throat of the carb.<br /><br />It sounds like his decarbing didn't work out so well, but it'll probably clear up with some additional running and the carb overhaul he's planning.

 

[CATransplant]

Re: Low RPM on '62 40HP Johnson

Oh yeah...one more suggestion for the '62 40hp. Before going to lots of work to get the WOT RPMs up to spec, it would be worthwhile to experiment with the tilt settings. It's so easy to change the degree of tilt on that motor that I wouldn't do anything with swapping props until I had tried the available tilt positions.

 

[Namcali]

Re: Low RPM on '62 40HP Johnson

I have the OEM repair manual so I'll take a look to confirm this.<br /><br />So your suggestion is to try different tilt angle for optimum performance?<br /><br />I think it's easy to do. Will give it a try though.<br /><br />Nam<br />

Originally posted by CATransplant:<br /> Oh yeah...one more suggestion for the '62 40hp. Before going to lots of work to get the WOT RPMs up to spec, it would be worthwhile to experiment with the tilt settings. It's so easy to change the degree of tilt on that motor that I wouldn't do anything with swapping props until I had tried the available tilt positions.

 

[Paul Moir]

Re: Low RPM on '62 40HP Johnson

It's good to hear back from you Nam! I'm looking forward to hearing your results <br /><br />CATransplant - they eliminated that inspection/access hole in '59 or the very early '60s. On some flywheels stress cracks developed around it which lead to flywheel failures. I can only imagine the excitement of having that heavy flywheel liberated at 5000RPM. Don't worry about yours - I'm sure if it would have had problems it would have developed them a long time ago.