1975 70 hp Johnson...Take off problem...Update and more information

cvlngineer · Mar 12, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

ob, That looks like the one. Except, in mine, there are two pressure relief valve springs (#23), two pressure relief valves (#101), and two relief valve grommets (#78). They sit next to each other in the same chamber. Other than that, it looks the same. It looks like I did get the thermostat installed in the right direction. I tore the crap out of the housing gasket, hopefully my gasket sealer will work. If not I will have to run over to the shop here and see if he has another one. Thanks, cvlngineer

cvlngineer · Mar 13, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

Here goes... I took the controls apart because there was too much play in the throttle. I found a loose screw on the warm-up lever/high idle or whatever it is called. I tightened it and it solved that problem. I took the boat down to the water, and tested it out, and it was doing the same old thing, bogging down while trying to accelerate. I fiddled with it a little and made it worse, then put it back like I had it and loaded the boat up before I got really hacked off and unbolted the motor and kicked it into the bay. We have ruled out a couple of things. Is there any way to test the powerpack, stator and coils with a multimeter? Thanks for all of your help, cvlngineer

cvlngineer · Mar 14, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

I forgot to add this: I tested the motor with the cowling on and with it off and there was no difference. It was close to dark and I looked at the back of the engine during the bogging, and I didn't see the coils arcing on anything. cvlngineer

ob · Mar 14, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

cvlngineer,If you have any patience left , next time you take it out try bringing some 50:1 premix in a spray bottle.Running with the cowling and silencer cover removed ,when engine bogs,try spraying some premix into carb throats and see if engine picks up.This will tell us whether it may be ignition related or fuel related problem.

cvlngineer · Mar 14, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

ob, I still have a little patience left (c; I will do that and let you know what it does. I have the business end of the motor down in a barrel of water now, so I can tell how it is going to idle and rev when submerged, but I can't put it in gear or it will blow all of the water out of the barrel. I need a portable lake. Thanks, cvlngineer

rickdb1boat · Mar 14, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

cvlngineer Just out of curiosity, have you replaced the fuel pump yet? Thought you might have a pinhole in the diaphram that may be screwing you up. Also check for fuel fittings that may be sucking air. As for that screw that was loose on the fast idle control, mine used to forever work it's way loose until I put some locktite on it. Just so you know. Hope you're making progress on your motor and by the way, I checked out your website and have to say you did a heck of a job on the boat. Lotta work!!

Solittle · Mar 14, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

Might want to get the manual for your motor.

SCO · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

How much is a new powerpack for that unit? That light switch description is sounding more and more like powerpack.

cvlngineer · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

Rickdb1boat, I haven't checked the diaphragm in the pump yet, I will look at it today. Thanks for the compliments on the boat! It was a LOT of work, but it was all worth it, at least looking back now.

cvlngineer

cvlngineer · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

SoLittle, You are right! I am going to pick one up next time I am in town. Thanks, cvlngineer

cvlngineer · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

SCO, Shhhhhhh, those things cost about $200! At least at the place I called. If that is what it turns out to be, I will call around and see if I can find it cheaper. Thanks, cvlngineer

cvlngineer · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

I took the boat over to the shop, and had the guy check out the ignition system under a load. Everything checked out okay, but he said that I have 2 number 2 carbs on it. This is preventing me from synching the bottom carb properly. He gave me another carb that I can clean up or part out. I will work on it today. I also found out that I have a big job ahead of me. He listened to the motor and used his stethoscope and found that the knuckle bearing on the top cylinder is rattling. Once I get done with the carbs and get that problem straightened out, He said that he would coach me on replacing the bearing. While I am in there I guess I will replace all three, and put in new rings. Thanks, cvlngineer

SCO · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

That will be interesting. I for one would like to read a blow by blow of the internal work. Also, what is your boats dressed out weight less engine?

cvlngineer · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

SCO, The hull weight is about 650-700 lbs. With anchor and all of the goodies in it, minus the engine, I would guess around 850-900 lbs. cvlngineer

SCO · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

Sorry to go off topic, we're already off anyway, but the angled portion at the bottom chine area, is that so the boat won't trip in a turn, or to direct spray outward? Sounds like a good shop that diagnosed the knuckle, who was that, OB?

cvlngineer · Mar 15, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

SCO, I believe the angled chine does both. But its main function is to prevent chine-tripping. A previous shorter version of this particular boat had a stepped chine that was supposedly more effective at deflecting spray, but someone complained about the chines digging in during tight turns. The shop that diagnosed the bad knuckle bearing is a little shop here in Kingsville. He is a good, guy and from what I have heard and seen, he does good work. He checked my motor out for $20 and gave me another carb for free. OB was right about the carb problem. I pulled the shaft that holds the throttle plate off of the new carb (it was a newer model than the three I have installed) and put it on my #3 carb. I got the carbs synched as close as I could with it getting dark. The motor seemed to run better in the barrel, but still needs some fine-tuning. I was afraid to run it too much after hearing about the knuckle bearing. I'm paranoid and thought I heard it getting louder, so I had to cut my tuning short. I guess I will pull the powerhead and get started in the next couple of days. cvlngineer

cvlngineer · May 2, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

I have completed the rebuild, finally. I took it apart, to see what all would be required, and had to wait a month or so to save up the money. I ordered a kit from powerheadkit.com and installed it. The kit cost me about $430 or so with shipping. I replaced the pistons, rings, wristpin bearings, rod bearings, lower main bearing, seals and gaskets. I cleaned out the motor, and had the cylinders honed, and put it back together. It was not all that difficult to do, just time consuming, especially removing all of the old gasket stuff. I am now back to trying to fix the bogging problem. I have replaced all hoses and the fuel pump, along with the shift-shaft seal in the lower unit. I am getting pretty good at this stuff! I have taken the boat out twice to test it, but came back early, completely hacked off. I am extremely paranoid about any engine sounds, either imagined or real. I just know that this thing is going to come apart on me. My dad, who rebuilt car engines numerous times with great success, rebuilt a mini-bike motor for me when I was a kid. About a month later, it threw a rod, though I am sure that it was me over-revving the motor, and not the rebuild that was the cause. I had discovered that if you reached down and pressed on the governor with your hand, that it was a great "turbo boost." Regardless, I have been very leery about rebuilt motors since then. I torqued the rod bolts the the required torque, according to my manual, which was something like 32 ft-lbs. I put lock-tite on them, but I am still quite worried. I have adjusted the pickup timing, and tested the motor in a tank at the local marine service shop. It sounds like the latest round of fiddling has done quite a bit of good. I put the motor in gear and brought it up to around 2000 - 2100 rpms and it didn't bog down at all. I couldn't get it any higher than that, because it was throwing too much water out of the tank and I didn't want to have to replace my impeller. I will probably take it out and test it again on Sunday. I will post results at that time. cvlngineer

cvlngineer · May 11, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

IT WORKS!!! I think. I took it out today, after reassembling the motor. (I had to replace the upper main bearing. While I was at it I replaced the center mains as well.) I replaced the fuel coupling on the motor and replaced the hose, bought a new 12 gal fuel tank and changed out the #2 coil. I also discovered that the float drop on one of the carbs was too large, so I fixed that. One of these things seems to have done the trick. I would imagine that it was the coil. I backed the boat into the water, but left it on the trailer, started the motor, let it warm up, and then shifted into forward gear. I gave it the throttle and it didn't bog down. I think I can actually drive the boat on the trailer now. I will take it out for a test run tomorrow. Hopefully all will go well. cvlngineer

Paul Moir · May 12, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

Did you ever figure out what blew the top main bearing?

cvlngineer · May 12, 2003

Re: 1975 70 hp Johnson...Take off problem...Update and more information

Paul, I guess it was that little hole in the carb mounting plate. It looks like it catches any fuel that may run out the front of the carbs and pool up at the bottom of the silencer cover. It was plugged up with gasket sealer. I cleared it out and ran it today for a couple of hours and it isn't sqealing, so I am hoping it worked. It only took about 30 minutes for it to start squealing last time. The boat ran a lot better today, although there is still a slight hesitation in accelerating, but nothing like it was. I actually drove the boat on the trailer. cvlngineer

1975 70 hp Johnson...Take off problem...Update and more information

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