'75 Johnson 70hp is running really rough!!

[Greaser]

Just got my hands on boat with a 1975 Johnson 70hp Loopcharged outboard. We hooked it up to the flusher to see if it would start up and if the water pump was working. All seemed to be good...it idled fine and was pumping water out fine.

We then decided to take it out on the water to see how it really ran. Well, it didn't do too well. Got it started, but once we got out of the no wake zone I throttled it up but it would not do much of anything but bogg down. Once I gave it gas it would sputter pretty bad and sometimes if I left the throttle open long enough, it would eventually catch up, but would only run strong for a few seconds before bogging back down.

I found out that the boat had been sitting up for about 4-5 months before it was sold to us, and i don't know if the gas was ran out good before it sat up. I have heard that the 70 hp Johnsons are pretty good motors, but that the carbs are prone to getting pretty dirty easily, but I am no boat mechanic so I don't know. Let me know what yall think the problem is. Thanks, Ben.

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!!

Something else I noticed that I forgot to mention. I also noticed fuel spilling out of the front of a couple of the carbs...thought that may help a little bit.

 

[iwombat]

Re: '75 Johnson 70hp is running really rough!!

If fuel is spilling out, then you've got float issues. Either a stuck float needle or a misadjusted float level. You gotta take 'em apart anyway - might as well pick up rebuild kits and do it right.

 

[jtexas]

Re: '75 Johnson 70hp is running really rough!!

yup, carb rebuild. and if you haven't already, get some fresh gas in there. compression test would be a real good idea as well. And if you don't know the age of the water pump impeller, go ahead and put that on your agenda, just to be on the safe side.

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!!

Ok. I took the advice and got carb rebuild kits and just got finished installing them. This leads to a few more questions. Will I need to readjust some stuff once I get the carbs back on? I found the needle adjustment post in the FAQ section, but I am not sure which one pertains to my carbs. I am thinking that it is the single needle carb, but I could be way off. There are two screws on the front, but I am not sure which one would be the adjustment... I wanna say it is the smaller screw, but I just want to make sure. Let me if I am on the right track, and any advice would be greatly appreciated! Thanks!

 

[jtexas]

Re: '75 Johnson 70hp is running really rough!!

That motor has fixed jets - no adjustments needed. Both those screws are "screw plugs" - to give you access to the jets for cleaning. The larger one near the bottom is also the drain plug for the carb bowl, should be a hex-head screw - use a wrench on it. Should be a third screw at the top on the port side coming out at about a 45? angle - that's your off-idle circut. There's a special tool for removing the jets - don't try it with a screwdriver, you'll just mangle 'em - better to clean 'em in place.

take 'em apart & soak 'em overnight in carb cleaner (I use b-12), then spray aerosol carb cleaner through all the tiny little holes.

Remove the core plugs on top of the carb - gives you better access for cleaning out orfices: carefully drill a hole in 'em, try not to bust through, you've got about a half-inch clearance, then pry 'em out with a sharp tool. Some people prefer to punch a hole in 'em with an awl. To replace 'em, set the new one on the hole & flatten it out with a hammer & punch.

If the float is not saturated with fuel it can be re-used. I re-use the plastic float hinge pins cause the metal ones in the kits don't seem to fit my carbs very well.

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!! UPDATE

Re: '75 Johnson 70hp is running really rough!! UPDATE

Well, I have some bad news. I cleaned them out last night. Got everything rebuilt and got them on today. The were sorta dirty and the valves and floats didn't seem to be functioning right, so I guess they needed to be rebuilt. BUT, I still have the same sort of problem. I got the motor started up and it idles nice, but as soon as you give it gas, it will speed up and run steady for 15-30 seconds or so, slow down to almost an idle for about 3-5 seconds, and then speed back up. Sometimes it will speed up to a certain speed, slow down, and then speed up to an even faster speed. I have noticed that it spits out alot of water at the faster speeds, but then not as much once it slows down. I think this is normal though? Let me know what you guys think about the whole situation. Thanks!

 

[jtexas]

Re: '75 Johnson 70hp is running really rough!! UPDATE

Re: '75 Johnson 70hp is running really rough!! UPDATE

the water pressure will vary with RPM, that's normal.........but as mention, it would be wise to replace the water pump impeller soon - at least then you'll know what "normal" water-flow is for your motor - then schedule it for every couple or three years afterward.

did the fuel leak situation get resolved?

if you have a manual, follow the link & sync procedure......if you don't have a manual, order one now (kencook.com will have your original factory manual), meantime, check to make sure that your choke valves stay open (horizontal) except when the choke is engaged, and that the throttle valves are all moving together, parallel, closed at idle and horizontal (but not beyond) when the throttle lever is all the way forward (WOT).

then, if you haven't dumped all the old gas already, do it now, get some fresh fuel in there.

Is your fuel line holding pressure (primer bulb gets & stays hard - stop laughing this is serious)?
Is the tank vent open?
Are the carburetors spitting fuel back out the throats at idle?

Tilt the motor up far as it will go (engine off) - does any fuel run out through the carb throats?

Pump the primer bulb when the engine starts running bad - does it improve the situation?

Observe the back side of the fuel pump while somebody squeezes the primer bulb, does any fuel come out through that little hole?

If you haven't done a compression test, this would be a good time - no sense throwing more money into an engine with bad compression.

 

[Lodgepole]

Re: '75 Johnson 70hp is running really rough!! UPDATE

Re: '75 Johnson 70hp is running really rough!! UPDATE

If you are sure you have the carbs cleaned and floats adjusted to proper level with no fuel coming out of front of carbs, then I would check fuel pump also fuel line for air leaks. My 78 70 pees a good stream at idle or at rpm. Don't ignore the impeller. That is the first thing to check when you pick up a motor.

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!!

There is no longer any fuel spilling out of the front of the carbs... fixed that in the carb rebuild. They are all linked and synced right.

One thing I have noticed (that you brought to my attention) was that the primer bulb never really gets hard. I do pump it several times before starting it, and it starts up just fine. But I did go out and pump it 10+ times with no real change in its hardness, and it didn't seem to flood the engine because it started right up. What does this mean?

I will go ahead and order an impeller. Should I go with the full kit or just the impeller?

 

[jtexas]

Re: '75 Johnson 70hp is running really rough!!

It should hold pressure for hours - otherwise either the line is sucking air somewhere through worn out fittings, or the bulb is wearing out. Or you've got a fuel leak somewhere. You can rule out a fuel leak by visually inspecting all the lines from tank to pump to carbs while somebody squeezes the bulb. Sometimes if you listen close at the fittings you can hear it sucking air while you pump the bulb. Go ahead & spend the extra $7 or so for the BRP or other name-brand bulb, the aftermarket bulbs don't have a good reputation for reliability. quick-disconnect fittings are pretty cheap, too, just go ahead & replace 'em.

On the water pump...get an "impeller kit" which will include replacement gaskets, or a "full pump kit" which will include a new pump housing. The housing only needs to be replaced if its scratched or scored like from debris running through the pump. Not sure the price difference in the two kits. Thing about water pump is, its not too costly or too difficult but failure is catastrophic.

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!!

Thanks for the info. I checked a little bit earlier, and I found that with the fuel line unhooked from the engine, the primer bulb will get hard after a few pumps. It is only when hooked to the engine that it never hardens. This seems like it would be a leak somewhere else.

I will be out of town next week, so I won't be able to try anything for a while, but I will let you guys know how things go when I get back. Thanks again!

 

[Jacob645]

Re: '75 Johnson 70hp is running really rough!!

Also you might try to check your coils for any cracks or silicone repair. I have a 1975 50hp that did the same thing. I put a new coil on and put a couple of cans of DEEP CREEP through it, and it ran great! Just food for thought! Good luck!

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!!

Ok...I replaced the fuel all the fuel lines in the engine, the line from the tank to the engine, all the fittings, the primer bulb, and the impeller. BUT, once I started pressing the primer bulb, I could hear an air leak somewhere, so I searched and found it to be coming from the edge of the fuel pump between the metal part and the rubber part, and upon further investigation, that rubber piece was shot. So, I ordered what I thought was the fuel pump rebuild kit for my engine (Sierra part #18-7820), but when it arrived, the pieces were alot smaller then the fuel pump. It was not even close to fitting my pump. The part number in my parts manual says that the # of the fuel pump is 0385784, but the pump in the motor is labeled 0433390. According to a couple of websites, the part # changed a few times and is now 0438559? ( http://www.dixiemarinesales.com/detail.aspx?ID=515 )

SO...does anyone know if that pump that I have on there is even the correct pump. I would really rather buy a rebuild kit than having to spend $70-80 on a new pump, but now I don't know which kit I need to buy

With these symptoms, does it sound like a pump rebuild would fix the problem?? Please Help!! Thanks!

 

[jtexas]

Re: '75 Johnson 70hp is running really rough!!

The rebuild ought to do it....does your repair kit look like this:

it should fit - can you post a picture of your fuel pump?

you'll need gasket cleaner and gasket sealer (I use permatex), when removing the old gasket material be careful not to scratch the housing.

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!!

For some reason, I couldn't see your picture, so will post a few of my own. A couple of the fuel pump (the number on the sticker is 433390), one of the rebulid kit, and one of the rubber piece from the kit on top of the pump that I have.

 

[jtexas]

Re: '75 Johnson 70hp is running really rough!!

take a look at sierra part# 18-7821 (iboats has the image) looks like it might be a better fit, maybe they'll exchange it for ya....the seloc manual has a picture of the pump with a caption that says something like, "this is the throw-away pump used on some 3-cylinders," and the OEM manual says to replace the whole assembly - but the 18-7820 kit fit my 1979 model just fine. good luck.........

 

[Greaser]

Re: '75 Johnson 70hp is running really rough!!

Well, that was the same news I found out from a mechanic in town earlier today. He sold me that kit, and I just put it in to find that that didn't fix the problem. The primer bulb still doesn't seem to stay hard. It will get firm for a bit, but then it won't stay hard once the engine gets going. If it is pressed when the engine is running/bogging it will pick up. I thought that meant that the pump was bad, but I just rebuilt that.

One thing I have noticed is that the hose that runs from the pump to the bottom carb is sorta kinked by the bottom of the motor cover. It was like that when we got the boat, and I don't see any other way to get that hose on there without it being like that. It almost makes me think that that carb is not even supposed to be on the bottom. I moved the bottom carb up top, but I couldn't get the engine to stay running. I seemed like the fuel pump couldn't pump it up that far. I don't know where to go from here.

What do you think?

 

[mikesea]

Re: '75 Johnson 70hp is running really rough!!

still sounds like carb issues,did you soak them,if you saw gunk ,then the passages have gunk in them,sometimes it takes a good soaking and some air pressure to clear them out,as for the squeeze ball,the ball will soften after the engine starts because it is drawing the fuel,when you squeeze the ball it pressurizes the fuel lines and carb bowl,once the floats cut the flow off,the ball will get hard because the fuel has no where to go,thus the ball hard,

 

[ragewhelchel]

Re: '75 Johnson 70hp is running really rough!!

I myself had the same problem, I have a 74' and my father in-law has a 75. Make a long story short, we had ours side by side at the beach trying to figure my problem out.

What is your choke set at: ON/Automatic/Off?

Also, there is a canister with a little pin/piston connected to the spring right next to all the linkages, make sure the spring isn't bent a little or that pin/piston is in the canister. This solved my problem with all the bogging at full throttle, give it a few minutes if this is the problem. I thought it didn't fix it, and started heading back in to the beach, then all of a sudden it took off.

Sorry if my technical terms aren't there, I'm new to the boat engine dept. and learning as I go.

Also, I was told that you should use the prime ball that is specifcally for Johnson/Evinrude