70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help...

[Nathan T]

Hi, this is a friends boat. I don't know what the boat itself is, but it's a small sport type boat.

The engine is around a 1976. It is a 3 cylinder 70 horse (according to my friend, I haven't checked any serial numbers yet).

My friend asked me if I would look at it. Before I even looked at it he had a local boat dealer try to fix it. They failed. I forgot what they charged him, but they put 3 new coils on it, "rebuilt" the carbs and I will have to ask him exactly what all else that they did. After they failed to get it to run right they told him to come get it out of their shop because they didn't want to deal with it anymore...

After that he had another supposed boat mechanic look at it. This guy told him that it needed new reeds. They bought a used set of reeds and installed in it. It is still running the same as it did before anyone worked on it.

The motor starts fine, but all it will do is surge. Like maybe it is just running on one cylinder. I immediately noticed that there was a lot of gas spitting out of the carbs with it running, so I took the carbs off of it and took them apart. The carbs were very clean, BUT all of the floats were set at different heights. And not one of the floats were even close to being set right. I have the manual for the motor and set the floats right (1/16" above the carb body when turned upside down, with the gasket installed). When I took them apart they were all set so that the float hung way down inside the carb body before the needle closed (letting way too much gas in). Another thing that I found pretty ridiculous is that one of the carbs only had one nut holding it on. And these guys are mechanics???

I did a compression test before I even took the carbs off, and they are within spec (117, 125 + 127).

I checked the fuel lines and they are good.
I checked the fuel filter and it was clean.
The engine is definitely getting enough gas.
The plugs are right and gapped to .030".
I checked all electrical connectors on the engine and didn't find any that were corroded or anything.
I checked the spark when I did the compression test, but I didn't use an actual spark tester, I just used the old fashioned touch the plug to ground and check the color of the spark method and it was bright blue like it should be.

I probably left some stuff out but I need some help with this.

What should I do next? When the engine is running you can move the "timing arm" and it doesn't make it run any better. I am a certified automotive mechanic, so I don't know a ton about outboards, but I am a very good auto mechanic. I just need some help from you outboard pros to figure this out.

I would have checked the points if it had them but this has the CDI setup.

My friend doesn't think that I can get it running right since he already had the other people work on it and not get it fixed. He's really getting on my nerves with his comments about how I can't fix this motor. So please help me figure it out.

He told me that he watched the guy that put the used reeds in it adjust the timing and says that it started running better. But my friend knows absolutely nothing about anything mechanical. He doesn't even know how to change the oil in his car. Or check it for that matter.

One more thing, when we had this thing running the first time that I heard it run, for about 1-2 seconds it actually ran great. It was like someone flipped a switch and it ran like brand new for a second or two. I was pretty confident that after I got the carbs adjusted right that it would either be fixed, or at least run noticeably better but I was wrong.

I will post a video of it tomorrow so you can see/hear it run.

Thank you for any help/advice that you can give me.

 

[abarron]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

It sounds like the floats? or sucking air from somewhere? Carb gaskets? Cracked Carb Base? Man I AM JUST GUESSING????????????

 

[tashasdaddy]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

USED REEDS???? who puts in used reeds. linc n sinc, timing.

 

[jonesg]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

Re-do the spark test with a 3/8th inch gap , its the only way to know.

 

[jtexas]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

Did ya do a cylinder drop test? That motor will run on 2 cylinders, but not on one.

Are the carbs still spitting up? too bad you didn't get a chance to inspect the reeds for yourself when they came out.

You said "when the engine is running you can move the "timing arm" and it doesn't make it run any better."

Are you referring to the "timer base" (see pic below)? that is the spark advance -- RPMs should pick up when you move that forward.

I'm wondering about a sheared flywheel key or shifting magnets or something.

 

[BigB9000]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

Im guessing the timer base.

I had a 77 and it took me a long time to figure it out.
The timer base moves back and forth with throttle, as does its wiring.

when trying to hunt down my problem i tested the ohms/resistance on the timer bases plug. which checked out fine. until I retested one day with a full throttle, and it checked out bad. Turns out the wire had an internal break, I removed the base, repaired wire, reinstalled, and sold all my problems.

Only difference, I only had 2 mechanics give up on my engine.

 

[wilde1j]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

Maybe an OEM shop manual might be helpful, instead of guessing?

 

[kenmyfam]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

I have not heard compression mentioned yet ????
How is that middle cylinder ???

 

[Challenger84]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

I did a compression test before I even took the carbs off, and they are within spec (117, 125 + 127).

....

 

[kenmyfam]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

....

OOPS !!!:redface:

 

[Jet Wrench]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

I've got the same engine. If these "jokers" who call themselves "mechanics" gave that engine back to you with hardware missing, I would first inspect everything they laid a hand on! If the carbs are spewing fuel, the floats are definitely suspect. Did they install new floats? Probably not. Did they clean all of the internal passages of the and install new caps? Probably not. You need to check the low and high speed jets to make sure they didn't fold over the brass trying to get them out. If you don't have the right tool, you can really screw them up. They may have installed the jet's incorrectly too! Detailed visual inspection will uncover quite a bit. I'm off my soapbox!

Jet Wrench

 

[Nathan T]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

Thank you for all of the replies.

I mentioned in the original post that I have a manual for it.

I took the carbs off myself and set the floats. I couldn't find a spec for float drop, but the float height is set perfect now. But like I said in my first post, when I took the carbs off and took them apart they were extremely clean. Not a single speck of dirt in them anywhere. But the floats were WAY off. Instead of the floats being level with the base (where the bowls mount, that surface) they were all hanging way down inside of the carb. So the bowls were filling up with way more gas than they were supposed to before the needle seated. If it was even seating at all?

It was already pointed out but I did do a compression test before I did anything else. The bottom cylinder was the one that was the lowest.

The timer base is what I was referring to, yes. It is always all the way forward when it is running. You can't get it to do anything but idle. If you try to rev it up at all it just wants to stall. And then does.

I didn't do a cylinder drop test. I was going to do that today because I did work on it a little more today. But I forgot to do it. I will do that tomorrow.

I have the reeds that came out of the motor. But I have no idea what shape the ones that they put in are in. But it isn't popping or spitting out of the carbs.

It just won't rev up at all. And it won't do anything but surge.

I meant to post a video for you to check out today, but I forgot to take my camera with me when I went to work on it today. I will make sure that I post a video tomorrow. So you can see for yourself exactly what is going on.

I don't know if they installed new floats or not. But I am kind of guessing that they did, since they were so far out of adjustment. But I could definitely be wrong. I spent several hours on taking the carbs apart and setting the floats, and making sure all of the passages in them aren't plugged. I used carb cleaner and compressed air both. I am extremely confident that the carbs are now in perfect shape. Unless like you said, that they screwed the jets up. But from what I could tell I don't think they took them out. I don't know what all comes in a carb rebuild kit (I thought that new floats usually aren't included?) but I don't know how the floats could have been so far out of adjustment unless they put new ones in without setting them after installing them.?

Today what I did was tried syncing the roller on the carb linkage with the lower mark on the cam "thing". I followed the manual, made sure all of the carbs were fully closed, then moved the throttle lever until the roller just touched the cam and it was way off. But I couldn't get the mark to line up with the center of the roller just by moving the adjustment screw on the carb roller. The only way that I could get it to line up was to remove that arm from the cam and turn it 8 turns. After turning it that far I was able to get the roller to line up with the lower mark when it just started to touch the cam like the manual said. But I don't know if I was supposed to adjust it that way or not? It was the only way that I could get it to line up though so I tried it. It didn't run any better after doing that. I think it actually ran a little worse.

 

[jtexas]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

At this point we may need to pinpoint the year; it's a few minor differences along in there, like how many jets the carbs have, and fixed or adjustable idle jets.

you're on the right track, you'll get there eventually Here's some random observations I hope will help:

jetwrench is right about the jets, it's easy to mar 'em if your using a regular screwdriver on 'em. The jet removal tool is easily fabricated by using a dremel or belt sander or something on a screwdriver , it's shown in the first post on this thread: http://forums.iboats.com/showthread.php?t=244013

When I hear "surging", I usually think the engine is getting air from somewhere other than through the carb throat...you should have a mounting gasket for each carb, and one for the intake manifold (which they removed to replace the reeds). Some models have an additional adapter plate and gasket for the manifold.

That "cam arm" (throttle rod), it should measure 4 31/32" from the center of the hole on the bellcrank to the aft edge of the plastic yoke it's screwed into.

When there's a load on the motor, it'll stall out & die when you throttle up if the throttle valves are openning before the spark advance begins. But I assume you're running the motor on muffs (as opposed to a test tank or a lake)?

OEM carb kits come with floats, but sierra and others sell kits without floats, they cost way less and the floats last a long long time anyway.

The timer base will be fully forward when the hi-idle lever is full up, and also when the throttle/shift control gets about 3/4 the way to WOT.

 

[backyard mechanic]

Re: 70HP Johnson surging, won't rev up, 3 mechanics have given up on it, please help.

A few things struck me right off... Good job getting the compression test done. Next you say it's spewing fuel from the carbs and the link and sync were way off. Hmmm one out of three isn't too bad! Just because your buddy took it to a mechanic doesn't mean the guy was a mechanic. A patch on a shirt or a certificate on the wall does not make one a mechanic either.

Carbs redone with settings per factory spec is job one. The spew MAY come from float levels too high but typically that's reed failure. I'd look into that while the carbs are off. Later in your post you say they are not spewing. Which is which? Spewing or not? Reeds are an important part so don't pooh pooh the reed idea. They should cover the hole and be relatively tight to the reed block but easily moved with slight pressure. Are the reed stops all at the same height? If not they are not the reeds were not installed right.

If the three coils were replaced then it's likely the spark is getting to the plugs. Are they all the same/correct plugs and are they gapped equally and correctly?

Now a link and sync. There is more to set up than primary and secondary timing. Assure the throttle/trigger arm pick up point is correctly adjusted. Assure your carbs all reach WOT and that all carbs are in sync with the others at WOT and at idle (no throttle opening at all. Idle screws should all be set to 1 1/2 turns to start. Once it is running be sure the idle is set with no throttle opening at all. Any RPM changes should be made by trigger arm movement at this point (before primary pick up). Use the manual for specs on primary pick up timing, secondary timing is typically at WOT so you need to do that in a tank or on the river/lake etc.

Kinda hard to wrench this thing off the I net so be sure to to read, follow and fully understand all that the manual tells you to do. It cannot be overstated, settings done right will make the engine run right.