1974 Johnson model 70ESL75E help needed

[archis]

Hi,

We just bought a 1974 Starcraft Supersport 16 with a 70 hp Johnson. We are trying to get her ready for a sea trial but are having some issues with the motor.

Before we bought the boat we did a compression test on all three cylinders and they were the same, I can't remember the number. The motor started and appeared to run good when we made the purchase. I have been since doing some research and have heard that the motor can sound like its running well but be missing a cylinder or two.

We are trying to figure out how to determine if all three cylinders are firing. So far we have determined that

1) All three have spark
2) The motor will run if the both of the top two plug wires are off, but will not run if the the bottom plug wire is off.
3) The uppermost coil has been replaced
4) The two lower coils are cracked and we have seen arcs between one of these coils and its mounting bracket.

We are going to replace the two lower coils and the plugs. Can anyone tell me how to determine if she is firing on all three in the yard and if after we replace the coils/plugs she in still not firing on all three, what we should look for next?

Thanks,
Jim

 

[Bob_VT]

Re: 1974 Johnson model 70ESL75E help needed

Welcome to iboats.

Yes just about any outboard will idle with a cylinder or two not connected.......

Use an old school timing light to check the spark.

If you have verified the spark that eliminates that......now how about fuel? Are you sure those cylinders are getting fuel?

 

[archis]

Re: 1974 Johnson model 70ESL75E help needed

Whats the best way to verify fuel to those two cylinders?

I'm still not clear on the best way to determine how many cylinders are firing, is my method of pulling a wire and listening for a change valid?

Thanks for your help.

 

[Bob427]

Re: 1974 Johnson model 70ESL75E help needed

put some gas oil mixture in a spray bottle with it running and the carb silencer off spray in each carb if rpm goes up problem with that carb if rpms go down carb should be ok at least on the low speed side

i have the same motor on my starcraft and its great as soon as you work out the bugs


Bob

 

[mrcj001]

Re: 1974 Johnson model 70ESL75E help needed

It sounds like the engine needs some attention:

You can get a spark tester at a auto part store for around 10 bucks.

If the engine has good compression all all three cylinders:

Check the quality of spark. With the tester, you should have a good blue steady spark that can jump at least 7/16". Check each cylinder.

I would replace the ignition coils if they are cracked. Thus, you said they were arcing. The engine wont run right with arcing ignition coils.

I would also replace the power pack. It`s old, unless is been replaced recently,chances are it will fail the first time out when the engine gets hot.

Chances are , the carbs need attention also.

It best to get a OMC Service Manual for your engine. It has in detail on how to repair and troubleshoot your engine.

You can get one here:

http://www.outboardbooks.com/

 

[archis]

Re: 1974 Johnson model 70ESL75E help needed

Thanks for everyone's help. Great ideas on helping us get her running right!

 

[archis]

Re: 1974 Johnson model 70ESL75E help needed

We are still having trouble with this motor.

The last time we had it in the water it would only go about 6 knts wide open and had to be moved from neutral to wide open to avoid a stall.
We have since replaced the powerpack. We also found that the plug wires were not property installed on our last trip to the water..

We have since properly installed the plugs wire and replaced the powerpack.
Yesterday in the tank (55 gallon drum on its site) it still stalled when we went from neutral to gear. If I floored, it seemed like it sounded stronger than when we were in the water but it was hard to tell since it blew all of the water out of the tank in about 2 seconds.

We have good spark 1/2 blue spark on all cylinders, new coils and a new powerpack. The compression was great the last time we checked.

Any thoughts and test tricks to help us get her running right would be appreciated.

 

[ezeke]

Re: 1974 Johnson model 70ESL75E help needed

Follow the tune-up steps in the first section of your factory service manual; this will properly synchronize the carburetors.

Make sure that the idle circuits in the carburetors are clear and check carefully for any air leaks in the fuel system.

If the automatic choke system is still connected, you should disable it.

 

[archis]

Re: 1974 Johnson model 70ESL75E help needed

What is carburetor synchronization? Can someone clarify the spray bottle test? What should happen if we spray fuel in each carbs throat and the carb is OK?

Thanks

 

[mrcj001]

Re: 1974 Johnson model 70ESL75E help needed

Check the carburators and timing synchronizaton. If it out of adjustment it will fall flat on its face when you hit the throttle..

 

[Joe Reeves]

Re: 1974 Johnson model 70ESL75E help needed

Coils arcing to ground = no spark to cylinder = replace coil.

Carburetor synchronization means...... All throttle butterflies start to open at the same time and also close at the same time (linkages between carbs), coupled with all of the butterflies just starting to open at a specified time in relation to the timing (scribe mark on cam just arriving at throttle cam roller dead center).

If you have proper compression..... what are the psi readings? Just stating that the compression is great doesn't tell us anything.

If compression is as it shiould be, and you have spark that will jump a 7/16" gap with a strong blue lightning like flame... a real SNAP, and that cylinder isn't firing, then the only missing element is fuel..... clean and rebuild the carburetor(s) paying particular attention to the brass high speed jet that is located in the center bottom portion of the float chamber (it is no doubt clogged).

S/Plugs should be Champion QL77JC4 plugs gapped at .040 .

Your first entry on this topic states that this 3 cyl engine will run if plug wires #1 & #2 are both removed at the same time? This would have your engine running on the bottom cylinder on only. If so, and again I state... if you have compression and spark on all cylinders, the problem is fouled carburetors.

Let us know what you do to the engine between posts so that we do not suggest something that you've already done.

 

[archis]

Re: 1974 Johnson model 70ESL75E help needed

Joe,

Thanks for the advice. I thought I did a pretty good job stating the work we did several posts back but I'll restate it again. New coils, powerpack, plugs and plug wires. Spark test is nice and blue at 1/2 inch. Compression as I recall was around 105, all were the same.

I think our plugs may be a 30, we'll get that fixed. We'll dig into the carbs.

Thanks Again,
Jim

 

[soundchaser]

Re: 1974 Johnson model 70ESL75E help needed

Make sure all three cylinders have good solid 1/2" spark on one of those little stupid testers. Sometimes you think you have spark because you see some. But in reality it's actually intermittent. Look close to see if it sparks properly every time. And if not switch coil feeds around on the cdi to make sure the coil is firing on one of the good terminals of the cdi. And then switch the sensors around on the cdi to make sure the sensors are working. Of course do this with the plugs out so it doesn't start the motor while doing so. You should be able to determine what the actual problem is that way. It sounds like your cdi is having problems. But this way you can check your sensors too.