Stubborn To Start 1979 9.8

[Mc Tool]

Sounds like maybe the timing is out now, are the plug leads on correct plugs ( assuming not waisted spark ....how many ht coils does it have ), or cut flywheel key.
I feel for you dude ,maybe you have more than one fault to deal with .

 

[keithb7]

Tried swapping the spark plug coil wire positions. No improvement. Also coils (2 qty) tested in spec. Flywheel keyway is in place.

As mentioned in my post, the cut in ‘74 flywheel magnet seen here. Wonder if this sets the trigger coil to collapse?

 

[keithb7]

Reviewing my outboard technical textbooks there are 8 different Mercury ignition systems that they used. You pretty-well need to be an electrical engineer to decipher them all. Lol. Seems as the magnets pass the trigger they do their own separate induction magic and send its own separate voltage the CDI, signalling the capacitors to discharge. With so many different types of ignition systems listed, and the ‘74 trigger installed I may as well try installing the ‘74 flywheel as well.

Another note, I did swap the 2 trigger wires ( they as the same color) to see if maybe swapping polarity would help. No improvement.

 

[keithb7]

The Ignition system looks ample to me. I need to comfirm it’s occuring at the right time. These engines are pretty basic, fool proof. I am a bigger fool than average. Lol.
View attachment IMG_2138.mov

 

[Nordin]

Does it jump spark 3/8 in or more in atmosphere?
Check the flywheel key if it is shared.
My experience from ealier (1973-1977) 7,5, 9,8 and 20Hp is that the ignition coils dry out in the insulation in the coil.
Under load/compression and when the coil has to jump a large distance the spark jump internally because of bad insulation.
You have spark at the plugs in atmosphere but when plugs in the spark will not jump at the plug.

 

[keithb7]

@Nordin I think you are on to something there. Under compression the spark may not be firing. What you say makes sense and is possible. Everything else I’ve tried isn’t improving things nor computing in my head. I don’t have a spark gap tester. I have ideas to try though. I have 2 spare coils and an inductive voltage tester. See if I can get a volts reading on the coil wires with these coils, and compare to my spare coils that I will install.

 

[jimmbo]

A spark tester is quite easy to make, with a bit of wire, a dry board, a couple of clips, and a couple of nails

 

[cyclops222]

Does it have REED VALVES ? Did the Ultrasonic Cleaner knock some small carb part loose ? Out of sight and loose in a carb passage ?
I have forgot a tiny round gasket around a main jet. Ran terrible. 4 th careful rebuild I found the new gasket on the floor.

 

[keithb7]

Well here it is, the spark easily jumping a ¾” gap.

I’m laughing at this point. It’s becoming comical. I really thought we were onto something with the spark that may not jump the gap under compression conditions inside the cylinders.

I have fuel in the combustion chamber
I have 80 psi in both cylinders
I have a strong spark
I ran it on the water last week for over 2 hrs

Today I found 2 more 9.8 engines for cheap. I’m looking at them tomorrow. If they have over 90 psi they’re coming home. I’m going to double down and get something running, at some point. Law of averages. Lol.

Determined, and stubborn I will sort this out.

 

[Mc Tool]

Are those magnets tight inside the flywheel ? Cant move ?

 

[cyclops222]

Nothing beats more than 3 engines not running right. I will raise you by 2 more.
Law of averages does not work with very used and abused engines.

 

[keithb7]

Ya but I’m having fun and I will beat this. Lol. The two I just picked up both measure 105 psi. Both offer lots of spare parts. Both have perfect 2 blade props. Worth the price just for the props. I also have a 7.5 that can use all the parts as well. Its a win!

 

[cyclops222]

I did that with a 40 or 50 year old riding mower. One spring the paint layers just allowed the parts to fall off of the blade deck. No machine has ever come close to it.

 

[keithb7]

Coming home with 2 more 9.8 Mercs must have been intimidating for this problem child. Running great this afternoon.

View attachment IMG_2153.mov

What did I do to solve this? I’m not 100% sure.
I did swap over the flywheel from the ‘74. The two appear identical. I’m not convinced that solved it. I also unbolted the 3 coil mounting screws. I made sure the grounding wires hidden in behind each coil was making good contact. I re-installed the coils, then fired it up first pull.

It’s smooth and running great. Idling nicely and starting on the first pull. I wish I had a more concrete answer. Maybe I had poor ground contact on the backside of the coil?

All’s well that ends well. Bounus, we have 2 more 9.8s to fix up. They already fired up!

Thanks for all you tips and ideas.

 

[Mc Tool]

Sometimes the magnets get loose under the flywheel and rotate in relation to the flywheel thus throwing the timing out .
Im thinking that the gap in the magnets may be supposed to line up with the key way, not sure , but anyhow ,Im pleased its going now .

 

[cyclops222]

My magnets have captive pockets to hold them place.

 

[racerone]

Looked at one of many flywheels.----Gap in magnets does not line up with the keyway.

 

[jimmbo]

What Yrs are the latest 9.8s? Pics Please

 

[keithb7]

I’m all-in now. L-R: 1991 8, 1976 9.8, 1977 9.8, 1979 9.8, 1981 7.5

 

[jimmbo]

Now go hunting for a 68 or a 69, those Years are the Best Looking