Chrysler 75hp, need direction.

[Tapphouse]

Hello everyone, long story short I had my boat out the other day for first rip in a long time. Need advice on where to start……low idle it would move along ok, from approximately 20%-90% it would “struggle”, not sure how to properly word it. More like it would load up but not go or take off, At 90%-95% throttle it would surge “go, stop, go, stop”, like it was really trying to take off. Then at WOT it would take off and pull like a bat outta hell and plane off in 2 seconds. Runs great a WOT. all the reading I can find is opposite to my issue, most die off at WOT. I’m thinking it’s a spark thing? As I’ve replaced all fuel lines, and cleaned carbs, etc. does anyone have any info/advice to what this could be? Or what to check? Appreciate any direction. Thank you! (1978 Chrysler 75hp outboard 3cyl)

 

[topgun3690]

You say it was the first trip in a long time.....how old is the gas? I see you have a portable tank in your pic. Would be easy to clean that out if it had water or stale fuel in it......
Wouldn't hurt to do compression and spark tests first.....make sure there are no problems here before doing anything else.....easy to do and no money spent yet.....

 

[Tapphouse]

You say it was the first trip in a long time.....how old is the gas? I see you have a portable tank in your pic. Would be easy to clean that out if it had water or stale fuel in it......
Wouldn't hurt to do compression and spark tests first.....make sure there are no problems here before doing anything else.....easy to do and no money spent yet.....

The old tank has been cleaned, fresh fuel, fresh fuel line and primer. It starts up perfect every time. New plugs and wires, compression test done last fall but I forget the actual numbers.
The way it acts under load makes me think it’s a spark issue and not a fuel issue. But what baffles me is how good it runs under full throttle. Wouldn’t it run terrible at high throttle if there was a fuel or spark issue at low/ mid throttle?

 

[Nordin]

Do as topgun3690 says.
Check compression, spark at all three cylinders with a spark tester.
The spark should jump 3/8 in or more in atmosphere.
Clean the carbs and set the float level if necessary.
Check and I would suggest you to change the fuel pump diaphragm.
They are cheap and they will go stiff and after some years, especially when sitting for years and not been in use.

 

[Tapphouse]

Ok…… thanks, I’ll check those out. also I’m going to go over the setup again. Frank A has a couple videos online, very useful info.

 

[topgun3690]

While you're in there, wouldn't hurt to check the recirculation system.....Is a dog bone shaped cover to the right of the fuel pump.....it has 3 reeds (one for each cylinder) with little screens that can get plugged up. It's job is to take excess/unburned fuel and route it up to the intake where it is run through again......a plugged up recirc system can cause issues at idle and lower rpms. Make sure the hose that goes from dog bone to intake is not plugged up too. Might need to get new gaskets if you remove the cover......not many dollars spent checking this....pretty simple but can cause problems.....

 

[Tapphouse]

While you're in there, wouldn't hurt to check the recirculation system.....Is a dog bone shaped cover to the right of the fuel pump.....it has 3 reeds (one for each cylinder) with little screens that can get plugged up. It's job is to take excess/unburned fuel and route it up to the intake where it is run through again......a plugged up recirc system can cause issues at idle and lower rpms. Make sure the hose that goes from dog bone to intake is not plugged up too. Might need to get new gaskets if you remove the cover......not many dollars spent checking this....pretty simple but can cause problems.....View attachment 389372

Life saver, I’ll give it a look. Thanks!

 

[Tapphouse]

Alright, so I’m in the midst of starting at the beginning. I checked the timing, seems right. I pulled the plugs and grounded them, key on, and at TDC the top plug sparks. When I turn the flywheel slowly I can hear a few pops inside distributor as it turns. Only the top plug will fire at TDC.
So I took of the black/white wire and touched it to ground. Top plug fires. As I turn the flywheel by hand and scratch the black/white wire, I can make all 3 plugs spark at different positions of the fly wheel.
So……. If I’m doing this right….what do I check up inside the distributor now? I believe it has an optical something something.
As always appreciate the help. Thank you!

 

[Nordin]

You says only the top plug spark at TDC and that is right if you mean TDC is when top plug is at TDC.
Each plug should spark when each piston is at it´s TDC.
Sparking/poping inside the distributor is normal.
There will be a little spark inside it when the rotor is pointing at one HT wire post/terminal as there is a small gap between the rotor and the post.
I would suggest you to remove the dist. cap and take a look inside the dist.
Clean it up and check the posts and the center carbon tap.
There might be some carbon dust and dirt in there.

 

[Tapphouse]

You says only the top plug spark at TDC and that is right if you mean TDC is when top plug is at TDC.
Each plug should spark when each piston is at it´s TDC.
Sparking/poping inside the distributor is normal.
There will be a little spark inside it when the rotor is pointing at one HT wire post/terminal as there is a small gap between the rotor and the post.
I would suggest you to remove the dist. cap and take a look inside the dist.
Clean it up and check the posts and the center carbon tap.
There might be some carbon dust and dirt in there.

Yes only the top plug fires at top dead center. The other two plugs DO NOT fire when turning flywheel by hand. I can only get all three plugs to fire if I pull the black/white wire and ground it as I turn flywheel by hand.
The popping inside distributor is normal, but it’s not making its way to the plugs. It only makes its way to the plugs if that black/white wire is off and grounded.
So is this a ground issue? An optical preamp issue? Or something I’m missing? Thanks.

 

[Nordin]

Open up the distributor and check.
As you have a 1978 year engine it suppose to have the electronic dist with a preamp instead of points.
The preamp is a photo electric diod and there is a disc with windows that trigger the preamp to give signal to the CD box to discharge the capacitors in the box.

 

[Tapphouse]

Open up the distributor and check.
As you have a 1978 year engine it suppose to have the electronic dist with a preamp instead of points.
The preamp is a photo electric diod and there is a disc with windows that trigger the preamp to give signal to the CD box to discharge the capacitors in the box.

Yes that info is correct. The preamp is red in colour. I’ve read that I can’t test the unit and it’s a replace to fix it. Before I buy one I would like to rule out any other possibilities.
What has me stumped, because I don’t know, is the spark not making it to all three plugs…..UNLESS I ground out the black/white wire.
I’ll take a Q-tip and clean the lil optic, but what else can I check in there?
THANKS!!

Edit***
I cleaned the optical but didn’t seem to be anything in it.
I also turned the flywheel by hand again and as before the top plug fires no problem. Here’s where I’m lost…. The #2 and #3 plug will fire IF I go past its position and reverse the flywheel. Fires every time. I marked the 1,2,3 positions in flywheel so I know where the plugs fire.
Why doesn’t it fire when turning the flywheel in the proper direction (counter clockwise looking from above)?

 

[topgun3690]

Why doesn’t it fire when turning the flywheel in the proper direction (counter clockwise looking from above)?

You have it backwards.....it turns CW when looking down from above.
There is a static test you can do for the preamp, but I don't think it has anything to do with your issue......

 

[Tapphouse]

You have it backwards.....it turns CW when looking down from above.
There is a static test you can do for the preamp, but I don't think it has anything to do with your issue......

For real?? It spins clockwise? I was going off how the starter cog goes up to spin the flywheel.
ok so distributor is good, CDI box is good, coil is good, I need to look at the stickers on flywheel to confirm timing is good….
Geeeez been along day, I think I’m starting to get lost in it all.
Appreciate the direction!

 

[Nordin]

I know the preamp is pretty expensive, about 170 dollars.
There is one other way to check the preamp BUT it is not 100% true that the preamp is good if it checks out good.
Use a credit card or similar to cover and uncover the optic eye in the preamp.
The plugs should spark each time you cover/uncover it.
But as I said not 100% true it is okey.
I have had one 75Hp engine that the preamp checked out good with the credit card test but when I tried to start it up the preamp gave signal intermittent.
I changed the preamp and it ran as it should.
BTW: If the preamp is red it is the OEM preamp (maybe from factory when build or replaced one time). The aftermarket from CDI Electronic is black.
Maybe it has worked for 45 years!!!!! Time to replace.

 

[topgun3690]

I have the 85HP version of your engine, they are basically the same except for output. Had a problem develop where running with engine warmed up and under load, would shut off.....like you turned the key off. Would restart like nothing was wrong....then at high rpms would do it again, over and over. I did the static test per the manual, it tested good. There was a paragraph about a condition where the preamp could break down when warmed up or under load.....and the static test would not disclose this condition. So the only way to find out for sure was to replace with a new one and try it. Bought a new one from Franz Marine.....fixed my problem.
You said your engine ran great at WOT so I didn't think it would be a preamp problem......but Nordin may have proven me wrong, as his was acting up when starting his engine. If you want to see the factory manual pages for the preamp testing I could email them to you......it is copyrighted material so can't post it on this forum. Send a PM if interested.....or get a manual like this one on ebay, is exactly like mine.....item#134710531445. Less than $50 and good to have.....

 

[Tapphouse]

Ok, so after some rest and cleared my head, grounded out the plugs and turned the motor over. YUP IT TURNS CLOCKWISE (thanks topgun). All 3 plugs are sparking. I’m assuming that side of things is ok for now.

Looking into the plug hole at the pistons, I see the top piston is dry/brown and looks like maybe some of the half moon is missing? Like brittle and fell off or has melted abit by previous owner? Not sure, Hard to see in tiny hole. The middle and bottom pistons are black and damp and look to be in good shape.

**Compression test** top=135, middle=140, bottom140. That’s with brand new guage.

What causes dry/ brown piston?
All plugs came out damp looking the same.
Again, I really appreciate the chats.

 

[Nordin]

Clean all carbs.
As there are three carbs, one feed each cylinder.
If one is clogged, that cylinder will go lean and you will damage the piston.
Put a clear cheap inline filer between the fuel pump and the carbs.
It will help you a lot, most for troubleshooting but it will filter the fuel too.

 

[Tapphouse]

Clean all carbs.
As there are three carbs, one feed each cylinder.
If one is clogged, that cylinder will go lean and you will damage the piston.
Put a clear cheap inline filer between the fuel pump and he carbs.
It will help you a lot, most for troubleshooting but it will filter the fuel too.

I went thru the carbs a year or so ago, as it’s been in my garage being slowly worked on. I’ll go thru them all again completely and see if anything comes up.
So you think top carb was/is causing lean conditions? ……..that sucks.
Thanks Nordin, I’ll dive into that and see where it takes me.

 

[Nordin]

As the compression are good and pretty equal at all three it seams okey.
But to be sure no cylinder are running lean just look at the carbs and clean them.
Are you sure the top cylinder is running lean??
Did you look into the cylinder holes with a camera or just with a flash light?
It is hard to look and see how the pistons and cylinders looks like with just a flash light.