Troubleshooting problem on 79 Evinrude 100hp 100999S

Brandon12345

Cadet
Joined
Jun 12, 2011
Messages
29
First time poster as well as first time boat owner. Long story short, bought a bass boat with '79 Evinrude 100hp 100999S. I wasnt able to test it on the water, but ran it on the muffs and had the PO do a compression test for me. He said the carbs hadn't been cleaned for awhile, so I knew going in that I would probably have to do that. I have ordered the OEM carb kits for both carbs and they should be in this week. However, I wanted to see if anyone had any ideas if the issue I am running into might be strictly related to the carbs or something else. Here is a rundown of my activity and what is happening:

1. I can run it on the muffs just fine, no problems there

2. On the water, the engine starts when I launch it in the water and with the starter lever up, idles in the 1600-1800 range. once I drop the lever, the idle drops down to around 500-600 range. If i slowly put it into either forward or reverse, it dies. If I do it swiftly and forcefully, it will usually stay running but occasionally dies as well. After getting it running in forward, I try to run it at WOT but it will sputter and die. After doing this a couple of times, the engine will not turn over and start again for 1+hours(both times i took it off the lake within 45 minutes because it wouldnt start). i have inspected my fuel lines for any obvious leaks and I see none. I prime the prime bulb to start the engine, but even when it starts, the bulb doesn't ever get tight. I plan on changing the spark plugs because they look like they have a bit of corrosion on them, but I didnt think they would be the source of the problem I am having. (edit: i will also add that the current spark plugs are not the Champion QL or L77JC4's)

Does it sound like a carb rebuild "should" do the trick? From the research I have done on here, sounds like it is a carb/float problem to me but I am definitely not a mechanic.

Any other ideas or suggestions on what I can/should test? Obviously I am rebuilding the carbs regardless but I am hoping i dont have to replace the fuel pump or anything else.
 

Brandon12345

Cadet
Joined
Jun 12, 2011
Messages
29
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

Anyone have any suggestions or pointers on things I am right or wrong about in my description and diagnosis?
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

A couple of thoughts. The engine runs properly on the muffs because there is no back pressure in the exhaust. The engine idle is to slow, should be 700-750 IN the water IN gear. The primer bulb should pump up firm, but with the engine running it will be kind of soft. You didn't say anything about spark, did you check it, will it jump a 7/16" air gap and be bright blue? You mention the plugs have corrosion on them, could it be caused by water in the cylinders? The sputtering does sound like the carbs could use some attention. Still thinking about the starter thing, the pinion gear on the starter does not stay engaged in the flywheel with the engine running does it?
 

Brandon12345

Cadet
Joined
Jun 12, 2011
Messages
29
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

I haven't tested the spark, so I do need to do that. The corrosion on the old plugs was all where the plug wire connected to the plug and not where it is connected to the cylinder, not sure if that matters. The pinion gear, as far as I have noticed so far, doesnt stay engaged on the flywheel with the engine running.

Would the starting problem have anything to do with the carb/float problem, because it isnt getting either enough or too much fuel after the carbs have fouled during the engine running causing it to die and then not re-start?
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

You might try getting the idle set properly and see what happens.
 

Brandon12345

Cadet
Joined
Jun 12, 2011
Messages
29
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

Outboard 001.jpg

This is probably something i should know but on the image attached, which is the idle screw I should be adjusting? Thanks for the replies and suggestions
 

emoney

Commander
Joined
Jul 19, 2010
Messages
2,551
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

Have you started it yourself on the muffs or just the PO? You also mentioned that you had the PO do a compression test, what were the numbers?
 

JWH0420

Seaman Apprentice
Joined
Jun 6, 2011
Messages
49
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

blue is ur idle rpm adjust
 

JWH0420

Seaman Apprentice
Joined
Jun 6, 2011
Messages
49
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

green is not correct thats the stopper for max timing advance
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

I corrected my post.
 

JWH0420

Seaman Apprentice
Joined
Jun 6, 2011
Messages
49
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

where am i looking at #75??
 

Brandon12345

Cadet
Joined
Jun 12, 2011
Messages
29
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

Have you started it yourself on the muffs or just the PO? You also mentioned that you had the PO do a compression test, what were the numbers?
I have started it on the muffs myself. I don't remember the exact #'s, but all were in the 110-120 range.
As far as the low idle goes, I would turn the idle screw counter clockwise to speed up the idle correct? I am guessing a quarter or half turn at the most? Is that going to impact the ability for me to correct the starting issues or is that just going to increase the idle so it won't die once actually started and/or shifted into gear?

Edit: Should I wait to do any tweaks until the carbs are rebuilt or will I have to make adjustments regardless of the carbs being rebuilt?
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

Man, I can't do anything wright tonite, look at the orignal post.
 

JWH0420

Seaman Apprentice
Joined
Jun 6, 2011
Messages
49
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

i would wait untill carbs are done to adjust it but clockwise would increase rpm counter clockwise reduce rpm
 

JWH0420

Seaman Apprentice
Joined
Jun 6, 2011
Messages
49
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

#75 on BRP parts catalog for that motor shows as the blue screw follow the line it goes to middle of the arm
 

RZR2007

Petty Officer 2nd Class
Joined
Apr 6, 2011
Messages
137
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

I would also plan on changing the plug wires when you change the plugs, they'll be just as corroded as the end of the plugs...
 

JWH0420

Seaman Apprentice
Joined
Jun 6, 2011
Messages
49
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

the green circled screw would be # 15
 

Brandon12345

Cadet
Joined
Jun 12, 2011
Messages
29
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

I would also plan on changing the plug wires when you change the plugs, they'll be just as corroded as the end of the plugs...
This is definitely something I will do. I see that I can get kits to make my own here at iboats store, but any idea if I can buy these a a local auto parts store like O'Reilly's or advanced auto parts? Do I just need 7MM Copper core wire and then standard boots/terminals?
 

Brandon12345

Cadet
Joined
Jun 12, 2011
Messages
29
Re: Troubleshooting problem on 79 Evinrude 100hp 100999S

IMG00086-20110624-0631.jpg
A couple of thoughts. The engine runs properly on the muffs because there is no back pressure in the exhaust. The engine idle is to slow, should be 700-750 IN the water IN gear. The primer bulb should pump up firm, but with the engine running it will be kind of soft. You didn't say anything about spark, did you check it, will it jump a 7/16" air gap and be bright blue? You mention the plugs have corrosion on them, could it be caused by water in the cylinders? The sputtering does sound like the carbs could use some attention. Still thinking about the starter thing, the pinion gear on the starter does not stay engaged in the flywheel with the engine running does it?

I was able to rebuild the carbs with no problem and found out that one of the carbs the pin and needle of one of the floats was broken, so I am pretty sure swapping those out for new helped with the carb issue. However, I had it on the lake this morning and it wouldnt start. I am thinking it might be a starter issue because the pinion gear (wheel on the starter that engages with the flywheel?) is not "meshing" with the flywheel very well at all, or at least to my knowledge. The "teeth" of the starter pinion barely touch the flywheel and when I try to turn it over, it is barely able to spin the flywheel a quarter turn at most, and then drops back down. Is this a starter issue do you think or do I have cylinder issues? Here is an overhead picture of the starter "engaging" the flywheel. I should also add that after the last time out when I couldnt get it restarted and now after this time, there are a lot of metal shavings presumably from the starter grinding on the flywheel, and I assume this is not a good thing.

If anyone has advice, please let me know as I am a bit helpless now.
 
Top