'77 6HP Evinrude, Where to start to determine whats wrong?

[mp_2008]

Motor: 1977 6HP Evinrude
Model #: 6705M

General Description and Problem: Starts first pull almost every time and runs good for the most part at first with the occasional stall when in idle or putting it into gear. After about 5 minutes of trolling or a few at full speed it starts having problems. If I'm at full speed, it will start to bog down gradually as if it was "losing power" and then it will what seems to be a backfire and then go into a nice idle after letting off the throttle. If I'm trolling in gear at a slow speed, it will do pretty much the same thing when at full throttle. It will sound great and then start to bog down and backfire and then sound great. It will usually stay running throughout this process. It looks as though the cooling system is working well, water is coming from where it should be. I just don't know where to start.

Question: Does anyone have a clue on what it might be or not be? Where is a good place to start to troubleshoot my problem?

Thanks, Mike

 

[fireman57]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

I would start with a good carb cleaning. Make sure you run a thin wire like off a bread wrapper with the plastic removed thru the jets. Spray through them well with carb cleaner. If it still persists make sure that you have good spark. Must jump 7/16" with a bright blue snap. Just out of curiousity when was the last time you bought new plugs and gapped them?

 

[mp_2008]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

I would start with a good carb cleaning. Make sure you run a thin wire like off a bread wrapper with the plastic removed thru the jets. Spray through them well with carb cleaner. If it still persists make sure that you have good spark. Must jump 7/16" with a bright blue snap. Just out of curiousity when was the last time you bought new plugs and gapped them?

Never. I just got this motor a week ago and it is my first boat motor so my knowledge is limited, though I am willing to do the research and work to get it fixed. I did take the spark plugs off and clean them, it looked as though they were sparking well and weren't fouling out. I'll probably take your advice and buy new plugs and gap them, then do a good carb cleaning. Thanks for the advice.

Any other advice or thoughts from anyone?

Mike

 

[samo_ott]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

Hmmm... Odd... Maybe fuel supply? As in the pump. It doesn't sound like a common problem. Are you sure it's not overheating? Can you touch the head after it's been running? How hot is it?

 

[mp_2008]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

Hmmm... Odd... Maybe fuel supply? As in the pump. It doesn't sound like a common problem. Are you sure it's not overheating? Can you touch the head after it's been running? How hot is it?

No, I'm not sure if it's overheating or not, the fact that it takes a bit to show problems makes you think it would have something to do with that but it shows a steady stream of water out of the end of the upper cooling hose so I didn't really expect overheating. There were no obvious signs such as smoke that indicated overheating but I'll go warm it up in the morning and feel how hot it is. Thanks

Mike

 

[Urbina]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

hey what about checking your spark with a timing gun ?
some times coils fail under pressure and when hot or warm.

 

[Urbina]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

also get your self a repair book they really help.

 

[mp_2008]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

hey what about checking your spark with a timing gun ?
some times coils fail under pressure and when hot or warm.

Unfortunately I don't have a timing gun. But it's something else I'll look into, thanks. I just picked up a compression tester so I will also be checking the compression of the cylinders tomorrow.

Mike

 

[mp_2008]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

also get your self a repair book they really help.

Ya, I have looked into it recently but I'm not sure how severe the problem is. It's probably inevitable either way.

Mike

 

[Urbina]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

Unfortunately I don't have a timing gun. But it's something else I'll look into, thanks. I just picked up a compression tester so I will also be checking the compression of the cylinders tomorrow.

Mike

Ok lets think about this.
If you had bad compression the engine would not stay on.
try running some sea foam in your gas let it sit in the motor a night our two.
Then take it to the lake and see if it improve if it does you will probably just need a can carb rebuild.

 

[fireman57]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

Harbor Freight has a timing light for 14.00 if there is one near you. Start with cleaning the carb. It's an easy task and is probably your entire problem. Don't jump from one thing to another, all it does is confuse the issue. Carbs are easy and I bet you have no trouble at all doing it.

 

[mp_2008]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

Ok lets think about this.
If you had bad compression the engine would not stay on.
try running some sea foam in your gas let it sit in the motor a night our two.
Then take it to the lake and see if it improve if it does you will probably just need a can carb rebuild.

Good point, but I checked it anyways, needed the compression tester for the snowmobile as well. Both cylinders on the motor read exactly 75 psi after 3 pulls so ya, no problem there.

 

[mp_2008]

Re: '77 6HP Evinrude, Where to start to determine whats wrong?

Harbor Freight has a timing light for 14.00 if there is one near you. Start with cleaning the carb. It's an easy task and is probably your entire problem. Don't jump from one thing to another, all it does is confuse the issue. Carbs are easy and I bet you have no trouble at all doing it.

Thanks for the info and advice. I'll clean the carb. first and see if that's it. Then move on after that.

Mike