1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

[jandb]

1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Greetings All,

I am boat newbie and purchased a small aluminum boat with motor to get started. I am having a bit of motor trouble right off the bat and hoping some of you can provide assistance with troubleshooting this issue.

The motor is a 1984 Mariner 8M 8hp, serial number 6G1S010817. I have uploaded a few pics of the motor so you can get a look at the beast.

The issue I am experiencing is the motor ?bogs down? when given throttle. What I mean is that when the motor is given gas, it sputters out and smokes? quite a bit, and from places other than the exhaust out of the lower unit. The motor never really gains any power. I also see a bit of oil coming from the lower unit exhaust.

The motor starts up on the first pull and seems to idle fine. And I really do not see any smoke when idling. I also believe it is cooling fine because water flows from the pilot hole when running.

When I first got the motor, there was water in the lower unit. I drained the oil and refilled with new. After running it in the water for a bit, I rechecked the lower unit oil. There is no water present.

I have done much reading on this site before posting in hopes to come across a solution. Here is what I have tried so far?

1. Replaced lower unit gear oil
2. Greased prop
3. Fresh fuel in a new tank; mixed 50:1
4. Replaced fuel filter
5. Took carb apart and cleaned; adjusted float to rest parallel to casing
6. Replaced spark plugs; BR7HS-10 (NGK) gapped at .035 in.
7. Checked plugs for spark; both plugs do spark

I am not sure where to go next. I hope someone has some thoughts. Thank you all for contributing to this great resource!

Brandon

 

[Mi duckdown]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

jandb. First thing I noticed IS. you have a long shaft motor on a 15 inch transom. I would check compression. The cheapest test to do. than Go from there and report back.

 

[Mi duckdown]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

jandb. First thing I noticed IS. IT looks like, you have a long shaft motor on a 15 inch transom. Picture may be deceiving. I would check compression. The cheapest test to do. than Go from there and report back.

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Thank you Mi duckdown for the quick reply! I have seen this test mentioned on here just not sure how to go about it. I will look into performing this test and get back with the results. Thanks again!

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Hello,

I have finished the compression test as requested. Both cylinders tested around 115 psi. It took 5 or 6 pulls to get there.

I have read 70 and above is ok. Is this true? Please let me know what you think of this information.

Also, Mi duckdown, thanks for pointing out the transom/long shaft issue. I was unaware this was a problem. I will be sure to fix this before taking the taking the boat for a cruise? if that ever happens. :facepalm:

Thank you very much!

 

[Mi duckdown]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

jandb those are very good numbers. are you running 50:1 gas oil mix? Sorry. I see that you are.

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Thank you again, Mi duckdown. Yes, that is the ratio I used and fresh fuel. Do you have any suggestions to what else may be an issue?

 

[Mi duckdown]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Have you ran this motor on the water yet? or just in a barrel or muffs, in the driveway.

 

[RebeccaBurg]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Hello Brandon. Had same prob with older Merc. Would most likely be one or both: weak spark, ignition system issue (leads to incomplete combustion & oily-wet residue) or carb inlet needle- if it's older and worn- not seating right & flooding engine (it'll bog & have excess fuel reside).

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

I put it in the water once for about half an hour after changing the lower unit oil. Just to see if water reappeared in the oil. It did not.

I just putted around for a bit. Gave it throttle a few times though with the same results. A lot of smoking and misfiring and could not pick up any speed.

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Thank you, RebeccaBurg! I will look into testing the ignition system and post back my results.

Also, I did take the carb apart and clean the parts thoroughly. Even though it looked like someone had already cleaned it recently. The needle did not look worn to me.

If the ignition system checks out OK, I will pull the carb apart again and post some pictures of the needle and other parts for all to look at. I will let someone else be the judge as I am not quite sure what I am looking for yet.

Thanks again!
Brandon

 

[RebeccaBurg]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Okay If you end up disassembling the carb again, check the seat where the inlet needle's conical nose fits in. Scratches or anything around that teeny hole will cause poor fuel metering too.

 

[Mi duckdown]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Also run apiece of 25 lb. mono fishing line thru every orifice on the carb to check for any obstructions. FUEL pump?

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Thanks to both of you! I will be away from the house today but will hopefully look into your suggestions tomorrow afternoon and report back.

Best,
Brandon

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Hello,

I had a chance to test the spark today using an inline spark tester. Managed to shock myself a few times but both plugs work great. So that is good news!

Since the ignition system seems to be in order, I went back to the carb. This time though I was able to find a service manual online for the motor and it had a great section on the carb. It showed me how to disassemble/reassemble, set the float properly, adjust the pilot needle, and look for wear and tear, etc.

This manual is very helpful! I just want to include a link to the site in case others may be looking for similar documentation for their motor. Here it is?

Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years!

Anyways, the needle and seat look good and I cleaned the carb again, including running fishing line through all orifices. But (and I believe this is big :joyous when putting the carb back together following the manual?s steps, I noticed something was missing. Have a look?



The pilot jet plug shown in this picture is missing!! It appears the person who cleaned the carb before me failed to replace it. I assume (hope!!) this is the problem. I am going to call around to a few boat shops tomorrow morning to see if I can find this plug and go from there.

Thank you both for your assistance so far! It is greatly appreciated. I am not sure I would have gotten this far on my own.

Brandon

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle

Replacing the pilot jet plug in the carb fixed my issue! The motor is running great now.

Thank you all for your assistance with troubleshooting my problem!!

Best,
Brandon

 

[Mi duckdown]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Brandon. Great. Glad you posted results. We all learn from your PROBLEM AND YOUR REPLY. I wish more PEOPLE WOULD DO THAT. Thanks AND SAFE BOATING

 

[Mi duckdown]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Brandon. where in the heck did you find that jet plug?

 

[jandb]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Mi duckdown and RebeccaBurg, many thanks to you both for the guidance and assistance. And as much as I learned from everybody on here during this process, glad I could contribute a little back!

Regarding the plug, it turns out this particular Mariner was made by Yamaha. I was lucky enough to find a replacement part at the local Yamaha Marine shop.

But if that did not pan out, this site had the part available as well...

www.boats dot net (could not post actual link, show us as www.********** )

Safe boating to you as well, Mi duckdown!

Cheers!
Brandon

 

[RebeccaBurg]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

Re: 1984 Mariner 8M 8hp 2 stroke "bogs down" and smokes when given throttle [SOLVED]

AWESOME! Have a great boating summer...hooray for the little plug!