No top end, low rpm's

[fishnsled]

Hello,

First time poster with a motor problem.

Last weekend at the end of the day on the run back to the launch my motor lost power, bogged down, and then picked up again. I thought it might be a dirty fuel filter so I changed it. Out on the lake yesterday I had no top end. Motor sounded OK, started OK, got up on plane but a bit sluggish, but when WOT I could only get 4000-4200 RPM and 31-32 mph. Usually I'm about 5300 and 41-42 mph. Maybe a bad fuel filter? Since there was a slight problem last weekend I'm thinking not but who knows.

So the question is what might be causing this, is it OK to run like this for couple more trips? (This late in the season, I would imagine that I won't get the boat back anytime soon with all the winterizing going on at the mechanics) Is it something I can fix myself? The motor is a 2002 Mercury 2 stroke 115hp. Going out to have a look to see if a pinched the fuel line or if the filter is leaking fuel,(if leaking fuel might be sucking air?) didn't notice that happening yesterday. Maybe a fuel pump problem? Your input is greatly appreciated and hopefully will be able to add my input here from time to time. Thanks!

 

[bullet 101]

Re: No top end, low rpm's

Try new spark plugs,sounds as if you lost fire on a cylinder.

 

[HORACIO]

Re: No top end, low rpm's

Hi, yerterday i fix a problem like that. I had almost normal running condition at cruising but low top speed and rpm going up and down. After check fuel lines between tank and engine, I took out the fuel tank and found suction pipe cracked at top so engine was sucking air. I have find out that using a small piece of transparent hose suited in line with the standard hose. This outboard motor is Mariner V-175 carb.
Maybe this help. Best regards.

 

[fishnsled]

Re: No top end, low rpm's

Thanks for the replies. I'll pull the plugs and have a look. New set this spring but you never know when these things will go. I'll also go over the fuel lines again. Thanks again!

 

[fishnsled]

Re: No top end, low rpm's

Checked the fuel lines again and were still firm from the weekend, don't think it's a line problem but maybe while running. Pulled the plugs and one plug was wet and another was questionable, these were the bottom 2 plugs. The top 2 were fine. Got a compression tester coming on loan and will do the test later in the week. I've put in last years plugs for now but hope to grab a new set later in the week. If the compression is good and still having problems, I'm guessing a coil would be the next thing to check? Can they be tested or do you just replace them? If compression is bad then I guess my season just got cut short. PLEASE let it just be a bad set of plugs....

 

[fishnsled]

Re: No top end, low rpm's

Update - Compression test done and everything checked OK. Fired up the motor (in the driveway with the garden hose) with the old plugs I put in and seems to be running better. Water test on the weekend. I'll be replacing the plugs with new plugs on the weekend. If all runs well then that will be it for this year, hopefully. For next year I will replace the fuel lines just as a precaution. Seems like that might be the next problem so might as well avoid it be for it happens. Thanks for the help and great advice. Will update after the weekend.

 

[starcraft1982]

Re: No top end, low rpm's

Ok,first,NORMALLY spark plugs arent bad.Something MAKES them not function properly.Did you check spark to bottom 2 plugs?Get a gap tester at autozone or similar and check to verify good bright blue spark jumping a 7/16"gap.Then I would read up by using search function on here for testing your electronics.Could be dropping a cylinder or two at higher rpms.The other possible culprit is fuel delivery.Is this a carb motor or efi?If carb,pull and clean rebuild them.Rebuild fuel pump.You need to be testing things,not running it.You may have ok compression now,but run it lean and you wont have very soon.Testing is the key to fixing and doing it w/least money possible invested.good luck

 

[PrinceValium]

Re: No top end, low rpm's

Ok,first,NORMALLY spark plugs arent bad.Something MAKES them not function properly.Did you check spark to bottom 2 plugs?Get a gap tester at autozone or similar and check to verify good bright blue spark jumping a 7/16"gap.Then I would read up by using search function on here for testing your electronics.Could be dropping a cylinder or two at higher rpms.The other possible culprit is fuel delivery.Is this a carb motor or efi?If carb,pull and clean rebuild them.Rebuild fuel pump.You need to be testing things,not running it.You may have ok compression now,but run it lean and you wont have very soon.Testing is the key to fixing and doing it w/least money possible invested.good luck

Ok this might be a silly question...but I see everyone throwing out the 7/16" gap for plugs. Is this a standard for all motors? It would seem to me that they would all be different.

 

[SeaKaye12]

Re: No top end, low rpm's

Testing spark in the open air...7/16" is what you should use....If it can jump 7/16 in the open air that would indicate that it is strong enough to jump the much smaller gap under compression....

Chuck

 

[fishnsled]

Re: No top end, low rpm's

Ok,first,NORMALLY spark plugs arent bad.Something MAKES them not function properly.Did you check spark to bottom 2 plugs?Get a gap tester at autozone or similar and check to verify good bright blue spark jumping a 7/16"gap.Then I would read up by using search function on here for testing your electronics.Could be dropping a cylinder or two at higher rpms.The other possible culprit is fuel delivery.Is this a carb motor or efi?If carb,pull and clean rebuild them.Rebuild fuel pump.You need to be testing things,not running it.You may have ok compression now,but run it lean and you wont have very soon.Testing is the key to fixing and doing it w/least money possible invested.good luck

Some great advice starcraft1982, thank you. I'll be sure to pick up those testers, pretty inexpensive.

I did take the boat out on the weekend (Didn't see your post till now sc1982)with my mechanic (automotive) buddy. Seemed to run fine, no missing, top end was back, all seemed good. Fished for a couple of hours (with the electric trolling motor), on the way back to the launch it started acting up again in a different way, motor would just shut off. My buddy thinks it may be the stator or fuel pump, I don't have a clue. So I dropped it off at the Marina to let my outboard guy take a look at it. Will up date when the results are in. Thanks again for the input everyone.

 

[fishnsled]

Re: No top end, low rpm's

Well the verdict is in and it's not good. Apparently the gasket has let go and water was getting into the lower cylinder. Been told the engine needs a rebuild.

 

[jeffersondodson561]

Re: No top end, low rpm's

Ask to see your parts, get them to show you the gasket and the head, if water was getting in the head of that cylinder should be a lot cleaner than all the others...unless you trust your shop.

 

[Faztbullet]

Re: No top end, low rpm's

That engine does not have a head.. If the exhaust plate or gasket is leaking just replace them unless piston is scuffed do to water ingestion. You posted on 10/20 compression was fine so if it is still inline with others I would just do plate and gasket...

 

[fishnsled]

Re: No top end, low rpm's

Thanks for the suggestions Faztbullet and jeffersondodson561. Going to have the head pulled next week and have a look at it with my mechanic buddy. He also suggested I just replace the gasket and plate if all looks good. We'll see what happens.

Thanks again.

 

[fishnsled]

Re: No top end, low rpm's

Well it's been a long winter and spring. The motor was rebuilt, crank, piston, rod, bearings, all do to a leaking gasket. They showed me my parts and what a mess. (a good buddy of mine's brother-in-law did the work - marine tech) Kept the piston as a "souvenir" I've had the boat back for a 3 weeks now but have yet to fire her up. Lost my Dad at the time the boat came back and been just preoccupied with the funeral and stuff. Hoping to get it in the water this weekend and see out it runs. I'll report back when I get the boat wet.