12.5' with 9.8 running slow!

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Thanks fbpooler! The tach has different setup options being it only connects to one spark plug wire. I wasn't sure which to set it at but I assumed it would idle around 700-800 so I set it so it would read that. I was surprised to see it only increase to 2300 but after plugging that into a prop calculator the theoretical speed was 6.1 mph with a 7' pitch 2:1 and 20% slip. So that makes sense. Ill have to see where I can take it as the guys who changed the plugs and fluids failed to mention that I was only getting half my power. Leaving all variables the same if I can get 5000 rpm then I should easily see 10 mph eh? You've restored my optimism for this lil motor!!

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

The folks at Tiny Tach are very good to work with. If you have a question about the setting, give them a telephone call.

Don't know if you are mechanically inclined, but a two cycle engine is pretty simple. You can remove the carburator on most of them and see the induction reed port(s). With spark cables disconected from the plugs and someone pulling the starter rope, you may be able to determine if there is vacuum produced across the reeds.

Carbs are pretty simple and you should be able to get at the high speed jets to confirm that they are not plugged. I have had them plugged with clear gum which you could not see, but blowing through them quickly tells you if that is the problem. Hopefully this is the problem with your engine.

 

[Sea Rider]

Re: 12.5' with 9.8 running slow!

You must adjust TT to fire 2 sparks per revolution, then check with you alone max rpm at wot, post whatever rpm is achieved ?

Happy Boating

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Yo must adjust TT to fire 2 sparks per revolution, then check with you alone max rpm at wot, post whatever rpm is achieved ?


Happy Boating

Thank you Sea Rider I didn't know how to setup my tach. It's not an actual tiny tach but a cheaper make that came with limited instructions. My local shop said that I may have setup the tach wrong and my max 2300 could actually be 4500 and then leave me back where I was at the beginning. I'll setup my tach and let ya know what it outputs in the test tank (trash can) and real world test this weekend.

 

[Sea Rider]

Re: 12.5' with 9.8 running slow!

Check if that brand has spark timing if not and factory fixed probably won't read precisely your horse's rpm. Those 2 sparks per revolution is for 2 strokes Tohatsu engines, assume your horse as well. Sometimes is wiser to invest a bit more on a Tiny Tach as the new model is completely programable. You must test tach reading at wot and load at open sea or idle rpm to about 900-950 at neutral on trash can to have a good idea if tach is reading well.

Happy Boating

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

My 15 HP two stroke motor is rated 750 +/- 50 RPM at idle, approved WOT 4500/5500 RPM which is common for a two stroke and is better than 6:1 ratio between idle and WOT. You read 700/800 at idle with 2300 at WOT which is a 3:1 ratio. I do not doubt your tach setting. If you were reading 1/2 the RPM, the engine would be really running fast at idle and still not getting rated RPM at speed.

Check that the engine is in proper operating condition. The tach indicates an engine problem which is in agreement with the performance you found during operation.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Thanks fbpooler I have a theory that I'll test tomorrow. I suspect I have been drastically under inflated. If I am under inflated can that create drag in the rear end and result in bogging and reduced rpm? I need to try in the trash can to see if I can reach 4000 without any load other than water. I'm hopeful that I'm just an idiot and have been under inflated. My wake looks really rear heavy as in I child almost wake surf if I were moving faster! I will be ecstatic if tomorrow I get on plane all because I fully inflated my dang boat! I have an electric pump that says will pump to 2.5 psi then I've been using the bellows foot pump to top off but the other night before gluing on some scotty pads I inflated it well beyond what usually have been inflating to and it felt much more rigid. Let's hope I'm an idiot! In other news I purchased a 73 mercury 20hp off craigslist so my speed fix should be quenched! If I end up only reaching 2000 rpm on that thing I'm back to golf! Thanks again updates to follow!

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

On the water I was able to get my rpm up to 3400 but wouldn't budge past. I'm planning on having the shop that checked it out originally go back and see if they can find where my extra 600-1000 rpms are hiding. Thanks again all.

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

I still believe you have a motor problem. Our 9.8 Nisson pulling a 7 1/2" pitch prop will run a 14 ft x 60 in beam fiberglass boat with rounded chines loaded with with two heavy men and fishing equipment at a slow plane if the load is positioned right. It pushes an 11 ft Avon to a clean plane with no problem in the high teens with two aboard.

You will have to get your RPM's higher than 4500 in order to utilize the power of that engine. Think of it this way, 2,000 RPM is just a fast trolling speed.

Hope you get to the bottom of your problem, but there is nothing more I could suggest other than what has been suggested.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

I still believe you have a motor problem. Our 9.8 Nisson pulling a 7 1/2" pitch prop will run a 14 ft x 60 in beam fiberglass boat with rounded chines loaded with with two heavy men and fishing equipment at a slow plane if the load is positioned right. It pushes an 11 ft Avon to a clean plane with no problem in the high teens with two aboard.

You will have to get your RPM's higher than 4500 in order to utilize the power of that engine. Think of it this way, 2,000 RPM is just a fast trolling speed.

Hope you get to the bottom of your problem, but there is nothing more I could suggest other than what has been suggested.

Thanks again fbpooler! Ill be taking it in and demanding my extra rpms!!

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Ok guys update, I got a 73 mercury 200 20 hp, hooked up to same boat, same load, same fuel tank and line, and just like my 9.8 it tops out at 6.2 MILES PER HOUR!!! Could this be a fuel tank/ line issue? I'm so pissed! The common denominator between my 9.8 and my 20 is the same gas tank and line I'm hopeful a new tank and line will solve both motors. What are the odds I have 2 bunk motors that both top out exactly at 6.2 mph??!!

 

[Sea Rider]

Re: 12.5' with 9.8 running slow!

Check if both engines achieves wide open butterfly at wot, if not, adjust throttle. Seems that brand tach is not reading well...

Happy Boating

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

Sounds as if you have a fuel flow problem. Can you borrow a tank and fuel hose to see where the problem is?

You do have fresh fuel don't you?

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

That's what I'm hoping. I have just purchased a new Atwood 6 gallon tank, fuel line, mercury bayonet connector and brass 2 prong connector to connect fuel line to tank. The gas was fresh and mixed to 50:1 ratio in the previous tank. I have a family friend/car mechanic working on cleaning out the carb. Hopefully the tank will clear everything up or my next step is carb rebuild.

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

I assume you are checking your speed with a GPS. It is strange that both engines top out at the same speed, but 20 HP should push the boat at good speed.

If that is an old gas line, there is an excellant chance that alcohol has caused the inside to be plugged and gas flow reduced. As you see the same problem with both engines, it almost has to be the gas line.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

The tank appears to be fairly old, it's the metal style and the line doesn't appear any newer. As this is my first outboard tank combo I assumed it was ok being I replaced the gas and it fired up fine. Hopefully I'll be able to test out the new tank and line next weekend. Thanks for the tips!

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

Have you tested the engine with the new tank and fuel line?

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Bumping this baby back up. I took it out a few weeks ago with new line, tank, and renewed hope. Had it running on muffs like a dream. High rpms, smooth throttle response, thought I was solid. Took it to the lake only to have more of the same problems. Bogging at wot, stalling, barely made it away from the ramp. Then she got stuck in forward and in my haste I snapped the shifter. Rowed back to shore, packed up,andhaven't looked at her since.

Ordered a carb rebuild kit and shift handle which I got this week. Now my question is do I need any special tools? Best manual for the job, any tips or advice, how mechanically inclined should I be to undertake this? Difficulty of job versus cost of taking it in etc.

Do you folks think this might solve my issues of what I can guess is fuel delivery problems? Any extra ideas of what I could do while I have her opened up? Thanks again fellas

 

[zurk]

Re: 12.5' with 9.8 running slow!

what makes you think its the motor ?
your trim is probably not adjusted properly or the leg is not correct below the bottom of the boat.
adjust it correctly before playing around with the motor. chances are your transom mounting/motor placement is incorrect.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

what makes you think its the motor ?
your trim is probably not adjusted properly or the leg is not correct below the bottom of the boat.
adjust it correctly before playing around with the motor. chances are your transom mounting/motor placement is incorrect.

I wish it was something that simple. I've tried everything with weight distribution, trim settings, transom height is correct, etc. The fact it bogs and stalls at wot leads me to suspect a fuel issue. Since replacing the tank and line didn't solve it my next guess is a dirty carb.