12.5' with 9.8 running slow!

[fbpooler]

Re: 12.5' with 9.8 running slow!

If the fuel line decomposed as it probably did, then there is a good chance that particles of foreign matter went into the carb. Cleaning the carb, any filter, and inspecting the reed valves would make sense. Is their any rubber hose on the motor itself? If so, has it also decomposed?

It does not take that much mechanical ability to put a kit in a carb if you follow some general guidlines. Do not force or bend any parts and work in a clean area. If there is a float drop measurement, make sure it is correctly set. Any rubber gaskets in the carb could well have been ruined by alcohol and require replacement. Tiny particles may be blocking small passages in the carb and will have to be cleaned out. Make sure any linkages to the throttle, etc are correctly made.

Sealing of the crankcase is of primary importance in a two stroke engine, so it should be checked if the carb work does not solve the problem.

If working on an assembly like this bothers you, pay a mechanic to do the work. You have enough time and money invested already, so you want to make sure the work is done right.

Three things have to be available for an engine to run. The proper amounts of: compression, spark, and a proper air to fuel ratio. A two stroke also requires oil in the gasoline mixture.

You are getting quite an education with the situation you are in. After it is solved, you will have an understanding of some useful things.

 

[Sea Rider]

Re: 12.5' with 9.8 running slow!

Meantime,

Is that a 1982, 2 stroke 9.8 engine or it's the boat age ? If that engine is that old will need a complete overall re torque as gaskets always cede with time and heat including a worn dried out head gasket too.

You could have a CD, Ignition Coil internal heat bummer, is it just a bog down or engine shuting dowm issue at wot ? If you prime bulb while engine bogs down, does the issue still persists ? Could be a worn diaphragam ? Are internal tank filter mesh and carb small fuel filter inmaculate clean with good fuel flow to carb ?

Happy Boating

 

[zurk]

Re: 12.5' with 9.8 running slow!

makes no sense that a 20HP would not push it on plane.
first measure transom height and height from anti cav to bottom of outboard clamp. they should both be dead on within +/- 5mm.
do 6 runs with the 6 trim settings over a 600 ft distance. align your boat parallel to shoreline and open it up full throttle. write down trim position #, WOT RPMs, angle of bow (use your smartphone with an angle displaying app such as anglemeter which is free, align phone parallel to water surface), GPS speed (run smartphone app in background which can record max speed like garmin's mobile xt or something). then post it all here. i should be able to compare with mine which will let us know whether the boat is struggling to get on plane or not.
mine only gets on plane on trim setting 3 FYI. all the other settings dont work. mine is a hugely overpowered engine (15HP 4cyl) for a 10.5ft inflatable. i also have more stuff in it than you do including 2 ppl, 2 x 6 gal tanks, fishing stuff etc etc

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

In post #31`he reported that he had poor results with a 20 HP using the old gas line and tank, so the common denominator is the fuel system. If repairing the fuel system does not perk up things, then it might be advisable to consider if a full rebuild is needed. You can easilly check compression with a pressure gauge, but checking crankcase pressure is more difficult.

If he had not had the same problem with the 20, then fuel pump problems would look to be the culprit and pumping the bulb would tell you that as you say. I forgot to mention the fuel pump diaphragm, so you are right to check that when repairing the other parts of the induction system. Alcohol eats diaphragms and seals.

 

[zurk]

Re: 12.5' with 9.8 running slow!

the common denominator is also transom height and leg height. that would be more likely than the gas line and tank as the engines have enough gas in their float bowls to run fine at full throttle for a few minutes. mine runs for at least 2 min at full throttle with no gas tank connected.
i do engine flushes with no gas tank connected for a full 3 min at idle too.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

the common denominator is also transom height and leg height. that would be more likely than the gas line and tank as the engines have enough gas in their float bowls to run fine at full throttle for a few minutes. mine runs for at least 2 min at full throttle with no gas tank connected.
i do engine flushes with no gas tank connected for a full 3 min at idle too.

I have two motors a 1982 9.8 and a 1973 20 both bought used off craigslist with no knowledge of the history. Currently the 20 is in a new shop doing a diagnosis and carb rebuild. Both have 15" shaft lengths and have been trimmed to maintain a level. Zurk you bring up a good point I should've checked before buying a new tank and line. When disconnected it exhibits the same symptoms such as the stuttering and bogging when opened up. It idles fine connected or otherwise and starts up first or second pull. Squeezing the bulb when running also doesn't change anything. I should hear something back from the shop tomorrow or Thursday. Hopefully my troubles will be fixed. Thanks for all your input folks!

 

[Sea Rider]

Re: 12.5' with 9.8 running slow!

It's very easy to check a fuel restriction issue. With sufficient fuel level on tank, with a point, pen, whatever push ball, pin whatever inside engine hose connector end all the way in while priming bulb and check the flow. If poor is restricted, if with good flow, it's ok. If your transom has at least 15" you should not have any issues runing both engines.

It's useless to play with all trim holes, engines that have no electric trim must be seated to be perpendicular to boat for the anticav plate to ride parallel to water surface once well ballanced boat is at full plane. Generally it's seconf or third trim hole out, final setting will depend entirely on transom's angle.

Happy Boating

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

It will be interesting to hear what the diagonisis is on the 20 and how it performs in service. So far all we have come up with are questions.

Cut the old fuel hose lengthwise and examine the inner surface of the elastomer. Is there evidence of particles of it sloughed off? If so, particles could have been introduced into the carbs of both engines.

Even with a full float chamber, the fuel has to make its way to the combustion chamber. Foreign material in the passages will have a negative effect. Gaskets allowing air to be sucked into the system will lean out the mixture and could even cause the fuel not to be drawn into the engine. The pressure difference between atmospheric and the pressure inside the crankcase force fuel into the crankcase. An air leak in the crankcase is detrimental to the power the engine can produce.

I would like to have a shot at checking out both engines, but that is not possible. Hopefully the shop will check out if the engine is capable of running properly regarding compression, etc.

Is there any chance you could run your engine on a friends boat to see if it performs? Also, do you have an oppurtunity to try a known good engine on your boat? Having problems with one engine is one thing, but having basically the same problem with two engines is puzzleing.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

It will be interesting to hear what the diagonisis is on the 20 and how it performs in service. So far all we have come up with are questions.

Cut the old fuel hose lengthwise and examine the inner surface of the elastomer. Is there evidence of particles of it sloughed off? If so, particles could have been introduced into the carbs of both engines.

Even with a full float chamber, the fuel has to make its way to the combustion chamber. Foreign material in the passages will have a negative effect. Gaskets allowing air to be sucked into the system will lean out the mixture and could even cause the fuel not to be drawn into the engine. The pressure difference between atmospheric and the pressure inside the crankcase force fuel into the crankcase. An air leak in the crankcase is detrimental to the power the engine can produce.

I would like to have a shot at checking out both engines, but that is not possible. Hopefully the shop will check out if the engine is capable of running properly regarding compression, etc.

Is there any chance you could run your engine on a friends boat to see if it performs? Also, do you have an op
opportunity to try a known good engine on your boat? Having problems with one engine is one thing, but having basically the same problem with two engines is puzzleing.

Fbpooler, any proximity to Arizona? Unfortunately I have neither friends with boat or engine. I'm optimistic this shop will be able to help. The last place I was taking both motors to charged me up the *** basically to change the plugs and fluids. It's a prop shop pretending to be mechanics. They failed to notice the choke mechanism wasn't functioning and actually called me to ask if it ran before bringing it in. Overall my foray into boating hasn't been wonderful. I'm hopeful I'll hear some good news later today though and I'm beginning research into a trailer project. I'll keep ya updated.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

SUCCESS!!! Received my 20 hp from the shop and took her out. Throttled up smoothly and while it took a while to get on plane I was reaching gps speeds of 20+ miles per hour! Being this is my first time on plane with my boat is it normal to take a while to get on plane? I'll give it full throttle, the bow will rise then it seems to drag on bow up until it settles down and takes off. I have the 2 blade higher pitch prop could that explain it? One or two times with other boats wake and wind chop it seemed to make it harder to get on plane. Should I be working the throttle differently? All in all, I'm happy my motor worked, didn't catch any fish and I broke my launching wheel on a ditch on the boat ramp but I'm excited about my boat again! Thanks for all your tips! As far as I know he just rebuilt the carb. Now for the 9.8 and see what happens

 

[Sea Rider]

Re: 12.5' with 9.8 running slow!

If you are boating solo, secure tank at bow and move your weight forward, could even sit inside deck just for the test. Trim engine to be perpendicular to water level, throttle fast to at least 3/4 throttle, bow will rise and come down shortly. The faster throttle you give the faster up-down bow response. Will need a tach to determine max rpm achieved at wot to check min, max rpm parameters factory stated for that engine. Playing around with prop pitches is a wild guess that could harm your horse...

Happy Boating

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

If you are boating solo, secure tank at bow and move your weight forward, could even sit inside deck just for the test. Trim engine to be perpendicular to water level, throttle fast to at least 3/4 throttle, bow will rise and come down shortly. The faster throttle you give the faster up-down bow response. Will need a tach to determine max rpm achieved at wot to check min, max rpm parameters factory stated for that engine. Playing around with prop pitches is a wild guess that could harm your horse...

Happy Boating

I had a buddy and cooler up front and played with trim settings. 3rd pin hole made a crazy wake and wouldn't get on plane. 1st is what I was using and seemed to work. Water was coming over the back of transom but that was because of my launching wheels were down. Either way I'm pretty excited about this setup again! Being a broke my launch wheels maybe I'll look into trim tabs.

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

Any drag from protrusions below the hull will kill your performance. If you had launching wheels down, you were lucky to get 20MPH.

It will be interesting to see what the 9.8 will do with a clean carb.

I believe you said you had a tach which is what is needed to check the prop as Sea Rider said. You can spend a lot of money just trying different props to see how they perform. Tabs should be helpful.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Any drag from protrusions below the hull will kill your performance. If you had launching wheels down, you were lucky to get 20MPH.

It will be interesting to see what the 9.8 will do with a clean carb.

I believe you said you had a tach which is what is needed to check the prop as Sea Rider said. You can spend a lot of money just trying different props to see how they perform. Tabs should be helpful.

I quickly lifted the launch wheels once the spraying started. I figure Ill be using this motor more this winter in the larger warmer bass lakes being the trout lakes up north (mostly 10hp restricted) will be either frozen or closed. The tach is currently on the 9.8 so Ill move it to the 20 and see what happens. I also want to start on a trailer project so maybe Ill forgo the launch wheels for trim tabs. As for props, my motor only has 2 available props a 3 blade 9" pitch or a 2 blade 11" which I have now. Depending on what my tach says and at the advice of you guys I might need to track down a different prop.

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

Sounding better and better now that you have the particles out of the carb. Hopefully he got all of the internal passages clear now, so you can start making sure the transom height etc are proper. It will probably not make much difference though. One of the boats which I played with transom height yielded 0.5 MPH difference when changing the relationship of the cavitation plate in relation to the bottom of the boat.

From the pictures of the boat, it appears that the forward seat on that boat is a bit farther back than some designs. No problem with that, but getting the boat over the hump may require your passenger to move forward until you achieve a clean plan when accelerating.

An honest 20 MPH would be acceptible to me with a soft bottom boat. Checking the prop pitch and trying tabs sounds like your next move.

Don't know your altitude, but that may be playing a part. Hopefully the 9.8 will give decent speed even if it does not hit a good plane once it is running rigt.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Sounding better and better now that you have the particles out of the carb. Hopefully he got all of the internal passages clear now, so you can start making sure the transom height etc are proper. It will probably not make much difference though. One of the boats which I played with transom height yielded 0.5 MPH difference when changing the relationship of the cavitation plate in relation to the bottom of the boat.

From the pictures of the boat, it appears that the forward seat on that boat is a bit farther back than some designs. No problem with that, but getting the boat over the hump may require your passenger to move forward until you achieve a clean plan when accelerating.

An honest 20 MPH would be acceptible to me with a soft bottom boat. Checking the prop pitch and trying tabs sounds like your next move.

Don't know your altitude, but that may be playing a part. Hopefully the 9.8 will give decent speed even if it does not hit a good plane once it is running rigt.

Yup progress is being made!!! I'm researching trim tabs at the moment and there seems to be a wealth of information and testimonials here on iboats. One thing that I'm concerned with is both the maxi marine lifters, and nauticus smart tabs would hinder my ability to mount my trolling motor on the transom. Secondly I need to decide if I'm going to keep the launch wheels which would mean ordering another set or skip the wheels and use the wheel replacement funds to go ahead on tabs/lifters. Thirdly I need to figure out my trailer project. No one has replied on the other thread I bumped back alive concerning the harbor freight utility trailers turn flatbed inflatable trailer. So in no particular order here are some questions that I am tackling and would greatly appreciate any and all input.

1. Harbor Freight utility trailer used for inflatable towing. 8" wheels vs 12" wheels, bunks vs deck, opinions etc

2. where to mount trolling motor with either trim tabs or lifters?

3. tabs vs lifters (I know I know there's a TONS of threads but still, I am not convincingly swayed one way or another)

4. How come all this time and money I'm pouring into my boat isn't netting me more fish

 

[fbpooler]

Re: 12.5' with 9.8 running slow!

Stopped using 8" wheels on my trailers years ago. The do not handle high speed.

The other folks will surely answer your other questions.

 

[Sea Rider]

Re: 12.5' with 9.8 running slow!

Points :

1-Go for 12-13" wheels and trailer with side bunks to support both tubes & engine better.

2-Trim tabs, lifters, trolling motor, can only pick just one at transom area, unless a bow mount is found for trolling motor.

3-It's a must check engine rpm at wot with tach, probably need a prop pitch that betters your actual hole shot and that's it. For the cost of trim tabs or lifters could buy a new prop and use your trolling engine at transom.

4-Fish are always one step further...

5-Sorry to say, but you need at least a 9.9 engine to perform as nearly expected for that size sib, other 380 sibbers have had bad or poor performance with same engine. 380 sibs are rated for min 15 HP engines.

6-Trade in, sell yours, get a used Tohatsu 9.9 D2 and for peanuts cost pass it to a 15 HP, will be the way to go.

Happy Boating

 

[Elkhornsun]

Re: 12.5' with 9.8 running slow!

I had a 10' inflatable powered by a 15 HP engine and it struggled to get on a plane with two divers and their gear on board. I bought a 14' inflatable and with the same 15 HP motor and same divers and gear the larger and much heavier boat easily got onto a plane and traveled at double the speed of the smaller inflatable. The difference was simply that with more surface area to support the weight the tubes sat higher in the water and there was less drag.

This is the same as what happens with a catamaran which while faster than a monohull is much more vulnerable to overweighting of the craft in impacting performance. With an inflatable with a capacity of 700 lbs. and with an actual load of 500 lbs. there is going to be a lot more of the tubes in the water creating a lot more drag that the motor has to overcome as compared to the same 500 lbs. sitting in a boat with a load capacity of 1500 lbs. and this has a far greater impact than the "dry weight" of the two boats.

 

[saabsaviorlee]

Re: 12.5' with 9.8 running slow!

Recent update. Purchased a doelfin hydrofoil for my 20. Haven't tried it in my bass lakes in the valley but just got back from a trip to a northern lake in flagstaff. Elevation around 7000 ft. Down here is more around 1200. Today we were loaded with 3 guys and one wife. Rough weight estimate would be 700lbs total in boat weight. Wouldn't plane and maxed at 6.2 mph lol I'm assuming this is hull speed. I understand elevation affects the mixture which can reduce my hp. Aside from rejetting every time I head north what can I do? 1972 merc 200 20hp so prop choices are limited. Thoughts? Thanks!