15hp strange loss of power

[Gmcken34]

Hi All,

I have a 15hp (15fhm) 2 stroke and here is the issue.

Engine will start up fine 1st pull
Engine will idle fine
Go into gear and idle fine
In idle will rev up fine
However under load wont go past half power. at points with WOT it seems to try
every few mins I hear a slight rpm change

New plugs. Carbs cleaned, fresh fuel, fuel filter cleaned, swapped coils(no change)

any one any ideas could this be the CDI or Rectifier ?
Thank you

[grf00]

How did you clean carbs? Did you remove , take the bowls off and screw the two jets completely out and make sure they are open. Then spray carb cleaner up thru passage ways to ensure they are open. Since it idles, the small jet should be OK. Only take a few bowls of dried up gas to get these jets stopped up. It also leave a bunch of junk floating around in boles that causes random problems.

[Gmcken34]

Hi Thanks for the fast reply, ya i did all the above and used compressed air just to be sure. At times i think i can hear a misfire but it is few and far between

it is almost like one cylinder is not running when at full power but as i said above i have tried swapping the coils and even starting on one cylinder at a time and its no problem

[TownsendsFJR1300]

Agreed with grf00.

Sounds like crap in the carb. Especially the main jet.

It is IMPERATIVE to actually pull the jets out and see light thru them. When you drain them/it, try to catch the fuel in a small CLEAN tuna fish can and check for debris, cloudyness(water), smell (varnished, bad fuel smells funky). The idle jet usually clogs first as its smaller, but your description is a classic clogged main jet.

Carb cleaner, air compressor, won't necessarily clean a really badly clogged jet.


Had the engine sat for at least a month with un-treated fuel in it? It is a recipe for a clogged carb.


Can you please post the year engine, can't look up the parts fisch without it..

[Gmcken34]

Thanks

Ya its a 2006 and here is the kicker .... it set for just over 3 years if you can believe it. So I recon I'll be taking the carb back off tomorrow morning I will let you know if there is any change

thank you

[grf00]

Some carb sprays are better then others. Be sure the one you have will dissolve dried gas varnish. Got one Name brand at an auto parts store and it did nothing as compared to an older GUNK brand one.. Also, I have a few stiff wires that are tempered and stiff. Be careful that it is smooth since the jets are small and even a slight increase in size will mess them up. You can also harm an older pre mix 2 or 3 cylinder multi carb outboard if the main jet starves the cylinder of lubrication (I think?) So do not push it till you get it correct. Townsend has been advising me on mine and it set a lot. Years ago, took me a couple times to get the junk out. (first time, I missed the idle jet under the plug) This latest time, engine had set so long, Went thru carbs twice again. Second time, I was careful to check bowl level of gas and the top bole had little gas. Think my fuel pump diaphram had gotten so old and stiff, the fuel pump was weak. Any way, I rebuilt it and thru carb kits in and engine runs fine. Still waiting on some more lower unit seals and stuff however now to see if engine is truly OK since I may have a bearing going from long term letting it sit and may have rusted it. What I am saying here is if your fuel pump is stopped up, it could starve higher bowl. However mine did not appear to have crud in it, just old and stiff (1998 motor)

[99yam40]

check timing to see of it is advancing as it should when problem is there. timing light will also show if there is spark on all cylinders if you hook light to individual plug wires.
check fuel pump for leaking diaphragm, too much fuel or too little can cause cylinder to not fire propery

[Gmcken34]

Thank's grf00,

I have reinspected the carb this morning and will be hitting the water in about an hour so I will be able to give a Yea or Nea.

Took out the jets and using a LED light all passages look clear.

Using HOLTS carb cleaner

[Gmcken34]

Hi 99yam40,

I have a timing light however this engine has not been messed with(all settings as new). It was fine 3 years ago then yesterday when it was taken out of storage this problem started. it almost seems like when i go above a certain RPM the spark is not strong enough as the engine sounds like it wants to go. its like if i could just get that extra 2RPMS it would take off

[grf00]

Added some more to post 9. Did not noticed you where online. Have you messed with the timing? These engines are very sensitive to the pull in on the carb roller where they start at on the timing. I had to put an indicator on my bell crank on the carbs to see it move since when the roller first touched was not the correct position on the flywheel timing mark. Should be OK as long as no one has messed with it. Mine was way off since I put a remote control on and took the tiller off and the remote pulled from back. My roller also had a big flat on it and I had replaced it.

[Gmcken34]

grf00,

My engine is a single carb 2 cylinder setup took off the pump and had a good look using a light behind it. I dont see any holes .
just heading to the water now so I can give an update in about 20 mins

[Gmcken34]

Well no joy, still the same half power under load. hard to test on my own but it seem like bottom cylinder has no spark under load/ 1/4 throttle. aaahhh

Could it be the CDI unit ?

[TownsendsFJR1300]

Well no joy, still the same half power under load. hard to test on my own but it seem like bottom cylinder has no spark under load/ 1/4 throttle. aaahhh

Could it be the CDI unit ?

Did you put the timing light on the questionable cylinderspark plug wire and simply watch the light when under load/acting up?


Just trying to confirm that your actually loosing spark (not really concerned about the timing degree's at this point)

Just curious, where you located?

[Gmcken34]

Townsends,

Yes put the timing light on and at mid RPM it seemed to act up cant be sure as engine was on the water and its hard to keep an eye on it .. Im in Ireland

[TownsendsFJR1300]

Townsends,

Yes put the timing light on and at mid RPM it seemed to act up cant be sure as engine was on the water and its hard to keep an eye on it .. Im in Ireland

A "helper" staring at it compared to the other plug wires would probably do it.

It seems you've already pretty much have that intermediate lack of spark documented/ as your issue.

I know you already swapped coils, no change, just a shot in the dark before dropping the big $ on a CDI or ?.

Pull, clean and check ALL your wiring connectors, especially the ground wires. Check the actual tiny connectors to the CDI and make sure all the pins are clean, straight and fully in thier harness. The slightest bit of corrosion, (greenish tint) will cause all kinds of electrical issues.


I had issues with occasional/random misfire, etc on my old Yamaha FJR motorcycle while under warranty. The dealer couldn't find the issue and was on the phone cross country with Yamaha headquarters. Charged me $125 for a throttle sync which didn't help and they did incorrectly). Left there, problem un-resolved (literally spent the entire day there).

A search on one of the FJR forums indicated a connector (six or eight wire-forgot), under the fuel tank tended to collect moisture and corrode. Pulled the tank, sure enough, lots of green... Cleaned it all out, some di-lectric grease, ran like new again...

Thats what your looking for or corroded aluminum under a ground starp, coil, etc...

Good luck.