Backfire...

[Mikey]

Finally got the boat out yesterday for the first time this season. Still running on OLD gas/treated with stabil.
Boat for the most part ran fine most of the day,till we started skiing and then we started noticing a Big surging issue.
When under full throttle out of the hole the boat starts fine,then about 2500,3000 rpm a big drop in power then a surge and then fine all the way up from there.Wihile trying this without a skier i even got a couple small backfires????

Boat was running top notch at end of season last year and was winterized ,and fuel filter was changed as well as impeller etc.The only thing i noticed out on water while checking oil was level was a little high/overfull. Temps were completely fine all day long. Oil is still very clean.
Note wires and plugs are still original,maybe likely due for change,as i just hit 170 hrs. Before i get a chance to pop into a dealer to talk to a mechanic to pick there brains looking for any suggestions?

I'm thinking Gas should be replaced although i burned close to 3/4 tanl so i will likely just top up with fresh. Wondering for suggestions where to go from here?

Also these things only showed up while under FULL THROTTLE conditions....

[KSmith]

Sounds like it could be bad gas. I'd drain it before trying new gas, but that's just me. Or you could go run through most of the remaining tank before filling with good gas.

[wolfeman131]

Sounds like it could be bad gas.

Hate it when I have this problem. Usually happens after I have BBQ & beans.

[maxpower220]

I would fill the tank and add Stabil to it, then run for 20-30 minutes. After that, check for proper function. Also, you said it happened when pulling skiers, does it do this now without skiers?

[KSmith]

Hate it when I have this problem. Usually happens after I have BBQ & beans.

Mmmmm BBBQ & Beans

[mmandley]

IS your engine carbed?
Does it have a Distributor or electric coil packs?

Backfire can be caused by bad fuel but im thinking dut to your RPM it might be a timming issue. As the engine goes past 2K it should be at max timming advance so if its retarded at lower RPMs then when you reach high it cant advance enough causing the engine to mis fire, lack of power, surging and backfires.

[Mikey]

Max power, answer is Yes if given full throttle outta the hole but not nearly as bad as when loaded with a skier.
Mmandley,answer is Fuel injected 2007 325Hp likely same motor you have and as for Distributer or Coilpacks i'm not 100% sure as i never had to deal with any issues like this and its just stumping me right now.... Unfortuneetly i've been swamped with things i needed to or had to do since i got back and have not even untarped the boat to have another simple look.
Trying to get as much info as possible so when i can i will give things a look over.
Gonna have to check my fuel gauge as well to see how feasable syphoning OLD gas out would be and possibly replace,Sure my Lawnmower and or truck will not care as much???

[maxpower220]

Your engine is the same as mine, so you have a distributor. You may want to check your coil wire going to the distributor (it's the only wire not running to the spark plugs). Also, get a screwdriver (or torx bit) and pop off the cap and check the rotor. I found mine to be very corroded this spring. You can use some emory cloth/sandpaper and clean it up, but I just replaced mine as the rotor had a lot of wear.
Also, see if you can move the distributor by hand (rotate it). If you can, then you know that your timing is off. It should not be loose. Since you have EFI, you should not be getting backfires and timing may be the reason for it.

If you do remove the old gas, I would put it in the truck (not lawn equipment).

[Mikey]

I'm going to do all of the above except put in the lawn mower. I popped into the local MC/ Moomba dealer today and general concencious is likely bad gas and a fouled plug. I bought some plugs today at the dealer,wich i am returning tomorrow after i drove away without giving the invoice too much notice. Spark plugs were 16.00 EACH....... Yikes. I stopped at an Auto value on a whim later in the day first to see if they carry the same products? Yes they do.9.20 Each.

I'm thinking i will give the dealer a chance to readjust the price to reasonably close price or i Want MY MONEY BACK.
I realized i'd pay a premium at a dealership but didn't think i would get RAPED doing it.

MY Mistake and hopefully they will rectify this or thats the last they will be seeing of me.I know the General Sales Manager fairly well so hopefully i will not have to have a chat with him......
Next will be syphoning the old gas,Filling fresh,adding a little injector cleaner....suggested,change plugs,check rotor and hopefully HAVE FUN for the rest of the summer.

We have a very short window for nice weather so i don't want to miss it!!!!!!

[Mikey]

Quick update... Motor does not have distributer,its got a sealed Rotor type cap to coil packs. Told not to touch,likely not the problem....Also double checked fuel filter.
Drained the fuel tank,added fresh gas and a can of seafoam to get rid of remnants of possible water and help clean the injectors etc. Fixed all my trailer issues and Finally got out for a day at the lake. Boat ran flawlessly. Running smooth and strong. Had a great day or skiing and wakeboarding etc. Now just a tired and sore puppy... Took a small crash ,skiing harder than i should have been ..... Trying to catch up for lost skiing time i guess.
All my stereo and battery issues are good . Finally now just go out and enjoy....Whew....