Losing power - Indmar 350 (310 HP w/carb)

Geoff Standish · Addict Joined: 13 Jan 2003 Posts: 843 City: Calgary

We brought our boat out of storage and we've been out afew times this year. I've been noticing that we don't have as much power as we did at the end of last season.

Our boat used to top out at 42 mph, now it only makes it to 33. It's also alot slower out of the hole (I am running a bit more weight this year). It just seems like the engine isn't all there. I've scheduled a tune up, but I am just wondering if anyone could give me some suggestions or has had the same thing happen to them.

I did switch over to synthetic motor oil this season, not sure if that has anything to do with it...

Any comments or advice would be much appreciated.

Partyb · Posted: Jun 04, 2004 10:25 am Post subject:

Well, the best thing you can do is go to a professional as soon as possible and not take the advice of a bunch of wb.com'ers. Excellent that you have already done that.

I doubt it is the oil. Could possibly be something as simple as fuel filters. That is what I always replace first. It does wonders. Could also be valves. It is very hard to say via the internet. Good luck. Unless it is making strange noises it shouldn't be that bad.

jklein · Posted: Jun 04, 2004 10:31 am Post subject: Replace the fuel filters...first

That would be my recommendation too. Replace the fuel filters (both of them). 43Mph sounds a little low to me. You should pull off at least 46 or 47Mph if it's a BU, or MC.

You might want to pull the plugs and just make sure none of them look fouled. If you fogged the cylinders a ton, one or more could get fouled I guess.

I always replace my fuel filters, spark plugs, cap / rotor, oil, and tranny fluid as well as the impellar at the start of the season.

Geoff Standish · Addict Joined: 13 Jan 2003 Posts: 843 City: Calgary

Thanks, it goes to a performance marine mechanic on tuesday. I will replace the fuel filter this afternoon. See if that makes a difference.

It's not making a weird sound (Actually sounds the same), just not all there. I did the oil/tranny fluid at the start of the season. I think the plugs need to be replaced for sure. I did fog it. You are right about that...they didn't look too good (I'm no expert). I'll leave it to this mechanic to pick a replacement though. I was thinking about a new rotor/cap...that might do it too. It will be interesting to see what these guys come back with on tuesday.

BTW it is a 2001 Moomba Mobius.

Thanks guys, anyone else's comments would be awesome too.

Partyb · Posted: Jun 05, 2004 7:15 am Post subject:

Ohh, a Moomba. Those are slow anyway. Just Kidding. Depends on prop for top speed too. Anyway, sounds like you are doing everything right.

DiyGuy · Soul Rider Joined: 26 Dec 2003 Posts: 460

I would be suspicious of the rear two barrels kicking in. Could be a carb float stuck, mechanical link or a jet restricted.

When you go wide open does it have that traditional sound like it is trying to suck a golf ball thru a garden hose?

Geoff Standish · Addict Joined: 13 Jan 2003 Posts: 843 City: Calgary

That's a good question. We were out last night, and I thought about that. I'm no carb expert, but the flap thing wasn't really moving and it was open all the time. I never really listened to it without the cover on. I will try that. How do I check to see if a float is stuck? If it is stuck, how do I fix it?

Gonna replace the fuel filter today.

Thanks for the advice, I'm trying to go to this mechanic with as much of the stuff I can do on my own done so I don't have to pay him.. You guys rock.

Geoff Standish · Addict Joined: 13 Jan 2003 Posts: 843 City: Calgary

So I think regardless of what the problem is, I'm gonna change out the plugs. Anyone know what the best plug for this engine would be? Should I just replace them with equivalents or is there a higher performing plug I should be using?

Partyb · Posted: Jun 06, 2004 1:46 pm Post subject:

use the same plugs

DiyGuy · Soul Rider Joined: 26 Dec 2003 Posts: 460

With the engne off, take off the spark arrestor (air filter), so you can look directly down the carb. Engine OFF, advance the throttle all the way

Are the big 'flaps' (butter fly) opening full?

There is no way (engine off) to check if the back two barrels are spewing fuel as it should.

Start it up, give it a quick (in neutral) full throttle and back. If the backs are kicking in, it will really make a deep throat sound.

Black smoke - fuel
White smoke - oil
No smoke - A good thing