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SMLmalibu

Engine bogs with lots throttle and in bumps

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SMLmalibu

Hey guys and gals,

I've been fighting this issue for about 6 weeks now to no resolve.  I have a 2001 Sportster LX with the 5.7 carb Vortec motor.  It ran fine last year, but this season the motor is hesitating when I hit waves, and bogging down almost to the point of shutoff under wide open throttle.  Here's what's I've done so far:

1. changed water/fuel separator filter.  It was full of water the first time so after changing the filter I ran it down to 1/8 tank and then filled up with ethanol free gas and added marine Stabil.  Then I ran it some more and changed the fuel filter a second time and the gas looked fine.

2. spark plugs

3. spark plug wires

4. distributor cap and rotor.  The rotor button was fairly blackened.  After changing this is ran great for a tank of gas, then the problem returned.

5. Checked for loose wires

I'm really not sure what else it could be.  Carburetor needs adjustment?  Fuel pump?  Grasping at straws here...

Any help would be appreciated.  Thanks!

 

 

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BlindSquirrel
3 hours ago, SMLmalibu said:

Hey guys and gals,

I've been fighting this issue for about 6 weeks now to no resolve.  I have a 2001 Sportster LX with the 5.7 carb Vortec motor.  It ran fine last year, but this season the motor is hesitating when I hit waves, and bogging down almost to the point of shutoff under wide open throttle.  Here's what's I've done so far:

 

 

 

What about the fuel filter(s)? have you changed those? 

What about the fuel lines, are they the original ones? On my dads 04 XTi his looked good, but the inside collapsed cutting much of the fuel.

Is your fuel pump loud? If it is humming loud, it is either close to quitting or is not getting enough fuel because of one of the above reasons.

Tossing some more ideas out there for you. 

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SMLmalibu

Thanks for the quick reply.  My boat seems to only have a water/fuel separator, no other in line filters that I've been able to locate.  I'll listen for the fuel pump tomorrow and check the hoses.  

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MadMan
13 hours ago, SMLmalibu said:

 the motor is hesitating when I hit waves, and bogging down almost to the point of shutoff under wide open throttle. 

This sounds like it could be caused by the fuel level (float level) in the carb.

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drh

@SMLmalibu Check the connections on the oil pressure switch by the distributor. It should have three wires connected to the top of it - purple, red and orange I believe. Could be that when you hit waves you're loosing connection here which will cut power to your fuel pump and starve the engine of fuel. Look for any corrosion too. You can jump the red wire to the purple wire which will bypass the switch and take it on a test drive to be sure. 

I agree that it sounds like it could be a float issue as well just strange that it showed up out of nowhere. Maybe the water in the gas rusted some part of the float mechanism causing it to stick at times.

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SMLmalibu

I ended up putting her in the shop and they replaced the fuel pump.  I've driven a few hours since getting her back, there is no longer a hesitation, and it's noticeably smoother.  Unfortunately I did find that at wide open throttle it still bogs and I have to back off the gas.  She rides great cruising up to 35mph with 4 people in the boat, but any more throttle and it bogs.  I'll check the carb next.

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Woodski

@SMLmalibu:  If you are talking the transition from lower to WOT, your fuel control is from the accelerator pump, you can visually check that at rest by actuating the throttle.  Sounds like there may be some debris in that circuit.  If at more of a steady speed the issue is lack of fuel supply at a high demand rate.  That can be the fuel pump or also the anti siphon valve on the fuel tank causing a vacuum (if the fuel cap seals the tank) not allowing the fuel pump to deliver maximum amount.  Debris, fuel float level or carb fuel filter can also contribute to that including old fuel lines that are not ethanol compatible.

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SMLmalibu

@Woodski initially the boat had issues both with hesitation while maintaining speed, and with transitioning to WOT.  After replacing the fuel pump the hesitation while maintaining speed has been corrected and the engine runs very smooth.  If I am at idle and then go WOT it will bog or if I'm cruising and go WOT it will also bog.  I do believe the fuel lines to be original, but the mechanic said he tested to make sure there was proper fuel flow when changing the fuel filter.  I run ethanol free 93 octane.  With the boat off I also took the flame arrestor off and had a friend give it gas, and the 2 streams of fuel into the carb look strong.

It sounds like I need to research accelerator pump and float adjustment as I'm a novice with carbs.

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MadMan
1 hour ago, SMLmalibu said:

  If I am at idle and then go WOT it will bog or if I'm cruising and go WOT it will also bog.

Is the bog momentary or several seconds?

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SMLmalibu

@MAdMan Several seconds.  If I keep it at WOT I think it will actually kill the motor so I back off pretty quickly.  It's OK at 80% throttle, just not WOT.

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Rednucleus

What rpm's are you able to get up to before the problem starts?

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SMLmalibu
4 hours ago, Rednucleus said:

What rpm's are you able to get up to before the problem starts?

@Rednucleus I wish I knew... my tach doesn't work (on my troubleshooting list).  

 

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SMLmalibu

This evening I put a can of Seafoam in the gas tank (1/2 tank fuel), ran her hard for about 2 hours wakeboarding and tubing, and to my delight the issue seems to have gone away.  I was able to get up to 40 mph on GPS at WOT.  I also checked the accelerator pump mechanism and everything looks to be in line with videos I watched on youtube. 

Here's a video I captured trying to reproduce the issue:  https://photos.app.goo.gl/qNX2sEKWT4DN8FC37

 

The problem seems to be resolved... for now!  

Edited by SMLmalibu

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justgary

It's probably worth pulling the carb and giving it a bath anyway.  It is not hard to do, and may add a little to your top end while smoothing the low end.  

A gallon can of carb dip might cost a bit, but it will last you a long time and works much better than a spray can.  A spray can does work well to rinse the dip if you don't have compressed air.  Remove rubber parts beforehand, and either clean them separately or replace them if you have a kit with new parts. 

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drh
9 hours ago, SMLmalibu said:

@drh I wasn't able to locate the oil pressure switch, but did find something with a red and purple wire shown in this pic: https://photos.app.goo.gl/xbKPcf3j5o2w1tuBA

 

Also, is it safe to assume one of the plugs on the distributor cap should be empty?

https://photos.app.goo.gl/8r8TFjTxU7pmSGCC9

 

Looks like someone's done some custom work back there by the distributor and coil. Don't think that's the factory location of the coil. That's a bit of a wiring mess.

Yes that plug on the distributor is empty on mine too - it's where the timing shunt plugs in to adjust base timing. 

Has your distributor always been at that orientation? That doesn't look right to me. The plugs should be facing almost directly towards the back of the engine - it's almost like someone was trying to advance timing without having it in base timing mode. I would check your timing if you have a timing light before troubleshooting anything else.

And yes I think the thing with the red and purple wire going to it is the oil pressure switch but it looks like it's mounted in a different location than usual. Wondering how it even gets oil pressure from that location. Anyway it doesn't really sound like that's your issue anymore though. 

Is the video you posted WOT?

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JeffK
10 hours ago, SMLmalibu said:

This evening I put a can of Seafoam in the gas tank (1/2 tank fuel), ran her hard for about 2 hours wakeboarding and tubing, and to my delight the issue seems to have gone away.  I was able to get up to 40 mph on GPS at WOT.  I also checked the accelerator pump mechanism and everything looks to be in line with videos I watched on youtube. 

Here's a video I captured trying to reproduce the issue:  https://photos.app.goo.gl/qNX2sEKWT4DN8FC37

 

The problem seems to be resolved... for now!  

A friend had a go-fast we were working on and it did a very similar thing.  Not saying this is your issue, but I feel like I should throw it out here.  It would start to bog down at WOT and would recover as we let of the throttle.  I eventually took all of his fuel lines off and we pulled out what looked like a ball of teflon tape that would get sucked hard enough into the fuel pump screen that eventually it would restrict flow.  As soon as we came off the throttle, it would clear and run like a top.  Your engine sounds really strong by what I could hear in the video (which sounds awesome through my home stereo cranked up BTW) - insert the wife rolling her eyes as I play it over and over again.  "I'm just trying to help out a friend, honey."  Based on that, it didn't feel timing or tune related since it seems to perform really strong, but that's always so hard to tell when not in person.  I'd be checking fuel delivery, carb, etc if it were mine. 

Hope it stays resolved.  If not, that's where I'd start.  Where are you located?  I agree that the carb bath feels like a good idea.

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Woodski

@SMLmalibu:  Item #1:  Seafoam is a band aid, a carb clean / rebuilt is stitching your cut and I suggest a full carb rebuild so the problem does not come back, you certainly blasted some debris away, there may be more and it will come back exactly when you don't want it to.  Item #2:  Given you tach does not work and looking at the picture from above the transmission, I would invest some time in tidying up all the wiring, using the resource guide on this site or a google search to get a wiring diagram to identify your wires, your tach may simply be a bad ground or disconnected wire, tach signal will come from the coil and IIRC is purple (on Mercs it is).  Item #3:  oil pressure switch can be just above the filter, at the back just behind the intake manifold just left of the distributor, you should have 2, one for pressure to gauge and one as the low oil pressure warning switch.

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drh
4 hours ago, Woodski said:

@SMLmalibu:  Item #1:  Seafoam is a band aid, a carb clean / rebuilt is stitching your cut and I suggest a full carb rebuild so the problem does not come back, you certainly blasted some debris away, there may be more and it will come back exactly when you don't want it to.  Item #2:  Given you tach does not work and looking at the picture from above the transmission, I would invest some time in tidying up all the wiring, using the resource guide on this site or a google search to get a wiring diagram to identify your wires, your tach may simply be a bad ground or disconnected wire, tach signal will come from the coil and IIRC is purple (on Mercs it is).  Item #3:  oil pressure switch can be just above the filter, at the back just behind the intake manifold just left of the distributor, you should have 2, one for pressure to gauge and one as the low oil pressure warning switch.

Sorry I should have called it the fuel pump safety switch. It cuts power to the pump if no oil pressure is detected and is at the back of the engine by the distributor. Normally has three wires running to it. The tach should be a gray wire for Indmar I believe.

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SMLmalibu

Thanks for the replies everyone. Yes, the video is WOT until it got up to speed and then I backed off to about 80 percent. At the time of the video the speedometer was not calibrated and GPS on the digihud app shows it topping out at 40mph. The motor was rebuilt by the previous owner about 5 years ago, hence the wiring mess and possibly the reason the tach does not work. I may spend some time cleaning up the wiring this winter. At one time the boat belonged to the Ski Club at Virginia Tech. They had blown the motor and it was rebuilt by the person who purchased it from them, and I purchased the boat last year. Still working through a few minor issues and I intend to have the interior redone this winter to bring her back to her former glory.

@JeffK I'm at Smith Mountain Lake in VA

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JeffK

Wish you were closer.  I'd be happy to lend a hand.

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drh

You're still down on power for some reason. Maybe the secondaries aren't opening up all the way or you have a fuel delivery issue on the secondary side when they do open up. Here's a WOT video I took last year for reference. Same boat and engine, ACME 515 prop: https://photos.app.goo.gl/rhKVTb5oW3Pq4tsi9

Edited by drh

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SMLmalibu

Wow, yeah @drh there is a noticeable difference. Next time I pull her out of the water I'll check to see what prop I have.

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SMLmalibu

Just a quick update.  I brought it to a local marine shop who deals with Indmars and they changed the fuel pump.  It ran good for a couple trips and then started having the same bogging problem.  Next I changed all 3/8" ID Fuel line throughout the boat.  Put her in the water tonight and the boat seems to be running great, although I only drove it for about 20 minutes tonight.  The boat still tops out around 41 MPH and I did note that I have a CVP 13x13 LH prop, which I believe is a different pitch than the OEM ACME 515 prop.  I'll post another update after a few more trips.

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SMLmalibu

Boat ran great on Sunday for a long session. Tonight we stopped for about 15 minutes to unload a tube and switch to wakeboarding. When we got back out on the lake the engine bog returned. After a few minutes I returned to the dock, opened the clam shell, and waited 15 minutes. Also poured cold water on the fuel pump. Returned to the lake and it ran great at 24mph pulling a boarder with the wedge down for the next hour or more.

Vapor lock?

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