2011 Mer 4.3 inboard on Tahoe Q5i - engine bogging down

[kbryant]

Hello,
losing power -- it's been bogging down when it gets to about 25 mph. I've changed sparkplugs and new fuel filter. Any other thoughts I could try to fix. I also, dropped some seafoam in it.

 

[Scott06]

Hello,
losing power -- it's been bogging down when it gets to about 25 mph. I've changed sparkplugs and new fuel filter. Any other thoughts I could try to fix. I also, dropped some seafoam in it.

carbureted or fuel injected? Have a engine serial number.

Does it eventually recover or doesnt go past 25 mph?

What did the contents of the fuel filter look like

start with some basics -
engine compression.
check ignition timing including total advance
test strength of ignition with spark gap tester.
measure fuel pressure

 

[stresspoint]

ok , im also going to ask for more info.

has the boat sat or was it running and suddenly lost power ?.

efi or carb ?.

has anything recently been changed out or altered ?.

 

[kbryant]

ok , im also going to ask for more info.

has the boat sat or was it running and suddenly lost power ?.

efi or carb ?.

has anything recently been changed out or altered ?.

Hello,
It's Carb.
Fuel was clear when change fuel filter
It does get past 25 put really runs rough. It idles great runs great until about 25 mph.

 

[Scott06]

Hello,
It's Carb.
Fuel was clear when change fuel filter
It does get past 25 put really runs rough. It idles great runs great until about 25 mph.

Would be looking for anything restricting fuel flow like the antiphon valve, if you can measure fuel pressure at that rpm would be good.

Would think you may be looking at a carb rebuild.

 

[kbryant]

How hard is it to rebuild a carb?

 

[Scott06]

How hard is it to rebuild a carb?

it is not hard, just requires cleaning and attention to detail. You likely have a mercarb at Mikes carb parts they have good quality kits and instructional videos. I use a harbor freight ultrasonic cleaner for the parts.

Before you tear into it rule out fuel flow restrictions and make sure the ignition system is operating properly.

I rebuilt the holley 2 bbl on my friends Volvo 4.3 last Saturday. Spent some time the previous weekend ruling out other issues like fuel contamination and timing. He had a rough idle and miss off idle some intermittent bogging at higher rpm ... rebuild cured it.

 

[kbryant]

it is not hard, just requires cleaning and attention to detail. You likely have a mercarb at Mikes carb parts they have good quality kits and instructional videos. I use a harbor freight ultrasonic cleaner for the parts.

Before you tear into it rule out fuel flow restrictions and make sure the ignition system is operating properly.

I rebuilt the holley 2 bbl on my friends Volvo 4.3 last Saturday. Spent some time the previous weekend ruling out other issues like fuel contamination and timing. He had a rough idle and miss off idle some intermittent bogging at higher rpm ... rebuild cured it.

I will try and find the Carb Kit on Mike's and order that and do the testing to see about the fuel. It runs perfect at lower miles per hour -- gets on top of the water fast but as soon as we get close to that 25 mark she starts to run rough and then will smooth out a little after until I give it a little more gas.

 

[Scott06]

I will try and find the Carb Kit on Mike's and order that and do the testing to see about the fuel. It runs perfect at lower miles per hour -- gets on top of the water fast but as soon as we get close to that 25 mark she starts to run rough and then will smooth out a little after until I give it a little more gas.

The carb number is stamped in the float bowl this is 100% fool proof way to get correct kit. Since the mercarb uses a foam/plastic float would get a replacement for it as they can be brittle when taking apart the carb.

Would also make sure the power valve spring is working smooth. Would think some combo of accelerator pump or power valve not working plus maybe some debris in passages are causing this. Of course assumes ignition system is ok

 

[kbryant]

Would be looking for anything restricting fuel flow like the antiphon valve, if you can measure fuel pressure at that rpm would be good.

Would think you may be looking at a carb rebuild.

Hello
What is the Antiphon Value? Where is that located?

 

[Scott Danforth]

It's the barbed fitting on the tank pickup tube.

Also check the pickup tube for a strainer. They get plugged . Remove it and throw it away. It is not needed