Mercrusier 165 inline 6 bogging down under load/getting up on plane

[Cbastuan]

Hey guys,
Been having more issues with my motor again, had another thread but this seems to be a different problem now occuring so I figured I'd start a new thread.
Had a previous issue of hesitation/missing and the motor not running properly while cruising and up on plane.
Motor now runs perfectly once up on plane, not missing, no hesitation or surging lots of power and very responsive, now getting the boat up on plane is a different story, seems to miss and lose power/falter while the motor is trying to push the boat up and out of the water, but once the boat is out of the water it flies and runs awesome.


The parts I have replaced so far are:

Pertonix ignitor module
Plugs
Cap
Rotor
Fuel pump
Fuel/water separator filter
All fuel lines
Rebuilt carb
Distributor
Compression an even 130 across all cylinders

Not quite sure what to look at or where to start with this new problem so hoping I can get some guidance here

Seems to be one thing after another with this motor so far this season, and thanks for all the help so far.

 

[wahlejim]

Check your carb again, this is the item most often assembled and/or calibrated incorrectly. You have to follow instructions precisely.

Check your fuel filter, you mentioned lines but no mention of why you did the lines or the shape the tank and pickup tube are in. If there is crud in the tank, it could be causing issues. You could have cleaned everything only to suck up more junk.

That is where I would start

 

[wahlejim]

Also, I would check your pertronix installation, gaps and timing

 

[dozerII]

What rpm are you running at at WOT, is it within spec? If your running too much prop it could be robbing you of the power needed to get on plane?

 

[Oshkosh1]

Check you accelerator pump. Ensure it's working properly. Look for vacuum leaks as well. Very small ones can sometimes only manifest themselves under high demand. They're harder to find but not impossible.

 

[Cbastuan]

Check your carb again, this is the item most often assembled and/or calibrated incorrectly. You have to follow instructions precisely.

Check your fuel filter, you mentioned lines but no mention of why you did the lines or the shape the tank and pickup tube are in. If there is crud in the tank, it could be causing issues. You could have cleaned everything only to suck up more junk.

That is where I would start

Sorry, forgot to mention I had made a new stainless steel tank because the boat was stern heavy with the kicker motor and all the other gear in the back, so I moved tank up front, so I'm fairly certain its not sucking up crud.
I double checked the timing after I installed the new distributor, and gapped plugs to .035

 

[Cbastuan]

What rpm are you running at at WOT, is it within spec? If your running too much prop it could be robbing you of the power needed to get on plane?

I don't run my boat at WOT, my tach recently busted so I have it completely disconnected at the moment to make sure it wasn't causing an issue, but I only run the motor at maybe around 2000-2500rpm
The boat is a starcraft holiday 18' aluminum with the 165hp inline 6 swapped in place of the 120 that it originally came with, so it definitely isn't lacking power.
It currently has on a 14" diameter 19" pitch prop.

It was working fine before with pushing it up on plane and I haven't messed with the pitch of the prop


With the extra power should I I be looking at a different size prop? I don't really care about top speed or running at wot all the time, just use the main motor to run out to the fishing spots.

 

[Cbastuan]

Check you accelerator pump. Ensure it's working properly. Look for vacuum leaks as well. Very small ones can sometimes only manifest themselves under high demand. They're harder to find but not impossible.

I had to replace the accelerator pump after the first time I built the carb cause the rubber skirt fell off, so I just put a new one in 2 weeks ago and confirm it is squirting fuel when I pump the throttle.
Where would the most likely spot be to get a vacuum leak? And what is the best way of finding them? Is there a trick to finding where they are?

 

[dozerII]

I don't run my boat at WOT, my tach recently busted so I have it completely disconnected at the moment to make sure it wasn't causing an issue, but I only run the motor at maybe around 2000-2500rpm
The boat is a starcraft holiday 18' aluminum with the 165hp inline 6 swapped in place of the 120 that it originally came with, so it definitely isn't lacking power.
It currently has on a 14" diameter 19" pitch prop.

It was working fine before with pushing it up on plane and I haven't messed with the pitch of the prop


With the extra power should I I be looking at a different size prop? I don't really care about top speed or running at wot all the time, just use the main motor to run out to the fishing spots.

with a 165 in an 18' holiday, a 19"will be under propped. My 18 holiday has a 120 with a 14.5 x 19 aluminum and it is right on,

 

[Cbastuan]

with a 165 in an 18' holiday, a 19"will be under propped. My 18 holiday has a 120 with a 14.5 x 19 aluminum and it is right on,

Yeah, I kind of figured it would be, but as I said in my other post, I don't run my boat at Wot ever, and I take it pretty easy on the throttle, I'm happy with running my motor at 2000rpm and cruising at 30mph is fast enough for me.
This problem has just recently manifested itself so I didn't think the prop is the issue, but is it possible that it could cause the issues I'm having?

 

[dozerII]

Yeah, I kind of figured it would be, but as I said in my other post, I don't run my boat at Wot ever, and I take it pretty easy on the throttle, I'm happy with running my motor at 2000rpm and cruising at 30mph is fast enough for me.
This problem has just recently manifested itself so I didn't think the prop is the issue, but is it possible that it could cause the issues I'm having?

I don't think it could as you have more than enough power to spin that prop.

 

[Oshkosh1]

I had to replace the accelerator pump after the first time I built the carb cause the rubber skirt fell off, so I just put a new one in 2 weeks ago and confirm it is squirting fuel when I pump the throttle.
Where would the most likely spot be to get a vacuum leak? And what is the best way of finding them? Is there a trick to finding where they are?

Check all around the manifold, and carb mounting. Use starting fluid, an unlit propane torch, or even fine mist water. Spray it around while holding higher RPM's and also while revving it. I had the identical engine/prop setup and it should easily turn it with plenty of power. Good luck!

 

[Cbastuan]

Check all around the manifold, and carb mounting. Use starting fluid, an unlit propane torch, or even fine mist water. Spray it around while holding higher RPM's and also while revving it. I had the identical engine/prop setup and it should easily turn it with plenty of power. Good luck!

Ok, thanks for the reply, I will check that next time I take the boat out.
I will also try to make a video and post it up as well.
Thanks

 

[johnkom]

Check the timing at higher than idle rpm. It should advance with the rpm if the distributor weights are not stuck. If they stick at basic the engine will be doggy. Happened to me once on a 165.

JK

 

[Oshkosh1]

Yeah...definitely check the "all in" timing(base+advance). You'll need to rev it up to about 3k and hit it with a light. If you're not around 38? or so you've probably got dizzy issues. Check the weights and advance springs. They can have a habit of sticking(weights) and coming off(springs) in older dizzys.