2009 Mercruiser 4.3 out of hole issue

[JohnBChargrave]

I have a 4.3 mercruiser on 20ft glastron. I just purchased this boat 2 weeks ago. It also has nauticus smart tabs. When its just me and the wife in the boat. it takes off and runs fine. however yesterday we had acouple friends + installed new subwoofer second battery and put all the gear/ ice chest in the boat. it struggled badly out of the hole. would take 15-20 seconds to get on plain. and wasn't increasing RPM till it was on plain. sat about 3000. The boat is an 2009, and the previous owner doesn't believe the spark plugs were ever replaced. so was going to start there. and maybe spray some carb cleaner.

My questions are, am I going about this in the right order? And was also wondering if I could install 4.3 vortec spark plugs from auto zone in it. as the motors are basically the same thing?

 

[R055]

If the sparks plugs have never been changed, it's time for a full tune up. It shouldn't have any problems getting on plane especially with smart tabs.

 

[SeaDooSam]

The pitch of your prop may be too high. If it is too high, the prop won't get enough "bite" and won't be able to plane easily when loaded. My Chaparral with a 4.3 had great hole shot as well when it was just two people, but when loaded it struggled. Therefore, I dropped from a 19 to 17 pitch. Just make sure your Rpms stay in the correct range

 

[JohnBChargrave]

The pitch of your prop may be too high. If it is too high, the prop won't get enough "bite" and won't be able to plane easily when loaded. My Chaparral with a 4.3 had great hole shot as well when it was just two people, but when loaded it struggled. Therefore, I dropped from a 19 to 17 pitch. Just make sure your Rpms stay in the correct range

The boat does have a 21pinch prop on it. I'll see about getting a 19 or 17 tomorrow. I also changed the plugs today. Boat starts a lot easier now. However the old plugs weren't in terrible condition. Definitely needed to be changed though

 

[achris]

We need to ask a few questions.
1. MPI or carb?
2. What are the wide open throttle revs with just you and the wife? (use a proper calibrated tacho, not the one in the dash)
3. what is the pitch of the current propeller?

Spark plugs need to be Merc spec, not automotive. You can still buy them at autozone, just make sure you get the right ones.

Chris.......

 

[JohnBChargrave]

We need to ask a few questions.
1. MPI or carb?
2. What are the wide open throttle revs with just you and the wife? (use a proper calibrated tacho, not the one in the dash)
3. what is the pitch of the current propeller?

Spark plugs need to be Merc spec, not automotive. You can still buy them at autozone, just make sure you get the right ones.

Chris.......

The motor is MPI. And 4500-5000 is the highest I've ran it. Don't like going max throttle. Specially since its been choppy since I bought the boat. Current propeller is 14 1/4 x 21 3 blade

 

[achris]

At some stage you are going to need to get on the water with a calibrated tacho (not dash) and max it out. You need to be pulling 4400-4800rpm at wide open. I have the same engine as you, in the same size boat. I have a 1.62:1 drive. With a 19" (pitch) prop I pull 4600rpm, right in the middle of the rev range. Theorectially that's spot on. In practice, it's a little too big. Makes the boat 'heavy' and doesn't respond well to the throttle, especially in a swell. I dropped down to a 17" prop and it's a different boat. Far more responsive and gets up on the plane quite quickly. At wide open I'm just banging on the rev limiter, but as the weather isn't often good enough for max, that's fine by me. You might look at dropping a couple of inches in prop size....

Both of those props are 3 blade stainless steel 'Vengeance' props. I'd love to find an old 'Offshore' 4 blade prop of 18"...

Chris.......

 

[stonyloam]

sounds like you put a couple of folks and the battery in the stern. You might want to try moving as much extra weight as far forward as you care. If you have a bowrider, put a person or two up front. In spite of what they say, your tabs are not going to do much more than generate drag until you build some speed. Trim the outdrive all the way down initially and start to trim up as you come on plane. You want to minimize the bow rise, and keep as much hull in the water as you can to come up onto plane ASAP. Dropping to a 19" pitch prop would help, but just trimming and changing the weight distribution should help a lot. If you can get in the 4500+ RPM range, sounds like your engine is doing OK.

 

[Rick Stephens]

I wouldn't squirt some carb cleaner in a carb, let alone an mpi. Either take s carb and rebuild it or leave it alone and with mpi you really need to run injector cleaner through it and not a spray. I often run a quart of dextron III in my fuel tank to clean up injector systems. Real cleaners can work as well, just my method.

As stated, run the Mercruiser listed plug or exact equivalent from auto parts. Not plugs matched to road vehicles.

I run SMART Tabs and like them. They slow the boat a little in early acceleration since they lift the stern. I get on plane earlier with them though, no matter how loaded. My boat is lighter than yours, so your results will be a bit different.

Rick

 

[SeaDooSam]

The boat does have a 21pinch prop on it. I'll see about getting a 19 or 17 tomorrow. I also changed the plugs today. Boat starts a lot easier now. However the old plugs weren't in terrible condition. Definitely needed to be changed though

IMO a 21 pitch is too high for a 4.3l. See if you can find a local prop shop that will let you try before you buy. Although some stingrays could work with 21p, the chaparral hulls are not designed for speed. They have a deeper v and need more bite to get it out of the water. therefore need smaller prop pitch.

 

[achris]

IMO a 21 pitch is too high for a 4.3l. ..

Without knowing the drive ratio you can't say this. My previous 4.3 had a 1.84:1 drive ratio (factory supplied) and swung a 21" Merc Vengeance prop at 4900rpm....

Chris.......

 

[Rick Stephens]

Mine also has a 1.84 ratio drive. I run a four blade 21 pitch, could almost certainly swing a 23 pitch three blade prop.

 

[JohnBChargrave]

How can I tell what the drive ratio is on the boat? I found a shop that sells a 14 1/4 x 19 for 125$. So probably gonna go pick that up. But have seen Afew stainless on CL. Not sure about buying a used prop tho. Due to rehubbing?

 

[SeaDooSam]

I stand corrected, but isn't 4900 rpm a bit high?

 

[achris]

How can I tell what the drive ratio is on the boat? I found a shop that sells a 14 1/4 x 19 for 125$. So probably gonna go pick that up. But have seen Afew stainless on CL. Not sure about buying a used prop tho. Due to rehubbing?

Most props now have the 'flo-torq II' hubs, so that makes life a lot easier. If the prop has a rubber hub, move on, nothing to see.... Most of the props I have are ones I've bought off ebay.

I stand corrected, but isn't 4900 rpm a bit high?

If you're running at wide open for days on end, yes. But for normal cruising, 4900 is fine. The engines good to around 6000rpm, it's just the cam profile that determines that the maximum power is produced at 4600rpm, so the spec is 200rpm either side. The difference in driveability of my boat between a prop that spins at 4500 and 4900 is night and day. The vast majority of my running is at between 2800rpm and 4000, so 'light loading' the engines has many advantages, less wear, boat speed is easier to hold especially going up and down long 10' swells and I can load up the boat a bit (scuba tanks, people fish, beer ) without pushing the engine into an overload condition... And with the rubbish fuels we have these days, you definitely don't want to be overloading engines (detonation)....

Chris........

 

[Rick Stephens]

How can I tell what the drive ratio is on the boat? I found a shop that sells a 14 1/4 x 19 for 125$. So probably gonna go pick that up. But have seen Afew stainless on CL. Not sure about buying a used prop tho. Due to rehubbing?

Ratio on Mercruiser outdrives is stamped on the side below the upper filler plug. Unfortunately that stamp is often under the wrap around sticker.