broken exhaust shutter valve

[fsamie1]

My 1989 5.0L mercruiser is not running good after 29 years. Cannot get more than 3000 rpm at wide open throttle. Changed filter/water separator and spark plug and those did not do it. Interesting thing is that it runs good, no misfire, no noise, no smoke. Idles just fine. I do not think it is fuel pump, carburetor, coil, rotor, and other simple stuff. I checked secondary jets and they were fine. removed the exhaust and noticed one shutter valve is not there. looked into y-pipe with endscope camera and did not see it. couple of questions:

1. could this be the cause for engine problem? can broken shutter valve block the exhaust so engine cannot go over 3000 rpm?
2. Can I remove the y-pipe with engine in the boat?

Thanks ​

 

[alldodge]

can broken shutter valve block the exhaust so engine cannot go over 3000 rpm?

Yes, if it was restricting the exhaust flow, but should also be running rich, bbut you said the piece could not be found.

Can I remove the y-pipe with engine in the boat?

No, just no way to get at the bolts, and then also to get it out. Remove the drive and look thru the exhaust boot

It could be you just have a tired motor. Check compression

 

[kenny nunez]

Another place to look is where the exhaust goes into the drive. With the drive raised use the endoscope to look in that area also. Also the shutter may be lodged in the drive. Just as AD said a restriction in the exhaust can cause a problem as well as a tired engine.
If you have a Quadrajet take a close look at the secondary linkage. The choke linkage can restrict the secondary butterfly from opening if it has become rusted or binding. Have you tried running the boat with the flame arrestor off, this will show if the secondary system is working. Is the flame arrestor clean ?
Is the timing advancing from the base setting? What about the carburetor inlet filter and the fuel pressure ? Try using a 6 gallon outboard tank to the fuel inlet at the filter to by pass the tank.

 

[Scott Danforth]

many times with the drive off for annual inspection, you will find shutters. another place to look is the lower unit itself. you sometimes find shutter pieces when R&R'ing a raw water pump

 

[fsamie1]

Another place to look is where the exhaust goes into the drive. With the drive raised use the endoscope to look in that area also. Also the shutter may be lodged in the drive. Just as AD said a restriction in the exhaust can cause a problem as well as a tired engine.
If you have a Quadrajet take a close look at the secondary linkage. The choke linkage can restrict the secondary butterfly from opening if it has become rusted or binding. Have you tried running the boat with the flame arrestor off, this will show if the secondary system is working. Is the flame arrestor clean ?
Is the timing advancing from the base setting? What about the carburetor inlet filter and the fuel pressure ? Try using a 6 gallon outboard tank to the fuel inlet at the filter to by pass the tank.

What about the carburetor inlet filter?, Thanks. I think that is it. I did not even know it is there and my neighbor also told me about it. I removed it and it is clogged up pretty good. It has not been changed since 1989, 29 years old and service manual calls changing it every year.​

 

[Scott Danforth]

what other maintenance hasnt been done in 29 years?

 

[fsamie1]

what other maintenance hasnt been done in 29 years?

Good question:

1. plugs changed 3 times
2. filter/water separator 2 times
3. bellows once
4. transom bearing once
5. distributor, rotor, coil once
6. engine oil, lower unit oil, u-joints once a year or once every two years
7. prop once
8. starter once, this year
9. always used fuel conditioner for winter
10. boat can do 45 mph, but always run 20-30 mph, 3500-4000 rpm
11. bilge pump once
12. drive shaft coupling plate once

Did I forget something?:lol: I may have overdone some stuff.:lol: Never seen a mechanic. Always ran good even with this little dirty filter ran good and I fished out of it many times.

 

[Scott Danforth]

You are supposed to be pulling the drive every year to check alignment, gimbal and bellows. The lack of alignment check is what took out your coupler

gear oil gets changed every year

Prop shaft splines get greased every year

Fuel filters get changed out every year

Engine oil and filters every 50 hours or once a year

Belts checked every year, replaced every 5 years

Rubber hoses checked every year, replaced every 15

Bellows checked every year, replaced as soon as you see any cracking or checking (about every 5 years)

u-joints greased every year

 

[stang32]

You are supposed to be pulling the drive every year to check alignment, gimbal and bellows. The lack of alignment check is what took out your coupler

gear oil gets changed every year

Prop shaft splines get greased every year

Fuel filters get changed out every year

Engine oil and filters every 50 hours or once a year

Belts checked every year, replaced every 5 years

Rubber hoses checked every year, replaced every 15

Bellows checked every year, replaced as soon as you see any cracking or checking (about every 5 years)

u-joints greased every year

thats a great guide scott

 

[Scott Danforth]

its basically paraphrasing the chart in the manual(s)