85 BlackMax 150 Revs when I pull covers.

[1BadTitan]

When I take the clamshell hoods off, the motor climbs about 200-300 rpms. Whats that about? Is something wrong here?

 

[mercurymang]

Re: 85 BlackMax 150 Revs when I pull covers.

Either your clamshell is interfering mechanically with the throttle linkage somehow or you have added insulation (or something) that is restricting air flow causing the motor to run slower. Does it run decently at WOT with the cover on?

 

[1BadTitan]

Re: 85 BlackMax 150 Revs when I pull covers.

The only insulation is the foam stuff that is glued to the inside of the hoods from the OEM. It isnt interfering with anything mechanical, I double checked that first.

 

[Faztbullet]

Re: 85 BlackMax 150 Revs when I pull covers.

If it does this in the water what is happening is lower cowling seals are bad and exhaust is creeping into cowling. Engines dont like their own fumes

 

[1BadTitan]

Re: 85 BlackMax 150 Revs when I pull covers.

That sounds exactly like what could be happening. When I'm running it at lower speeds, its eventually chokes out. Its hard to restart unless I open the covers. That could be why it loads up and stalls at idle while I'm in the water too. Especially since I can set teh idle at 500 rpms on the trailer and it will run perfect on the muffs. but as soon as I get on the water, I get all these symptoms. I cant find a part number for cowling seals, nor can I locate these seals. Could I fix this by simply venting the cowling with louvered covers.

 

[glenn property of pam]

Re: 85 BlackMax 150 Revs when I pull covers.

That sounds exactly like what could be happening. When I'm running it at lower speeds, its eventually chokes out. Its hard to restart unless I open the covers. That could be why it loads up and stalls at idle while I'm in the water too. Especially since I can set teh idle at 500 rpms on the trailer and it will run perfect on the muffs. but as soon as I get on the water, I get all these symptoms. I cant find a part number for cowling seals, nor can I locate these seals. Could I fix this by simply venting the cowling with louvered covers.

you do not set tick over at 500 rpm on a trailer you set that in water or you set the rpm higher as there is no exhaust back pressure. The main 2 reasons for the cowling messing with the engine is either exhaust smoke from a bad gasket under the power head or a bad plug lead jumping to the metal bracket used to hold the hod on. If you lift the cowling 1/2" and the engine stops messing about then its probably the exhaust gasket.

 

[1BadTitan]

Re: 85 BlackMax 150 Revs when I pull covers.

There is smoke that escapes when I open the hoods up....What if I try to run with the hoods off? They are the clam shell style that swing open from the sides.

 

[Chris1956]

Re: 85 BlackMax 150 Revs when I pull covers.

Locate the seam where the powerhead bolts to the midsection. Start her up on muffs with the cowling off and see if you can detect any exhaust at that seam. If so, you will need to pull the lower unit and then the powerhead and replace the gasket. On second thought, see if the powerhead mounting nuts are tight.

 

[1BadTitan]

Re: 85 BlackMax 150 Revs when I pull covers.

Locate the seam where the powerhead bolts to the midsection. Start her up on muffs with the cowling off and see if you can detect any exhaust at that seam. If so, you will need to pull the lower unit and then the powerhead and replace the gasket. On second thought, see if the powerhead mounting nuts are tight.

I'll check it out when I get home. If thats the issue, would it run just fine with the hoods off? I'm gonna try it today

 

[1BadTitan]

Re: 85 BlackMax 150 Revs when I pull covers.

Either your clamshell is interfering mechanically with the throttle linkage somehow or you have added insulation (or something) that is restricting air flow causing the motor to run slower. Does it run decently at WOT with the cover on?

It does run good at WOT. But last outing, I was at WOT for about 10mins straight and out of nowhere, it started bogging and losing rpms... Ultimatly stalling it.

 

[Faztbullet]

Re: 85 BlackMax 150 Revs when I pull covers.

you do not set tick over at 500 rpm on a trailer you set that in water

In the water idle RPM should be 550-650 in gear and about 750-950 out of gear, on a hose this will be about 1100 rpm.

I cant find a part number for cowling seals, nor can I locate these seals.

The part # is 707482 and its item # 28... you will have to google it to find one as they are NLA.
Mercury, Mercruiser, Force, etc. - DRIVE SHAFT HOUSING AND EXHAUST TUBE - 150 H.P. XR-2 MARATHON MAGNUM (V-6) (1978-1985 COMBINED BOOK)

I was at WOT for about 10mins straight and out of nowhere, it started bogging and losing rpms... Ultimatly stalling it.

Hope engine didnt ingest any water spray while running.. check your compression and change fuel pump diaphram if ok.

 

[1BadTitan]

Re: 85 BlackMax 150 Revs when I pull covers.

I put her in the water last night, adjusted the idle screw all the way out. Idling at 750, she frigging ripped!!!! It hasnt run that good since I bought it. I ran without cowling. It must be the base gasket. I will be replacing that asap. Is there any danger to running without the cowling, aside from water intrusion? Just wondering, because she ran awesome.