Boggs down

[Jrod22]

I have a 1986 45hp mariner. I can accelerate it in neutral 3,4,5k rpm and No issues. Once I put in gear it bogs down in 5-10 seconds. It will do it under load or out of the water with the muffs on. Once it begins to bog down I can shift into neutral and it purrs like a kitten. I’ve changed bulb and fuel pump…. No difference. Any ideas what could be the issue. Almost seems it’s link to when it’s in gear.

 

[racerone]

How did it run for you last season ?-----Post compression values.----Test for strong spark on all leads.----Replaced water pump impeller ?------Blockages in exhaust tuner ?

 

[QBhoy]

Carbs clean and float check, I’d suggest.

 

[airshot]

Yep...needs tests and results so we know where to start to try and help you out...compression results, spark plug pics, spark plug gap jump results, make and model will also help

 

[Jrod22]

Yep...needs tests and results so we know where to start to try and help you out...compression results, spark plug pics, spark plug gap jump results, make and model will also help

Compression is 119 to 121 on all 4 cylinders. New spark plugs were installed and they are gap less plugs. It’s a 1986 mariner 45 hp.

 

[tpenfield]

Revving in neutral means nothing.

I'd work the carburetor (cleaning) and see if that improves things.

 

[racerone]

Does spark jump a gap of 3/8" ( 1 cm ) on all leads ?----The type of sparkplug has nothing to do with that test.----Might be running on 3 of 4 cylinders.----Clean carburetors.-----Remove lower unit and check for carbon blocking the exhaust.

 

[jimmbo]

Keep revving it up like that in Neutral and soon you might not have to worry about it Bogging when in Gear, or even running for that matter...

 

[Chris1956]

So you said that it revs freely in neutral, but bogs in gear on the flusher? If so, that is unusual as the flusher unlike running in a barrel, provides no load on the engine.
Perhaps there is a load in the gearcase, like a bad propshaft bearing? Just a SWAG.

 

[Jrod22]

Carbs clean and float check, I’d suggest.

Carburetors have been completely rebuilt and problem still persists.

 

[Jrod22]

Does spark jump a gap of 3/8" ( 1 cm ) on all leads ?----The type of sparkplug has nothing to do with that test.----Might be running on 3 of 4 cylinders.----Clean carburetors.-----Remove lower unit and check for carbon blocking the exhaust.

Checking for carbon blocking is next on the list…. Thanks

 

[QBhoy]

Carburetors have been completely rebuilt and problem still persists.

Honestly. What you’ve described is typical float issues. Worth another look. If not..it’s a fuel starvation issue at least

 

[Jrod22]

Honestly. What you’ve described is typical float issues. Worth another look. If not..it’s a fuel starvation issue at least

The key issue is it only does it in forward. Neutral and reverse it can run forever….

In neutral 7 plus minutes no issue
In reverse 7 plus minutes no issues
In forward between a minute to a minute twenty it bogs down. Played around with it for about half an hour and these time test are very consistent.

I hot fuel into the carbs as it began to bogged out and it didn’t help any.

It has to do something when it gets engaged in forward is what it’s pointing to …. But what??

 

[Chris1956]

Are you running the same RPM in forward, neutral and reverse, or is RPM in forward higher?

 

[Jrod22]

Are you running the same RPM in forward, neutral and reverse, or is RPM in forward higher?

Same RPM’s

 

[Chris1956]

OK, more obscure issue, I would think. Time for some SWAGs.

Observe the shift linkage as you shift into forward. Does the shift arm rub any electricals? Does it pinch off a fuel line, or a vacuum line to the fuel pump?

 

[Jrod22]

OK, more obscure issue, I would think. Time for some SWAGs.

Observe the shift linkage as you shift into forward. Does the shift arm rub any electricals? Does it pinch off a fuel line, or a vacuum line to the fuel pump?

All that has been looked at. Had a mobil mechanic come in and troubleshoot it and everything is in order.

I’m wondering if it’s something with lower unit that causes extra load only in forward gear…. Almost like picking up fishing line on your prop. Again it boggs only in forward at 60-80 second after engaging fwd.

 

[racerone]

Your mobile mechanic should have no trouble figuring this out.-----But test run with another tank and hose.----Test run with a timing light one cylinder at a time out on the lake.----See if you are losing spark.-----Checked the flywheel key ?----Any sign of water on the plugs ?

 

[Chris1956]

I could not think of anything that would cause drag in the gearcase only in forward gear. In neutral all gears are turning. In fwd or reverse, all bearings and gears are turning. Nothing normally different about fwd.

But why not try a test?

Remove all spark plugs. Put her in forward and turn the flywheel with a wrench. Put her in neutral and turn flywheel, repeat for reverse. See if one is tougher than the others. I cannot imagine what it would be,