Logo

Mercury 500 Thunderbolt Help

BennesV

New member
Hi, I'm relatively new to boating just bought an old runabout with a Mercury 500 Thunderbolt, was running beautifully on muffs until hitting the water, have Mercontrol and idle up was on for about 10 minutes pulled down all the way idles ok, noticed when shifting into forward the idle up lever came up about a quarter of the way with it, didn't take much notice just pushed it back again, when shifting further down to accelerate the engine stalls, starts up straight away but keepa doing that when accelerating. Pulled it out came home had a look around and found what looks like a vacuum or vent hose just sitting there, its located close to the water outlet hole and not sure where it shouls connect to and could this have been causing my issue? See photo of similar hose. Had a service with timing ans carbs etc done not long ago. Thanks any help would be appreciated. IMG_20200129_234234.jpg
 
Everything in the picture is black.----Therfor hard to see what is going on there.---How big is this loose hose ?----I believe there is an oil return hose from bottom bearing to upper bearing.--------Take it back to the shop that did the service work.
 
Last edited:
That might be the oil suck out hose. Older Mercs had them just dump the oil into the water--shame! Newer ones have one cylinder suck out the excess oil from another.

Look for a small barbed fitting hiding in there.

Jeff
 
That looks like the tell tale hose, it goes from a fitting in the back of the block between the spark plugs or on the top of the block, to the tell tale outlet in the lower cowl (Nrs. 11-15 in diagram) If this hose isn't connected water is possibly flooding the plugs and causing your problems.
850-lowercowl.jpg
 
Thanks, oil suck out hose makes sense, cleaned out oil in the bottom when I got it, maybe disconnected for a reason, where I live they're really strict on the environment, already government talk to ban 2 strokes on our waters. Any idea what might have caused the other issues then?
Thanks
 
You " cleaned out oil in the bottom " ----Are you referring to the gearcase ?-----The oil recirc hose on the block has nothing to do with the gear oil in the gearcase.----How big is this loose hose ??----There are also some cylinder balance hoses that must be installed.------Get this checked out by your local friendly shop.
 
Last edited:
You " cleaned out oil in the bottom " ----Are you referring to the gearcase ?-----The oil recirc hose on the block has nothing to do with the gear oil in the gearcase.----How big is this loose hose ??----There are also some cylinder balance hoses that must be installed.------Get this checked out by your local friendly shop.


Just a bit of oil residue in the bottom of the bottom cowl assy below the starter motor area, there's no leaks coming from the engine. I will open my cover and take a better photo, the photo used above is not from my engine just one I googled
 
There should be no oil collecting in the lower cowling.----How big is the loose hose or do you want to keep it a secret ??
 
Here's some pics of the mystery hose, also pulled the spark plugs opinion if you think it has been serviced recently, just before I bought it 2 weeks ago?

Thanks
 
Last edited:
If there's a plastic pan below the carbs to catch fuel look for a channel that the hose might be attached to, those plugs are used up and should be replaced. The crap on them shows that the oil previously used was inferior - my recommendation is a synthetic oil at 50:1, also synthetic in the gearcase.
 
Back
Top