1987 mercury force 85 hp does not want start and backfiring

[Pan84]

Hi everybody. I bought my first boat with 85 hp mercury force outboard, it was sit about one year. I try start motor after cleaning carburettors and dont start, only made 2 time backfire, and fuel cam out from top and bottom carburettors (of the back side), it is should by like that? After this i take fuel pump diaphragm out, on it there were cracks. Now I wait new diaphragm and seal for fuel pump. What else i have to check? im new on it. I just change spark plugs and all fuel hoses. Where is my problem? diaphragm or wrong timing? and how check timing? One more question, motor should start without carburettors cover?

Sorry for my English i am Russian
Thank

 

[JB]

Re: 1987 mercury force 85 hp does not want start and backfiring

Hello, Pan.

Welcome to iboats.

Was the backfire a loud BANG!! from the exhaust, or a CHUFF!! from the carburetors?

A loud BANG from the exhaust is from spark plugs firing at the wrong time. Either the wires are on the wrong plugs or the flywheel has rotated on the crankshaft due to a sheared key.

The carbutetor cover is merely a sound barrier. The motor should start well without it.

Good luck. Let us know what you find.

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

Yes it was very loud bang from exhaust. What is it "sheared key" and where is key?

 

[JB]

Re: 1987 mercury force 85 hp does not want start and backfiring

The position of the flywheel on the crankshaft is fixed by a "key" that fits into slots on both. If this key fails the flywheel can rotate away from the required position.

Since you have been doing several things to the engine it is also likely that spark plug wires are on the wrong plugs. Check this first.

You really need a Service Manual, Pan. Your lack of understanding of how the engine works makes it dangerous for you to work on it.

 

[roscoe]

Re: 1987 mercury force 85 hp does not want start and backfiring

With fuel leaking out from the back side of the carburettors, you need to replace the gasket between the carburettors and the intake manifold.

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

With fuel leaking out from the back side of the carburettors, you need to replace the gasket between the carburettors and the intake manifold.

Fuel cam from hole where sucks in air to cylinder, not gasket between intake and carb.

I have repair manual but nothing about firing order, i hope spark plug wires from first coil go to first cyl, second to second, third to third (i mean top to top, mid to mid and bottom) right?

Timing key it is lock on crankshaft? So timing not adjustable on these engine? if not i have fuel problem or mix wires

Auto mechanic is my job, but it is my first 2 cycle motor (except single cylinder) to work on it and i confuse a little

Thanks for any reply

 

[roscoe]

Re: 1987 mercury force 85 hp does not want start and backfiring

Correct, firing order is 1- top, 2 - middle, 3 - bottom.

Timing is adjustable.

First, the flywheel must be installed securely, on the crankshaft.
The key fits in the keyway to hold it in position. Then the nut is placed on the crankshaft to secure it.

If the key has "sheared", or the nut was not tight enough, the flywheel will not be in correct position.

Timing is adjusted with the timing linkage, which extends under the flywheel.

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

Ok, I try install new diaphragm and see what happens

 

[jerryjerry05]

Re: 1987 mercury force 85 hp does not want start and backfiring

Do a compression test first.Post the results.J

 

[JB]

Re: 1987 mercury force 85 hp does not want start and backfiring

How would a compression problem cause his symptoms, JJ??

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

i check compression today, top and bottom 115 psi, mid is 60 is it should start like these ?

 

[kend301]

Re: 1987 mercury force 85 hp does not want start and backfiring

Sounds like a stuck piston ring , broken piston ring or perhaps a burned piston in the middle cylinder , Try Spraying some penetrating oil (WD40 ) in the cylinder and spin the motor by hand several times then re test , if it is a stuck ring you may be able to free it up .

"How would a compression problem cause his symptoms, JJ??
If he has severe blow by or a burnt piston it will force compression past the rings and back out the intake port , if the cylinder still fires it will backfire then spit fuel . It should start but if his fuel pump diaphram is bad as he stated then he may not have enough fuel to fire 1 and 3 , or the blowback from 2 is messing flow up in the intake and killing all fuel mist to the cylinders .

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

May by head gasket bad? i will try change head gasket first and spray wd-40

 

[jerryjerry05]

Re: 1987 mercury force 85 hp does not want start and backfiring

SEE bad compression.

1ST rule!!!!!!!!!!!!!!!!! Do compression test FIRST!!!!!!!!!!!!!!!!!! Then all other tests follow!!!!!!!!!!!!!
It needs EVEN compression all cylinders to operate.It causes back pressure, backfiring,mis-firing etc.J

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

Now i broke cylinder head on five pieces and bend block when try take it of. I dont know if head gasket was bad

 

[kend301]

Re: 1987 mercury force 85 hp does not want start and backfiring

You need to stop where you are and post pictures of the damage !!! Or get a marine tech to look at it . We need to know if you broke the head cover and damaged the head or did you break the head and damage the block ? This will determine if you have a fixable problem or not . Also please let us know if the head bolts broke off or did they come out ?

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

Yes, 5 bolts broke in cylinder head it is why i broke head when try take it off. I already bought head and block in ebay, and all gaskets and seals from iboats. I thinks i can restore these engine. And it is still cheaply fix these one then get other one.

 

[kend301]

Re: 1987 mercury force 85 hp does not want start and backfiring

If you are going this far with it , get new pistons , rings and bearings .. you are in way deep , do it right !

 

[Pan84]

Re: 1987 mercury force 85 hp does not want start and backfiring

If you guys interest, it was stuck piston rings in cylinder 2 both rings, first and third cylinders only second rings.
Now i wait parts

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[kend301]

Re: 1987 mercury force 85 hp does not want start and backfiring

Good news is nothing looks burnt but you need to find out if there was a cause to the rings sticking , Is you motor a pre-mix fuel motor , if so you need to double up on the oil mix or add oil to fuel to double the oil mix for an oil injected for the break in period of rebuilt engine !!

Keep us posted as you can see you get alot of great advice here from many different members !