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Mercury 70HP Blue Line plug welded up need help with diagnostics

It runs fine that way. The factory started doing it after a bunch of burnt pistons. Idle is unchanged.

Be sure to remove and plug that dopey water line running to the fuel pump from the adapter section (right side) below the block. This sends all of the cooling water through the P H and it needs it!

Jeff
 
Ok, great. I checked the water line. In the 700 motor that I just bought, the water line comes out of the top of the block which is different from the other 700 that I have, where the water line comes out of the top of the fuel pump. the motor is made in Australia. Maybe they wised up about it. The compression is good, and it runs fine. I'll change the jet and put in a new impeller in the water pump before I take it out. and new premium fuel!
 
fastjeff said:
It runs fine that way. The factory started doing it after a bunch of burnt pistons. Idle is unchanged.

Be sure to remove and plug that dopey water line running to the fuel pump from the adapter section (right side) below the block. This sends all of the cooling water through the P H and it needs it!

Jeff
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A 2mm drill bit is 78.7 thou, (we have metric in Oz) and the spare parts mob recommend just drilling the old jet with the drill bit held in the fingers. btw, I am keen to know what the best fuel oil mix is for triples? thanks for everything, Pad
 
fastjeff said:
Finally, the top carb should be running a 78 (or so) jet and the lower one a 72 (or so). This too was a running change to save the top pistons.

QUOTE] Jeff, can you help me identify the jet you are referring to? Is it the fuel bowl vent jet (mine is marked .072) The main jet running fuel up into the main air intake is currently reading .086 thanks pad
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The main FUEL jet is in that plug that screws into the bottom of the carb (1/2 inch socket).

The water line to plug goes to the fuel pump from the lower right side of the motor, just below the epower head.

Jeff
 
A 2mm drill bit is 78.7 thou, (we have metric in Oz) and the spare parts mob recommend just drilling the old jet with the drill bit held in the fingers.
Click to expand...
You never drill a jet as it will leave swirl marks in brass and can actually make it run leaner To enlarge jet it has to be reamed to size with reamer kitlike in link below. The water cooling for fuel pump needs to be left in place as its to prevent vapor locking, all it needed is a restriction in the line which the inside if a yellow butt splice connector works good. As for jetting you will need to go by the serial # and carb series as different series carbs use different jetting, With todays fuels raising the mains in both carbs .002 will not hurt it and I have not found any Merc TSB's on jetting top carb with larger jetting. The #1 reason for top cylinder failing is cooling followed by fuel and timing, the aluminum plug you had is from ignition problem. Overheating and lean out gauld the cylinder/piston and rarely produce throw off as you seen in spark plug hole.
http://carcraftstore.com/jetreamerkit.aspx
 
fastjeff said:
The main FUEL jet is in that plug that screws into the bottom of the carb (1/2 inch socket).

The water line to plug goes to the fuel pump from the lower right side of the motor, just below the epower head.

Jeff
Click to expand...
are you saying that the main jet in the top carb must be larger? mine reads .086 which is way above .078
 
faztbullet said:
You never drill a jet as it will leave swirl marks in brass and can actually make it run leaner To enlarge jet it has to be reamed to size with reamer kitlike in link below. The water cooling for fuel pump needs to be left in place as its to prevent vapor locking, all it needed is a restriction in the line which the inside if a yellow butt splice connector works good. As for jetting you will need to go by the serial # and carb series as different series carbs use different jetting, With todays fuels raising the mains in both carbs .002 will not hurt it and I have not found any Merc TSB's on jetting top carb with larger jetting. The #1 reason for top cylinder failing is cooling followed by fuel and timing, the aluminum plug you had is from ignition problem. Overheating and lean out gauld the cylinder/piston and rarely produce throw off as you seen in spark plug hole.
http://carcraftstore.com/jetreamerkit.aspx
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thanks this is helpful. I gather from what you are saying, the ignition problem is a result of a timing problem. ON that motor I had the shop replace stator and cdi. Could they have not set the timing properly? can you give me any good tips as to the best way of setting the timing on CDI? What is 'lean out'? many thanks
 
Could they have not set the timing properly?
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Anythings possible in shops today....
can you give me any good tips as to the best way of setting the timing on CDI?
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Always check the timing pointer setting with a dial indicator, set MAX timing at cranking speed with all plugs removed, reduce MAX timing 2° from factory setting.
What is 'lean out'?
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"Lean out" means less fuel in fuel/air mixture going to the engine cylinders. This is caused by: dirty/partially clogged high speed jets,float levels set to high,fuel pump not being about to keep bowls on carbs full. On the triples the #2 cylinder scavenges off upper/lower carbs so if you see a lean pattern on #1 cylinder #2 will also show a slight lean running also.
I gather from what you are saying, the ignition problem is a result of a timing problem.
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Thats correct but it could also be a bad switchbox(bias circuit), trigger or incorrect timing setting. When I used to race we kept advancing the timimg till we saw bubbling on the piston deflector and the reduced timing a couple of degrees, this would meltdown a engine if ran at mid-range but we on idled and ran WOT only.
 
HI, what's the best way to determine how deep to sit the motor in the water. Where should the water line come to on the leg? My boat currently has a wooden packer which is lifting it about an inch and a half off the transom. cheers and thanks
 
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