Help with timing?

[Dakoda boater]

Ok i have a 1980 70hp 3 cyl Merc that is rough running with no ability to idle and back fires some at higher RPM's. I've started with new plugs, new gas, rebuild carbs now whats next... The video should support the rough running engine followed by some back firing...

 

[CharlieB]

Re: Help with timing?

Check fuel pump output to the carbs, you want to see a strong pulsed flow. Check the fuel pump vacuum hose to the crankcase, it should be dry, fuel here is often a sign of a pinhole in the diaphragm, flooding the cyl that connects to it.

If no one has messed with the carb linkage and timing lever it should be fine, however, it never hurts to ensure all adjustments are set following the steps spelled out in the service manual.

Check here to see if your manual is still available for download.

http://forums.iboats.com/showthread.php?t=309079

 

[ajgraz]

Re: Help with timing?

http://johnsoldmercurysite.com/whitepapers/manuals/3-CYLINDER MODELS.pdf

 

[Dakoda boater]

Re: Help with timing?

CharlieB, thanks that will give me something to do tomorrow. I do have a manual on order.

Ajgraz, Thanks for the link!!

 

[Dakoda boater]

Re: Help with timing?

Took the fuel pump vacuum lines off and drained out about a teaspoon of water out of these two lines, is this just condensation and a normal operating condition? No gas found in either line. So timing issue then??

 

[Dakoda boater]

Re: Help with timing?

Hey Charlie, you state

Check the fuel pump vacuum hose to the crankcase, it should be dry, fuel here is often a sign of a pinhole in the diaphragm, flooding the cyl that connects to it.

So does the vacuum lines connect to a cyl or the crank case?

 

[ajgraz]

Re: Help with timing?

^^^

On my 1978 70hp there are two fuel lines (one in, one out) and two other lines which water runs through the triangle pump housing. What do the water lines do? Cool the fuel? Modulate the diaphragm motion somehow? I dunno. But water does run through them.

 

[Dakoda boater]

Re: Help with timing?

Ok so those two hoses circulate water from the water jacket, cool thanks.

How about the three small lines that are interconnected under the carbs?

Shouldn't you be boating? Lol..