Mercruiser 260 timing

[chris0061]

working on a built 350 for my boat. they rebuilt it with a 78 block, flat top pistons, mild cam aftermarket heads, edlbrock intake. when I got the engine it had a quadrojet 4 barrel carb on it, ran fine. I switched out the carb for a edlbrock and when I checked the timing it was bout 2 inches above the numbers on the cover. when I tried to bring it down to 8 degrees it would die. I took the boat out and seemed to run fine but something kept tugging at me. so last weekend I did my comprehension test on it, new plugs, oil change and talked the timing again. I adjusted it towards the 8 degree and adjusted the idle as I got closer and it would want to die. I got it to 8 degrees Idling a smooth 600 rpm and seems to turn over better and still revs fine and sounds good. I haven't taken it to the river yet to test on load but does any of this make sense to you all? the man said it was built to about 330 hp if that adds to anything. Is there anything I should check to make sure I have this timing right. it does have the thunder bolt ignition on it. thanks in advance.

 

[chris0061]

sorry bout the miss spelled words dang autocorrect

 

[Scott Danforth]

What cam is in the motor? Is it installed straight up, or advanced?

stock timing is no longer what you work with BECAUSE YOUR MOTOR US NO LONGER STOCK.

Compression ratio, cam, and head material will determine what your new base timing is

What exactly was done to your motor, what ignition, and what is the advance curve?

 

[chris0061]

the cam # is 1103 heads are 152123 both from summit. I have no idea how the cam was installed nor do I know the curve is, the ignition is the thunderbolt IV

 

[chris0061]

I do remember the seller saying it was built for low end power.

 

[chris0061]

would I be good do you think if I set it at 36 degree total timming????

 

[Scott Danforth]

That cam is ok in a car, however way to agressive in a boat. Too much duration for wet exhaust

270 degrees of duration is max with wet exhaust or you suffer reversion

you need a marine cam.

My guess is your suffering reversion at idle, which is why its dying unless you give it enough throttle or advance the timing enough for it to keep running while its sucking water from the exhaust

The heads are 72cc heads with 165cc runners. kind of sloppy on the combustion chamber and the runners are ok, not stellar

 

[achris]

Timing curve could be anything. Need to know what's on the ignition module. It'll look like "V8-xx",

Chris......

 

[chris0061]

if that was the case would the plugs give a tell, tell sign? what would you recommend for a solution then?

 

[achris]

Plug read tells you the fuel mixture, not the timing. Post what's stamped into the module and I can post up a timing curve for you. Mercruiser 260 had about 4 different modules that could have been used, each programmed differently. Either get out a timing light, tacho and a sheet of graph paper, or read the numbers off the module...

Chris.....

 

[chris0061]

its V8 24 on the module

 

[achris]

its V8 24 on the module

 

[Scott Danforth]

if that was the case would the plugs give a tell, tell sign? what would you recommend for a solution then?

pull the motor, change the cam. the cam you have has 288 degrees of duration.

you need a marine cam with less than 270 degrees of duration.

 

[wellcraft-classic210]

Tagging along here -- Interesting read -- good catch on the cam duration affecting the tuning !!!!