1978 Mercruiser 470/170hp backfires

[Westdevil]

I have a 1978 Mercruiser 470/170hp motor on my Bayliner boat. Timing is set according to the book and runs good when out of the water but backfires when it's in the water and giving it gas. I turned timing and it runs good but when it's hot it is hard to start. When motor is cool, starts easy. Any suggestions? the motor has points the motor runs cool.is there any thing i need to un hook before i check the timing.i don,t have a manual book i check plugs wires for right fireing order. ok

 

[j cat]

I have a 1978 Mercruiser 470/170hp motor on my Bayliner boat. Timing is set according to the book and runs good when out of the water but backfires when it's in the water and giving it gas. I turned timing and it runs good but when it's hot it is hard to start. When motor is cool, starts easy. Any suggestions? the motor has points the motor runs cool.is there any thing i need to un hook before i check the timing.i don,t have a manual book i check plugs wires for right fireing order. ok

I bought my 470 mercrusier 1986 now - today... I changed the ignition points to pertronix ignition module ..the other issue you have to change the lower unit water pump....engine runs hot...
my engine runs good .. lower gasoline usage ..I use 93 octane with marine gas additive.
WELLCRAFT 20 FOOT SUNCRUISER......1978 .. RUNS GREAT..
I took out the voltage regulator and put in a 12volt generator ...

 

[achris]

I have a 1978 Mercruiser 470/170hp motor .... Any suggestions?

Plenty, see below.. ;-)

the motor has points the motor runs cool.is there any thing i need to un hook before i check the timing.i don,t have a manual book i check plugs wires for right fireing order. ok

Nothing to unhook for setting the timing, but a few things to check.

Make sure that the engine is actually at TDC when the indicator on the balancer is at the 0 mark. Check to ensure you have a solid strong spark at the spark plugs.
Once you've set the timing, accelerate the engine and make sure the timing is advancing. If it's not, the weights in the distributor may be seized.
If the ignition system is good, it may be that the carb needs a pull-down and clean out.

Chris......

 

[nola mike]

I have a 1978 Mercruiser 470/170hp motor on my Bayliner boat. Timing is set according to the book and runs good when out of the water but backfires when it's in the water and giving it gas. I turned timing and it runs good but when it's hot it is hard to start. When motor is cool, starts easy. Any suggestions? the motor has points the motor runs cool.is there any thing i need to un hook before i check the timing.i don,t have a manual book i check plugs wires for right fireing order. ok

Don't "turn timing". Set dwell, set timing to 6'. Then check your fuel. Have you changed fuel filters? Do you have a fuel/water separator? How old is the fuel? If all good, next move is a carb rebuild. No need for 93 octane. Electronic ignition won't make your engine run any more (fill in the blank). It will allow you to not mess with points.