1989 mercruiser 3.7 L hard cold starting

[gs49]

My mercruiser is hard to start when cold.I have to crank it about a minute or so before it runs I also get occasional backfire until it kicks in and runs Initially I was not getting a spark at the coil. I removed the grey tachometer wire and it rolls over and runs all day at speed and at trolling.I can shut it down and it will fire up without issue. I replaced the plugs,plug wires,coil points,rotor and condenser. Could this be related to the point gap. I have not replaced the distributor cap. Any help or ideas would be greatly appreciated
Regards gs49

 

[poconojoe]

Maybe a problem with the choke? I'm having a similar problem with my 4.3, but no backfiring. I'm going to check the choke butterfly functionality in carb. I too have given mine a good tune-up (due to a no spark situation). Cap, rotor, wires, coil, distributor sensor. But initial startup only when cold is a struggle. I have to crank for several minutes. After that, it runs great and starts immediately. That's why I'm thinking it's the choke. Gonna get out there today and investigate.

 

[wahlejim]

Someone with more knowledge on this may correct me, but I think I read somewhere that a faulty tachometer will mess with your timing. The fact that you can pull the tach wire and it fixes the problem would lead me in that direction.

 

[AnthraxBird]

A faulty tach could do that. It could ground out the coil.

 

[Scott Danforth]

My mercruiser is hard to start when cold.I have to crank it about a minute or so before it runs I also get occasional backfire until it kicks in and runs Initially I was not getting a spark at the coil. I removed the grey tachometer wire and it rolls over and runs all day at speed and at trolling.I can shut it down and it will fire up without issue. I replaced the plugs,plug wires,coil points,rotor and condenser. Could this be related to the point gap. I have not replaced the distributor cap. Any help or ideas would be greatly appreciated
Regards gs49

specifically go thru the steps you do when starting a cold motor.

list every step, no mater how mundane you think it is.

 

[gs49]

I turn on the battery switch, run the blower for 3 to 4 minutes engage the quicksilver shifter without engaging the gearing and roll the engine over. If I were to isolate the tach by disconnecing all wires to it would that eliminate the potential timing problem? Regards Gary aka GS49

 

[Scott Danforth]

your not fully priming the motor and setting the choke

here is how you should be starting a cold motor with a carburetor

with boat in water or on muffs

1. turn on battery switch
2. turn on blower
3. in throttle only, one to two full pumps of throttle (all the way to the stop). the first one sets the choke and gives it some fuel to prime the motor, the second one may be needed - each motor is different
4. then back the throttle to about 1/3
5. then turn the key
6. when the motor fires, back off throttle to about 1500 RPM for a few minutes, then drop back to neutral.

 

[Lou C]

Try starting it as Scott describes above. If that works, then you know it was just your starting procedure. Those of us who learned to drive in the 60s and 70s when all cars had carbs intuitively know this lol.
If not then you should verify proper choke function:
with a cold engine, remove the nut retaining the flame arrestor, remove the arrestor and then advance the throttle all the way forward (shift system dis-engaged) the choke plate (top flap in the carb) should close nearly all the way or all the way.

When the engine starts, there is a vacuum operated linkage that will pull the choke open a fraction of an inch (typically 1/8 to 1/4") to give the engine enough air to keep running but that is also the reason why after priming the engine you must advance the throttle 1/3 or so forward, it needs that fast idle to keep running.

As the engine warms up the choke should gradually open all the way. If it does not close it may just need a good cleaning of the choke blade and shaft & surrounding area in the opening of the top of the carb and linkage. These attract dirt and can get sticky. If it still doesn't close you may need to replace the thermostatic spring that closes it. If it does not open up you have to find out why, some chokes are opened by a spring mounted to the intake manifold above an exhaust crossover (Rochester style) others are electrically heated (Holley and Edelbrock/Weber style). In the case of the former, dirt on the choke and linkage can stop it from opening, or a cold running engine that never heats the intake up enough (on my Q jet it would have to get to about 120 on the top of the manifold to open), in the case of the latter (electric) a lack of 12V to the positive terminal on the choke cap or a defective choke coil.