Erratic spark

[pontoon chief]

I am working on a 115tlrb 2 stroke motor.It has a hard starting problem and will not idle for beans.
I decarboned the motor using Powertune and changed the fuel filters etc,and still the problems persist.
Using a timing light I checked for consistent spark and was quite surprised when both plugs on the left side of the motor were not firing.I then changed all 4 plugs and restarted the motor.The same rough start and the same rough idle were present.I again used the timing light and found that the plugs that were not firing were now firing,however the plugs on the right were not firing.
Anybody else ever have this occur,and if so what was the cause?

 

[rodbolt]

Re: Erratic spark

give up the timing light and use a DVA meter on the ign coil primaries.
its a lot better and way more informative.
check the iputs to the CDI from the charge coils and pulser coils and then the output to the coil primay. use an analog meter and the needle will show any iregularities.

 

[pontoon chief]

Re: Erratic spark

Thanks Rodbolt.

 

[pontoon chief]

Re: Erratic spark

Rodbolt,
I tested the pulser coils,the 1-3 lead was 4.6,spec is 2.5
2-4 is 3.6,spec is again 2.5 these are done cranking.
Charge coil low speed is 160.which is spec,however the high speed charge coil was 48.5 and the spec is 45.
The CDI output was 100,and spec is 125.
Any idea's

 

[Ray Neudecker]

Re: Erratic spark

My personal feeling is that you will find a carb adjustment or fuel restriction causing the problem. You might want to check all the grounds for the electronics for insurance and go to the fuel system after doing a compression or leakdown test.
Those readings look close enough to belive the system will fire correctly.
rodbolt may have a different opinion and will certainly say so if he does.

 

[pontoon chief]

Re: Erratic spark

Thanks Ray,I will give that a shot.

 

[rodbolt]

Re: Erratic spark

I am with Ray, your voltage numbers are generally higher than spec and remember spec is plus or minus 20%. the 100V output,if cranking, may be due to a battery or cable issue causing slow cranking speed.
the ign coils can usually supply a spark with primary voltages as low as 6ov peak.
that engine uses a very simple striaght fwd ADI ign system. to let it beat you to death.
rent or make a spark tester, they are not hard to make. test that the system can arc a 7/16th gap at cranking speed with the plugs out and in.
if it can look at the carbs, particularly the idle fuel jets and circuits. we dont have much problem with idle air circuits.
the design of those carbs actually determine the air to fuel ratio.
the only thing the mixture screws determine is how much of the A/F ratio bypasses the closed throttle shutter at idle.
the actual ratio is determined by the size of the pilot fuel jet and piolet air jet not the screw.
doesnt take much trash at all to seriously mess up low speed operation.

rerun the CDI output test with the white wire and the pink wire removed from the terminals but if you allow the motor to start ya cannot shut it off.
thats where the spark tester come in handy.

 

[bosavy]

Re: Erratic spark

i have the same situation with mine spark is good. Is the jets in the bottom under the screww or is a disassambly process

 

[Ray Neudecker]

Re: Erratic spark

The jets are either the bottom outside item in some models or lacated behind the bolt in that position. !2 mm wrench or socket needed to remove, plus a screwdriver if behind the bolt as in later models.
If you are having a problem it is best to tear down the carbs completly, clean and rebuild. Be sure and replace the bowl gaskets.

 

[bosavy]

Re: Erratic spark

thanks