2003 Tohatsu 18Hp four stroke MFS1882

[rcb130]

Motor will start and idle for approx 2-3 min at which point it will either stumble and stall or go into a higher rpm and run quite smoothly. I have disassembled the carb and soaked it over night in carb cleaner, blown all passages out with compressed air, replaced all rubber gaskets with new. Timing is on the button. I have run a separate fuel line to the input side of the fuel filter to eliminate possibly sucking air at connector fitting. squeezing the bulb when the engine is about to die does nothing. What should I look for next?
Thanks
rcb130

 

[pvanv]

Test the ABS and wiring.

 

[rcb130]

ABS? Auto bystarter? This motor has extremely weak spark, has trouble jumping a 1/4" gap and is not a strong blue spark. Bad coil?

 

[pvanv]

Possibly. Test the electronics before just replacing expensive electrical parts. Full info is in the Factory service manual, available from any dealer (including several forum members... even me), but unfortunately not from iBoats.

 

[rcb130]

I have the factory manual, got it from a dealer in Solomans, Md. ABS coil is within factory spec. What else is there to check on it after cleaning carb passages and a visual on the "O" ring?

 

[rcb130]

Pulser coil measures 221 ohms, exciter coil measures 16.6. primary side of ignition coil measures .2. When I measure between the two high tension leads I get 18.2K ohms, Individual high tension lead and ground is 0. I do not think I should have a reading between the two high tension leads, should I?

 

[pvanv]

Ignition coil primary should not be that low. Re-check.

 

[rcb130]

The factory manual states .26-.35 between black and orange leads. This is the siamese coil. How should I be doing a resistance check on this coil? Please state lead hookups and expected readings.
Thanks

 

[pvanv]

I would expect a primary coil reading of at least .25 ohms, still .2 is not bad. inductors tend to have a wide tolerance. Your method is OK. Are you using an analog meter? If you have DVA capability, check what pulse voltage you have going into the coil from the CD. Odds are you still have a tiny spec of something floating around in the carb somewhere.

 

[rcb130]

how could crap in the carb cause a weak spark? Does not compute.

 

[Sea Rider]

Nothing to do with each other. Is it possible to try a used Ignition Coil and seee if engine springs back to life ? Electric components can fail when least expect to do so.

Happy Boating

 

[rcb130]

will have a substitute coil on Tuesday next week. will let you know if any change.

 

[pvanv]

how could crap in the carb cause a weak spark? Does not compute.

Probably isn't as weak a spark as you think; odds are still that a microscopic bit is sloshing around in a carb passage. If you have a coil that gets out of spec when warm, that could be a problem... and tricky to find, since it only fails hot.

 

[rcb130]

I have disassembled carb and put back into cleaning tank. I am soaking it for approx 16 hours at which point I will blow out with carb cleaner and the air blow dry and try again. The owner gave me the old coil he had replaced without my knowledge and it tests exactly the same as the coil on the boat. So, Paul, what you say may be the case of dirt in the carb still. Will post back later today hopefully. Thanks for all the help and advice. Do I check DVA with coil connected or not?

 

[rcb130]

Reinstalled carb and problem is still there. Starts and runs for a few minutes and stalls. restart and the same thing happens. On occasion it will pick up rpms as though it was running on one cylinder. The more I start it up the harder it gets to get the motor to start. Do I check DVA with coil connected or not? I will try to check pulser and exciter coil when they are hot.

 

[rcb130]

I reinstalled the owners original coil and the motor is off and running although it is difficult to start when cold. ABS checks out at 20 ohms.What should voltage be on ABS leads and how long should it be present? This was all caused by a defective brand new coil. Go figure. I have an occasional miss on no.1 cylinder. Any thoughts on this?

 

[pvanv]

Either you have a thermal issue with the ignition, or a too-rich carb condition, since the problem deteriorates the warmer it gets. Not unusual to run on 1 cyl as you get to the threshold where it barely runs. Check DVA to the ignition coil with everything connected; slip the probe into the silicone connector to make contact. Verify the plug color and wetness to help determine mixture and/or loss of spark.

 

[rcb130]

I am not getting 12 volts across the ABS leads. I am getting millivolts. How long should the 12 volts be present across the ABS leads? Could this be caused by a bad rectifier/regulator? I test the rectifier and I do not get the values the manual states. I have all the wiring exposed, checked the grounds behind the CD unit and they were all clean and tight. Advise on next step.
Thanks

 

[pvanv]

Hmm. Changing the ignition coil should not cause a loss of 12v power to the ABS. The ABS should be receiving power any time the motor is running. If the ABS is not activating, the motor should start fine, but run too rich after it warms up.

Your running symptoms don't agree with your electrical tests. You may have 2 problems at once... if the ABS is not extending within a couple of minutes (leaning out the low-speed circuit), yet the motor runs well when warm, that is indicative of both an ABS and carb issue.

Is the motor charging the battery? If not, is there AC going to the rectifier/regulator? The rectifier is a diode bridge, so testing with an analog (not digital) ohm meter should be definitive. If you apply 12v to the cool ABS, does the needle slowly extend?

At this point, I would test all the electrics, including the charging system and ABS, to determine whether you have either (or both) an ABS and carburetor issue.

 

[rcb130]

Paul,
I did not mean to allude that changing the coil affected the ABS. It just happened that I tested ABS voltage after changing the coil.I test the rectifier with a digital "true rms"multimeter and get flakey readings. I test with an analog and it tests ok. When I have the motor running and probe the yellow leads at the ABS I do not get 12 volts DC, but millivolts. Applying 12 volts to the ABS does cause the needle to slowly extend. Motor appears to be charging battery.