Exciter voltage

The spark on this Honda is not snappy like you would see on an Evinrude. So, the spark is probably good.

You should squeeze the fuel bulb until it is hard. That should fill the carb bowls and if they do not overflow, all is good. If they do overflow, then one or more of the carb float valves are stuck open.
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When you go to start the motor, the fast idle lever will activate the choke, if you push it up all the way to the shifter handle. You should see the choke activate. If the throttle cable was hooked up, the throttle would also be advanced. So, since it is not, you will need to have someone advance throttle about 1/4 to 1/3 throttle. That may be your only issue at this point. If the throttle is not advanced you will flood the motor if you have activated the choke (whether manually pulling out the choke or activating it from the shifter.

Once it starts, you can deactivate the choke and slowly bring the throttle back to idle, as the motor warms up.

Mike

Thank you Mike. I really appreciate your help.

Primer bulb pumps to hard and no overflow so that is good.

I have been advancing throttle and using manual and remote lever choke in various combinations.

We rebuilt the main engine's carbs and installed them. No start. Not even a cough.

We tested fuel pump output and it was fine at 6 pounds.

We tested compression at the beginning of this journey and they are good. I can't remember the value just now.

We used an ignition timing light pointed at the camshaft pulley. The light for each cylinder lit up the appropriate number next to the T on the cylinder head. I think that means the timing is good.

The timing light did not fire when the ignition wire was plugged into the spark plug, but would fire if the cable was unplugged.

I am beginning to suspect that we have weak spark, possibly from a weak exciter coil.

Do you think that ordering a power coil from a newer model Honda with the same flywheel will be a good replacement for the exciter coil? The specs call for a 30590-ZV7-003 exciter. I researched the flywheel 31110-ZV7-750ZA, that flywheel is used on newer models so I ordered the power coil 30595-ZW2-F01 from those newer models.

Cheers

It might be ok with the flywheel (if it mounts the same), but the cdi that is used with the newer exciter is different. So, I am not sure how compatible the new exciter will be with the older cdi.

I have found that on some Honda motors, a timing light does not work. I do not remember if the 25 is one of those models. Lately, I have been using a hand held tachometer that can be used as a kv meter that I just have to hold close to the plug wire to check the voltage at the plug wire.

I would recommend that you check the open circuit output of the new exciter, before you connect it to the cdi. If it is a lot higher output than the one you have now, I would be very apprehensive before I connect to the cdi. It could blow the cdi.

Mike

Good idea. I am only getting 35 volts open circuit from the current exciter but suspect that that is too low. Specs call for resistance to be 272-368 ohms. I am getting about 200 ohms.

How would I know what the open circuit voltage should be or what is too high.

I would by the correct exciter but cannot find it anywhere. Honda does not have any. I even talked to Honda Japan.

Looked up the compression numbers. All 3 cylinders are about 150 psi when cranking at warm engine with battery turning at about 150 rpm. Manual says 212 psi cranking at 500 rpm. Not sure how they expect us to crank at 500 rpm unless the engine is running

Hey Mike. Turns out that we did not remove or check the pilot screw when redoing the carbs.

The pilot screw has a large metal tab on it which prevents turning it more than a out 45 degrees.

Do pilot screw need cleaning or reseating? How do we do that?

Thanks again for you great help.

If you use the ratio of 200 to the 272 - 368 as maybe a relative potential of increase in voltage. 272/200 = 36% increase.
368/200 = 84% increase. I am not sure how valid those assumptions are but at least that gives some relative difference.

Ideally, it is good to remove them. However, if you have replaced the jet sets, they are normally the issue with poor idle.
You can check rest of the idle path, without removing the screws by removing the jet set and sticking the straw from a can of brake kleen or wd40 up into the hole that the jet set and its o ring sit in. Then observing the small pin holes at the top of the front of the carburetor barrel when you spray the liquid into the hole. If there is a good spray out of all of the pin holes, then your idle and intermediate circuits are probably good.

I have found that even if the idle circuits are plugged, the engine will start and run (although poorly) with just activating the choke and advancing the throttle. That assumes that the main jet is not plugged and the float valve is functioning properly.

If all your cylinders have the same compression (within 10%), timing marks are good and valve clearances are good, then odds are pretty good that the internal engine is ok.....although, that is not always a guarantee. It has always worked out for me.....so far.

Mike

Thanks Mike.

The engine is running now. Thanks for your help.

I believe the issue was that the regulator was not providing DC to the CDI unit. The rectifier inside the regulator was not working which I suspected based on the diode tests in the manual; however what I read online was that the regulator had no impact on the CDI. The service manual certainly did not mention the regulator as a possible cause of no start.

I suspect that with these engines, the regulator fails and lets the charge coil pump high voltage into the CDI and battery which then destroys the CDI.

We did buy a new exciter/power coil which came brand new with a resistance of 7 ohms and produced 25 volts on crank. It made no difference to starting over the old exciter coil that had 200 ohms and put out 35 volts on crank.

That's weird....many, if not most, of those motors have no charging system at all. They come with none of those components. That's why it's universally known that the charge coil, rectifier and battery have no connection to the magneto ignition system. Or does it?

I guess anything is possible.

Glad you finally got it going.

So I have been looking at the schematics again and I think I might have been wrong. There really is no direct connection from the regulator to the CDI.

Probably the replacement coil did the trick.

Jen said:

So I have been looking at the schematics again and I think I might have been wrong. There really is no direct connection from the regulator to the CDI.

Probably the replacement coil did the trick.

Click to expand...

Hi Jen, I have the same engine which won't start. Did the exciter coil replacement gave you better spark. Mine seem to be weak. My exciter coil gives me a ohm reading of 180.