300ex- no spark - Honda TRX Forum
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post #1 of 23 Old 06-04-2019, 04:25 PM Thread Starter
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300ex- no spark

Hey guys I have a 2001 300ex that lost spark, or mostly lost spark. When turning over, I get a couple sparks, and then nothing. Come back later, maybe get a few sparks again, then nothing. The plug had only been used for maybe 5-6 rides, was new last year, but tried a new plug and no help. Replaced cdi box with 2 other boxes, one used and one brand new, still no help. Tried 2 other coils, one used and one brand new, still no help. Tried another pulse generator and stator (both used)- no help. All 3 coils measure properly per the service manual. Both pulse generators and both stators measure properly per the service manual. Took measurements right at the cdi plugs to also test wiring. I'm getting 12V on blue/white wire right at the cdi, the 12V supply is lost when either the kill switch or key switch is open, so I believe both switches are working. Green wire is grounding properly when not in reverse, and opens when in reverse. I even disconnected the wire at the reverse switch and grounded it to be sure. I'm about out of things to test or replace at this point. Any further ideas? There is just not much to the ignition circuit, so this is getting frustrating.
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post #2 of 23 Old 06-04-2019, 04:32 PM Thread Starter
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Oh, and I took the original cdi and the used one I bought, and tested in a 97 300ex, both work fine
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post #3 of 23 Old 06-04-2019, 07:45 PM
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You have a seemingly impossible problem that most likely has a simple solution. 93 to 03 were all wired the same, so if you have one that you can swap parts to, swap all the parts (one at a time)from the non running one to the running one until the running one will not run - replace the part that caused the running one not to run - if you have swapped all the parts except the stator, install a new stator in the non running one.

There is no blue/white wire at the CDI box - you should have 12 volts on the black white wire when the both the key switch and the handlebar kill switch are in the on or run position.

The green white wire at the CDI box should have continuity to ground - the dark green wire is ground - test at various locations - green/white to frame, engine, green wire a the coil. Disconnect the gray wire from the reverse light switch.

One test I'm pretty sure you have not done is to check the AC voltage on the yellow/white wire at the CDI unit - unplug the stator from the wiring harness (2 plugs one with 3 yellow wires and one with a yellow/white, blue/yellow and a green white. The green/white should have continuity to ground - the blue/yellow should have continuity to ground, but a higher resistance than the g/w to ground - the yellow/white should have continuity to the three yellow wires, but the resistance will vary depending on which yellow wire is checked - none of the yellow or yellow/white wires should have continuity to ground - if there is continuity to ground on any of the yellow wires, the stator needs replaced.

If you have 12 volts, good ground and a known good CDI unit, the problem is either the pulse generator, stator, coil, spark plug cap, spark plug or flywheel out of time.

Hope this helps
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post #4 of 23 Old 06-05-2019, 02:13 AM Thread Starter
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First off bud, thanks for the reply. Yes, I have done many of the checks you indicated-

I meant to say blk/white wire, not blue/white. Unplug the 2 wire connector at the cdi, have 12V on that plug- 12V supply on blk/white is lost when key switch or kill switch is off. Gray wire on that connector has continuity to ground when not in reverse, opens when in reverse. This is opposite of what the honda service manual says, but I think the manual is wrong. The Clymer manual states it how I am reading, which I believe to be correct. Disconnect the gray wire from the reverse switch and it will not turn over at all. Makes sense, since the 97 will not turn over at all in reverse.

Green/white wire has continuity to ground. Checked at battery, ground connection near coil, and the engine itself.

Yellow/white wire measures 3VAC while turning the engine over. Disconnected the 3 wire plug at the stator with yellow/white, blue/yellow and a green white wires. Checked continuity of all 3 wires to the 4 wire plug at the cdi. All have continuity.

Yellow/white wire has around 1 ohm resistance to all 3 yellow wires. All 3 yellow wires measure about 1 ohm to each other. All 3 yellow wire open to ground on the stator side

Blue/yellow wire measures 320 ohms to ground at the 4 pin cdi connector. Same measurement as the pulse generator that I took out. I get between 300-400mV peak on this wire while cranking engine. About the same at the original pulse generator was putting out

The machine did give me a couple issues in the fall, where it would just randomly die every once in a while and be hard to start up again. I thought that went away, but maybe not.

While troubleshooting this, at one point I whacked the stator cover a couple times with a dead blow hammer. I suddenly got good spark, started and ran the machine for a few minutes, then it died. Checked spark, and it was lost again. Was able to duplicate this a couple times, and this is what lead me to swap out the stator and pulse generator. It didn't fix the issue, and I have not been able to duplicate getting that spark again. Its back to a spark or 2 then nothing, come back in a little while, spark or 2, then nothing.

I'm an electronics guy, and know my way around in that field, and like you my initial thought is something easy and dumb is going on. I'm starting to lose that optimism now though....
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post #5 of 23 Old 06-05-2019, 01:22 PM
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OK - now we are getting somewhere

Then gray to the reverse switch turns on the reverse light when in reverse - it also activates the 'reverse inhibitor' box to limit speed in reverse - the switch is normally open (the neutral switch and the reverse switch are the same part number 35600-HA0-003) - the engine will start in gear (both forward and reverse as long as the LH lever is pulled in and the lever switch closes.

The reverse inhibitor box also interacts with the neutral light circuit to prevent the electric starter from spinning when not in neutral.

Disconnect the gray wire at the reverse switch and see what you get - if not the fix, then swap reverse inhibitor boxes with the running machine and see what you get - just because the reverse light is not on does not mean all is working right. The reverse inhibitor is responsible for turning on the light. A failure of the unit can prevent spark when the reverse light is on or off and it may turn the light on, but not limit reverse speed. Simple test - ground the gray wire and it should turn on the reverse light even when the neutral light is on. The yel/wht wire going to the CDI box from the alternator is basically a 'tach' wire - it triggers the ignition to limit speed to about 2500 RPM when in reverse.

I got a degree in electronics in the 70's which helps troubleshooting electrical systems. I was already a mechanic when I went into electronics. I was not happy working on TV's and radios - in 1975 I got laid off from General Electric and started working on motorcycles, cars, tractors, lawn mowers; whatever needed to be fixed while I was drawing unemployment. In 1978 I rented a gas station and started doing mechanical work full time. In 1981 I gave up the gas station and opened my own motorcycle repair shop. I have had franchises and walked away from them. My forte was repair (not sales), so I concentrated on maintenance and repair. Today I am trying to figure out how to retire in seven years when I am 75 so I can spend time riding my dirt bike and finish restoring my 72 Triumph 650 Bonneville and my 75 Suzuki RE5 Rotary.

Let me know what you figure out - I'm curious as to what ends up being the problem. Do you have a service manual and a wiring diagram?
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post #6 of 23 Old 06-06-2019, 12:33 AM Thread Starter
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I disconnected the gray wire right at the switch and reverse light comes on, neutral light goes out. Will not turn over either with or without the clutch lever engaged. This sounds correct at the 97 will not turn over while in reverse, with or without the clutch engaged. I am pretty sure that neutral switch is normally closed, and opens when you engage reverse. It says the opposite in the Honda service manual, but I think it’s wrong. I have found a couple mistakes in the manual. I also have a clymer which states the reverse switch the way I said.

Got my electronics degree in 2000. I spent a lot of time in the industrial electronics repair field. Mainly AC and DC drives/motor speed controls. Field service and bench repair, start ups, etc. Lots of cool applications, but I was basically married to the job, and had to be ready to respond to emergency breakdowns. Just got burnt out after awhile. Now it’s all hobby, or fixing junk that friends and family bring to me
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post #7 of 23 Old 06-06-2019, 12:34 AM Thread Starter
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Here is a pic from Honda manual about the reverse switch
Attached Images
File Type: jpeg B60AD87D-E2C8-4DBD-A122-8118866E8041_1559781258408.jpeg (908.0 KB, 3 views)
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post #8 of 23 Old 06-06-2019, 12:35 AM Thread Starter
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And here is the clymer with I believe to be correct
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File Type: jpeg 9CB313B4-CBD9-406B-9987-08789C9F94E1_1559781310343.jpeg (835.9 KB, 3 views)
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post #9 of 23 Old 06-06-2019, 12:36 AM Thread Starter
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Ignition diagram that I have been using to trouble shoot
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File Type: jpeg 3D257837-96CE-466B-B7ED-ABC6C2850E80_1559781371164.jpeg (1,014.6 KB, 4 views)
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post #10 of 23 Old 06-06-2019, 04:56 PM
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What Clymer manual are you using? It is wrong for your model and Clymer manuals have more errors than the Honda manuals. I have corrected both from time to time.

The Clymer manual I have is M465-3 (revision 3)

Attached to this post is the ignition circuit and wiring diagram from the Honda service manual and in the next post is the ignition and wiring diagrams from the Clymer manual #456-3
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File Type: png Honda TRX300EX 1993-2001 Ignition System.png (703.6 KB, 2 views)
File Type: png Honda TRX300EX 1993-2000 Wiring Diagram.png (592.2 KB, 3 views)
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