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Discussion Starter · #1 · (Edited)
Ok guys, I haven't had this wheeler long. Its a 2000 300fw It's had this condition of not raving past about half throttle since I've had it.

I've rebuilt the whole top end, new piston, bored .020 over and new timing chain, rebuilt oem carb and adjusted valves.

It still doesn't rev past half throttle. Tried a know good carb off a good running bike, still won't rev.

It just starts breaking down and back firing.

Tested the stator, pickup and coil. All test good. Still need to test rectifier.
Bike charges at 14.5v

I've ordered a new cdi thinking that it's not advancing the timing. Should have it Monday.

I don't have another bike to borrow the CDI from because everyone else has a pre 96 bike and the CDIs are different.

Do you guy have any other thoughts or suggestions? I'm completely stumped.

Going to check for timing advance with a timing light today.
 

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You've done a lot of good things so far. One more thing you could investigate would be to see if air is leaking in anywhere between the carb and the cylinder head. While the engine is idling, spray starting fluid around the joints of the rubber boots and listen for any change in idle speed.
 

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I would guess from your description of what you did and taking in to consideration it was done right , the timing is off either from you not putting back right when you did the top end or the chain is slacked and should have been replaced
 

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Discussion Starter · #5 ·
I would guess from your description of what you did and taking in to consideration it was done right , the timing is off either from you not putting back right when you did the top end or the chain is slacked and should have been replaced
A new Honda timing chain was installed. It has been checked since reassembly and it is dead on.
I checked by setting the engine to TDC and confirming timing marks on cam gear with a bore scope. Also re affirmed with a timing light today.

The timing advances what seems to be appropriately, once the rpms increase it starts breaking down as soon as the two advance marks come into view. The two marks that look like this "II" as soon as I see those she starts breaking down.

I've tried with the air box lid off and even with the filter removed. Same condition exists.
Going to get a coil from a friend today to try out.

I checked for air leaks with acetylene and had no change. Though I will try carb cleaner to re affirm.

Is it possible the chain tensioner is allowing to much slack at higher rpm?
 

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When using the timing light, you say it starts breaking down once the two II marks come into view. Does the light itself start to break down then? If so, at least that would indicate your problem lies with ignition rather than fuel or something like that.
 

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Discussion Starter · #7 ·
When using the timing light, you say it starts breaking down once the two II marks come into view. Does the light itself start to break down then? If so, at least that would indicate your problem lies with ignition rather than fuel or something like that.
Absolutely, the light breaks down also. Good thinking!

That's what makes me think I'm not far off base digging into the ignition.
Though I'm beginning to have doubts the CDI is at fault.
I'm thinking ignition coil, pulser or maybe a diode.

The wiring harness on this bike is immaculate, so I doubt it's a wiring issue. I've tested all wiring I've had my hands on and all is well so far.

I feel ridiculously out of place working on this thing, I've always been into racing Cars and trucks and even built a few rock crawlers. Never had this kind of issue diagnosing a problem.
 

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Discussion Starter · #10 ·
Unscrew the spark plug cap off the wire and trim about 3/8 off the wire and screw it back down. I had an old YZ 250 do this very thing.
misterclean59 mentioned the most likely cause of your problem already... Right HERE.

Exhaust may be plugged up too... I'd take it apart and clean the muffler and spark arrestor out.
I actually tried this, it appears someone has done the same before me. There is also a stretched spot in the insulation on the plug wire.
The ignition coil I got from a friend earlier was from a big red... so didn't even bother trying it.

Going to order one and hopefully have it before the end of the week.
Also should add, I tried spraying carb cleaner around the intake and no change.

I'll keep this thread updated
 

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See what you have a for AC and DC volts using a good 25 dollar-ish multimeter measuring at the battery with the bike running. A bad voltage regulator / rectifier can send dirty, AC polluted, high or low voltages all over the bike that can confuse the CDI and burn out expensive things. And the AC certaintly isn't any good for the long term health of your DC loving battery.

This is a very simple, non invasive test that should cost you nothing if you can borrow a good multimeter. The cheapie meters struggle with measuring small amounts of alternating current. Hope for around 14.5 volts DC and less than .2 volts AC - two tenths of a volt . . . a tiny amount. Anything much different and I'd be worried about the regulator / rectifier.

Rick
 

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Discussion Starter · #12 · (Edited)
See what you have a for AC and DC volts using a good 25 dollar-ish multimeter measuring at the battery with the bike running. A bad voltage regulator / rectifier can send dirty, AC polluted, high or low voltages all over the bike that can confuse the CDI and burn out expensive things. And the AC certaintly isn't any good for the long term health of your DC loving battery.

This is a very simple, non invasive test that should cost you nothing if you can borrow a good multimeter. The cheapie meters struggle with measuring small amounts of alternating current. Hope for around 14.5 volts DC and less than .2 volts AC - two tenths of a volt . . . a tiny amount. Anything much different and I'd be worried about the regulator / rectifier.

Rick
Took these at idle, hard to hold probes take pictures and push the throttle

This is My backup meter I just got back from calibration, I only use it for low voltage.
 

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That is a very good meter and acceptable values for AC and DC power. Your reg/rec is not the problem. Sorry . . .

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk
 

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Discussion Starter · #14 ·
Just a quick update.
I received the New CDI yesterday and installed it this afternoon, the bike does seem to actually run slightly better. Though that could all be in my head. And the issue still exists.

I did also order a new OEM coil and pickup that I should be receiving Thursday and hopefully will have installed Friday afternoon, hopefully these two parts will resolve my issue..

I will update this thread with the results. :happy2:
 

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Discussion Starter · #15 ·
Okay guys, so I got the new coil and pickup today. Installed the new coil and there is definitely a change, though still popping in the higher RPMs.
So I moved on to getting the side cover off and installing the new pickup, I did however notice when I removed the wire from the old pickup it came off with no effort. When I slide the connector back on I can feel movement between it and the terminal. Same on the new pickup so I lightly crimped the connector for a firmer fit.

Also, in the manual it shows the wire running through the slot on the side of the pickup, the one I removed wasn't installed this was as the wire is much to short to do so...

Anybody else that has had their left cover off remember if yours was installed the same?
 

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Discussion Starter · #17 ·
I said I would update, so the results are she is all well again.

Installed a new Honda pickup coil, what I did notice was someone at some point had put engine restore in this thing...

Finished putting everything back together this afternoon and it revs without a hitch, she runs and goes like a dream. Well, for the short couple laps I took around my house. It's raining pretty hard..

So I think some minor carb tuning and she will be 100%.

Thank you everyone for the help and support!
 
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