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Old 08-24-2013, 04:33 PM   #31
dhallilama
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Quote:
Originally Posted by anotherguy View Post
Points are never an upgrade from CDI. Ever. Longer duration at lower energy means nothing regardless of RPM. Adequate at best.
definitely not an "upgrade"... but there's something to be said about simplicity :)

that being said, i've more than one old vehicle with points that make plenty of HP/torque through the RPM range. my daily driver went from magneto/points to electronic... back to magneto/points. i'm old and stubborn, though...
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Old 08-25-2013, 01:40 AM   #32
Twin-shocker
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Points are never an upgrade from CDI. Ever. Longer duration at lower energy means nothing regardless of RPM. Adequate at best.

A points system that works and is easy to repair if there are problems, seems to me to be a clear upgrade over a CDI system that doesnt work, and isnt that easy to repair?

In terms of ignition almost all modern bikes and cars are now using inductive, as the lean burn motors are designed to work using the longer duration spark provided by transistor triggered inductive.

2T motors which operate at very high rpm will work better with CDI, but the OP's relatively low revving DT will run perfectly with points system.
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Old 08-25-2013, 01:45 AM   #33
Twin-shocker
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Originally Posted by dhallilama View Post
definitely not an "upgrade"... but there's something to be said about simplicity :)

that being said, i've more than one old vehicle with points that make plenty of HP/torque through the RPM range. my daily driver went from magneto/points to electronic... back to magneto/points. i'm old and stubborn, though...

In some cases an inductive system will be superior to CDI, especially in the case of older 4T machinery, which might not take kindly to the very short spark duration provided by CDI systems.
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Old 08-25-2013, 09:06 AM   #34
Inane Cathode OP
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Well, got the new cdi for ac two stroke motors hooked up and got spark. Taped the whole thing together so it wouldnt fall off, hopped on for a spin down the block. Runs just as shitty as ever, now with heavy pinging at low RPM.

I don't know what to do at this point, I'm all out of ideas. I'll throw the new choke plunger i got in there, maybe it's floating open at high rpm or something but for god sake i've tried everything.

Next step is filing the entire ignition in the circular file bin and going to points. I'm sure it'll still run shitty then too, but at least it'll be one more fix to try.
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Old 08-25-2013, 09:25 AM   #35
dhallilama
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Well, got the new cdi for ac two stroke motors hooked up and got spark. Taped the whole thing together so it wouldnt fall off, hopped on for a spin down the block. Runs just as shitty as ever, now with heavy pinging at low RPM.

I don't know what to do at this point, I'm all out of ideas. I'll throw the new choke plunger i got in there, maybe it's floating open at high rpm or something but for god sake i've tried everything.

Next step is filing the entire ignition in the circular file bin and going to points. I'm sure it'll still run shitty then too, but at least it'll be one more fix to try.
man, i've been in this exact situation before... one step before throwing matches at it and walking away with burst of flame behind me.

200% sure of no air leaks?

crank seals good?

all wires to/from cdi good? (i throw an ohm meter on each wire and wriggle/bend it along the length of the wire... i've found wonky wires that way)

coil to plug wire good?

sorry, probably repeats of what's already been mentioned... hang in there man
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Old 08-25-2013, 09:54 AM   #36
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Its well worth carefully checking the CDI earth, and whether the motor is earthed to the frame properly (that really only applies if frame has been painted or powder coated). Had a Honda with bad earth last week, and as I was kicking bike over was getting an HT shock through the frame.

If you have fitted a CDI intended for another bike, you may well find its giving more advance, which will cause pinging at lower engine speeds. The timing light test will give a basic idea as to whether problems are linked to ignition or not, but if you can find someone with a scope, they should be able to tell you for sure if your issue is ignition related or not.
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Old 08-25-2013, 10:34 AM   #37
Inane Cathode OP
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New choke plunger, no change. Still won't rev out.

I've checked the ground on everything, there's no voltage drop anywhere and everything mounts cleanly. The problem isnt in the CDI, two different CDI acting exactly the same, it has to reside elsewhere. I still can't make heads or tails of what the timing light is saying. Its a little too advanced at idle, with RPM it doesnt change now (it wouldnt, cdi has no advance that i can tell) then at high rpm when it runs crappy it.

I don't know, i'm starting to think that maybe it just is supposed to run like it is. I've never even heard of a bike so resistant to fixing. Not a single thing i have done has made a lick of difference in how it runs wide open. It starts a little easier with the new CDI, and seems to be running hotter than it did when i first got it. I'll take a video of how it rides and post it, see what you guys think.
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Old 08-25-2013, 11:27 AM   #38
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Have you done a crankcase pressure check? Has the bike been standing for a long while, and if so have you tried a different carb? There is also the possibility of a badly blocked exhaust, but crankcase pressure test, and alternative carb should probably be tried first.
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Old 08-25-2013, 11:46 AM   #39
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not to get off topic, but which cdi are you using? the $10 ebay dealios or the treatland one with advance?
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Old 08-25-2013, 01:02 PM   #40
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not to get off topic, but which cdi are you using? the $10 ebay dealios or the treatland one with advance?
One of the better reviewed ebay ones. Seems like the spark is good quality, nice and blue and snappy. Old cdi was somewhat wheezy but obviously still good enough to run.

Crank case pressure is fine, just put brand new seals in it. I think i might try a new top end, i know it needs it (its pretty scrape-y looking through the intake).
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Old 08-25-2013, 01:33 PM   #41
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If you continue to just guess and throw money at it frustration is the only guarantee. Diagnose the problem and fix it.

Start electrically and once that's verified good move on to fueling.

He's got something with verifying the ground,especially with the shocking gas tank mentioned earlier. It's either a bad ground or an intermittent short to the chassis.

Slow down and approach it methodically. If you do not have a factory manual use a progressive process of elimination-by testing not replacement. The fact you've replaced the CDI and still have the same symptom tells me to check the wiring harness for a broken/chafed wire that only happens under extreme vibration. I have a big bore Yamaha I know how they shake at higher RPM.
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Old 08-25-2013, 01:52 PM   #42
Inane Cathode OP
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If you continue to just guess and throw money at it frustration is the only guarantee. Diagnose the problem and fix it.

Start electrically and once that's verified good move on to fueling.

He's got something with verifying the ground,especially with the shocking gas tank mentioned earlier. It's either a bad ground or an intermittent short to the chassis.

Slow down and approach it methodically. If you do not have a factory manual use a progressive process of elimination-by testing not replacement. The fact you've replaced the CDI and still have the same symptom tells me to check the wiring harness for a broken/chafed wire that only happens under extreme vibration. I have a big bore Yamaha I know how they shake at higher RPM.

You need to re-read the thread, the shocking gastank was the lighting coil wire shorting to the gas tank through a worried hole in the harness by the seat. I'm not guessing anything, there is no diagnosis that i have found that will tell me why this thing is acting this way. I'm trying to eliminate possible causes, and i'm just about out of reasons why it would be running like this. I have the factory manual covering early yamaha enduros and the specific 1975 dt400 factory service manual. I've tested everything i possibly can at this point.

There is no break in the harness, there is no dirty connection, the charging coil and pulser coil test perfectly fine by resistance and AC voltage output. Neither the stock CDI box or the replacement have any effect on running that i can tell. The coil tests perfect according to yamaha specs, it doesnt break down under heat, and it isnt leaking voltage. As far as i have been able to tell there isnt a problem with the bike, i've literally taken apart, cleaned, replaced, or checked every single related system to the engine besides putting a new piston in it.

It's entirely likely that it's just very down on power due to the top end being wasted (compression is 85-90, about 5500 feet here, doesnt seem too low) and expecting it to 'wind out'. Every video i can find people are short shifting these things (sounds like it at least) and they're not really revving out like i would figure.

I have the factory manual covering early yamaha enduros and the specific 1975 dt400 factory service manual.
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Old 08-25-2013, 02:09 PM   #43
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You do realize that thing only turns about 6 or 7,000 RPMs , right. It's not going to turn 10 or 11,000 RPMs like a 125 and it's got a flat power curve like a 4-stroke. Not much of an obvious powerband. And if you start getting snotty with people , no one will want to help you.
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Old 08-25-2013, 02:34 PM   #44
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ok, i have a 83 rm125 that refused to rev out, it crackled and broke up like crazy after 1/2 throttle. sometimes it would 'catch up' and scare the shit outta me - all of a sudden bingo full power. then crackle/surge again. everything checked out great. took the needle out and was checking the numbers on it with a loupe. noticed the needle was bent very slightly at the end. ... . new needle, runs like a champ.

a top end with low compression will still run ok at the top of the rev range.. usually they get hard to start/noisy and you know it's time for a bore/rings..

either way, it should rev cleanly through the entire rev range underload..


sometimes it's really hard to troubleshoot on the internet :) we've all been just as frustrated with an old bike that should run, but doesn't.
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Old 08-25-2013, 04:39 PM   #45
anotherguy
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Quote:
Originally Posted by Inane Cathode View Post
You need to re-read the thread, the shocking gastank was the lighting coil wire shorting to the gas tank through a worried hole in the harness by the seat. I'm not guessing anything, there is no diagnosis that i have found that will tell me why this thing is acting this way. I'm trying to eliminate possible causes, and i'm just about out of reasons why it would be running like this. I have the factory manual covering early yamaha enduros and the specific 1975 dt400 factory service manual. I've tested everything i possibly can at this point.

There is no break in the harness, there is no dirty connection, the charging coil and pulser coil test perfectly fine by resistance and AC voltage output. Neither the stock CDI box or the replacement have any effect on running that i can tell. The coil tests perfect according to yamaha specs, it doesnt break down under heat, and it isnt leaking voltage. As far as i have been able to tell there isnt a problem with the bike, i've literally taken apart, cleaned, replaced, or checked every single related system to the engine besides putting a new piston in it.

It's entirely likely that it's just very down on power due to the top end being wasted (compression is 85-90, about 5500 feet here, doesnt seem too low) and expecting it to 'wind out'. Every video i can find people are short shifting these things (sounds like it at least) and they're not really revving out like i would figure.

I have the factory manual covering early yamaha enduros and the specific 1975 dt400 factory service manual.

I gotta stop trying to help people.
Good luck.
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