Choppy power band
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Check your plug bud. If it’s black and sooty then yes…
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Today's quiz: is this the spark plug of a rich, lean or normal mixture? It has only been in use for about 40 miles, but I drove vigorously.
The shiny spot on the far side is where I touched and got the oily soot on my finger. So I'd say it is on the rich side. -
Looks weak to me, if anything…
It would be black if it was rich, in my tentatively humble opinion (because I have made some gaffs lately)
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Don’t know why I didn’t notice it before, but have you put the magnetic speedometer reader (
) switch back in its place? Or moved it completely away?
I think you may still be having troubles with it. It’s right around the rpm’s you’re having trouble at…Read mrShadi’s post (deristrict Yamaha dt 125 r 1997) on his fun with deristricting!…
I’m probably wrong but you never know…
Or did it sputter before you deristricted it?… -
I figured that it was plenty sooty enough considering how short I have driven with it, but I am not certain. Hence asking. Tomorrow I plan to experiment with jetting. I got a new set of main jets.
Yes, it did sputter before but I thought that was part of the restricting. Both my old DT's were unrestricted ('87 and '90) from start. Though I do remember a failure once where the YPVS wouldn't switch to high which felt a lot like this one when it was restricted, minus the sputtering. So I guess it should not have done that?
I don't think the reed switch is a problem, because it reads velocity and cuts at something like 80 km/h, not the rpms. And mine does 110 km/h happily once it gets into the upper power band. Although the front wheel needs truing so I dare not quite find out top speed yet.
My new tachometer cable got stuck at the customs so it will take a while before I know what rpms we are talking about.
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Yeah, I know it cuts in at 60 or so. I just thought it might’ve been doing a ‘strange one’
I’d check the mangled pilot first, replace that. If you have access to a sonic cleaning bath I’d strip down and clean the whole carb. Have you removed and cleaned the emulsion tube? (thing needle sits in) There’s a lot you can do to a carb, all the tiny passages through it with carb cleaner spray or airhose. Even the gasket on the slide body. If the main jet is clear, I’d personally look at the rest of the carb first…
You’ll get there. If I managed to iron out my bike anyone can!
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I should report that the last weeks the sputtering has improved significantly without me doing much of anything.
Well, I did twist the air screw a bit, and my new main jets arrived and lie here on the table, and I am waiting for a Mikuni rebuild kit - but in the meantime the bike decided to behave better. It is weird.
It still hesitates a bit around 7000 before coming into force until 9500, and I can probably improve that with a bit of tweaking, but it is largely acceptable as is. And actually it feels like a bit more than 23 hp, comparing the seat-of-the-pants feel with my old '87 and '90 DT's. They would hesitate at 5000, then come alive at 6000 and lose breath at 8500.
I can't imagine that a 2003 bike that seems unchanged in design since 1989 would have anything like modern self-learning ECU tricks, right? I just assume the CDI box would be rather primitive. Right? Right...?
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This post is deleted!
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@Hark_Ptooie no sensors around to learn from...
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@Mr-Shadi had the rev limiter cutting in at around 6000rpm in all the gears at one point. I know it’s not what you want to hear but it’s got to be worth checking, no?
Just try reconnecting it to see if it revs freely in the lower gears. If it’s the same then At least you can cross it off completely. Added bonus is I’ll shut up about the read switch 🤩 -
The engine pulls freely to redline on all gears. It was just around 7000 where it sputtered and coughed. Still does, but far less.
If there are no sensors, then the only remaining reason why it would run better now than before would be that I filled up with new gas. I suppose the old stuff had been sitting in the tank for a long time when I bought the bike...
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Could there be a chance that it’s affecting it partially? It’s not that big of a job to check and cross it off completely. Remember, the added bonus is I’ll shut up
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The reed switch is thickly wrapped in electrical tape and put far away from everything, as far as I know.
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Just for closure I want to add that the sputtering went away by itself after a hundred kilometers or so.
I'm guessing old grime in the vaporizer that recent use dissolved. It had been standing in a garage for quite some time when I bought it.
Bike now goes like my old 1990 did, only even more cheerful what with the Athena expansion chamber.
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