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Makotosun

['78 SR500] Stator fixed, spark, not running.

  • 19stuberd
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Hi everyone! I posted some time ago reporting that my bike had no spark, and as some of you identified, the source coil did in fact need to be rewound. I sent it off to Rex's Speed Shop in England and they used their specialty equipment to rebuild my entire stator to be brand new at the cost of around $600 and now I have it back. I reinstalled the stator and flywheel and kicked the bike and sure enough it fired right up! I went to the gas station to fuel up, got my gas, and then I took it back out onto the street. A few blocks later the bike started to backfire like I was in the Vietnam war which I thought sounded great until I lost ignition entirely. Cue me having to tow my bike home at just after midnight. 

Upon arriving at home I firstly realized I had a stripped plug hole, but I used a back tap and fixed that issue to cut a long story short. Now I see that I have a very consistent spark and that my new stator is reading correct values at all points, and yet when I go to kick the bike I am still getting nothing but loud backfires. This sounds to me like it may be an issue of ignition timing, possibly stemming from the fact that I just arbitrarily screwed the stator plate back onto the bike wherever felt right. I wanted to come here to verify that this may be the case, MOST IMPORTANTLY asking if the stator plate position alone is enough to cause the engine to not run at all or if someone might suspect something else is wrong. This is also complicated because the bike ran wonderfully for a good while both at idle on multiple occasions and then the entire way to the gas station.

If anyone is more familiar with these bikes and knows what might be wrong and what I could do, please let me know. Luckily I work for a racing team and so I have access to a timing light, so I will likely try to check it myself (even though I cannot make the engine run right now, please advise about that). I again very badly want to be riding this bike as the weather is beautiful right now and any help I can get I will gladly take. Thanks everyone, I hope to hear from you soon!

Daniel
 
28 May 2024 15:45 #1

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Try putting in a new spark plug.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
28 May 2024 15:49 #2

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Ok without reading it all i'd put money on "It's shorn off the flywheel key". I'll post a pic [that i just posted a minute ago for someone else] showing how i hold it & tighten it.
photos.app.goo.gl/ZSNSV7ypGZ98s4UF9
Last edit: 29 May 2024 00:08 by RT325.
29 May 2024 00:08 #3

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  • 19stuberd
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Replied by 19stuberd on topic ['78 SR500] Stator fixed, spark, not running.

Interesting idea. Does this method of yours prevent the flywheel key from shearing or is it just a convenient way to pull the flywheel without having to shove a ton of string in the engine? Any thoughts on how the key might have shorn? 
29 May 2024 02:55 #4

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Well, they must be tightened very tight because they're a heavy flywheel with a lot of inertia & believe me i've seen every second hand yamaha 360 i've bought with a ruined crank taper from under tightening & crank damaged from a broken key then spun flywheel.
I've never broken a crank key myself i might add & you can see why.
Ok call it 'over the top tightening' but the main thing is to hold it solid.
I guess rope down the plug hole trick comes up solid but not 'as solid' as a direct hold on the flywheel.
But check that key please so you can tell me i'm wrong. I can take it--i hope!!
Worked in the yamaha shop from "62, well we became yamaha shortly after.
You asked why i came to that conclusion.The erratic running then stopping then backfiring on kicking all points to that.
I'm more than happy to be wrong & sure wouldn't be the first time.
But if it 'is that' then at least it's an easy fix & cost almost nothing.
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Last edit: 29 May 2024 04:18 by RT325.
29 May 2024 04:07 #5

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Bump--any updates please.
09 Jun 2024 16:31 #6

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