(SOLVED) Electric issue but can anyone make sense of this? (with video)

[DayBreakJim]

So my latest wheeler is a 04 Yamaha Bruin 350. It had all the wires cut from the stator and a few others and no wiring harnesses. The previous owner had them all twisted together and the bike neutral light would come on it would start (hard to start) but then would idle fine. It would die when you gave it gas so I soldered all the wires together and went on inspecting assuming it was a carb issue. Later after the carb was cleaned and adjusted I got this (see video). The bike would want to die anytime you gave it gas and there would be this horrible knocking sound but only when you gave it gas. I was worried it was the rod bearing and electrical still messed up somehow.

Upon further inspection of the wires coming from the stator there was a W/R wired to R and a R wired to W/R. I switched them so they matched per the service manual (W/R to W/R and R to R) and the bike started right up, idled and revved out fine and the knocking noise disappeared. This was the problem the whole time. It was just really hard to tell bc the oem wires coming from the stator were so brown and dirty I could barely make out which was which.

Where the hell did that knocking noise go? and what was causing it?? Just racking my brain trying to figure out what it was so I know for next time but I can't make sense of it... Really thought it was the rod bearing but it didn't make the noise at idle so I was questioning it...Luckily I kept searching!!

 

 

 

 

[Mech]

In a big bear those colours go to the cdi, so I'd assume it was firing a hell of an advanced..

Good work spotting it.

[davefrombc]

Knocking  noise was most likely detonation from the  over advanced condition as  Mech mentioned.

[Mech]

Hi there Dave.  How are things with you ?  Good summer ? Heatwave didn't knock you out ?

[davefrombc]

Heat wave and drought has been brutal with no end in sight yet, but I've been surviving it.  At least I  haven't  had to put in the 2 hours every week bouncing on my riding  lawn mower  instead of the quad.  We haven't had a total of an inch of rain since the beginning of June, and  August is normally our driest month, so there likely won't be any mowing  needed until  next spring. Down side is  the bush is  so dry and there's so many fires  going riding isn't  a very good idea.  Here's a map  of the fire situation in BC now. For perspective, the province of BC  is 3.5  times larger than New Zealand.

 

[DayBreakJim]

15 hours ago, davefrombc said:

Knocking  noise was most likely detonation from the  over advanced condition as  Mech mentioned.

 

15 hours ago, Mech said:

In a big bear those colours go to the cdi, so I'd assume it was firing a hell of an advanced..

Good work spotting it.

Wow I've never come across detonation! So what is actually happening there? Is it improper timing of ignition causing multiple combustions at the wrong time or what? Just trying to understand so I have an ear for it in the future...

[davefrombc]

Detonation is  just that. The fuel  mixture exploding in the cylinder instead of a rapid (VERY RAPID)  burning  in the cylinder.  It can be  caused by ignition too far advanced or by  use of fuel  too  low a grade for the compression ratio /  cylinder pressures.   When  everything is right,  the fuel  actually burns rapidly as the piston descends on the power stroke.  When detonation because of over advance causing cylinder pressure to  increase  far over normal  or fuel grade is too low the fuel  instantly  burns (detonates) rather than burning continuously during the power stroke.  The rattling  noises you hear with many diesels when idling are actually mini- detonations with the  high  compression  and very lean diesel  mixture.

[DayBreakJim]

Wow that's so interesting I could have sworn the knocking was mechanical metal on metal but I guess that was the sound of detonation occurring! So interesting thanks for clearing that up guys! Already I'm learning so much here. Do you know is there a quick way to tell the difference between rod knock and detonation? Or is it just by ear?

[Mech]

Good explanation Dave.

It's a bit hard to differentiate, and detonation can cause rod knock anyway. If you have a bad rod bearing it might make noise without the detonation though when the engine is under a load. If you have a manual shift bike you can test the rod bearings to a degree by putting the bike into gear with the brakes on hard, and keep your toe holding the shift lever down till you've given the engine enough revs to lock up the centrifugal clutch, then gently let your toe up till the shift clutch starts to engage and put a load on the engine. If the rod bearing is bad you might hear a knocking sound. 

[davefrombc]

Rod knock is usually, but not always, a duller sound than detonation ping.  It is easier to tell in a multi-cylinder vehicle like  car than  in single or twin  cylinder ones in ATVs.

  A loose rod or wrist pin can knock either under load, when backing off or  if fairly  bad even when  idling  but normally detonation only occurs under load.    When it is happening in  car,  it is  often  described  as "marbles"  rattling around in the cylinders .

Detonation is hard on everything  and if not taken  care of by  backing off the timing advance a bit or by going to  higher grade fuel can result in holes hammered or burnt  into  the pistons.