Installed new gauge!! Now 3rd cylinder isn't firing?? What?!

I installed my nice, new Acewell gauge over the weekend, and at the conclusion of the installation, my 3rd cylinder isn't firing. Just wanted to check here to see if there was a known quick fix/issue before commencing diagnostics. I'm 99.99% sure it's electrical, as I was cutting and splicing that bird's nest of wires in the headlamp.

As I said, haven't started the diagnostics yet, just know it's the 3rd cylinder from disconnecting/reconnecting the spark plug cables.

 

If your problem is electrical? Wouldn't #1 cylinder be having a problem also since they share the same coil????


MN

 

Really good point. Seems logical - Unless the plug is bad. I'll check tomorrow if I'm getting spark.

 

on the 650. 1 and 4 share the coil. 2 and 3 share the other coil. is the 750 different?

you might not be getting spark from #3. either break in the plug wire or the plug cap not making the connection. OR, the plug just took a crap.

 

You are correct on the cylinder order. I thought 1&3 were on one coil and 2&4 on the other. I just checked the manual and its 1&4 on one coil and 2&3 on second coil. Sorry about that.

In any case the #3 cylinder misfire or no fire would have to be something on the plug wire or the plug or something wrong with that cylinder. Or it could be something caught in the pilot jet in that carb so there is no fuel in that cylinder. I think that makes since, because if you had an issue with electrical to the coil both cylinders would not fire.

MN

 

IIRC, #3 is where your vacuum line comes from for the fuel petcock.

It can suck enough air to make that cylinder dead at idle and still open the petcock diaphragm.

If you still have misfire off idle, this is not the problem. But it's easy enough to check, so I thought I'd mention it...I always look at any cylinder with vacuum lines first when hunting idle misfire...and being #3, it sounded plausible.

 

did you wrap the sensor wire around the plug wire or go right to the coil
one of the reasons i went to the coil was with old plug wires if the insulation should break down and arc to the sensor wire it would do bad things to the tach
probably would never happen but at the coil it can't

 

are you sure the cylinder is not firing? maybe it's not getting fuel? maybe a plugged enrichment jet? keep updating and I'm sure you'll figure it out with the help of the forum.

 

Turns out the plug was just fouled. The bike has been running real rich ever since I bought it (earlier this spring) and apparently running the engine for short periods of time, at low rpms, allowed the plug to be fouled enough to prevent firing.

Pulled all the plugs and cleaned em up. All of a sudden the engine snapped up to 6k with just a twitch of the throttle.

I'll get to tuning the carbs this winter, once it gets too cold to ride

Cheers.