Exhaust off, bike running, I see blue flame from exhaust?

Hello, total n00b here.

I'm replacing/cleaning/repairing portions of a 1982 Maxim XJ750.

I've got the exhaust completely off... when the bike is running, I notice blue flame coming out of three of the four cylinder exhaust ports. I just did a valve clearance adjustment.

Of course, I'll get to the carbs once my front and rear brakes and exhaust are in spec... but I'm curious, the 'flame' is intermittent, meaning not every fire, I see it.

Bike has trouble starting (it takes a few to 10 seconds cranking)

I have not checked the plugs or wires.

Questions:

1. Is this blue flame normal?
2. What color should my plugs be?
3. How do I test my plug wires? Is an Ohm meter sufficient?


Thanks!

 

You really shouldn't run it without exhaust at all. there needs to be some back pressure. Plus it's got to be crazy loud.

With no exhaust yes a flame certainly could come out it's going to depend on your mix which won't be set right until you have the bike in running condition.

Your plugs should be lunch bag brown.

You can measure between the two plug wires from the coil.

This should cover your ignition questions http://www.xjbikes.com/Forums/viewtopic ... oting.html

 

Some flame is normal.... More importantly, you'll burn a valve by running with no exhaust. Plus your fuel/air ratio is going to be screwed up without the exhaust on.

plugs should be light brown, at least 3/4 around the bottom ring (surrounding the white insulator)

Depends on what your testing the wires for...

 

1: With the exhaust completely off, you have no backpressure for the cylinders. This means the fuel you are pulling into the carbs is not getting a complete burn, and the excess is going out the exhaust port and (most likely) being ignited when enough builds up for the hot exhaust port to ignite it.

FYI carb tuning will be a NIGHTMARE if you try it without an exhaust. Don't.

2: Plugs on a properly tuned motor will look like a brown paper bag. I'm guessing yours are probably not.

3: Yes. I don't remember the OHM specs, but you can OHM them out to check for continuity of the wire and plug cap.

 

Glad I didn't run this too long (not longer than 3 minutes), I did rev it up a few times though, didn't think it would harm anything, but I'm not very smart lol.

Hope all is OK

I will not try and tune anything without the exhaust back on, in fact, I won't even start it again until the exhaust is back on!!!!

Thanks, and I'll look at the plugs in the morning.

 

You can KILL an exhaust valve running with no pipes like that; don't repeat the experience.