How important is that #2 vacuum plug?

On my carbs, there is suppose to be a plug on the vacuum tube by the #2 carb. I forgot to put it on on my first test ride after cleaning the carbs, syncing, and what not. I rode for like an hour.

Get one on ASAP.
Without it would lean out that cylinder which could cause some problem, maybe even hole a piston. :ohmy:

Pull the spark plug for the #2 cylinder. It will be very white. The key is there MUST NOT be any aluminum metal specs on it. If there are, you have a bigger issue.

By running lean on that one cylinder, you could have caused the piston top to start to melt - and the first sign of that is those specs of aluminum on the spark plug.

I put the plug back on. I rode about 28 miles like this.

I don't see any specs of aluminum on the spark plug but the little tip is white. Should I just change the whitish spark plug then?

Alright, this is what the #2 spark plug looks like right when I removed it to check. The tip is very white.

I will say that I did ride around after putting the plug back on before removing the spark plug and taking a picture. The bike was really riding nice. Feels very strong, and pulls. I also want to reiterate that the vacuum plugs on the #2 vacuum tube is a plug about the size of a valve stem cover. When I did ride without the plug it was about a 14 mile street ride going about 45mph...with a 10 minute stop...and then 14 miles back home.

If you don't see any specs of aluminum then you are probably ok. I wouldn't change the plug. All you can do at this point is just keep riding it.

Is the spark plug factory specified heat range?

Good Luck!

Other than the leanness, that plug looks healthy enough.

Just as a preview of what can happen with a lean issue:






:S

Oh man what a scary thought, I could of ruined my bike over this mistake. Riding with the plug back on yesterday, I did notice a huge performance improvement. The bike is running great now especially considering how it ran when I first got it. What a huge improvement by just cleaning the carbs/jets and giving the bike a carb sync. No more having to run with the choke on, no more stalls at idle, just smooth running, both on street and freeway. Too bad it is getting a bit too cold out to ride

On one note, I think I did have the idle adjustment screw set too high when I did run without that plug...so perhaps this created some kind of balance and saved that one piston from running to lean or whatever? Because when I put that vacuum plug back on I had to back down on the idle adjustment screw to get the idle right.

KZ250LTD wrote:

Other than the leanness, that plug looks healthy enough.

Just as a preview of what can happen with a lean issue:

:S

Tim what kind of motor got sacrificed in the pics? Total destruction, OUCH

slightly lean on the street isn't usually too bad. Very lean is...

It's when you are putting load on the engine for sustained periods when it can turn into a terminal problem.

Kawickrice wrote:

Tim what kind of motor got sacrificed in the pics? Total destruction, OUCH

'83 honda xl600, big thumper, big boom


As Jeff said, it was jetted a little lean from the factory, I was just pushing it too hard for too long and it also had a few leaky gaskets = perfect storm. Went from 75mph to nothing in a very short period of time :blink:

sakiguy wrote:

.........The bike is running great now especially considering how it ran when I first got it. What a huge improvement by just cleaning the carbs/jets and giving the bike a carb sync. No more having to run with the choke on, no more stalls at idle, just smooth running, both on street and freeway. Too bad it is getting a bit too cold out to ride .................quote]

Thats great news sakiguy. I have watched your posts here over the past few weeks and with each one you made progress. It must give you a great feeling of satisfaction that you learned this stuff and made the bike work and run the way it should.
Well done:)