More about Carbs

My plugs have always been a gray colour, not brownish like I'm used to seeing. Couple of weeks ago, I notice one exhaust wasn't getting hot on start up, and also noticed some backfiring on decel, so I figured it was an airleak someplace. Sure enough, a propane test found a leak in the intake manifold on the suspect cylinder. I pulled the carbs off, replaced the old gasket, put it all back together and it still wasn't heating up. Since I don't have a sync tool, vacuum guages, or colour tune I bit the bullet and took it to the local shop. I bought the bike last january and didn't know when it was last set up so I figured it was time for a 'real' tuneup anyway. I had already checked the valve clearances so I knew that wasn't going to be an issue. Turns out the leaking manifold was still leaking as I had put the gasket in askew and the bottom bolt didn't go through the gasket. My bad. There was some dirt in the suspect cylinder's carb - the primary circuit to be exact. Compression was 145 - 150 in all four. On the ride home I noticed some 'light' popping on decel, something it didn't do all summer. I called the shop and advised them of the problem and will be taking it back into them this week if it doesn't rain. The tech said the popping might be dirty plugs, so I put new ones in, and it still does it. He said he set the idle screws at 2 turns out, which sounds about right. It is a 4 -1 exhaust and it does have a KN filter. I don't know if any previous owner had rejetted it though. So - a professional tuneup, and some light popping on decel once it gets under 2000 rpm. Sound like a lean condition to you?

 

On ALL STOCK Bikes:

Factory Preset ( To run Lean enough to pass emissions testing at the Port of entry -- for early '80's EPA Standards ) ... is:
2.5 Turns Out (Published)

2.5 Turns Out generated an abundance of Service Issues related to Lean Conditions.

To reduce having New Bikes return for Hesitation and Stalling complaints; many New Bikes were Dealer Preset to:
Between 2.75 + 3.0 (Splitting the difference closer to 3.0)

Sounds like a Lean Condition, ... Yes.
If 3 Turns Out doesn't get you sufficient richness, ...
You'll need to Increase the size of the Pilot FUEL Jets.

NGK Color Chart

http://www.ngksparkplugs.com/tech_suppo ... aqread.asp

 

Just checked the old plugs - looks like they certainly aren't the problem. I'll mention to the technician that perhaps he should check out xjbikes.com

or ....... maybe I'll just suggest that I heard a lean conditon might cause the bit of backfiring I'm hearing and see what he suggests . lol

 

You might want to see exactly what jets are currently fitted.

"Popping" does indicate a lean condition; and a 4-1 with a K&N filter will generally mean some re-jetting required.

You said you "had previously checked the valve clearances" HOW previously? They need to be done every 5000 miles.

 

Do a "Flutter-Test" and rule-out an Exhaust Leak.

Tape a "Flag" of Tissue to the end of a long probe.
Check the Headers: Top & Bottom
The flag will fill flutter if there' a leak.

A Lean Condition is hard on Header Donuts.
Loose Collars or Leaking Donuts will contribute to popping and backfiring.

 

I checked and adjusted the valve clearances about 800 kms ago. Only one valve was a bit tight but it's good now. The engine didn't backfire before the tune up, so I'm sure the tech - like he said, opened the adjustment screws 2 turns out. When I called the shop today to report the problem, the 'phone guy' said that 'quiet' popping on decel would be common and when I told him it didn't do that before the servicing, he said I probably had the the mixture set a bit rich. In any event, they said to bring it in on the next nice riding day, and they would re adjust the low speed jets a bit, which should cure the problem. I'll post up again after my next visit.

 

Seriously bud.... I wouldn't bother taking it to the shop.... you'll get better results by asking for help on here. And if you get stuck on it , or don't have the tools, ask on here... offer up some food + beer. You'll have a great garage party going! Especially that a lot of us are starting our wrenching season....

Most of us have bad should shop experiences.... took my wheels to Yamaha for new rubber + needed some partsfood a couple of months ago, 2 mechanics +some customers were giving me a hell of a time that I should put the $ on a new bike. One of the 'senior' guys (worked for Yamaha longer than i've been alive) joined the conversation and stated that a properly running xj will kick most any bike's ass that's on the showroom floor

 

I haven't been able to get back to the shop due to all the rain we get here, but I was lucky enough to find a pocket thermal reader at a really good price. I think I read on here that you can tune an engine by measuring the heat on the exhausts, so I thought I'd test it out. I fired the bike up and let it get hot, - and of course it started popping irregularly. I checked the exhaust temps and found one that was about half of the reading of the others. This just happened to have been the cylinder that had the airleak in the intake manifold that was causing all the problems. I started turning the adjustment screw out a little at a time and noticed the popping was becoming less frequent. After a full turn and a quarter - no more missing. I rechecked the exhaust readings and they are all relatively close to each other - I realize the heat readings aren't going to be exact, but they were close enough to give me an idea of where to start looking.

 

Now THAT was a good bit of mechanics! You had a problem, asked for help, learned what can cause your problem, saw an opportunity to try to solve it yourself and did....congrats for using your head instead of your wallet.

jeff

listen to what the guys are telling you about taking your bike to the dealer and remember that their agenda is different then yours.....they are there to make money, plain and simple....a great place to buy a brand new bike but little else...at least for most of us. A few short years of common sense mechanics will give you not only great personal satisfaction but also the knowledge that you can go anywhere, anytime with the confidence that you can fix whatever comes up. A pretty good feeling when your 600 miles from home and 100 since the last gas station......

 

I hope I don't sound preachy,

But you could have bought the tools you need for
what you prob spent on the shop.

As for "set to 2 turns out", as mentioned by our gurus,
is just a baseline. You Have to check/recheck those plugs.
Adj/re-adj those pilots-only 5-10 degrees at a time.

Read some of Ricks,Chacal, and Fitz' tutorials on tuning these
carbs-then start the tuning.