I'm now owning for half a year a 93 4BRA European version, after purchase checked the valves they are almost in spec with ,01mm on two valves. (Had an absolutely clean sound like an electric engine). Synced the carbs and ridden 4,5 thousand kms on it.
On the last few hundred kms I heard the exhaust sound getting deeper, the engine running not smoth on idle, anticipating that the engine running rich and out of cync.
With infrared measured the pipes, values were in a wide range from 500 to 690 F, which not indicates a rich condition.
And that bothered me...
Decided to clean the carbs, try to set the mixture screws and resync.
So done this, made a thorough ultrasonic cleaning, washed clean, blown out with air all the holes I could find.
After reassemble the bike runs instantly on choke, and runs without choke when warm.
It's not a story so far, what happened tried to undarstand on the last two days, reasoned and googled really lot.
The symptoms were:
- IR mesurements gave 640, 240, 530 and 520 F, really strange
- when warm the engine gets rpm easily on throttle, but goes back slowly from 3000 with a step on 2000, which is a sign of a massive air leak somewhere. Boots are new,no craks.
- tried to play with the mixture screw, the first cylinder's pipe did not get cooler, for the second cylinder's screw were absolutely unresponsive
- tried the choke and it gave a whistle, strange
- tried to sync them: 3 and 4 were on absolutly sync, but the first two were not syncable, what could be expected.
This all can be cured with carb reassemble, not a big deal, can happen.
And then I got an other one:
the second cylinder started to leak oil from the second stud's base:
http://1.1.1.4/bmi/www.xjrider.com/gall ... l_Leak.JPG
Closed the experimentation, disassembled the carbs from the engine.
Found two things to cure so far, maybe there will be more too.
For the oil leak can be an interpratation the heat difference between the pipes: the second cylinder either running far too rich or far too lean....
Here is the spark plug, what I can't read, it should be
http://1.1.1.3/bmi/www.xjrider.com/gall ... _small.JPG
The first thing comes to mind, that it should be black if it were running rich, it should be white if it were running lean,
but can't be lean beacuse it's pipe is not hot. The spark plug is way too clean If it were running without fuel.
It can not be running without fuel, because the engine not stotters like it were running only on three pots.
And it's exhaust pipe should have a tempreature slightly over 100F.
Maybe it got some fuel but not enough ?
Disassembling the second carb found that the Choke piston has a really strange shape, it's like it has been chewn.
Turned to google and found that other bikers have problen with this kind of choke assemble.
http://1.1.1.4/bmi/www.xjrider.com/gall ... Piston.JPG
My explanation is that it has been treated with high temopreature heat, what is caused by backfire on choke operation.
Here is a pic showing its position in the tube, exposed to the temperatures in the venturi (the tube's other end is in there in the venturi below the throttle valve)
http://1.1.1.5/bmi/www.xjrider.com/gall ... Opened.JPG
It would be a good engineer act to make it out of brass as other parts of the bike like on other carbs.
On afew biker forum it is a common theory that the damage causes unwanted richening which might be plausible but not because the peak rod had lost some of its diameter but because its base melted too, which actually would have the purpose to close the fuel tube.
Here are two pics showing the choke piston's base and the it's seat what should be closed on it's intent:
http://1.1.1.2/bmi/www.xjrider.com/gall ... n_Base.JPG
http://1.1.1.1/bmi/www.xjrider.com/gall ... n_Seat.JPG
It hasn't got any more the "smooth" surface like on the undamaged side so it leaks fuel when choke is closed, though there are other element on the choke piston, the small steel plate which has two functions:
Firstly it saves the plastic piston from the heat when choke is off, on the other hand it somewhat has a sealing effect on the enricher tube.
Shown on that pic:
http://1.1.1.2/bmi/www.xjrider.com/gall ... ston_2.JPG
Maybe it is salvagable by polishing the surface,maybe not I'll give it a try.
The bottom clue is here, the bikes with that type of choke assembly are not to be riden with choke on, far further even not to operate the throttle when warming up, the choke piston could be damaged by backfire what is inevitable by changing gear.
The affected bikes are ours' european version, the Tenere, Exup, some FZRs, TRX, TDM, maybe more...
Disassembling the carb I found also that the diaphragm has two cracks, which accounts for the whistle on choke, since the choke's tube sucks the air from before the diaphragm where actually just a little room for air to extract.
http://1.1.1.4/bmi/www.xjrider.com/gall ... racked.JPG
Back to the main issue, any thought is welcomed on what to look for with second carb,
and if I'm doomed to tear apart the head for a base plate change
r
zoli