Lack of power in top two gears.

The problem I have began last August when the small throttle cable between the carbs broke. The bike is a European model XJ600 1991 (Non Diversion). The cable broke about two and a half miles from home.

I rode the bike home on the engine idle. I was impressed how well it pulled up hills at around 800rpm. I then switched it off (to avoid overheating) and rolled down the other side. This was done for five hills of varying lengths and gradients on the way home. I mention it as it may be relevant.

Three weeks later when the shop finally got me a cable in I fitted it to the carbs and put them back on the bike.

Now to try and describe how the bike now rides. It will rev out freely in first to third gear. There is occasionally what I can only describe as a mild surging feeling in fourth, but it usually revs ok. It is once the bike is in fifth and sixth that the problem becomes very pronounced.

From around a quarter to a half throttle there is a huge flat spot where the engine simply has a surging sensation and does not gather speed. Wind the throttle fully open and it starts to try and speed up again. Hit a hill or headwind and it struggles badly. When you shut off from doing this and try to open the throttle again within two or seconds there is nothing. Sometimes it will misfire. Keep a closed throttle for a few seconds and then open it and it will run as before.

I have had the carbs off about half a dozen times. They have been checked, cleaned and synched. I have even tried another set and the bike ran EXACTLY the same. I have replaced the air filter, spark plugs and ignition coils, leads and caps.

The bike ran beautifully before the throttle cable broke.

All I did was take the carbs off and put them to ne side unti the cable arrived and put them back on the bike. Has anyone any idea what has gone wrong? I have had nearly a year with no bike and it's getting me down that I can't get a fix for it.

 

Welcome to XJBikes Gazzafield !

I might be completely wrong, but your symptoms sound like you need a "clunk test". You set your carbs off to the side, they got damp, or a bit of dust got in the "sliders".

In short, the sliders and their bores are polished with 1,500 grit, and without the spring, they drop with a "clunk". This is also why we can't ride around without an air filter. Hope this helps.

Use the "search" feature for "clunk test"

 

<quote> In short, the sliders and their bores are polished with 1,500 grit, and without the spring, they drop with a "clunk". This is also why we can't ride around without an air filter. Hope this helps. </quote>


Right, so. Take carbs back off and poish slides and bores with 1500 grit. Is this done with WD40? I read that somewhere this morning. (Been reading so much this morning I don't know where I read it).

Is the "clunk test" done with the carb tops back on? Pardon me if this is a stupid question but I just want to be sure I do it right.

 

The complete procedure is described in several posts by our carb-tweaking guru RickCoMatic.

Before you begin, clunk them, and tell us how they are.
Pull the hats and the spring, lift it about 30 MM and let it drop.

WD-40 is good, 1,200 - 1,500 - 2,000 grit in steps.
Polishing compound inside the carb bores if you want to go all-out.

 

<quote> Before you begin, clunk them, and tell us how they are.
Pull the hats and the spring, lift it about 30 MM and let it drop.

WD-40 is good, 1,200 - 1,500 - 2,000 grit in steps.
Polishing compound inside the carb bores if you want to go all-out. </quote>

Will do. Weather has turned turned rather wet here so may be some days before I can get the carbs off, if you could keep an eye on this post I'd appreciate it.

 

<quote> Before you begin, clunk them, and tell us how they are.
Pull the hats and the spring, lift it about 30 MM and let it drop.

WD-40 is good, 1,200 - 1,500 - 2,000 grit in steps.
Polishing compound inside the carb bores if you want to go all-out. </quote>


OK. Rain stopped tonight so I pulled the carbs off - AGAIN! Took off the hats and pulled out the springs as instructed. Now, when I first tried a clunk test they didn't make any effort to clunk as the diaphragm was holding them up. I had held the diaphragms in pace with instant gasket on re-assembly last time.

When I had the diaphragms free they easily slid in and clunked to the bottom every time. So how is the test done? With a free diaphragm? I will polish them up now anyway now that they are off.

What would be my next move?