running too rich

Hey Chaps, got an interesting bothering problem here which I would like to share with you. It's about a XJ900F with 31A engine type. Maybe we can help others too.

The story in short:

1.) Bought a used 31A carb at ebay
2.) refurnished the carb. New diaphragm, supersonic bath
3.) set pilot srews to 2,5
4.) synched the carb
5.) bike is running perfectly with much more power
6) after 500 km's it starts to run bad again
7) checked sparks, each one completely black
8) checked pilot screws again, euch one different (2,5 to 3), set them all to 2
9) after another 50 km's I noticed the power is not as before, bike still runs not well
10) checked sparks again. Look at the pic. Consider that I cleanded spark 1 already. It did look like 2 before the cleaning
11.) Checked compression. On Each cyl I got 8. Needles of my compression tester behaves equal on each cyl during the test

Based on the spark pic there must be a problem with the carb. When using my 58L carb with broken diaphragms the bike is even running better.

I'm going to take off the carb now and check the main jet as well as the floaters. Will keep you informed.

/Ramon

 

OK, current state is:

Spark 1 completely black, others look like 3 and 4 before. I will adjust pilot screws again. The problem is to find the basement. How far do they have to be screwed in? I think the needle should be visible for 2-3mm when sitting at basement. From there you have to screw out 2 to 3 times?

 

OK. Next Step. Screwed the pilot screws completely in and screwed them out 2 turns. After 35 km spark one is still black. 2-3-4 are much better. Changed 1 to 4. After another 40 km's 1 is black again and 4 is clean.

Strange. Any ideas?

 

A lean mixture can at times cause the black sooty plugs. Unburned fuel collects until enough is there to ignite. I would try 2.5 turns out and also check the resistor caps on the plugwires. A weak spark can cause this too.

 

Those plugs look the same as mine, I am pretty sure I am running lean, have some popping in the pipe and power up top fades too fast.

xj650rj
ported head
4 into 1
k+n

 

Which cylinder is the petcock vacuum line attached to?

 

What should I say? Human failure.

A few weeks ago I took the carb to a specialist requesting him to refurnisch the carb. He cleaned it with supersonic, checked it. Did all the stuff needs to be done. But did make a small mistake with a huge impact!

Now as I saw that the problem is carb 1 I took out the piston valve. We noticed that the jet needle was competely fixed. That is definitly wrong! The trick ist when you put in the needle that you have to check wether its nose is inside the hole which is in the bottom of the valve. We did correcgt it. Reajusted pilot screws. After 70 km's I checke spark 1. Excellent now! Even the engine runs much more better.

Consider this whenever you play with the jet needle. By the end of the week I will put in some pics showing the details.

/Ramon

 

What do you mean by "the jet needle was completely fixed" ?

BTW, You speak much better English than I speak German, but I am just trying to learn from your experience. Glad you got it sorted out.

 

Uhh, just noticed that my english could be abetter! So let's exercise.

"completely fixed" means the jet needle didn't had any play. But it has to have. Is this better?

Anyway. Attached a pic which I hope makes everything clear. In background the bottom og the piston valve. The borehole where the nose of the jet needle needs to be put in marked red. On the bottom the jet needle. The nose marked red. Notice the notches for resetting the jet needle on the needle.

/Ramon

 

Great photo Ramon! Glad it was a simple fix.

 

Ich studierte Deutsch in der Universität aber nicht häufig kommen, um Deutsch zu sprechen.

gutes Foto!! Dank..