XS-400 rough idle

[Fixandfly]

Hello New to forum.
I have had the same bike for 30 years since college.
Every time I set something it runs great for one day then falls back and rough idle again and wants to stall.( only at idle) above 2000 rpm fine

Compression 120-130 both sides
Idle at 1200 RPM wants to stall.
Timing is correct. (Left and right)
Today I used Vacuum gauges. They are equal.
The carbs are cleaned. The sliders are clean. ALL jets cleaned And it will not run correctly unless the mixture is turned 4-5 turns. I know that is excessive. It should be 3 or so.

Any thoughts
What am I missing?

Thanks

[JimR]

Originally Posted by Fixandfly

Hello New to forum.
I have had the same bike for 30 years since college.
Every time I set something it runs great for one day then falls back and rough idle again and wants to stall.( only at idle) above 2000 rpm fine

Compression 120-130 both sides
Idle at 1200 RPM wants to stall.
Timing is correct. (Left and right)
Today I used Vacuum gauges. They are equal.
The carbs are cleaned. The sliders are clean. ALL jets cleaned And it will not run correctly unless the mixture is turned 4-5 turns. I know that is excessive. It should be 3 or so.

Any thoughts
What am I missing?
Thanks

Welcome to the forum !!! what have you got the dwell angle set to & mixture screws set to 5 ish turns out ? If the mix screws are mounted to the top of the carbs there is a chance the air screw point may be broken off .. supply some more info

[Fixandfly]

Hello JimR:
The Timing @ 2000 rpm is right in between the I I marks. ( left and right0
I have personally taken both screws that are on top out of the 36 mm Mikuni Carbs and the are in the correct shape.

Fixandfly

[JimR]

Originally Posted by Fixandfly

Hello JimR:
The Timing @ 2000 rpm is right in between the I I marks. ( left and right0
I have personally taken both screws that are on top out of the 36 mm Mikuni Carbs and the are in the correct shape.

Fixandfly

Hi
I would adjust the timing as follows :-
set the bike to idle @ 1000 rpm
start with the left cylinder
adjust the dwell angle to 22.5 degrees
adjust the timing (using a strobe) to the mark LF (left fire point)
rev the engine to ensure the advance works, the strobe will show the I I marks and the datum point should between the 2
Then move to the right cylinder & do the same but use the RF mark.
It is very important the dwell angle is correct to get a good idle but I am still wondering why the air screws need to be set to 5 turns out, but any how let me know how you get on setting the dwell angles etc
Regards Jim

[Fixandfly]

Thank you;

I will start on the Dwell check first.
LT is for valve, LF is for stobe fireing correct?

Fixandfly

[JimR]

Originally Posted by Fixandfly

Thank you;

I will start on the Dwell check first.
LT is for valve, LF is for stobe fireing correct?

Fixandfly

Spot on Correct for the left cylinder the marks RT & RF are for the right cylinder, remember to set up the left side first as the points are connected to the back plate & the right side set has its own sub plate, so as you adjust the l/h side it adjusts the r/h side so once you have the l/h side spot on you can then the r/h. Because of this as you adjust the l/h side the engine may tend to cut out so you may have to make idle adjustments to keep the bike running at 1000 rpm & when you adjust the r/h side the revs will rise, so again you will have to adjust the idle back to 1000 rpm.
The idle screw is the big white screw between the carbs to rear by the air box
part 42 at [Only registered can see links. ]
If you are going to do a valve check make sure you have the bike on the right stroke both valves open & the LT or RT mark against the datum mark

[Fixandfly]

I will go to work.
You are a genius.
I honestly thought if the mark was between the I I at 2000 rpm meant everything was ok.
I was wrong.
But now that you told me about the dwell I will check this today.


Thanks

[JimR]

Originally Posted by Fixandfly

I will go to work.
You are a genius.
I honestly thought if the mark was between the I I at 2000 rpm meant everything was ok.
I was wrong.
But now that you told me about the dwell I will check this today.


Thanks

You have a dwell meter !!! like wow I wish I still had mine !

[Fixandfly]

Hello Jim R:
The dwell meter I have is for a car and it says 4 cyl 6,cyl or 8 cyl.
Which scale do I use?
I did change the timing so at idle 1200 +_- 100 it lines up with LF or RF.
I did notice that when I did this adjustment that the racetrack oval pattern for the points and timing adjustment is at full course deflection.
Is this correct? One would think it should be in the middle somewhere.
The idle is a lot better thanks to you.
Where did you get the 22.6 dwell number from?

We are very close.
Thanks to you.

Fixandfly

[JimR]

Originally Posted by Fixandfly

Hello Jim R:
The dwell meter I have is for a car and it says 4 cyl 6,cyl or 8 cyl.
Which scale do I use?

you need a single cylinder dwell meter to do the job

Originally Posted by Fixandfly

I did change the timing so at idle 1200 +_- 100 it lines up with LF or RF.
I did notice that when I did this adjustment that the racetrack oval pattern for the points and timing adjustment is at full course deflection.

what the hell does that mean lol
a simple English boy does not understand oval patterns & full course defection .. this sounds like a modern slant on an old problem

Originally Posted by Fixandfly

The idle is a lot better thanks to you.
Where did you get the 22.6 dwell number from?

to be fair the correct number is 22.5 degrees & as I actually repaired the bikes back then I just remember the settings
it's a memory thing