1 cylinder not firing - spak plug flooded

[sotirisp]

Hi guys,

I had my XJ400S Diversion stored for about 2 years (during this time i started it only a couple of times per year).

Recently i decided to use it again on a weekend basis.

First time it tried to start it, the bike started but cyl #3 was not working.

First thing i did, i removed the spark plug of cyl #3 to check its condition.
It was wet of fuel...really wet.

I figured out to remove the carbs (4xMikuni BDS28 same like 600 but with different jetting) and check the floats.

EDIT: Correction, XJ400S carbs are 4xMikuni BDST26 not BDS28

Voila! i did find that the float valve of carb #3 was stuck. The float valve spring didn't compress (didn't move in) when the float tab was pressing it.

I tried to push it with my fingers just to see if it's going to get unstuck or i'd need a new float valve.

Well i did push it in using finger force and it seemed to get unstuck, so i decided to give it a clean with a carb cleaner spray and install it again as i did.

By the time i installed it, it was working fine (the float tab was touching it and pushing it in with just little force as it should).

So i re-installed the carbs and started the bike. For about 15mins everything was running fine. All 4 cylinders were working including the #3 cylinder.

Yesterday (1 day after i re-installed the carbs on the bike) i started the bike again to do a carburetor fine tuning by means of adjusting/checking the mixture and synchronizing the 4 carbs, as the bike stayed unused for a very long time...

Guess what -> cylinder #3 does not fire again and the plug is wet again!

Is there a chance that something else instead of the sticky float valve floods cyl #3 ?

Or, is it possible that the float valve of carb #3 got stuck again?

Please advice me what to do...should i disassemble the carbs again and check again the float valve of carb #3 ?

Thanks in advance...

[taint]

In this case, it could be that spark plug 3 is also not firing. It may be worth checking the spark plug first before re-dismantling the carbs.

If it is sparking, it could be that the spring needs replaced.

Hopefully one of the more technical users will have some more suggestions

T.

[sotirisp]

As i mentioned in the first post, spark plug #3 was wet fouled again yesterday, but the day before yesterday (during the 1st test, after the carb #3 float valve cleaning) it was firing...

So i guess the (once again) wet fouled situation of spark plug #3 is the symptom not the cause....

My thought is that cyl #3 is flooded again but i'm wondering if float valve of carb #3 got stuck again within 1 day or something else is happening.

Note that ignition coils and spark plug caps have been checked with ohmmeter and found within specifications, and last time i checked the #3 spark plug wire for spark, it had it...

Yesterday after i realized that cyl #3 was not firing again, i moved its spark plug to cyl #1 just for testing and then cyl #1 and #3 were not firing...But i expected it to be like that, since the #3 spark plug was wet fouled once again.......

( EDIT: During the spark plug switch between cyl #1 and cyl #3, cyl #3 fired for a couple of minutes then stopped and fouled again the spark plug i had switched with cyl #1. )

[General Gman]

It would be worth checking the float valves again, and cleaning / renewing fuel lines / fuel filter.
Drain the tank and fill with fresh fuel, make sure all the fuels lines are free of crud - you may well have a load of crap in the lines which is cloggin the float valve.
Strip the carbs and clean eveything, and also have a good look at the fuel tap filter.

[sotirisp]

I will remove the carbs once again this weekend and disassemble it to check the float valve again.

I will also drain all fuel from tank and carbs and give the carb a good thorough clean and check fuel lines and fuel tap filter.

This model does not have a fuel filter in the fuel line that comes from the tank (i know that 600 has one but this 400 import didn't come with one and I double-checked this in the parts list book...).

I'll need to bring up again this topic in 1 week in case i need some more advice/help...

Pardon a forthcoming topic bump...i hope it's tolerable in such situations.

Thanks for the answers!

[taint]

If there's no fuel filter, it may be worth fitting one. Any of the small inline filters should do. Something like this www.mandp.co.uk/productInfo.aspx?catRef=568230 might be ideal.

It's better to have one than not.

Hope this helps

T.

[General Gman]

I've got a couple of red anodised ones at home that were gonna go on my gixxer which had problems very much like these.
Bike got wroted off before I had a chance to fit em.

[sotirisp]

bad news maybe...

I removed and disassembled the carbs once again, but the float valve on carb #3 wasn't stuck this time...seemed to work fine (like all the others at least).

I'm doing a swap of the #3 float assembly with the #4 carb (put #3's float in #4 carb and vice-versa).

I will install again the carbs onto the bike and check what happens...
If now it's cyl. #4 that floods then i definitely need to replace the float valve that i swapped there from the faulty #3 carb.

Else...dunno what to do more instead of a compression check of cyl. #3.

[sotirisp]

Hi guys,

today it's a good day for my Divvy.

Problem with cylinder #3 not firing: solved.

Instead of the sticky float valve that was cleaned, i also found the main air jet of carb #3 totally clogged! I cleaned it up yesterday night and this morning re-installed the carbs on the bike and voila!

Everyting runs fine, all cylinders working.

I also did a compression check on all cylinders just to be sure about their condition.

I took these measurements:

Cyl #1: 153 psi
Cyl #2: 158 psi
Cyl #3: 152 psi
Cyl #4: 155 psi

I guess that they are good measurements and indicate a good condition of the cylinders but i want your opinion as i am not very good on interpreting compression values.

Manufacturer's compression ratio is: 10.5:1
and bore x stroke is: 47.7mm x 55.7 mm
Total displacement: 398cc.

Are my compression levels ok?



EDIT: edited for typos..

[joriff]

Where is the main air jet located?

[darren]

just had a look at the autodata, and your compression levels are good, its states 10-11 bar from new upto 1996, no data afterwards, but suspect the same upto 2000 14.503861psi=1 bar

so at 11 bar you have 159.542471 psi at 10 bar you have 145.03861psi which gives you 14.503861 to play with inbetween

[CD]

Before you worry about the main jets (which only work above 6000rpm or above 2/3 throttle) check the choke plungers and mechanism as they can stick and the rubber sealing pads harden with age.

[joriff]

His is fixed now

[CD]

What caused the problem?

[sotirisp]

hi sorry for the late response..

The problem was caused by 2 things:

1. the float valve on carb #3 was stuck
2. the air-jet on carb #3 was totally clogged.

Both cleaned.

The main air-jet is located there (see the red arrow in the picture):



(EDIT: or the other hole next to it, can't tell well from the picture which one is screwable - the screwable one is the main air jet, the other one -> i have no idea but i cleaned it too...)

[joriff]

sotirisp, if i have any further problems with my bike i'll check this jet, we had the same problem but mine was intermittent.