Cyl1 and 2 not firing

[HWB]

Ok i just want to say ive removed the carbs more than 8 times rechecked everything a million times i cleaned them twice thouroughly pressure blown them  vaccum tested everything and my problem remains.

I have fuel in 1 and 2 bowls, if i remove the bowl screw fuel comes out. I have no kink in my fuel lines. Number 3 and 4 run perefct.

I checked spark and all 4 have sparks. I checked compression and all have good compression at around 10 bar each.

Header downpipe temperature of 1 and 2 are very low naturally but the weird thing is if i pull the choke then they fire and temps build up to normal untill i close the choke and it stops firing again. Timing is good too no skipped teeth no worn rotor. 

So what the hell is going on ??!!

Carbs are cv40's on an N (oem)

[Dezza]

Has it been standing for a long period with fuel in the carbs and/or tank?

[HWB]

Yes dezza its been sitting on its sidestand for a year

[Blubber]

Long shot... 

Have the carbs been recently balanced?

Almost "feels" like carb nr 1 and 2 are out of whack with carb 3 and 4

[HWB]

10 minutes ago, Blubber said:

Long shot... 

Have the carbs been recently balanced?

Almost "feels" like carb nr 1 and 2 are out of whack with carb 3 and 4

I recently bench synced them. If i rev the bike for a couple of minutes the temps dont go up, only 3 and 4 go up. Does that rule out syncing ?

[Dezza]

1 hour ago, HWB said:

Yes dezza its been sitting on its sidestand for a year

This and the description of the running of the motor choke on/off, suggests to me that some of the fine drillings/ pilot jets in the carbs 1,2 have become blocked with varnished fuel. My guess is the bike won't run correctly unless the carbs are cleaned and maybe also the tank flushed. You could try new fuel first though.

It may take several cleaning cycles to work.

Edited May 18, 2020 by Dezza

[HWB]

1 minute ago, Dezza said:

This and the description of the running of the motor choke on/off, suggests to me that some of the fine drillings/ pilot jets in the carbs 1,2 have become blocked with varnished fuel. My guess is the bike won't run correctly unless the carbs are cleaned and maybe also the tank flushed. You could try new fuel first though.

But i cleaned them thoroughly and blew them with pressure, boiled the jets, fine wire inside to unclog (nothing was clogged but did it anyways) cleaned again and blew them.  

[HWB]

And i dumped the old fuel from.the tank and filled with new fuel

[Dezza]

Sounds like it's time for an ultrasonic clean of the carb bodies.

[HWB]

Will do that mate thanks

[Blubber]

1 hour ago, HWB said:

I recently bench synced them. If i rev the bike for a couple of minutes the temps dont go up, only 3 and 4 go up. Does that rule out syncing ?

 

Yeah...if bench synced they should pick up only a bit later. 

And as you mentioned :

it runs on choke, so you know fuel is getting there, spark and ignition are there.

Must be something in the carbs.

What Dezza said - ultrasonic bath cleaning - has helped many others

[Dukeman]

I am in a similar situation.

1-2 cylinders running very low temp, when I rev the bike they pick up.

Carbs off twice, full strip and ultra sonic clean, BUT the carbs leaked and I have needle and seat x 4 on order.

Looking to change leads, also new carb rubbers etc on order to make sure there is NO air leak.

I had a similar compression test, cold engine.

Interested to see how you get on, Im waiting on parts.