After fixing the fuel leak pouring out from the overflow hoses, I have managed to get the engine running.
It starts well and idle OK, I did use the carbtune to balance the carbs as much as I could, but I am now getting the following issue on cylinder #1


It seems that there is no vacuum on cylinder #1
When I pull the hose from the carbtune and check from vacuum, it's pulsating like crazy. Pushing and pulling air. However if I do the same check on all other cylinders, the vacuum is there, rock steady.


What am I missing this time again?

edit:
running NC35 carbs.

Is the vacuum take off for the fuel tap connected or have you had the tap mod done? Maybe if the port on the side of the cylinder hasn't been blanked following the tap mod, this could cause the issue?

all the 4 vacuum ports are connected to the carbtune, the fuel tap has vacuum applied to it with a small hand vacuum pump.

The idle is rock solid at 1500 RPMs, just this cylinder #1 is acting odd.
It wasn't the case with the NC30 carbs, I have a video of it if you want to see.

thunderace wrote:Is the vacuum take off for the fuel tap connected or have you had the tap mod done? Maybe if the port on the side of the cylinder hasn't been blanked following the tap mod, this could cause the issue?

is there any vaccuum when you rev it?
and does the hose stick to your finger when removed from the guage?

give the carbtune a bang on the groud the metal float sometimes stick.

When I rev it (5k to 7k) the metal bar (in the carbtune) goes up very slightly.
On cylinder #2 #3 #4, if I disconnect the carbtune hose and stick it to my tongue, I can feel a good vacuum.
However on cylinder #1, when I do the same test you can feel air popping in/out, like a pulse.

I have dismantled the carbtune, it's all OK. And if let's say if I move the vacuum hose from #1 to #4 on the carbtune, it will shows the same (ie: not moving).

porndoguk wrote:is there any vaccuum when you rev it?
and does the hose stick to your finger when removed from the guage?

give the carbtune a bang on the groud the metal float sometimes stick.

have you adjusted cylinder one on the carbs yet?

just adding some info.
I used my infra-red thermometer to check the exhaust temperature and #1 pipe is way off the chart compare to the other pipes, which (correct me if I'm wrong) would indicates a very lean carb.

Talking about temperature, #2 #3 #4 are not the same.
#2 is twice as hot as #4 (I can hold #4, and barely touch #2)
#1 is off the scale... #3 is warm

Bike was not fully warmed up to running temperature, but idling perfectly fine at 1500 RPMs without the choke.

as:
#1 rear left (fuel tap side)
#3 rear right (rad overflow tank side)
#4 front right (throttle side)
#2 front left

What do you mean by "adjusted cylinder one" ?

porndoguk wrote:have you adjusted cylinder one on the carbs yet?

gonzothegreat wrote:What do you mean by "adjusted cylinder one" ?

porndoguk wrote:have you adjusted cylinder one on the carbs yet?

well looking at the guages, 1 is way out of balance hence not having a strong vacuum, the purpose of balancing is to get all the same as cylinder 4

you need to adjust 1,2 & 3 in little stages and the vacuums will all be the same, its not unusual for one to be really low down.

mine was the same until neosophist sorted mine

ok, well it's way too cold and too dark now and I'm hungry... to go back to the garage.
I'll give it another go at balancing it either tomorrow after work or next week-end,

thanks for the advice, will keep you all posted.