Serviced carbs ran for a bit now won’t start.

Yes l think that is a possibility. As fuel is getting to the carburettors it should be getting drawn into the engine especially as your bike was running beforehand.

 

The tank was super clean, The gas is fresh supreme gas, the petcock was cleaning and new diaphragm and o rings put in. New external filter too.
I drained each float bowl to make sure gas was travelling to the bowls and the floats were working properly.

 

Filter that can cause problems. What type is it? Did you fit it before the throttle cable? Is there an arrow on the fuel filter for direction of flow?

 

I even put gas down the fuel line via a little funnel so that bypasses the filter.

 

Can you put the kill switch in the off position. Then crank the engine with the throttle open. The vacuum should draw fuel into the cylinders and make the plugs wet. If this happens l think your float bowl jets could be blocked. The brass coloured tube goes into the float bowl body. At the bottom of each carburettor is a tiny jet that allows fuel to travel up the brass tube into the intake to richen the mixture for cold starting. If you are correctly cranking the engine on a closed throttle and these jets are blocked the plugs could be dry.

 

It won’t crank with the kill switch off. I found that unusual. But it will crank over as if there was a kill switch on.
I still find it so strange that all 4 carbs are acting exactly the same. It makes me think that it can’t be an internal carb problem. But anything is possible.

 

Yes you are right, even if it were an internal carb problem it would not affect them all simultaneously. It is strange how you are getting no fuel to any of the cylinders.

 

open vac line or port would make a lean situation fuel would burn but not explode to start bike plugs would be dry.

if vac line fell off port or petcock no fuel would flow.

if butterflies were open due to tight throttle cable the suction/vacuum created from motor would be lessened due to larger orifice with butterflies open and draw less fuel possibly no fuel through pilot jet or enrichment circuit
also the wider the butterflies are open more air leaner mixture,
throttle grip should have a few mm play before the cable lifts the throttle shaft.

you bike was running you changed the cable bike not running.

i went through this with someone recently no fuel flow past carbs his throttle cable was very tight that when it did start it redlined. losened cable to point of stall adjusted idle knob to proper idle readjusted throttle cable fired up.
this may or may not be the problem but it is the work you did last

 

Jeez, really, read that again over...

 

Sorry, a bit harsh there from me. The last bit - cable too tight might be valid, except that was addressed further up^...

 

OH MY GOODNESS. I FEEL STUPID. ‍♀️ I actually have the tank off so I was feeding it fuel through a tiny funnel so that I could see if the fuel was being taken down. I didn’t put much importance on the petcock vacuum line. I plugged it with my thumb a few times to try it but this time I pinched it off with vice grips and it started with a little spray into the air box

THANK YOU ALL

 

a golf tee or 2 is a good plug keep some your tool box

 

Don't feel stupid. We've all done stupid things.

 

I don’t know if I’m doing this right but I hope that the previous readers read this again.

I thought that I found the problem because the one vacuum line was not plugged. When I plugged it it started right up and took fuel from the carbs. But it only did that once. Now it’s back to not taking fuel again. The vacuum is sealed off at each carb. I have a question about that. If the vacuum is sealed at 3 carbs and open at 1, wouldn’t the 3 cylinders suck in the fuel anyway. The big mystery, to me, is that all 4 carbs are acting the exact same way. What do they all have in common that is causing them to not fuel the cylinders?
Recap. -carbs were removed, cleaned,
reinstalled, synchronized
-ran great until I installed new
throttle cable
-all carbs have fuel in bowls.
-all cylinders have spark
-throttle cable is correct
-can’t find vacuum leak ( but
wouldn’t that be an
individual carb problem?)
-using fresh premium fuel
-fuel system totally clean

any advice please

 

Had a similar problem with an xj550 bad fuse holder was preventing proper voltage to ignition box and was not starting. Even though I did get a spark at the plug there was no spark when under cylinder pressure. Also check voltage at battery when cranking. Less than 10-10.5 volts box won’t fire coils.

 

To clear up the mystery, the vacuum line to petcock only allows fuel to flow out of the tank , via the petcock, to the carbs. All four carbs get the fuel from the one fuel line, none from the vacuum line.

 

What height did you set your floats at?

 

Does the switch unit that the throttle cable is fitted to have a proper earth onto the handlebar? Oops looking back at the thread I have asked you that already .

 

This is an interesting question. I eyed them up and they were all exactly the same height. So I left them alone. What are you thinking?

 

This could be the problem, I bench set mine to 17.5mm , float needles tips can dry out and get a groove on them this can effect float height as well not much but still there . If the float height is low you may not get enough fuel on float bowl. What you could do put a container under the float bowl drain screw collect pour it into a measuring cup see if all are the same. To wet set you need some clear hose on the drain nipple , open drain screw hold hose up to the top of carb float bowl should be within 3mm , there are some threads on doing this , Hogfiddles can help you with it .