Fuel starvation when trying to start engine

[davidrsmith]

Hi

I got the carbs back in the bike and tried starting the engine , no luck!

From previous posts I set the float heights to 14mm, but I saw a reply to my previous post which may indicate I did it slightly wrong and the weight of the floats were on the float needle valve.
Pre fitting I had the carbs on the bench and connected them up to the petrol tank, the carbs filled with no overflow.

However when fitted to the bike and the petrol turned on, no petrol flowed into the carbs (I had left some in there from the bench test), I took the petrol pipe off the carbs and petrol flowed.
I checked the plugs and they were dry and no evidence of unburnt fuel. I loosened the drain plugs in the carb bowls and petrol dribbled out of the overflows.

Does anyone have any ideas of what could be wrong?

Also on the float valves what is the little plunger supposed to do, my guess is that it should cause the rubber tip to protrude, am I right?

Many thanks
Dave

[davidrsmith]

Sorry forgot to mention, when I disconnected the fuel pipe and opened the choke and turned the engine over it sounded like it wanted to fire, so I was guessing the air/fuel mixture was incorrect.
The petrol/air screws are set to about 1 and a half turns out.

Which way do you turn the screws to add more fuel to the mixture?

Dave

[K2-K6]

If you've no air filter on the carbs then blow a small amount of fuel down each carb,  close the choke and try to fire it then. If it runs briefly then stops after the additional fuel is used then you've got nothing being drawn into the intake from the carbs.

You may find if it catches it will then continue to run on its own though.

If air filter box is fitted, try the same by removing the filter and spraying some carb cleaner down the box then cranking it.

For fire risk do the above outside away from flamms risk.

[K2-K6]

The idle/air screws shouldn't really affect the starting much as they are a very fine tune of tickover mixture when engine is warmed up and running off choke. They should be fine to start it where you've got them.
The choke will override most mixture settings when it's applied so I doubt you'll see any effect if you move the screws from what you've got.

As the plugs are dry, then as previous post,  try to get a little fuel into it by fairly crude methods and it'll probably run if other things are operating correctly.

[Bryanj]

If this is a 550 K3 they are a pig to start if left for a while and also need petrol that is less than 2 weeks old

[hairygit]

That thought crossed my mind too, but lack of fuel precludes that being an issue, persistent flooding would be the case if that were the issue.

[mike the bike]

Have you checked the fuel cap breather or eliminated it by having the fuel cap open?

[Seabeowner]

Same position on my 550K (1978). A DK import and obviously off the road for some time. Spent a week cleaning inside and outside of the carbs and used up many new parts. Starts on ether spray, but immediately dies. About to take apart again and get ultrasonic cleaned. Suspect slow running jet or passageways. The result may be a few weeks off though. I note Bryan's comment on starting. Is it just the pd carbs or pd carb/550 as pds were also on the later 750s as well weren't they?

[hairygit]

Yes, and were just as troublesome!

[Bryanj]

Have you actually removed the push fit pilot jets as they clog up for a pastime and yes all the PD are a swine

[davidrsmith]

Hi

No I didn't take out the push fit pilot jets, the carbs were stuck, and the float bowls, float needles and emulsion tubes were well gunged up with petrol residue. So I took all those out and cleaned them. I have just watched a couple of you tube videos on how to set float heights, so I probably have done them wrong in that I had the carbs upside down, whereas they should be on their side at an angle ( I don't know that that angle is), and then the floats are measured all along their length.

I did try opening the petrol cap, but that made no difference, I had the air filter etc on as well, so before I take the carbs off again I am going to disconnect the air box from the back of the carbs and then spray some petrol in, see how that goes.

I also found out that the float valve plunger is just a shock absorber.

Dave

[Bryanj]

You need to remove and clean those pilot jets or you wont cure the problem

[davidrsmith]

Are the pilot jets you are referring to the slow speed jet that is between the emulsion tube and the floats, or are you referring to the petrol/air mixture screw that has a spring, washer and rubber grommet on it?

I did take the petrol/air mixture screws out and cleaned them, but as I now have the carbs out of the bike again I may take them out again and blow them all through with an air gun.

When I took the bowls off the carbs they were full of petrol, so I still don't understand why there was no petrol being sucked out into the engine.

Any other suggestions on what to look at and check would be very welcome.

[Bryanj]

They are the pressed in jets that stick into the float bowl and I can just about guarantee they are blocked and that is why you are not getting fuel into the engine

[deltarider]

Like in the pic below.