Hunting Idle

[alexanderfoti]

Hi all

My bike has just started doing this odd hunting idle thing.

Come to a stop, Rev sit at 1100. wait 30 seconds or so, they rise to 1250, stay there for 30 seconds, then drop to 1050, rinse repeat.

Its just started doing this. It only does it when hot.

[albertaphil]

I have had several large diesel engines act just like that when they we're getting air in the fuel system.

[alexanderfoti]

I have had several large diesel engines act just like that when they we're getting air in the fuel system.

Interesting. I will re-check pipe work. Many thanks

[alexanderfoti]

Your theory seems to be right.

Its gotten worse to the point that on my most recent ride, a long 50mph section, I started getting misfiring and surging, like a big air leak.

Really annoyed me. The problem is all my fuel pipe is veg compatible, all of the joins have hose clips AND are really tight on the connections.

I have

Tank - to this to a lift pump, then to a CAV296 assembly, then to the lift pump.


There are no leaks that I can see. I have also checked my leak off line so see if thats what was causing it, all good there. I have good flow if I take the fuel pipe off the injection pump and turn the fuel pump on. Whats the best way to find out where there may be an air leak?

[albertaphil]

Well, presumably the leak must be before the lift pump or you would be leaking fuel out rather than air in.

My guess is that it is the gasket of the sediment bowl in your picture. Much harder to seal properly than the pipe or hose joints.

Probably the lift pump produces enough suction against the thick veg oil to pull air in but there isn't enough hydraulic head from the fuel in the tank to squeeze the same thick fuel out the gasket when the engine is off. That's why you can't find the leak.

[alexanderfoti]

Went over the hole system last week, found 2 rather suspect hose fitting and one that was definitely leaking air, all patched up now so lets see how it goes!