Hot starting issues.

[Vard66]

Right.

I've seen a couple of threads on this, but nothing with progress in it, merely 'have you got them?'.

It's getting to the point of rediculousness with my bike - so much so that I have started allowing myself about 25-30 minutes if I'm going to need to fuel up on my way to work.

Thinking about it for the last few hours, I'm suspecting to a degree, vapour lock being somewhat of a possibility.

Another thing worth thinking about more specifically, is the routing of the fuel line - resting atop the gearbox and directly behind the carbs and top of the cylinder head as it is, it's got to be subject to some fairly high temperatures, so that's worth thinking about. Not only that but it has an uphill section to the line, which if vapour lock is ocurring within the line more prominently, would be a bit of a bitch to solve.

Worth trying I think is a) adding breather lines to the float bowls - allowing vapour (being less dense than fluid), to escape the float bowls and denoting reliable fuel feeding, and b) attempts to cool the fuel line, or simply heat shielding it to a degree, by switching for metal braided line, and possibly afterwards, wrapping said line with some heat shielding tape.
Option c) is a bit more involved, if neither of the above work. Option c involves a small, low pressure pump, installed in either the tank or the fuel line itself, to keep oh, say, 2 or 3 PSi of pressure on the fuel line, and avoid any complications caused by either, or a combination of the uphill section and slight vapour pockets, not allowing the line to flow correctly. An electric carburettor pump, if you will.

The only things that would thwart that theory somewhat initially that I can see, would be the float bowls on the carbs already having breather pipes built in, or the bike already being fitted with an electric carb pump. It'd still be possible, but they ought to alleviate the problem fairly well.

Can anyone answer me the question of whether or not the ZXR 400s had breather pipes routed from the float bowls as standard, (and if so, across the range, or only on some models).

The same question for Electric Carburettor Pumps.

The bike in question is a grey L4, in case anyone is wondering.

[Vard66]

Doing some more thinking.

It strikes me that I haven't spotted a carb pump, and I've had the tank off enough times to have noticed one if there was one there.

It also strikes me that a carb pump is a more practical approach to the situation because if would pretty much negate much of the probability of vapour lock occurring in the float bowls, as the fuel would be recondensed under the pressure after the pump.

So a further question - presuming my not noticing a pump is the correct assessment, and there isn't one fitted, could anyone tell me what sort of PSi I would have to pump for in order to push the pressure behind the float bowl just over the normal flow rate of fuel at full chat under full load, and just keep the fuel line under pressure?

[zimm]

you saying your bike doesnt have a fuel pump ?

cos it should

float bowls are vented as standard.

[tk400]

Zimm after doing alot of data logging on ignitions of late I have some theories on this. What CDI are you running and do you have an alternative one to experiment with. cheers

REgards TK400

[Vard66]

I didn't honestly know, Zimm. I'm just trying to throw any theory I can at why it's still doing this, because it's really pissing me off.

[zimm]

Zimm after doing alot of data logging on ignitions of late I have some theories on this. What CDI are you running and do you have an alternative one to experiment with. cheers

REgards TK400

interesting angle

pm sent anyway ..

I didn't honestly know, Zimm. I'm just trying to throw any theory I can at why it's still doing this, because it's really pissing me off.

the fuel pipe should run through the filter to the pump, then to the carbs.. does it

oh, try disconnecting the carb heaters if fitted, tae some heat away from the carbs

[Vard66]

Worth trying. Tomorrow morning the tank's coming off and the carbs apart, and she'll get a good dousing down with carb cleaner. Might also flush the fuel lines through, so I'll pull of the carb heaters then.

[Vard66]

Can anyone confirm for me whether the carb pump runs to prime the system before pressing the starter button, or only during actual running of the engine?

[zimm]

pump only runs once the engine is spinning, even then its an occasional tick rather than continuous running

[Vard66]

Ok, that's pretty much what I suspected, thanks dude.