Idea's please........

Having probs getting enough fuel to carbs after a long full throttle run, problem was showing itself at Donnington after going down straight on full throttle i was running out of juice before i wanted to brake, just tried a few things which haven't made things any better, pretty sure it is lack of fuel, just been out on a couple of test runs/blasts, runs great runs out of fuel (i think) back off give pump time to catch up ok again ?

1) Do you think it is fuel pump related ?

2) Running standard pump but the tank is at very front engine is, as you prob know at rear, the pipe run is long.

3) Not sure a after market pump would do the job as to get the pressure down to suit bike carbs you have to regulate them and lose lots of flow.

4) It dont show under "road" driving conditions but only after continuous wide open full throttle runs.

5) What do you think to putting a 2nd bike pump and line in and feed 2 carbs with each pump?

Any body had a prob like this that turned out not to be fuel pump related, am i barking up the right tree ?

Ta Jon.

oh, the fuel pump is 6" of pipe and a filter away from tank and pumping all way to carbs, would it work better nearer the carbs ?

The twin pump idea sounds reasonable Jon. If they are like the one on my bike they should be o.k supplying 2 carbs each as it only has 2 carbs.(NTV) Would gravity get the fuel to the pumps if you mounted them at the engine end? If so they might be better there and not have to work so hard.

quote:

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Originally posted by Jon Ison
oh, the fuel pump is 6" of pipe and a filter away from tank and pumping all way to carbs, would it work better nearer the carbs ?

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Just a daft thought Jon, but would it help if you had your breather pipe 'fed' from the front ie pressurised by the air flow at high speed, this might aid the fuel to the carbs, as to pump location, it depends on the type of pump, some need to be near the tank and others should be near the carbs, no idea how the bike pump needs to work, but your suggestion about using twin pumps might work, you will definitely get double the flow

Jason

Pull the line loose at the engine and pump fuel into a known size container.

Most engines use less than .5 pounds of fuel per horsepower per hour. Since you want a safety margine you might look for 1 pound of fuel per horsepower per hour.

Sooo....

If you have 150 hp engine you would pump 150 pounds of fuel per hour, or @6 lbs. per gal for gas 25 gallons per hour, or .42 gallons per minute.(1.6 liters per minute)

I would think the factory pump for the engine would have enough excess capacity to run, even with the extra line length, unless the motor is modified.

You may also want to check fuel filters, and possibly change to a high flow unit if not using one already.

If you use dual pumps paralell them at the tank with a "Y" on the inlet and outlet. The check valves in the pumps will regulate the flow. If the pumps were split to feed the carbs seperately a single pump failure could starve 2 cylinders un-noticed.

what about a one litre tank near the engine, filled by a low pressure pump, with a high pressure pump to send it the rest of the way? like a glorified swirl pot.

I had a similar problem with a bike I used on track days, at cadwell it was ok untill I went down park straight.
We traced it, after loads of head scratching, to the vent hole in the filler cap. As the pump was sucking the fuel out a vaccum built up and stopped the flow at full throtle. Hope this helps, good luck.
Kipper

Cheers,

I have a non return in tank, will pull it off and give it a blast, could be stuck, not checked it,

Good point about 2 carbs running out of fuel with seperate lines.

Gravity will get it to rear of car, think i'm gonna pull breather off, if its not that move pump to rear, if that dont sort it maybe add a second pump.

is the pump mounted so it is gravity fed by the tank, if it has run for a reasonable amount of time without a gravity feed they become lazy, i had this problem on a freinds grass track car, a new pump would only last two / three meetings, once we made the pump gravity fed he has done 17 meetings and no problems, when i asked honda about this they confimed that was the case.

Normally the bike pumps are ultra reliable

hope this helps

regards

marc

just re read your post john, you need to have the pump as close to the fuel tank as possible and mounted below the feed from the tank to make sure it is gravity fed

hope this helps

regards

marc

[Edited on 28/9/04 by marc n]

Bike fuel pumps are usually Mitsubishi pumps similar to those fitted to Subarus etc, but they differ in their delivery.
DO NOT try a gallons per hour test with these pumps. They are designed to run only intermittently or for very short times at full capacity (think how a bike works). You'll burn it out quickly if you ignore this.
Mount it as close to the tank as possible as was mentioned above, pumps push many times better than they suck.
Do make sure it's gravity fed.
Do make sure the bore of all fuel lines and fittings are at least as big as the ID of the pump inlet and outlet.
If you've fitted an aftermarket free flowing air filter in place of the restrictive standard air box configuration, your engine may just be seeking more fuel than the pump can provide, but I doubt it.
As already mentioned, a belt and braces solution would be to fit two pumps, but they should simultaneously feed all four carbs. You'll need to fit one way valves in the fuel lines between the pumps and carbs to do this to prevent the pumps trying to pressurise each other and shutting down. Bike pumps will shut down at around 1.5-2 psi, so it's not difficult.

Jon

Ive got a spare pump if you want to try two.

quote:

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Originally posted by Mk-Ninja
Jon

Ive got a spare pump if you want to try two.

I'm sure I've got one, just don't know where I've put it

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Jon,

how about a small header tank above the carbs that holds a small amount of fuel to allow for long open throttle runs when the fuel line might be too long for hte pump?

Ned.

Ned - would that be the same as Joels suggestion then

thnx for the input, got home to late to do anything tonight, will keep you posted what cures it.

Just been a blast with non return removed, defo better but still there, bit o work on fuel pump next, the fact its better with non return took off tells me it must be fuel flow related ? Wot u think?

What size fuel pipe have you used. Most bike pipework is 10mm.

smooth bore 10mm copper flexi easy bend stuff, think its just the distance its traveling, the pump i seem to remember came off a CBR600, they all look the same, well this one looks exactley same as a blade pump, i wonder if they are all the same ?? anyone know ?

Dont know if there different between units. As I said before Ive got a spare off a ZX9R if want to try it.

If so I would guess you need a bigger pump.

If not... do you have a screen on the in-tank pick-up? It could be clogged by trash.

Given the fact that removing the non-return made a difference, I bet you need a bigger pump.

Jon, having 10mm bore fuel lines means nothing if the fittings reduce the diameter. As I mentioned before, the entire system must be larger than the pump inlet and outlet. You may need to use rubber hose to connect the pump barbs to the copper line and don't use any brass or plastic unions that could reduce the ID.
The distance from pump to carbs won't be a factor.
If the pump is off a little 600, then it may not be man enough for the job. I would compare pump part numbers at your friendly local bike shop and then, if necessary, source the correct pump for your engine.
It may even be worth fitting the pump from a larger capacity bike. Just don't try a car pump with a regulator as the regulators won't provide consistent low pressure as required by bike carbs.

Jon,

why not get MK Ninjas fuel pump for ZX9R and try that in place of CBR600 pump as another alternative.

It was a combination of tank breather and fuel filter, just had another iccle blast with no probs at all, the fuel pump must be marginal though so gonna source summat suitable, maybe the one i have aint 100% ??

anyway can get on with reverse now, thnx for the input.