Engine not running well.


HI All,
I have acquired a kit car with a Hayabusa engine - having a few problems. I believe it is a standard Gen 1 Hayabusa engine. Normally the engine runs very lumpy at tick over - and does not have a lot of power. To my ear it seems a fuel starvation problem. I put a gauge in the high pressure fuel line - 45psi all looks okay. I played around with the pressure regulator (its not the standard Suzuki one) and found that if i increase the pressure to over 75psi the engine appears to start running fine. It ticks over fine, and I took the car up to about 80mph without any issues. My concern is that I believe a standard Hayabusa should run at 42psi - plus this is what the pressure regulator was already set to.
Engine doesn't look like it is running too rich, exhaust is not coloured and doesn't smell like an engine running rich. My thoughts are that maybe the injectors are blocked and need a good clean? Does anyone else have any thoughts that could help me. If someone has played with the ECU, would they ever remap to a fuel pressure as high as 75psi ( i assume this would need special injectors). My next step is to remove the injectors and give them a good clean. But as each injector has its own little filter - i struggle to see how the increased pressure would seem to suit all the cylinders? As you canb see I am a bit of a novice so any help gratefully received.

Kiwi Rider

The spark plug color (black and sooty, white and lean, golden brown etc) will give a good indication of how the air/fuel ratio (mixture) is applied through the injection system.
Does it have a Power Commander attached? If so, disconnect it.
Is it a Gen 1 motor or Gen 2? Does it have an O2 sensor in the exhaust system? Does it have secondary throttle flaps? these questions are to determine the year model engine you have.
Have you checked the amount of fuel the pump can deliver?
Fuel pressure is one thing, but an adequate delivery volume over a given amount of time is also crucial to supply enough to make it run correctly. This check is often over looked.

The fuel discharge amount is 458ml in 30 seconds with the pump running on a fully charged battery, and at least a gallon of fuel in the tank.

If it's less than that amount, that is a problem that needs to be corrected before you go any further. Check these items .....
1) Is the fuel pump screen/sock blocked?
2) Is the pump worn and tired from old age?

The fuel pressure should be 42psi as you said, 75 psi is way too high. The fact that it runs better at higher pressure only shows there are other factors causing the fueling to be so 'lumpy' at 42 psi.
I really think you need to start at the basics and eliminate all the obvious possible causes first, before getting into the more complex areas of ECU mapping etc.
Hope this helps . . . let us know what you find re the fuel pump delivery.
PS . . post up some pics if you can, would be cool to see the beast.


Guys many thanks for all the replies so far - really useful. I will check the fuel delivery amount tonite - I eyeballed it previously and it seemed a good flow on an 8mm bore tube - so i think it will deliver 458ml in 30 secs - but real easy to test.
Power commander - it does have an additional small black box attached to the ECU - i didn't know what it was - i will investigate if it has any writing on it. I have just received the Haynes manual for Hayabusa bike so I will be able to locate and check for the O2 sensor. I will also hopefully get the plugs out tonite and see if their colour tells me anything.


Fuel pump is pumping over 500ml in 30 secs so that looks okay. Spark plugs bit black but not worst I have seen. Going to take the injectors out and get them ultrasonic cleaned - see where we go from there

Kiwi Rider

Going to need an impact driver to get the fuel rail screws out
Try a sharp small cold chisel on the edge of the philips screws, or even a sharp dot punch. I have used a dot punch on front rotor bolts that were loctited and rounded off in the internal hex, undone all of them successfully!
Just another technique for unscrewing stubborn screws and bolts.
Hope it works out for you.
I really like the kit car, very cool, and that is a Gen 1 motor by the looks.
Nice property you’re at, that tree is a bit overgrown, needs a prune ASAP lol.


Put it all back together yesterday - new plugs plus cleaned injectors . Set fuel pressure to 42psi runs sweet as a nut. Just need some sun to get it on the road. Thanks for you help Kiwi

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