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Symptoms of a bad throttle body

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I am converting a dirt bike to EFI. The only small throttle body (28mm) I can find that fits well in this bike is a chinese one. Cheap enough, so I purchased it. The build quality is mediocre. The TPS is cheap and the injector is cheap too. I am predicting am going to have problems with this little guy. I was wondering: what kind of issues would I see with a cheap throttle body? Some of the thing I can think of are:

- TPS is not consistent

- cannot fit a "real" injector, so have injector flow inconsistencies

- butterfly valve could leak air, causing erratic idle

Other things? The reason I ask, is that I can get a machinsit to make one for me, but it will cost $$$. But I can then use my own injector and TPS. We can also do a better job of controlling machining tolerances.


Is there a similar sized dirt bike that already has EFI (say another brand). Perhaps you could adapt their throttle body.

There is only one, and it is much too big for this bike. Unfortunately throttle body EFI for the small bikes is not common.

Have you considered separating one trumpet from a 4 cylinder sports bike? Or looked at modern scooter engines?

The scooter - yes. That is the one that I found (Zumo) - separating 1 from 4 - good idea - I will take a look around.

All of the issues you've guessed at are on point. The biggest issues would be inconsistent throttle closing which will affect idle, or alternatively leaking around a poorly sealed throttle plate. Beyond this an inconsistent signal from the TPS will give you a lot of trouble. Is it not possible to machine the throttle body to take a conventional injector? If so I'd be very wary of the supplied injector quality.