Could use some advice please. I have a 919 blade powered Westy (SEW not the Megablade version).



I was doing some work on my intake system today adding some cold feeds to try and improve the quality of air getting to the engine. After doing this took the car for a run and after about 5 mins on the road it developed a misfire and lack of power.



Brought it home and checked a few things, all ignition seems fine and the miss fire is with both Cylinders 3 and 4. Took the air box off and the carbs on cylinders 3 and 4 were both full of fuel (1 and 2 were fine). Also when idling there was fuel running out of the carb overflow (quite a bit).



I drained off Carbs 3 and 4, then the engine seemed to run fine. Took it out for another run and generally seems OK, the performance feels different but might be down to what I have done with the intake (cold feeds fitted and sealed direct to the standard 919 Honda supplied airbox). It seems to be a bit rough at low speeds.



Things I am confused about.



1 - Could what I have done with the intake have caused this issue?

2 - Just draining the Carbs does not seems like a reasonable fix, could there be something else underlying? (carbs were serviced at AB performance just a couple of months ago so I'd be surprised if they had an issue)

3 - Are there any common reasons for having a misfire on 3 and 4?

Any thoughts or advice would be great.

I run 919 carbs on a pinto and often find if the car has been stood for any length of time and the fuel has evaporated, the needle valves on the floats won't shut off the pump when the bowls are first filled, but knocking the top covers helps if one of the needles doesn't seat. I usually just let the pump fill the float bowls and wait to hear it stop clicking before I start, but the first time it did it, I also drained the float bowls and refilled and it sorted itself. Not sure why yours has presented mid run though.

I'd probably whip the carbs off and check the condition of the floats and needle valves in 3 and 4 for a start and go from there. I doubt your intake mods have had any influence on this.

A bit left field, but your dad wouldn't happen to be called Pierre would he?

Thanks very much for the advice, appreciate it. I'll get the Carbs off this weekend and give them a good inspection and clean.

My Dad is Pierre (and there can't be two), do you know him from CTT? Small world :-)

They are also extremely sensitive to exhaust or inlet changes so removing or replacing the airbox or even putting in a K&N filter element will upset, if you move away from standard bike parts look for a dynojet kit or similar to restore power.

Thanks for the the reply,

I am just running the stand honda airbox with some hoses connected directly to it and routed to the nose cone to pick up better air.

Hi All, here is the update.

I took the carbs off today, cleaned them out and replaced all 4 float needs. Everything else looked in good condition.

But unfortunately the carbs are still filling up with fuel, with the engine off and the fuel pump energised after about 30 seconds fuel starts coming out of the carb overflow pipe.

The fuel pump does not stop running for some reason, its the bike spec pump with the Mitsubishi logo on the top.

New fuel pump do we reckon?

Also, please could someone confirm that the fuel pump cu toff functionality is inside the pump? Its not related to any other external sensors?

Would appreciate any replies, thanks very much.

Here's a thought:

Are you sure the floats actually 'float'?

It's possible they are cracked slightly and thus letting fuel in and not actually floating - and thus not closing the float valve.

Or, the little tabs on the floats are slightly bent and thus the floats are not closing the valves.

If you remove carbs, fill them with fuel from a suitable vessel (pop bottle with a tube) to act as a tank - do they flood?

If so, then if you swap 1&2 floats over to 3&4 which ones flood?

Thanks for input, good idea. Like the idea of testing the floats by filling the Carbs manually.

Although I did inspect all the floats when cleaning out the carbs and they looked in good condition with no obvious cracks or damage.

Can anyone please answer the other question in my previous post? About the functionality of the how the fuel pump regulates itself?

Thanks very much.