high speed, throttle off/on, bike hesitates

[icenian]

This will be familiar to many of you: riding with revs around 5000rpm in 4th or5th gear. roll off throttle a bit, then roll on, and you get a couple of seconds hesitation. Perfectly possible to ride through it, but obviously not the correct throttle response.

The standard answer (high Yen!) is an air leak between airbox and carbs. Overtighten the collars and the airbox-carb rubber bits slip off the carbs.

But... what if you've checked that out (and in fact the airbox hasn't been off in maybe 3000 miles) and it's fine?

Air filter fine. Plugs look fine. Engine runs perfectly at other revs; power and fuel consumption seem normal; idle even and predictable; drops from higher revs down to idle speed smoothly; no odd noises, smoke from exhaust, etc.

What to check next?

[StumpyFingers]

It sounds very much like the standard air filter. I had similar responses on my Transalp until I fitted a Piper Cross air filter.
It gives a better air flow and seems to remove the flat spot.

[Chris.R.]

I picked up somewhere that with a DynoJet kit is a drillbit (I think 2.5mm) supplied in order to enlarge certain holes in the carb slides - this gets you a faster throttle response, it did it with mine.

There must be some post about it in this forum.

[icenian]

It may be possible to improve throttle response with modifications, but what I have is simply a failure to respond like the stock bike. I've had the bike long enough to know that this is something different to its normal behaviour.

This has been described before, where the airbox isn't sealed to the carbs properly (usually attributed to over tightening the collars). But that's not the issue in this case.

Last night I found that the outlet at the bottom of the airbox (where the drain tube attaches), which is a separate bit of plastic, doesn't look tightly sealed to the bottom of the airbox. Doesn't look significant enough to cause a problem, but have sealed this with silicon sealant anyway.

[BobA]

Loose wrist?

[Loudpedal]

The symptons you decribe are similar to my bike.
I changed the fuel pump which cured it

see the link below
AT Fuel Pump: to recap


Loudpedal

[icenian]

Loose wrist?

nah, I ride an Africa Twin, not a BMW

(there's never a smiley-with-lederhosen around when you need one)

[icenian]

The symptons you decribe are similar to my bike.
I changed the fuel pump which cured it

thanks, I'll try bypassing the pump if none of my fiddling has had any effect (which seems very likely)

I assume the fuel line out of the pump will fit the fuel filter, so should be a 2 minute job to bypass the pump. And unplug it of course!

[YEN_POWELL]

thanks, I'll try bypassing the pump if none of my fiddling has had any effect (which seems very likely)

I assume the fuel line out of the pump will fit the fuel filter, so should be a 2 minute job to bypass the pump. And unplug it of course!

By-passing the pump will get the engine running, but high speed riding is a bit iffy, even with a full tank. I found that at 60 or 70mph, if I overtook anything the engine would cut out, I would roll to a stop and have to restart the engine. Not enough fuel getting through on higher throttle settings so I assume I ran out for a few seconds each time (well the carb did anyway).

[Farmboy]

I had the same when I first got my RD04.

I changed everything on the bike apart from the Airfilter as it looked clean as a whistle.

In the end there was nothing left to do as I had tried almost everything else so I threw a new standard airfilter on and bobs your uncle, it has never been an issue since.

Unless you know your Filter is new and in good order you cannot go by looks alone.

HTH

Chris