Fuelling Problem??

[SteveLee]

A couple of times recently I've experienced what feels like the engine cutting out. Both times it has been after slowing down from a long period of 70ish cruising on the motorway. If I open the throttle wide it then picks up again and seems to be OK.

It did this a few times yesterday on the M42 coming back from the National Rally, but never fully cut out. When I came off the m/way it ran OK. Also both times I was probably down to the last 5 litres in the tank.

Anyone had any similar problems.

(Bike is '02 RD07, 16k miles)

Steve

[DaveS]

Yep I've experienced this myself and I believe its a common "complaint" with AT's.
I've read lots of debate as to what causes it, from fueling to electrics. I'm not sure there's a definitive answer.
Some AT's seem to suffer others not.
The best explanation I heard was that it was the air filter cover that was tightened down too much.

I had an AT that would now be 4 years old if some scrote hadn't knicked it, ermm anyway this suffered from that problem off and on. My latest AT, that was new 2 years ago, also initially suffered from it, but then hasn't since then.
Very strange.

[SteveLee]

Cheers Dave.

I thought it might be the fuel pump problem at first but I was under the impression that this was fixed on the later models. Also if it wasn't getting enough fuel why would it pick up when the throttle opened up?

Not sure what effect the air filter tightness will have but I'll check it out. I might have look at the pump as well, see what the contacts look like. Maybe fit a new fuel filter as well.

Steve

[samih]

This used to happen on my bike ( RD07a '98 ) on high speed cruising (motorway)

1. Riding fast with pretty much throttle
2. Close the throttle -> high vacuum in the inlet manifold
3. Open the throttle somewhat to maintain the speed -> bike feels like stalling for short while (approx. 2 seconds ?)
4. The engine starts to pull again.

I think this is how the AT carbs should work. The are CV model, which means that the slides are controlled by the inlet manifold vacuum, but there is a slight delay on how quickly the slides (and the needles attached to them) are allowed to react to the throttle. The result is that the bike runs on VERY lean mixture for a couple of second or so before the slides adjust (the icarbs momentarily only supply enough fuel for idling while the throttle is already on wide open position).

This is why the Dynojet kit includes a drill bit to drill the slide lift holes (via them the manifold pressure is lead to control the slides). This sharpens the throttle response and is highly recommended. The downside is that the ride can be a bit jerky on lower speeds as the carbs react to throttle almost instantly.

The drill bit with Dynojet kit is 2.5 mm I was told and this was the size I used. I'm very happy with the bike with this mod. The above motorway behaviour is now history.

Edit:

Yeah, and the fuel pumps still fail, too. I have had a Pierburg electric with VERY low pressure (0.1 bar system, 0.4 bar max static) in place for few months now. Ah, that's another load off my mind when thinking about AT weak spots.

[YEN_POWELL]

Re the air filter tightening.

When the airbox is pushed onto the carb mouth it seals quite well. However when you start to tighten up the clamps the front boot starts to lift upward losing the seal. I used to get the hesitation mentioned and found that if I don't tighten the clamps up too much it doesn't happen.

[samih]

When the airbox is pushed onto the carb mouth it seals quite well. However when you start to tighten up the clamps the front boot starts to lift upward losing the seal. I used to get the hesitation mentioned and found that if I don't tighten the clamps up too much it doesn't happen.

I noticed the same when putting the bike back together after the carb operation, they are a b*tch to put back. Maybe I was suffering from incorrectly installed air box all along, although the joint appeared well seated when removing the box.

[SteveLee]

Thanks for the advice guys, see what you mean about the airbox now.

Interestingly I have only experienced this since it's last service! I guess the airbox would have been removed to check the valve adjustments.

This, plus the prices that Abingdon M/C charge these days may tip the scales in favour of doing my own servicing in future!

Steve

[SteveLee]

Update:

I did the first longish run on Sunday since it's 16k service, and there was no sign of the problem. At the service they said that a couple of valve clearances were out and the carbs were slightly out of sync. I guess the airbox was also removed/re-fitted during the service as well.

Steve