Hitchcocks Forum

When I go down a slope (plenty of them in Norway), and brake on the engine for more than approx 500 metres, I hear little explosions in the exhaust, and then the engine may even stop. What can this be due to ?
My Bullet starts normally, and during driving on flat areas, or uphill, I never have engine problems.

Start by checking all exhaust joints for leaks especially around the header & silencer joints & seal with silicon sealant that's the usual cause.

"They all do that, Sir" . . . . quote from RE Dealer. My B5 used to do the same - tighten header studs to 20Nm. Don't use silicon seal at the header joint but it is a good idea for the down tube to silencer joint.

NicoV, what do you mean the engine stops? Stops firing, then clears with a bang in the exhaust and keeps running?

The problem could be as other have described or it could just be you need a hotter running spark plug.

I use silicone sealer on the head joint - no problem.
Air leaks anywhere on the exhaust system can cause popping on the overrun. I don't see how your engine can stop if your on overrun?

If this is an EFI then "reversion" or "deceleration popping" is a common problem on any fuel injected motorbike. Part of the problem is unburnt fuel going down the exhaust, which is hot, the ECU having cut the spark (because the TPS is shut), it then explodes, the other part of the problem is cold air gets sucked back into the exhaust, which is hot and so it expands rapidly with resulting bang. This is not back-firing where the timing has gone all wrong. The situation gets worse if there is a pair-valve in the system, these things are designed to make fuel burn in the exhaust. Air leaks at the head and between down pipe and silencer will exacerbate the problem.

Best seal I've got at the head is by using two copper ring gaskets (for a previous Bullet model) rather than the "cement biscuit" original fitment.



The popping can largely be cured with a Power Commander (PCV) by setting it so that at high revs and zero throttle, it cuts off the fuel completely. Which I have done and it does work except for the occasional solitary pop before it manages to shut the injector off.



If you have an EFI without the PCV then you may find opening the air bypass valve a little more may help, that's the brass one practically under the seat.



Trying to kill the motor on a long decent may be the O2 Lambda sensor telling the ECU the mix in the exhaust is very, very rich, thus shutting off the injector completely, and so it dies as if running out of fuel.

If I remember correctly you have a push fit exhaust? Remove pipe and clean joint, decarbon. Smear with clear silicon, refit and leave overnight to cure.. Turn in the pilot screw by 1/8 to richen pickup from tickover but may need slightly richer slide number..

Another thread where we don't know which flavour of Bullet we are discussing.

I've never been too sure how the push-fit exhaust is supposed to stay in place A good soldering iron uses silicone insulation on its lead, these things can run to 800°F and the silicone doesn't melt or burn if you touch the iron to the insulation. So yeah, silicone rubber bath sealant makes a jolly good exhaust sealant, clear or white. Silicone sealant not acrylic... better than exhaust gasket goo.

The "cement biscuit" on the EFI however is worse than useless, when I went to fix it, it simply was not there, it had disintegrated and disappeared down the exhaust; cleaned it all out with a rotary port brush.



Reversion is not unique to fuel injection, with a carburettor the throttle slide could be lifted a little too high at zero throttle, which allows too much fuel to be drawn from the main jet on a decent. As an afterthought do check the plug as long descents may lead to fouling (where the plug is not getting hot enough to self-clean), which can cause missing and then then motor cutting out.

Sorry, forgot to mention it. A 1999 Bullet 500.
Yes, after about 500 m the engine stopped. I parked it, and had to restart it. It started after a few kicks.
I just talked to an Indian colleague, and he mentioned he experienced that several times during trips with an Indian non-UCE Bullet 350.