OK, I do understand that blipping the throttle causes the engine to die because it's going fast enough to suck fuel in but no fuel is coming. I sort of accepted this even though it doesn't happen on my gs500, in fact one particular method of testing the carburettor is to bring the revs up to a few thousand and then shut it down and the engine is supposed to quickly drop back to idle with no wandering.

This is how it behaves on my GS which is a similarly archaic machine. Blipping the throttle on the GS no matter how aggressively will not shut the engine down. So why does it not shut the engine down on the GS but it does on the S40.

I've raised the idle when hot speed to 1300 in order to try and avoid this. Occasionally if I'm not careful the engine will die and I've sort of gotten used to it and it does not happen very often now. This is how it's been since ever.

However yesterday I have discovered that this could in fact be a life threatening problem. I'm about to install some new front brake pads which have lasted a surprisingly long for OEM's 12,000kms this seems to be about double the 4000 miles I've seen reported. Anyhoo so before installing the new pads I thought I'd practice some emergency braking on the old pads so that after the new pads are broken in I can see if there is a difference in emergency braking with better quality pads.

This is when the aforementioned life threatening problem manifested. OK so I'm tooling down the road at a decent speed, not too fast but fast enough to test the stopping power, at about 80 km/h shut the throttle, remain in gear grab a handful of brake and just before I come to a stop I pull the clutch in but the engine dies. This can be problematic if someone is coming up behind me and I need to take off quickly. In fact this is the very reason that we are urged to remain in gear during an emergency brake.

Do other people have this problem? How do you solve it, do you put the idle speed up even higher? Running a 52.5 pilot.

You're not downshifting and working the throttle and brakes together?

Yeah I do that when riding normally but not during an emergency braking procedure.

justin_o_guy2 wrote on 06/06/17 at 18:00:52:

If I do an emergency stop and grab the brakes and clutch and chop the throttle instantly.....the engine may stall, and often does.

It is a situation that does occur as the engine just isn't getting enough fuel when the needle drops into the jet and the only fuel flow is the Pilot jet.  On your GS with multiple cylinders it just isn't as likely to happen....maybe it has something to do with the engine size vs. the carb size....not sure.

I don't think the Dial a Jet will help if you installed one - as it is on the air filter side of the slide.

Can you get any "pure" gas in your area that doesn't have ethanol mixed in?  That might make the TEV circuit more helpful as the ethanol runs a bit leaner than pure gasoline.  Also make sure your TEV is clean and the diaphragm isn't stiff - as they age the diaprhagm becomes stiff and the TEV doesn't work as well.

You need to downshift and keep the engine spinning over.
Can you Drive with it in fourth gear and ten MPH on the speedometer?
You're killing the motor with the brake if you don't downshift.

justin_o_guy2 wrote on 06/06/17 at 19:25:00:


The issue he is having is not with a normal reduction in speed that provides you with the opportunity to shift gears and slow down casually.  His concern is in an "emergency stop".....you are cruising along at 60 mph and you need to stop "NOW"!  So you chop the throttle and pull in the clutch....and apply the brakes as hard as you can. The engine has instantly gone from 4,000 rpm to a closed throttle  (There is no time to downshift while you are  doing everything you can do to stop and avoid locking up a wheel or hitting the deer/car/truck/moose).

Under these conditions, the engine can stall and I don't know anyway to change that condition.  Once the emergency is over you have to hit the starter button and then once the engine re-fires you downshift 3-4 times to get in the correct gear - or you are stopped and you need to rock the bike back and forth while you downshift to 1st gear.

This scenario sometimes happens, and eau de sauvage is doing a really good thing by practicing it - he will know what to expect when it happens for real.

Mine never stalls when chopping the throttle. Sometimes the revs might sag a little but it doesn't stall.

Eau, I had the same problem with my bike. Then I read on the forum about the various idle speeds that guys on here set their bikes to - anywhere from 1100rpm - 1500rpm.

I originally had mine set to about 1250, and would experience the problem you described. I upped ithe idle to 1400, and the problem seems to have been resolved.

As a bit of background; when I was tuning the carb (warm engine) I tested the lower threshold of the idle by giving it a bit of throttle and then chopping it, while The bike was stationary and in neutral. The bike would stall if the idle was below 1250. So I took that to be my minimum idle speed. Given the problem with cutting out, on the road, in emergency braking situations, I figured my minimum idle speed needed to be higher to account for that possible scenario.

As I mentioned, so far so good.