I've bumped a few bikes over the years but wasn't aware of the technique used by the biker in this video where he simply pushes the bike and drops the clutch without mounting the bike then swiftly pulls the clutch back in . It appears he considers this a normal technique but how common is this method ?..to me it seems rather dangerous in that unless you're quick the bike could easily run away from you. It also surely wouldn't work on many bikes such as a big single due to the rear wheel being likely to simply skid along without any real weight on it. I've also wondered about people bump starting bikes by jumping on side saddle ..this also seems to be a recipe for trouble? I personally prefer to be properly mounted before dropping the clutch whilst putting my weight to the rear.
he talks a fair bit but eventually gets it going towards the end btw around 3 mins in .
i notice he warmed the engine up before trying to start. Probably different scenario 7.30 am on a cold January morning.
You managed to watch that video?
I forwarded to the "action"! seriously though i was surprised to see inexperienced people commenting it worked great and nobody appeared to damage their bike as it jerked in to life.I was fairly amazed it even worked without any weight on board but as said the bike was probably warmed up and also a multi cylinder not a big single Pot.
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I push started my NS125R and an RSX100. You know when it's starting, and you just pull the clutch in and give it a handful. Jump on and off you go.
I've bump started my CBR1000F a couple of times down a hill (warm starting battery issue) Not sure if it would work push starting it on the flat, I think feeding the clutch in would just stop the bike. I reckon there's enough weight in the bike to keep the back wheel from skidding though, it's a lardy bastard.
I’ve also wondered about people bump starting bikes by jumping on side saddle ..this also seems to be a recipe for trouble? I personally prefer to be properly mounted before dropping the clutch whilst putting my weight to the rear.
you get weight on the saddle/back wheel quicker than if you went with foot on the peg, other leg round and down. And it doesn't work first go you can start running again quicker than if you were sat astride it. Have a look at some old TT footage when they all had to start that way.
Same thing really but if you sit on the bike you have more weight to stop the back wheel simply locking up. Running along with the bike with a small two stroke no problem, litre twin or 650 single not a hope in hell, at least not from cold in my experience.
There's no way a big single would start like that. That technique needs a low compression or large valve overlap, and a small multi.
It's also evident that he hasn't done it before on that bike.
You want to be on the bike when it fires up. I've seen enough bikes head off into the scenery when the owner didn't get on in time. It's amazing how far a bike can stay upright without a rider. 🙂
(In my younger days I spent 2 years with a highly tuned Dodkin Velocette Venom with rearsets and no kickstarter, so every start was a bump start. It was my only vehicle.)
In what way does a "large valve overlap" help? presume it reduces compression on that part of the 4 stroke cycle but you've still got the compression stroke to overcome? With regards to jumping on side saddle it just seems dangerous as your balance won't be as good as if you stand on both pegs then drop down once you reached your top push speed.I can see the advantage /need in a race start in case it doesn't fire and you need to try again. also the seats are fairly low in comparison for example to adventure style bikes etc.I've bumped big trail bikes but wouldn't want to do it side saddle and probably couldn't ,also the sudden acceleration if you're not quick on the clutch can be quite aggressive !
He probably realised that doing it wrong would drive more traffic and ad revenue his way.
It depends on the bike and engine - i used to have a gpz1100 with a dicky starter motor and the only way to do it was to push and then jump on from one side - I became quite proficient at it!!
i also have a zx7rr with a high comp motor and that absolutely cannot be bumped until the engine has been warmed up with the engine starter (lawnmower engine and go kart wheel affair). Once warm it bumps no problem.
kaiser
In what way does a “large valve overlap” help? presume it reduces compression on that part of the 4 stroke cycle but you’ve still got the compression stroke to overcome? With regards to jumping on side saddle it just seems dangerous as your balance won’t be as good as if you stand on both pegs then drop down once you reached your top push speed....
Large valve overlap means there's actually less gas in the cylinder to compress at very low revs, ie kickstarting or bump starting speeds. At higher engine speeds the column of gas is moving faster so more of it gets into the cylinder. That's a very rough explanation, but in practical terms it means it is easier to push the engine past compression at bump start speeds. Early Ducati V twins were great like that.
As for side saddle, it's far easier to get the moment right sidesaddle than leaping astride the bike. I never had a balance problem in years of bump starting. Nor did anyone I know.
Maybe back then we had more practise at it because most very highly tuned bikes were pigs to start and we didn't have the benefit of modern electronics. Also we usually removed decompression levers because they were a potential point of failure, and there were already enough of those on a British bike. Then add a racing carb like the Amal GP which was not designed to idle...
I never had to bump any of my big trail bikes so I can't comment on those. They were so much more reliable.
About the only bike I felt trepidation on was my BMW. The transverse torque reaction on startup was disconcerting, but if expected easily countered. However that was a rare thing because it was only necessary when the battery started disintegrating from rough outback roads.
Got shown the speedway start in Wales whilst trail riding in the boondoocks and a mate stripped the kick start spline. Bike in 2/3rd gear, everything on, mate holds bike over on side stand with rear wheel in air then grip rear wheel and twist - amazingly it did work (small 2t trail bike)
When bumping I always ran along and the jumped on sidesaddle whilst letting clutch out - worked for me (but I couldn’t get a foot down on a traile without sitting to side on one thigh to make my other short leg reach the ground)