how come 2t bikes are often harder to start?

[trevor saxe-coburg-gotha]

Having been out of the country for a couple of weeks I'm not relishing the prospect of trying to kick me crm up. I know from passed experience it will take some encouragement to get lit. However I don't get why. Perhaps because it's not electric start? But this can't be the whole story cos my w650 can sit for a fortnight or more and still fire on the first kick. Although it *is* a lot younger. So why *are* the smokers often more reluctant??
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"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125

[_Iain_]

[N cee thirty]

can't say any of the strokers i've had have been harder to start than 4t, other than if they were knackered, but they'd start eventually
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[stevo as b4]

What Iain said, and it's kick start 4 strokes that are hard to start never first kickers.

I think it used to take more than 2-3kicks to start even my old CG125 when it had been left a week unused. All my KMX's were often 1st or 2nd kick starters generally, unless they became flooded, I ran out of fuel, or like on my old 200, when I had dirt in the tank causing a mixture of flooding and fuel starvation at times.

I'd love to see some BCF'ers with big 4strokes post up 1st time starts, I bet there's not more than 2-3 at the most!

[Baffler186]

I never had problems with an old TY175, choke out, no throttle, fired up with one kick. In fact a 4 stroke XL185 I had was harder to fire up. I don't know enough about engines to offer a reason, but I guess it could be dependent on a fair few variables like plug condition, air temp and humidity etc etc.
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Current: 2009 SV650 S, 1990 Kawasaki GT550
Previous: 2009 CBF125, 1998 GSF600, 2004 FZ6 Fazer, 1978 CB400a Hondamatic

[smegballs]

My RXS would start first kick after being left for a few weeks no probs.

[_Iain_]

[trevor saxe-coburg-gotha]

If my crm has been used the day before - i.e. ridden and got hot - it'll start first or second kick the following day. But the number of kicks increases with the amount of time it's been stood. And my mate's 250 gas gas is the same. I just assumed from this that it was not at all uncommon.

The crm's plug is new btw.
____________________
"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125

[Teflon-Mike]

Theoretically, two-strokes shouldn't start at all!
A piston ported 2T has symmetrical port timing; so piston rises, port's opened, letting charge get sucked into the crank-case; but as the piston falls again... ported by the piston, it will remain open all the way back down again... and everything that got sucked in OUGHT to get squashed back out!
Reasons a two-stroke runs at all, is down to a thing called 'trapping efficiency'; if you design the inlet tract to have better forwards flow than backwards, you get a bit of charge trapped in the crank case and might get the thing to work; add a flap valve, like a pair of fire bellows, though and you can hugely increase this trapping efficiency,
Four-strokes, with positive and asymetric 'poritng' via mechanically controlled valves, dot suffer any where near as much, but, there is an interval at the end of the exhaust stroke and the beginning of the inlet when both valves are open at the same time, and exhaust gas buggering off down the pipe can suck fresh charge with it, or bur it off, before it has a chance to get used.
This gets worse, the more highly tuned an engine is; as there will tend to be a larger interval of 'over-lap' and valves will tend to be pushed further open during it.
Highly tuned 4T's can be a total bastard to start...
So can highly tuned 2T's.
And you aren't really comparing like with like... CRM is a highly tuned race engine... W650 is, err... not!

BUT... and here in I suspect is your problem....

when a 4T is turned off, the piston will tend to stop half way up on the compression stroke, when there is most resistance against it, and the valves are both closed.... your spark plug is the sat, while the bike dormant, in sealed chamber full of oil, fuel and air.

When a 2T is turned off... piston will stop half way up the compression stroke, when there is most resistace against it... BUT, having 'run into the buffer' of compression... a two stroke engine can turn BACKWARDS.. 4T's dont tend to like this, and the resistance of cams and valves and stuff, as well as plain bearings sort of stop it happening, but on a 2T... the piston will hit the compression, then bounce back, and it will stop, when it has vented whatever compression it made, when the exhaust ports open...

This means that your spark plug, when the bike is laid up ISN'T in nice almost hermetically sealed chamber with a little air and a bit of oil and fuel floating around... its open to the atmosphere....

Vented to atmosphere, iron piston rings tend to corrode into the alloy piston grooves, loweing fire up compression, while the spark plug will gain a layer of corrosion.

Usually 2T's due to lower frictional losses will tend, for the same state of tune, to start more readily than a 4T, especially as you can swing them through a couple of cycles for the same kicker effort...

But, if laid up... could probably do with the plug popping out and a quick clean, to make sure it delivers good sparks, and a couple of kicks through while its out, to free up the rings and get a bit of lube on the bearings and bore, before you pop plug back in... and with 'the knack'... ought to start just like it had been running yesterday... Give it a go.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Irn-Bru]

Many years ago when my brother had an rx50 he could easily start it from cold by hand on the kick start, or by walking and letting the clutch out slowly in 1st. Thinking back it was probably not smart, wonder if a 50 could still break yer wrist?
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KTM 990 SMT & Suzuki DR-Z 400 SM

[Fladdem]

[G]

Remember a 2 stroke needs to get (maybe fresh?) fuel through the cranks and into the expansion chamber.

How's the rings etc?

I've certainly had it where one that's not been used for ages wouldn't fire up without a load of hassle (cue me being towed by a landrover on a pampera), but once it's been going for a bit, been fine.

While 4 strokes are often the opposite - my Husaberg would fire up ok from cold, but I once spent half an hour trying to get it to catch from hot, until I gave up... and took a pampera out, I think .

[Teflon-Mike]

[trevor saxe-coburg-gotha]

It's got a pump - one guy in the local trf said go pre-mix 'for peace of mind.' BUt eh - not sure I will tbh. In any case, I'll shake the bugger side to side before getting busy with the boot.

How are the rings, g asked - I think they are fairly decent. It will smoke blue from cold for a few minutes but not loads, and afaict, not once warm. Other than twirling spanners and doing proper spannery things is there a way to get some sense of this?
____________________
"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125

[Fladdem]

Played with the mopeds today, just before the rain came in.

It seems like a fair test in my mind, both are low stressed air-cooled engines, similar capacity and both Honda.

I got my dad to start the cub, he has ridden it more than me and has the knack better than me, equally, I started the MT5 because I have the knack for starting that easier.

I had to put some fuel in out of my TTR 250 tank, into the 50, because I had ran it dry before storing it because I was going to start stripping it down to stick the H100 engine in it.

In all fairness to the cub, it would have gone in two or three kicks but we snapped the kickstarter on the first attempt.

We filmed it, we had about 30 minutes of footage that I edited down to about 9 minutes, if anyone is interested in wasting that much time on two idiots, well three, my uncle, the one who gave me my GPZ turned up and messed about with us.

The results are surprising and brought back my lust for a smoker.

https://www.youtube.com/watch?v=nF7i5AUc5BE&feature=youtu.be
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Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[Teflon-Mike]

How to turn a normally mature, responsible, grumpy middle aged man, into a blithering, irresponsible, grinning idiot.......
"D-a-a-a-d..... I cant get my moped to start!"
I remember vividly, aged about ten, having abandoned my pedal & pop on the drive in a pique, hearing the tones of a tortured two stroke, in the back garden... as I bounded out to find out what had happened, I had a brief glimpse of my Grandad wobbling up the garden path, stood on the saddle, arms akimbo... followed very shortly after by a scream of revs, and a crunch.... I tore up the drive to find out what was wrong, to discover bike wrapped around teh cristmas tree, Pops wreathing on the floor.. clutching his belly... I was about to tear off inside to call an ambulence when he stood up, and stammered.. "S'all right... 'm only laughing!"
Groan-ups... MAD as hatters. Decided it must be something to do with alchohol
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[P.]

[tony_d123]

They aren't, my 38 year old KH500 starts first kick every time. It's a little bit of technique but mainly setup. Go though service items and check timing. It's also worth taking the carb off and getting it ultra sonically cleaned. Check crank seals, base gaskets etc for leaks, low primary compression can make 2-strokes very difficult to start.
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Blackpool, Lancashire

[CHR15]

people dont know how to use a kickstart properly.
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Turbocharged drag thing / project death weapon / GK73A
Ste: I'm not entirely sure how you'd go about verbally abusing someone with a potato but I'm sure it's possible.

[The Shaggy D.A.]

[trevor saxe-coburg-gotha]

Okay - think I've sussed it. Wheeled 'er out this evening to go for a play on a nearby quad bike course someone's set up (I'm not meant to use it but eh, I'm quick, clean and quiet so...) and was prepared for a bit of a right foot work out due to not riding it for a fortnight (see OP).

Here's what I did: turned tap to 'on', choke lever right down, walk away from bike. Go upstairs, faff around with vape recharger, yell at t'kids for a bit, go for a quick slash, get me clobber on, etc. etc.

So when I come back to the crm it's been a good ten minutes since the tap;s been turned. Started third go. Difference being that previously I wheel it out, turn tap, set choke, kick. Nowt. Nowt again. Nowt, nowt, nowt, etc. etc. THEN it fires. But tonight was different - it's as though the priming time is minutes rather than mere seconds, or something. Dunno.

Obviously it's a bit early to know if simply leaving it with the tap open for a while is "the knack" - but I'm cautiously optimistic that this really is all there is to it. Anyway, in other news, it ran bloody well tonight - and seems to improve with each outing. Smoother, quieter, more tractable in second over the humps and ruts, and just generally a happier feeling bike all round. I am liking.
____________________
"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125

[G]

4 stroke dirt bikes tend to have 'accelerator pumps' - often you'll give a couple of flicks of the throttle before starting to dump some fuel through.
This gives you an idea - https://www.youtube.com/watch?v=ZbzBbLYeATw .

Oh and (If I haven't said it already and you haven't done it - got a feeling you had) I would strip the carb and clean out each jet indivdually. No need for ultrasonic cleaning generally - as you saw at last year's BBQ, using your mouth and possibly a small bit of plastic from a washing up brush or similar should do it.

[trevor saxe-coburg-gotha]

Yeah carb's been off and blown through. That and the new plug were what cured the stalling problem that was the cause of my three hour journey taken to cover the 10 miles from the seller's place to mine. Incidentally, Mr. Rafferty's in york that did it for me has still yet to give me an invoice for this, despite the fact that I ride in most weeks, buy him a coffee and ask him for the bill. Would've done it myself but you weren't here with headtorch and large canine accomplice, without which my abject spannerphobic tendencies would have led to an inevitably regrettable outcome.
____________________
"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125