7 replies to this topic

[Neo]

Hi All,

My bike is running like a dream at the moment ....but there just one problem that's got me wondering....

After (and only after) a cold start the engine runs fluffy (poppy) and will not rev clean until revved right up for 20 seconds and cleaned out. After that she runs almost prefect.
It happens every time now and is still apparent no matter how long a spend working the bike up.

I'm using Castrol TT synthetic but it was the same with the previous synthetic two stoke oil too.

Does anyone have any idea what could be causing this?


Best of balance.

Neo

[tombo46]

Neo, on Mar 14 2009, 11:53 AM, said:

Hi All,

My bike is running like a dream at the moment ....but there just one problem that's got me wondering....

After (and only after) a cold start the engine runs fluffy (poppy) and will not rev clean until revved right up for 20 seconds and cleaned out. After that she runs almost prefect.
It happens every time now and is still apparent no matter how long a spend working the bike up.

I'm using Castrol TT synthetic but it was the same with the previous synthetic two stoke oil too.

Does anyone have any idea what could be causing this?


Best of balance.

Neo

Im pretty sure this is normal, mine and all my friends bikes are the same, let it tick over until its warm (fan comes on) then ride it about a bit, steadily increase the revs more and more over 5 mins riding or so, then just "clean it out". I dont think you have any fault with your bike though.

All the best

Tom

[trialsnutterman]

Could be one of two things

1 The motor is cold so it is still running a little lean.

2 A build up of fuel in the crankcases so it runs rich when you rev it, maybe from using the choke.

Both are normal behaviour, you should always take your time to warm your bike (and yourself) up properly, ride the bike around though just taking it easy.

[yamahaty250xox]

100% normall.

[Neo]

trialsnutterman, on Mar 14 2009, 11:42 PM, said:

A build up of fuel in the crankcases so it runs rich when you rev it, maybe from using the choke

This is exactly what I originally thought was casing it this problem (and this theory's supported by the grey exhaust smoke that clears when the engine does)...But because the choke only stays on for no more than 5 seconds But it takes so long to clear (10 to 20 seconds) I was concerned there was something else go on

Could a build up of fuel in the crankcases happen in just 5 seconds of cold running on choke?
If this diagnoses is correct, just to confirm it, should it run Fluffy again if I use the choke for 5 seconds when the bike is warm?

Thanks for your feedback so far gents.
Best of balance.

Neo

Edited by Neo, 15 March 2009 - 01:08 AM.

[copemech]

Sounds to me the lads have pretty much covered it. Seems pretty normal, much of it just seems to me that the combustion process just does not happen well off cold and without extra enrichment. The fuel does not stay atomized well.

Other things like transporting the bike and the resultant sloshing could spill some excess into the motor. I always turn off fuel when transporting, and have seen some that will cut off fuel and run them down even before transport as a precaution.

One thing of recent note that I have encountered on the Serow 4T is the fact that if you let it sit for days or weeks, it WILL NOT start even off the choke, will crank till the battery is dead! Requires a shot of starting fluid! Then still VERY cold natured requireing the choke.

Reading up on this upon the Serow forums, seems the theory is that when left set, all the high aeromatics in the fuel left vented in the bowl vaporize off, leaving a fuel that just does not want to combust well untill the stuff is run out and fresh fuel in. So the recommentadion is to run them dry before setting.

I can attest to the fact that the *******s will not start and am running that theory, yet have not started mine in a week yet.
If this common theory is even remotely correct it could well apply to the 2T's as well, so that initial fuel remaining in the bowl just does not work well and must run through before things are right, yet the 2T's may be a bit more tolerant and still start. Something to think about!

[Neo]

Hi Cope,

Interesting information on the fuel and starting. I generally ride everyday and she starts 1st or 2nd kick every time. So I don't think the fuel is lacking anything.

Can you think of any simple tests I can do to confirm the "fuel in the crankcases" theory?


Best of balance.

Neo

[copemech]

Neo, on Mar 15 2009, 12:58 AM, said:

Hi Cope,

Interesting information on the fuel and starting. I generally ride everyday and she starts 1st or 2nd kick every time. So I don't think the fuel is lacking anything.

Can you think of any simple tests I can do to confirm the "fuel in the crankcases" theory?


Best of balance.

Neo

I cannot think of any specific tests, yet as 2T's are different in the fact the intake fuel charge mist is exposed to a lot of COLD rotating mass inside the motor, logic dictates that a portion of the vaper mix is likely to condense upon the cold surfaces through normal exposure. Add the fact that our now common fuels are basically designed for CARS, which are primarily directly injected so they do not have this problem. Add to all that the fact oils require more heat to properly ignite and burn off cleanly, then you may get your transition range of the oil added too the initial cold start. Seems to me that keeping some heat in the motor is a prime consideration for performance before attempting sections, as they will not clean out otherwise. Most Pro's just rev the crap out of them to get heat in them!

FYI, the Serow started and ran quickly today after sitting more than a week with fuel off, so there is something to this theory for sure, yet probably less applicable to the 2T's, still applies!