UK Karting - Notice Board (2-Stroke Karting) : John..... as full a description as I can manage!

Notice Board (2-Stroke Karting)

John..... as full a description as I can manage!
Posted by 'itpro' on 10 Sep 2010 @ 11:23

| View Message Thread | Reply to this message |

itproJoined: August 2001
Total Posts: 6
[ View User Profile ]

Firstly, I have placed, what I consider to be the KEY question at the end of this posting. By all means, ignore my long explanation of the carb.... just answer the final question.....

The reason shutting of the butterfly does NOT promote seizing...... in MY opinion, is pretty simple and is actaully contained in the CONCEPT of Walbro and Tillotson carbs.....

The fuel-feed to the carb delivers the fuel in TWO places. Yes, there may be MULTIPLE feeds which are on the up-wind side of the butterfly but, effectively, there is only TWO supplies: that whcih is up-wind and that which is down-wind of the butterfly.

The concept is that the fuel flow needs to be FAR higher when the buterfly is open than it does when the butterfly is closed and a PROPER carb (i.e., the Tillotson and NOT the Walbro!) should be adjusted so that more fuel enters via the up-wind 'port/s' than by the down-wind port.

That's how you set up a Tilly! The small quantity of fuel that is delivered from the DOWN-wind jet is SUPPOSED to be sufficient to maintain the engine (at least) at minimum tick-over (for clutched engines) and to be pre-primed for the application of FULL throttle for DD engines.

When wrongly adjusted, the transition from no throttle to FULL throttle is a nasty moment for an engine. The fuel delivery on the up-wind side as negligible when the buterfly is closed, and ( without the addition of a 'surge squirt' of fuel on throttle opening, as found in 'car-sized' Webbers and Dell'Ortos), and engine will momentarily STALL (fail to fire) when FULL throttle is applied simply because the Air flow now VASTLY exceeds the correct ratio of fuel to enable the engine to run.

This is because the delivery of fuel via the 'high speed' (up-wind) jet is in RESPONSE to air-flow. The commensurate increase in fuel flow happens A*F*T*E*R the increase in airflow (Bernouille effect). Thus, the engine is in danger of giving a HUGE 'hesitation' after the 'transition' from no-throttle to FULL-throttle.

That is solved in simple karting-carbs by adjusting the SLOW speed jet (down-wind) so that there is ENOUGH fuel altready in the 'choke' (down-wind side of the butterfly) so that the sudden HUGE increase of air-flow at 'transition' can be handled by this fuiel that is 'WAITING' to be used. What that REALLY means is that the down-wind jet is set to deliver TOO MUCH FUEL for ideal running on over-run..... hence the reason why DD karts would tick-over SO badly if allowed to do so.

Thus.... a PROPERLY adjusted Tillotosn is ALREADY delivering EXCESS fuel and oil (i.e., more than the engine can BURN with the current air-flow).... and THAT excess SHOULD be enough to prevent the seize in the moment BEFORE you apply the hand to the choke!

Now, the Walbro is SUCH an abortion that it runs the settings BACKWARD with the MOST fuel being delivered on the DOWN-WIND side.... even at FULL throttle! That places the Walbro karts in the 'even better' anti-seize condition of having VASTLY too much fuel being delivered when the throttle is CLOSED which makes it even LESS likely to seize than with the better carb!

*******

I hope that explains my understanding of the situation! It MAY BE WRONG in MANY places if not ALL places...... BUT....... it has served me for a ..... fairly.... long while and I have yet to suffer a seize during the 'over-run' period. However, your .... greater... experience informs you diffrerently! That is all well and good and you are FULLY entitled to YOUR opinion on the subject...

B*U*T......

The KEY to the matter.....
********************************

The KEY to this matter is HOW you adjust your carb.... I do NOT mean: "what SETTINGS do you use".... I want to know *H*O*W* you arrive AT those settings?....!

Ian

Message Thread:

Choking by 'ivanmalley2' (07 Sep 2010 @ 0:02)

Re: Choking by 'Traxtar' (07 Sep 2010 @ 0:23)

Re: Choking by 'Attack2001' (07 Sep 2010 @ 1:19)

Re: Choking by 'itpro' (07 Sep 2010 @ 1:48)

Re: Choking by 'Reg' (07 Sep 2010 @ 13:38)

Re: Choking by 'AlfieMoon' (07 Sep 2010 @ 14:46)

Re: Choking by 'Attack2001' (07 Sep 2010 @ 14:54)

Attack 2001, I grant you that accolade. by 'AlfieMoon' (07 Sep 2010 @ 16:56)

Re: Attack 2001, I grant you that accolade. by 'Attack2001' (07 Sep 2010 @ 17:04)

Re: Attack 2001, by 'itpro' (08 Sep 2010 @ 1:34)

Re: Choking by 'BigJohn' (08 Sep 2010 @ 11:58)

Re: Choking by 'itpro' (08 Sep 2010 @ 12:35)

Re: Choking by 'BigJohn' (08 Sep 2010 @ 14:06)

Re: Choking by 'itpro' (08 Sep 2010 @ 14:46)

Re: Choking by 'BigJohn' (08 Sep 2010 @ 15:32)

Re: Choking by 'Newshound' (08 Sep 2010 @ 16:35)

Big John by 'itpro' (08 Sep 2010 @ 16:51)

Re: Big John by 'PaulMRotax' (08 Sep 2010 @ 22:30)

Re: Big John by 'itpro' (09 Sep 2010 @ 10:21)

Re: Big John by 'BigJohn' (09 Sep 2010 @ 18:26)

John..... as full a description as I can manage! by 'itpro' << You are here!

Re: John..... as full a description as I can manag by 'BigJohn' (10 Sep 2010 @ 19:55)

Re: John..... as full a description as I can manag by 'itpro' (10 Sep 2010 @ 20:18)

Re: Big John by 'PaulMRotax' (09 Sep 2010 @ 19:20)

Pauly-baby by 'itpro' (10 Sep 2010 @ 11:26)

Re: Pauly-baby by 'PaulMRotax' (10 Sep 2010 @ 17:28)

Re: Choking by 'brinjono' (08 Sep 2010 @ 17:51)

But you CAREFULLY avoided my request. by 'AlfieMoon' (08 Sep 2010 @ 12:43)

Re: But you CAREFULLY avoided my request. by 'itpro' (08 Sep 2010 @ 13:10)

Still avoiding it then , so it does not exist:} by 'AlfieMoon' (08 Sep 2010 @ 13:29)

Re: Still avoiding it then , so it does not exist: by 'itpro' (08 Sep 2010 @ 14:49)

Re: Choking at other times by 'pccsystems' (08 Sep 2010 @ 17:04)

So is the other 50% spent by you in Soho? NT by 'AlfieMoon' (08 Sep 2010 @ 17:26)

Re: Choking at other times by 'Traxtar' (08 Sep 2010 @ 17:50)

Re: Choking at other times by 'ivanmalley2' (08 Sep 2010 @ 21:19)

Re: Choking at other times by 'PaulMRotax' (08 Sep 2010 @ 22:35)

Re: Choking at other times by 'Liam' (09 Sep 2010 @ 0:22)

Liam by 'itpro' (09 Sep 2010 @ 0:27)

Ivan by 'itpro' (09 Sep 2010 @ 0:25)

Re: Ivan by 'markmorton' (09 Sep 2010 @ 21:42)

Post a Reply:

You may post a direct reply to this message which will appear in this thread.
To post a new or unrelated message use This Form. Top of Page
Notice Board Index

[ UK Karting Main Index ]


News	Karts & Karting	Notice Board	Market Place	Companies Directory	Tracks Directory	Events Calendar	Race Results	Photo Gallery	Links