Carburettors

[Rockburner]

If you ever felt that you lacked an understanding of how they work, you could do worse than watch this:



Yes, it's american, yes the guy claims to be an engineer and yet not know how a carb works, but through that lack of knowledge he's gone to some length to show the fundamentals in a very clear manner.

[Rockburner]

oh, I also loved the interactions with his dad, hit a chord with me.

[Mr. Dazzle]

His videos are really good for the most part. He's a weapons tester / high speed photography specialist working for the DoD in Huntsville Alabama (the home of the US rocket industry), so he knows his stuff about a lot of things!

I love that video though. I've known how a carb works for a long time, like most of you, but still enjoyed seeing how the fuel "floats" up in the venturi and then gets 'smashed' into tiny drops on the intake stroke.

I liked his "1000mph baseball" ones, but I really liked watching garden strimmers in super slow mo

[Count Steer]

Enjoyed that.

I sort of 'absorbed' how carbs worked as a yoof but it's still educational to be able to see it in action.

Now, if he could develop it to show how they switch from idle jet to main jet, that would be cool.

[Mr. Dazzle]

He's got a later vid where he goes to the Holley factory, but I've not watched it yet. He tends to do a couple on any one topic.

[Le_Fromage_Grande]

Enjoyed that.

I sort of 'absorbed' how carbs worked as a yoof but it's still educational to be able to see it in action.

Now, if he could develop it to show how they switch from idle jet to main jet, that would be cool.

They don't really, it's just once the vacuum gets strong enough it sucks fuel through both the main jet and pilot.

[Count Steer]

He's got a later vid where he goes to the Holley factory, but I've not watched it yet. He tends to do a couple on any one topic.

Thanks. Just watched it. Quite complicated but it covers a lot of ground. 2 barrel, 4 barrel, automatic choke etc.

The little robot is in the early bit is v cute. Reminds me of the Pixar 'anglepoise' lamp.

[Count Steer]

Enjoyed that.

I sort of 'absorbed' how carbs worked as a yoof but it's still educational to be able to see it in action.

Now, if he could develop it to show how they switch from idle jet to main jet, that would be cool.

They don't really, it's just once the vacuum gets strong enough it sucks fuel through both the main jet and pilot.

Kind of counter intuitive though, you'd expect a low vacuum venturi (tickover) to draw through the bigger jet in preference to the smaller one....or am I misremembering my jet sizes? (Not unlikely, given how long ago I had a carb in pieces - probably involves the needle too. More Youtubing needed for me I think. )

[Tricky]

I already did

viewtopic.php?p=101285#p101285

[Mr. Dazzle]

The main jet is plugged by the needle at low throttle though. That's kinda the point of it in fact!

In older/slide carbs you move the needle directly with the throttle cable. Thus if you whack the throttle open you open the needle and then main jet before the engine is sucking enough air through and you bog down.

To get around that you can use a CV carb...constant vacuum...which is what most modern carbs are (well "modern" IYSWIM). The position of the needle/size of the jet is controlled by the manifold vacuum and not the throttle position. So believe it or not on most modern carbed bikes you're actually only indirectly controlling how much fuel/air is going into the engine and its the carb which makes the final "decision".

Edit:

Here you go....pink fuel sits in the bowl and is sucked up through the various jets by vacuum in the carb. The tapered needle moves in the jets (5) and by moving up and down it can change the size of the hole as appropriate.

You can see that hole (4) which lets air into the space at the top of the carb. As the air pressure inside changes the piston is sucked up/down to control the height of the needle and the vacuum pressure in the carb. Hence the "constant vacuum" name.

[Le_Fromage_Grande]

What about Lectrons?

[Mr. Dazzle]

Its all the same basic idea and answer to CSs question innit? There is some mechanism which changes the size of the 'hole' fuel comes out of thus making sure the right amount of fuel flows in for the air you've got.

'Course, the sensible thing to do is measure the air and then use a computer controlled sprayer to err.....inject I suppose you'd say....the fuel

[Le_Fromage_Grande]

Its all the same basic idea and answer to CSs question innit? There is some mechanism which changes the size of the 'hole' fuel comes out of thus making sure the right amount of fuel flows in for the air you've got.

'Course, the sensible thing to do is measure the air and then use a computer controlled sprayer to err.....inject I suppose you'd say....the fuel

The few fuel injected bikes I've ridden haven't had the instant throttle response you get with good carbs.

[Mr. Dazzle]

I'm guessing you've not ridden anything new though.

[Le_Fromage_Grande]

I'm guessing you've not ridden anything new though.

2002 GSXR750 is the newest bike I've ridden, the throttle response wasn't as good as the early SRAD with carbs.

I'm sure you've ridden loads of brand new bikes from the late 90s to compare with modern injected bikes.

[Mr. Dazzle]

The last two big day to day bikes I've had were a 95 VFR and a 98 CBR. In fact the CBR has banjaxed carbs as per my previous thread.

Just seems odd to me that someone would complain of poor throttle response in an EFI bike, IIRC when they first started becoming popular people usually complained the throttle was too responsive

[Skub]

Modern FI is compromised by having to conform to 'clean air' regulations. That fuel stop and subsequent jerky pickup from a dead throttle ruins many a good bike. KTM are a notable example.

Once the emissions kit is junked and fuelling adjusted via the ecu,then throttle pickup is as smooth and sweet as a good carb bike.

[wull]

Seen that before, I’ve watched a few of his videos where he goes above and beyond to explain how things work.

[Taipan]

Modern FI is compromised by having to conform to 'clean air' regulations. That fuel stop and subsequent jerky pickup from a dead throttle ruins many a good bike. KTM are a notable example.

Once the emissions kit is junked and fuelling adjusted via the ecu,then throttle pickup is as smooth and sweet as a good carb bike.

Hate bad fuelling. I've always rejetted carbs and now would probably always have a Fi bike remapped after experiencing the night and day difference Mototune made to my F800.

[Le_Fromage_Grande]

The problem for carbs is modern fuel, if you leave it in the carbs it can him up the pilot jets and small airways, especially if you use the bike gently, remember thrashing a carbed bike is good for it.