Why so many carbs?

[Arkaloid]

......because multi-point injection is better than throttle-body injection (or so I assume, since that's the modern FI incarnation). ;-)

throttle body F.I. is really no better than a precisely engineered carb setup. it was a cheap alternative for F.I. that detroit used to save on costs.

 

[Pete Logan]

You also must keep in mind that any manifold is a compromise. fuel distribution will not be equal across all cylinders with a one-carbed/manifold setup.

Now there ya go talking sense again - what have I told you about that

Get on the page girls. It's obvious that each cylinder should have it's own carb and it's own exhaust.

The only way to deliver the same charge to each cylinder is to have it's own carb with the exact same entry path as every other cylinder, and the only reason manifolds were invented was to save money on carbs, which are a bloody sight more expensive than manifolds.

Which is why manifold EFI is a bust and the only way EFI is gonna beat carbs is by direct injection.

Which is what a multi-carb setup did in the first place, only cheaper.

God, I'm good when I'm drunk

 

[Pete Logan]

throttle body F.I. is really no better than a precisely engineered carb setup. it was a cheap alternative for F.I. that detroit used to save on costs.

\\/ \\/ \\/

 

[t3rmin]

throttle body F.I. is really no better than a precisely engineered carb setup. it was a cheap alternative for F.I. that detroit used to save on costs.

Well I suppose precisely engineered is the key phrase there! But it's still going to be slightly more precise, with infinitely-adjustable computer control rather than a finite number of circuits (idle, off-idle, mains, power valve, etc.), plus (as I just read on Wikipedia) FI atomizes the fuel better. Then there's the maintenance-free aspect...

I see what you're saying, though. Throttle body FI is basically the same thing as a carburetor.

Not that I'm crazy about FI. I'd rather ream out a clogged jet than mess with a tangle of wires any day!

 

[Pete Logan]

I see what you're saying, though. Throttle body FI is basically the same thing as a carburetor.

Almost.

Throttle body FI is almost the same thing as carb through a manifold.

Direct injection FI is almost the same thing as one carb per cylinder.

Throttle body FI can be better than manifold carbs, but never as good as one carb per cylinder.

Direct injection FI can be better than that, but only with a good ECU and a better tuner.

Fun round here,ain't it

 

[t3rmin]

Well.... that's what I meant. ;-)

 

[ghwrenchit]

Maybe we need to toss timing and firing order into the mix, for a thought. For HP and good fuel economy, intake runner and exhaust length per cylinder is critical from what I know (little ).

On old big block tunnel ram intakes, nobody really cared if you got 8 miles to the gallon, just dump it in and go.

On small block's with good throttle response in every range, tuned (balanced) intake runner's and tuned headers (all pipes same length) were the way to go.

Old 6-pak setups 3x2bbl on 340's, common on Chrysler products in the late 60's early 70's were designed as progressive carb's, as they didn't all open equally at once but in series.

Newer hypo cars with fuel injection still balance the intake air runners and exhaust for length to each cylinder.

Perhaps on a bike, the realestate for a balanced intake/timing was not in the picture.

Dunno, just guess'in

ghwrenchit

 

[t3rmin]

I'm just bitter because I found gas in my oil and now I've got to go over the carbs. ;-)

 

[Tnutz]

carbs are ****....i hate them in every way. Too lean, to rich, runs but won't idle blah blah blah....my buddy's victory is EFI and all it does is start....no ****ing around....all he had to do was get a ecu flash for his pipes and it runs like a dream...No parts to wear out like a carb, no synching...maybe a clogged injector someday....but thats about it....:-D technology! once you go efi you will never go back.

 

[ghwrenchit]

carbs are ****....i hate them in every way. Too lean, to rich, runs but won't idle blah blah blah....my buddy's victory is EFI and all it does is start....no ****ing around....all he had to do was get a ecu flash for his pipes and it runs like a dream...No parts to wear out like a carb, no synching...maybe a clogged injector someday....but thats about it....:-D technology! once you go efi you will never go back.

..... I'm just bitter because I found gas in my oil and now I've got to go over the carbs. :wink:

All part of the "hobby"..... think the guy crank starting the model T wished he had a electric starter??? Be proud, fix, and ride!!!! :-D :-D

G

 

[t3rmin]

All part of the "hobby"..... think the guy crank starting the model T wished he had a electric starter??? Be proud, fix, and ride!!!! :-D :-D

Yeah yeah yeah... Except I haven't even gotten a chance to ride mine yet.:? I have a right to be bitter! :-D

 

[ghwrenchit]

Yeah yeah yeah... Except I haven't even gotten a chance to ride mine yet.:? I have a right to be bitter! :-D

Know the feeling man... what's left on the laundry list? Just make sure it's safe for the first ride, OK?

G

 

[Tnutz]

ha, gas in the oil...the ef was FULL...because of the dinosaur technology carbs..

 

[ghwrenchit]

ha, gas in the oil...the ef was FULL...because of the dinosaur technology carbs..

Dinosaur??? your prize GS is only 25yrs young.:-D Be proud, fix it, and ride. If things get the best of you put the tools down for a few days, especially the hammer.

G

 

[t3rmin]

Know the feeling man... what's left on the laundry list? Just make sure it's safe for the first ride, OK?

Well fortunately I'm (somewhat) patient. I've just replaced the ignition with a Dyna S, which I still need to permanently mount, route the wires, and adjust timing (but at least it's finally running!). Then I've got to clean the carbs 'cause I've got gas in the oil. Then I need to change the oil and put on a new valve cover gasket and half-moon seals. And I'm either almost out of gas or the petcock is bad, so I need to test that. And I guess the front brakes feel a bit squishy (although I'm not sure what it's supposed to feel like), so I may need to bleed 'em. Also I need to clean the air filter and re-seal the box with some weatherstripping tape (per forum advice).

*sigh* At least I've got a whole weekend ahead with which to bury myself in the bike. I'll have to convince the wife to bring my meals out to the garage. :-D

 

[ghwrenchit]

...I'll have to convince the wife to bring my meals out to the garage. :-D

No.... take the time to grill her the best steak she ever tasted. After that make her happy...It'll take 2 hours tops!!:-D :-D, then get back to the bike. H~ll, maker her happy on the bike... doesn't need to run. She may even offer to hand you wrench's after the fact, now it's becomes "OUR" project.\\/

G

 

[West]

A purely pragmatic approach:

If one carb and a manifold made any sense for cost reasons, you can bet your ass the engineers at the bike manufacturers would have figured out how to do it (On the orders of the bean counters). If it made any sense for performance reasons, you would have seen race bike's with 'em.

The only bike's that used one carb throat for multiple cylinders were a couple of old Triumphs and Harley's used them up until just recently. No suprise there - 'Harley, unimpeded by 75 years of progress'. I am sure there were a couple of others - maybe a Norton?

For all those who say 'carbs suck!, FI is great!', well, for about 100 years carbs were great, and FI was a f-in dream. You are taking some very difficult to develop technology for granted. FI is great no argument, but so is the Internet, and both were impossible for all of recorded history but the last 15 years or so.

 

[dpep]

New FI systems work better than our 25 year old carbs. I am curious how well those FI systems will be working 25 years from now. Will it be possible to repair them and if they can't be fixed will replacements be available? It will be 25 year old electronics technology by then. The carbs on our GSs will still be working like they do now and we will be able to service them the same as we do now.

I am not against progress. But I am always a little cautious about developments that take a part of my bikes functioning away from me and give it to a black box.

 

[jimcor]

The only bike's that used one carb throat for multiple cylinders were a couple of old Triumphs and Harley's used them up until just recently. No suprise there - 'Harley, unimpeded by 75 years of progress'. I am sure there were a couple of others - maybe a Norton?

Another engine that used a single carb to feed twin cylinders was the 300 Honda Dream. When the 305 Superhawk was unveiled it had twin carbs. These engines are relatively hard to tell apart visually, but according to an article I read years ago in one of the bike magazines (probably Cycle, but could have been Cycle World) they are two very different engines. Here is where memory fails me, but the author went into quite a bit of detail explaining the tuning of the Super Hawk engine and why a single carb would not work. So there are engine tuning considerations involved in a seperate carb for each cylinder, too.

 

[Clone]

Well, for me the benefit of multi-carbs I refer to my old Beetle. 1 carb for a 40hp 1200cc with a really long intake. The upgrade was to down-draft Webers, one for each bank of cylinders, shorter intake, better throttle response, easier tuning, increase in power.

So for me the multi-carb arrangement is to give more power from a smaller engine size. From breathability, response, mixture control. Ahm, that's all I got.