Topic: Carbs/ jetting 1124cc dragbike

[Don R]

 While going through the carbs on my dragbike restoration project I realize they are stock, probably 71/72 750. A lot of the high perf parts were swapped off the bike after it was parked, I assume that was the case with the carbs.
  I have a set of K0 4 cable carbs so I assume they would be the ones to use unless I swap to something bigger. I'm not likely to invest in a set of CR's for a mostly show bike. Ideas?

[Old Scrambler]

Webers would SHOW real well

[gschuld]

Visually, Webers and Hilborn injections have the most WOW factor IMHO, with Hilborn being WAY less usable on anything other than a high compression methanol/nitro dragster.  1124cc is a lot of displacement for stock carbs to handle, though the bored K1 carbs I did for Benton to test (on Cobra Girl now) seem promising, but way too early to tell for sure how they measure up against other options.

Byron Hines reportedly made a solid effort to see what he could get out of factory carbs performance wise with their big bore motors.  He bored them out, rejetted them, and reportedly they did a good job overall.  The Webers won out in an all out drag race, but the bored stockers were(reportedly) not too far behind.  RC Engineering charged $95 (in 1976 anyway) for a bore/blend/rejet of a factory set of carbs.  This was about 1/3 the going price for a new RC manifold Weber setup(1976 prices).  Your not likely going to impress anyone with a set of bored factory carbs though, if that matters, even if they are capable of performing well.   

There are re-racked big Mikunis, etc. that others will be more knowledgeable about.

George

[Retro Rocket]

Visually, Webers and Hilborn injections have the most WOW factor IMHO, with Hilborn being WAY less usable on anything other than a high compression methanol/nitro dragster.  1124cc is a lot of displacement for stock carbs to handle, though the bored K1 carbs I did for Benton to test (on Cobra Girl now) seem promising, but way too early to tell for sure how they measure up against other options.

Byron Hines reportedly made a solid effort to see what he could get out of factory carbs performance wise with their big bore motors.  He bored them out, rejetted them, and reportedly they did a good job overall.  The Webers won out in an all out drag race, but the bored stockers were(reportedly) not too far behind.  RC Engineering charged $95 (in 1976 anyway) for a bore/blend/rejet of a factory set of carbs.  This was about 1/3 the going price for a new RC manifold Weber setup(1976 prices).  Your not likely going to impress anyone with a set of bored factory carbs though, if that matters, even if they are capable of performing well.   

There are re-racked big Mikunis, etc. that others will be more knowledgeable about.

George

Hi George, what would you charge to bore out a stock set of carbs...?

[754]

Yeah but the stock carbs bored are a sweet secret weapon..
 Nothing like whipping someone on a 40 year old bike that looks like it has stock carbs.

[Retro Rocket]

Yeah but the stock carbs bored are a sweet secret weapon..
 Nothing like whipping someone on a 40 year old bike that looks like it has stock carbs.

I agree 100%....

[Jerry Rxman Griffin aka MuthaF'er]

Yeah but the stock carbs bored are a sweet secret weapon..
 Nothing like whipping someone on a 40 year old bike that looks like it has stock carbs.

I agree 100%....

And stock cylinders 

[Retro Rocket]

Yeah but the stock carbs bored are a sweet secret weapon..
 Nothing like whipping someone on a 40 year old bike that looks like it has stock carbs.

I agree 100%....

And stock cylinders 

I agree again    , billet block is getting fuel injection....

[gschuld]

Visually, Webers and Hilborn injections have the most WOW factor IMHO, with Hilborn being WAY less usable on anything other than a high compression methanol/nitro dragster.  1124cc is a lot of displacement for stock carbs to handle, though the bored K1 carbs I did for Benton to test (on Cobra Girl now) seem promising, but way too early to tell for sure how they measure up against other options.

Byron Hines reportedly made a solid effort to see what he could get out of factory carbs performance wise with their big bore motors.  He bored them out, rejetted them, and reportedly they did a good job overall.  The Webers won out in an all out drag race, but the bored stockers were(reportedly) not too far behind.  RC Engineering charged $95 (in 1976 anyway) for a bore/blend/rejet of a factory set of carbs.  This was about 1/3 the going price for a new RC manifold Weber setup(1976 prices).  Your not likely going to impress anyone with a set of bored factory carbs though, if that matters, even if they are capable of performing well.   

There are re-racked big Mikunis, etc. that others will be more knowledgeable about.

George

Hi George, what would you charge to bore out a stock set of carbs...?

Sorry for the thread drift, it wasn't my intention.

I can't say that I'm looking for business here.  I did the one set as an experiment on a Bridgeport the hard way.  If I end up doing more, I will make up some far more elaborate jigging and guide patterns with a 3 1/2" cutting length milling bit so I can do the milling part much easier for the same accuracy.  To be ideal IMHO, it still requires hand blending between the new machined bores and the taper to round transition on both ends, plus smoothing up the protrusions a bit, then wet sanding and polishing out the whole throat area from front to back like I did on that set.  The amount of time I spent on this one set was fairly ridiculous, not a money maker for sure .  Unfortunately, for the hourly rate I charge at work, I could buy a mint set of Webers on RC manifolds for less than the hourly time it took me to do these carbs.

I was really hoping Bill was going to be able to Dyno test and tune these carbs against a set of stockers, but he ran out of time.  When MRieck is done with my 1000 motor, perhaps I will steal the carbs back and do a dyno comparison with stockers with my engine.  I may well do a few more sets at some point, but can't commit to anything at this point.

I do like the understated sleeper aspect of them...

George

[Retro Rocket]

Thanks for the reply George, I'm just weighing up options mate, I have a 900cc engine with a big head and i'm trying to work out what carbs to use, I currently have a nice set of VM29 mikuni's but i'm not sure I want to use them..

Sorry for the hijack Don...

[calj737]

Jumping Jupiter those are gorgeous! Beautiful work on those. Tragic to cover them up 

[Jerry Rxman Griffin aka MuthaF'er]

Sounds to me like Bill needs to heal and make a run over to Brian's dyno! Maybe Jim French can help out when he goes over there.

[KickOnly849]

Wow gschuld, those carbs look nice! Mind if I ask you a question on them?
Are you planning on using wider flange or extended velocity stacks on these to make up for the removal of inside material in regards to recreating the venturi effect you've almost completely eliminated?

You can PM me so we don't further highjack this thread, I may have a few more questions too

[Don R]

 I don't mind the thread wandering, it is all good info. I read about the seca 750 CV carbs, I went through a set of mikuni's on an 850 yamaha, of course there are only 3 of them. The cv's seem cheap enough. I doubt this bike will make a pass in anger, it's more of a restoration but I don't have the original info. and the PO sold off a lot of the goodies.
 Webers would be awesome of course. I read there are chinese repop webers now but the jetting and everything is way off. My former apprentice sold his midget car 750 stuff for 10% of what he had in it. Dang. Hilborn and everything.

[gschuld]

RC Engineering catalog options circa 1978

George

[gschuld]

2 more...

George

[Bill/BentON Racing]

I still plan on a back to back comparison with stockers. We got to know!  Bill

[Don R]

 I ran a 30 mm lectron on our first jr dragster, it was on alky of course. I didn't have an o2 sensor back then too bad, the pyrometer was misleading. They worked well enough but the needle/seat in the float valve didn't come apart for cleaning.  I don't hear much about them, more like injection than carburetion.