Size Of Bike Carbs

[bales 1]

Hi,

 

I have been reading all the posts on bike carbs conversions with interest especially as a good value for money conversion. I have been thinking about getting weber 45's originally, but this has interested me.

 

What bikes do they come off are they all 1000cc ones such as R1's and gsxr's. The reason for asking is that I have acess to lots of 600cc bikes carbs at uni for free, mostly off the yamaha r6, will these be able to flow enough air (the r6 makes 120bhp i think).

 

Also i have read that a manifold needs to be made specially to fit, if i can get the carbs for free do people think that this might actually be cheaper than DCOE's and are the power gains similar to webers. I am planning on adding a 285 cam and mildly tweaked head aswell over summer. Thanks for your advice.

 

Alex

[Dom9 2]

Hello and welcome to the forum!

 

If you do a search you will see that it is generally accepted that a bike carb flows more than a Weber for a given diameter. This is because the flow in the Weber is limited by the choke size. In other words, you might have a 44mm ID Weber, but the choke might only be 36mm, which means that the equivalent bike carb would only have to be of the order of 36mm...

 

I don't think anyone is 100% sure whether this works 100% in practice, but since the bike carbs are choke-less, it would seem to make sense! If memory serves correct I think that most 600cc bike carbs are about 38mm, so they should be big enough for a standard-ish engine.

 

However, being that you are going to tune your engine and the fact that bike carbs tend to cost the same regardless of what size they are... Well, they tend to be cheap anyway... It's probably worth looking at the bigger bikes. I have a set of Blackbird carbs at the bottom of the wardrobe and they are about 42mm ID I think and should suit applications upto around 180-200bhp... Well, that's what the bike guys think anyway!

 

R1 carbs are also popular as are ZZR1100 carbs and (I think) ZZR1200, Bandit carbs. There are certainly a few on eBay at the moment if you search the bike parts for carbs... e.g. http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...AMEWA%3AIT&rd=1

 

They are worth upto £100 I guess, but can be had for much less... Add the manifold from Shenpar or Bogg Bros at about £150 and a total price of £250 + consumables seems very reasonable when people are paying £400+ for Webers, with other bits and pieces on top.

 

Good luck with the project and keep us updated if you go down this route!

[bales 1]

Thanks for the info that sounds really interesting, i might have to start seriously considering this. You said that the manifolds are about £150, do u need a different fuel pump aswell, i have heard some people say that they use the standard one and others that you need a different one, how much are you looking generally for one of these is it a red top fuel pump or am i getting confused with batteries?

 

I am in my final year of uni at the moment so I dont have a huge amount of money so its more of seeing what i can do for the funds at the moment approx £500-600. I was considering a 285 deg cam aswell, but i wasnt sure whether the head would need machining for this (also out of interest is this because the cam physically opens the valves higher as well as for a longer durations. Or is it the actual lobes on the cam that are larger)

 

I have read all the threads on this for 8v tuning and all the big valve arguments and the fact that you cant get much more out of 8v head without spending serious money. So is it wiser to go for carbs, a cam and standard head with higher compression ratio, or to not get a cam and spend some money on the head (bearing in mind it seems to be a lot of money for decent headwork). Sorry if i am going over old ground on this. I have say though i have been on quite a few forums but this is the best by a long way for advice and technical knowledge it is really helpful indeed!

 

Thanks

 

Alex

[number2301 1 1 Cars]

I've thought about this myself alot as well, I know Bogg bros will do the whole lot for ~£700 but does anyone know what all the bits you'll need would cost as well as the kind of expertise you'd need to fit it all?

[Guest smokinslim]

Glad i had a look at this thread, had no idea that you could pick bike carbs up so cheap.

Clicked te ebay link n had a look through the sellers items; carbs for a 600 had an ID of 37mm, for a 1200 ID was 38mm. Would the difference be more in the jet size used for different size engines than the choke size then?

Does anyone have a rough idea how much a custom manifold would cost? I've haven't come across any bike carb' manifolds for the TU engine yet

[Dom9 2]

Thanks for the info that sounds really interesting, i might have to start seriously considering this. You said that the manifolds are about £150, do u need a different fuel pump aswell, i have heard some people say that they use the standard one and others that you need a different one, how much are you looking generally for one of these is it a red top fuel pump or am i getting confused with batteries?

 

I am in my final year of uni at the moment so I dont have a huge amount of money so its more of seeing what i can do for the funds at the moment approx £500-600. I was considering a 285 deg cam aswell, but i wasnt sure whether the head would need machining for this (also out of interest is this because the cam physically opens the valves higher as well as for a longer durations. Or is it the actual lobes on the cam that are larger)

 

It is possible to use the standard pump, but you still need to do something about the high pressure it runs at. A lot of people use low pressure Facet fuel pumps and alike, but it may also be easy enough to pick up a fuel tank with a built-in pump from a carbed 205. Bike carbs need very little fuel pressure, I actually believe that some are even gravity fed! If you can do the plumbing and installation work yourself I think the £500-£600 budget is very realistic. Lets say the bike carbs cost you £300-£350 to be fully sorted and running... 279° CatCam from Mattsav, some 3 angle seats and a hefty skim should set you back around £300 and you should be seeing some good power... He may even clean the ports up for you if you ask nicely! The head shouldn't need machining for the cam, in fact, I don't think the 8v needs machining for anything but mega-mental cams... The extra power does comes from increased duration and increased valve lift, but you should still have clearance with a cam like the 279° even with a hefty skim. It's probably not worth spending £100's on headwork when this spec should probably net you between 140bhp and 150bhp and that's with my conservative hat on... Aim for 11:1 compression ratio but do get in touch with Matt at QEP and see what he advises.

 

 

I've thought about this myself alot as well, I know Bogg bros will do the whole lot for ~£700 but does anyone know what all the bits you'll need would cost as well as the kind of expertise you'd need to fit it all?

 

I think that is a very reasonable price for a drive in - drive out conversion!! I considered dropping the car in there for that, 'cos I think it represents excellent value for money! I think the gains to be made are worthwhile and peole forget that a good head job might cost you £300+ but you have to pull the head off and strip it, then put it back on with all new gaskets, then to get the best out of it, you still need new induction... When you sit down and think about the start to finish cost of even installing a cam, £600-£700 for what could be a large power gain is very good. I would guess the kit is pretty simple... You need carbs, a manifold, air filters, throttle linkage, throttle cable and some way to reduce the fuel pressure, well, I guess there might be a few hoses and random other pieces, as well as new jets for the carbs and setting up.

 

Glad i had a look at this thread, had no idea that you could pick bike carbs up so cheap.

Clicked te ebay link n had a look through the sellers items; carbs for a 600 had an ID of 37mm, for a 1200 ID was 38mm. Would the difference be more in the jet size used for different size engines than the choke size then?

Does anyone have a rough idea how much a custom manifold would cost? I've haven't come across any bike carb' manifolds for the TU engine yet

 

The thing is, most 1200 bikes are tourers and have fairly low-stressed engines, therefore they only make a similar power to 600cc sports bikes, which means they only need carbs of a similar size! If you look for the carb size on 1000cc sports bikes, you will find they are a fair bit bigger... If you are seriously thinking about doing the conversion, it is worth putting in a call to the Bogg Bros and seeing what they recommend, although the only two carbs I have seen them recommend in print are the Yam R1 and Honda Blackbird... I think I am going to fleabay my carbs in the next couple of weeks, so you guys may be able to pick up a bargain, I will stick them in the for sale forum on here too...

 

There was a topic in the TU tuning forum on here with some pictures of a TU engine on bike carbs, see if you can search for it. All bike carb manifolds for car engines are effectively custom and the Bogg Bros see to charge about £150 regardless of what engine it's for, so just pick up the phone and see what they have to say!

[bales 1]

Hi,

 

I have heard quite a few people mention 3 angle valve seats, sorry to sound a bit dumb but why exactly is this done.

 

Thanks for your info again, i might be interested in your carbs if you are selling them, but it wont be be probably till summer as i have to finish uni first so it depends whether you still have them then, cheers.

 

Alex

[Dom9 2]

Hi,

 

I have heard quite a few people mention 3 angle valve seats, sorry to sound a bit dumb but why exactly is this done.

 

Thanks for your info again, i might be interested in your carbs if you are selling them, but it wont be be probably till summer as i have to finish uni first so it depends whether you still have them then, cheers.

 

Alex

 

That's cool.... I've been trying to pretend to sell them for months, just can't be bothered... So they may well still be languishing at the bottom of my wardrobe this time next year!

 

Do a search for 3 angle valve seats and it should throw up a few results... In effect the valve seat is cut 3 different times at 3 different angles to smooth the airflow from the inlet port into the chamber and vice versa on the exhaust. Effectively the smoother transition from port to chamber helps the gases flow more efficiently around the valve head and into the chamber... More gas into the chamber per inlet stroke, the more power you get...

 

In fact, I think someone posted some pictures up a while ago, it might have been petert...? A quick google for images may also sort you out!

[l337dave 0]

It is possible to use the standard pump, but you still need to do something about the high pressure it runs at. A lot of people use low pressure Facet fuel pumps and alike, but it may also be easy enough to pick up a fuel tank with a built-in pump from a carbed 205.

 

Does this mean I don't need to replace the pump, just add a regulator?

 

 

 

I think the manifolds you are talking about are the ones from boggbros - £187ish, they have a 3 week waiting list at the mo tho so I'm having a go at my own currently - old inlet manifold section to 4 ali pipes with silicon hoses / jubilee clips depending on the fit. prolly won't look as cool as this tho:

 

(from bb site)

 

They do recommend other bike carbs than R1 / blackbird (I only know because I rung them up the other day) I went with some ZX9R ones cause there seems to be upto a £100 differance between them and the R1's (if you can find them) I can't remember which other ones they recommend too tho sorry!

 

dave.