General bike carbs

[Garf]

Engines gone on my cinq so looking to replace it with another 1242 spi. wanting more power this time but want it cheapish and no turbo. been looking on a few threads but not sure what bike carbs to use or how easy they are to install and setup. Anyone on here done anything like it got any advice?

 

[fingers99]

They will be barstewards to set up and you may never get it right. Expect horrible flatspots. Carbs really belong in the last century.

If you've the fab skills you might be better off with individual bike TBs, although the problems are not to be discounted. But, ITBs really only come into their own (over a plenum set up) with lumpy cams. (See Brooky's ITB development for some ideas.)

Getting 1.4 16v type power from an 8v 1242 will be expensive.........

 

[craigb244]

and its not going to be cheap to set up... look at a minimum of 500quid just for the ecu(before tuning!)

plus even the smallest of bike tbs are to big for our engines (altho ive been looking at the tb fitted on chines 125cc bikes/scooters, can pick them up for about 50quid each(need 4)... they are the PERFECT size.

 

[Garf]

was actually planning on using the mckrick chip thats already on. done abit of research and thinking best suited are honda cbr 250 itb's. difference in surface area isn't all that much comapred to 40mm tricker:

tricker 40mm tb 1256mm2
cbr250 25mm each 1962mm2

can use original fuel hose just increase fuel pressure, fabricate inlet manifolds get all sensors hooked up and bobs ur uncle. well in theory that is unlesss anyone else thinks different, i might be wrong

 

[craigb244]

was actually planning on using the mckrick chip thats already on. done abit of research and thinking best suited are honda cbr 250 itb's. difference in surface area isn't all that much comapred to 40mm tricker:

tricker 40mm tb 1256mm2
cbr250 25mm each 1962mm2

can use original fuel hose just increase fuel pressure, fabricate inlet manifolds get all sensors hooked up and bobs ur uncle. well in theory that is unlesss anyone else thinks different, i might be wrong

what about fuel?
You cant just connect the bike injectors to the spi wire. fuelling will be totally wrong... also... mpi needs to be timed right. they usually inject fuel on a closed valve (at idle... once above a couple o krpm nothing really matters)
Injecting fuel at any random pattern with mpi can end with changing mixtures/odd mixtures between pots. it sounds simple but it really is not... sadly

 

[fingers99]

You'd need -- At least -- a remapped MPI ECU. 'Squirt might make more sense. See Dave Walker's column in PPC for some of the issues -- he hates the things!

 

[fordliu]

was actually planning on using the mckrick chip thats already on. done abit of research and thinking best suited are honda cbr 250 itb's. difference in surface area isn't all that much comapred to 40mm tricker:

tricker 40mm tb 1256mm2
cbr250 25mm each 1962mm2

can use original fuel hose just increase fuel pressure, fabricate inlet manifolds get all sensors hooked up and bobs ur uncle. well in theory that is unlesss anyone else thinks different, i might be wrong

You are reasonable . I think you are right. Thanks.

 

[Renrut]

I looked at it before I made the sensible decision to just put a bike engine in.

Bike Carbs belong on bikes. Carbs are far less forgiving of a less than ideal setup although possibly easier to get to a kind of running point assuming they've been sized correctly.

I looked at CBR600 ITBs. They seemed a bit big (38mm iirc) but being injection would be more ok (still possibly far from ideal). To get the benefit I'd still need:

Headwork,
lumpy cam,
Adaptor plate to head,
custom fabricated intake,
different injectors (modern high performance bikes tend to use 8 with 4 in the airbox which will not fit under the cento bonnet),
mapped fuelling (MS probably as mine was SPI),
Lots of setup time,

Add all that up and its a lot of money, the cheaper option if you want lots of NA power is 1.4 16V - its cheaper, easier and will be far more effective in an everyday car, and give a bone stock reliable 100bhp.