Choosing Carbs over EFI... Madness?
scootz - 12/4/12 at 08:17 PM
I'm trying to trim some of the trike-build costs and one of the big money-pits will be the EFI system (when I around to it!).
Just to re-cap... I'm using a BMW flat-twin bike engine from the HP2 Sport. Despite being BMW Motorrads flagship flat-twin, it's still just
a 1200cc air-cooled lump, so not the most refined!
The throttle-body assemblies came with the engine, but there was no ECU. The BMW unit costs £STUPID to buy new and £NUTS secondhand (hens teeth) so
it would have to be an aftermarket jobby. Then swirl pots, high pressure pumps, mapping... the cost soon mounts up!
So how about flogging the TB's and using the funds to buy a couple of Keihin flat-slide carbs???
The trike will be used once-in-a-dry-warm-blue-moon and never for anything other than banzai blatting, so I'm not too fussed about losing a bit
of midrange, or it being a little rough.
Big mistake? False economy?
Thoughts welcome! 
paulf - 12/4/12 at 08:24 PM
What about the ignition ? is that a separate system? if so then it must be relatively easy to get a pair of carbs from a similar model BMW and fit
them.Im sure that performance wise it would not make a lot of difference the main reason they all use EFI now is due to emissions.
Paul
mookaloid - 12/4/12 at 08:46 PM
I wouldn't hesitate - fit some carbs
The worst that can happen is that it isn't great and you have to go back to injection. If this is the case then sell the carbs (which you will
have paid to dollar for) at a loss (as usual) then fit the fuel Injection. 
I wouldn't worry though - the carbs will be fine
matt_gsxr - 12/4/12 at 09:00 PM
I'm probably biased because I hate bike carbs.
In-tank gsxr1000 fuel pump includes a regulator (about £30), build it into the bottom of your tank and you don't need a swirl pot or external
regulator. Megasquirt it (£300) and tune with an LC-1 on the road (£180, which you can reuse on something else later, or sell on).
cloudy - 12/4/12 at 10:06 PM
Have to go with Matt on this one - there's plenty of ways of doing EFI on the cheap! Carbs are hateful things 
l0rd - 13/4/12 at 04:33 AM
i never thought you scootz would be considering the money.
do it once, do it properly.
Daddylonglegs - 13/4/12 at 07:34 AM
Scootz, you obviously need to sell loads more stuff to sort out the financial quandry
D Beddows - 13/4/12 at 08:13 AM
Flat slide carbs are 
but as has been mentioned how are you going to make a spark at the right time?.......then there's getting a manifold
to mount the carbs.......then there's finding someone who can set up flat slide carbs properly........ then there's getting a decent map for
your aftermarket ignition......
Still going to be quite expensive and a huge amount of faffing about if you ask me!
scootz - 13/4/12 at 08:49 AM
Hmmm.... so that's a maybe!!!
TBH, I just want too get the thing done and go out to play in it. I'm past caring if TB's are marginally better than Carbs... or even if a
trailing-arm front suspension performs fractionally less-well than a double-wishbone.
The only thing I don't want is a complete disaster... irritatingly poor engine control, or undrive-able suspension.
l0rd - 13/4/12 at 08:56 AM
Over the years, you broke for parts more than 10 cars. Don't tell me you haven't kept an ECU
scootz - 13/4/12 at 09:01 AM
I don't have one
BaileyPerformance - 14/4/12 at 10:20 PM
quote:
Originally posted by scootz
I don't have one
we do COMPLETE megasquirt EFI systems, inc all parts, installation and mapping for £1000.
this price assumes you have all the stock inlet manifold, fuel rail, injectors and fuel system in place.
we provide all sensors required
if you are running a CAT the cost will be slightly more.
let me know if you need anymore info
Cheers Dale.