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Bike carbs onto engines
designer - 25/9/12 at 08:47 AM

Octobers Classic Car Mart has an article on converting to bike carbs.

coyoteboy - 25/9/12 at 11:51 AM

What's the desire to run bike carbs when you can run throttle bodies (maybe other than cost)?

rusty nuts - 25/9/12 at 12:00 PM

PPC have covered fitting bike carbs a few issues ago . As for fitting carbs instead of T/Bs it's horses for courses, some don't want to fit T/Bs but are happy to fit carbs and bike carbs being simpler, stay in tune longer and cheaper than twin 40s etc whilst giving better driveability .

whitestu - 25/9/12 at 01:35 PM

quote:

What's the desire to run bike carbs when you can run throttle bodies (maybe other than cost)?


For me it was easier to make them work, cheaper and they seem to work at least as well as TBs on an engine in standard tune.

Stu

Bare - 25/9/12 at 03:53 PM

Not overlooking that Used Bike carbs WILL require a competent refurbish.
Neither dead easy nor inexpensive to do.
And if one doesn't.. then a myriad of tuning problems follow.. seemingly forever.
Don't ask

RK - 25/9/12 at 04:29 PM

Taking them apart to clean isn't hard. I have not put any bike carbs on a car engine, but have refurbed carbs for cars (a long long time ago). Yes, everything has it's negative side, but if that were the only consideration, we wouldn't get out of bed every day.

coyoteboy - 25/9/12 at 10:44 PM

quote:
Originally posted by whitestu
quote:

What's the desire to run bike carbs when you can run throttle bodies (maybe other than cost)?


For me it was easier to make them work, cheaper and they seem to work at least as well as TBs on an engine in standard tune.

Stu


I guess I must come at it from a different viewpoint. I've fitted and tuned a fair few ECUs/injection systems now. I can't imagine anything more unintuitive than tuning a carb'd engine lol. But plenty of folk do so it clearly has benefits for some people.

spiderman - 26/9/12 at 12:21 AM

Might be that those fitting bike carbs to their engine may not have fuel injection to start with i.e. x/flow. Just a thought.

blakep82 - 26/9/12 at 12:55 AM

its easier to wire up and set up, thats why i went for carbs.

EDIS you can have it running on 1 sensor (crank) and a power connection
Megajolt, you add 2 wires to the megajolt unit from the edis, and add a throttle sensor, upload an ignition map
job done!

here's my first start
http://www.youtube.com/watch?v=MP78CTkhEew
ALL of my ignition system is on that bit of ply wood (megajolt not added yet) yeah it doesn't run perfect, but it works! wired up in about 10 minutes, with no exhaust

fuelling will need set up, drilling main jets to 1.6mm is a good start for a 2 litre, not looked much into setting up fuelling yet, but seems fairly straight forward

how many sensors do you need to set up for megasquirt? wiring up injectors, setting up fuelling timing, sensors etc, its a whole mess of wiring, something i'd look to do later, but for now, i'll stick with simplicity of carbs.

i've still got my bmw 328 sitting outside, some sensor problem and it won't run properly, not a clue whats wrong with it. could be anything...

[Edited on 26/9/12 by blakep82]

cliftyhanger - 26/9/12 at 07:51 AM

Not done the bike car b thing, but reasonable experience with SU's over the years (bike carbs similar I believe)
I struggle to see how a simple drill out of jets will make a carb change from being suitable for one engine to another, without the use of an oxygen sensor or rolling road session. SU carbs have loads of needles, a simple cam or exhaust change requires needles to be swapped, so a 600cc bike engine to a 2 litre car engine? it is bound to require a fair few changes? or have a I misunderstood.
I guess the bike carbs could be similar to webers, but again, they have a fair few variables. a few jets at least.

Saying that, once set up correctly (like any carb) they should perform well. Not as accurate or flexible as EFI, but could well be close (or a million miles off and melt the pistons!)

FASTdan - 26/9/12 at 09:37 AM

The example I like to use is our own 2.3 duratec - runs on 40mm ZX9R carbs. On totally standard jetting with only the air correctors blocked these carbs fueled fine until 5k revs. Once drilled to 1.7 the car put out 165bhp @ the wheels. Thats a stock 2.3 with the only other mod being a 4 branch manifold (and thats a hacked pinto one, not a £500 custom tuned job). Being conservative then, thats 190bhp @ fly. Drives fantastically, will pull in any gear at any rpm with no flatspots.

So outlay:

£340 for carbs manifold and hoses (thats based on a kit price from me)
£240 for complete megajolt with everything required (full package supplied by triggerwheels)
£80 rolling road 1.5hrs

£660

How much would it have cost to do Jenveys and management on the same engine? Plucking a few figures off the top of my head:

£800 Jenvey throttle bodies
£500 ECU (minimum?)
£250 mapping (again, minimum?)

£1550

I dont doubt that this set-up would improve power and driveability marginally, but at £900 its not making for great power/£ ratio. You could of course source second hand jenveys to make the comparison fairer, or even bike bodies but its still a considerably more expensive route. For simplicity and cost I dont think you can beat the bike carb route.

In the case of the 2.3 I'd say there's probably more potential gain from bodies simply due to the limited size of bike carbs (40mm is generally as big as you get without sourcing rare ones), but in the case of the average 2.0 the gains will be less.

[Edited on 26/9/12 by FASTdan]

coozer - 26/9/12 at 09:55 AM

Can I add that with zx9 carbs mine gave 40mpg, then the 'upgrade' to fuel injection cost me £££££ and the mpg went to 26.

IMO it was basically a learning curve that cost me tons of wonga!

FASTdan - 26/9/12 at 10:29 AM

I'll also add that ZX9's gave our 2.3 Indy 37mpg to le mans and 22mpg on a 'brisk' 130 mile group drive out in the Yorkshire dales recently

matt_gsxr - 26/9/12 at 12:37 PM

If you go with bike carbs then use the standard bike pump and refurb the carbs replacing all the rubber bits.
Otherwise you will just leak fuel in all the wrong places.

Personally I prefer the Megasquirt/EFI route, which needn't be that expensive (gsxr1000 throttle bodies at £100, MS ECU is £200, plus some other bits and bobs).

coyoteboy - 27/9/12 at 12:03 AM

As with Matt, your costs are vastly out of line with my experience, especially if you self-tune the bulk of the map, but each to their own - i wasn't judging.

[Edited on 27/9/12 by coyoteboy]

whitestu - 27/9/12 at 07:08 AM

quote:

The example I like to use is our own 2.3 duratec - runs on 40mm ZX9R carbs. On totally standard jetting with only the air correctors blocked these carbs fueled fine until 5k revs. Once drilled to 1.7 the car put out 165bhp @ the wheels. Thats a stock 2.3 with the only other mod being a 4 branch manifold (and thats a hacked pinto one, not a £500 custom tuned job). Being conservative then, thats 190bhp @ fly. Drives fantastically, will pull in any gear at any rpm with no flatspots.



My experience was similar.


My ZX6R carbs and pump cost £35. I drilled out the jets to 1.6mm, gave them a quick clean and lifted the needles one notch after checking the mixture on the road with an AFR Meter.

Other than adjusting the mixture screws to make the idle mixture a bit leaner that was all I did. I've done several thousand miles and 4 track days and the car runs perfectly, with no flat spots or hesitation. I thought I had a problem with one of the carbs a couple of weeks ago but it turned out to be a plug.

I get about 40mpg on 'normal' driving. No idea what it gives on track but it seems reasonable given how often I need to re-fuel.

After years of messing about with Webers on Alfas and Citroens I also wouldn't have believed you could put 600cc bike carbs on a 2.0 car and make them work but it really is that easy.

Like Coozer I quite fancy playing about with TBs and Megasquirt but my fear is the car won't run as well if I do.

Stu

mcerd1 - 27/9/12 at 08:09 AM

quote:
Originally posted by FASTdan
So outlay:
£240 for complete megajolt with everything required (full package supplied by triggerwheels)

you don't need to pay as much as that for the MJ setup either, I got the donor parts myself and it only cost me £125 for the lot

[Edited on 27/9/2012 by mcerd1]

FASTdan - 27/9/12 at 08:26 AM

quote:
Originally posted by mcerd1
quote:
Originally posted by FASTdan
So outlay:
£240 for complete megajolt with everything required (full package supplied by triggerwheels)

you don't need to pay as much as that for the MJ setup either, I got the donor parts myself and it only cost me £125 for the lot

[Edited on 27/9/2012 by mcerd1]


Absolutely! But in the interests of being fair I tried to stick to 'off the shelf' pricing for both routes.

coyoteboy - 28/9/12 at 07:42 AM

Curious as to the comments about decreasing economy when running MS. Not sure how that's physically possible unless you've really messed up the tuning on one of them. To get to 40+mpg on a petrol 2+ litre petrol from the 80s/90s era you're running leaner than I would class as safe, but likewise if you're getting 25 from normal driving with one you're running really rich.

FWIW I paid £150 for my megasquirt kit and built it myself. I paid £125 for my wideband. I built it into a stock ECU case/connector which cost me a fiver.

I have since, for the hell of it, replaced coils/injectors/you name it at some expense, but I had a usable drivable car with a half-decent map for under £300 and a bit of time, but I already had a soldering iron and the injection parts!

Other engines I've done used later MS's (£250 kits) and had to have the injectors/throttles bought for them. The injectors cost £40 online and the throttles about £100 IIRC. £40 for stick coils and a couple of IGBTs for firing them, so all in probably around 500 from a bare engine.

[Edited on 28/9/12 by coyoteboy]

mcerd1 - 28/9/12 at 10:17 AM

at the DIY end of the scale and assuming your starting with a bare strait 4 engine and that you already have a suitable laptop etc…
(I'm also assuming that your engine doesn't have a dizzy that your going to keep)

carbs = £50 - £80 (depending on the model and how lucky you are)
megajolt = $181.95 (TPS, no hard rev limit, +delivery from US) = ~£112.14 at todays rate
EDIS, coilpack, leads, VR sensor and wiring from a donor car = ~£20 - 30 from a decent scrapyard
bike fuel pump = £20 - £60

= £202 - £282

or

Throttle bodies, inc fuel rail and injectors = £100 - £150
DIY ECU kit = ~£250
coilpack / coils = £10 - £40
VR sensor = £5
fuel pump = £25 - £80 (assuming an EFI bike one is suitable)

= £390 - £520

Either way you'd need to add:
Trigger wheel = ~£25
flange for DIY manifold = £26.98 (steel from FastDan inc P&P)
tubes for manifold = ~£10 or less
rubbers and clamps = £30.99 (from FastDan inc P&P)
Air filter / air box = £50 - £250 depends what you want, DIY airbox with a cheap cone, off the shelf race spec or anywhere in-between….

= £140 - £340

Giving grand totals off:
Carb's = £342 - £622
EFI = £530 - £860

Feel free to correct my figures and add anything I've forgotten

Also the carb + MJ setup has only a handful of wires to connect, so if your like me and hate working with electrical stuff it’s a much more appealing setup

whitestu - 28/9/12 at 10:52 AM

quote:

Feel free to correct my figures and add anything I've forgotten


Swirl pot / modified tank / return fuel pipe for efi could add another £50 or more on top of your estimate.

Stu

coyoteboy - 28/9/12 at 10:45 PM

quote:

Feel free to correct my figures and add anything I've forgotten


Nope, that's pretty comprehensive on an older engine not originally designed for EFI. Though I'd correct your prices on the mega-parts (both sides) as import tax, postage and all that cack usually adds up to about 30% extra on top of those sections.