Bike Carbs

[tractor]

stop talking and get it done

[Guest janis]

Im still happy with my accuspark..done many thousan miles now and always starting first time etc..

[Longboarder]

If the dizzy and module you have are identical to the picture below then it is a bosch inductive unit. If it works OK then you will get no benefit from changing it. It is the equal of an accuspark unit in all respects apart perhaps from the advance curve. The advance curve can be tweeked by altering the bob weight springs once the engine is running and you can look at the advance curve with a strobe light. Save money and keep it on there.

 

Nigel

[Guest alexpink]

Just took the plunge and ordered some carbs from danST

£433.97 for carbs, manifold, hoses, gasket and 1.6mm jets, plus next day postage. Going to source a pump and choke cable elsewhere.

Will be fitting the FR32 and crush gasket with a standard carb head; this isn't ideal of course, but gives me a chance to upgrade the head at a later stage.

Will be using the standard dizzy with an accuspark module and no vacuum advance, so will let you know how I get on.

[jaimo]

Yeah please do alex

[maccavvy]

@alexpink i got a choke cable and universal throttle cable from my local motor factors

 

i used a sytek regulator set to 2.5psi and i use the original mechanical pump. no need to make it any more complicated than it needs to be

[Guest alexpink]

Like this? http://www.demon-tweeks.co.uk/performance/fuel-pressure-regulators/sytec-pro-flow-fuel-pressure-regulator

Before seeing that I was going to fit an electric pump next to the fuel tank for added security (and safety in a crash) but I may just use the regulator for the sake of simplicity.

Is the choke necessary on bike carbs? I have no problem fitting one, but my friend has a mk1 Fiesta with a zetec on bike carbs and doesn't use the choke and doesn't seem to have an issue. Is it a matter of preference or is it really necessary?

[maccavvy]

yes mate just like that. i got mine from ebay. was cheaper than DT

 

mine wont start and tickover without choke.(cbr900 fireblade carbs ) i mounted mine under the dash above the throttle so it cant be seen anyway and a choke cable aint a lot of money

 

some people like to sit there tickling it till it runs fine.

[cb750]

If the carbs are running rich at idle then you probably won't need the choke. Mine are running a bit lean and the choke does help it to start and idle better from cold. Really needs bigger slow running jets. I used the bonnet release on the Sierra column to operate the choke. I ended up with 1.55mm main jets using the fr32 cam, high compression injection head and megajolt all set up on a rolling road.

[Guest alexpink]

That'll explain it then- my mate is definitely a tickler lol.

 

I'll probably just have the choke anyway then for if ever I do need it, and it's another retro item to add to the interior

[theduck]

Will be worth bringing it over to Steve walford when it's finished Alex, just for fine tuning of the carbs.

[cb750]

I recommend Steve as well!

[Snapperpaul]

I just want to add a little to this thread as there are some omissions & inacuracies.

Megajolt is not difficult to wire up or fit if you follow the advice on the autosportslabs forum.

Megajolt will optimise your ignition across the whole rev range something standard electronic ignitions including accuspark will struggle to do as the curves are linear

The Megajolt also extrapolates between Rev & load sites.

When you increase compression, add better induction and longer duration cams your engine will burn the mixture quicker meaning less advance however the longer duration cam needs more idle advance this means the required advance curve from idle to max is shorter and the ramp steeper.

This is where dizzy's struggle

An accuspark with switchable curves can do a simple version of the right curve.

Where the Megajolt starts to really prove its worth is the ability fine tune every Rev and load site simply from a laptop and for you to create a bespoke map with less advance on cranking to allow an easy start with a long duration cam and high compression then as the engine kicks in to life the next rev site goes to the cams required idle advance, on to a short period of the same advance and then on to the ramp and on up to the required advance ( typically 34 to 38 degrees) at 3400 to 3800 rpm

Once you have fitted a Megajolt whatever you do to the engine can be accommodated.

When you change engines to a different type most of it will transfer straight over.

As stated before you won't get anymore power at peak revs but you will get a smoother power delivery, lumpy cams will idle better and pull better from lower down the rev range.

If analysed the torque curve will be smoother without those annoying dips.

It will feel smoother and faster on the road

[cb750]

I agree with you Paul. When I went to Steve Walfords he set up every bin on the megajolt map to give the best power and torque curves to suit the engine. When he had finished we road tested the car and it was backfiring on overrun after flooring it. He put the lambda probe up the exhaust and connected his laptop. Went out again and did the same run and by slightly altering the ignition map he cured the backfire. Being able to do this in real time was great.