Hi Everyone,

Just starting a new topic as I am taking my bike to the dyno on Saturday to test some CDI's back to back to try and see what is really going on with them. I have the following cdi's to test:

Standard 3TJ-00 box

Modified 3TJ-00 box (same as BDK do, thanks Stuart)

Standard 4DX cdi.

I know the plugs on the 4dx cdi are slightly different but hopefully fairly straight forward to cobble something temporary together for the dyno test.

The spec of the bike is standard 3tj-1 apart from it has 3tj-2 SP carbs fitted (all jets standard). Standard headers complete with functioning exup. A micron can with huge baffle.

The pipe is full of carbon soot at the moment so I think it is running a bit rich. I'll be sticking it on the dyno as is first to see what power it was making when I was riding it at Cadwell a few weeks ago.

I'll update this thread with the results at the weekend.

Cheers,

Dan

Hi guys,

Right I have some data to share. First off the bike was being strangled by a shit micron can with an awful baffle in it that looks like this:



This also made it difficult to get a useful AFR reading as we couldn't get the probe in as far as it needed to be to get a decent reading. The micron can itself has an internal bore of about 4 inches so not ideal at all. If it was 2" all the way through I would have just taken the baffle out. Also we were getting problems with ignition spikes being picked up by the engine speed sensor. Despite all this we did get some useful info:



All three of these runs were done with the same main jets and no other changes apart from swapping the CDI. The mains were 110 on the outer cylinders and 107.5's on the inner cylinders. We had no idea what the fuelling was doing so just fiddled with the jets a little bit.

Green run: Standard 3tj-00 cdi.
Red run: Standard UK model 4dx cdi.
Blue run: Modified 3tj-00 cdi to kit spec.

Obviously there is a lot of spikes messing up the curves but there is enough there to go on. On my bike, the kit cdi opens the EXUP valve too late which creates a hole in the midrange. However if you look from about 12500rpm onwards the extra advance that the kit cdi has gives a 4bhp increase at 13000rpm and the power holds on just that little bit longer. I reckon this would be noticeable on the track. For my bike in the state it was in on the dyno the standard EXUP timing works best. The EXUP timing in the kit cdi is actually designed for the optional kit EXUP set up anyway so it's no real surprise that it isn't ideal for my set up as well as the fact that my bike is not set up to anywhere near kit spec lol.

When I sort my exhaust out I'll be going back to the dyno to have another go.

This next set of curves shows the bike with standard main jets (100 outers 97.5 inners) and standard 3tj-00 cdi Red curve. Versus the blue curve (uk cdi with 105 outer mains and 102.5 inner mains):



There really isn't alot between the two cdi's. Sadly I don't have a comparison of the uk cdi with standard jetting. The engine wasn't breathing properly at all at the top end and it was very slow to build up the revs, which is kind of how it felt on track too.

As the bike made better power with the smaller mains it was more than likely a bit rich, anyway I can only speculate on that as we couldn't get a reading at the business end of the power curve.

The upshot of this is that the only real difference between the 4dx cdi and the 3tj-00 cdi is that the 3tj-00 has the speed limiter.... that's it! There may be a slight difference here and there but not alot.

So my bike was making 52bhp on a dynapro dyno with SAE air correction as it was at cadwell a few weeks back. I managed a 1:55 on it in that state of tune so I am quite pleased! To put it into perspective, a good 92 TZ 250 makes 70bhp on this dyno.

Hope that is of use to someone.

Dan

I think youre right about the pipe it looks to be killing the fueling

I'd be interested to see ex-up and ex-up removed comparison? see how much the mid range differs.

I'll be adding to this post in a few weeks time hopefully. Should be able to get some more useful data this time!

Dan