Another question on 400/600 conversion

[Firebird3]

I am interested in putting a 600 motor in a 3tj and using it as a trackday tool.
I am not too sure which engine I can get hold of at the moment, but if I use the 4jh then I will follow fzrtims conversion as it seems relatively straight foward. But if I use a Thundercat engine I was wondering which combination of carbs and CDI to use.
Knowing that the Thundercat had ramair is it ok to use the Thundercat carbs and CDI (with TPS connected) or is it better to use the 4jh carbs and CDI. I am thinking which is going to be easier to set up with carb rejetting etc, or because I am using the modded 3tj airbox with maybe the 4jh snorkel mod, standard air filter and just a race end can, does the carb need rejetting or needle position change at all.
Also with using either of these engines does the sprocket line up ok with the standard 3tj back wheel.
Many thaks for any help.

[Evilchicken0]

4JH is the engine designation and both the FZR600R Foxeye and Thundercat use it. The T'cat had slighting higher compression and stronger crank as a result although there wasn't so much between the two.
Use 600R carbs, CDI and loom - this ensures most of it will plug in although there a couple sensors that might change place. The T'cat carbs have a throttle sensor which is over complicated for this bike.
Change the coils .... the 3TJ ones are (apparently) different.
The crank cases are common between the 3TJ and 4JH, which is why this is sauch a relatively easy conversion.

The only difficulty is with the airbox and there seem to a couple of solutions. The main problem is in getting air to the snorkel on the airbox .... if it's a trackbike then you can simply raise the tank on some spacers.

Most important of all, and I can't streess this enough is to keep a regular supply of pictures to this forum
Welcome and good luck with the conversion

[Firebird3]

Many thanks for the reply.
Ok, if I go with the Thundercat I will use the FZR600R carbs and CDI if you think they will work ok.
As for the loom, I will probably do the same as fzrtim and graft the 600 CDI onto the 400, as it seemed to work for him alright.
With the coils, I presumed fzrtim used the 400 as I can't remember him saying otherwise, but pehaps somebody could clarify.
With a standard air filter will this setup require the carbs to be rejetted?
Also does the sprocket on the engine line up with the rear wheel sprocket?

[plodder]

Mine has the full 4JH foxeye setup including loom and the 4JH carbs had the dynojet kit fitted when I bought them (it was a cheap job lot) plus thundercat headers (2 port gaskets to make up for allignment), a FZR1000EXUP link pipe and can.

It was very lean on the pilots (i.e. just off idle), so I went from a #35 pilot to a #42 pilot with no other changes. There's a place in new zealand that did 4 jets delivered in a week for about £12.

I also dispensed with the snorkel, held the filter in with some wire crossed over the top of the filter and cut a hole in the bottom of the airbox below the centre of the filter, to get more air in.

It's pretty good but if you give it full throttle below about 6000rpm it growls without pulling very hard; when it gets above about 7000rpm it takes off like a scalded cat.

I did list my full spec somewhere on this site, so have a look.

I did try thundercat carbs and they're OK just even less midrange on WOT but not bad off idle, so I think they need smaller main air jets or bigger main jets (althoguh the mains are huge, so I was going to try blanking off the main air jets with temporary blanks.

[Evilchicken0]

The crankcases are common so the sprokets line up without a problem

[fzrtim]

Just to clarify, i did and still am using the 400 coils. I also used the standard fzr6r carbs with standard jets. Not had any fuelling issues with it but air starvation in is the main problem that was pointed out on the dyno. Might have been made worse with no forced airflow on the dyno but it ran fine with the tank raised, and on track the problem is not too evident. I fitted a k+n filter from the 3he fzr6 (just fits). Was going to make some sort of air scoop but not figured out a way yet!

[plodder]

The message here is that we all do things slightly differently, so the set-ups are slightly different but they all work.

Sometimes it's just down to making the parts you already have work for you.

[Firebird3]

Thanks for all the replies.
Now I have a clear picture of what I am doing, so it is a question of sourcing all the parts and then I can get going.
I'll get some photos sorted out as well.

[cagiva996]

talking about coils i swapped the 400 coils on my t/cat 3tj hybrid for the thundercat ones and it made a big improvement in throttle response and pickup and made the motor feel smoother.i was so impressed that i bought some 3ohm dydnacoils to put on the rebuilt one -ill let you know if the dynacoils are any better.just as a note the the 400 coils are 1.8-2.2ohms and the thundercat(and i assume 4jh fzr600) are 2.2-2.6 ohms

[Firebird3]

Cheers, that's noted.