3TJ carbs on a 4JH hybrid
Posted: Mon Jan 25, 2010 12:46 pm
I have a spare 4JH engine and a spare 3TJ trackbike that I robbed after I crashed my hybrid a couple of months back, so I think you can see where this is going.
Now the 4JH engine is an odd one in that it has a 3HE generator/rotor/pickup and 3HE inlet rubbers.
I have examined the ignition assembly and have tested that it will run on a 3TJ loom with about the same ignition advance as the 4JH would give it, albeit the 3TJ has a 14k redline comared to the 13K of the 4JH, so this part of it is OK.
Now to the question of carbs, which is the main subject of this thread:
The 3TJ has 32mm Mikunis and the 4JH has 34mm Kehins (there is also the option of fitting 36mm Kehins off the thundercat to 4JH inlet stubs as well but I never got that to work very well on the road due to a big mid-range hole). My existing hybrid (with 34mm Kehins) does not really do much below 7K and then takes off (even managed to keep up with an early R1 on my last trackday).
So the question is would the 32mm Mikunis improve the bottom end without robbing too much of the peak power? I was thinking I might use one of the bikes as a road bike and make the other one a dedicated track bike, so the Mikuni carbed one would be for the road.
If these will do the job then does anyone have experience of the jet sizes to use for this combination? I've got the 3HE sizes to use as a base line but only got 3TJ jets, which will be too small or FZR1000 jets, which will be too big. Obviously I can suck it and see or get a dyno setup but I'm not going to pay out for a dyno and a bit of experience may save time on the initial setup. and wasting money on the wrong jets.
If I can get some 3HE carbs cheap then that may be useful. Anyone got any?
Ta
Now the 4JH engine is an odd one in that it has a 3HE generator/rotor/pickup and 3HE inlet rubbers.
I have examined the ignition assembly and have tested that it will run on a 3TJ loom with about the same ignition advance as the 4JH would give it, albeit the 3TJ has a 14k redline comared to the 13K of the 4JH, so this part of it is OK.
Now to the question of carbs, which is the main subject of this thread:
The 3TJ has 32mm Mikunis and the 4JH has 34mm Kehins (there is also the option of fitting 36mm Kehins off the thundercat to 4JH inlet stubs as well but I never got that to work very well on the road due to a big mid-range hole). My existing hybrid (with 34mm Kehins) does not really do much below 7K and then takes off (even managed to keep up with an early R1 on my last trackday).
So the question is would the 32mm Mikunis improve the bottom end without robbing too much of the peak power? I was thinking I might use one of the bikes as a road bike and make the other one a dedicated track bike, so the Mikuni carbed one would be for the road.
If these will do the job then does anyone have experience of the jet sizes to use for this combination? I've got the 3HE sizes to use as a base line but only got 3TJ jets, which will be too small or FZR1000 jets, which will be too big. Obviously I can suck it and see or get a dyno setup but I'm not going to pay out for a dyno and a bit of experience may save time on the initial setup. and wasting money on the wrong jets.
If I can get some 3HE carbs cheap then that may be useful. Anyone got any?
Ta