Omfg! 3tj Won't rev past 4000rpm??

Bennybrown · Post by **Bennybrown** » Tue Aug 06, 2013 10:33 pm

Real head scratching going on here! I got the bike with farings removed and carbs but it was running, I saw it, albeit lumpy at idle. The carbs had been split from their banks and we're well worn and buggered around with so I found a good used set and stuck them on..... And now my problem, it starts, well it idles not bad considering I haven't yet touched the carbs but I get one full rev right up the range and then like someone flicking a switch it's limited to exactly 4000rpm turn it off then start it again and it does the same???? It's a 3tj model and it's had the exup removed and replaced with a full system, I understand this might play around with the low rev range but it was running mot'd and rideable 6 month's ago!

Sorry about the short novel but any help would be HUGELY appreciated!!

pearson* · Post by pearson* » Tue Aug 06, 2013 11:58 pm

You say it's had the Exup removed and replaced with a full system. Did you remove the Exup servo too?

Removing the servo triggers an automatic limiter in the ECU at around 4k rpm (or thereabouts). Sometimes takes a second or two to kick in though.

This might be what your experiencing.

You'll probably find your right in the low end dissapearing, not so much on strait horsepower, but while my exup was being refurbed a quick run on the dyno lost me about 30-40% of torque (bear in mind not having it retuned for without wont help either). So id be prepared for that too.

My knowledge runs out after mechanical/electrical aspects so if the servo isn't the problem you might have to find someone that know carbs better than I do. Although, a good clean might help, and it's not nearly as hard as people think at all.

Bennybrown · Post by **Bennybrown** » Wed Aug 07, 2013 7:51 am

It's all a bit strange really, like I say it was running and I can't quite believe it's the carbs, it a very defined limit and like I say picks up beautifully when first started (but who am I kidding, I'm no exper!)
So the exup...... It has been completely removed and replaced with a full system, and the plug under the seat is dangling there empty, could this be mu problem??? Is there something I need to wire in to make it thinkthe valve is open or do you think I need to plug an exup back in????

Thanks for your help already!

Post by **Evilchicken0** » Wed Aug 07, 2013 9:29 am

You see the red fuel line and the fuel pump ? Just left of it (up in the picture) you se the back plastic box .... your's should be there, it's the exup servo and will have a pulley wheel on it - make sure it's connected, it should make a "weep weep" noise when the ignition is turned on.
There's a wiring diagram in the Document Library on this site (right at the top of the page)

Post by **Hogdigerdy Dog** » Wed Aug 14, 2013 4:52 pm

i'd go with the others and say the servo needs to be attached even if the exup aint

but having said that, once you get the servo in place (which you will need to do) if your still having the same problem it'll be worth checking the fuel pump as the 3TJs pump pressurizes the carbs/float bowls to about 2psi and without this it wont rev past about 4Krpm, i know this to my cost as when i got mine it never had a pump and before i found this forum and the manuals i didn't know it should have

Omfg! 3tj Won't rev past 4000rpm??

Omfg! 3tj Won't rev past 4000rpm??

Re: Omfg! 3tj Won't rev past 4000rpm??

Re: Omfg! 3tj Won't rev past 4000rpm??

Re: Omfg! 3tj Won't rev past 4000rpm??

Re: Omfg! 3tj Won't rev past 4000rpm??