Bandit 4 won't rev past 6000 - solved

[reggit]

Hi all, I'm new to this forum and I'll jump right in with my problem.

I've got a '93 UK spec Bandit 400, it was bought as a non-runner.  I've replaced the engine with a 1989 one.  Changed the signal generator wheel to the 93 one, so it should be able to run with my electrics/cdi.  Are there any other differences in the motors?

The engine will run, but not rev past 6000 rpm, even off load.  The carbs appear to be clean, I've stripped them and cleaned the jets/passages as best I can.  The diaphrams appear good, ant there isn't a major inlet air leak.

I've a suspicion that I've missed something silly with swapping the motor, but can't work out what.

Anyone any ideas where I sould look next?

[Banditmax]

Hmm not revving past 6000 is an odd one. Cleaned the air filter? all the plugs sparking?

[reggit]

Yep, filter's good, plugs sparking - it even feels crisp upto 6k, then just stops dead. 

Had another look, it will rev to about 6500rpm, that's it.  That's about half of what the engine should do before it limits.  Is it possible that the CDI is seeing double the actual revs and cutting the ignition?  Hmm just thoughs going round in my head

[Chris H]

Bandimax, go over to the 400 greybike forum and have aread of Reggits post, it will save a lot of rewriting.
Hi Reggit i replied to your post over at greybike regarding the seventh wire and from the pictures of the rotor it is clear that there are strong differences between motors, the book sayes 15 deg btdc timing for all models (no differences) so if your sure youve missed nothing then id say there is still something different about the motors, is the key way on the crank in the same place? the timing could be way out in conparison to the valves, like i said id also change the gear selector and maybe the pickup from your old motor and dont want to scare you but do you know if the new motor is any good to start with?will help all i can.
Chris.

[interfuse]

What are your carb settings? 7k is where the needles start to come into play...

I've had that problem before when the fuel mixture was too lean...

[reggit]

For those interested, the 400 grey bike topic is here.

I have the motor idling and running fine upto 6000ish rpm.
Carbs are stock at least jet wise.  They've to come apart again cause it doesn't start easily, so I want to check over the starting circuit anyway, so I'll have a good look at the needles whilst I'm at it, not 100% on this bit of how the carb functions tbh.  I had to reset the pilot screws on 2 carbs to stock positions as they where a mile out, this should only affect idle and the transition to midrange as far as I understand though.

I've changed the pickups and signal generator, but not the gearchange switch.  Decided that it wouldn't come into play as the bike's now running a matched cdi and signal generator - but you never know.

Fuel mixture is a possibility as well, as the airbox only has a gauze filter in it, not a foam one.

Lesson to be learnt so far - never trust an ebay description   

[Chris H]

Hi Reggit,
If you want a foam for your air box ive got one spare you can have, contact me with your contact.
Chris.

[reggit]

Thanks for the offer Chris, but the more I look at the bike, the more I'm convinced that the problem is electrical. 

I had a look at the carb needles yesterday and discovered that they are a size different (richer) than standard, which will compensate for the air filter.
Running it without the airbox, I can see the carb slides start to lift under throttle and you can clearly see the fuel from the main jets entering the airflow. spraying more petrol into the carbs just bogs the engine down, suggesting that it isn't a lack of fuel it is suffering from.

I think I'll swap the coils out 'just in case' cause it's an easyway of eliminating them from the equation and I can pinch some from one of my other bikes.

[reggit]

I'll just stick a reply on here to update you all.  It annoys me when people don't.

Got the motor running properly, it needed the carb o-rings replacing. 

[txbanditrydr]

I'll just stick a reply on here to update you all. 

 

[gsxr400 racer]

 :banghead:Ahhh Orings