Topic: 75 CB400f how best to set full throttle pull...

[Lil Red]

In romping around on my bike I,ve noticed that I can turn 11 grand in first and 10.7 in second and third, but only if I let off the throttle a quarter to one half inch...if I wind it to the stop...then its 10 grand in first and it starts to break up at 9800 or so in other gears...in messing about with the cables...if I limit the top cable it begins to not want to spring back to idle...the bottom cable...well it seems to not have an affect on anything...any suggestions...am I missing something?...i feel like might be splitting hairs here, as i can just limit it manually, but it would be fun to get the thing perfect. It's a ridiculously fun little bike.

Thanks in advance.

[trueblue]

The rev limiter on these bike is meant to be built into the computer, which is located a couple of foot above the seat, some computers are faulty and allow the engines to over-rev, this may damage the top end if it isn't brought under control, it is usually easy to reprogram the computer to let off the throttle before any damage can occur.  In the worst cases the engine can float a valve and do some serious damage.  This normally causes a sudden reprogramming of the computer, because the computer has to shell out a substantial wad of cash to rectify the damage.

[FuZZie]

The rev limiter on these bike is meant to be built into the computer, which is located a couple of foot above the seat, some computers are faulty and allow the engines to over-rev, this may damage the top end if it isn't brought under control, it is usually easy to reprogram the computer to let off the throttle before any damage can occur.  In the worst cases the engine can float a valve and do some serious damage.  This normally causes a sudden reprogramming of the computer, because the computer has to shell out a substantial wad of cash to rectify the damage.

Great post... LOL!

[cosmicvision]

Holy moly...that whole post I was thinking "A computer?? Where?? They must've gotten all futuristic with those 400s" until the last line. Too good

[oldbob]

Sounds as if it needs larger main jets.

Bob

[m00ntan]

The rev limiter on these bike is meant to be built into the computer, which is located a couple of foot above the seat, some computers are faulty and allow the engines to over-rev, this may damage the top end if it isn't brought under control, it is usually easy to reprogram the computer to let off the throttle before any damage can occur. 

Maybe, in this scenario, it could be best to replace the PCM with a throttle position sensor known to be in good condition.

[veloracermike]

Lucky for me I started to develop the sensitivity in my right hand at a young age

[cougar]

+1  trueblue

[Lil Red]

So theres no way to limit the throttle pull? The things a spinner...I'll look at the manual again...something about the carb slides at 1mm or soemething...It's not floating...it s fuel limited....and somethings going on where it's pulling to far. i guess...its certainly not going to blow up...well maybe....I m mechanically sympathetic...it's not like I hold it there and wonder...

[vames]

1) Look at tach.
2) When needle hits red zone, stop twisting.
3)  Shift.
4) If you cant do #3 because you're in 6th gear....Game over, insert coin, buy another bike.

[cougar]

LIl Red ; The difference in the running is caused by a fuel situation. Now to try to be Nice on what others are saying. STOP taking the bike to it's MAX REDLINE. I may seem a bit anal here, but what your doing shows No Respect of your bike. Yes the tach may say it can run 11,000 rpm's but that doesn't mean you should.And the redline goes away after 11,000 so does that mean that above redline everything is Fine ??  I'm hard on my cb750 but I VERY rarely get near redline! 1 reason is because the motor is 36 years old (NOT NEW) , secondly you get very little advantage in the last couple of grand. Unless you've built this bike to Race, Please respect it and turn your throttle hand back some so you can have a nice ride for a long time. Please for the bikes sake !!   ...cougar...

[Lil Red]

found the throttle stop screw...all set to specs...no more break up just zip up to valve float with the throttle pulled to the stop..just as Soichiro intended. You guys can go back to polishing parts now.The siren song of the tearing canvas wail beckons me

Yet a-GAINNNN!  CHEERIO!