Hi Guys

Im new to the site .im having a problem with a cb400 super four Vtec when riding the bike it will not pass 5000 revs . Its not a fuelling issue carbs are clean and its not running out of fuel the bike will stay riding fine at 5000.
But the engine was over filled with oil by about 3 litres (not by me) and there was a lot of oil in the air box from the crank case breather pipe. is it possible that the pressure inside the engine caused a problem with the Vtec ..or is there any other reason this could happen .
I would also like to under stand how the V tec in this model works .
any help would be great

Regards
Venturi

Vtec kicks in at around 7500rpm, I would suggest a new air filter, changing the oil to the correct amount and cleaning the airbox and carbs thourghly. After that then see if the problem persists.

ive just cleaned the carburettors and the airbox ,the correct amount of oil has been filled into the engine and a new oil filter and air filter ,ive also replaced the plugs ..took the bike out for a test ride and it still will not pass 5000rpm ..max it will do is about 5500..
the bike is not fitted with a limiter and this problem started since the bike was over filled a lot (8 litres) with oil
Or has anyone got a workshop manual for this bike would also be a great help..

8 litres!
Christ my 3.0 Toyota hilux takes that amount.
Was it smoking with that amount of oil or is it smoking now?
I think the vtec system works off oil pressure and that oil pressure shouldn't change if over filled,
Just like when the oil level is low the pressure stays the same untill the oil drops below the pick-up.
It could have damaged the rings and you are losing compression. Possibly bent the rods too.
Check the crankcase breather see if it has a filter on it and replace that.
I would also check every pipe into and out of the carbs like breathers, overflow etc in case something has got blocked with oil. ( I'm assuming it took a good lung full if it was started up like that) The tiny drillings to the carb tops that pull up the diaphragm' s might be blocked stopping he sliders from lifting.
Good luck.

Is it possible that there is a limiter on this bike . to get out of first gear the bike will rev all the way out to 8000 revs and the power valve will cut in at 7500 at 8000 she needs another gear . In second it will reach about 6500 and every gear after that it stops at 5500 ,the girl who owns the bike says its went more than that but she has the bike 9 months and it spent 3 months not in use....help