RF400 won't rev passed 5000rpm!

[Dark Crystal]

Hi all,

Well after changing the plugs and getting her running... she'll start, but won't rev passed 5000rpm... she sounds like she's not firing on all cylinders.. but at idle sounz perfect...
Any ideas? Would the CDI cause this to happen - coz i was thinking that perhaps it would break down at higer revs.. or the coils maybe?

[James Deuce]

Coils, HT leads, Spark plugs.

[crazybigal]

is it starving for fuel? check filter and lines and all vacum lines.


Hi all,

Well after changing the plugs and getting her running... she'll start, but won't rev passed 5000rpm... she sounds like she's not firing on all cylinders.. but at idle sounz perfect...
Any ideas? Would the CDI cause this to happen - coz i was thinking that perhaps it would break down at higer revs.. or the coils maybe?

[nudemetalz]

Awww sheeez, not you too with RF400 problems !!!!

Hmmm,...beginning to wonder about these machines. Ours goes into the shop this week.

[riffer]

Ah shit. I've got the opposite problem with my RF900.

Runs on three at anything less than half throttle. Then takes off like a raped ape. And it's not the first time. I've already replaced the jet needles so it must be something else.

Lets face it guys, the Mikuni carbs on these bikes are a liability. I'm not too sure how much different 400s carbs are to 900s, so I'll give advice based on the 900 (so I could be completely wrong here).

First point of call could be to drain the carb bowls. Then pull the bottoms off and unscrew the main jet. Blow some compressed air through the sucker. Check the jet needles - there could be excessive wear there. In fact clean out all the jets you can get at and unscrew. And change the spark plugs while you're at it.


Then reassemble and test ride the bike. If its still not pulling it wasn't blocked main jets.

Then start looking at the coils. A good way to isolate coil problems (thanks Frosty for this tip) is to swap around the coils. If No 1 cylinder ain't working right (you can tell - after a short ride at reasonable revs the header will be colder) swap the coils around so that the other coil provides spark to the no 1 plug and try again. Problem persists - it ain't the coil.

After that it could be worth looking at blockage in the fuel hose, or the fuel pump itself.

Very unlikely to be the CDI. They either go or they don't.

[Pwalo]

For what it's worth it sounds as if it's a carb related rather than an electrical problem.

Is the problem directly related to revs, or to your throttle position (ie half open, just off open). This might give an indication of which jets are causing trouble.

Good luck.

[cowpoos]

sounds to me like an electrical problem...get her running and get the multi meter out and hav a play...

[ManDownUnder]

My RF fouls plugs if I'm not careful (see Riffer's comments about the carbs) which makes it miss on one cylinder except under full power... after it's warmed up... and has done a few miles... then it cleans itself out and away she goes.

Re the 400 not passing 5k rpm... probably what Jim2 said. When the system gets stressed (i.e. high load) anything electrical can/will start to fail till the load goes off again.

[bumsex]

sounds electrical to me....
do not discount the cdi as the cause. It is not true that they either go or they don't: does the bike backfitre and slputter when you try to rev it past 5000?

I would fist of all check timing with a timing light. Chech that the woodruff key has not been shawn and check for advance and retard.

[Dark Crystal]

Yay i fixed the little f*&ker... i mean the sweet beautifull thing..

I rang a Honda dealer in East Tamaki (he was closer to me that in town).. he asked what sort of bike... and what fuel i'm running... i said 96. That's ya problem he says... he reckons 96 is thicker than 91. So i emptied the tank and filled her with 91, drained all the fuel lines too. Before i started her up, i pulled the carby's off and cleaned the bowls and all jets.. although there didn't seem to be any obvious clogging at all, just a smidgen of dirt by the drain screw. Put her all back together, and she purrs like a kitten... like when you pour water on a kitten... ha ha!

I have another post in here too, so i'll copy and paste this post on that one too...

Cheers for all the help people!!

Matt

[nudemetalz]

91 huh ???

Hmmm,...might try that myself.....

[riffer]

Interesting point you make - I've recently started running the bike on 96 full time as it seemed to run smoother.

How did you clean out the carbs?

[avgas]

I've drank 91, 96 and diesel (dont ask you know how)
96 didnt seem any thicker. Sounds to me that changing the fuel was a bandaid and the solution was to clean out the lines and the carb

[Dark Crystal]

I cleaned the carbs by removing them as a set of four, removing the bowls, removing all the main jet and the 'other' jet, cleaned each with a pin (carefully!!), then cleaned the bowl out with a petrol and a rag.. did that for each one, also pulled to top caps of each carb, f knows why, there aint' much under their, but all the diaphrams were sweet.

My bike did run smoother and quicker on 96, i have been running 96 for about 3 months without probs till now... now that iv'e sorted the prob, i might actually fill her up with 96 again after this tank to see if i can replicate the problem... but that could take months!!!

[tommorth]

i have a gsxr400 that did exactly the same thing turned out the battery was to flat charged it for a few days and fixed