RVF 400 Low RPM issue

[peter62]

Hi guys, Im have a nightmare of a time with my twin brothers RVF 400 that weve recently picked up

The original issue was the fact it wouldnt start everytime when you wanted it to that was down to pilots aka slow jets being blocked so ive cleared them however after puttin it back together it ran rought at 5k then i checked mixture screws and set them (only very slight difference) also checked float heights and they seem almost bang on maybe 0.5mm out, then it started running rought at about 3k and tries to stall upon slippin the clutch slightly, so ive had the plugs out cleaned and gap checked colour was rather dark but that maybe cause by a misfire i have just put new plugs in and still no joy.

I have checked all multiblock connectors and put a little WD40 there incase also checked primary and secondary coils resistance all seemed fine, checked pickup resistance but it would only flash up for a split second the reading i got was within spec to haynes.

I have new air filter to put in and standard exhuast but the exhaust didnt make a difference previously, Running ou of ideas now only other thing i would check is carb balance and needle heights or to do a plug chop

All and any help or suggestions would be greatly appreciated, Ive also heard the VFR 750 have had similair problems

Thanks for reading, Peter

[mo haggs]

Sounds like the speed restrictor is disconnected. Check that all the wires are connected at the back of the speedo.
If the cdi does not recieve a signal from the restrictor it will run in the "limp home" mode - running on front 2 cylinders and only up to 5k rpm. The offending wire is blue and orange. Check both ends of the loom to see if it has been alterd or broken.

[peter62]

No it will rev past 5k all the way to limiter if i wanted, it feels like its missing but only for a around half a second whn setting off or below 3k

I forgot to mention i have isolated front and rear cyclinders, Rear 2 seem to rev ok abit of a splutter at 3k but the front cyclinders dont was to rev past 1,200Rpm, Im left completely in the dark with this one its driving me insane.

Thanks ever soo much mo haggs for you reply but im fairly certain thats not the issue thanks again

[Neosophist]

Hi guys, Im have a nightmare of a time with my twin brothers RVF 400 that weve recently picked up

The original issue was the fact it wouldnt start everytime when you wanted it to that was down to pilots aka slow jets being blocked so ive cleared them however after puttin it back together it ran rought at 5k then i checked mixture screws and set them (only very slight difference) also checked float heights and they seem almost bang on maybe 0.5mm out, then it started running rought at about 3k and tries to stall upon slippin the clutch slightly, so ive had the plugs out cleaned and gap checked colour was rather dark but that maybe cause by a misfire i have just put new plugs in and still no joy.

I have checked all multiblock connectors and put a little WD40 there incase also checked primary and secondary coils resistance all seemed fine, checked pickup resistance but it would only flash up for a split second the reading i got was within spec to haynes.

I have new air filter to put in and standard exhuast but the exhaust didnt make a difference previously, Running ou of ideas now only other thing i would check is carb balance and needle heights or to do a plug chop

All and any help or suggestions would be greatly appreciated, Ive also heard the VFR 750 have had similair problems

Thanks for reading, Peter

Most likely a carb issue.. have you blasted some high pressure air through the slow running circuit (the three small holes that come out by the butterflys?)

If the slow circuit is gummed up it can be a pain to get running clean again. What are your float heights and air-screws at?

Is the airbox standard.

[peter62]

well ive replaced plugs anyway ill keep the old set as spares, No i dont have an air line but i do at work so maybe i should take them in a give them a blast as for float heights they are pretty much to spec give or take 0.5mm, mixture screws are set but i marked the old setting out and ive set them to spec of manual but its slightly richer only by 1/8 of a turn, that could also cause my low rpm issue...correct? I might do a plug chop to check this theory.
Airbox is standard but its got an aftermarket filter in ive just recieve my genuine one so need to put that in at some stage doubt it would fix the issue.

[peter62]

Anyone know where i could send the carb off to for ultrasonic cleaning? maybe that is the answer?

[duanebray_08]

My next door neighbour might do it. He aquired a ultrasonic cleaner 2 weeks ago and used to run a dyno workshop so would be able to see if anything is wrong as opposed to an untrained eye.

[CMSMJ1]

http://www.mailorderrepairs.co.uk/

This lad does carb cleaning as a business. Is well recommended on the PB mag forum.

[peter62]

Thanks for the reply duanebray_08 ive sent pm :), Ive mailed them on the link you gave me CMSMJ1 just waiting for a reply thanks, ill be abit upset if i get them ultra cleaned and its some thing else or something else goes on it

[skinnydog0_0]

Whats the battery and reg/rec like? what voltage are you getting from the battery and whats it like with the engine running?