Honda CBR 400 NC29 Float Height

[slyshot]

Hi Everyone

Hope you are all enjoying the sun! weather is amazing at the moment.

Having some top end running problems on the bike, the bottom and mid range on anything up to 3/4 throttle is absolutely fine, once you get over about 9 grand and give it full throttle it feels like a hesitation and wont rev out cleanly.

I have emptied the carbs out and ultrasonically cleaned the 3 jets I can remove from each but still the same. Carbs all balanced as well.

Upon checking the float heights two are at 13.7mm but two seem to be nearer 16mm and the two that are to high have brand new valves in them......when comparing the valves from the correct and incorrect height they look identical in every way, also checked the floats themselves and no deformaties, to confirm I moved the valves and it then moved the float height problem so definitely them, any idea how this might happen? have ordered 4 new ones to see if it improves.

Also the tank is flowing just fine, new fuel filter added, new plugs, clean air filter.

hopefully this will fix the running issues, anyone else had similar problem?

Thanks in advance

Sam

[CB1pod70]

According to Haynes manual, the float heights on a 29 should be 13.7mm and it would appear that you can't adjust the float height so new needle valves as you have ordered is the only real answer.

Incorrect float heights would certainly cause the issues you're describing

[slyshot]

Brilliant thanks for getting back to me, new valves arrived today so i'll get them in on Sunday...hopefully....got to get my stag do out of the way tomorrow first! could be painful!

cheers guys

[slyshot]

Hi Everyone

the bike ran a little better at the top end but still some hesitation, im going to strip the carbs down again and see whats what.

When stripping I remove the main jet,pilot jet and the needle jet. am I able to get the needle seat out and any other parts for a more thorough clean? I assume they need punching out as the others all have flat blade cut or take a 6 mm hex?

Thanks

[CB1pod70]

Personally I just remove the 3 jets and leave the rest in situ as you're likely to cause more damage trying to remove them. If you can get the carbs ultrasonically cleaned, that's really the best otherwise its carb cleaner and compressed air.

[slyshot]

Hi CB1

I split the bank last night so this evening they can all go in my ultrasonic cleaner, so fingers crossed it'll clear them right out.

when splitting the carbs I can see through the fuel passage into the bowls that there is a little filter in the bottom of each carb, this is sitting behind the needle valve seat so im assuming it should be removable, any ideas anyone?

[slyshot]

Hi

So carbs were fully stripped and through the cleaner twice, all jets removed and sonic cleaned, plonked it back together and balanced them.

Took it for a test and is exactly the same......so for now i need to assume its not the carbs which is fine, at least i know.

it feels fine up to about 9 thousand but after feels like its hesitating and anything over half throttle it doesnt feel right plus when it hesitates i can feel a funny vibration from the motor coming and going with the hesitation.

Any ideas? im planning on going through the electrics now, any suggestions on an order as to what might be the biggest culprit?

Thanks again

Sam

[dunkenb]

Have you checked the TPS ?

[slyshot]

Not yet, just going to start working through the various sections today, how would i test the TPS?

Thanks again

[slyshot]

So checked the TPS as per the haynes manual, the wiring itself between the connector and the ignition unit it passes.

It then says to check the TPS itself by setting a multi meter to ohms and checking between each pair of connectors the resistance should increase as you open the throttle, with the 3 pins i make it 3 pairings to check, the first pair goes as stated the resistance increases, however, the next pairing the resistance just stays the same and the thirs pairing the resistance decreases as i open the throttle.

That doesn't tie in with what the haynes manual has down, has anyone else had an increase in resistance when testing all 3 pairings?

Thanks

Sam