Changed Carb parts now leans out 1/8th throttle

[jedidude04]

Hey guys, i got my rvf400 serviced and setup and after that i fitted 112 main jets, 1mm needle washers and hrc replica carb springs. The bike is fine from 1/4 throttle all the way to wot - no flat spots from 3k up. However i have now ran into the problem where if i crack the throttle 1/8th open then it sounds like the bike leans out, it has no power and it stalls from a stop without giving it a fair few rpm. You can hear the motor move past 1/8 throttle to 1/4 - 1/2.

Just wondering if anyone has encountered this problem? My idle screws were set at 2 turns out. I noticed with the choke i need to help on to for a while otherwise the rpm will dip below 1000rpm.

Also the idle is irregular, dips and rises which i assume means your need a carb balance?

[magg]

If you think it is lean, then way not turn the idle mixture screws out a turn and see what happens.

[jedidude04]

Ok, i reset the idle mixture screws to 1 5/8 out and bench synced the carb. Was still running into the issue so i did another small turn out each screw. This improved it slightly however the bike is bogging hard and im needing to slip the clutch alot to get moving. I'm going to have a look at the float levels next and see if anything is amiss

[Neosophist]

turning the mixture screw out on the rvf leans the carbs out.

check obvious stuff first like you dont have airleak on carb rubbers

[magg]

As both the NC30 and NC35 mixture screws are fine needle types located after the throttle valves, why would the adjustment actions be opposite.

The fine needle type usually reduce the air/fuel mixture volume as the needle is screwed in, making the mixture leaner.

Whereas the course needle type are usually located before the throttle valve, in the air passage to the idle circuit and reduce the air volume when screwed in thereby making the mixture richer.

Interested to know what changes exist between NC30 and NC35 carburetors would account for this claimed reversal of function.

[jedidude04]

From what i know the mixture screws were changed between the nc30 and nc35. Fuel and air screws? as you said. Haynes manual specifies 1 and 5/8th's out for the nc35.

Anyways, i had some time off so i stripped the bike again, carburettor out. I replaced the float valves, the seals were alright but the needle was pretty knackered and not sitting on the tab right. Reset the heights to 12.5mm - they were mostly correct, probably 2 set at 10 or 11mm, 1 around 13-14mm and the other one was pretty much right.

I then turned my attention to the carb boots as my clamps had come down slightly. I discovered at least 3 torn carb boots and the fourth i haven't checked yet..so that might explain my funny running symptoms, hunting idle and no power/leaning out just off idle.

I'm going to replace the carb boots with some oem ones, from what i can see they are 45mm outer diameter. I would like to replace the clamps just wondering if slightly bigger then 45mm will be fine? Reason being is that the stock clamps are 50mm and weren't completely sealing on the boots.

[magg]

From the pictures I have seen of NC30 and NC35 idle mixture screws, they are both of the fine needle type and thus should function by reducing the amount of mixture as they are screwed in. Eventually someone will clarify the situation.

[st22041967]

What Magg said, In lean out rich

[jedidude04]

Good news guys, got my carb boots today. Spent the afternoon fitting them with some new clamps, spent about 40 minutes trying to wrestle the carburettor into the new boots with some wd40 and hooked it all up. Started up alright, warmed up quicker and i could turn the choke fully off 40 sec - 1 minute.

Hooked up my carbtune to the bike (you don't need to remove the tank to do it) and got started on that. Cylinders 2 and 4 were almost spot on/equal. Cylinder 1 to 3 was horrible, cylinder 1 was showing 1hg on the scale where cylinder 3 was showing 20hg..that's from me trying to bench sync it lol.

Synced the carbs to roughly 1hg of eachother - not going to get closer at this stage i think and i had to turn the bike off 3 times to let it cool down :p (pretty sure i pissed the neighbours off - oh well).

Bike runs so much smoother, revs clean and idles nice with no hunting. However from me resetting the float heights there's a tiny bit of a flat spot in the midrange and as it transitions to mains it pulls hard. I haven't touched the idle jets because frankly i wanted to call it a day and not mess up something that's working well.