Carb advice

[icarus001]

For some reason I can't create a thread in 'Technical'.

I had the idea that possibly my bike was running too rich, it seems to fuel ok but if I'm in 5th or 6th at 6,000 revs and I open the throttle wide it just bogs down, plus if I'm flat out and roll the throttle off a bit then it picks up just that little bit. Sounds from what I've read like its slightly too rich.

So just to have a play I raised the needle clip up one place on both needles to drop them down further and gave it a try to see if leaning it out would help.
It was awful, almost stalled whenever I tried to pull off, and was like a kangaroo at 6,000 revs, the transition over the last 1/3rd of the throttle was crap, the bike was stuttering and didn't want to play.

I have the old type carbs 4LO-00, with 150 main jets in, but the new type 5K1 needles.
Its got K&N's and Micron exhausts.

Perhaps I should just leave well alone, its not bad at all, it just seems to bog down a bit with a handful of throttle and it may be rose tinted specs but I'm sure I remember my old LC as bring crisper and with more torque.
It makes reasonable power across the rev range and from 7,000 revs kicks in quite nicely and although the power seems to be all done before 10,000 revs it will happily rev on to 11,000 without any apparant drop in power.

One thing I noticed is when its quite cold it does a similar thing to when I just adjusted the needle.
So perhaps its actually running too lean on the needle? My thinking being that when its cold there is more (denser) air going into the mix and perhaps not quite enough fuel.

I should do plug chops really, just haven't got around to it yet.
The plugs look reasonably ok, dark brown colour.

[muttsnuts]

I would tyry 170 mains, with the clip in the mid position, I'd also check the needles, I can't remember exactly without checking my notes but I think the needles you are using are wrong for tha carb, they are right for the 4L0-01 carbs, but will need to check what it should be, it could be right, but 150 mains is too small, especially with the K&N's on

I am assuming its a 350 and nort a 250 mind!, has anything been done to the engine also ?

[paulo]

31K needles are for the LC2 carb, so as muttsnuts has said - wrong needle for carbs. From experience I would completely strip, clean and inspect carbs - even send them off to be cleaned. Then a new set of needles & needle jets from Allensperformance, best £45 you can spend to rule these out. Mains two up for microns, not sure what up jet for pod filters. To help with the Micron flat spot, you can try one of the following or all of them, 6mm reed cage spacers, fibre race reeds or upgraded ignition coil. I know microns are a top end pipe, so you need to keep it bubbling along above 6,000rpm in 3rd & 4th then nail it in each gear up to 6th. I've now fitted F2 pipes which are a more usable pipes, rolls on from 4,000 in 6th with no flat spot - microns now hanging up in the loft !.

[icarus001]

Jun 29, 2013 17:49:18 GMT 1 muttsnuts said:

I would tyry 170 mains, with the clip in the mid position, I'd also check the needles, I can't remember exactly without checking my notes but I think the needles you are using are wrong for tha carb, they are right for the 4L0-01 carbs, but will need to check what it should be, it could be right, but 150 mains is too small, especially with the K&N's on

I am assuming its a 350 and nort a 250 mind!, has anything been done to the engine also ?

I think the engine is standard.

I'm convinced its too rich at the top end, if I open the throttle to the stop anywhere under 9,000 revs then it just bogs down.
I put the needle back on the middle position and it feels miles better compared to how it was earlier.

And you're right, its the wrong needles for the 4LO-00 carbs.

The bike came from Germany and the bloke apparantly knew what he was doing, it handles like a dream and appears very well set up with aftermarket suspension, so I have to assume there is some reason its a 1982 engine with those carbs and those needles. It doesn't appear to be a cobbled together bitsa.
He must have put them in there for a reason.

[icarus001]

Jun 29, 2013 19:18:06 GMT 1 paulo said:

31K needles are for the LC2 carb, so as muttsnuts has said - wrong needle for carbs. From experience I would completely strip, clean and inspect carbs - even send them off to be cleaned. Then a new set of needles & needle jets from Allensperformance, best £45 you can spend to rule these out. Mains two up for microns, not sure what up jet for pod filters. To help with the Micron flat spot, you can try one of the following or all of them, 6mm reed cage spacers, fibre race reeds or upgraded ignition coil. I know microns are a top end pipe, so you need to keep it bubbling along above 6,000rpm in 3rd & 4th then nail it in each gear up to 6th. I've now fitted F2 pipes which are a more usable pipes, rolls on from 4,000 in 6th with no flat spot - microns now hanging up in the loft !.

The needles are 4LO needles, but out of the later 4L0-01 carb.

I've just been out on it after putting the needles back to how they were.
In the first 4 gears it will pull very cleanly from 3,500 revs all the way to 11,000 revs, no stutter. I have an NK boost bottle on that smoothed everything out, when I first put it on it felt like I'd switched to a YPVS, lol.

The problem is it doesn't like full throttle, if its over 9,000 revs then it will take it but prefers 3/4 throttle.
If I open the throttle full even at 7,000 revs it just bogs down.
If I let the revs build on a gradual throttle its nice and smooth, or drop down right into the powerband and give it a handful then its ok.

It reminds me of my old TZ250 race bike, very sensitive on the throttle and a handful of throttle in the wrong place would mean someone would get past me as it bogged down.

[dex46]

I would chuck a standard air box on it if you have one and set carb's up as standard but go two sizes up on the main's for the micron's ive never been a lover of the pod filter's I remember year's back when Leon moss was alive (Ledar) took my Lc to him to set up 31k motor in a 4l0 ss stage 3 tune and micron's he couldn't get it right until we put the standard air box on