Left hand carb running lean

[harrington]

Hi, I’m a new member with a carb(?) problem. I have bought a 1983 German import lc350. The left hand cylinder is running much leaner than the right hand one. I’ve cleaned carbs, fitted new carb kits from Yambits and when ticking over and revving in the garage, the right side seems to be firing correctly, but the left side is running much too lean. It’s got micron exhausts and I’ve retained the 240 jet in the carbs and set the needle on 4th groove from the top. Pilot jets were replaced with new ones supplied in the kit. I also fitted new needles. The air screws are both at 1 and a half turns. I’m running stock new standard air filter. Both carbs are synchronised at tickover and open fully equally when throttle is fully open. The left exhaust doesn’t get as hot as the right exhaust and doesn’t sound as “crisp” when revved as right hand side. The float bowls are on the correct sides, and set to 21mm. Is there a difference in the actual floats I should check? Tomorrow I’m going to check compression, but after that, I’m at my wits end with sorting it out.. 
Anybody got any ideas as to what I’m missing? 

[shaunthe2nd]

Hi and welcome.

It could be a few things I think.

What are the refs stamped on the sides of carbs?
The Stock settings for 4L0 01 carbs with std exhausts are:

Emulsion tubes type 345-P-2
Standard needles type 5K1. Fitted 3rd clip down.
Main jets 220
Pilot jets 22.5
Air screw set 1.5 turn out
Float valves set to 21mm

I think a lot of people go up to 240 mains with Microns, but hopefully someone will confirm.
The Yambits carb kits can be suspect, so if you can get hold of gen Yam/Mikuni carb internals that's a better starting point.

A classic problem with old carbs and new fuels is dirt and crap in the air correction circuits. Have you done the 'balls out' carb clean? It's an easy job and helps with running.
Another is getting the float bowls wrong way round, the choke one has the little hole, but you indicate you have checked that.

Another quick check I've done in the past is to switch plug caps L-H to see if problem goes with it. If remains as before, its not electrical.
You can also switch the carbs L-R and use a long choke connector pipe to see if switches, if so its the carbs.

Good luck with it, will be something simple.

[muttsnuts]

hopefully you have kept all of the original internals as the yambits kits aren't good, one thing that is very wrong in the kits is the air screw, I've had 200 made that are an exact copy of the original Yamaha one, there where 2 types of air screws, the yambits kits contain the wrong one, only the very early carbs had the early style air screw in

Even if you turn the air screw fully in it will still be too lean

If you have the original metal air screws then I'd refit those for a starter for 10, seat them as the yambits ones will have screwed the seat up a bit, then turn them out 1 full turn and see what it does then, I'd also chnage the needles back to the 5K1's as again the needles are the wrong ones

I am assuming the carbs are 4L0-01's if not, then the needle advice is mute, but the air screw advice still stands

[alanski169]

have you rebuilt engine? or been rebuilt recent? if no probably the l/h crank seal leaking air so check under the generator cover for moisture around crank end and also check crank for end float or play up and down by pulling on flywheel whilst cover is off

[harrington]

Thanks to both of you for your responses. 
The carbs are 4L2-00, are these 250 carbs? The emulsion tubes have 357-?? on them. I watched a dilly dilly vid and he said 346 tubes were 250 so I presumed as they weren’t that number then they must be right. You were right about the air screws, I kept all the original parts in separate bags and both of the originals are the same but a different profile to the new Yambits ones. And the spring is longer when compressed which would back up what was mentioned. 
so I guess I’m looking for new carbs and starting all over again? 
Any further help ref correct carb, emulsion tube will be gratefully accepted. 

[midlifecrisisrd]

4l2 were restricted 250 carbs

Maybe see what else you can find for sale

Steve

[harrington]

Alanski, no I have recently bought it so no engine work has been done as far as I’m aware. I have checked for air leak on the in
et manifolds , rubbers etc and all seem good and relatively new. I hadn’t considered air entering crank via seal. I shall try carb fixes first and if that doesn’t solve the issues I shall check condition of main seal. 
Thanks for your suggestion. 

[harrington]

Midlife crisis lc, it is a German import 250 with a 350 engine. I knew German imports had restricted exhausts but didn’t realise there was a restricted carb as well. I think I am looking for a new pair of carbs.. 
Would any body on here have a set for sale? 

[shaunthe2nd]

If its been converted, check its been fitted with the 350 oil pump and worm. Otherwise you will get a seizure.

As said above, 4L2-00's are the restricted German 250 carbs. Some claim to have had them converted but as far as I know the air circuit is different size, so very hit and miss.
I would be looking at 4L0-01's if I was you, with genuine internals, see my earlier post re standard settings and needles/emulsions. 4L0-00's are very different.

I would check if you have the correct exhausts too, German restricted ones were 4L2's. UK 250 and 350 were both stamped 4L0 but have different internals, and if you have an unmatched pair it could affect the running. 250's had 6 internal holes from memory, and 350's had 8. Use the search facility to find previous posts on the 250/350 exhaust differences.

[4l04ever]

I think the 4L2 carbs are the same spec as 4L1 carbs apart from coming with 170 main jets instead of 190 for a 250LC.

The non-removable air jet is 1.0mm compared to 0.8mm in a 350 4L0-01 carb.

[alanski169]

I have been restoring/rebuilding/selling these since they were new and importing lots from Germany past 5 years and all have needed engine rebuilds mostly cranks despite running and I always budget for full engine rebuild when costing due to this. always check carb id and exhausts as 3 different types on all models easy to tell from flange thickness on header and 350 has 0 stamped on the rear of footrest mounting bracket on silencer check the exhaust thread on here if in doubt and check its a 350 oil pump as stated above. They are 40 + years old and most have been fiddled with to various degrees mix matched bits etc. The left crank seal fails first as dries out if stood the right has gearbox oil on one side so usually lasts longer, if carbs are clean and inlet rubbers good as you say despite being wrong both cylinders should run at same temp unless you have air leak or poor compression/worn cylinders which you can't hear unless realy bad on lc due to the water jacket masking noises.