The only thing I can think of that could have changed is if the bike was originally jetted to allow for the missing air box parts and now you have gone back to standard you will most definitely be running very lean
As once said we chose to build a hybrid not because it is easy. But because it is hard👍
I have just been reading that the bike runs on Premium fuel. If I recall, this is 98RON petrol as where normal fuel is 95RON. If I have 95 fuel in it will this cause the problems I am experiencing or is it insignificant? i.e poor mid range power.
Having had an enjoyable week of completely rebuilding the engine mainly to change the crank seals, today I finally fired her up. Added to this I have ultrasonically cleaned the carbs, cleaned and checked the piston and rings (all good) and renewed all seals and gaskets. Thanks to dusty’s expert advise on here it was quite easy. So now she ticks over nice, revs a little easier and still flys at 6000rpm. Disappointing I still struggle around 4000rpm with stuttering and a lack of power. I have put new jets, seals, etc. In the carbs, balanced them, recleaned behind the brass ball and tried adjusting the needle up and down. I am running standard exhausts with 22.5 and 220 jets. The carbs are just stamped with 4LO and it’s an early 1980 bike. Saying that it’s not matching frame and engine so I don’t know how old the engine is although it has 4LO in the cylinder casting??? I don’t have and leak testing kit so I can’t verify how tight the engine is. Timing is spot on. On the plus side the exhausts seem to be running a little cooler and there doesn’t seem to be any backfire. Am I missing something? I still feel it’s a carb issue. Any advise welcome.
Apologies if this has already been covered but are your carbs stamped 4L0 00 or 4L0 01?
An update. Firstly the carbs are 4LO 00 on a 1980 bike and the jets are all back to standard. I still have no upper air box nor snorkel but I have now fitted new Allspeeds. After a lot of 'fine' tuning, she's now running much better. The needles seemed to make the most difference but it is now set with the circlip in the lowest grove. Tick-over is perfect. Mixture screw is wound-out by 1 1/2. Low rev's performance is greatly improved but still feels a little flat. High rev's is great. Just wondering if I should change the needle jet so that I can mid-point set the needle and thus giving me a little more adjustment to play with?
I am no mechanic, but having read your post, i really really think you should get an air filter, air box lid and snorkel before you do anything else. The bike will be running way too lean if you are using standard jetting and it will seize eventually. The bike is designed to use that jetting with a complete air box, not having/removing the air box/filter will have a massive effect on how the bike performs, but you must jet accordingly.
You say the bike goes well at high revs which it will but it will be brief! There is no point adjusting/tweaking other things until you have a complete airbox, unless you really understand the jetting side of things.
Also i once spoke to Stan Stephens and he said you really need the carbs marked '4LO 01' the others never worked properly and are early versions.
Hope you don't mind these comments, I don't mean to cause offence, just trying to help you having to sort more problems
I totally agree with mouse. Sourcing the air filter and airbox lid at the very least should be a priority. I have never had the snorkel so can't comment on this but can say I didn't have a problem without it until I fitted standard barrels. But you will definitely struggle to get bike running well all round with this set up.