TOPIC:

Hello from Sunny Sussex in the united kingdom !

I know what nightmares the carbs & their settings can be & although my bike is up & running, I still have a problem.
Bike is a 78B2A (with vm24's fitted, as I took advice from here & jettisoned the 22's!!!
I've done a top end rebuild as had a hairline crack on the cylinder head which was leaking oil from the oil supply to the cams etc.
I've checked the timing & done the valve clearances (great fun those shim things) took the carbs 100% to bits, ultrasonic cleaned them, rebuilt , synced them, colourtuned the pilots (bloody brilliant tool)
Fitted & checked the carb inlet rubbers (ok no leaks) new denso 24 plugs, std air filter & a Jardine 4 into 1 exhaust ( loud but nice)
My problem is my mid range is very poor, especially when the bike gets warm.
She runs great on low throttle openings & accelerates fine on pilots, but when I open up to above 1/4 throttle , it's not so good. Once I'm above 3/4 she kicks in great & I've been up to 105 mph with a lovely exhaust noise for those behind me !
Spark plugs don't look bad to me (see photo)
Tried choke on when accelerating, but doesn't seem to make any difference.
Standard pilots, needle in no 4 & 102.5 main jets fitted. Done the float wet levels check & they're perfect. Last thing, compression test readings are brilliant, as per the manual top readings.
Thanks in advance.
By the way, my bike is an import from America so thanks to your nice weather, it's still in pretty great condition.

Could be that the mid-range is lean, and the needles need to be raised a bit.

Here is a pretty good explanation of getting the carbs just right.

www.factorypro.com/tech/tech_tuning_proc...igh_rpm_engines.html

Mid range points to main jets range as you know. With a fairly restrictive exhaust like a Jardine 4 into 1 (with baffle) the two things I would try. Firstly try it without the baffle and see if theres any improvement. If there is I would replace the baffle then increase the mains to 107.5 to richen mid range.
You can get genuine mikuni jets from allens performance.
www.allensperformance.co.uk/shop

Thanks Texas & Warren. You are both like encyclopedia Britannica !
Firstly, I don't think there's much baffleing left in my exhaust & can't see any way of removing it ! (one screw that probably won't budge) it's pretty noisy .
Secondly I don't really want to strip the carbs down again so I will first try it with no air filter. If it runs worse, I'll go up on the main jets.
Does that seem ok ?
I know they all merge together (all these needles & jets) but they certainly do my head in !

removing the filter will certainly weaken it throughout the entire range so may give you bit of indication to the issue.
If its ridable and you can get it to my place by Brands Hatch we can spend a day going over it if you fancy

Search changing main jets without pulling carbs....... some have done it with stubby's and or allens but to me it might be easier to just pull the carbs. 105s or 107.5 mains sound like a good thing to try to me too.

Go with 17.5 pilot jets, 105 mains with the needles on the MIDDLE slot.

As usual, cheers for the replies.
Right then, yesterday I ordered a set of 107.5 jets, then I found a set of 105's in a box in the garage. I also removed one float bowl to have a look inside & all was nice & clean.
Today if I get some time I'll give it a test without the air filter.
Will drop all the bowls at once & try the 105'sthen as my 107's won't be arriving till Friday.
I love the smell of petrol but my wife hates it ! Better not smoke when I'm fiddling with the stuff.

What a pain to remove the floatbowls in situ. 13 of the screws were ok but the other 3 were a real nightmare, not done up super tight but just getting access.
Anyway fitted the 107.5 jets as they arrived .
I'm not doing anything now until I've bought 16 Allen bolts as I'm not attempting to use the screws again.

Be careful when tightening allen bolts into the carb bodies, those threads are easily stripped with the extra torque you can get with an allen key.

Got my 16 Allen bolts & spring washers yesterday. Fitted the bowls back today.
What an evil way to spend an hour. Then I had to reconnect the pumper spindle which was even worse.
I'll never attempt this again. The carbs will come out next time.
No time to do a test run today but my wife is doing a 32 mile run tomorrow, so I'm off out in the morning with fingers crossed.

Went out for a test ride and now great up to just over 1/2 throttle but over that seems to be running rich & runs better when I throttle back from fully open. Should I fit the 105’s or lower the needles ?