Carb problems

[Worty]

So, took a deep breath and entered the world of pain that is British Motorcycle Maintenance to address the top end fade.   Whipped off carby and raised the needle one notch.  There are five notches on the needle and I've put it on number four (from three for those of you without a maths degree).   Everything inside looks clean and shiny.  The number stamped on the top of the thing I took out from the bottom of the carb read 106 and the jet at the bottom was 260 (I'll check that as it's written down in the garage).

After putting it all back together, I thought I check the tappets whilst the tank was off - OH MY GOD!   All but one had closed up to almost nothing, one of the inlets was at .0015 from .010 (I think that's right), the other inlet was a bit bigger and one of the exhausts was at half what it should have been .008 instead of .016.  Maybe this is the cause of my weird engine sounds and poor top end?????

Anyway, will see how things fair now that I've raised the needle.  By the way, is there a way of getting to the needle without removing the carby?  Can't seem to remove the slide 'cause the frame gets in the way.

[Worty]

Ok, took her for a run with the tappets adjusted and needle raised one notch - no difference   Runs well at speeds up to about 60-ish, good acceleration through the gears, but no throttle response above 60-ish.  Engine fades and starts to make some odd noises (no power and 'clinking/tinking' noises).  Once not under load (level or downhill, or even slight inclines), seems happy again.  That jet has 290 stamped on it for those in the know.  Even ran with brand new plugs (B6HS) which I've always used without problems.

Plug chop on the new plugs showed tan on the curved electrode, but sooty around the bottom electrode and around the base of the plug.  This suggests to me that it's a bit rich, but perhaps not unduly so.

Struggling to think of what to try next.  Do I leave the needle where it is?  Is 290 the correct jet??  Timing seems fine up to that 60mph mark??  Tappets are good.  Oil returns. Oh, and I do still have the ball bearing in the scavenge pipe.  Bits of hylomar on the gauze, but no metal.  I'm at a bit of a loss guys.

[Worty]

Hmm, not sure whether it's either.  Don't think it's pre-ignition, if it was, surely that' occur a lower speeds too.  Could be pinking, but the timing was set up pretty well (5/16 btdc) and, again, runs well at speeds under 60mph.  It can't be lean mixture as the plugs indicate a bit of a rich mix, and the fuel is super unleaded with a bit of Valvemaster+.

ATD seems to be functioning well and the maggie is fresh from Priory.  I guess I could try retiming to either advance or retard a little, or could try hotter/cooler plugs.  There is a little bit of carbon on the piston crowns, but nothing dramatic.

[Worty]

Isn't 13/32 more advanced than 5/16?  5/16 is about 7.9mm btdc and 13/32 is around 10.3mm?

[Worty]

By the way, bike spits and kicks back at me before starting.  I start without any choke and the airscrew is two full turns out.

[Angus]

Hi Wortluck
I am sure its been asked before or was it on another thread. Does it rev out feely in 2nd and 3rd e.g. do 50 to 60 in third.

[Worty]

It is a 389/47 carb.  Needle is 106, main is 290.  Carb was brand new and bought/fitted by someone else.  Needle is now position 4, but makes no difference.  I'm assuming the rest is standard.  Tappets are set at .010 inlet and .016 for max power, air screw is currently two turns out, timing is 5/16 based on the super unleaded fuel used and previous pinking issues.  Plug gaps are .018 which I understood was standard for the GF.  I believe it's a stock motor for cams/pistons.

Angus - I reckon it must have been addressed before, but I'm trying everything I can think of based on what's worked before.  Can't get 60 in third, no way, but it does run well up to about 55/60mph.  It's the top end that just won't happen at present.  Plugs are tan on the top electrode, but sooty around the base of the plug.

Maybe SHM is right in saying going back to standard settings.  However, my handbook differs with a few of those.

By the way, why would a standard 389 be fitted with a 290 main.  Needle is 106, which I believe is standard.

[chaterlea25]

Hi Wortluck,
If the bike is kicking back when starting then the either the auto advance is sticking or the ignition is set too far advanced
I came across an A10 that would do a similar stunt at 60 odd MPH, it was a faulty mag slip ring, That's very unlikely as the mag has just been rebuilt by Andrew

The next thing I would try is to run without the silencers (if you can find a place to do that) in case they are restricting flow 

John

[Black Sheep]

I had to up the main jet to a 300 on my alloy head GF as it was running weak at motorway speeds. 2 things to try. Turn off the petrol when running. If it gets better before cutting out, you are too rich. Then try a bit of choke. If it gets better you are too lean. I would have a good check of the ignition timing. It does sound too advanced.

[berger]

worty have you checked to see if the points have closed up?

[Black Sheep]

"He's timing to 5/16"  How could he be too advanced."

It's still exhibiting symptoms which could be explained by over-advanced ignition. Hence my suggestion to check again.