Pilot jets for std carby set

[OzzieDave]

I have recently done some maintenance on the old trex, shimmed the valves and replaced the carby internals with a ky0570
repair kit.
It idles well, the carbys have been synchronised, testing in the shed was fine, revs rise quickly and drop down quickly as well. On the road it bogged down at low throttle openings. I had set the pilot screws at 2 turns out, then tried 2.5, then 3 turns out. It only has a slight hesitation now at around 2 - 2.5k revs.
Everything I have read suggests the pilot jet needs to be replaced with possibly the next size larger, if I do that, how many turns out does the pilot screw need to start at.
Where would be the best place to buy these from (I am in Australia).
The air filter and air box are std, the mufflers are Staintune slipons, std NGK plugs, Ignitech ignition using std map with TPS set. Km about 101000, compression lh cyl 125 psi, rh cyl 175 psi.
Prior to the kit being installed the needle in the slide was set at the top notch, when I installed the kit I set it at the middle notch, as the plugs looked, to be a little on the lean side.

[OzzieDave]

Bought some .475 pilot jets from Show and Go motorcycles, $14 ea, they reduced the problem, started at two turns out, ended up at 3 turns out, still with the problem.
Bought some micro drills from Jaycar for about $12, used the .50 drill to open up the std jets.
Have set the pilot screw to 1.5 turns out, all traces of the hesitation have now gone at low revs in second and third gear.
There is still a slight problem under load in 4th at about 60kmh if going up a hill, will try 1.75 turns next.

[OzzieDave]

The lh spark plug gave out the other day, it would seem the problem may have been the plug all along, it just wasn't working to spec for some time, reterminated the plug leads at the cap as well.
I bought it new late last year and it has barely done 2000km.
Have now reverted to the std pilot jets, as the .475 were too large, after replacing the plug, I could wind the pilot screw in all the way and the bike did not stall.

[cobbadiggabuddyblooo]

Your not the only one I've heard who has fallen into this trap Dave.
I've spoken to 2 others in this last fortnight who has only recently replaced the plugs but found issues they couldn't resolve.
Back in the old days they used to coat the centre electrode insulator with ??? i can't remember...
( I'm sure I saved the link on a great explanation to spark plug manufacturing and I'll try to look for the exact info)
This coating allowed the plug to clean themselves to some degree if the plug got fueled up.

Such is life, plug manufacturers still glaze the ceramic but no longer do this other coating due to the shift in technology and efficiency of fuel injection plus a cost cutting measure.
It doesn't take much with a carburetor motor to deposit a residue of unburnt fuel on the centre electrode insulator and what you find is the spark will always find it's easiest path to earth.
So the spark no longer jumps to the earth strap but instead arcs down the centre electrode insulator and sparks deep inside the plug body cavity and onto the inside edge of the plug body.
So you still may get a spark which may ignite some of your fuel mixture but it's in no way optimum and most cases not strong enough to burn all your fuel mixture.

So many people state the same and I've fallen into the trap before myself...
Yes I just replaced the plugs and yes I have a strong spark when I check the coil with an old plug earthed off on the motor and don't use the plug from the cylinder and are in the belief that the plug screwed into the head will be ok...

[OzzieDave]

If the plug is just dirty, do you know of any way to clean it, I cleaned around the top with a small wire brush in the Dremel,
but this will not reach right down into the plug.
I do have a sandblast gun, not sure if this might be too aggressive even at a low pressure.
I swapped the plugs over to check if one was playing up and cleaned them then and checked the gap.

[HolerTogni]

Hi OzzieDave!

For cleaning spark plugs I use (as ever) a small brass wire brush and a tiny amount of elbow grease ;o)

Simple mechanical but very effective greetings from Munich!

[cobbadiggabuddyblooo]

Throw them in the bin, spend a couple of $$$ and buy new plugs otherwise you'll damage the glazing on the insulator because they no longer have the sacrificial coating from the leaded/carburettor days.
Some suggest soaking for a short time in brake cleaner and a soft brush to remove anything that chooses to come away but the price of a can of brake cleaner will get you 2 new plugs.
91 Ron fuel is a good carbon builder too.
Iridium plugs due to the nature of how they are constructed are another good choice as they promote the chance for a cleaner burn and less chance of fueling up the plug.

[OzzieDave]

I know have the pilot screws adjusted correctly (fingers crossed), the lh is 2.5 turns out, the rh is 2 turns out.
Rebalanced the carbs by ear, all signs of hesitation are now gone, I can ride at a low throttle openings without surging or other problems. The std .45 pilot jets are fine.

[OzzieDave]

I will just put it in the bin.
The bike ran fine for one ride, then started with the surging again, although reduced.
I was fiddling with the pilot srews yesterday, as I was refitting the airbox I decided to check it for air leaks.
Found the connectors which go over the carby inlets were quite loose in the airbox and over the carbys.
I cut two narrow strips of fabric duct tape and applied to the outside of the carby inlets (after cleaning with Simple Green),
this took up most of the gap.
I scraped off a residue of some kind which appears to have been applied to seal the connectors in the airbox, then cleaned with Wax and Grease remover, (my spare airbox had the same residue).
Once the connectors were centred I applied some silicon sealant around the connectors, a couple of hours later I refitted the airbox, the connectors fitted better onto the carbys.
Went for a ride this morning early, due to the forecast temperature, it ran like a dream, I must have been getting an air leak or two, which were upsetting the low throttle performance, as it ran fine from 3,000 rpm before.