gt500 Hanging idle problem

[uzidzit]

I have a Idle problem with my 76 gt500, when the engine heats up the idle hangs at about 3k and is slow to come down. so far here is the list of stuff done it is improving, at first it would run away when hot and even try to diesel when the ignition was killed(definatly lean/sucking air).
carbs spotless, and very low milage (look like new inside)
new outer crank seals (now passes pressure test cold)
new intake boots (and airbox rubber for that matter)
timing spot on with a light at 3k
petcock working properly (and makes no diff running with plugged vac line on prime)
jetting is stock (1000ft above sea level)
air cleaner rebuilt with uni foam and oiled correctly
new ngk b7hs plugs
cleaned and lubed cables (slides do not appear to be sticking)
set oil pump (was set to move a ton of oil)
gas tank vent ok(runs same open as shut)
no tranny oil burning
exhaust system clean
exhaust seals a bit tired and leaking.
some two stroke oil on top of the engine after running or sitting a while(like a week or so) (banjos tight, no bubbles in the oil lines, smokes very little while running)
starts first kick on the choke and sets at about 2500 high idle, it will idle off choke in about 45seconds
float level set at 25.7mm as per oz tune up data not 27.3mm as haynes and factory man listed. (it still has all oem parts in the carbs that look and work like new)
air screws about 1 1/4 out
new head, intake, and head gaskets
compression 126lbs left, 124lbsright

As I said it is improving it does not run away anymore but the idle will still hang high, and the surge at closing the throttle is pretty bad, it will stumbles off idle pretty bad. I have a hard time believing I need new pilots as at 1 turn out the exhaust will water your eyes it is so rich (and at 1 3/4 it will starve). however they me need to be upped, by the point you hit 3500-redline it runs like a scalded dog (really strong runner, I have a few others).

Any body got a clue? I am almost at the point of a complete crank rebuild out of desp. I am going to clean carbs again just to make myself feel better but not holding out much hope.


ps when I get a chance I'll post my $7.00 rectifier replacement.

[rbond]

I think I got my rectifier cheaper at Radio Shack.... anyway everything sounds good for what you have done. Only thing I can think of at the moment is to check the mainjet needle. It maybe too high in the clip. Check a manual, but I think it is supposed to be in the middle position. Out of curiosity, when you timed the ignition, where did the stator mark fall after adjustment? Mine was about a 1/4 of an inch to the left of case mark.

[uzidzit]

with the marks lined up according to the factory manual, the timing light was showing the center mark about 3/16" advanced (to the left of the mark on the case at 3k rpm). when I changed the seals I set the timing plate to just beyond the mark on the case. now at about 3k the center mark on the rotor is aligned with the case mark. The $ figure for the rectifier included 2 heatsinks, and the shrink tubing, the 25 amp bridge rectifier was about $3.49 including tax.

I use the same rectifiers on my xs-650s, you just use 2 mounted to a plate under the battery, 1 input is unused but no harm no foul there. These things seem to be the berries for vintage charging systems, they seem to be fine for any charging system under ~300watts with a little air and a simple small heat sink

Ps I am going to lower the clip a notch, I have some needle shims if that seems a bit much

Just looking for anything I may have not thought about, sorry the post was long but I wanted to cover what I had done to save everybody time

[rbond]

Good price on the bridge rectifier, but what other rectifiers are you mounting on heatsinks? It sounds like you mean zener diodes to control the charging voltage. I only replaced the bridge and am using a V/R from Electrex in England. It is slightly overcharging, I did find a 'homebuilt' V/R circuit on the net. I built one, but have not had the chance to try it. If you have not seen it, I have a 'sticky' on this board for a homebuilt CDI for the GT500's. Never heard of needle shims either. I have only seen the 'e' clip to move them up or down on the slide, anyway keep us posted.

[uzidzit]

The needle shims are .5mm washers that go under the clip (1/2 a step clip positions are1mm)

The bridge rectifiers are just for making dc, I usually use zeners in a seprate package for the voltage regulator, That allows me to keep stock stuff to plug and play just in case I show the bike (well I never show the bikes but it makes me feel better that I can return them to stock)

[tz375]

It looks like you have approached it in a logical manner.

Do the throttle cables have enough slack in them? both slides should click down closed and there should be a small amount of freeplay at the throttle.

If that's OK, you could try one size larger on the pilots just to see what difference it makes. If it gets worse, try one size smaller. It's a cheap and easy thing to try.

[uzidzit]

I have left a bit of extra slack, at the moment, and did the finger sync in the intakes, I did dig out pilots today so I am giong to try 32.5 and see what happens, also moving the clip down a slot. I have had smallish pilots not work well even on a dyno tuned bike the afr was good on, it would stumble a bit, the larger pilots with the same afr after the mix screws were set a wee bit different did the trick.

[uzidzit]

I moved needle clip down 1 slot, and went up 1 pilot size to32.5, and it seems to have improved some. I will need to take it for a longer ride this weekend to report back. starts easy but seems to come off the choke early(not a good sign)

[uzidzit]

moving the piollts up to 32.5, and moving thr needle clipdown on slot a position, now has the thing running great.