Hot Idle

[gwowzer]

So for the life of me, I can't get the idle right when the motor is hot. After a good 25 minute or so-ish ride, if I come to a light or a stop, I have to rev it just a touch for a second to keep it from stalling. It's not a slow stall, just sort of an erratic idle and then dead.
If I am stopped while the engine is hot, it sort of does an erratic idle type deal between 1100 and 1600 rpm (as indicated on gauge) and just doesn't run great or smoothly.
On start up or if the engine isn't hot, I have a nice strong thumping idle at 1500 rpm (as indicated on dash gauge).
If the engine does die out when hot, it restarts immediately when I hit the starter button.
Is this a carb issue? I think it is but I started to get suspicious maybe an electrical component was getting too hot. The bike runs awesome at all speeds and temps, except for a hot Idle.
The bike is 2020 Brozz 250, aftermarket exhaust, Nibbi PE28 carb (I downsized from the PE30 which did the same thing), UNI Pod foam air filter, new battery, new voltage regulator, new CDI, new ignition coil (stock electronics and battery ordered from Peace Sports), carb is jetted at 45 pilot, needle at one up from middle, main at 118. 2 turns out on the fuel screw. I've messed and messed with the fuel and air screws and 2 turns out on the fuel screw and then adjust to 1500 rpm with air screw seems the best.
If the bike cools off for 10-15, it seems to run good at idle again.
Is there a part of the diagnosis I am missing? Like air temperature of the head at a hot Idle?

[DohcBikes]

A 45 pilot is way too fat for any of these bikes.

I had a 233cc modded on street legal 200x 3 wheeler that would smoke the tires through 3 gears and run 80. It would not idle correctly on a 42.

Get a 40.

[Megadan]

Great cold start, erratic hot idle that stalls out is too rich on the idle mixture.

The idle mixture screw on a PE carb is an air screw, not a fuel screw. The more turns out, the leaner it gets.

If it is 2 turns out and bogging at idle still, drop down to a 40 pilot and try again. Repeat as necessary.

I am running a 38 in my pe30 at 2 turns out. While it isn't a direct comparison between our bikes, it should give you an idea

[gwowzer]

That's odd because it seemed to have the best idle with the 45 PJ, I've had it all the way down to a 38 PJ and it still did the same thing.
So on the PE carb, the brass screw is an air screw? What is the red handled knob for then? They are both air screws?
Maybe go with a 35 PJ and only 1 1/2 or 1 turns out on the brass screw?

[gwowzer]

Yes, that should put you in the ball park. The way I do this is to set the needle in the middle groove, and the idle mixture screw at 1 1/2 turns out from lightly seated. Then I change pilot jets until I get a strong 1250 to 1400 rpm idle. By strong I mean that the machine can pull itself along on level ground with no action on the part of the rider in second gear, once you've gotten it moving with clutch and not more than 1/8th throttle. Once you've gotten this far, then crack the throttle to 1/8th again in second gear and you get instantanious acceleration up to where the engine wants more throttle, open it up to 1/4 throttle. You are looking for immediate response. You have now reached the upper limit of pilot jet range. Next, with the engine well warmed up, check main jet performance...ARH

I was going off of this thread. Does he really mean it should pull itself in second gear?

[tknj99]

I also had idling issues with the PE30 initially where it would stall at lights.. i had it fat as well initially up to a 48 pilot / 140 main and the needle at position 2 (one up from middle).. i later backed down to a 40 pilot / 140 main and needle at position 3 (middle) as well as adjusting the A/F screw properly and has since ran with no issues, idles perfect..

[Megadan]

Originally Posted by gwowzer

So on the PE carb, the brass screw is an air screw? What is the red handled knob for then? They are both air screws?

There is only one "air screw" on the entire carb, and that is the idle mixture screw. The red knob is the curb idle adjustment. All that knob does is move the throttle slides idle position to dictate the idle rpm.

[TxTaoRider]

I'd try turning the air screw out 1/4 and see if it gets better. If it gets better, try 1/4. If you get past 2-1/2 turns out, then you might consider a larger pilot.

[Megadan]

Originally Posted by TxTaoRider

I'd try turning the air screw out 1/4 and see if it gets better. If it gets better, try 1/4. If you get past 2-1/2 turns out, then you might consider a larger pilot.

Turning the idle mixture screw out on this carb makes the idle mixture leaner. If you keep turning it out and it runs better, you would want to go with a smaller pilot.

[TxTaoRider]

Originally Posted by Megadan

Turning the idle mixture screw out on this carb makes the idle mixture leaner. If you keep turning it out and it runs better, you would want to go with a smaller pilot.

I'm no expert on PE carbs, but on the pics I found, that screw is on the mouth side of the carb, making it an air screw, not a fuel screw. So turning it out would make it leaner. The opposite of our pz30/vm26 carbs. So you're correct it would need to go down a pilot size. Good catch.

[Megadan]

Originally Posted by TxTaoRider

I'm no expert on PE carbs, but on the pics I found, that screw is on the mouth side of the carb, making it an air screw, not a fuel screw. So turning it out would make it leaner. The opposite of our pz30/vm26 carbs. So you're correct it would need to go down a pilot size. Good catch.

For what it's worth, I had to stop and think about it for a second myself and I am intimiately familiar with the PE carbs... especially considering I was the originator of installing them on the Hawks lol.