How PAJ2/coasting enricheners work

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maleko89

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Okay, I learned something today. I have always said that PAJ2 is blocked off at idle and only opens at off-idle throttle angles similar to the piston slide. I was WRONG.

I did an experiment using a straw on one of my spare carbs. I originally was going to mention suck and hole but figured I would get Lankee all hot and bothered. Sometimes a burrito just doesn't keep him from humping your leg. Anyway, I could get air through PAJ2 with the plunger all the way in the bore. If I pulled it out a tad then no air would go through. I looked at the plunger itself and the very tip of it is what closes PAJ2. If you look at the included picture you can see the end is thicker than the rest of the plunger. So, the coasters actually open to close off PAJ2. Normally, air would go from the air vent at the top of the carb (same vent used to open slides), go through PAJ2, go around the thin part of the plunger and on to mix with pilot fuel. There's a small passageway that leads from below the butterfly to below the enrichener cover. When you close the throttle at high rpms there is high vacuum and thus low pressure. So, low pressure signal travels up the enrichener port and the PAJ2 air pushes on the diaphragm to open and closes off PAJ2. So, the only time the enrichener opens is at high vacuum. When you chop the throttle off at high rpms it pulls the enrichener open which closes PAJ2. When the rpms drop to a sufficient level then the enrichener closes which opens PAJ2 again.

I learned something today, I can have a beer now.

Mark
 

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I verified this today.
When I put the bigger cams in my bike I was having some lean issues in midrange that shimming the needles would not take care of.
So I dropped in a smaller PAJ2. Well last night I rechecked my A/F mix and was running rich so I turned in my screws and achieved a 13.5 at idle. Still choppy but better.

Tonight I decided, just for the fun of it, to put back my original PAJ2 of 170s and do another A/F mix check and low and behold it went up to 14.5 and off idle throtte response is much crisper now. So yes the PAJ2 has a profound impact on the idle circuit.

Went out for a ride and my midrange was still stumbling a bit.
Came back and adjusted my needles 4 clips from the blunt end and took her out again and Holy Mother of Mary.:rocket bike:
It felt like what a built bike is supposed to feel like. Like a freakin rocket strapped to my ass.

Time for a dyno run!!!!!!!!!!
 
I've had a hot idle problem with my 'MAX since I've owned it - I did a half-assed carb float adjustment last year , but never a good "overhaul". Last week I pulled my carbs COMPLETELY apart & guess what I found ? All my coasting enricheners were gummed up & one was even melted into the cover - no wonder I had my pilot screws out to 3 1/2 just to get a basic idle that went away when hot. Thanks to a cool Bro here known as Maleko89 who sent me a spare diaphram just for the cost of shipping, I now have a smooth running VMAX !!! I don't know if alcohol fuel is to blame or just sitting for a long time, but the beast is MUCH happier now!!! Thanks Mark, this burn-out's for You ...:rocket bike::rocket bike::rocket bike:
 

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Hi, I rebuilt carbs and like the fool I am I did not mark were each jet goes. Asa result the bike is running lean and popping through carbs. Can't seem to find anything tht shows were they go. Any ideas? Thanks
Okay, I learned something today. I have always said that PAJ2 is blocked off at idle and only opens at off-idle throttle angles similar to the piston slide. I was WRONG.

I did an experiment using a straw on one of my spare carbs. I originally was going to mention suck and hole but figured I would get Lankee all hot and bothered. Sometimes a burrito just doesn't keep him from humping your leg. Anyway, I could get air through PAJ2 with the plunger all the way in the bore. If I pulled it out a tad then no air would go through. I looked at the plunger itself and the very tip of it is what closes PAJ2. If you look at the included picture you can see the end is thicker than the rest of the plunger. So, the coasters actually open to close off PAJ2. Normally, air would go from the air vent at the top of the carb (same vent used to open slides), go through PAJ2, go around the thin part of the plunger and on to mix with pilot fuel. There's a small passageway that leads from below the butterfly to below the enrichener cover. When you close the throttle at high rpms there is high vacuum and thus low pressure. So, low pressure signal travels up the enrichener port and the PAJ2 air pushes on the diaphragm to open and closes off PAJ2. So, the only time the enrichener opens is at high vacuum. When you chop the throttle off at high rpms it pulls the enrichener open which closes PAJ2. When the rpms drop to a sufficient level then the enrichener closes which opens PAJ2 again.

I learned something today, I can have a beer now.

Mark
 
Mikuni 170's go under slides (PAJ2). PAJ1 are at the top of each carb and are Mikuni 90's.
 
Damn Dan-o, im gonna be emailing you for carb advice before too long.
Im a believer in a few elementary things when it comes to carbs, one is write every change down! Two, once you've found a close combo between the clip and mains you can have fun with the air jets and increase tuning significantly. Of course you have to understand what each do...so thank you for educating us Dan!
 

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