Hi Squall,
Sorry if I hurt your feelings.
Just because you cannot "grasp" how a lean idle on a 2-stroke will make the engine race doesn't mean it's not so........................
Pilot jets don't cost $80..........about $5......much cheaper than a new carb.
A 2-s motor runs "richer" than stoich for many reasons......among them cooling of the piston/combustion chamber.
If you get a 2-s motor lean enough/hot enough it will go into an "auto-ignition/diesel" condition where it will "run away" even w/the ignition off/throttle closed, as the small amount of air leakage past the slide or where the throttle cable comes in allows it to keep running.
When slides wear (they all do) the air to fuel ratio at idle goes leaner as air is bypassing the idle discharge port and needle jet nozzle.....................
Simple remedy...........jet the pilot circuit richer and drop the slide(idle RPM screw) a freckle.
I/we do a 42.5mm "race carb" out of the OE Zilla carbs that will have a little "daylight" under the slide even w/it all the way shut and it idles perfect.............
It's all in matching the air to fuel ratio curve..........
Oh, and running 87 octane fuel in a Zilla motor is about the worst thing you could possibly do.
Big bore singles have generally poor combustion qualities and the stock Zilla motor has a HORRIBLE head design that makes it EXTREMELY octane sensitive.
Hope this helps,
RK

 

ok to reply thanks for the recommendation about the octane sensitivity i will switch to 89 or above if you think that is good or should i go higher?

Now let's break down the combustion process you need three things to make a succesful combustion.
1. Air
2. Fuel
3. spark

Without one of these you will not get combustion, you must have all three.
Auto ignition implies in it's name that there is an igniting source
Diesel is different it does not require a spark it has glow plugs.

My cylinder head had an imprint of a screw in it, that is where i had my hot spot which would allow the engine to run with the ignition off, after i had that fixed when the engine went crazy i pulled the ignition and the engine shut off.

Now examine the carbeurator:
The pilot circuit has controlled air passage via the air screw
The air picks up fuel in a controlled amount via the pilot jet
So as long as my air screw is in it would never allow more air in than the factory would allow no matter what setting.
The idle screw will raise and lower the throttle slide to allow more air passage across the exit for the pilot circuit in turn enhancing the whole process not changing the mixture.

The way a carbeurator controls rev is by allowing more or less fuel and air to combust.
An idle position in the carbeurator will only allow 50cc of material in to combust
A full open position will allow 500cc to combust thus giving it more thrust to revolve and compress faster

The reason a leaky head gasket or throttle slide will allow the engine to race out of control is because the carbeurator is mostly cut out of the equation you have an unlimited supply of air to compress a full 500cc

Now the fact that changing the throttle idle screw setting would help when the engine was out of control is because it would shift the throttle slide and would allow it to seat correctly.
I pretty much know that the slide was not correct because my jet needle had actually bent from the slide moving so much. Have you ever heard of that happening?
Again like i said it was not the difference of a couple of hundred rpm in which case i would say you are definately right. It was the difference of propably about 3000rpm in which case the only way the pilot circuit would be able to do that is if you completely removed the air screw and pilot jet. Basically taking all the control out.

But like i said if it was a small difference and it happened everytime instead of intermitently i would say you are right but this was not the case.

Also the throttle slide was 80 dollars and i know the jets are five dollars but the way i do things is thorough so if i had a 170 main and a 50 pilot i would buy 165 168 172 175 45 48 52 55 and that is just to start so i asked for recommendation so i would have a better idea of where to start.

Again i am not an idiot i spent 2500 dollars on the quad and put 1000 at least before the carb to try to fix this thing and i have been working on it for about a year and a half with the help of the guys at my local suzuki shop and my local kawasaki shop and they are also proffesionals.

But once more i thank everyone who has responded to my article and i will jet this week and get back to everyone.
I don't know what i would have done without all you guys you all made a good support team
Even the guys who try to teach me a lesson i am always willing to learn

 

Squall311, you began to convince me that you were engine (and more specifically LT500R) savvy up until you mentioned using 87 octane in the Zilla. Even though that quad's compression ratio is pretty low, the flame-front has a relatively long distance to travel due to the large bore. If the head design were better, the bore size would not be such an issue. However, a poorly designed head mated to a large bore means that detonation is prone to occur around the outside edges of the piston.

Simply stated, if you are using 87 octane in the Zilla, you do not know engines NEARLY as well as you think you do.

I'm not claiming that your fuel octane is effecting your idle but since you don't even have a rudimentary understanding of what causes detonation, it is probably safe to assume you know very little about pilot jet function and effect. Also, if you will carefully reread my first post, you'll notice I point out that flat-slide carbs are notorious for not coming immediately down to idle when the throttle is let off. However, they idle fine once there. A worn slide exacerbates this problem. I had to pay $40 for a new slide seven years ago but the problem ended immediately upon it's installation. As stated before though, the PWK is still well worth the extra dough.

BTW, you don't need that much of an orifice or air source to have your engine race. There is no real power behind the racing engine you describe. If you were to begin to let out the clutch, the r's would drop and even die ounce the clutch is fully engaged. Try this with a wide-open throttle and you will quickly find yourself on your back. Equal r's do not necessarily mean equal power being produced.

Read posts carefully and don't be so quick to dismiss suggestions that don't immediately make sense to you. You have already made it obvious that you do not understand your machine as well as you think you do.

I'm quite sure you are going to take offence to this post rather than simply taking it for what it is. I'm trying to get you past your stubborn preconceptions/misconceptions so that some real knowledge can sink in.

 

I'm going to put this in all caps so that you can't miss it.

MY ENGINE RACED TO MAYBE 4 or 5 GRAND WITH THE THROTTLE TOTALLY CLOSED!

This would happen after the engine was fully warmed up, the thumb throttle was released and the clutch was pulled in.

THIS PROBLEM DISSAPPEARED WITH A NEW SLIDE!

I always perform a leak-down test on any single cylinder motor I reassemble (milti-cylinders are too time consuming and I have been lucky with them so far). There was no other air leak.

 

Well Squall,
You have convinced me as well............. you are either really stubborn or know just enough to be dangerous.
Your counterpoints are completely full of holes and missapplied theories....WTF do you think a glow plug is????????????? It's an ignition source used to start combustion on a diesel until the cylinder/chamber get enough heat in them for the engine to run.
Spark is not the only kind of "ignition" ..................heat and pressure are 2 others.
And you forgot "compression" is necessary for an internal combustion engine to function.
I DON'T want to get into a bashing session......I was just trying to help.
REMEMBER.................Your'e the one who can't get either of his carbs to work right........................not me.
Think about it...............................
"You can lead a horse to water, but you can't make him drink"
I'm done,
RK

 

Please use the highest pump octane you can get with a stock lt500 !!!
93 is good

Running 87 octane in your lt500 is like keeping your pedigree Rottweiler chained up outside in the middle of an Arizona heat wave with no water [img]i/expressions/face-icon-small-frown.gif[/img] ... it makes me sad to see someone abuse a poor old Zilla...and not even know they are being abusive. ..Mind boggling to me.

No need to break anything down. Nope.... None.

The top guy for lt500 in the WORLD (DR Q aka RK) responded to your post and you refuse to take his advice, along with all of us other lt500 owners ?

Some can learn from others mistakes ...some have to make them themselves....I predict an engine rebuild in your near future.



check out this lt500 hillclimb love the brraaaaaaap after the last jump at the top.... thats lt500 power
LT500 hillclimb

allcool

 

it is not that i refuse to take anybody's advice it is just that i cannot understand how the pilot would do that but to humor myself i will try a bigger pilot it can't hurt right.
What size does RK think mind you i have the stock one on.

I do not regret the purchase of the keihin though this way i can eliminate the carb as a possible source of the high rev problem.

I do not mean to disrespect RK in any way if i didn't want his help i would not have signed up to the message board.

The only person who could tell me that they had the same problem was f250r and he told me a new keihin carb fixed it.

Again by all means i mean no disrespect to RK his pictures speak a 1000 words.
I would like to thank RK for actually having a discussion with me about the topic and even though i could not see his point he was at least willing to give me a thorough explanation rather than just telling me what to do. He offered his service when i was in need and i thank him graciously for that.

I have been sick this week so no time to jet but will let everyone know what the deal is when i do it

Thanks again everyone especially RK and f250r

 

WOW after reading everyone's posts i must be a big dick!
Sorry everyone

 

hey I saw and earlyer post of yours sayin ur runnin 20:1 Mixture, That keihin carb is designed to Run 32:1 out of the box, Like i said i had the same problem as you but i was mixin my gas at 40:1, then got the new carb and it said mix at 32:1 and the problems disapeard. The slide in your new carb is chrome plated and will last the rest of your life lol.
mix ur gas at 32:1 and dont touch the jets and let me know how ya make out.
F250R

 

"The only person who could tell me that they had the same problem was f250r and he told me a new keihin carb fixed it."

WHAT!

Did you read any of my posts? My problem was EXACTLY like yours! That doesn't mean my solution has to be the same but it is a good possibility. Your response proves that you aren't even really reading the free info given to you. We are only trying to help but you don't seem to want to accept any response that doesn't conform to your own theories.