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cfauvel

2000-2001 lta500 quadmaster - Idle jet adjustment

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ok help so according the service manual, Idle Air Mix Screw (aka Pilot screw) should be initially set to 2.5 turns out from fully seated.

If I do that the motor doesn't want to start or stay running...right now the pilot screw is probably somewhere near 5 turns out....I'll take the carb off tomorrow to count to know for sure.

mind you the carb got a new float seat,float needle and various other components in the kit.

To get the motor running I hard to turn the pilot screw out quite a bit, and turned the idle speed screw in quite a bit...I didn't hook up an inductive tach to know what it is idling at, but does sound about right.

What should the idle speed adjustment screw initially be set at (the one that has the black cable sheath with a knob you can twist easily)?

Is there a special tool to turn the idle/pilot mix screw whilst the carb is on the running motor? I am using a slotted screw driver bit (normally goes into a driver) by hand..makes it hard to turn the driver and hard to tell how many turns .

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When the  carb  was worked on,  did  you  make  sure  all  the  passages and  jets  were  clear?  There  could  be  a  partial  plug in the  idle  air  circuit or  the   needle  could  be deformed a  bit  requiring it  be  turned out  farther than normal to  get  the  right   mixture ..  2 1/2  turns  is an  INITIAL  setting.  On every  motor final   setting  may  be less or  more. . Most  manuals  say  start  at  1 1/2 to  2  turns  out  from  LIGHTLY  seated.  More than  one  carb  and  needle  have  been damaged  by  someone turning the  screw  in too tightly. They  usually  still  work ,  but  settings  on a  damaged one  could be  far  from  what  they  should be.  I'm  not  familiar  with  the access  to the  carb to  say  what   would be the  easiest  way to  access the  idle  air  screw  to  adjust it ,  but there  are  screw drivers  available  with  flexible  shafts and cupped  heads  to  keep them  on the   screw.  They'd be  a specialty  item  you  might  have  fun tracking  down. Could  you   possibly  find extension  shafts  to  use with  an  insert  type  screw  driver ,  or  a  long screw driver  that  will  allow  you  to  be  able  to  reach that  screw from  farther out  of the  frame where  there  is  more room  to  turn  it?

 

One   other  thing ,  when  you  say  5  turns,  is that  five  full  rotations  or   five  half rotations  on a  slotted  screw?

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First thank you for the nice detailed response.

Yes I thought a good job clearing out all of the passages, but the carb was SO varnished up there could still be crap in the passage...

funny story(not really but has a happy ending)...with the carb kit that I bought it came with new jets (main pilot, etc). I put in the new pilot screw and turned it 2.5 out from lightly seated.

Installed the carb and worked on gett the motor started, so messed with the pilot screw...apparently went the wrong way and fully seated the plot screw and then once realised turned the screw counterclockwise, but wasn't happy with the results, so let it cool down and took carb off...took out the pilot screw only to find that the tip broke off in the orifice....panic sets in....I see the tip of the pilot screw and figure I'll just push down to get it unstuck from the orifice....that promptly bent the tip so that there was NO WAY it was going to come out from whence it came....MORE PANIC NOW  .....dremeled the tip off and used all kinds of picks to try to push the remainder from the orifice.... no luck....look on ebay for used one, none to be found, look at the price of a new one and freak out.....

As a last ditch I used an OMC/Johnson/Evinrude orifice cleaning tool (mostly super tiny drill bits, smaller than 1/16") and hand twisted clockwise for 10 minutes to drill through the brass tip that was left. Once I was through, the hole was actually smaller than the orifice, I could see some brass still there...had my daughter with the good eyes use a pin to push the remaining sliver of brass out. Under a bore scope, which magnifies pretty well, I could see the orifice wasn't boogered up.

So there HAS been some stuff done to the pilot screw orifice. :-(

As far as the 5 turns, it is just a guess as I was doing this with the engine running and getting my hands burned...I'll take off the carb after work to see actually how many turns I'm out currently.

I do have a screw driver with a flexi shaft...going to try that, may save me from burns too.

Right now it takes a lot of cranking to get it running and messing with choke. When warmed up it revs easy enough (I'm not riding it yet, just neutral) , when i left off the gas and let it idle a bit then turn it off it back fires through the exhaust if that is helpful information.

to me any backfire means lean, at least it does on my outboard.

 

Chris

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Backfire   is  most often  lean....  My ride'em  lawnmower does it every time  I shut  down the throttle and ignition   motor dies  with  last gasp  backfire  after  it  has  stopped. You could  make  your  screw driver  stay  on the  needle  valve by  cutting  a  small piece of plastic tubing that  has an  opening   to fit over the  screw  heard   and attaching it  to the  end of the  screw driver.

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What do you think of the following to adjust the idle mixture (ie pilot screw)? Assuming I find a way to turn the pilot screw without burning myself anymore.

1 - add a T to the vacuum line from the carb to the gas tank's petcock

2 - screw in the idle speed screw (the screw linked to the throttle under the black side cap) so that the motor idles well enough

3 - adjust the idle mix/pilot screw in or our until I get the maximum vacuum 

4 - lower the idle speed screw to meet the 1500 +/- 100 rpm range.

 

NOTE: I'm not seeing a fuel pump mentioned in the service manual....I assume there IS NOT one for the quadmaster 500....just gravity fed with the vacuum at the petcock to let fuel run into the carb with selector is on ON or REV. When on PRI just gravity fed.

UGH just rethinking the vacuum port on the carb....not sure if it will be a steady vacuum or a pulse...easy enough to test.

 

Edited by cfauvel

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Just checked the pilot screw # of turns out and it was only 3. I must have turned it in to try to get it to lean out then back out until it sounded better and ended up at 3.


I'm going through the carb one more time cleaning out the ports again...and double checking the float level one more time.

Looking at the gas I'm seeing a yellow tinge, like the color of cadmium plated parts, so fuel might be an issue too...will get some REC gas once I have the carb back together.

Also looking at the idle speed screw and cam under the black plate, it doesn't seem like I screwed in the idle speed screw much at all..

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Just checked the pilot screw # of turns out and it was only 3. I must have turned it in to try to get it to lean out then back out until it sounded better and ended up at 3.


I'm going through the carb one more time cleaning out the ports again...and double checking the float level one more time.

Looking at the gas I'm seeing a yellow tinge, like the color of cadmium plated parts, so fuel might be an issue too...will get some REC gas once I have the carb back together.

Also looking at the idle speed screw and cam under the black plate, it doesn't seem like I screwed in the idle speed screw much at all..

UPDATE:I checked the float level and the setting was a little low, the manual states it should be 13.00 mm +/- .5mm, so I had to raise it about 1.5mm...right now it is at 13.2....When I raise it, it seems to me that it would lower the level of fuel, right? As it is closer to the bottom. We'll see tomorrow how it behaves.

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Ok put the carb back on with pilot screw set at 3.5 and tried starting it. Put the fuel pet cock to PRI for about 10 seconds and tried...kept cranking , kept cranking, tried the "choke"  and only with the choke NOT engaged did it finally start up.

once started and idling if I tried the throttle it would hesitate and die.

only after a warn up period of several minutes did the throttle behave and not hesitate and die.

and once warmed up it seems to idle fine....I don't have a functioning inductive style tachometer to know my true RPM...I am open to suggestions on a brand/model of a inductive tachometer.

 

So what do you all thinK? unscrew the pilot screw a bit more?  Screw the pilot screw in more?

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Choke off to  start  sounds like  too  lean. Try turning the  screw in a bit  at  a  time   I  think you'll find it  better  at about 3  turns out  rather than the  3.5

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Thanks Dave, will try that saturday....off to office tomorrow :-(....I get back in the dark.

I was hoping the mentioning of where the choke was when it finally started would be a clue.

Any recommendations for a brand/model for inductive tach?

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Sorry ,  Can't  help  on the  tach .  I  see I  mistyped in last message    It should have been  2 turns , not 3 ,  but  turn it  about 1/4  turn  at  a  time.   Turn  it   in  or  out  a  bit when  you  find the spot  it starts  ok  and doesn't  die  when  you open the  throttle to  fine tune  that  sweet  spot .  It  should  run after  a   couple of minutes warm up   and not stumble  when  you  "blip"  the  throttle ..   If  it  does ,  it  can  be   because it is  too  lean at  idle  ( air screw  out too  far )  or a  problem  with an  accelerator circuit..   It's  hard  to  cover  bases  with suggestions   from  afar, especially  when  not  familiar  with   the  specific  carb(s) on  various  bikes.  All  I can do is  point  in directions  to  look  for  problems.

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Thanks Dave and no worries, you've been a great sounding board. I hear ya about trying to diagnose from afar.

I don't know these carbs either so get confused as to whether this Pilot Screw is an idle air bleed or idle fuel jet....on my 225 evinrude the idle circuit is controlled by idle air bleed, meaning they let in air, so larger orifice means more air not more fuel....Sounds like the pilot screw is an idle air limiter based on your suggestion of screwing it in more...

Thanks again...I'll keep ya posted. BTW My flex shaft screw driver is going to work.

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GRRR and YAY..

set the carb to 2.5 turns out and cranked and cranked and cranked until the engine started. It idled pretty well right off the bat, but if you goosed the throttle it would WOMP and almost die....I screw in the pilot screw a little bit at a time and kept trying the throttle. After several adjustments trying the the throttle it would rev nicely without dieng . 

had to take the classic 69 mustang out to put xmas lights away in the attic and decided to re-test the inductive tach that I had...it worked...So went back to ATV and tried it again...it didn't work...then I saw a protective sleeve over the spark plug wire....cut that back a little to get the pickup directly on the wire...first try nothing, flipped it 180 degrees and got a reading. At first it was pretty accurate then for some reason it started doubling and tripling...I managed to set the RPM at around 1600 when it seemed accurate, then the tool read 4000 - 6000 whilst idling.....ugh.

 

over the course of an hour I turned off the motor and went back where it would start and idle perfectly.

let it cool for several hours and it WOULDN'T start after cranking a lot...finally the battery had enough.....put a Battery Tender on last night and will see in a bit how it does.

If these are like outboards, you need a good battery to turn the magneto fast enough to produce the right amount of starting spark for the CDi ignition to charge up the capacitors to discharge. I'll keep you posted.

 
 

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GRRR
just tried the engine

1 - turned petcock to PRI, waited a few seconds

2- set the enricher to all the way...cranked...nothing

3 - set the petcock to RES and enricher to halfway...cranked....nothing

4 - set the enricher to nothing....cranked ....nothing

5- sprayed starter fluid into the air box, started right up and idled nicely and throttle response was good after warming up a bit.

Thoughts?

 

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Check to  see if the  enricher /  choke  is actually  working  or  not.  If it  is  a  "butterfy"  type  choke  plate,  check to see if  it  is closing  Maybe  disconnected ?..  Other than  that ,  I'm  afraid it's a head scratcher  you will have  to  hunt  down .

 

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Unfortunately this is a Mikuni carb where the choke is actually an enricher and doesn't move the butterfly. Very similar to the Johnson/Evinrude method of 'choking' the engine. The latter is a solenoid that lets fuel behind the carbs into the intake manifold.

The choke level when fully on, pulls a needle out of an orifice, and when no choke is on the needle is blocking the orifice. When I do get the motor started and idling, if I employ the choke it kills the motor as one would expect...this tells me the orifice is not clogged (at least not fully)

I 've been running with the gas tank away from the carb via longish fuel line and vacuum line...I am thinking that is the issue...normally the fuel line and vacuum line is about 3 inches and 4 inches respectively...with the fuel line I am using being  about 3 feet long it might be creating a P-trap...I think I'm going to mount the tank properly and give it another try.

 

 

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A little update.

been starting this motor everyday since last update and a slight adjustment to pilot screw after installing the tank in the poper place with short fuel and vacuum line....It has become progressively easier to start, though still quite a few cranks of the engine....

Then yesterday I started seeing smoke come around the air filter box....took the rear fender off and found the voltage regulator smoking....poking around here I found this thread

 

The OP's symptoms are very similar to mine...obviously a new regulator has been ordered...we'll see the outcome around Feb 6....

 

in the meantime I'll be working on the seat foam and upholstery. 

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OMG - UPDATED

Put in the new voltage regulator in today, the motor started quickly with the right amount of choke/enricher employed....took maybe 5 cranks or less. 

The motor had been sitting for several days, so it was as cold as possible...let it warm up for a minute and played with the throttle and once warmed it didn't hesitate .

It kind of makes sense I guess....if the magneto is giving the voltage to the regulator, the regulator in turn feeds the coil (or goes to some CDI component elsewhere), then having a bad regulator would affect the spark.

 

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Glad you  got it sorted out; and glad  you  let us  all  know what it was..  I'd  have never thought of the voltage regulator myself.  Something to remember  next time  someone  has  an  odd "fuel"  problem.

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4 minutes ago, davefrombc said:

Glad you  got it sorted out; and glad  you  let us  all  know what it was..  I'd  have never thought of the voltage regulator myself.  Something to remember  next time  someone  has  an  odd "fuel"  problem.

I know I would have NEVER thought of that, I guess 'thankfully' the regulator was smoking as being the clue. I went with a $17 after market unit from amazon...I could buy 4.5 of these for the price of OEM, we'll see how long it lasts.

Now for new tires and reupholstery of one more seat and then I'll be able to hand both ATVs back to my bro-in-law.

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