What do you guys know about Carbs? - page 1 - General - VWDiesel.net The IDI, TDI, and mTDI source.

• What do you guys know about Carbs? by 8v-of-fury on 13 Mar, 2009 15:19
• This thread doesn't apply to a Volkswagen, or even a Car :lol:
  
  It is regarding my Polaris Atv. It doesn't really matter because it is a carb related question. Polaris and Vw use a ot of similar parts both my car and atv have VDO gauges, Sachs struts, and if i had a carb car it would probably have a similar Mikuni carb.
  
  Anywhoo.. the weird thing is, is that it idles fine right where it should at 1100rpm but when i go to move or put a load on the engine it bogs down. This problem will go away if i pull the choke out to a point if i let it idle down it will stall itself out.
  
  It runs ok just this minor issue..maybe a mixture issue? what ya'll diesel guys think?
  
  I know I am asking for you to go outside your comfort zones and deal with a gas contraption.. but you guys are good here... lmao  
• #1 by jtanguay on 13 Mar, 2009 15:38
• check the air cleaner?  :lol: thats about all the input i have.  as i haven't had much experience with carbs.  there was one time where some dufus put gas in the oil, and made a huge mess.  with a flush of the oil it ran good afterward but would chugg/stall if the air filter was put on.  soaked in gas, the gas turned black because it was saturated in the super thinned oil.  :shock: afterwards it ran just fine!  :lol:
• #2 by clbanman on 13 Mar, 2009 15:49
• Pull the air cleaner off and with the engine running take a piece of cardboard and slowly put it across the carb throat.  If the engine speeds up slightly before it stalls out, you are too lean.  If it just dies instantly, you are too rich.   This presumes of course that your problem is with your air/fuel mixture.  With what you are doing with your choke, I think it points to lean.  I am not familiar with the carb on your Polaris, but most have some type of enrichment circuit to inject a bit of extra fuel as you first apply the throttle until the air flow can pull more fuel into the carb.  It could be some type of squirter, secondary linkage adjustment or power valve.  Best bet is to get to your local library and see if you can find a decent manual that tells you how to adjust your carb.
• #3 by DCC on 13 Mar, 2009 16:11
• Quote from: "8v-of-fury"

  Anywhoo.. the weird thing is, is that it idles fine right where it should at 1100rpm but when i go to move or put a load on the engine it bogs down. This problem will go away if i pull the choke out to a point if i let it idle down it will stall itself out.

  
  
  The choke increases the fuel ratio in the mixture, so IMHO it is probably running lean in the lower revs. There are generally a couple screws to adjust both the idle mixture and the throttle position at idle. Don't touch anything else if the engine is running well in the mids/highs. Get a manual, as clbanman sugests.
  
  Could be that you got some moisture in the carb. They have a drain screw.
  
  
  Check the sparkplug(s)!
  http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm
• #4 by 8v-of-fury on 13 Mar, 2009 20:52
• This is the reason why I LOVE THIS FORUM! :lol:
  
  For some diesel freaks you guys responded fast to a gas question
  
  Another weird thing is, is this sometimes goes away when it is Fully warmed-up. Air cleaner is off at the moment it was saturated in gas last fall and deteriorated over the winter
  
  

  Quote

  Pull the air cleaner off and with the engine running take a piece of cardboard and slowly put it across the carb throat. If the engine speeds up slightly before it stalls out, you are too lean. If it just dies instantly, you are too rich. This presumes of course that your problem is with your air/fuel mixture.

  
  
  I think it is a air/fuel thing, but only an idle deal. it will hum along fine through the range (2500-6100) its just that initial start off seems a little weak, some sputtering and surging.. also notice a small backfiring sound coming from the carb... but it all goes away with a small movement of the choke.. this is beyond me
  
  

  Quote

  Check the sparkplug(s)!

  
  
  I would assume it needs a tuneup bad, along with a fuel, air filter and oil change.. but its running fine.. so it doesn't need it yet I have a Polaris shop manual for it, i will drain the carb, and i will check out these adjustment screws. thanks guys!
  
  Here is a pic for kicks last night after i put all the plastics back on with zipties !! bolts are over-rated.. plus all the mounting holes are trashed
  
  
• #5 by zukgod1 on 13 Mar, 2009 20:52
• Main jet is plugged..
• #6 by 8v-of-fury on 13 Mar, 2009 20:54
• i would have agreed with you there Dan when i pulled it out of my backyard a couple months ago after parking it where it died 9-10 months ago.
  
  it ran like total CRAP, then i ran some ATF through it and it seemed to clear it up insanely well. maybe it needs some more.. how else would you free a main jet easily.. without removing the carb.. :lol:
• #7 by Turbinepowered on 14 Mar, 2009 02:57
• I know enough about Carbs to know they are the work of the Devil and should be exorcised from any poor blighted car that ever passes into my possession with such an affliction.
  
  And they make you fat.
• #8 by theman53 on 14 Mar, 2009 07:16
• one cylinder engines are very touchy to air volume. I had to rejet my honda when I added a K&N filter. My friend had a kawasakii and had to rejet for every 10-15 degree temp change up or down=race bike. All that said if it is doing this when you have no air cleaner on it that could be the deal. If it was doing it before the air cleaner was removed then I would say it could be the jet(s)/fuel/spark. If it is like the honda carbs they had an idle jet and a main. I don't think you'll need to rejet unless you changed something like the air cleaner/head pipe. But I would say that the idle jet could still have crap in it as it is really only used a idle and then the needle takes over right off idle up to WOT where it is unrestricted main jet. Maybe you could dump the fuel out*especially if its old* and try some carb cleaner straight into it leave it soak. Or take the carb off and inspect and clean. I usually changed the plug in mine every 5-10 hours or so of running but I was anal about that stuff.
  Why did it die 9-10 months ago??? That could be a better place for me to start.
• #9 by 8v-of-fury on 14 Mar, 2009 07:43
• Quote from: "theman53"

  one cylinder engines are very touchy to air volume. I had to rejet my honda when I added a K&N filter. My friend had a kawasakii and had to rejet for every 10-15 degree temp change up or down=race bike. All that said if it is doing this when you have no air cleaner on it that could be the deal. If it was doing it before the air cleaner was removed then I would say it could be the jet(s)/fuel/spark. If it is like the honda carbs they had an idle jet and a main. I don't think you'll need to rejet unless you changed something like the air cleaner/head pipe. But I would say that the idle jet could still have crap in it as it is really only used a idle and then the needle takes over right off idle up to WOT where it is unrestricted main jet. Maybe you could dump the fuel out*especially if its old* and try some carb cleaner straight into it leave it soak. Or take the carb off and inspect and clean. I usually changed the plug in mine every 5-10 hours or so of running but I was anal about that stuff.
  Why did it die 9-10 months ago??? That could be a better place for me to start.

  
  
  Hmm, What you say sounds about right. It is a Twin engine but i'm sure it is sensitive to air volume as well as with the singles. It does not have the stock exhaust so this could be where the problem arose? I have a cherry bomb glass-pack on there right now, sounds real good too So by removing the air cleaner and putting a straight through exhaust then this engine is now capable of moving the air through it with very little to no restrictions correct? There wasn't much fuel in it when i parked it so its all been run out now, as i have filled it twice since then and run ATF through both tanks and it seemed to help a ton with the over all running condition of the engine.
  
  The reason it died 9 months ago wasn't engine related, it was the charging system.  wouldn't recharge while running so it ran the battery in to the ground. I didn't ride it much at the time so it sat until last month when i was bored one weekend and went to dig it out surprisingly when i hooked up a new battery to it, it fired right up. Now miraculously it is charging now.. this thing is EFFED LOL
  
  thanks for all the help guys.
• #10 by theman53 on 14 Mar, 2009 09:15
• New pipe=mixture screw or jetting required.
  I like to do a jet kit with a fat needle when doing that. It will increase the off idle performance even more. on the side of the carb there should be  a screw that is like an air screw on the bigger 4bbl carbs. like everything make marks and record where to go back to and make adjustments 1/8 to a 1/4 turn at a time. You might not have to jet it that way.
• #11 by Dakotakid on 14 Mar, 2009 18:37
• Does this carb utilize an accelerator pump? If so, this is the range where an accelerator pump diaphragm (damaged) would show up.  I used to have a Honda XR which utilized an acc. pump.
  Is this a 4 stoke engine? The carb really needs to be disassembled and cleaned.
  
  The bottom end (lower revs) is where the pilot jet (idle jet) begins handing off to the needle jet, which eventually hands off the assignment to the main jet.
  
  However, carburation is not THAT regimented. There is overlap on the job of the jets while controlling fuel. It's all a never-ending ballet of gas flow and the path it takes based upon vacuum.
  
  And if you think about all of what is going on while you blast through the woods.....you will hit a tree!!!!!
• #12 by Dakotakid on 14 Mar, 2009 19:31
• Sorry, I did not take the time to read Lucas' explanation of jetting above.
• #13 by MRDART on 15 Mar, 2009 01:20
• I would take the carb off, dissassemble and clean it, put it back on install a new air filter and a new spark plug. Then it will run fine...
   To me it sounds like a clogged main jet or maybe accelerator pump issue...
   Ultrasonic cleaner is really handy for cleaning carbs if you have acces to one. Best regards/ Tommy
• #14 by subsonic on 15 Mar, 2009 04:30
• Quote from: "Turbinepowered"

  I know enough about Carbs to know they are the work of the Devil and should be exorcised from any poor blighted car that ever passes into my possession with such an affliction.
  
  And they make you fat.

  
  
  The one exception of course would be a 1967 Dodge Charger fastback with a 440 6-pack or cross ram dual quads :twisted: