Home Forums Shifter Karts CR80 Fuel Issue (Newbie Help Please)

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    • #55779
      Jason Shoulet

      I’m new to karting and this website and I have a fuel issue that I’m hoping to get some feedback on.

      Problems: On a straight run, the kart would bog at the top of 5th gear and all of 6th.  After (2) or (3) runs up and down the street it will bog down regardless of the gear you are in and completely die.  I rebuilt the fuel pump yesterday and one of the small diaphragms looked slightly bent.  After the fuel pump rebuild the bog in 5th and 6th  was solved.  The kart pulls hard 1st through 6th but it still dies after (2) runs up and down the street.

      Additional Information:

      • When I put the fuel pump back in I noticed the idle screw was all the way out almost falling out of the carb.  I screwed it back in and the kart idles fine.  After a few minutes of idle at 4,000 rmps it will drop down to 2,000 for a minute or two then go back up to 4,000.
      • When I first purchased the kart I discovered if I filled the gas tank half way or more the kart would bog after decelerating and it would take a 10 seconds or so to pick back up after getting on the gas.  This doesn’t happen if there’s 1/4 or less gas in the tank.  I mention this as I’m wondering if theres an issue with the tank.
      • During earlier troubleshooting before rebuilding the pump I didn’t realize the hole in the tube connecting the (2) vent/overflow ports on carb was intentional as part of the pump around system so I taped it up to see if it fixed the issues which it did not and made it worse (I removed the tape before rebuilding the pump).
      • On my last attempt to make a run last night I got a red light on my mychron and could see the temp rising beyond normal. It was up to 143 degrees and would normally never breach 139 after running it hard before my issues started.  There’s no water in the overflow and the radiator is full of fluid.
      • All fuel lines are clear with no bends or crimps and tightly secured to the carb and pump.

      Kart Background: 2005 Birel with a CR80, Mikuni square slide carb and Mikuni fuel pump in the pump around setup (the pump requires (2) rebuilt kits for a complete rebuild).  The kart was professionally built by a shop in Lodi, CA and I bought it after the most recent motor rebuild.  I have put maybe 5 to 10 hours on the kart running around my neighborhood over the last 4 months without issue until (3) weeks ago when the problems started.

      Thanks for your help.


    • #55783
      Timothy Strawkas

      I can not tell in the pictures, but it almost sounds like you have the feed pump feeding the pump around line, and the pick up pump sucking the feed line. Or both pumps are feeding the carb and none are pulling the fuel out of the carb.


      Oh I just seen the other comment you had. This kart is not A street toy, They don’t run great there because there not designed for it. Keep it off the street.

      • #55784
        Jason Shoulet

        Thanks for such a quick response.  The lines are set up the same as they were when I purchased the kart (never touched anything before the issues started) and it ran it without issue for months.  I can also see the fuel return line feeding fuel back to the gas tank (I can see it in the line coming from the carb and I can see it draining in the tank itself).

        What’s really stumping me is the ability to make (2) long 1st through 6th gear passes without issue before it dies.

    • #55873
      Jason Shoulet

      After some additional troubleshooting I believe I have a blown head gasket that is allowing coolant into the cylinder.  The exhaust is now white, it’s overheating, I can see bubbles in the radiator and after a quick cold start the plug is soaked.  A slow coolant leak would also explain why it can make (2) passes before fouling the plug and shutting down.  Changing the gasket tonight.

    • #55878
      Dave Holstein

      I would like to put my two cents into this, I race 80s at my local 3/4 mile track, and I would like to advise you to NOT drive this on the street, you are on a very low/no grip condition and all you need to do is eat a cars bumper once and you’ll be driving a wheelchair forever if your lucky!

      hate to sound like a real pain but I would recomend you get out on a track and push it till it breaks loose and then you will see just how helpless you are when you loose traction, if your in the area of central/northern California the Sanzaru karting championship runs at Sonoma raceway and has an 80 masters class (32 and up).

    • #56083
      Jason Shoulet

      Thanks for the concern/advice Dave.

      Here’s an update on the troubleshooting progress:

      1. Replaced the head gasket which fixed my temperature problem and my bubbling radiator fluid problem.
      2. The kart is still running rich which was slightly improved via an adjustment to the air screw (had to go 3 turns out which is another indication it’s running rich and the jetting is off)
      3. After running the kart for 5 or 6 laps up and down the street it dies.

      I’m going to pull the carb apart to adjust the needle clip up one notch and see what jets are being used.

    • #56195
      Jason Shoulet

      I am posting this to close out the thread and hopefully help someone else with these issues.  Before breaking the carb apart I decided to change the spark plug which resolved the issue of the kart dying after a few laps.  After changing the spark plug the apparent rich condition was also eliminated once the engine was brought up to temp (110 degrees).  As a side note, I also added an additional breather tube to my gas tank cap using a 1/4 inch copper barb which eliminated a bogging issue I was having when I had more than a half tank of gas and I would come off the gas and try to get back on it.

      To summarize, here’s the issues I had and the things that fixed them:

      1. Bogging in top of 5th and all of 6th gear. Rebuilt Mikuni fuel pump which solved this issue (one of the two small internal diaphragms was bent).
      2. Excessive white smokey exhaust, heavy bubbling in the radiator and overheating. Replaced head gasket which resolved all these issues.
      3. Kart dying after 2 solid laps.  Changed spark plug which resolved this issue.
      4. Bogging when coming off the gas and then getting back onto it when the gas tank was half or more full. Added breather tube on gas cap which resolved this issue.
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