Thursday, June 23, 2011

My Adventures in Rebuilding a 1998 Harley CV Carburetor: Lessons learned

I had just bought this (new to me) 1998 Dyna a few weeks ago and was so happy.  It was Dyna Convertible with all the chrome (though I’m not a chrome guy) and a Wide Glide front end which for me was perfect.  She had been ridden and showed a little road wear but at some point someone took very good care of her, but apparently not the guy I was buying it from.  2Kewl and Junior member Hardkore were with so 2Kewl could give the bike a closer, wiser inspection than I could and gave me the thumbs up.  I slapped the cash over, signed the title and bill of sale and started the bike down the road.  The bike was running rich; I could smell it and also blowing a little black smoke which I initially dismissed as a combination of sitting idle for over a year and the fuel stabilizer the previous owner added before putting her away.  Getting home was an adventure but that’s a story for another day.

The bike was sluggish, seemed to lack any power and the top end seemed irrationally low.  The smell of fuel just permeated the ride and I knew this sucker was running WAY too rich and I later discovered why.  So the first thing I did when I got her home was pull the spark plugs, just as I suspected they were black which is indicative of running too rich.  I also noticed the spark plug cables were the stock cables that came with the bike 13 years ago or so it appeared (not good).  So off to the dealership I went and swapped out the cables and plugs.  I fired the bike up and had a very, very slight improvement but still nowhere near where it needed to be.  The idle on the bike was set pretty high; she was running rich and had no performance.  It looked like the carburetor needed a complete overhaul, likely from sitting around gumming up for over 12 months and likely because it had never been rebuilt in its 13 years and 21K miles.
First things first, I weighed my options.  I could take the bike in to have the carb pulled and rebuilt, buy a new carburetor or just attempt it myself.  Given that I had no experience or “know how” in rebuilding a carburetor I did what any “logical biker” would do, I busted out my wrenches and started in on it myself.  I figured the worst that could happen is I screw up the rebuild and have to pay someone to rebuild it anyway (seemed logical at the time).  Now I had never removed an air cleaner all the way, nor had I disconnected the throttle on a motorcycle or removed a carburetor before.  This was an entirely new experience but I made sure to document the process as I went along so that I could put everything back with no “spare parts” left over when I was done. 
After removing the carburetor I ordered a rebuild kit from since not only do they sell a complete kit, they also have the EZ-Just adjustable mixture screw and have several articles related to rejetting and tuning a CV carburetor on a Harley Davidson motorcycle.  Now I don’t know if you’ve ever tried to adjust a Harley’s mixture before on the fly, but let me tell you something, it’s a three handed, upside down operation involving a tiny screwdriver, red hot exhaust pipes, slightly less than red hot cylinder jugs and an itty bitty screw hanging upside down in a tiny little tunnel at an angle that almost makes it seem like some engineer at Harley Davidson gets his kicks in knowing that you are going to burn the poon-doggy out of your knuckles trying to get to it.  The EZ-Just sticks out just far enough that you can get your fingers back there and turn it manually or use a screwdriver that keeps your knuckles a healthy distance away from those jugs.  For the money it was worth it and that’s saying a lot because I’m cheaper than Bill Clinton on a “date night” with Hillary.
The kit came in just a few days and I immediately tore into it.  To my utter dismay there were no instructions on how to rebuild a carburetor…dang it!  So I did what any red blooded American male would do, I did it without the instructions.  I took the carburetor apart, noting where everything came from, matched the gaskets up and sprayed the carburetor with enough carb cleaner that the EPA started checking the local neighborhood water supply for contamination.  To say this thing was filthy would be doing an injustice to the word “filthy”; this thing had potatoes growing in it.  I rejetted the carburetor to one size larger than the jets that were in it since the bike already had a high flow air cleaner.  Time will tell if this was a good move or not but I plan on running Thunder City Monster Baffles in the Screaming Eagle slip on pipes soon so the exhaust will be very free flowing, which works best with big jets but I digress.  I took the new gaskets that most resembled the old gaskets and replaced the old ones, one at a time.  It didn’t take long, maybe a couple of hours because I was being very, very careful and in the process I stripped some of the soft brass screws that were on the carburetor trying to get them off.  A pair of mini-vise grips helped me out there and a quick trip to the dealership replaced those nasty, gnarled up screws with brand new, shiny ones.  The carburetor looked almost new when I went to reinstall it.  I cleaned the K&N high flow filter (which I will provide details about another post) and again, that thing was incredibly nasty.  I mean that thing was so dirty I think I found a Congressman in it (rim shot)...Thank yewwww!  Not funny?  Okay moving on…
I finally reinstalled everything, cleaned up and had it looking good (I was so excited).  I went to start the bike and it wouldn’t kick over but it sounded like it wanted to.  “Whrrrrwhrrrrwhrrrrwhrrrrr!”  What the heck could it be?  Did I forget to put a screw somewhere?  What the heck?  I checked the petcock and sure enough, the fuel wasn’t on.  Okay, chalk that one up to excitement.  I try again “Whrrrwhrrrwhrrrrrwhrrrr!”  Still not starting, it’s 10PM, its 90 degrees in my garage, I have a severe cold (did I mention I had a cold?) so I went to bed. 
Rule #1 of working on your own scoot; never do anything when you’re frustrated!!!
The next morning I jump on a Harley Davidson tech forum and asked for help.  Someone asked if I hooked up the fuel line.  Duh, yes…next question please.  Someone else asked if I checked the petcock.  I didn’t own up to the fact that I did indeed leave it shut off earlier, I just assured them that I did check it.  Lastly someone asked if I hooked up the vacuum line.  I immediately thought “Vacuum line?  There was a vacuum line?” and Googled it.  Sure enough there it was I can’t believe I forgot such a major detail.  I thanked everyone and reassured them that I had things in hand now. 
I went home, plugged up the vacuum line and the bike immediately fired up.  “Victory!” I thought to myself as I triumphantly goosed the throttle over and over again.  Soon I started smelling gas, a lot of gas.  I stuck my hand near the carburetor under the air cleaner while revving the engine and felt a mist hit me.  I looked and saw my hand was damp with gasoline.  I quickly shut the bike off, shut the fuel off and looked to try and pinpoint exactly where the carburetor was leaking.  There was gas everywhere so I quickly removed the air cleaner and carburetor (which I was getting pretty good at by now) and dumped the remaining fuel it had in it in my front yard just outside of my garage.  The EPA was really getting angry by now.  I cursed my luck and noted that it looked like fuel was coming out of the accelerator pump on the bottom of the carburetor.  “Now what?” I thought to myself.  I was pissed and frustrated so I wiped all the gasoline up and went to bed for the night.
The next weekend I was feeling better, optimistic and somewhat resigned to possibly having to have a professional take a look at my carburetor.  I thought it wouldn’t hurt to have just one more look at everything though and I took the carburetor apart again.  I made sure the float in the float bowl moved freely, checked that all the gaskets were aligned and double checked the accelerator pump gaskets.  There is a tiny, itty, bitty little gasket in the accelerator pump that lines up with a pinhole and sits in a recess in the carburetor.  I was 90% sure it was the right gasket but truthfully, when they get that small it’s hard to tell.  I decided to just go up to the dealership and pay the $1.80 it took to buy a new one just to be sure.  I replaced it, tightened the bejeebers out of each and every screw, and carefully rebuilt the carburetor (this time without the influence of cold medicine).  I reinstalled it and went to bed without trying to start the bike; I was tired and didn’t have the emotional capacity to face another failure at that moment.
The next day I come home from work, change clothes and walk out to the garage to start up the bike in full anticipation that I’m about to have to clean up yet another gasoline spill.  I rechecked all my connections on the carburetor (including the vacuum line) and fired it up. The bike backfired and started right up.  I adjusted the mixture screw and idle speed until I could let go of the throttle and it wouldn’t die on me with the enricher still pulled out.  After the bike warmed up it idled without the enricher and I continuously looked for any sign of a leak seeing nothing.  I backed the bike down the driveway halfway expecting it to stutter and die or start blowing gas but it just idled as happily as could be.  I kicked it into gear and raced it up and down my street a few times, no issues.  I decide to go around the block a couple of times (but not further than I could push it), still no issues.  Now I was starting to grin like an idiot on Christmas.  I decided to take her on the freeway, unmercifully gunning the bike in every gear, even redlining it a couple of times to try and find a “dead spot” in the carburetor or experience the dreaded “carb fart” that comes with a misadjusted carburetor.  It performed flawlessly and was running like a new bike.
I came home happy, kissed the wife, hugged the kids and kicked the cat.  I was on top of the world.  I couldn’t believe I rebuilt a carburetor all by my lonesome, plus I learned a lot about my bike (which is the point right?).  I had a new level of confidence and felt the satisfaction that only hard work and trial and error gives.  A few things I learned:
1.) Rule number 1 is always going to be, never work on your bike when you’re frustrated or angry.
2.) Document everything as you remove it and/or take it apart either with pen and pad, digital camera, etc.  Keep your screws in the original order and if at all possible, keep the parts as fully assembled as possible until you are ready to work on them at that moment.  If you’re going to walk away for a while, reassemble as much as practical since it only takes a minute to undo later but a lifetime to find that stupid tiny screw you lost (which is inevitable if you leave them lying around).   
3.) Be prepared for failure and ready to address it if and when it comes.  Don’t jump up and down cursing your luck and asking God why he hates you, if you work on your own scooter not everything will go your way all the time.  Just be ready for it and refer to rule number 1 when it happens.
4.) Those little parts diagrams at the dealership that show every screw and washer to a given part are an excellent reference to make sure you have everything where it belongs when rebuilding a part.  Plus they will give them to you free.
5.) It is better to have a service manual than to not have one, it will save you time and it will save you frustration.  If you have to ask a friend to borrow theirs, if they’re smart they’ll say “no” but maybe loan you the money to buy your own instead.
6.) Know when to stop and ask for help.  Don’t make any permanent changes to your bike or parts without consulting expert or experienced advice.  This involves anything having to do with a drill, angle grinder, saw, etc.  In fact, try to avoid power tools altogether if you can.
7.) Nothing on your bike is as hard to fix as you first suppose it to be.  It’s the stuff you think is “easy” that will hose you up.  In this case it was a tiny $1.80 gasket/o-ring.
8.) Don’t rush the job.  If you don’t have a few days in a row to work on your bike and can afford to let it wait, then let it wait until you have the time.  A good indicator of whether or not you can let it wait is to ask yourself “am I sitting on the side of a freeway right now?”  If the answer is "no", it most likely can wait. 
9.) Some things in life are worth the extra $10.00 to $20.00.  The EZ-Just screw is one of them.
10.) Last but not least the best trainer in the world is experience.  You learn by doing.
Coming to remove your Harley Davidson carburetor (a picture tutorial).


  1. Good Stuff. I'm attempting my own rebuild and appreciate the insight of your experience

    Fellow Harley Owner

  2. Excellent job , well written, humorous and informative

  3. I woke up the house laughing, good story with lots of humor, thumbs up man, I can relate, asking God why he hates me, then when it all works hug and kiss and grin like its Christmas! thank man ride safe. Daniel.

  4. Where are the photos? Guide for dummy s like me :)
    I just started on mine and I'm already frustrated

  5. Hahaha, Great story. I'm glad I looked online for the help and was fortunate to find your awesome story. I will attempt to rebuild my carburetor this weekend and will keep all your learning experiences in mind. Thank you.

  6. Rebuilt the carb for the first time. tried to fire it up and nothing. Some starting fluid will fire it, so it's not getting gas. Next step is apparently checking the vacuum line.

  7. Are we the same person? I recently got a 98 Dyna with SE pipes and rebuilt the carb myself. Haha. Nah. Mine is a Low Rider. I found out carbs are simpler than they appear...just a lot of little parts. Congrats dude!