Tuning a Zenith 14992 Carb on a 1/2 VW

Discussion in 'Half VW' started by Dee, Dec 6, 2018.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Dec 6, 2018 #1

    Dee

    Dee

    Dee

    Member

    Joined:
    May 11, 2018
    Messages:
    14
    Likes Received:
    2
    Location:
    Baton Rouge, LA, USA
    I have a Hummel 45 hp 1/2 VW engine with a Zenith 14992 carburetor. I attempted to adjust the carburetor per the Hummel manual to no avail. The engine stutters with the advance of the throttle. Also, and most concerning, the engine kills when running at 2300 RPM or full throttle. Per Scott Casler at Hummel, it's not getting fuel… however, fuel pressure gauge is showing 3 PSI plus. Any experience with tuning a Zenith carburator would be appreciated period.

    Thanks for your response, Dee
     
  2. Dec 6, 2018 #2

    N8053H

    N8053H

    N8053H

    Well-Known Member

    Joined:
    Jan 31, 2013
    Messages:
    2,521
    Likes Received:
    441
    Location:
    Right here in front of my computer
    Check and see if it will run with the choke applied. You spoke with Scott and told him you have this series Carb on your 1/2vw?
     
  3. Dec 6, 2018 #3

    akwrencher

    akwrencher

    akwrencher

    Well-Known Member HBA Supporter

    Joined:
    Oct 16, 2012
    Messages:
    1,104
    Likes Received:
    393
    Location:
    Gustavus, AK
    Before tuning a carb, you need to know if you have any vacuum leaks, timing is good, etc, and that the carb is clean and in good condition. Forgive me if you are already there, but you made no mention of the situation or condition of the engine.....
     
  4. Dec 6, 2018 #4

    N8053H

    N8053H

    N8053H

    Well-Known Member

    Joined:
    Jan 31, 2013
    Messages:
    2,521
    Likes Received:
    441
    Location:
    Right here in front of my computer
    When it comes to the 1/2vw, the zenith carb is not used straight out of the box. It must be opened up and a jet must be solder shut. I have series 12665 zenith carb. This is the carb needed for the 1/2vw. I believe the series you mentioned is used on a Full vw and not the 1/2. Call Scott and speak to him about this.

    If you need a carb for this 1/2 let me know. I have one in like new condition. It will need to go to Scott and have him do his little thing to it. Then it will be good to go. You can have this carb for 100 bucks. I spent 350 bucks for the one I had on my 1/2 vw. The last carb I sent to Scott for a friend who has a 1/2 vw to have Scott solder this jet closed. It cost my buddy 25 bucks to have this done. What was nice when my buddy got this carb back he knew the carb was good to go. If there was any problems it would not be carb related. His engine ran great after Scott worked on this carb. Before Scott did this work the engine would load up at mid throttle and die.
     
  5. Dec 6, 2018 #5

    Dee

    Dee

    Dee

    Member

    Joined:
    May 11, 2018
    Messages:
    14
    Likes Received:
    2
    Location:
    Baton Rouge, LA, USA
    Thanks to everyone for your advice and information. My Hummel engine, carb, etc. is new from Scott Casler and was pre-run at Hummel; i.e. engine and carb in new condition (first run). I assume that Scott would have sent me the correct carb for the engine and it would be set up correctly. I'll check with Scott. I will check for vacuum leaks, timing, etc. I really appreciate your advice. . . . . Airport mechanics around me do not work on VW engines.

    PS: It did seem to start easier with choke and / or aux. fuel pump on. (equipped with mechanical and aux. fuel pump).
     
  6. Dec 6, 2018 #6

    N8053H

    N8053H

    N8053H

    Well-Known Member

    Joined:
    Jan 31, 2013
    Messages:
    2,521
    Likes Received:
    441
    Location:
    Right here in front of my computer
    Dee well shucks this goes to show the number on these carbs is confusing to say the least. Why Scott is my go to man when it comes to anything VW related to aviation. He knows his stuff. If Scott ran this engine and all was good, it is something you have there or something you did. Not really much to cause air leaks. The rubber tubes connecting the intake would be about it or the only place I could see this happening.

    You say it starts easier applying choke. My 45 hp 1/2 vw would not start cold unless you chokes it. It could have been 90 outside and it still needed choked. All carb engines do. Without going into fuel mixture ratio's at different engine temps, lets just say this is the nature of the beast. The colder the outside temp the richer mixture needed to start a cold engine.

    The best way to detect what you have going on is start your engine. As you apply throttle and she starts to die try applying choke. Don't just pull the choke and give it full choke, you may flood the engine. Pull the choke out slowly and see if the engine smooths out. If it does you are running lean for some reason. If it just dies you are not running lean. This will tell you a lot.

    But from what you explain, it sound like fuel starvation to me.
     
  7. Dec 6, 2018 #7

    N8053H

    N8053H

    N8053H

    Well-Known Member

    Joined:
    Jan 31, 2013
    Messages:
    2,521
    Likes Received:
    441
    Location:
    Right here in front of my computer
    Dee are you using a gascolator purchased from GP? Something tells me you are.
     
  8. Dec 6, 2018 #8

    delta

    delta

    delta

    Well-Known Member

    Joined:
    May 27, 2011
    Messages:
    1,929
    Likes Received:
    193
    Location:
    Brookside Utah
    As an updraft carb I doubt if it has an accelerator pump. The engine will have to be up to temperature before it would stop hesitating. Keep turning the mixture out after warm until it starts running bad and then turn it back in until it runs smooth. Run it a little rich I'd say until you get it broke in, but keep an eye on your plug color.
    There's a chance a piece of dirt got lodged in your main jet but I kind of doubt it. There's also a chance your float level's to low too, but I doubt that also. If adjustment is ineffectual you'll have to clean out the carb.
    Sometimes a small piece of dirt can be sucked on through by revving it up and momentarily choking it down.
     
  9. Dec 6, 2018 #9

    N8053H

    N8053H

    N8053H

    Well-Known Member

    Joined:
    Jan 31, 2013
    Messages:
    2,521
    Likes Received:
    441
    Location:
    Right here in front of my computer
    No VW engine I have come across hesitates one bit. They run great from start up to shut down. Also no need to mess with mixture. Set it and forget it. Unless you like to run LOP during taxi as I do.
     
  10. Dec 6, 2018 #10

    Rockiedog2

    Rockiedog2

    Rockiedog2

    Well-Known Member

    Joined:
    Dec 12, 2012
    Messages:
    2,286
    Likes Received:
    1,607
    I'm curious...is that a recent built engine or one that's been around a while and just hasn't been run?
    Last time I flew my Legal Eagle was a couple years ago and around that time Scott had issued a "directive" that the 45 not be run over 3K rpm due to there had been a couple cranks break. Well, I decided after some research and thought to pretty much run mine like I had been doing. He was recommending at that time that the cylinders be pulled and shimmed and the comp lowered and it would be a 42 then. I didn't do that.
    What's the status of all that now?
    My 45 came new from Scott and I had problems with it. I won't go into all that but will give you the carb stuff. It never would run right. I intensively/extensively worked on that carb and everything imaginable on the engine looking for the problem. Had all the stumbling, won't turn up, won't make power, rough idle, popping, missing both on the ground and airborne type problems. Changed carb to a bigger one Scott sent me and then a smaller one. Had the mixes all over the chart, plugs, even plumbed the crankcase for a pressure gauge looking for excessive drag in the case. Pressurized the carb; it was leaking at the throttle shaft fixed that and still wouldn't run right. I got about 12 or 15 pages of all that was tried and the results. It performed near exactly like the good running 37 I took off it. Cleared the trees here at the strip just like that one did. Couldn't tell any difference. Best pull was 180#, the 37 consistently pulled 175#. A techie friend in CA precision built a club and computer program to plug the results into and it spits out the horsepower. Homemade dyno. My 45 made 38.2, friend with a new 45 had been following my efforts so sent him the club. His made 37.
    The intake Y on the 45 is longer and bigger diameter. The mix has gotta be sucked up a long way to get to the intake. I decided there was a breathing problem and changed out the Zenith for dual mikunis. Holy crap...even before it was tuned it was an entirely different motor. Didn't take long to get it singing with those carbs. Experimented with jets and found the sweet spot. I consider dual egt essential if you really wanta get the most out of it. The power doesn't come on til around 1300 egt and max egt per Scott is 1400 so we don't have a lotta room to play with there. I tuned mine for 1350 at ful throttle each side; a 150 jet and a 140. Now it runs like what it is a 1200 cc hot rod.
    There's a lotta power potential in that motor but in my experience it'll never get anywhere near max with a zenith on it. IMO, the only way to go is dual Mikunis. Some are perfectly satisfied with it with the Zenith but I found that a 37 will do as well on my plane and would rather have it if other choice is a 45 with a Zenith.
    Good luck with that and if I can be of help just ask.

    Edit
    my plane climbed average 400 fpm with both the 37 and the Zenith "45". With the dual Mikunis it climbs 865 fpm and pulls 205
     
  11. Dec 6, 2018 #11

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,145
    Likes Received:
    6,035
    Location:
    USA.
    I also have problems with the Zenith until I install the hot oil box. Was not getting consistent CHT and EGT's. Mixture was lean and rich and back and forth on each cylinder. The problem was the long intakes length and the intakes being cooled by the incoming air from the air intake before getting to the heads. The charge was condensing into droplets before getting down into the heads then the droplets collected and ran into the intake of the heads at one time making the mixtures rich, then as the droplets were collecting the cylinder would be running lean. Heating the intake at the base of the carb with the hot oil stopped all of that and it was a different engine. Powerful and smooth and adjusting the carb was very easy. Like you Joe, my mixture was all over the place. While flying the engine always had a roughness that shouldn't been there when everything was balanced. Sometimes it even missed a beat while flying. Never missed a beat since then.

    Joe, maybe you were having the same problem and now your very short length intakes solved the problem.
     
  12. Dec 7, 2018 #12

    Rockiedog2

    Rockiedog2

    Rockiedog2

    Well-Known Member

    Joined:
    Dec 12, 2012
    Messages:
    2,286
    Likes Received:
    1,607
    Could be Dan. The intake tubes on both the 37 and the 45 both sweated as did the carb hanging down under there.
    But I could never go back to the zenith cause of the weight difference alone. It's in my notes somewhere... seems like the Zenith and associated Y and tubes etc weighed 7.5# and the 2 Mikunis less than 2. I ended up extending the mount 2" to make up for it. My 37 weighed 85# dry; the 45 with Nikisil 94 mm cylinders, 86 crank and 2 carbs ended up 79# dry. and Leonard always said go to dual Mikunis and you'll be amazed at the difference. He was right in my case.
     
  13. Dec 7, 2018 #13

    Dee

    Dee

    Dee

    Member

    Joined:
    May 11, 2018
    Messages:
    14
    Likes Received:
    2
    Location:
    Baton Rouge, LA, USA
    Yes, gascolator from Aircraft Spruce.
     
  14. Dec 7, 2018 #14

    Marc W

    Marc W

    Marc W

    Well-Known Member

    Joined:
    Apr 1, 2017
    Messages:
    299
    Likes Received:
    203
    Location:
    Colorado
    The Zenith carb on my CX4 was full of aluminum shavings. I figured some disgruntled Zenith employee thought he would get even with someone. The shavings were everywhere in the passages. In the emulsion tube and packed around the idle screw. It ran better after I cleaned them out.
     
  15. Dec 7, 2018 #15

    N8053H

    N8053H

    N8053H

    Well-Known Member

    Joined:
    Jan 31, 2013
    Messages:
    2,521
    Likes Received:
    441
    Location:
    Right here in front of my computer
    In almost 10 years flying behind a 1/2 vw I never had these problems. I too had Scotts 45 hp version of this engine. I loved the zenith carb. Both Scott and I believe the broken cranks are due to dual carb setup. If a throttle cable stretches and the carbs get out of sync you now have an engine that is acting like two separate engines. But with a common crank. Something must give. Scott and I talked about this in length.

    If you have a carb leaking at the throttle shaft, you have a carb with a lot of hours on it.
     
  16. Dec 7, 2018 #16

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,145
    Likes Received:
    6,035
    Location:
    USA.
    I didn't weigh my Zenith carb , but it is light. Light 1 1/4" dia aluminum intake Y , light wall SS intake tubes above the cylinders, ( not as light weight as aluminum but couldn't find alum tube bent to the radius as I needed) Light wall 9.5" SS 1 1/2" dia exhaust tubes, ( to take the heat). Guessing the total of about 4/4.5 lbs. My complete firewall forward weight as you unbolt the engine mount from the firewall is 141 lbs. Ready to start and fly. I also replaced the round steel sump cover on the bottom of the engine case with one I made from alum. Used an aluminum oil pump cover plate instead of the heavy steel cover plate.
    A 4 cylinder VW long block weights 116 lbs. With a firewall forward weight of 141 lbs. So everything else firewall forward weights a total of 25 lbs. Carb , airbox, intake manifold with couplings and clamps, Exhaust pipes with one SS carb heat box and nuts and gaskets, Prop hub , Prop and prop bolts, GPS mag mount, Slick mag with harness and aviation spark plugs, 4130 steel engine mount and shock rubbers and bolts to engine . SS oil hose from oil pump to hot oil box , SS hose from hot oil box to VW doghouse style oil cooler, aluminum box over oil cooler , SS oil hose from oil cooler to engine block. Aluminum Oil block off plate on top of engine. Alum air scoops over cylinders and two 2" dia scat air hose to oil cooler box. Also alum baffle below the engine case lower fins on bottom of engine.
     
    Last edited: Dec 7, 2018
  17. Dec 8, 2018 #17

    Dee

    Dee

    Dee

    Member

    Joined:
    May 11, 2018
    Messages:
    14
    Likes Received:
    2
    Location:
    Baton Rouge, LA, USA
    Update on tuning my Zenith 14992 carburetor. Today I ran the Hummel 1/2 VW utilizing only the engine mounted mechanical fuel pump. The engine ran for 30 or 40 seconds then it killed. I turned on the auxiliary fuel pump and then the engine ran with no problem. I disassembled the mechanical pump and found broken parts inside this new mechanical pump (the complete engine is new). Thanks for all your suggestions… It seems I have solved the problem.

    My settings on the Zenith 14992 carb is currently 3 1/4 turns open on the main jet and one and three eights turns open on the idle jet. I would like to know what others have found to be the best settings for the main jet and idle jet on this Zenith 14992 carburetor. Thanks for your feedback.
     
    akwrencher likes this.
  18. Dec 8, 2018 #18

    Dana

    Dana

    Dana

    Super Moderator Staff Member

    Joined:
    Apr 4, 2007
    Messages:
    8,633
    Likes Received:
    3,015
    Location:
    CT, USA
    I too had good results with the Zenith on my Mosler 1/2 VW. I don't remember the settings, the manufacturing tolerances are different enough that no two engines will be the same. I had bought aluminum tubing to wrap around the intake manifold to use oil to heat the intake like Pop's heat box but I never got around to it before selling the plane.
     
  19. Dec 8, 2018 #19

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,145
    Likes Received:
    6,035
    Location:
    USA.
    Seeing all the 1/2 VW engines with the aluminum hot oil tube wrapped around the intake and asking why, is what I copied. Then I realized the Lyc did the same thing on their engines.
     
  20. Dec 8, 2018 #20

    N8053H

    N8053H

    N8053H

    Well-Known Member

    Joined:
    Jan 31, 2013
    Messages:
    2,521
    Likes Received:
    441
    Location:
    Right here in front of my computer
    Make sure the pumps you use flows fuel when in the off position. If something happens to said pump and it shuts off you want it to still flow fuel. It sounded like a fuel starvation issue. Glad you found it. But this is why I like gravity feed.
     

Share This Page



arrow_white