1. trondd

    trondd Loyal Comrade

    How does one go about tuning the Trabi carb? I've got a 28HB-2 and the only adjustments are idle mixture and idle speed.

    I don't quite get the interaction between the mixture adjustment and the throttle speed adjustment. The idle "mixture" adjustment seem to be more about how much of the mixture and not the richness of the mixture, as that's accomplished by the size of the idle air jet and idle fuel jet as far as I can tell.

    So what do I adjust the mixture for? Highest RPM sounds silly if it's just opening up the tap. The manual states it's tuned from factory for lowest CO but I can't measure that. On a "modern" carb you can tune for highest vacuum but the Trabi has no vacuum ports.

    Do you just set it to 2 turns out then tweak the rpm with the idle speed screw and just get on with it?
    trabant601 likes this.
  2. A Spooky Ghost

    A Spooky Ghost Loyal Comrade

    The mixture screw is for the low speed circuit. In other words- the fuel air ratio, at idle. When it is working right, the idle will smooth out, or get worse depending on the way you turn it. A good way to do this is to :

    Warm the car up, make certain the choke is all the way off. Then set the idle speed a little bit higher than normal. Now play with that mixture screw until it sounds the smoothest/ and has the highest idle. There is a bit of a delay, after you turn the screw. It is not a instant change.

    Lastly turn the idle screw down to your liking.

    Tada you did it!

    While you are there, put your hand over the opening of the carb- it should instantly die(remove carb elbow first). If you removed the metal carb elbow, and it then runs while your hand is over it- " You have a leak somewhere!". Case halves, cylinders, carb base, and or crank seals :eek:.... Just sayin.
    Last edited: May 1, 2019
    RogerDerSchrauber likes this.
  3. trondd

    trondd Loyal Comrade

    Alright, I finally got around to the Trabi again.

    I put the idle screw back to 2 turns to start with and the car seemed to like it a lot better but struggled to stay running. I gave it another half turn open and that seemed to be good. Adjusted the idle speed with the lights on until it was just running.

    Seemed good on a test drive.
    RogerDerSchrauber likes this.
  4. RogerDerSchrauber

    RogerDerSchrauber Premium Member Forum Donor

    Right on the money!
  5. turbofiat124

    turbofiat124 Premium Member Forum Donor

    I've got this same carburetor on mine. I don't know if I need to bump the idle mixture up a bit or not. The engine has to be pretty much at normal operating temperature or it will stall at red lights. Like within 3 or 4 miles depending upon how cold it is outside. This maybe normal. My Craftsman (Poulan) chainsaw is the same way. It keeps wanting to stall unless it's warmed up. The one I got from Sears before that was even worse so I took it back and they gave me another one. You know, back when there was a Sears....

    As soon as the engine starts, I turn the "starter valve" which really isn't a choke completely off. Otherwise I'm afraid I'll foul the plugs. Which I have done by getting over zealous with the starter valve and filling the parking lot at work with huge plumes of smoke.

    28 HB-2's "starter valves" has a tendency to dump more fuel than necessary if your not careful and foul the plugs. I never pull it out more than 1/4 way.

    So yes that's one reason the engine needs to be completely warm before you try to adjust the idle mixture. That carburetor does seem to have a tendency to want to stall when the engine is not warmed up.

    I've been meaning to put the 28 H-1 (later style) I rebuilt and ran briefly back on because I think the car actually ran better. And I like the fact that it has a fast idle circuit built into the choke. So I don't have to feather the throttle to keep it going when the engine is warming up.

    I noticed this morning my Trabbi was idling allot smoother than usual. The motor was quieter and it was not shaking the car as bad. That almost gives me a bad feeling...

    It had been idling kind of lumpy but not stalling. I guess the later is all that matters.

    I think it's because I haven't driven it much this year and the less it's driven, the more fuel evaporates leaving oil behind. So instead of a 40:1 mixture, it may be closer to a 33:1 mixture (just a guess). It has sat for a couple of months and I was down to three gallons the other day . I think at least one gallon had evaporated in the meantime. Since the oil doesn't really add energy to the fuel, it creates a leaner mixture. I topped it off so I've probably used anywhere from 1 to 2 gallons by now.

    The electronic ignition project is still on the back burner! If you recall, the car made it 20 miles before the plastic ring of magnets wore into the upper module! I think that was due to me using a flat washer under the bolt for extra security. Which warped the plastic ring. So that was counterproductive. I thought the plastic ring might fly off.

    I've got a new module but have not installed it on the plate yet. I need to get this wrapped up because I want to test it during the summer while there is plenty of daylight. That way I can see what I am doing if I need to throw the points breaker plate back on like I did awhile back. And of course it rains all the time in the winter.
  6. trondd

    trondd Loyal Comrade

    I pull the starter valve half way to start. Then push it in until the motor slows down a little. Wait a few seconds and push it in more until it slows, etc. After a minute or 2 the engine is warmed up and running with no additional fuel. It's good to go at that point and doesn't stall. I haven't driven it when the weather is too cold, though.
    RogerDerSchrauber likes this.
  7. A Spooky Ghost

    A Spooky Ghost Loyal Comrade

    Mine has the old style of carb. Needs full choke for the 1st start of the day. Once it fires- I push it all the way in. I might let it warm up 2 minutes(while reving it) before hitting the road. Longer in the winter. Since it has been near 100F' lately, it needs little warm up time.

    Most all 2 stroke engines need to warm up-so they can rev freely. Compression, and timing has a lot to do with it...
  8. turbofiat124

    turbofiat124 Premium Member Forum Donor

    I used to pull the starter valve out all the way (just like I would a typical choke) but seems I'd flood the engine most of the time and have to get out the can of ether or pull the plugs, shake off the fuel and turn the engine over a few times to clear the cylinders.

    So I got to where I'd start out about 1/4 way and if the engine failed to start pull it out more. It seems the colder it is, the more the valve has to be open. Since I've been doing this, I don't think I've had to pull it out more than half way.

    I'd like to find some way of adding a fast idle circuit to this carburetor without having to use the later "fuel saver" carburetor. I just haven't had time to investigate but I've wondered if it was possible to build a hybrid. Use the old style carburetor but the later style elbow that has the choke flapper. If the linkage that runs from the choke to the throttle would hook up. Then wire the starter valve shut with a piece of wire just in case.
  9. turbofiat124

    turbofiat124 Premium Member Forum Donor

    I've been having some idling issues with my Trabbi idling here lately. This carburetor seems to be very sensitive to ambient air temperature, humidity, altitude, etc.

    I can't seem to achieve a consistence idle speed even at normal operating temperature.

    The engine either idles smoothly or it idles too low (whole car shakes and goes on) and sometimes stalls after a few seconds while waiting on a red light to change. The other day it was idling smooth as silk. At 3 gallons, I topped off the fuel tank and this morning the engine stalled after 3 or 4 miles of driving while waiting on the red light to change. The engine should have been warmed up by then. I've got some old pre-mixed 2 cycle fuel I've been trying to get rid of. I know some of it was mixed up back in December but some maybe older than that. I have kept them in sealed containers and it's 100% gas, 87 octane.

    I run old gas in my lawnmowers with no problems but I'm thinking perhaps it's not the fuel but maybe the amount of oil in the fuel. I've heard the more oil you mix, the leaner the burn. Over time, the fuel evaporates in the tank but the oil does not. So the oil ratio get's stronger. I have no idea what the true ratio is right now in the tank.

    I thought maybe it was my headlights. It seems the engine idles better when they are not on. Even though I don't really need them this time of year. But I run them around dawn after getting off work at 6:30 in the morning.

    The downside to running this 60 amp A/C Delco alternator over the original 30 amp generator is it reacts to loads on the electrical system and causes the idle speed to drop. I converted my headlights and fog lights to LEDs (had to use a second step up converter to do it) and now the high beams and fog lights are pulling 4 amps as opposed to around 20. Normally these LED headlights don't make any difference.

    I've also bypassed the retard mechanism on the breaker plate. I stacked a bunch of 1/2" ID O-rings at the base on the piece the points hit against to lock the advance in place. It seems the engine idles smoother with more advance.

    This morning I got home and let the engine idle for a few minutes. Despite stalling on the way home while waiting for the light to change, it never stalled but decided to bump the idle speed up a bit more. Just a hair to where I could tell it.

    Before I start messing with the idle mixture, I'm going to run all of this fuel out and replace it with fresh gas. Years ago I ran several tanks (like 10) with this Opti-II oil. Unlike other oils which are 20 weight, this stuff is 30 weight and you mix it at a 100:1 ratio which covers all ratios. The engine seemed to suffer no ill effects. I have ran it in a small dirt bike which calls for something weird (like 25:1) and it has suffered no ill effects.

    It seemed the engine actually ran better using this Opti-II oil so I'm going to give it another shot.

    OH, one more thing. I discovered I had not flipped the breather tube from winter to summer mode! I've been driving around in 70 to 90 degree weather with the tube pointing down. While at it, I flipped it around to the proper direction.

    Today I started the engine and during warm up never stalled. Usually it dies after backing out of my garage. I got to work after driving 8 miles and it seems to idle much smoother.

    I wonder how much of an effect running that breather tube in the wrong direction has on drive-ability? I would think it would matter more in the winter than summer.
  10. A Spooky Ghost

    A Spooky Ghost Loyal Comrade

    Mine doesn't have any advance stuff, I'm running the EZ-2 kit from Trabi welt. Only draw back is, in the timing. You can only time the #1 cylinder- thats it. So #2 is a few .000's off when it fires. Doesn't seem to matter though.

    Since I did that 80 amp Nissan Alt swap. Mine idles very nicely. even with the lights on. You can feel it though, when it is revved, or taking off from a stop at night. Not to bad though.
    In other words it is consistent, no matter how it acts-it acts the same. Which is a good thing!:D

    Have you checked to see if everything is air tight? Try removing the carb metal elbow, and while it is idling- put your hand over it. It should die instantly. If not, there is a vacuum/ air leak somewhere.
    This causes many random idling/ running issues...... Also if the rings/pistons/bores are really worn, it needs to warm up longer-to build enough compression for a good idle.

    Might be time for a carb clean too.

    I'm sure it runs better with that Opti stuff. Because it has less oil in the engine. I stand by running- 40, or 50:1. No matter what a bottle says, 100:1 just worries me to no end...
    Wonder what a compression test would tell us?

    I had my air cleaner tube flipped wrong for quite some time. Really seemed to matter little. As with everything 2 stroke " your results may vary!" ;)
    Last edited: Jul 5, 2019
  11. turbofiat124

    turbofiat124 Premium Member Forum Donor

    Well this morning, I get home and the engine is idling smooth as silk. So perhaps the breather tube was the problem.

    I should have checked the intake manifold nuts while I had the grill off. Years ago I was messing with the timing and must have gotten the carbon buildup too hot and had a runaway 2 stroke! So I pulled the hose off and laid my hand over the elbow to kill the engine so unless something has changed I got no air leaks.

    Yeah 100:1 sounds weak. A guy I know who works on lawnmowers swears by it. He has never seen an engine failure do to it and I've never read anything negative about this oil on the net. I think Keri has been using some type of oil designed for ultralight Rotex powered engines at a 70:1 mix.
  12. A Spooky Ghost

    A Spooky Ghost Loyal Comrade

    I have not doubt that thin of a Mixture is ok for light lawn equipment. We pull around a lot more weight, than a string trimmer does... Short of running 2 rebuilt engines, until one fails- there will never be a definitive answer. Never seen a "run away 2 stroke", thats a new one..o_O
  13. turbofiat124

    turbofiat124 Premium Member Forum Donor

    You're probably right. I might ought to stick to the 40:1 Walmart oil I've been using. Yeah my engine was like a runaway diesel with a bad turbo!

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