My Trabant and poor mpg
Discussion
Some of you may know of my Trabi and the woes I'm having with fuel consumption.
Long story short, she was running like a dog when I rescued her from a barn and the carburettor was knackered. So I got a new one from Germany. She runs fine now, but only does 18mpg at best which is about half what she should be doing. There are no leaks in the induction side of the engine, the suction on the carb is akin to a vacuum cleaner. Same at the air intake for the air filter. And she stalls if you cover the air intake at all.
However, a strange thing happened by chance a moment ago, I hadn't turned the fuel tap on to move her into the garage, started fine and drove into the garage. As she started to run out of petrol she started to rev up significantly. There are no fuel leaks anywhere, but the fuel flow when the engine is running is high. What does this suggest? Not enough air getting to the mixture? I can regulate the fuel flow by a crude method of not turning the tap on fully, but it's been a long day and I'm struggling for answers.
Other than the fuel consumption, she starts and runs fine and ticks over beautifully.
Long story short, she was running like a dog when I rescued her from a barn and the carburettor was knackered. So I got a new one from Germany. She runs fine now, but only does 18mpg at best which is about half what she should be doing. There are no leaks in the induction side of the engine, the suction on the carb is akin to a vacuum cleaner. Same at the air intake for the air filter. And she stalls if you cover the air intake at all.
However, a strange thing happened by chance a moment ago, I hadn't turned the fuel tap on to move her into the garage, started fine and drove into the garage. As she started to run out of petrol she started to rev up significantly. There are no fuel leaks anywhere, but the fuel flow when the engine is running is high. What does this suggest? Not enough air getting to the mixture? I can regulate the fuel flow by a crude method of not turning the tap on fully, but it's been a long day and I'm struggling for answers.
Other than the fuel consumption, she starts and runs fine and ticks over beautifully.
Carb is brand new, came from a respected Trabant specialist in Germany. I haven't taken it apart, because there are only three moving parts on it!
I'm going to replace the spark plugs, and if that doesn't help, then I will have to delve into the inner workings of an East German carburettor and see what jets it is fitted with.
I'm going to replace the spark plugs, and if that doesn't help, then I will have to delve into the inner workings of an East German carburettor and see what jets it is fitted with.
I didn't touch the carb, it comes set up and ready to go. However, because of the poor consumption I did have a fiddle with the mixture screw and improved things somewhat. It has a very simple set up, an idle jet and a butterfly that opens the main venturi. The choke seems to be by means of shutting off some air enriching the mixture.
When she's up and running the choke causes the engine to falter and die, further giving weight to too rich.
I've got two new spark plugs on their way, the existing ones are looking quite black and sooty. It runs NGK B6HS am thinking I might try a grade hotter plug? At the moment I'm going with the existing temp.
There's really not a lot to these motors, two cylinder two stroke, single carb and a coil per cylinder using a pretty good electronic ignition. I'm not certain but I'd be fairly sure the timing is correct, because she goes like an absolute train and doesn't smoke when warm. Both indicators of good timing set up.
Definitely no leaks, I've left her ticking over for ages and checked. So the float must be closing off supply to the bowl.
When she's up and running the choke causes the engine to falter and die, further giving weight to too rich.
I've got two new spark plugs on their way, the existing ones are looking quite black and sooty. It runs NGK B6HS am thinking I might try a grade hotter plug? At the moment I'm going with the existing temp.
There's really not a lot to these motors, two cylinder two stroke, single carb and a coil per cylinder using a pretty good electronic ignition. I'm not certain but I'd be fairly sure the timing is correct, because she goes like an absolute train and doesn't smoke when warm. Both indicators of good timing set up.
Definitely no leaks, I've left her ticking over for ages and checked. So the float must be closing off supply to the bowl.
Tyre Smoke said:
Agree. But why?
Could be any one of the usual reasons;) but your new carb has to be a major suspect. Check the jet sizes, try and get a selection of jets to play with if you can.Also float level. Try bending float arm down a little to lower the level. Carefully! And take pics so you can return it to how it was if necessary.
Good luck!
dontlookdown said:
Could be any one of the usual reasons;) but your new carb has to be a major suspect. Check the jet sizes, try and get a selection of jets to play with if you can.
Also float level. Try bending float arm down a little to lower the level. Carefully! And take pics so you can return it to how it was if necessary.
Good luck!
Float level is the simplest thing to change. As you said, check the level, set it lower, and try. There's nothing to lose.Also float level. Try bending float arm down a little to lower the level. Carefully! And take pics so you can return it to how it was if necessary.
Good luck!
At worst, you have to set it back.
Tyre Smoke said:
dontlookdown said:
High fuel consumption and sooty plugs suggest it is running rich.
Agree. But why?Know anyone with an old school colourtune kit - we used to use them back in the day to get mixture close before doing the usual under load plug chop after max revs full throttle on a long shallow incline (mainly cos none of us liked melting pistons)
I had a bit of a middle of the night idea. The fuel tap is off in the 3 o'clock position, on in the six o'clock position and reserved is 9 o'clock.
There is a rudimentary fuel flow meter that is also an 'econoguage' for when you are driving along. The idea being you keep it in the green and out of the orange for maximum efficiency. The harder you press the accelerator the faster the fuel flows.
So yesterday I tried an experiment. I went for a drive. Normally I turn the tap to six o'clock and off I go. Fuel flow is usually all the way into the orange no matter how gently I drive. Yesterday I restricted the flow by turning it to about half past four. Fuel flow was well down in the green even with harder driving. No noticeable difference in performance, better if anything. So I've ordered some thinner diameter fuel hose. It's a bit tricky to get the fuel flow right, too little and she starves, too much and I'm back in the orange. Also, far far less smoke when warmed up. I used to get a bit of blue up hills and under load, but nothing noticeable yesterday.
I'm thinking it must be a float thing. Obviously when parked or refuelling the fuel is off, so no opportunity to leak. And when driving it is sucked in to the engine.
There is a rudimentary fuel flow meter that is also an 'econoguage' for when you are driving along. The idea being you keep it in the green and out of the orange for maximum efficiency. The harder you press the accelerator the faster the fuel flows.
So yesterday I tried an experiment. I went for a drive. Normally I turn the tap to six o'clock and off I go. Fuel flow is usually all the way into the orange no matter how gently I drive. Yesterday I restricted the flow by turning it to about half past four. Fuel flow was well down in the green even with harder driving. No noticeable difference in performance, better if anything. So I've ordered some thinner diameter fuel hose. It's a bit tricky to get the fuel flow right, too little and she starves, too much and I'm back in the orange. Also, far far less smoke when warmed up. I used to get a bit of blue up hills and under load, but nothing noticeable yesterday.
I'm thinking it must be a float thing. Obviously when parked or refuelling the fuel is off, so no opportunity to leak. And when driving it is sucked in to the engine.
Edited by Tyre Smoke on Saturday 28th August 11:00
Tyre Smoke said:
I had a bit of a middle of the night idea.
<snip>
So I've ordered some thinner diameter fuel hose. It's a bit tricky to get the fuel flow right, too little and she starves, too much and I'm back in the orange. Also, far far less smoke when warmed up. I used to get a bit of blue up hills and under load, but nothing noticeable yesterday.
I'm thinking it must be a float thing. Obviously when parked or refuelling the fuel is off, so no opportunity to leak. And when driving it is sucked in to the engine.
That is a terrible idea - sorry but it really is - set the float height and check the main jet size<snip>
So I've ordered some thinner diameter fuel hose. It's a bit tricky to get the fuel flow right, too little and she starves, too much and I'm back in the orange. Also, far far less smoke when warmed up. I used to get a bit of blue up hills and under load, but nothing noticeable yesterday.
I'm thinking it must be a float thing. Obviously when parked or refuelling the fuel is off, so no opportunity to leak. And when driving it is sucked in to the engine.
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