Thanks Rudy---That may be a simple carburetor, but I've seen the video of your engine running in hit and miss mode, and its beautifull!!! Novice???---I don't think so!!!
Brian Builds the Kerzel Hit and Miss I.C.
- Thread starter Brian Rupnow
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1hand said:
Thanks 1Hand---This is the first I have heard that its been published.---Brian
Now I know why the Kerzel lever had that big ugly end on it----So I could add an adjusting spring like this to the end of it to fine tune the hitting and missing!!!
The thought was as good as the deed on the kerzel lever spring adjustment add-on. However, I'm not happy with the way this engine runs. Its just not consistent. I have played with the 3 available adjustments, valve timing, ignition timing, and needle valve settings for two weeks now, and although the engine runs, it does not run consistently. The valves are sealing well and I have good compression. When the engine is running, it needs to run at a very high speed so as not to stumble. When I do get it adjusted to a more moderate pace, sometimes it runs as expected, but most of the time it runs for a very short time, then stumbles and quits. It always starts right back up again, but its a gamble as to whether or not it will stay running. I have everything set up fine for the hit and miss cycle, as proven by the bob-weight/lever/valve action when I speed the engine up or down by running it with my variable speed drill, but the engine doesn't run good enough to get into the hit and miss cycle. I know that my points, condenser, and coil are working correctly. The sparkplug I made appears to function correctly---If it didn't, the engine just plain wouldn't run for short or extended periods of time as it does. Valve and ignition timing are something that don't change. Once they are set, they are a constant, and will always give the same results unless a set screw holding the cam position comes loose, and that isn't happening here. The only variable left is this carburetor. It appears to function adequately, but it is the only "black art" peice on the entire engine, where I can't really know whats happening with it. I've seen a number of engines posted on here with the same bore and stroke as my engine that run just beautifully using the simple Upshur carb, which has a 1/8" dia. main air passage and no venturi. My carb has a 1/4" dia. main air passage and does have a venturi. If I assume that all other things are more or less identical engine-wise, then perhaps my engine would do better with the 1/8 bore upshur carb. That carb is not a terribly complex part to make, and I seem to have ran out of other options to get a good consistent runner.
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Brian,
If you haven't been, try filtering your fuel. Coleman fuel used to be notorious for lint in the fuel. On my Tiny, filtering the gasoline improved the consistency of the runs a lot. Of course the needle valve clearance is smaller on mine but the subject has come up with the larger engines also. I am going to build a fuel filter to go in line with the fuel line to the carb from the tank. It's drawn -- I just haven't gotten around to building it yet.
A cut up section of coffee filter seems to work fine. That's what I use to filter the fuel from bulk to my working bottle. I plan to use 25 micron lab filter paper in the in line filter.
Gail in NM
If you haven't been, try filtering your fuel. Coleman fuel used to be notorious for lint in the fuel. On my Tiny, filtering the gasoline improved the consistency of the runs a lot. Of course the needle valve clearance is smaller on mine but the subject has come up with the larger engines also. I am going to build a fuel filter to go in line with the fuel line to the carb from the tank. It's drawn -- I just haven't gotten around to building it yet.
A cut up section of coffee filter seems to work fine. That's what I use to filter the fuel from bulk to my working bottle. I plan to use 25 micron lab filter paper in the in line filter.
Gail in NM
What is the RPM at which it runs well and rpm when it runs poorly? What is the venturi throat diameter? I think you're getting to the source of the issue looking at the size of the carb throat. I wasn't following this thread until today. I just read all of it after bumping into the TB3 revival thread. This thread was great.
The main bore thru the carb is 1/4". The reduced diameter at the venturi area is 3/16". As for the rpm---I don't know, but click on either of the videos I posted of the engine running and you can get a good feel for the speed its running at.----Briandieselpilot said:
OK, from the clip I got about 1300 RPM. http://www.tunelab-world.com/rpmsound.html this app was not very good, but it did pick up 1300 when you weren't talking.
At that speed I would like to use a venturi throat of 2mm or smaller. The velocity through the carb is low right now. There isn't much chance of atomization. Fuel is running along the intake tract wall and being drawn into the engine inconsistently. For reference, I use a 4.1mm throat in a .48ci four stroke that runs at 10,000 RPM. And I'm working on a .52ci four stroke engine that runs ~4kRPM and makes 100+W at the shaft with a 1/16" throat. These are OS airplane engines.
Going to a smaller venturi throat will increase the fuel draw and you will find the needle to be more sensitive.
At that speed I would like to use a venturi throat of 2mm or smaller. The velocity through the carb is low right now. There isn't much chance of atomization. Fuel is running along the intake tract wall and being drawn into the engine inconsistently. For reference, I use a 4.1mm throat in a .48ci four stroke that runs at 10,000 RPM. And I'm working on a .52ci four stroke engine that runs ~4kRPM and makes 100+W at the shaft with a 1/16" throat. These are OS airplane engines.
Going to a smaller venturi throat will increase the fuel draw and you will find the needle to be more sensitive.
Yes, should have asked for area. I do take this into account. In that case 3/16" is equal to area of a 2.3mm hole. I'd still go smaller. It certainly won't inhibit the engines performance. That probably wouldn't happen until area was less 1mm diameter equivalent or .15" bore with the .125" spray bar.
Greg
Greg
Brain, got The Home Shop Machinist in today and you are in there, congratulations, shame they put the main support on a page split, a bugger to see, thanks again, Lathe Nut
Well there, by Golly!!! Other than the fact that I used about 5 times more soft solder than I really wanted to, old Hamilton would be proud of me. What we have here is the 1977 version Upshur engine carb, with a 5/16" thread on it to fit my Kerzel build. My God---Its tiny compared to what I've got on the engine right now. Thats the first time I've used soft solder in about 25 years---amazing how little heat is needed after using silver solder for the last 3 years building engines. Tomorrow I'll see if it improves the Kerzel.
Thanks Jpeter. The money from that article is going to buy me a quick change toolpost!!! Here is a video of the engine running on the carb I built yesterday afternnoon.
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Hi Brian, it seems that your engine is running much better and at a slower pace! That simple little carb did the trick!
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That seems a whole lot better Brian! THe number of times I've seen teenagers fit bigger carbs to their scooter/ped bikes as a 'tuning mod' only for them not to idle or pick up smoothly, I did suspect low airspeed might be a problem.
I had one great 15 minute endurance run, then it started breaking down, stumbling, same old, same old. okay---It probably wasn't the carb. when it began to stumble and fart it still had good compression and would start up again without a problem, but only run for a short time. I notice that my home made sparkplug really suffers badly from any flooding. It won't clear itself if it does get flooded and the fuel seems to be leaching up between the corian and the outer metal shield. I think I'm going to order the closest factory made sparkplug and give that a whirl.
