Open Column Twin - Tuning

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cfellows

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I decided I should continue this thread here since this seems to be have become another work in progress.

I got the new flywheels remounted and changed over to a carburetor that I had originally built for the engine. The carb is pretty basic, but it was readily available. The engine ran a little better, but still mostly on one cylinder. And, I couldn't get it to idle very slow.

So, I abandoned the carburetor and decided to go back to a vapor carb. I happened to have a glass jar that was 2 - 3 times taller than the pimento jar I had been using. And, it turns out, the pimento lid was the same screw size as the new bottle, so I just switched bottoms. This eliminated the splashing up into the intake tube and the engine smoothed out and ran pretty well, again, on one cylinder with the other cylinder firing intermittently. I increased the rocker arm clearance on both intake valves by quite a bit and this allowed me to slow the engine down to a pretty reasonable idle. The good cylinder was now firing ever time and the missing cylinder still fired intermittently. I removed the push rod from the intake valve on the good cylinder to see if I could get the engine to run on the missing cylinder. My thought was that maybe it wanted a leaner (or richer) mixture or maybe the other cylinder firing was interfering with the bad cylinder. However, I could barely get it to run on just the bad cylinder. I put it all back together and fired it up again. This time, I discovered when opened up the throttle a little, then I put a load on the engine by holding a rag against the flywheel, I could get it to fire on both cylinders pretty consistently at a pretty slow speed. I don't get it! But if all I have to do is put a load on the engine to make it run the way I want, so be it.

So here is what I've checked so far. Compression on both cylinders is excellent. Both intake valves are opening and closing at about the same position. Same with the exhaust valves. Ignition timing is identical for both cylinders. I'm beginning to think I might have a small air leak in the intake side of the bad cylinder. This is making run real lean and only firing ocassionally. Could be the manifold or it might be the valve stem on the intake valve. I might try putting a couple of drops of heavy gear oil on the valve stem and see if that seals it up temporarily. The other thing I haven't checked is the gap on the spark plugs.

By the way. Since this is a two cylinder, 4 stroke with the crank throws 180 degrees apart, the engine fires twice in one revolution, then goes a complete revolution without firing. This means one cylinder fires, then the second one fires 90 degrees later. The cylinder that is missfiring is the first in that firing order.

Chuck
 
.......Your tuning issue may be more of a fundamental nature than any leak or ignition problem. Being a 180 deg. twin with uneven pulses in the intake trac could lead to carburation issues. That being the charge for the misfiring cyl tends to be rich. The cure for these odd fire engines is separate intake manifolding and dual carbs. Read more about 180 and 360 twins! :) http://en.wikipedia.org/wiki/Straight-two_engine
 
I'm happy to report that the misfiring cylinder has been corrected. I pulled the plug and there was virtually no gap. So I widened the gap to about .035", reinstalled the plug, and the problem was fixed. Why don't I ever check the easy (and obvious) things first??? :doh:

It's still not running as consistently as I'd like, so I have some more work to do. But it does idle pretty slow and will keep running slow for quite a while. Longboy, you might be right about the carburetion problems with a 180 degree, 2 cylinder engine. One problem with the vapor carburetor is that the mixure keeps getting leaner as the fuel level drops. So, you have to keep adjusting the fuel mixture.

The other issue I have is way too much lift on the cams, about 0.125". I can compensate for that by adjusting the valve clearance extremely loose, but it makes the rocker arms look sloppy and I really only need a lift of about .060". I may remove the cams and take them down a bit.

And, of course, I still have to put everything in a more permanent and attractive package. That means building a base, a mount for the gas tank and a nice enclosure for the electrics along with safer and more attractive routing for the wiring. Stay tuned...

Chuck
 
I'm glad you blew the dust off this earlier build to continue as I am looking to do a simular open crank twin concept for my next winters project (a first multi cyl. for me). Looks like the spark plug cleared some problems. We won't have to come over there now and hit you on the head with a hard copy book of, "Troubleshooting Model Engines, Part One" now! :eek: Can a vapour carb use two feed lines to independent manifold runners in a twin? I'm thinking that having a maniforld runner/tube on one cyl. of a different internal diameter or even of a longer length, carb to cyl. , to speed up/ slow down the flow to a more favorable intake pulse these 180 engines seem to need. Would be nice to hook up vaccuum gauges to our models to tune fuel metering. Dave.
 
Thanks, Dave. You probably could run two tubes from a vapor carb to the cylinders, but I'm not sure that would gain you anything. Probably two separate vapor carbs would be better.

Here's another short video showing the state of the engine as of this morning. You can see the taller vapor fuel tank, the larger flywheels, and the better, slower idle. Still not running very smooth, but at least it's missfiring equally on both cylinders. The sound is kind of a cross between a John Deere and a Harley! Excuse the sloppy camera work... :-[

[ame=http://www.youtube.com/watch?v=nfe9sE1RdZ0]http://www.youtube.com/watch?v=nfe9sE1RdZ0[/ame]

Chuck
 
I love the way it Sounds Chuck!

Well Done.

Kel
 
OK, sorry to keep flooding you with videos, but this is the final one until I get the engine prettied up with a base and proper placement and connection of all the odd bits.

This video sounds pretty much the way I had originally hoped for. All I did was basically open up the throttle some then use friction drag on the flywheel to slow it down. Seems to do the trick.

[ame=http://www.youtube.com/watch?v=jAE9En2xsZg]http://www.youtube.com/watch?v=jAE9En2xsZg[/ame]

No more videos for awhile... ::)
 
Another great project that makes me itch to get back to my machines.
Looks and sounds great.

cfellows said:
No more videos for awhile... ::)

bummer
 
cfellows said:
OK, sorry to keep flooding you with videos,
...
No more videos for awhile... ::)

You losing your grip on reality or something? I don't think most of us here can even form a coherent concept of "too many videos".
 
cfellows said:
Thanks, Dave. You probably could run two tubes from a vapor carb to the cylinders, but I'm not sure that would gain you anything. Probably two separate vapor carbs would be better.



Chuck
Looks good/ sounds good on the last video here. My thinking on the two tubes in a vapour carb would be that it would mimic two model engine carbs on a 180 twin. Then the intake pulse no longer affects what happens in the other intake trac. The simplicity offered by one vapour carb feeding the two cylinders independently would be the gain over a dual venturi carb setup with its more involving intake manifolding arrangement and cost. I haven't seen a vapour carb on a multi cyl. model engine anywhere on the internet yet....either because it doen't work, or nobody tried it yet! scratch.gif Dave.
 
I'm new to posting on here but I would like to see the build thread for this engine. Chuck, can you post a link to it? Thanks.
 
Chuck That's just amazing ! To me any way. When I get back on my feet a little better I have got to try some of the things I see on here . For now I will keep on dreaming. Great job !Dale
 
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