I was wondering if anyone had any tips for tuning a PAW .35 (and diesels in general). It starts really easily after a few flips (im always underchoking too) but I am wondering where to set the needle. This engine runs under so many settings its rediculous, you can be really careless with the settings for getting it to start and run (no electric starter). I am thinking i sould set the needle like 30 degrees richer than maximum rpm, does this sound like a good idea.

Also, does the cold (40 degrees F and lower) have a negative effect on transition? I think its my poor tuning more than anything, im not very patient in 30 degree weather

Lastly, is the Davis diesel mix at Tower the oily mix?

Thanks again

The important thing with a diesel is to get the compression right before setting the fuel mixture.

Set back the compression to below where you think it will end up, and set the mixture rich to start the engine. Choke the carb and turn it over a few times until you get fuel in the carb, then try to start it.

When it is running (probably badly!) slowly screw down the compression screw until it starts to labor, then back off about 1/4 turn. Now slowly screw in the needle until the revs pick up then start to die. Now back off the needle until the revs pick up again.

When the mixture seems about right, you may have to increase the compression slightly, but it must end up slightly less than the point at which it labors. Diesels lean out a bit in the air, so it's a good idea to keep it slightly rich on the ground.

There should be noticeably more power output when the weather is cold, and it might need a little more leaning out to keep the temperature up.

It will tell you in the air if it's too lean as it will sound labored, which means either to much compression or too lean. You will need to experiment with that one, as the sound is slightly different, but too difficult to describe here!

I hope that helped!

-David C.

I have followed the Clutton (diary) and Carlson (webpage) advise on the running, and I try to set it with the lowest compression setting possible w/o miss and it seems to work ok, transition isnt bad its just not as good as it will be once I spend more time with it. Im just wondering if the needle setting being richer by 30 degrees or so is a good rule of thumb for performance and adaquate oil, or is this not really applicable/necessary to running a diesel?

So cold weather needs leaner mixtures to produce better transition (ill have to be careful there). I thought it seemed a bit rich, experimentation is half the fun though.

My experience is flying diesels in CL stunt with a fixed venturi, so I don't know anything about using an adjustable carb. The general advice on a diesel is to run it with as low a compression as you can and as lean as you can. OK, the airplane flys along level engine running beautiful. Put in in a maneuver, the engine loads and slows down--it is overcompressed. Put it in a maneuver and the engine misses--it is too lean. I like to run engines without changing anything unless the performance of the engine in flight tells me to change the needle or compression setting. For most diesels, the easy starting compression is more than the running compression. So I use a starter. For a 40-size conversion, I expect the engine to run ragged, warming up, for as long as it takes me to walk out to the CL handle, put on the safety thong, and wave OK to the pitperson. Maybe a miss or two in the first couple of level laps, but no more.

Jim

My experience with diesels is somewhat limited but throttling performance is always a big issue with me. So far it looks to me that glow and diesel throttling differs little. The real issue, once you get the correct compression for your fuel mix and ambient temperature is having the optimum mixture at all throttle settings. I like to dial an engine in with a healthy just lean mixture. NEVER rich in any way, for the sake of good throttling. A proper lean mixture is required at all throttle settings and this is the job of a properly designed throttle. Does the PAW .35 have any means of adjusting the low speed mixture, such as an adjustable airbleed or a secondary needle?

If the .35 is set up the same as the .40 barrel slides in and out on the main needle to do the metering. There is no separate low speed adjustment and none is needed. The .19's throttle barrel does not move in and out but throttles very well also.

Can you let any of these engines idle indefinetely with rock solid rpm and then crack the throttle open and get instant response with no smoke, spitting or hesitation?

If your engine isnt smoking, you are running too lean... I have not yet run a two stroke mixed fuel/oil engine that doesnt produce smoke...

Again, READ THIS

http://www.carlsonengineimports.com/...eselinfo.shtml

Max

Good point Andrew,

Let me clarify that, EXCESS smoke, spitting, or hesitation. I meant, does it accelerate cleanly WITH INSTANT RESPONSE.

Thanks Max,

Excellent information from one of the best sources of diesel engines around. I agree with everything except where it comes to the issue of idling. Both diesel and glow engines can be made to run at clean, lean settings that are not overlean but give you the max power out of your engine and fuel. A clean exhaust doesn't mean the engine is TOO lean. It COULD mean that the mixture is optimized for best power and fuel economy. No need to set ANY engine on any rich side with smoke pouring out. A properly set engine will certainly display an exhaust trail but in no way should it give you a smoke trail,,, unless that's what you want. Or you have WAY to much oil in your fuel. Something diesel fuels appear to have.

Setting an engine on the rich side to compensate for some other inadequacy will nearly certainly give you problems if trying to set the mixture at idle. If your main needle is clearly rich, this may take the idle adjustment out of the range that it's capable of coping with. In other words, way more fuel is being delivered at idle than the idle adjustment can handle.

I've added adjustable airbleed throttles to side port Mills diesels and once adjusted, throttling was virtually perfect,,, idle all day and instant response with no EXCESSIVE smoke, spitting or hesitation. I've also added the adjustable airbleed to stock PAW .061s and while throttling wasn't perfect, it was much improved over the stock arrangement.

Hobbsy,

If you've got a PAW, single needle throttle that you'd like to have an adjustable airbleed added, I'd be happy to do it for you for free. I'll even pay the postage back. It worked for me twice and I'd like to replicate the experiment and have it evaluated by a knowledgeable third party.

Luftman,

If some of the more knowledgeable folks in this forum can advise, what size glow throttle might suit the .35 diesel and depending on that, I'd be happy to supply you with a throttle to suit your .35 that has a means to adjust the idle mixture. It may provide dramatic improvement or only modest improvement but I anticipate that it will at least give you SOME improvement over stock. I'd be more than happy to do this for free just to prove me wrong,,, all in the interest of a good and worthwhile experiment and confirmation by a third party. Send me a PM with the dimensions of the PAW stem and your address. Again, no charge or obligation, I'll pay the freight back.

In my experience (and from what I've read) a diesel will not run TOO lean...it just quits. I wouldn't worry about it being too lean.
It seems to me on the other hand that running too rich could cool it down and may change the necessary compression setting to a point of causing hesitation or sputtering during transition from idle to high speed. This is SPECULATION, I have not tried it.
Just one more opinion.

George

George,

Well, I've run diesels lean and I found that they slow slightly and make an odd sound but they keep running. But you're right, running rich, even a tad rich is unnecessary. Why would you do that? Why not optimize everything by getting the mixture just right,,, not too lean, not too rich.

We, Dad and I, have experienced diesels that will run so lean they destroy themselves. On a German bicycle motor call the Lohman my older brother remarked on how it seemed to be gaining performance just before it quit, rather siezed. It was out of fuel and ran until there was nothing left at all. It is just like our model diesels with contra-piston, premix and all, bit about 30cc if memory serves correctly. I have leaned them until they quit but the cutoff is inconsitant. On a Mills .75 I couldn't shut it off by pinching off the fuel line, so I tapped the crankcase and dumped it to atmosphere to stop the engine consistantly. Diesels are strange animals in some ways, they're fascinating.

Not being a
machinist I took the dumb ass way out on my PAW40 ! adapted an MVVS carb twin needle to it
it is almost identical in response to my irvine 53 with its jetstream carb ( the irvine carb is great
OS could take lessons on this one)

Correction on that response it is very smooth on the PAW but the irvines is instant

I was running my PAW last weekend (had picked up in a swap) good eveything idle transition etc
This engine came from clutton I just noticed written on the box bottom quote
running a 9x6 comp as set needle 1 1/2 T cold start incr comp 1/2 to 3/4T needle 2T
evidently clutton put this on the box to the puchaser he may have test run it and set it up
before shipping orig paperwork dated 1992 it is a 19rc BR pretty neat how nice of him to do this

why would you have a contrapiston ona bike motor??was it diesel??

Yes,

Kudos to Eric Clutton AND Ed Carlson for making diesels of any imagined variety available to us. These two guys are always friendly and helpful and easy to talk to.

Golly Dieseldan,



Yeah, it's a diesel, pretty unique huh, but then the German's are like that. Underslung bike motors were popular in Europe in the late 40's and 50's, but most were common 2 strokers, the Lohman company decided to try a diesel.

I took the tank off one of my Mills .75 replicas (Indian) so I could connect an external tank. That little bowl is good for FF but I wanted longer runs for CL.

George