I have a PAW 80 that I am having trouble starting. It seems to take a lot of compression to start and then when it does, it labors and runs real slow. Any changes in the compression or needle valve kills it. I get the same results using either home brew or Davis fuel. How high/low do you need the compression to be in order to start? This is my first attempt at a deisel and the engine is second hand.

Any help would be appreciated.
Thanks
Tag

You should be able to slowly back off the compression once you get it started. I haven't run PAW's much, but I found they started at lower than running compression, unlike my other diesels. But it sounds like yours is overcompressed for extended running.

Turn out 3-4 turn main needle at carburator.

Back off compression screw and prime engine carefully and turn propeller fast while you are turning compression screw 1/4 between 10-12 turn of propeller until the engine starts.

When the engine are running, adjust the compressionscrew until the engine are running fast.

Overcompressed make the engine slow or oscillating cause too high compression and early "ignition timing". Undercompressed make the engine rough and slow cause "later ignition timing"

Then lean out the main needle until the engine are rough and turn back 1/4-1/2.

Read this instruction paper here: http://www.eifflaender.com/instruct.htm

Jens Eirik

Thanks for the help.
Jens, how are you turning the engine over, with a starter or by hand? I' only turning by hand and may not be getting enough to start it. My arm is sore clear up to my shoulder from trying to turn this thing!!!

Again, Thanks for all the help.

Tag

http://www.eifflaender.com/instruct.htm

Tag, here are complete instructions for all PAWs, you can print them.

Allways by hand, flipped 2-3 turn before the engine starts after careful priming. The Dieselengines do not like too much priming who are difficult to start. If too much priming, back off compression screw and start up the engine until all flooded fuel are burned away.

When the engine are ready adjusted and running nice.
Remember this:

COLD START = HOT RUNNING SETTING PLUS 1/4 TO 3/4 TURN IN OF COMP. SCREW.

HOT RE-START = HOT RUNNING SETTING LESS 1/4 TO 1/2 TURN OUT OF COMP. SCREW.

Jens Eirik

Is it a new in the box PAW or is it a 2nd hand one? to me it sounds as though the gasket on the crankcase may be leaking (its a paper ring) NEVER use an electric start on a diesel!!! you WILL bust it

It sounds like you may be a little lean on the needle unlike a glow engine a diesel will slow down and stop if too lean also make sure you have a good fuel draw, disconnect the fuel line from the tank and blow thru it to make sure you do not have a clogged carb It will start on a prime and quit if no fuel. I have used starters with no problem just make sure you do not have a hydro lock by hand flipping first which will break any engine. the rest of the steps described in the above replies are 100% on. some of my engines hand start quite
well other require a bump with a starter I use a starter on my PAW 40 and 19 sometimes if it does not light off after about 10 flips or so
martin

Again guys, Thanks for all the help. Boy I wish there was someone around here that ran deisels.

Andrew, the engine is second hand but supposed to be new. On your advise I checked and found the head screws were loose. I have not had a chance to try it yet so I'll keep you posted!

It's been tough not to just grab a starter and go at it but I'm resisting. I just keep telling myself that once I figure this thing out I'll love it!!

Thanks again
Tag

Yes, I know its a bigger PAW, but if yours has been apart, it might be a good idea to make up a gasket set from some stiff paper, so i copied the picture to give you an idea of where to locate the gaskets. Below the needle valve assembly is an "O" ring, check it present and in good condition, the cranckcase back screws into the crankcase and it has a thin paper ring gasket and the base of the cylinder liner also has a thin paper gasket between it and the crankcase. The smaller non R/C engine only has 2 paper gaskets as shown in the picture

Tag,

I think Jens has the solution. You probably have it so over-compressed that it is oscillating. Start it as you normally do and back off compression. If it kicks over in the wrong direction it will stop from lack of fuel (like running off a prime). If it kicks off in the correct direction it should continue running if the fuel setting is not too lean.
You might try backing off compression about 1/2 turn and use only an intake prime with fuel tank disconnected. When you can start it that way, then connect the tank. Solve one problem at a time.

Good luck,
George

One more thing to check is that the holes in the spray-bar are pointing fore and aft (at full throttle if it's an RC model), not up and down. They are a little offset from a diametric (is that a word?) line through the spray bar and they need to be pointing downwards and fore-aft.

Tag,
I would suggest you continue to resist that starter at least until you are able to get it running by hand. I don't use starters (except springs) on my engines.

Since you mentioned head screws, I assume you have an older version. Here are some pics. Sorry they are a bit dark.

George

George

That's the little beast. Unfortunately we have found that mine is probably unsalvagable. When I got itstarted again the head screws all broke.

Thanks
Tom

I have found the prop screws are on UNF thread, I dont know if the head screws are the same. If you send it all to PAW, they will rebuild it as per new at a not-to-excessive cost.

Hi Tom, perhaps the contra piston is gummed up and frozen down in the bore. Broken head screws would certainly indicate the piston has made contact with the contra or an hydraulic lock up (incompressable fuel filling the space between the piston crown and the contra piston ). I hope the conrod hasn't bent. Although you're adjusting the comp. screw, the contra piston may not be moving back up the bore when the comp. screw is wound out. I had the same problem with a N.I.B. 40 Y.O. DC Merlin I found on e*a*. It had probably only ever had a brief run at the factory, leaving enough castor inside to "gum up the works "after all those years. Soak the liner in lacquer thinners overnight to help dissolve the old gummed castor around the contra piston , sit the liner on a piece of wood, then using a WOODEN dowel, gently tap the contra back and forwards to free it up. An email to PAW or Eric Clutton ( Dr. Diesel ) should help find out what thread and size the screws are. Just my 2 cents worth. I hope you can get it running.

I cross drilled my PAW .40 and .60 above the contra-piston because fuel would get above the contra and then combustion would occur above the contra making an awful racket. The PAW .19 I have never did this. I believe this happened to one of Martins PAWs also.

It looks as if my Classic 80 is junk. The broken bolt in the crankcase can't be removed and the crankcase is unavailable. If anyone has one in their spares box, let me know. I really hate to scrap this engine.

Thanks
Tom

Yup my 40PAW did too it got the same cure and my 19 never had the problem. Checked the weather looks good Sunday morning
predicted winds >5mph Will fly the Lazy Bee TT10 davis head test ran today cranked right up, blue Thimble drone 8x3 really screaming
did not tach but my guess better than 14K will put the MAS 9x4 back on which will bring it down in the 10K range and quiet it down
for flying in the park hope to get some air pix which I will throw on the site martin
I still do not have the screw and spinner for the 074 conversion in the decathalon too bad I really wanted to fly it

Tom,

If the screw has broken flush with the top of the crankcase, you might be able to get it out if you can get hold of a really thin file (you probably need .02" or less), and then file a slot across the end of the screw.
You should then be able to remove it with a jeweller´s screwdriver.
You will have to file a bit into the crankcase too, but what the heck, if the alternative is to scrap it?
You can get spare screws from PAW in England.

The photos below show a broken needle that I got out of a ST carb with this technique, maybe you can use it too?

Tomas H.

Only use a starter if you have already bought a replacement crank, con rod and wrist pin. The need to use a starter just means that one hasn't mastered the technique for starting a diesel - often the case with people born and bred on glow engines.

Someone suggested a needle setting of 3 plus turns out for a PAW 80 - I would never use more than 2 1/2, and never more than one turn for the Classic 80.

When dealing with a problematical engine I find it best not to choke or prime through the carb. In fact I might disconnect the fuel line altogether. Put a drop of fuel in the carb, but only enough to lubricate the shaft, and turn the prop over gently. Turn the prop until the piston closes the exhaust ports and then turn the engine over gently to ensure the cylinder isn't flooded (it shouldn't be). Back the comopression off as much as 3/4 turn. then start flicking smartly while advancing the compression. The engine shopuld fire, and run out a short burst. When it does this and does so consistently, you have established the compression setting. Attach the tubing and choke the fuel up to the carb, but no further. Re-prime against the piston wall again as before, and again back off the compression about 1/4 turn. Turn over to check, then flick smartly while advancing the compression. If the needle valve is in the ballpark, it should run. Always err on the side of lean on the needle - it is better to have it run a short burst than flood itself.

Tank position is important. At this stage, the top of the tank should be level with the spraybar.

Regarding head screws, they used to be BA threads, but at some point PAW went over to metric (about the same time that they went from metric to American in nomenclature - the logic escapes me). I think the crank thread is UNF. The heat treatment of the head screws can be important. If the bolts are soft, you will always be tightening them.