Dave;
I seem to be having a problem setting up a 120SF in a DP Ultimate. Although old, it really has not had much run time as far as I can tell. I installed a new diaphragm and did the setup according to the manual. I starts ok but I have had problems getting it to maintain power until just recently. Here are the symptoms and results so far. With the regulator screw adjusted as per the manual (flush) it would start fine and run ok. At full thottle though it would start to loose power and was getting quite hot, even though there was a lot of smoke as if it is too rich. It seemed to run best with the NV opened about 1 turn, although opening or closing the NV did not seem to have a lot of effect - too far either way does kill the engine though. The manual suggest only adjusting the regulator screw for transition problems but I noticed that the fuel tube to the carb was not ful of fuel at high RPM so I decided to try adjusting the regulator screw. I finally got it running much better by opening the regulator screw about 1.5 turns from flush - sticks up past the case. Now there is plenty of fuel in the line to the carb and the engines runs cooler and holds its RPM much better - running Wildcat YS20/20 and a 16x8 prop yields about 8300-8400 RPM. Idle and transition seem to be the same no matter where the regulator screw was set and the NV still does not provide as much adjustment as I would expect. I flew it this way and other than seeming to lack a bit of power it flew ok (cowl off) and there was plenty of smoke. Q: Should I be concerned about the lack of adjustment with the NV and the position of the regulator screw or am I on the right track and just need to keep tweaking to get it set right? Any suggestions to help get it set right - I'm dying to get it running so I can put the cowl on and fly.

Thanks
glen

You can continue trying, but the engine is not right if the needle is soft. YS engines normally have a very crisp needle.

How does the engine feel when hot? Does it have good compression? If not, that will have a huge effect on the needle and regulator.

Dave;

I'll run it again to see if I can tell if there is much difference in the compression. As I stated, it seems to be running cooler now than before but I don't know how cool/hot it should be - certainly very hot to touch after running on the ground. My little DURATRACK temp gauge tells me it was almost 200F and the RPM would drop but it now holds the rpm and stays at about 150F-175F on the head near the exhaust. I don't think I changed the NV O-ring so I'll change that next too.

Dave;

Replacing the NV O-rings uncovered another question - 2 O-rings or 3? The parts manual only shows two but the NV socket had three when I took it out. Was there a change at some point or did one of them not belong? The unexpected ring was at the base of the socket where it screws into the casing. The others were near the tip of the inserted end and in the middle on the NV side.

Should be three on the old type NV body,and one on the needle itself.

Really? Can't see where I would put one on the NV itself. Do you have any drawings and part numbers?

You probably have the later assembly. That one has two on the inside part of the body, and one on the nv side.

Sorry for the confusion, YS has made several styles and it's hard to tell sometimes what a person has without seeing it in the flesh.

Dave;

As to your question about compression, it seems about the same when it is hot - probably a bit less but still compression. At no time is it really hard to turn over as compared to a typical two stroke. It almost always will fire up after a couple of cranks with a starter but is tough to start by hand.
I replaced the NV O-rings and I put in a new spring in the regulator with no luck. Basic problem remains the same - little NV adjustment and seems to get hot but dies if you try to richen it more. I even tried turning the regulator around in case I put it on backwards and it made no difference - is there a wrong way for that part??
I tore it down last night and everything looks clean inside - not that I am much of an expert at identifying possible problem areas. The only thing I noticed of some question was the carbon around the exhaust port and a tiny bit around the intake - closest to the exhaust port. I can't tell if it is having any impact on compression or if there is a leak. Is there something I can do to test this?
I am going to take off the regulator and check all those tiny holes for blockages if possible. I guess I'll have to remove the crankshaft to do that properly.

All in all it looks like it should run fine. I did see one head shim that could be removed if you think compression is a problem but I would like your opinion before I try anything in that area.

I too have an older YS with the EXACT problems... couldn't get the needles to set the engine correctly, seemed that it didn't matter how I adjusted them, and it got very very hot!! I gave the engine to a friend who took it apart and he found that the intake valve clearance was too tight, the paper gasket in the pump was partially blocking the fuel ports. I'm now waiting on the pump gasket, plunger, and spring as well as new o rings for both high and low NV's.

I know this is just in this case but your description is very similar to mine. Good luck in getting it fixed.

By the way when I tached it I could only get around 8-8500 and it would die if held at full throttle, now after he adjusted the valve clearance and gasket he was able to get over 10000 with a 16X6. The pump is just acting a bit funny(air in lines) that is why I need the parts.

Side note,

Is the shipment of parts due in soon? (sorry if I should not post this here)

Parts came in yesterday.

Thanks Dave.

You're welcome.

Quick update.... got the parts and the guy I was getting to look it over installed them and fired it up again, and the problems were the same or even worse. He then gave the engine back to me and after looking at if for a while I deceided to take a look at it. I took it apart and found one major thing. After looking at the NEW plunger that I received from YS and the original found in the motor, their was a noticable size differance between the two. The new one, installed with a new spring, would not even contact the diaphram so the regulator screw had no effect. Putting the old regulator in with the old spring it now contacts it just fine.

It now runs great and super strong. One thing I have noticed is that it is quite sloppy...alot of oil getting over the firewall etc. Is this normal or do I possibly have another problem?

Thanks.

These things have a tendency to run pretty wet. Get used to the mess if it runs OK.