Good old number 29

Mr. AKFlyer himself. Thank you very much for your assistance today. Leni and Bob both came to the airport and helped make it happen. This is the second takeoff. We made three prop adjustments, and went up a size on the jetting, to 165, between flights. I brought the bungee struts home to swap out the two 1080’s for one 1080 HD CW per side. Much too stiff as it was. Leni was the fearless test pilot. Everything went well. Engine and prop are silky smooth. Temps are good. It flies like a Kitfox.

https://m.youtube.com/watch?v=g4SV0OGmicc

It lives!

Kitfox Model 1 versus Model 4 comparison. 

THAT would be a score. Let’s all chip in on it. 

I wish I could have bought the whole package. I see the Yamaha motor is already sold, pending funds. 

It will probably be necessary for the buyer to get an Affidavit of Heir-at-Law from the seller in order to register it. 

This is on the Facebook Yamaha Aircraft Conversions page. I wish I could buy this one, myself. 

This is a great forum, but I’m spending way too much time on here instead of flying. Almost a month since I got the inspection, and still haven’t gotten it in the air. I got it tied down outside to make it more accessible when the moment comes. Today turned out to be beautiful, but the instructor I lined up was busy. Maybe Wednesday, if weather cooperates. I hate waiting. 

I wondered the same thing when I covered my new gear legs. I went as far as cutting fairings for each tube, but then just put the fairing on the back one and covered the whole thing with fabric. If covering the whole gear leg IS better than fairing the tubes individually, wouldn’t it also be better to cover the whole jury strut and HS brace the same way? I’ve never seen it done, but maybe that’s just because it would look stupid? 

Allen, on your 503, what prop are you running, and what RPM? 

Reading my 1984 ROTAX manual, it states that the 503 is designed to run 6,350 at wide open throttle with a full load. That is just past peak torque, and what I would ideally have wanted. I will be re-pitching the prop accordingly. I got kind of caught up with the idea that I should be able to hit redline, when I knew I should be aiming for peak power. I had 6,000 at .050” and 6,300 max at .040” on the ground. I’ll try .042” and give it the real test. With 6,500 at .025”, it seems like the prop was losing efficiency with too fine a pitch. 

I went up to 160 main jets. I have 145-180 in increments of 5, and 158, except no 165’s. 

If the weather cooperates, and God is willing, I’ll finally be able to fly it this week. 

There’s a note on the LEAF info that Bing carbs don’t come with jets. Apparently, the jetting that I have in my 503 was standard from CPS or Aircraft Spruce, while engines ordered from LEAF used the other setup. 

And also supports having the clip on the number one setting. Two sizes richer on needle jet. Three sizes leaner needle above half throttle, one size richer below half. One leaner clip setting. Confusing enough? 

The needle I have would be leaner above half throttle, but richer below half throttle. However, I also have a richer needle jet, which would make it richer across the range. This may explain why I was able to lean the air screw as much as I did, being that both the needle and its jet contribute to a richer mixture than the LEAF setup at lower throttle settings. 

Here is that LEAF chart. Looks the same as the other except for the needle jet/ jet needle. I have a richer jet, with a different profile needle set on a leaner setting. Offhand, I’d say it accomplishes the same thing. 

This is the same chart as I have in my ‘98-‘99 CPS catalogue, and matches the jets that were in my plane. I have a wide selection of main jets, and someone had installed 145 mains, but all else was the same, and everything looks good with their recommended settings. Based on the advice I’m getting here, and current local temperatures, I’ll try going richer before I fly. 

It sounds like the specs you’re using are for the dual intake silencer, note three on this chart. Note two is the single carb with silencer. I have the dual carb without silencer, and the jetting is as listed, except that I leaned out the idle by turning out the air screw. 

The 503 makes peak torque at 6250 and peak hp at 6500. I tried the needle on the second setting. Temps were low and plugs were black, so I took it back to the top notch, which was the recommended setting. The picture above was taken during a run with the 150 jets. At partial throttle, the smaller main was having an effect. With the colder, denser air, I might want to move the needle up or go to a bigger main jet. Like you said, I need to actually get it up in the air and see what it does. Today was beautiful, but I'm in fisheries meetings through the end of the week. I think it's close, but having colder air flowing freely through the cowling will probably prove you right on every point. It was flying previously with 145 main jets, so I'm not too worried about being too lean right now. It's probably a bit skinny on the pitch, but I wanted to be reasonably sure it could run up to redline, if needed. I first pitched it for 6,000 static, but I didn't want to be behind the power curve, unable to call up peak power on demand. If temps are high the first time around the pattern, the enrichener might actually become useful. I believe that the loss of rpms on static runs was because it was breathing the increasingly hot air inside the cowling, but that won't be the same issue when it's moving. The fan is quite close to the firewall. I might add a vent to the upper cowling to feed the cooling fan. It pulls air from the back of the engine compartment and blows it out the top of the motor, and out of the cowling, through the square vent on the top cowl. I know, there's not much reason to run it past the top of the torque curve, except that it's better to be above it than under it. 

Put your prop info and jetting here. There is a lot of mixed info on props and static rpm. Please put down the raw data, then expand on it if you care to. 

Rotax 503 DCSI

Powerfin “B” blade 

68” three blade

Set .025” from finest pitch

STATIC RPM and TEMPS

6,500 rpm max, down to 6,300 

EGT 1,025

CHT 425

Ambient temp 30° f

Main jets 158

Idler jets 45

Needle jets 2.74

Needle 8L2 in position 1 (top notch)

Air screw out 2 turns

I haven’t yet put a protractor on the prop to measure the pitch. Powerfin set it up to be adjustable using feeler gauges to measure the pitch, and that is how I set it up. This is the initial setup on my plane, which I intended to be more toward climb performance than cruise. The plane had 145 main jets installed when I bought it. I honestly didn’t see much difference in EGT with 150, 155, or 158 main jets. It never exceeded 1,100°. CHT was pushing 450° with prolonged pulls on the 150 jets, so I worked back up to the factory recommended 158s, and saw a minor decrease in CHT. Keep in mind that this is all static pulls, so it should drop with increased airflow when it’s actually moving. Plugs look nice and tan. I got the lowest CHT, about 400°, at 6,100 rpms and .040” on the prop pitch. I’ve seen a mix of opinions on redline, varying from 6,200 to 6,800. CPS quoted 6,800 max rpm for up to 5 minutes. Being that they’re a licensed retailer, I believe that’s accurate. Other information suggests 6,500 rpm as the continuous redline. I have no intention of running it continuously at 6,500. I do want to be able to reach 6,800. Snowmachines with the 503 revved to 8,000. With the plane locked down and the engine warm, at this prop setting, the rpms jumped as high as 6,500, then quickly settled at 6,300, fairly steady. I did notice that the engine would do that at full throttle, regardless of pitch or jetting. I’d see an initial high rpm, then a drop of about 200 rpm over the course of a minute, in correlation with the rise in CHT. EGT remained the same. All the carb setting are factory recommendations, except the air idle screw. I got the highest idle at 2.5 turns out, and turned it back in 1/2 a turn. 

It turned out to be a real bear to start without a primer, so I got one coming. I ordered a shut off valve to go with it. 

I really appreciate the time, money, and effort you’ve put into this. It’s a great site. The people here have been really helpful with my project. 

I did notice some problems posting pictures today. Uploads failed when I clicked the link, so I copied and pasted a pic, which appeared to work, at first, but after I posted, the post was just blank. I’m sure they’ll get it all worked out. Thanks again for putting this together, and to everyone else for being a part of it. 

That was my first thought, even though I did have the fuel valve off. More than a couple times, I’ve trailered snowmachines somewhere, only to get there with one cylinder flooded out, but I’ve never had one flood out like that while it was running. The primer is the same one that Jim posted a picture of. 

It was fortunate for me being able to diagnose it, that the fuel valve did not shut off fuel to the primer. I had considered changing the fuel system so the main valve would shut off everything, like it should, but never got to it. Had I done that, I might not have realized that the primer was the problem. Just a small, slow drip was enough to flood it out and kill it. 

I haven’t looked into it to see which style it was, but it’s not fixable. It looked like it unscrews, but when I twisted it apart, I found that it isn’t threaded, it was pressed together, metal to metal, without a seal. I don’t think I’ll trust it to seal again now. I don’t think I’ll trust one at all. I’m going to look for a better alternative. I wish these carbs had a regular butterfly valve choke, the ones that actually work. 

I just diagnosed this most irritating problem and hoped that this solution might benefit some others. 

The 503 in my Kitfox is fresh. It’s jetted right. It has new spark plugs. It has new points. The point gap and timing is good. It has good spark. It has good compression. It has good fuel.

I trailered it to the airpark for some taxi time, but when I got it off the trailer, the number two cylinder (the rear cylinder) was not firing right. I messed with it for a couple hours, but the same thing kept happening. The rear cylinder would miss, then eventually go completely dead. The evidence of this was plain, with low egt and cht on the number two cylinder. The number two spark plug was wet with fuel, while the other was dry. I didn’t have spare plugs with me, but it had a great spark at both plugs. I took both plugs out and spun it over to blow the fuel out. I switched the plugs. I eventually pushed it back to the trailer because it kept doing the same thing. I could clear the cylinder, dry the plug, fire it up, but it would immediately start missing on number two, and eventually that cylinder would stop firing completely. 

I replaced the new NGK B8ES spark plugs with brand new NGK BR8EIX iridium plugs. I checked the carbs and floats. The float needles were properly in place and the floats were floating in the fuel in the bowl, when removed. I pulled out the slides and checked the needles. I lifted up the tail, to level the plane, and fuel came out of the air filter. The fuel valve was off. I double checked the jets, floats, and needles. All good. I started to remove the engine to see if the points were arcing, but the spark looked good, so I put it back together. The points are brand new, with only one hour on the points. The manual recommends readjusting them after ten hours, because they will wear where the cam lifts the breaker to open it. Knowing the gap would be lessening as it wore in, I made the initial adjustment toward the upper end of the range, giving them a wide gap. Certain that the carbs were properly set up, I surmised that it may have flooded the engine while bouncing down the road on the trailer. Being tilted back, the fuel would flood the back cylinder. This was not the case. I put a torch to it and made sure there was no gas in the cylinders. I put it back together. Same thing. Fired up, starts missing, number two takes a number two. So, back to the points. I started taking the engine off again. As I worked, I noticed gas on the floor beneath me. The fuel valve was off. The fuel lines, I left connected, and removed the carbs from the engine. They weren’t leaking out of the vent tubes or overflow. I had taken the primer hoses off of the nipples on the intakes, and it was dripping. I had noticed before that the primer seems to push the fuel back and forth a bit, instead of a steady push in one direction, but the primer had been working, and the engine had been running fine, so I hadn’t thought much more about it. The fuel to the primer isn’t shut off with the fuel valve. There is a tee on the bottom of the panel tank. One side of the tee goes to the valve, the other side goes to the primer. I capped off the fittings and plugged the primer hose. I put everything back on the engine and put the cowl back on. The engine fired up and ran great. Thank God for little things. If this had happened in the air, it would have been a forced landing. Even if the fuel valve could have shut off the fuel to the primer, it wouldn’t have kept it from dripping while the fuel was on. It’s pretty hard to start cold, without the primer.  If I rebuild the primer, I’ll put a fuel valve inline, so I can shut off the fuel to just the primer, so it’s never a problem. Because the plane was tilted back, whether on the trailer or on the ground, the fuel was dripping into the back cylinder and flooding it out. Inflight, it could have drowned them both out. On one cylinder, I could keep it running, but it wasn’t pulling hard enough to move under its own power. Putting in a valve to shut off the primer while it’s running would be a good move, even if you’ve never had a problem. Mine was fine for over thirty years, until that one day it wasn’t. It would be the same with a dual ignition. It was great to hear how smoothly it ran, once I figured it out. Now I have another project to work on, but it’s huge load off my mind.