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Deskpilot

503 rebuild

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OK my friends. Another question. My engine is now fully back together, mechanically speaking , and it's time to sort the electrics. Unfortunately, the wiring harnesses were cut to pieces by some-one so I have to figure out what connects to what. Google, usually my best friend, doesn't help. So, can you help. First image shows the leads coming out of the magneto.

 

DSCF5265.JPG.0d4e0b8ee4e9ce642d0d22ce1c2d4cc7.JPG

 

Colours are from top down, green with black stripe, yellow with black stripe, plain green, plain yellow There should be, according to google, a grey wire for the tacho. Top left are the leads from the ignition coil? set bottom left, under the blue wires.

 

DSCF5266.JPG.d5c7c1c50c20d604be00e57d1cab20d9.JPG Clearer view. Where do the remaining leads go? Am I missing some parts?

 

Out of interest this is how it's looking. Will be changing plugs leads with Red cables and heads

 

.DSCF5262.JPG.fd4e0583e6527ddcf8a10ab042a485c3.JPG

 

Thanks for any help you can offer.

 

DSCF5261.JPG.97bed12dbb65b4d4bca3df14c1bf5c63.JPG

 

 

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Writing this whilst waiting for my heart to slow down

 

Been struggling to get my 503 started after a full strip down and rebuild. Had a good spark, cleaned the carbie, adjusted the timing and all that but I couldn't get a pop out of it. Late this evening I thought I'd try something else. I pored fuel into the cylinders And pulled it through. Nothing. Rechecked the spark, OK, pulled it through on one cylinder, nothing. Replaced plug pulled it again and it roared into life at about 300 revs. Scared the sh*t out of me. I closed the throttle to a more sedate rate and  shorted the 2 wires that I thought were the kill switch connection and it kept running. Resorted top pulling off the plug leads and when all was quiet, except my heart pounding in my ears, I came in and called it a night. WOW, I so did not expect ti to start. First time in over 5 years when it was last ground run. Now the questions are, 1, will I sleep tonight, and 2, will it run again tomorrow. Time will tell and I'll let you know.

 

 

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Answers. Yes, I slept well. No it didn't run again. After a backfire that ripped the pull cord painfully from my hand, I thought perhaps I had the ignition too far advanced so I re-timed it to a slightly later firing point. Still no luck. I'm wondering now, why is it so hard to pull over. I seem to have extremely high compression in both cylinders (gut feel only). It turns quite easily with the plugs out. Also, I have to pull the cord a long way out to get it spinning. There seem to be about a foot of cord pull before the motor turns over and then it comes out another 2 feet or so. Is this normal?. Suggestions please.

 

 

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Hi deskpilot

 

The choke only works when the throttle is completly closed  no choke no start

 

The black wire going to the coil is grounded to stop the engine they must be kept seperate ie double pole switch

 

If the points gap is set correctly the timeing should be right 

 

 

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Hi Desk pilot

 

Did you get the 503 going, is it for the single that's on the trailer?

 

 

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Yes and no  mate. Yes it will go on the T84? on the trailer. Yes  I got it going twice but only for a short time. I've checked the carbie and all seems well. My next check will be the pump as I'm not certain that it's working. My filter is between the pump and the carb' and whilst I can prime so that fuel fills the filter, it seems to run dry. Possibly a perforated/dis-integrating diaphragm(the reason why I put the filter there). Another, and probably the biggest problem is that it seems to have extremely high compression and I find it hard to pull it through with any force. 'Course, it could be that I'm just bloody weak.

 

DSCF5223.thumb.JPG.d7a5e8765dde3853b7c8a232fc8b2b3a.JPG

 

 

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OK, diaphragm is sound so I gave it another try. After pouring some fuel into the front cylinder, replaced the plug and 'gently' pulled it through a couple of time, a more strenuous pull resulted in the pull cord being ripped out of my hand when the engine back-fired. Found a gardening clove and tried again. Engine roars into life. Reset the slow running and mixture.My wife comes into garage and is talking to me, can't hear a bloody thing she's saying. Rotax exhaust appears to be useless. Garage now filling with smoke so time to pull the plug leads off. Wife tells me to put in some earplugs........a bit late pet. Thing is, do I now dare mount it on the plane? Nah, a few more test runs I think. Can't find my earplugs so it'll have to wait till tomorrow.

 

 

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Hi Doug

 

I had a 13hp Honda on an auger, if I didn't pull it hard enough it would snatch the handle for my hand

 

 

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OK, another day to try and start my recalcitrant 503 and video it. At the present time, I don't have a throttle cable so a piece of string suffices to lift the throttle slide assembly. Here goes.  

 

Sorry, video won't load but just to let you know, it ran after I enriched the mixture.

 

 

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Hi Doug

 

The 503 sounds healthy enough

 

The relationship between throttle and choke can be tricky

 

The choke on a Bing 36 is a valve that allows more fuel to enter provided there is sufficient  suction ie throttle  closed

 

Opening throttle on cold engine can cause stoppage

 

Having the choke on with a hot engine will result in no start

 

 

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first few pulls on a 503 engine is just to get fuel into the bowls, on my 503s they have a manual primer that pumps fuel directly into the carb. probably need to buy an electric fuel pump for redundancy and easier starting

 

 

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Wow, reading that, I just relived all the old motorbikes of my youth...and that moment they come to life after being a heap of bits................)

 

 

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I presume you have a prop on the motor. If you don't have much of a flywheel effect you will just about get your hand pulled off, cord starting it. Eliminate the pump as a problem with a gravity system for testing. Don't test an engine without the kill switch definitely working. and the throttle mechanism connected.. Nev

 

 

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Just a thought,

 

u do have a hole in that vent hose to allow air in carb. It’s difficult to see in video, I used to make it a big v with side cutters to ensure it did not clog.

 

 

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Yes Ken, all is as it should be except perhaps, the tuning. I'm not sure that that the tube is used to get air into the car though. I thought it was a balancing device of sorts.

 

 

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