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Old 03-02-2012, 02:46 PM
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Default mcculloch 4318 72 HP fuel question

Hi, I was wondering what type of fuel i should run in my mcculloch 4318. some one had told me i need to use 100LL in it with a 50:1 2cycle oil mix. If I am correct the LL stands for light lead. so my question is did they say that because it is high octane or does the lead do any thing for it? I know older cars used to use leaded fuel to keep from pre-ignition (or pinging), but higher octane will also help with that. I have also heard that you shouldnt run old engines with unleaded fuel because the valves are soft, but then i remembered that this engine is a 2 stroke it doesnt have valves. I was thinking of running 95 octane with an octane booster. also i am not sure what the right mixture should be for the oil. i have heard 50:1 but also 10:1. they are a lot different. if you run too much oil it will get carbon build up faster and that can cause you to burn a hole i a piston. Any information would be greatly appreciated.
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Jake
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Old 03-02-2012, 03:13 PM
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Hello Jake, I run 101ll with 80-1 amzoil saber and it has worked ok for me. Different oils use different mixtures. The MAC was designed to use 140 octane.
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Old 03-02-2012, 07:08 PM
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I also run 100LL and 80:1 Amsoil Saber.
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Old 03-03-2012, 04:50 AM
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On my 90 Mac, I broke the engine in on petro based oil mixing 16oz per 5 gallon of 100LL.
Now that the breakin is done; per Rick Wittridge, I use 14oz of Blue Marbles per 5 gallon of 100LL now.
The Blue Marbles also netted about 25 degrees cooler operating temps.

Make sure you are jetted correctly and turning the right prop, and do not starve it for fuel (weak pump). You can destoy it pretty quick by a leaning mixture and over temp a jug and melt it down and have a siezure.
I went from great cylinder temps to melt down in about 15 seconds.
The pic was after a prop swap, and was turning more rpm and leaned the mixture. Expensive learning curve!
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Old 03-04-2012, 03:44 AM
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David, I feel for ya man. But didn't that thing run GOOD for the first 5 seconds of the last 15?
THat's what I remember from all the lean seizures, "Man, this thing has some power" eek.
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Old 03-13-2012, 06:04 PM
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well I found an airport near by that has 100LL fuel. So i decided to run with that and 80:1 amzoil mix. today I got fuel at the airport, that was a first for me. I couldnt get it to run though. It would pop and some times start but wouldnt keep running. I took out the plugs and cleaned them. they all looked liked they were gaped different. tomorrow i hope to get new ones and gap them correctly. I am gonna paste a link to a video of my first attempt to start it. I have never tried to start an engine like this. it is scary trying to start it by the prop. if you see the video and think i am using the wrong technique please correct me.
http://youtu.be/d6t98kwtTs8
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Old 03-13-2012, 06:24 PM
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I have a couple qestions, did you squirt a little fuel in each of the exaust ports? How did you mount the prop?

You need to start to pull the prop from where it stoped the last pull and pull it through with one motion. It looks like you may need to spin the prop on the hub so it is straight up after you pull it through. It is more art than science starting a MAC. It looks like you have compresion and the mag is clicking like it should.
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Old 03-13-2012, 06:31 PM
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Jake, You should be standing beside your machine next to the throttle, Kill switch & prop with your right hand. When it fires you need to be on the throttle. When you hear that click is when the impulse is releasing & the mag is firing. You are about to GET HURT by propping the way you did in your video! If the fuel prime is right & the mag is HOT it will start when it clicks with your arm in the prop! A blade should be standing straight up when your ready to pull thru. It should click when the blade is at the 3 oclock postion thus releasing your hand away from the blade.
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Old 03-13-2012, 07:23 PM
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Damn, that was a scary video. Jake, if that engine had lit off while you repositioning the prop for the next pull it would have probably killed you.

I agree with Rick on the starting procedure, but I don't know if I would want to try starting a Mac with a 3-bladed prop. A 2-bladed prop will at least give you 180 of room before the next blade comes around.

I have done it on a Continental with a 3-bladed Warp Drive, and it made me nervous.
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Old 03-13-2012, 09:04 PM
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later it had poped over while i was repositioning the prop, i got my hand out quick. I then started hitting the kill when i would repositioning it.
Rick, I will follow your advice on starting it. I am new at this and I am open to all positive criticism.

Last edited by jake_the_snake; 03-13-2012 at 09:09 PM.
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Old 03-14-2012, 05:08 AM
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Three blades on a hand proped Mac is trouble!!I have a pulled place on me right thumb ball from just that! Scares me.
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Old 03-14-2012, 06:03 PM
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well i got it running today. I did as advised and stood next to it with one hand on the throttle and kill and started it with the right hand. I did some taxing it seemed a little sluggish on throttle response and didnt seem to have the power i thought it should. I dont know what it should feel like I am used to motorcycles. later i figured out that it was only running on two cylinders. I believe the coil that runs the front two cylinders is bad. I my have one from a motorcycle or snowmobile, but i am not sure if that would work right.
here is a video of my messing with it today.
http://youtu.be/F7ZlzUtvYxU
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Old 03-15-2012, 05:07 PM
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I was checking the spark today and it seems really weak. do the Macs normally have a weak spark or do i need to figure out why i have weak spark. It has an electronic ignition on it. I could trace down all the wires and clean them up. i know one of the wires on the one coil had some sort of silicone between the wire and the coil so it was insulated from it. who ever worked on it before me must have liked silicone because it is everywhere on that thing. any ideas would be appreciated.
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Old 03-15-2012, 05:59 PM
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Jake, If it is a ARD CDI you need to call me for the correct info before you go any further. There is a number stamped on one side of the mag case where it mounts to the engine. Have that number when you call. I will walk you thru the ignition test.

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Old 03-16-2012, 08:48 AM
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the number is 10457A I wont be around till monday. I was hopeing to get mess with it today. but i guess a few days of not trying to start that thing will be a good rest for my sore right arm.
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