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8N Carb Adjustment

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Delarar Bill

12-28-2012 07:54:27

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Hi All. Having trouble as follows: my 8N side mount, 6 volt is hard to start all the time (hot or cold) without the choke closed. I adjust the needles as advised, idle 1 turn out and main 1 1/2 turns out. When running, as I turn in the idle needle in to enrich, the engine sounds better, but turning it all the way in still does not make it idle smoothly or start properly. I can get it to idle at 300 to 400 rpms but it is not smooth. One observation: I have the hood off so I am running the engine without the air cleaner. Could it be running too lean regardless of what I do? As far as spark, I have hot spark with a dummy plug opened up to a 1/4 " gap and the plug wires are in the correct order.

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R Geiger

12-28-2012 11:35:29

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 Re: 8N Carb Adjustment in reply to old, 12-28-2012 07:54:27  
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If it starts if you use the choke, then I would say you do not have problem. But that is just what I think!! opinions will vary.

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Delarar Bill

12-28-2012 11:26:48

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 Re: 8N Carb Adjustment in reply to Delarar Bill, 12-28-2012 07:54:27  
Thanks for all the replies, but my main issue is the hard to start problem.

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12-28-2012 11:35:03

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 Re: 8N Carb Adjustment in reply to Delarar Bill, 12-28-2012 11:26:48  
Where do you have the throttle set when you try to start it??? On my late 1950 8N ford side mount I have the have the throttle set about 3/4 of the way open and it starts so fast most of the time you can not get your hand off the starer button fast enough but if you close the throttle down to idle it will NEVER start.You may need o play with the throttle bit and maybe even the timing. Also when was the last time you checked and cleaner the oil bath part of the air cleaner?? Had one where I had a guy call me about his hard to start tractor and I looked at it and yep hard to start. Asked him about the air cleaner and he said what you have to clean them. Found that was his problem due to lack of air coming in

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12-28-2012 09:39:08

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 Re: 8N Carb Adjustment in reply to Delarar Bill, 12-28-2012 07:54:27  
That low idle speed it just a thing that some want but is not really needed. Yes if you get it down to the low speed yes it will not run smooth because it is looping and is sort of hit and missing and that is part of the reason it is so slow and it is also running lean to be doing so. Just to have an old 8N that will do that is almost bragging rights and is a thing not to worry about unless it does not run well at higher RPM. That magic low RPM number is just a number that for some odd reason people seem to think they have to have and it is just a number nothing more

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Bruce (VA)

12-28-2012 09:48:19

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 Re: 8N Carb Adjustment in reply to old, 12-28-2012 09:39:08  
"..... and it is just a number nothing more "

Except on a sidemount when you are trying to set the timing. Then, under 500 rpm will work fine.

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12-28-2012 10:08:09

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 Re: 8N Carb Adjustment in reply to Bruce (VA), 12-28-2012 09:48:19  
Get technical why don't you LOL Shoot you know even getting the timing down to just so on something this old can be hard to do unless you have a lot of new and not form the land of almost right part so timing can also be a close to the ball park thing on a 50 year old engine LOL

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Bruce (VA)

12-28-2012 10:18:20

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 Re: 8N Carb Adjustment in reply to old, 12-28-2012 10:08:09  

I've only got 2 sidemounts on the place; the 51 8N & the 740. Setting the timing on the 51 was easy. The 740 did not want to cooperate. It would change 5* every time I tightened down the distributor. Took me three tries before I finally set it back 5*, tightened the nut & that got it dead on.

Sometimes I'm a little slow at the mechanic-ing stuff.........

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12-28-2012 11:20:03

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 Re: 8N Carb Adjustment in reply to Bruce (VA), 12-28-2012 10:18:20  
Here is a true story about a car my dad once had. He took it in for a tune up, back when I was around 17 or 18. He got it back and told me it just doesn't run like I think it should. I pulled out my new timing light and check it sure enough right on. I said hey let me drive it and bot and see if I can make it better, He told me sure why not. I grabbed a wrench and took off. I would stop and adjust the timing by ear a bit at a time till I got the power I wanted but then it would not start easy . Played with it a bit more and got powder and easy start. Took it back to my dad and told him try it. I also told him DO NOT punch it but he told me I'll drive as I want. He punched it and left tire marks, bad thing is from then on I got the job or working on his cars

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R Geiger

12-28-2012 09:07:37

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 Re: 8N Carb Adjustment in reply to JCinKY, 12-28-2012 07:54:27  
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The choke is there for a reason. What is wrong using it to start with? MIght be ioce for a show tractor to start without it but I see nothing wrong with having to use it when starting.

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Bruce (VA)

12-28-2012 08:18:14

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 Re: 8N Carb Adjustment in reply to Delarar Bill, 12-28-2012 07:54:27  
Make sure the tractor is at operating temp; that usually takes 10 15 minutes at idle depending on ambient temp.

Both Ford and Marvel/Schebler (assuming you have a M/S carb ) say to set both the side-pointing idlemix and the down-pointing mainjet to 1-turn as a starting point. I set the down-pointing mainjet to 1-1/2 turns and don't fool w/ it until the final step.

Then adjust the side-pointing idlemix for fastest idle; not the smoothest idle. Next, adjust the behind the carb idle-speed set-screw for very slow 400-rpms idle. Do that idlemix adjust for maximum idle at least 3-times. Make sure that you turn the screws slowly, like 1/8 of a turn at a time & wait a second or two for the engine to catch up. Take your time!

Do it like this:

1. Adjust idle mix jet until RPM increases

2. Adjust idle-mix set screw until the engine nearly stops (as slow as you can get it unless you have a tach that tells you 400 rpm)

Repeat steps 1 - 3 three times.

Remember the side-pointing idlemix is out for lean, in for rich.

If you do not have any problems inside the carb, it is easy to get the idle down to 350 - 400 rpms.

Your last step is to go back to the main jet. Remember, in for lean, out for rich. If you end up turning it OUT more than turn for max power (remember, you already had it 1 turns out) then stop right there because you have a dirty carb or a fuel problem

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