Carb timing

mitchkuzma

New User
I have an 8n ford tractor, 1948 I believe. After input from the board here I ordered a new carburetor (details below) and I put in on. I also added a new fuel line piece (copper) with a little fuel screen in it. It said that the carb comes already adjusted. Anyway, when I started it at first it sounded ok for a little bit but then the engine/rpm would drop then return. It kept doing that. At some point the rpm would drop very low and go dead. I can choke it and it would start again and do the same thing. A little later I realized that if I held the choke out it would stay running. I did play with the screws a little but I did return them as they were. Does anyone know the proper (hopefully) easy way to set the timing? I am not a mechanic but average intelligence on motors, but not carbs.

A LITTLE HISTORY FYI -
When I bought the tractor the engine ran great but I, or it would not maintain a steady speed/rpm/etc. Especially when I was pulling something. My (former) tractor guy said it needed a new governor so he put one on it and when I picked it up the tractor sounded like it was missing, sputtering, etc. but would run. And I could control/maintain the rmp. But he said I really needed a new carb. So I got one myself and put it on myself. I have no idea how to set the screws/timing.

Any simple help would be appreciated.

Mitch

8N9510C-HD Marvel Schebler Carburetor Ford Tractor 2N 8N 9N Heavy Duty New
a195946.jpg

a195947.jpg
 
" carb timing"

Now that's a new one on me.

It's called "adjusting the carb"

" I have an 8n ford tractor, 1948 I believe. "

You'd be wise to buy the manuals for a nearly 70 year old piece of equipment; see tip # 39 at the link.

To adjust the carb, 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 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 ½ turn for max power (remember, you already had it 1 ½ turns out) then stop right there because you have a dirty carb or a fuel problem.
75 Tips
 
here's a hint.. if it started and ran good when you installed the carb... then it was adjusted OK>

your tweaking messed that up.

When you felt it hunt and stall and that choke helped.. that was it telling you, over and over, that it was running out of fuel!

You should have checked fuel delivery... not adjust carb!
 
Mitch..........ummmmm.........carb timing? I have DUAL CARBS on my semi-race BMW 2002 that I haffta time. Yer single throat M/S has 'nuttin' to time ...but... it has 3-tweek'ems that shadetree mechanic wanna bees like to twiddle. While both Ford and Marvel sez to adjust each screw to 1-turn thats WAY outta the ball park. Heres HOW I doo itt. I adjust the down-pointing MAIN JET to 2-turns and LEAVITT!!! I adjust the spring loaded IDLEMIX fer FASTEST idle, NOT smoothest idle. Understand the difference? It adjusts BASSACKWARDS, out fer lean, IN fer ENRICH. Usually ends up about 1/8-turn. I adjust the BEHIND the carb idle speed fer ennythang under 500-rpms. I once gott my eazy starting 6-volt 8N to idle at 350-rpms with transistorized tachometer. I usually adjust the idlemix/idlespeed 3-times before I caller quits. As fer adjusting yer carbie, 2-turns on MAIN JET, and fastest idle on idlemix and you should be good to go. Make certain yer GLASS under the tank filter is 2-turns fer runnin' and ALWAYS turn yer glass valve OFF when thru fer the day 'cuz the carb float valve LEAKS and will FLOOD yer engine. When you FLOOD yer engine, replace yer FLOODED sparkies. Recommend AutoLite 437's gapped 0.025. ........HTH, Dell, yer self-appointed sparkie-meister
 
Mitch, I've offered you my email address several times.
Using it probably would have saved you some money and
frustration. Your carbs are probably fine.
The new one and the old one.

There are three screens in the 8N fuel system.
One in the elbow that goes into the side of the carb, one
above the glass sediment bowl and one above the sediment
bowl assembly, inside the gas tank.
The first two are pretty easy to check and clean.

All of them can be tested by taking the plug out of the bottom
of the carb, then turning on the gas two full turns and watching
the stream. Catch it in a clear container so you can check it for
dirt/water/etc. It should run a steady stream, not taper off.

About a pint or so in two minutes. If it piddles off or surges,
you have a different problem. The simplest of which may be a
plugged vent in the gas tank. Do that same fuel flow test with
the gas cap loose or removed. If that fixes it, try running it with
the gas cap loose. If that works, all you need is a vented
gas cap. You will need at least three gallons or so of fuel in the
tank for the tests to provide useful results.
 
Just 'my' personal thoughts (and experiences) here.

From your words I take it that the tractor ended up running same after a 'new' carb as it did with 'old' carb.
And that it ran like this since you bought it.

As others have said, good chance the main problem is dirty screens.
My question is how dirty is the inside of the tank?
It's amazing how much 'stuff' can get inside the tank while adding gas.
It's also amazing how something as small as a tiny wood splinter can, and will, slow fuel flow down to extent that tractor will shut off.
Others have stated about 3 screens needing to be clean already, but there is only 1 inlet hole in the fuel sediment bowl inside the tank and it's a lot smaller than you might think.
Start by checking flow as others have stated.
Only thing I would do different is instead of a pint jar use a quart jar or even a gallon jug.
Mine would fill a pint jar but wouldn't fill a quart jar before stopping.

My thoughts are you now need to get the carb readjusted, however, there is zero chances of getting it right till you find out why fuel slows and or stops running.

If you don't have the ability to adjust it, or have a buddy that can, it is worth the money to send it to someone like Royce (while there are many others here that can do it, Royce is the current carb go-to guy) to have it done, however it really is a waste of time and money if you don't get fuel delivery problems fixed.

Hint: While the inside of my tank looked great, I was unable to get ALL the tiny splinters that kept plugging up my fuel bowl inlet out of my tank and ended up replacing tank to clear up the fuel problems.
 
(quoted from post at 19:59:31 07/14/15) Mitch, I've offered you my email address several times.
Using it probably would have saved you some money and
frustration. Your carbs are probably fine.
The new one and the old one.

There are three screens in the 8N fuel system.
One in the elbow that goes into the side of the carb, one
above the glass sediment bowl and one above the sediment
bowl assembly, inside the gas tank.
The first two are pretty easy to check and clean.

All of them can be tested by taking the plug out of the bottom
of the carb, then turning on the gas two full turns and watching
the stream. Catch it in a clear container so you can check it for
dirt/water/etc. It should run a steady stream, not taper off.

About a pint or so in two minutes. If it piddles off or surges,
you have a different problem. The simplest of which may be a
plugged vent in the gas tank. Do that same fuel flow test with
the gas cap loose or removed. If that fixes it, try running it with
the gas cap loose. If that works, all you need is a vented
gas cap. You will need at least three gallons or so of fuel in the
tank for the tests to provide useful results.

Royse, is this the same guy that went away mad about three weeks ago? refusing to fix his wiring and insisting that the problem was the governor?
 
(quoted from post at 22:16:31 07/15/15)
(quoted from post at 19:59:31 07/14/15) Mitch, I've offered you my email address several times.
Using it probably would have saved you some money and
frustration. Your carbs are probably fine.
The new one and the old one.

There are three screens in the 8N fuel system.
One in the elbow that goes into the side of the carb, one
above the glass sediment bowl and one above the sediment
bowl assembly, inside the gas tank.
The first two are pretty easy to check and clean.

All of them can be tested by taking the plug out of the bottom
of the carb, then turning on the gas two full turns and watching
the stream. Catch it in a clear container so you can check it for
dirt/water/etc. It should run a steady stream, not taper off.

About a pint or so in two minutes. If it piddles off or surges,
you have a different problem. The simplest of which may be a
plugged vent in the gas tank. Do that same fuel flow test with
the gas cap loose or removed. If that fixes it, try running it with
the gas cap loose. If that works, all you need is a vented
gas cap. You will need at least three gallons or so of fuel in the
tank for the tests to provide useful results.

Royse, is this the same guy that went away mad about three weeks ago? refusing to fix his wiring and insisting that the problem was the governor?
I don't believe so Showcrop.
I think Mitch is just trying to get his tractor running and I'm
trying to help, but I'm not convinced the problem is with his carb.
If it turns out to be a carb problem I'd be happy to help there too.
Just can't see spending that money if it's not needed.
 

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