641 Carb issue

BBQChef

Member
My tractor just developed an issue today. I went to start it and it fired right up and ran briefly, then died. drained the battery trying to get it to start again. That's when I noticed a drip coming from the air intake hose on the carb. It was gas. I moved the hose a bit and even more gas came out. like a small stream. I went and turned the fuel cock off so I wouldn't lose more.

Obviously it is flooding. My guess is the float went bad or something happened to the needle/seat so that it overflows. Any other ideas before I take it apart tomorrow?

I have rebuilt many other types of carbs before, but never this model. I don't expect any surprises, but thought I would ask anyway.

And I believe it is the original Marvel carb too.
 
Are you sure you have ignition? That carb will do that if you crank and crank without burning any fuel. Before digging into the carb I would also check for fouled plugs.
 

They ALWAYS do that. It is simply the effect of combining the updraft carburetor with the choke and gravity. While cranking with it choked a lot of gas is being sucked up through the carb and manifold. When it doesn't fire up by the third revolution you have an ounce or so coming back down when you release the start button. Repeat five times you have five ounces. Don't assume flooding until you have checked plugs and they are dripping wet. As Andy said verify spark first.
 
When it's cold, I have to be careful not to flood
my Jubilee. Yesterday when I went to start it,
tractor has sat for about 3 weeks, it would only
start when throttle was in idle position and full
choke.

In winter, I have to crank main jet out 2 full
turns for it to run right. I use thinner 5w30 syn
oil in winter. Go back to 10w40 in summer

My carb is the original marvel. I installed a 12v
solenoid valve to prevent my carb from dripping a
few drops of gas while sitting. Gas will run out
of a side draft carb is you flood it, normal. So
I crank mine a few times before choking it.

I also wired around the coil's ballast during
start to give it a hotter spark when cranking
over. Mine is just cold blooded and particular
how it wants to start in winter too.
 
Maybe as simple as your air cleaner is full or water/ice which would cause that. When was the last time you cleaned it and change the oil in it?? Or it could have some dirt/rust in the float needle seat which can be cleared by pull the carb drain plug and let the gas flow for a few minutes. Catch the gas to check for dirt etc. Or yes you may have a bad float but I would start with what I said then go deeper
 
Thank you for all of your replies. I didn't know that this could be a normal thing. Will check the plugs first while battery is getting charged.

I checked the air filter last month, the oil that was in there was all white and thick like elmers glue. I cleaned it all out and put fresh oil in. Has run less than an hour since then.

I have only had to choke it to start one time, and it usually starts right up with no problem.

Thanks again Will update this afternoon.
 

I have had a lot of water get into the air cleaner of my 960 or 961 at least three times due to simply sitting out in a wind driven rain with the air intake to windward.
 

I know everyone here advocates not throwing parts at a problem but...

A carb/clean rebuild is very easy to do and costs next to nothing for parts.

The only concern is...you are adding another variable to the troubleshooting if it does not fix the problem.
 
Well, it took a long time to charge the battery, had it on slow charge. Plugs looked fine, air filter looked fine, I keep the tractor in one of those garage-in-a-box deals, so it is mostly out of the elements. Anyway, it runs. But I think I found out why it died and wouldn't start. The distributor was loose and moving around. I tightened it down, but will need to check the timing now to get it right.

I am still concerned about the leaking gas though. I know you all said it is normal, but I have never come across anything like this, so it concerns me. I mean, this wasn't just a few drops, it was more like a small steady stream like when you leave your faucet trickle to keep your pipes from freezing. I would estimate close to a half cup of gas or so before it stopped. I don't want to have it catch fire on me or something. But then again, this is my first old tractor too and I am still learning.
 
(quoted from post at 03:31:10 12/20/14) Well, it took a long time to charge the battery, had it on slow charge. Plugs looked fine, air filter looked fine, I keep the tractor in one of those garage-in-a-box deals, so it is mostly out of the elements. Anyway, it runs. But I think I found out why it died and wouldn't start. The distributor was loose and moving around. I tightened it down, but will need to check the timing now to get it right.

I am still concerned about the leaking gas though. I know you all said it is normal, but I have never come across anything like this, so it concerns me. I mean, this wasn't just a few drops, it was more like a small steady stream like when you leave your faucet trickle to keep your pipes from freezing. I would estimate close to a half cup of gas or so before it stopped. I don't want to have it catch fire on me or something. But then again, this is my first old tractor too and I am still learning.

If mine has been sitting awhile I drain 1/2 a cup out of the air breather hose. I just drain it, hit the starter and off it goes.
 
Turn off the fuel when it is not in use. Every time.
As said, if you choke it and it doesn't start, it will flood.
One thing you might want to check that wasn't mentioned
is whether or not your shut-off actually shuts off.
They are a common failure point.
Pull the plug on the bottom of the carb with the fuel shut off.
Does it stop draining or does it continue to drip some forever?
Also, "looks good" doesn't always mean "is good".
You can dry the spark plugs with a propane torch.
That will burn the deposits off. Only takes a few seconds.
Congrats on asking the right questions and keeping it safe!
 
Be sure it is a fuel problem and not ignition
before you go into the carburetor.
Gas in the intake is common if it is not starting.

Zane
 
OK, yesterday it was running, but not today. Grrrr. The fuel shut off does work. Here is what has happened today. I went to start it, and it won't turn over. The starter engages but that's it.

I hadn't planned on redoing a bunch of stuff just yet, like wiring and such, but I'm starting to wonder if I should start at one end go completely through it, New wiring, gauges, plugs wires and anything else that looks like it needs replacing.

The reason I replaced the exhaust was because it was leaking badly in multiple places. New gaskets and all, Not a big deal, but now all of this other stuff is happening.

Is this a common thing too? fix one thing and two other things go bad? LOL

I honestly don't mind all that much, cause I get to play and learn about this tractor, I had just hoped it would see me through the winter plowing snow before I had to go through it due to problems.

Supposed to be above freezing tomorrow and the next day, will see if it turns over then.
 
OK, Well now that it is in the 50's here today, the old tractor started right up. Not sure why it wouldn't turn over the other day except for the lingering thought that something internally was froze up. Hope not.

Anyway, another issue has reared its ugly head today. As I said, it started right up, ran great for a couple minutes at half throttle, and then it just dropped down to idle. Doesn't matter where I set the throttle, it won't run past idle speed. All linkage is intact and working, if I apply even the slightest amount of choke it dies. I really am at a loss on this one.

I have not touched the carb at all, fuel is coming through fine, Not sure what to think.
 
If you're opening the throttle plate with your hand and it
doesn't respond, either you're not getting enough fuel or
you have a blockage somewhere.
 
That was my thought too, just wondering if could be something else since I am new to this old tractor.

Thanks.
 
Did you clean the whole air cleaner or just change the oil? The filter elements can get clogged and cause the trouble you are having.
 
Cleaned the filter and canister completely to get rid of all the thick white goo and put new oil in. I did that a couple months ago and I did not have any problem until just the other day.

I've been working the past few days and got one more day tomorrow, so I haven't had a chance to really dig into it again. Either Monday or Tuesday I will see if I can figure this out.

Any chance that there might be an issue with the governor? I know it has one, but don't know where it is located. I haven't had much luck searching the internet either, I keep finding info for 8n, 2n, 9n and NAA but not a 601 series.
 
This is weird. First you have gas dripping out of the carb, then you have what sounds like it's not getting enough fuel. Have you tried starting it with the air filter disconnected at the carb? Could be something clogging the pipe between the carb and the filter. I don't think the governor is involved, especially if operating the throttle plate by hand has no effect.
My money is on trash in the gas has plugged a jet. I'd also take a look at the screen in the sediment bowl. If there's a lot of crap on it you may need to clean or replace the gas tank. My 640 was acting like what you are experiencing and the tank was the culprit. Rust particles would keep the needle valve from closing, and gas would drip out of the carb. I'd clean out the carb, and the drip would stop, and it would run fine for a few days. Then after sitting for a week or so, it would start, but would'nt run above a fast idle. The screen in the sediment bowl would be all clogged up. This scenario kept repeating itself until I replaced the gas tank. Now it starts on the first revolution and doesn't leak a drop. I always shut the fuel valve off before killing the engine, and if it's going to sit for more than a few days, I run the engine until it burns all the gas out of the carb.
 
Believe me, I know its weird. Makes no sense to me either. That's why I am here asking.

I have looked inside the tank and it is clean, no rust. No problems until I put the new exhaust on.

Only thing I can think of is a slug of dirt somewhere. Will be tearing into it on Monday I think. I hope it is as simple as just a good cleaning and all will be well again.
 
If you replaced the whole exhaust system, you may have a bad muffler. A baffle could be moving around and restricting outflow.
 
No go today, Battery had just enough to barely turn it over about four slow times and it was done. Me thinks I need a new battery. Will be a couple days before I can get one and try and figure out the problem.

I am thinking about a new wiring harness as the current one looks pretty dated and pieced together. Might splurge for some new gauges too as none of them are currently working.
 
(quoted from post at 18:19:13 12/30/14) No go today, Battery had just enough to barely turn it over about four slow times and it was done. Me thinks I need a new battery. Will be a couple days before I can get one and try and figure out the problem.

I am thinking about a new wiring harness as the current one looks pretty dated and pieced together. Might splurge for some new gauges too as none of them are currently working.


You need a booster pack. You could make progress if you could get over the hurdle of continually adding new variables.
 
Had a few minutes today to see what I could see. New battery installed. Had to choke it a little to get it to start, but it seemed to run ok, if idle speed is ok. Still nothing over idle speed.

Sediment bowl is full, and when I turn the gas on, there is a slow leak off the bottom, like one drop every couple minutes, It has done this since I got it, so nothing new there.

Exhaust seems to smell quite rich and has a lot of black in it.

It ran for several minutes, then seemed to slow down a bit, but after another couple minutes, it came back to normal idle speed.

I decided to turn the fuel off and let it go till it died. Ran less than a minute, but in the final 5-10 seconds, it revved up. I did have the throttle opened up, and as it gained rpms, it finally gave out and quit.

I did notice I had a few things floating around in the sediment bowl.

Will be taking the carb off tomorrow. I have waited long enough for it to correct itself and it appears that whatever is holding it up, needs more attention than just some sweet talk and a couple taps of a screwdriver handle to fix it.

Thanks again for all the help. You guys are the best.
 
Did a good cleaning on the carb yesterday. Put it on this morning and think I might have messed up the fuel line threads a tiny bit as it has more dripping now off the sediment bowl. And it is coming from where the line attaches to the bowl.

Anyway, the good news is that it is running and the throttle works fine like it should and no black smoke. Set the adjustments screws 1 1/4 turns out after bottoming them.

Next up is setting the timing as it sputters and pops a bit, more so with increased throttle.

There were some nasty's in the sediment bowl and some light gunk in the carb. Nothing really bad though, but knowing carbs, it doesn't take much in just the right place to mess it up.

Thanks again for all the thoughts and suggestions everyone.
 

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