Mercedes-Benz Forum banner

1 - 16 of 16 Posts

·
Registered
1962 Unimog 404
Joined
·
265 Posts
Discussion Starter #1
My 62 404 is getting harder to start in the cold. It was 48 yesterday and when I jumped in to start it, it turns over and it will just catch and then it will back fire thru the carb which then kills it. This happens over and over for about 5 minutes. When it finally starts it will not rev above 800ish rpms. During this time it will backfire thru the carb killing it. Finally after sometime it will clear up and idle and rev fine. It still backfires and kills the motor until it warms up. Once it's warmed up it's fine. It starts fine and drives fine. It has the stock ignition.

Thank you for your help.
 

·
Registered
1978 416.115
Joined
·
1,035 Posts
I had an old car that did that, it was the choke. Do 404's have chokes?

Anytime it starts hard and runs fine after warming up always seems to be a choke issue, at least for cars.

Could be a clogged jet too ... not sure if 404's have jets.
 

·
Registered
1962 Unimog 404
Joined
·
265 Posts
Discussion Starter #3
I had an old car that did that, it was the choke. Do 404's have chokes?

Anytime it starts hard and runs fine after warming up always seems to be a choke issue, at least for cars.

Could be a clogged jet too ... not sure if 404's have jets.
It has both. I wonder if the choke is out of adjustment? If that's possible. It doesn't like the choke being used either. Even when it's cold out and I try to use it. It back fires real bad, not in the carb but the exhaust and it just runs real crappy.
 

·
Registered
1967 404 Unimog (Belgian), 2010 Ford Fusion Hybrid
Joined
·
253 Posts
How much choke are you giving it? I've never needed to pull the choke all the way out on mine.

When I start in cold weather I always refill the carb bowl either cranking the engine with ignition off or the lever on the fuel pump. Then give it three (or more if really cold) shots with the accelerator pump. Pull the chock halfway and crank it. Once it catches try to reduce the amount of choke you're using; use just enough to keep running ~1000 rpm. Once the coolant temp gauge begins to rise I don't need the choke any longer.

Good luck.
 

·
Registered
1962 Unimog 404
Joined
·
265 Posts
Discussion Starter #5
How much choke are you giving it? I've never needed to pull the choke all the way out on mine.

When I start in cold weather I always refill the carb bowl either cranking the engine with ignition off or the lever on the fuel pump. Then give it three (or more if really cold) shots with the accelerator pump. Pull the chock halfway and crank it. Once it catches try to reduce the amount of choke you're using; use just enough to keep running ~1000 rpm. Once the coolant temp gauge begins to rise I don't need the choke any longer.

Good luck.
Ok I have a stupid question, but how do I turn it over with the ignition off? It seems like if I use any choke at all it just doesn't run good.
 

·
Registered
1978 416.115
Joined
·
1,035 Posts
Ok I have a stupid question, but how do I turn it over with the ignition off? It seems like if I use any choke at all it just doesn't run good.
The choke is just used to start it up. Pull it about 1/2 way out and start it. Once it starts to run, slowly push it in. If you have it out after starting, it'll run bad and if you have it to far in, it'll stop running. At least that's how it works for cars that I owned with manual chokes.

Once it warms up, you shouldn't need to have it out at all.
 

·
Registered
Joined
·
1,924 Posts
If your new to the Mog...getting to know how the choke opperates is important but it shouldn't dissallow you of starting the truck unless the choke is stuck open... So check the operation of the choke. Remove the jets and make sure they are clean...this is very easy. Check the exhaust manifold pre-heater spring on the exhaust manifold to make sure it's not broken...this can be a big cause for no start during colder weather. This happened to me and once it was changed...the vehicle started fine....If you don't know the condition of the fuel system...install a see through in-line fuel filter and monitor it for contamination. Check timing, check points/cap and rotor...This can be a issue too if they have not been taken care of...Make sure you put a couple drops of oil in the dist. drive gear tube(not too much). Well there you have it...this should get you in the right direction....If you find its a contamination issue...buy a few inline filters and clean your system out....If you have alot of rust in your tanks...Treat the tanks...POR makes a good product. Also check your Fuel/glass filter on pre/mechanical fuel pump....Just make sure it's clean.
 

·
Registered
1978 416.115
Joined
·
1,035 Posts
Here's the order I'd go in:

1. Choke
2. Exhaust manifold pre-heater
3. Jets

I'm guessing it's either 1 or 2 since you said it's been tough starting in colder weather and after it warms up it runs fine.
 

·
Registered
Joined
·
1,924 Posts
I agree with 1 and 2 first....Mine was the pre-heater....Unimog wouldn't start without me replacing this...It ran like .... unless it was warm....Problem is you get to your destination after fiddling around with it and it's finally warm....You leave it sit for 45 minutes and you come back out and its the same problem all over....Another thing is ...you shouldn't havet to pump it at all...The pulling of the choke lever should be all you need....This is probably just filling the float to overfull and it's pouring out then finally a spark occurs and then you flooding or it backfires which could earn you the right to buy a new muffler and plugs which aren't cheap if your running the military plugs still.
 

·
Registered
1967 404 Unimog (Belgian), 2010 Ford Fusion Hybrid
Joined
·
253 Posts
Ok I have a stupid question, but how do I turn it over with the ignition off? It seems like if I use any choke at all it just doesn't run good.
I assume you have a 404.1. The key has three positions: 0, 1 and 2.

0 is the off position. You can remove the key in this position.

1 is one click over. Here is where you can crank the engine but the ignition is off.

2 is the "run" position.

If I understand you correctly the choke seems to supply too much fuel even when only pulled out slightly. This makes me think of two things to check.

(1) the wrong jet is installed. It may be too large and supply too much fuel.

(2) the choke disk is installed incorrectly. This is the thingy that rotates as you pull out the choke. Check Expedition Imports site for a carb breakdown diagram and check that the disk and arm are aligned as in the diagram.

You will likely need to replace the gasket if you remove the cover to check the disk position. I'll bet Scott at EI has another for a few bucks.

That's all I can think of at the moment.
 

·
Registered
'88 U-1300L, '70 406, '78 406, '78 416 project, '82 406, '57 404, '65 404, '70 404, '68 Haflinger.
Joined
·
1,849 Posts
FYI, it's not usually beneficial to compare any Unimog function to that on some "old car". The engineers threw away the book before they started working on the 'mogs.

My 404's start right up with the throttle untouched (at idle) and the choke pulled all the way out. Let it start, push in choke just enough to keep it running smoothly, and when the choke is near off then compensate for loss of rpm with throttle.

Bob
 

·
Registered
Joined
·
1,924 Posts
FYI, it's not usually beneficial to compare any Unimog function to that on some "old car". The engineers threw away the book before they started working on the 'mogs.

My 404's start right up with the throttle untouched (at idle) and the choke pulled all the way out. Let it start, push in choke just enough to keep it running smoothly, and when the choke is near off then compensate for loss of rpm with throttle.

Bob
This is the way my mog starts up....Pull choke out then push the button in #2 position. If the choke is set too tight it could potentially cause problems too. You should be able to diagnose the issue with some basic trouble shooting. If the Mog ever sat around for a bit and has bad fuel in it or one of the jets has stuff in it or maybe the float has been varnished by bad fuel...it's easy get a carb out of whack.

You could just switch over to F.I....but that would take the funn out of a 404.
 

·
Registered
1970 MOG 404
Joined
·
12 Posts
If your mog is backfiring you should check/replace your sparkplugs,mine will run great for a while then when it starts backfire i change the plugs and she's all good again,even in the cold like it is here....-30 celcius...yuck
 

·
Registered
1963 Swiss 404
Joined
·
181 Posts
I have to back up Bob Ragain's starting procedure. I prime the carb, without ignition, pull the choke fully out, do not touch the throttle pedal, and it starts. Push the choke smoothly in until the idle smoothes out, then keep reducing the choke to keep the rpm at 1,000 until warm.
As I recall, this is the manual's recommended start-up procedure.

If you want another hint, based on personal experience, to counter the possible fouling of plugs, carbon buildup within the combustion chambers, and possible varnish buildup within the fuel system, try this: every 3,000 km or so, I add a gallon or two or diesel fuel prior to filling up with gasoline. You might get a little bit of white smoke, initially, but the diesel will reduce any varnish buildup in the fuel system while also doing a mild de-coking of the combustion chambers. It's best to do this prior to a longish run -- perhaps 50 to 100 km or so, to ensure sustained operating temperature.

Of course, this procedure is in addition to, not a replacement for, the earlier recommendations to check your jets, filter, etc., and I would check your valve clearances before and after doing the diesel trick, in case some deposits on any of the valves have been jettisoned/burned off.
 

·
Registered
Joined
·
1,924 Posts
Farm Diesel

I have to back up Bob Ragain's starting procedure. I prime the carb, without ignition, pull the choke fully out, do not touch the throttle pedal, and it starts. Push the choke smoothly in until the idle smoothes out, then keep reducing the choke to keep the rpm at 1,000 until warm.
As I recall, this is the manual's recommended start-up procedure.

If you want another hint, based on personal experience, to counter the possible fouling of plugs, carbon buildup within the combustion chambers, and possible varnish buildup within the fuel system, try this: every 3,000 km or so, I add a gallon or two or diesel fuel prior to filling up with gasoline. You might get a little bit of white smoke, initially, but the diesel will reduce any varnish buildup in the fuel system while also doing a mild de-coking of the combustion chambers. It's best to do this prior to a longish run -- perhaps 50 to 100 km or so, to ensure sustained operating temperature.


Of course, this procedure is in addition to, not a replacement for, the earlier recommendations to check your jets, filter, etc., and I would check your valve clearances before and after doing the diesel trick, in case some deposits on any of the valves have been jettisoned/burned off.
High Sulfur Farm Diesel is the best! Good suggestion.
 

·
Registered
1962 Unimog 404
Joined
·
265 Posts
Discussion Starter #16
ThanK you all for your replies. I appreciate it. The next time I drive it I will try the solutions out. :)
 
1 - 16 of 16 Posts
Top