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1963 Unimog 404
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26 Posts
Discussion Starter #1
I have a 1963 Swiss 404 with aprox. 12000 kilometers on it,it has a pertronix ignition,civilian cap and rotor,recently rebuilt carb,the centrifical advance moves freely and is timed to12 degres. This truck runs good,starts good does not smoke but runs out of power in the upper rpm range(above 3000). It will not pull to the 5 gear shift point on the speedo. this puts you at too low of rpms to have enough power to keep your speed up in 6 gear. Anyone else had this problem and found an answer? Don't want to hear about changing engines or other BS,this tuuck was designed to rev and pull to these points with the military ignition,crapy gas,retarted timing etc. Thanks Voudoux
 

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'88 U-1300L, '70 406, '78 406, '78 416 project, '82 406, '57 404, '65 404, '70 404, '68 Haflinger.
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1,849 Posts
Forget the timing spec's and tune ignition timing for best performance at top speed with the gasoline you plan to use all the time. These engines will seldom have pre-ignition problems (such low compression) so you can tune really early, for performance.

With centrifugal advance, you might be hitting 35 to 40 degrees BTDC when it runs best. The S-F adjustment is normally not enough range. Probably have to rotate the dissy by loosening the clamp on the backside of the dissy shaft (ie, near spark plug #1) with 5mm (or is it 6mm) Allen wrench. Then use S-F to fine tune. BTW, the S-F has about 10 deg range.

You are right that these engines don't make hp until at high revs. If it won't hit 5000 rpm temporarily, then something is still wrong.

When you advance the timing, keep doing so until you no longer gain top end rpm. You'll then start to lose rpm as timing is advanced more, then back off on timing.

You must do road testing to achieve best road performance. Pick a long hill climb and use that as your test bed.

BTW, what's your name and where are you located?

Bob

I have a 1963 Swiss 404 with aprox. 12000 kilometers on it,it has a pertronix ignition,civilian cap and rotor,recently rebuilt carb,the centrifical advance moves freely and is timed to12 degres. This truck runs good,starts good does not smoke but runs out of power in the upper rpm range(above 3000). It will not pull to the 5 gear shift point on the speedo. this puts you at too low of rpms to have enough power to keep your speed up in 6 gear. Anyone else had this problem and found an answer? Don't want to hear about changing engines or other BS,this tuuck was designed to rev and pull to these points with the military ignition,crapy gas,retarted timing etc. Thanks Voudoux
 

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1963 Unimog 404
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26 Posts
Discussion Starter #3
Thanks Bob,will trythe timing,and let you khow.I am Steve located in piedmont NC.
 

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'88 U-1300L, '70 406, '78 406, '78 416 project, '82 406, '57 404, '65 404, '70 404, '68 Haflinger.
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Thanks Bob,will trythe timing,and let you khow.I am Steve located in piedmont NC.
Nice to meet you Steve. Welcome to the forum. I am across the big hill west of you, southwest of Knoxville. We have a Southeast Mogfest in the Spring. Watch for it!

Bob
 

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1963 Unimog 404
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26 Posts
Discussion Starter #6
Does anyone know the running fuel pressure and volume or where to find these specs?Also the fuel filters,are thet avalable local(napa/world pack/MB dealer) ? Thanks Voudoux
 

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BenzWorld UNIMOG statesman
Unimog 404.1 Diesel (sold :( )1995 LMTV 1078
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5,857 Posts
just recall a thread we have in here about a performance issue after a carburetor rebuild. It was rebuilt with the wrong something (arm or spring orr?) in the accelerator pump if I recall right. Something to keep in mind.
 

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1963 Unimog 404
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26 Posts
Discussion Starter #8
I ran into a excelerater pump problem,it didn't involve the spring but a hole was not drilled in the check valve so there was no place for the gas to go.Another question the stock fuel filter looks to be on the suction side of the pump.On a military truck I can understand this because of the quality of gas available,but a filter on the suction side can cause all sorts of problems, it only has atmospheric presure to force the gas through it and a minute leek can cause a big problem. Thanks for the help Voudoux
 

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2015 Rubicon Unlimited (Let the shame be upon me!)
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A post pump paper filter with no particulate control can force crap, and in the case of the 404 rust, through the filter and destroy it's effectiveness. The 404 fuel system is profoundly simple to suit operation and maintenance in trying conditions and as such doesn't require high amounts of fuel flow or pressure so a gravity siphon filter and diaphragm pump will give you solid supply even with the truck nose high and laid over on two wheels.

What's the system you are trying to build? How do you propose to lay it out?
 

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404.0 Doka, 404.1 resto-mod
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I think there is a lot of benefit to ignition timing on these motors. Remember, this isn't terribly high compression in this thing, so making sure your advance is accurate will benefit you immensely.
 

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1963 Unimog 404
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Discussion Starter #12
Worked on the 404 today,ignition timing was 35-40 degrees at about 3000 rpm sounds OK.Fuel delivery was around 2 pounds at idle speed and fuel quanity was 8-10 oz. in 30 seconds. the fuel came out in more of a drible than as good squirt, is this the normal way it works or do I have a problem.It seems awful weak compared to what I have worked on. Plan to check the filters as soom as the new seals/gaskets get here. Thanks Voudoux
 

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1967 404 Unimog (Belgian), 2010 Ford Fusion Hybrid
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When running it should pump quite a bit of fuel with the line removed from the carb. How do I know?

A couple of years ago I was setting the fuel level in the bowl. At that time I was using the method of starting the truck, letting it idle for a few seconds then shutting it off. Then I would remove the fuel line and carb top and measure the fuel level. Adjust and repeat until correct.

It takes a few iterations to get just right. Being a bit absent minded, one time I forgot to reconnect the fuel line to the carb. Since the fuel line is routed on the passenger side of the engine compartment and I would walk to the driver side to push the starter button the error was not immediately apparent. The truck will idle a good while with just the fuel in the bowl.

Something prompted me to walk around to the passenger side and I saw the fuel pumping all over the place. Needless to say, I sprinted back around to shut the ignition off and grab a fire extinguisher. Fortunately, nothing ignited.

The moral to the story is this: (1) I'm a bit of an idiot and need adult supervision. (2) The stock fuel pump can really flow a lot of fuel with no restriction.


By the way, 2 pounds of fuel pressure sounds about right, but 10 oz in 30 seconds is much too little. Sounds like a restriction somewhere. I think you're close to solving your top end power problem. :)

Good luck.
 

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1963 Unimog 404
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Discussion Starter #14
404 performamce

I changed the fuel filter and cleaned the fuel pump screen,the truck runs no better or worse, made no diference. This truck runs very smooth, no stumbleing on acceleration, no skipping no dying out. It just will not pull or rev to the shift points on the speedo,it stops at about 60kph in 5th gear on level ground an will not go any faster. It acts like the carb is not opening up all the way (WOT). I checked it is. I have read about other 404 owners having runnng problems, but not this one. Does anyone know at what amount of total advance do the RPMS start to drop off? and is there any chance the timing marks could be off? Thanks Voudoux
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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I haven't had a speedo in my 404 for 7+ years, but I don't remember shift points on the speedo? Will she free revv fine.

What's you altitude?
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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Have you ever owned or driven a 404 before?
 

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U1300L Turbo x 3
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When you hit the accelerator the accel. pump should shoot the fuel into the carb. If you're seeing dribbles or drops of fuel your jets are clogged or at least, something's not right. Are you running with the air elbow off and looking down the carb throat with a mirror, borescope, or camera while the engine is running?

You might also have a weak pertronix. If it ever got hooked up incorrectly they can burn out or not work correctly - they're just a large semiconductor switch.

Do have a points set you can drop into the distributor to eliminate the pertronix?

Have you checked the spark that comes from the coil?

After the resistor for the coil, do you have approximately 12 volts at the coil?

Are you using wire core or aramid core wires?

Have you done a compression check?


Worked on the 404 today,ignition timing was 35-40 degrees at about 3000 rpm sounds OK.Fuel delivery was around 2 pounds at idle speed and fuel quanity was 8-10 oz. in 30 seconds. the fuel came out in more of a drible than as good squirt, is this the normal way it works or do I have a problem.It seems awful weak compared to what I have worked on. Plan to check the filters as soom as the new seals/gaskets get here. Thanks Voudoux
 

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1963 Unimog 404
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Discussion Starter #19
Please explain your remark ,Have I ever Owned or driven a 404. what are you getting at ?
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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I am getting at the fact that many people buy them with the expectation that they will go 70mph and drive like any other truck. No offense intended, it's an honest question.

Depending on your altitude you "might" not see much more performance out of it. Especially if its compression is low or the cam shaft is worn.

Lots of variables are missed with Internet diagnosis.
 
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