Some more 404 advice - a year later

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Baton Rouge, LA
Hi everyone, last year April I posted a video and asked for and got some great advice (some of which I'm still working on).
I've since then acquired all the service manuals including the Bundeswehr Microfiche service guides and scanned them all.

I fixed my stuck fuel pedal and throttle issue (turned out to be the fuel pedal itself) and I put a return spring behind it which Unipaser had.
But then around November I started on the task of replacing cracked exhuast manifold, in the process had to get a new carb and new fuel pump, and put in new exhaust. Finally yesterday, I got the truck started, still have smoke puffing on exhaust and idle is rough.

I let the truck idle for over and hour and was able to adjust carb idle enough so choke could be backed off, but after 30 minutes or so, had to adjust choke back 50% to keep idle up.I'm thinking vapor lock? it was really hot outside 90F, even hotter in engine, but carb was still weeping. so not sure what's going on.


  • Checked timing to be correct (10-14 advanced), spark on #6 is weak.
  • New NGK B5PES plugs, when I took old ones out (that I put in last year, they were all covered in black soot)
  • Recent Oil Change Shell Rotella 10w30 HD oil.
  • New Fuel Pump with diaphragm. Confirmed fuel pressure is good and delivery to carb.
  • New fuel line from Pump to carb
  • New gasket in fuel switch
  • Adjusting Idle screws on carb do not seem to have any effect. (2 half turns)
  • New Exhaust Manifolds and Exhaust, Muffer, Crossover and Tailpipe.
  • Engine Temperature is good, new coolant, new hoses, new o-rings
  • Last time I checked compression test had 130-135 pressure in all cylinders. Not great, but not bad.
  • Drained reserve tank and found intake filter to be intact, paint around intake is coming apart (future project)

I'm thinking rings on pistons may be letting oil into chambers?


  • Next step would be (??)
  • Pull engine cover and check valves / valve stems (as mentioned last April), I wanted to fix carb first.
  • Leak down test
  • Install Facet Fuel Pump (which I got) as auxiliary (not sure where to mount it or where to spline it in, advice?)

OR

Forget all this troubleshooting and just get a new engine?

Can you take a minute to watch this 1m video I posted?
Give me advice on what I should consider to do going forward? :-D

https://youtu.be/g5CfX2SPTFM

Just when I thought it could get any worse, I have an air leak at the treadle below my brake pedal, (this is an air over hydraulic system) any advice on that?

Many thanks.
 

The FLU farm

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Not that one turn on the idle screws is necessarily all that much on regular carbs, but as I recall, if they truly don't have any effect it's probably a vacuum leak. Having to run the choke on a warm engine would also indicate it's running lean.
On the other hand, sooty plugs would indicate an over rich condition.

I normally look for problems at the last thing I messed around with, but your list is quite long.
 

tennmogger

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Poor idle without choking plus no effect from idle mixture screws is a sure sign of plugged idle jets. Those are under the removable cover on the front of the carb. Easy to clean with just a 10 mm wrench and flat screwdriver.

Putting on the choke transfers the mixture source to the choke circuit which is a different part of the carb. That bypasses the plugged idle jets.
 
79
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6
Location
Baton Rouge, LA
Thanks for the replies, I neglected to mention in my post that this was a NOS Carb that I got from EI. After I did this little video and my post, I got to thinking it was maybe the carb(?), I took the carb off and upon opening it up I found this white dust crud inside (old gas? old storage solvent?, not sure but it mucked up the insides). The parts on the lid top were corroded and the best part was the float were frozen solid, no flex in the hinge. EI mentioned that there was a subset of their NOS Carbs that had this issue, they don't check NOS parts, my bad for assuming they did, I figured for the premium price that was being done. EI suggested that I replace the gasket and the float, which I did and it was still having issues. Adjusting the float by using a different thickness gasket didn't help. There were other problems with crud in the jets or other passages of the bowl.

MBaDyEm.jpg

I figured I'd have to rebuild it as I bought a rebuild kit for my original, but that's why I bought the NOS one to begin with, after some discussion with EI, they agreed to take it back and send me another one. I love EI, don't get me wrong, not trying to knock them here. Maybe this was just a one off situation. I intend to buy more parts from them, so glad they are working with me to resolve this issue.

In the meantime I've rebuilt my original, and now I'm having fuel delivery problems. My fuel pump is working, although the Facet Fuel pump is appealing if I can figure out where to mount the darn thing. I may try to use the 4 10mm holes on the side of the engine block to mount a plate with it attached (unless anyone has a better suggestion).

The cork gasket in the fuel switch was replaced with a EDPM Gasket, only to have the spring grind it into little pieces (as I set it per the service manual), so I'm going to get a different spring and a new gasket and try it again. If that continues to give me a headache, will resort to replacing it with a new one or (?? different valve or bypass it and bridge the fuel tanks using a Mod I got from Sheffield 4x4).

Tennmogger you mentioned in a post in 2013 on this forum that you put a fuel pump out of the drain bolt on the bottom of the main tank and fed it in series with your fuel delivery, how exactly did you do that? BelMetric sells a Double Barb Banjo Fitting. Your advice would be most helpful.

A neighbor of mine from Ecuador who is a diesel mechanic has been coming over and has helped me confirm rotor is correctly pointing where it needs to be, engine timing is accurate, spark plugs are cleaned and after a compression test, we set the spark gaps per the service manual.

I'm seriously thinking of buying another Mog to drive while I work on this one to get on the road, on the lookout for an SBU, as this 404 is going to take a while.
 
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79
0
6
Location
Baton Rouge, LA
Agree 100%, I believe the gentleman in Florida (William S) who has 2 404's for sale at the moment on CL has a great setup. I will try something similar as this is after the fuel switch.

04IvgtT.jpg

I got the same fuel pump, and found out after contacting them that this is a self-regulating pump, no need to put a regulator in upstream between it and the carb.
 
79
0
6
Location
Baton Rouge, LA
Tonight I finally (don't ask me why I didn't do this sooner), disconnected the battery and drained the tanks. I had already drained the reserve using a hand pump for part of it and the HF Battery operated pump for the remainder, then I dropped the bolt 19mm on the bottom of the main tank with a breaker bar and let it drain into a 5 gallon bucket, and had the same HF Battery operated pumping realtime into a 5 gallon Jerry Can, it was pumping at about the rate the tank was draining, I managed to switch off the pump and get the nozzle into another jerry can and restart the flow. Filled 2 Jerry Cans and part of another. When it had all drained out. I then dropped the bolts on the tanks using a 24mm socket with a breaker bar.

When I dropped the bolt on the bottom of the main tank I discovered it had no intake filter, bits of it came out in the drainage.
iLmruge.jpg

While the reserve had a filter, both fuel plugs look scorched.
65IbmXg.jpg

I have replacement intake filters, plugs and gaskets to match.

Still trying to figure out how you guys plumbed the drain plug on the bottom into your systems.
Did you plumb the output of the pump into the fuel valve and then used the factory pump to the carb?

Turns out previous owner(s) broke the bracket for the step ladder and spot welded on a step bracket to the koffer making removal of the fuel tanks a challenge. So taking off the main tank will require unbolting the fuel brackets from the chassis and taking it out from the side. Provided I can get all the bolts off (soaking in Acetone / ATF now, thanks FLU!). I could also lift the koffer off the chassis, seems like a lot of work though.
 
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Mog404

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Atlanta Georgia
Tonight I finally (don't ask me why I didn't do this sooner), disconnected the battery and drained the tanks. I had already drained the reserve using a hand pump for part of it and the HF Battery operated pump for the remainder, then I dropped the bolt 19mm on the bottom of the main tank with a breaker bar and let it drain into a 5 gallon bucket, and had the same HF Battery operated pumping realtime into a 5 gallon Jerry Can, it was pumping at about the rate the tank was draining, I managed to switch off the pump and get the nozzle into another jerry can and restart the flow. Filled 2 Jerry Cans and part of another. When it had all drained out. I then dropped the bolts on the tanks using a 24mm socket with a breaker bar.

When I dropped the bolt on the bottom of the main tank I discovered it had no intake filter, bits of it came out in the drainage.
View attachment 730810

While the reserve had a filter, both fuel plugs look scorched.
View attachment 730809

I have replacement intake filters, plugs and gaskets to match.

Still trying to figure out how you guys plumbed the drain plug on the bottom into your systems.
Did you plumb the output of the pump into the fuel valve and then used the factory pump to the carb?

Turns out previous owner(s) broke the bracket for the step ladder and spot welded on a step bracket to the koffer making removal of the fuel tanks a challenge. So taking off the main tank will require unbolting the fuel brackets from the chassis and taking it out from the side. Provided I can get all the bolts off (soaking in Acetone / ATF now, thanks FLU!). I could also lift the koffer off the chassis, seems like a lot of work though.

Hi Crunchylicenseplates,
I also own a 1963 Unimog 404.1. Do you have any update as to what you did to fully correct your issue? My mog is having the exact same symptoms of only running with the choke enricher halfway.
Thanks!
 

Ferretboy

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Hello mog404....i too have a 1963. 404.1 have the same problem from time to time....there are many great points in this thread....i always start by cleaning the carb jets....if the idle jets are clogged it wont idle unless you give it some choke....try cleaning the carb first...let me know how it works out...and welcome to ss
 

frank8003

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Maybe need better fuel? There are many many additives but maybe just use better fuel. The distillers no longer add into the mix what it is they used to do which gums things up big time.

Fuel used to be good for years, now is NG by less than 6 months.
If your engine has a carburetor then take precaustions. The new fuels fails them.
It, the information you need, is all over the internet.

Techron consists of five components:[5]
Distillates, hydrotreated light at 40-70% weight
Stoddard solvent at 15-40% weight
Solvent naphtha (petroleum), light aromatic at 5-10% weight
Benzene, 1,2,4-trimethyl at 1-5% weight
PEA (detergent), polyether amines at 20-49% weight



Techron is a patented fuel additive developed by the Chevron Corporation, usually consisting of gasoline mixed with 400 ppm of polyetheramine (PEA).[1] With the introduction of Techron, Chevron gasolines became designated as meeting Top Tier standards for fuel cleanliness. Chevron gasolines with Techron were some of the first gasolines to be named as a "Top Tier Detergent Gasoline".[2] "Top Tier Detergent Gasoline(s)" are agreed to lead to better performance in engines by BMW, General Motors, Honda, Toyota, Volkswagen, and Audi.[2]

Techron had been first patented and introduced as a concentrate available at Chevron stations in 1981.[3]Techron was then marketed in all Chevron gasolines in May 1995, and the Chevron Cars made their debut to promote this introduction in advertising.

Techron is available at Chevron, Texaco, and Caltex stations in all three grades of gasoline.[4] Techron is also available as a packaged concentrate, for use with gasoline that does not include Techron.
 

Ferretboy

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I use sta-bil buts says it only for 6 months....and some carb cleaner....i know how our gasoline is junk...it will evaporate and leave a grey powder in carbs or over time turn to varnish and is nasty to clean...i dont use my mog much but try and run it once a month....your right ....hello....thanks
 

Ferretboy

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Tips on cleaning carb jets....jets are made of brass....i have found that soaking them in vinegar is good....its nice to have very small gauge wire to run through the holes....old timers like me say...Dont use a tortch cleaner...or a drill bit....Dont want to enlarge the orface....just make sure is clean....
 

frank8003

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Tips on cleaning carb jets....jets are made of brass....i have found that soaking them in vinegar is good....its nice to have very small gauge wire to run through the holes....old timers like me say...Dont use a tortch cleaner...or a drill bit....Dont want to enlarge the orface....just make sure is clean....
That is why I have the numbers drill down to #80, just use the shank of it.
Yes, they are all for sale, pick a number.
 

Ferretboy

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Hey Frank 8003...you must be a Master Machinist....glad you joined in here...i kinda like talkin about old iron....carbs...ect...
 

Mog404

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Atlanta Georgia
Excellent advice....

Thanks for the response! I purchased my mog in February of this year so I'm new to the game. Sort of unbelievable but after 3 months of chasing this issue I located the root of the problem 30 mins after typing my comment above. My trouble shooting process has included rebuilding the carb, replacing parts of the electronic ignition (changed over by the previous owner), running entirely new fuel line with electric pump set to 2.5 psi, ect, ect, ect..

While rebuilding the carb a month or two ago, I discovered that it had previously been rebuilt incorrectly. I was able to confirm this with a receipt I found in a box of parts the previous owner included. However while installing the correct kit from expedition imports, I never thought to check the orientation of the large round brass enricher/choke circuit. For some reason I assumed it would not have ever been moved or changed in the past.

I noticed a small fuel leak developing around the choke circuit cover and decided to remove it and changed its gasket , as I already had a new one sitting around. I had a 32NDIX carb diagram opened on my computer for something unrelated and happened to noticed that the orientation of the brass enricher in the diagram was 45 degrees away from where it should have been when in the off position. I removed the nut and choke arm, rotated the brass piece 45 degrees, and installed it back on the carburetor and is running great.

Now I will actually be able to fine tune and take my first ride in this thing.

Hopefully this will help someone in the future.
 

Ferretboy

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Absolutely fabulous....great to hear the news....great to get them running good....happy you got an old thread going again...good to talk with all of you....love it....not many 404 owners out there....chatting.
 
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