August 7th, 2013.Dear Karl: The Unimog NDIX carburetor is not a device that tolerates pressure well, volume from the mechanical pump yes, but pressure, no. In the first iterations back in 2010-2011, I replaced 3 $300+ dollar pumps in 3 months, two of them new MB units.... Nobody had ever seen 3 pumps go that quick, then I raised the question of 10% ethanol in the gas....Your truck can't run on that...Well, that's all we have here in Illinois! The first 24 VDC pump and in line pressure regulator was from Expedition Imports (using Summit Racing Parts), with the pressure regulator set at 1.5 to 2.5 LBS guage. The truck would run, it just never could reach and hold 70 KPH like it did before, as it would outrun the standard pump supply. She would end up blowing one new pump and at least one pressure regulator a year, which I thought as odd that no one bypassed the excess fuel back to the tank (like we do on all diesel engines). Well, when the pump blew this last time in April, there was no pumps available as the suppliers had stopped carrying them, and when the pump had been put on, the pressure regulator failed. The mechanic replaced the regulator and the truck wouldn't start, and he wouldn't fix it.... So, I took the carb line off and proved no gas was getting through, so refund the money for the regulator & it's installation and I'll fix it. Done! I found a very old common sense (no computer) mechanic, that when I explained the issues, he merely said that I needed a new pressure regulator with by pass to the tank, which Holley Racing makes....Well, $65.00 later and some new plumbing, I have a 24 GPH marine pump (24VDC) and Holley Bypass pressure regulator (set for 3.0-4.0 PSI output) like they use on racing cars with electric fuel pumps on carbs.... Generally she runs much better, but she still will not cruise for long spans of time at 80 KPH, 60-65-70 is about it, and I suspect that too many people in the Unimog community do not realize that at 70-80 KPH these trucks are approximately at 90-95% open throttle, and they do use a lot of gas. Unlike most people on here, my Unimog has averaged 4,500 to 6,500 miles per year, a lot of them on the road, and probably the highest maintenance issues have been failure of hose clamps, as nobody today is willing to make the metal to metal couplings on the fuel lines that these trucks are designed with. The engines do move a little bit, and in off road work, the frame flexes a lot and an air leak anywhere will throw the truck off its stride. I love the S404.114, as long as you have common sense, or more importantly YOUR mechanic has common sense, they are wonderful trucks. Would I like a diesel U1300L, heck Yes! Can I afford one? Heck NO! But the Unimog S404.1114 with care will outwork and outlast the American modern pick up truck in off road work and hauling in almost every one of their iterations, yes, will it out run them, no! It is not a "Truck" but a very high speed tractor. I can probably dig around in my paperwork and hunt you the pump and bypass part numbers, JUST DON'T mount your pump on the cab floor like my guys did, the noise almost drowns out the engine (I should have been paying closer attention there)! Good Luck, and maybe one day MB or the Turkish folks that bought the S404 tooling, will wake up and make new rubber components out of the right grade of silicone rubber...all the other antique parts guys do!
The knowledge's has been hard bought, I assure you! I have a little more experience here then the guys who only play with their Unimogs on weekends and haul them on trailers everywhere. If mine has to be hauled on a trailer much, it needs a new home, seriously!
