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Thread: bad fuel economy (even after Weber install) 87 D50 (A/T)

  1. #1

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    bad fuel economy (even after Weber install) 87 D50 (A/T)

    Guys, I hope you can help me with this one.

    After doing my introduction, let me get to my persistent problem on the fuel economy of my ride.

    I'm getting about an average of just over 8 mpg on this truck (A/C is always on with our weather). A long time ago I took it on a long trip, 340 miles, and I think it got about 20 mpg.

    We don't have interstates or that much hi-way around here so this is all pure city driving. It's just an alternate ride so I have the convenience of using it whenever I just want or need to. My office is just about 6 miles from my house and when I put in about 2.6 gl of gas, I have used a significant amount of it when I get back home. I barely run into any heavy traffic with such a short distance.

    Everything about the engine for the longest time was stock and with the Mikuni carb. It has more than 81000 miles on the odometer. I never had any issues like stalling, hesitation, stumbling, dieseling, low power, etc. To the best of my knowledge, this is timed and tuned as can be and can do 75 mph on the hi-way effortlessly. The engine will start as soon as you turn the key even if I haven't used it for more than a week. Only last March, I had a problem with loose compressions with piston 2 and 3 because of the gasket. Took the engine apart and while we were at it, had new valves installed. The pistons, although sooty, were in great condition.

    So, as the title of the thread suggests, to solve my only problem of this poor fuel economy (after months of research and lurking on this site) I was able to do the Weber 32/36 DFEV conversion last weekend. I had a mechanic with me and I made sure he followed the installation and tuning instructions.

    The only thing we were not able to do was install an electric fuel pump, regulator and another filter before the weber carb.

    Sunday evening, I took it our for a test drive part hi-way and city. In my assessment, it did just around 10 MPG and there was hardly any traffic. I didn't get any WOW reaction and was totally overwhelmed with disappointment. I had dreams of making it a daily drive and for now I guess I will have to keep on looking for a solution.

    My question now is:

    1. What did I do wrong with the install?
    2. Could there be other reasons for the poor fuel economy? Aside from the carburetor, is there anything else that can make this truck do anything close to 20 MPG?

    Any insights, thought or suggestions would be great guys.

    Thanks.

    P.S.

    If I left out any info that you need to know just ask away.

  2. #2

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    Here is a photo of my Weber install for reference.



    Thanks

  3. #3



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    Float level to high - choke not opening correctly - That would be the first place to start.
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  4. #4

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    Oh is this the part were I take out the carb and measure the float level from the bottom surface of the float to the machined gasket surface of the carburetor body and it should be 1.5 inches or 38.5 mm? And if its out of that I have to literally bend the float tab?

    As for the choke, it opens slowly when I start the engine. When warmed up and filter on, I hear a click every now and then. Is the that right or do I need to adjust this also?

    Thanks.

  5. #5



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    the choke should open fully after about a minute. And yes on the float adjustment. It needs to be lowered some.
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  6. #6

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    camoit,

    If the float level is high, then does this mean that the carb is just dumping gas into the manifold without mixing it with air for combustion? Would this also explain why the exhaust has a really awful foul smell of gas?

    I also noticed that when I took out the Mikuni carb there was fuel residue inside the manifold. like gas was just dumped in there or something.

  7. #7

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    Quote Originally Posted by camoit View Post
    the choke should open fully after about a minute. And yes on the float adjustment. It needs to be lowered some.
    Done some checking and am I right that the original measurement of the float is 1.5 inches or 38.5 mm (from factory). So this means I have to lower it. Any suggestions by how much?

    Thanks.

  8. #8



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    Well what is going on is the level of fuel being to high makes it easer for the engine to suck it in. In the manual section first gen factory manual there is a good picture of a carb and how it works. The higher the float and fuel level the less speed is needed over the venturi to suck fuel in Lower it about 1/16 to 1/8 of an inch. Re-adjust the carb so it runs good again and recheck MPG and the power, along with the smell. Every time you make a float adjustment you may need to adjust the carb. Also in the UTI training manuals there is more info on adjusting the carb and preforming a "lean drop" if it's necessary. That is if you have engine run on AKA dieseling. If after you adjust the carb float 1/16" and she is not up to the 16-18 MPG you can lower it again. It's just a process you will repeat until you have it the way you like it. Just keep in mind what ever you do, can be undone and we are all here to help. If you take pictures of what you do and post them using the built in photo attachment system you can help the next guy that comes along asking the same questions. Then it's in your attachment manager on the board.
    Let us know how it goes.

    OH and don't over torque the screws. It's eays to do.
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  9. #9

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    Ok, so since this will be a process of trial and error, would you advise that i take out the whole carb or just the top where the float is? Next, i have worries about the gaskets? Are these things tough enough or do i have to replace them every time i take it out?

    Good thing you mentioned that adjustment is 1/16 to 1/8 at a time. I was thinking of going for a 1/2 inch adjustment on the first try.

    I'll try to take pics and update my progress as much as I can.

  10. #10



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    If it's OK so far, you can put a very, very, very light brushing of anti-size on it. The silver is good to use. It will make it so it will not stick to the parts but you can still re use it. I had mine on and off more time then you can count and never replaced it. It will be fine.


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  11. #11

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    Aight, thanks for the tip. That took some of my fears away. It's been quite a long time since I was last involved in taking out a carb to adjust the float or anything.

    Thanks.

  12. #12



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    You can just pull the top in the truck. Try to avoid pulling it from the manifold unless you have anti-seized the base gaskets or there new. anti-seize will quickly become your new paper gasket friend.
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  13. #13



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    Chapstick also works on the gaskets if you can find it there. The other problem I see with your setup is using the mechanical pump with the weber - you are overpressurizing the carb and forcing fuel past the needle and seat - no amount of float adjustment will fix that - you need to run an electric pump with an output of 3-5 psi. Putting a reg on the mechanical pump will kill the pump in short order. I have run a weber with an electric pump for nearly 30 years on Geronimo and get 20 to 25 mpg on a regular basis.
    Pennyman1
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    Living the D-50 lifestyle since 1980

  14. #14

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    The electric pump and fuel regulator is in the line up. If the results of the float adjustment are positive, it will really entice me to complete the setup.

    Chapstick?

  15. #15

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    So, I took the rest of the day off to work on the carb. First, I decided to take the whole thing out. I was careful with the gasket and lifted it just slightly to see if it was sticking to the carb or adapter.

    After that, it was on the table
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    Taking the top of the carb was pretty straight forward. Just took out the 5 screws on top and it was off. Again, I was careful with the gasket and made sure the float was not hitting anything as I lifted the top. I verified the factory setting and it was 1.5 inches from the gasket to the bottom of the float.

    Took out the float and bent the part that was touching the valve. I adjusted the float height by 1/8 of an inch.
    Click image for larger version. 

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    I decided to also check a small water leak I noticed. During the install, I was suspicious of one of the flat head screws was a bit shallow. Click image for larger version. 

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    I screwed in the flat heads by hand and it turns out the one on the left wasn't settling in all the way. Just cleaned the hole and it was good.

    I put everything back together and used anti-seize lubricant when setting back the gaskets. I placed a very very very very thin layer with cotton buds.

    Engine start was just as fast as before. Right off, I noticed that there was less smoke during the start and that awful gas smell was completely gone. After warmup, adjusted the idle screw a little. Reved it a couple of times and there was no hesitation. The short road test was also good.

    Hopefully I can get a good computation on the fuel economy over the weekend so I will know if there are any changes.

  16. #16



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    Yep sounds like you are on the road to recovery. It's part of the mandatory 12 post program you were ordered to take when buying these trucks. You already got your key chain, so I guess we will give you the float flashlight when this is done.
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  17. #17

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    With the heavy traffic there I would be really surprised if you get 20mpg out of that truck. I know you said the traffic isn't bad but from what I've I've seen in Manila traffic is always bad. The worst I've ever seen anywhere in my life. 8mpg doesn't seem to be out of the question for those conditions.

  18. #18

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    Well I can't argue with you about the traffic here. After visiting places like Hong Kong, Osaka, Seoul, Las Vegas and California, I've realized that traffic here is really bad and will just get worst at the rate its going. I'd be kidding myself if I expect to get 20mpg out of this truck. But for my application, considering I get up early in the morning to avoid the rush hour and my daily commute is just a short distance, I'd just like to see good fuel efficiency. I mean, people ask about my fuel economy and I tell them I get about 8mpg they ask me if my engine is a 6 or 8 cylinder.

    UPDATE:
    Adjusted the float by another 1/8 to see how it goes and I did the same run as last weekend. Roughly I can say that the truck did about 15 mpg. For me this is really good.

  19. #19



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    Sounds like you have it under controll. 15 to 20 is good for the miles you have on it.
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  20. #20

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    Guys, just a couple of updates and a few questions to whats happening to my truck.

    While waiting for a fuel pressure regulator (you can't find any for a carb here anymore) and other parts, i was afraid to wear out the needle and seat so i installed a Mitsubishi electric fuel pump cuz this thing stops pumping when the needle is closed.

    So, i went on to adjust the mixture screw cuz i was getting dark plugs. On my last adjustment, i got nice brown spark plugs but the thing is the mixture screw is only about 3/4 turns out from bottom.

    The idle speed sounded a bit too high so i turned it out about 1/2 turns. The engine settled down a bit and idling was still good even with the a/c on When i checked, the idle screw was no longer touching the seat.

    With that, I'd just want to ask if I have to rejet the idle jets to a smaller size? Do i also have to rejet the main jets?

    Or whould it be best to wait until i can install the fuel regulator and pressure gauge to make sure i have 3.5 psi of fuel pressure before tuning it again and see if the mixture screw will be above 2 turns?

    So far, aside from what i mentioned above, I have to problems with the performance of the webber carb. In fact its great and having fun with it.

    Thanks guys for all your help.

  21. #21



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    you need to lean down the idle mix screw tell it runs rough then turn up the idle speed screw. then when it runs good you turn down the mix screw just about 1/8 to 1/4 turn . Look in the manual section for the UTI training manuals> Fuel section> Lean drop

    You can also look here. Last Post.
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  22. #22

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    Yup, been doing the proceedure as instructed. When I turn the mixture screw in, it starts to rev up at 1/2 turns out from close. Backed it out another 1/4 turn till it idled smoothly again. Thats how i got 3/4 turn out from closed with the mixture screw.

    Turning out the mixture screw from 3/4 to past 3 turns does nothing to the engine. The idle still stays the same.

  23. #23


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    There is 2 adjustments 1- Mixture screws, 2- Idle set screw. Once you have the mixture screws set then turn the IDLE set screw in or out to increase or decrease the idle speed.

  24. #24

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    I was going through other post and I came across Natureboy's thread and having his secondary butterfly open and having high idle.

    Now, recalling during the install of my weber, before i installed the throttle lever for the cable, the primary butterfly was completely closed and the idle speed screw was not in contact with the throttle stop. But when I had to install the throttle lever, i remember I had to turn the primary shaft just a little bit in order for the throttle lever to fit onto the shaft. Cuz of that, the primary butterfly wasn't completely closed and had a small gap open. I just went on to turn the idle speed screw 1 1/2 turns in after it touches the throttle stop and installed the carb.

    Didn't think of it much back then until now that I checked that the idle speed screw is completely off the throttle stop and yet the engine still has a little bit of high idling.

    Is the primary butterfly supposed to be completely closed when the idle speed screw is not touching the throttle stop? My engine is suppose to stop, right?

    Thanks.

  25. #25


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    Yep, the other thing to look at is make sure there is enough slack in the throttle cable to let the butterfly close completely. I've run in to this a few times.

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