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Thread: Replacing a Mikuni Carburetor with a Weber Carburetor

  1. #26

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    Quote Originally Posted by BJH324JH View Post
    Yup, true. I guess I'll gamble. Maybe I can machine a stainless steel casing and get rid of the plastic casing.
    Don't. The plastic housing does a few jobs as mentioned and the pump is either cast into it or pressed in. Worst case scenario you could make a protective housing so it doesn't get dirt etc on it. Cutting it apart presents risks. They are pretty cheap to buy but kind of pointless if you butcher one or 2 while making modifications (just an opinion...)

  2. #27

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    Quote Originally Posted by geezer101 View Post
    Don't. The plastic housing does a few jobs as mentioned and the pump is either cast into it or pressed in. Worst case scenario you could make a protective housing so it doesn't get dirt etc on it. Cutting it apart presents risks. They are pretty cheap to buy but kind of pointless if you butcher one or 2 while making modifications (just an opinion...)
    I guess if all the bad reviews were right about this pump being garbage, I'll take the opportunity to upgrade it.

    Does anyone know what connections get blocked off and removed from the intake manifold? I took a picture with everything still attached to it. Someone please edit the picture in an image editing program, like in paint and circle what needs to be removed or blocked. Thank you.

    IMG_0017.jpg

    More close up pictures of the intake manifold with it's various components attached to it.

    IMG_0021.jpgIMG_0022.jpg
    Last edited by BJH324JH; 06-22-2019 at 08:16 PM. Reason: added more pictures of manifold

  3. #28

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    You can either remove the EGR valve solenoid and fit a blanking plate over it (easy to make) or just leave it in place with the vac hoses disconnected. The Christmas tree vacuum barb on the manifold needs to be removed and a threaded bung screwed into there. The water barb connection for the heater return and carb choke should be removed and a single upright barb installed (the original barb will most likely be paper thin from rust anyway) The rest of the vacuum connections are only vac thermo switches and pose no risk to vacuum leaks but you could delete them for appearances sake.

    I went a little nuts with mine and completely cut off the EGR gallery running around the manifold plenum and sculpted the manifold. Mine was easier to do as it was off a Gen1 G63B and didn't have a lot of emissions control ancillaries on it and didn't have jet valves either (I had to prepare the manifold for repairs anyway as the water jacket cover plate under the plenum had corroded out and had a few pin holes in it). I capped off the gas gallery that runs through the head into that EGR gallery and ran a metric thread tap through the coolant port that is located on the carb mounting face/seat and installed a grub screw in there to seal it off. Not entirely necessary but reduces the risk of coolant somehow backing up into the plenum if the carb install kit manages to develop a leak.

  4. #29

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    Quote Originally Posted by geezer101 View Post
    You can either remove the EGR valve solenoid and fit a blanking plate over it (easy to make) or just leave it in place with the vac hoses disconnected. The Christmas tree vacuum barb on the manifold needs to be removed and a threaded bung screwed into there. The water barb connection for the heater return and carb choke should be removed and a single upright barb installed (the original barb will most likely be paper thin from rust anyway) The rest of the vacuum connections are only vac thermo switches and pose no risk to vacuum leaks but you could delete them for appearances sake.

    I went a little nuts with mine and completely cut off the EGR gallery running around the manifold plenum and sculpted the manifold. Mine was easier to do as it was off a Gen1 G63B and didn't have a lot of emissions control ancillaries on it and didn't have jet valves either (I had to prepare the manifold for repairs anyway as the water jacket cover plate under the plenum had corroded out and had a few pin holes in it). I capped off the gas gallery that runs through the head into that EGR gallery and ran a metric thread tap through the coolant port that is located on the carb mounting face/seat and installed a grub screw in there to seal it off. Not entirely necessary but reduces the risk of coolant somehow backing up into the plenum if the carb install kit manages to develop a leak.
    Okay, like this right? Am I missing something?:
    Intake Manifold Components.jpg

  5. #30

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    Nope. Nailed it There is quite a considerable difference in the intake runner length between the early and the updated intake manifolds. Wonder if there was much of a difference in overall torque as a result...

  6. #31

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    Intake Manifold Connections

    Quote Originally Posted by geezer101 View Post
    Nope. Nailed it There is quite a considerable difference in the intake runner length between the early and the updated intake manifolds. Wonder if there was much of a difference in overall torque as a result...
    Thank you, I wonder though, isn't some of the sensors on the intake manifold used to measure the engine temperature? Check this out: https://www.rockauto.com/en/catalog/...+/+sensor,4748

    The sensor looks quite identical to the picture I posted above. I suppose things did change a bit from the 1st gen.

  7. #32

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    I'm mot 100% sure which of the sensors in the thermostat housing does what as there is at least one that is connected to the feedback system on Gen 2's. It would be the ideal place to hook up an aftermarket temp gauge and the sensors seem to be inexpensive. OOC - you got any aftermarket gauges set up in your truck?

  8. #33

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    Quote Originally Posted by geezer101 View Post
    I'm mot 100% sure which of the sensors in the thermostat housing does what as there is at least one that is connected to the feedback system on Gen 2's. It would be the ideal place to hook up an aftermarket temp gauge and the sensors seem to be inexpensive. OOC - you got any aftermarket gauges set up in your truck?
    I don't have aftermarket gauges installed.

  9. #34

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    If your engine had an O2 sensor in the exhaust, this is by far the best thing to help adjust your carb and get it running nicely by installing an A/F ratio meter. Add maybe a vacuum gauge and oil pressure as well and you'll know when something is running right or wrong.

  10. #35

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    Quote Originally Posted by geezer101 View Post
    If your engine had an O2 sensor in the exhaust, this is by far the best thing to help adjust your carb and get it running nicely by installing an A/F ratio meter. Add maybe a vacuum gauge and oil pressure as well and you'll know when something is running right or wrong.
    I'll think about it. Money is going out faster than I can bring it in. I'm going to let the piggy bank rest a while before I make more investments towards my truck. For now, I just need it running.

  11. #36

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    Quote Originally Posted by BJH324JH View Post
    I'll think about it. Money is going out faster than I can bring it in. I'm going to let the piggy bank rest a while before I make more investments towards my truck. For now, I just need it running.
    I hear ya. I've kept my 'bargain hound' mode on the entire time I've been collecting stuff for my truck. Now I need free time to glue everything together, never seem to have both time and cash...

  12. #37

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    Quote Originally Posted by geezer101 View Post
    I hear ya. I've kept my 'bargain hound' mode on the entire time I've been collecting stuff for my truck. Now I need free time to glue everything together, never seem to have both time and cash...
    I completely get what you mean about time and cash. Two things that we have to carefully manage.

    I will definitely try my best to keep you and everyone else that has been helping me through this conversion updated. I owe every helpful member here a big hug and can't express how grateful I am to have members like Geezer, who take their precious time to help people in need. Thank you everyone who has helped me and thank you Camiot for keeping this website alive.

  13. #38



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    FWIW re: electric pumps, I've long been a fan of the Carter P90091 (and the P60504 and P76438 it superseded) for use with Weber carbs requiring low fuel pressure -- quiet, compact and reliable, and its gerotor pump mechanism provides a smooth, continuous flow, unlike solenoid piston-driven designs. Maybe this tip comes a bit late if you already bought yours, but at least of benefit to others playing along here.
    1987 Dodge Ram 50 4G54 RWD longbed ("Elmo")
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  14. #39

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    Yet another option is finding a fuel injected tank (MY 1990+) and using this pump:

    https://fuelsafe.com/fplp/

    You get the longevity and quiet operation of a liquid cooled pump but they're costly.

    The Carter pumps are sturdy and reliable (I learned from a Datsun guy they use them to pump and cool differential coolers on 510s and Zs) but I thought they were a little noisy for my tastes. We used Airtex pumps at the restoration shop I worked at. FWIW.

  15. #40

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    Holy crap - $220+ for a fuel pump!?!! I bet they'd be good for that price though...

  16. #41

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    Quote Originally Posted by noahwins View Post
    Yet another option is finding a fuel injected tank (MY 1990+) and using this pump:

    https://fuelsafe.com/fplp/

    You get the longevity and quiet operation of a liquid cooled pump but they're costly.

    The Carter pumps are sturdy and reliable (I learned from a Datsun guy they use them to pump and cool differential coolers on 510s and Zs) but I thought they were a little noisy for my tastes. We used Airtex pumps at the restoration shop I worked at. FWIW.
    Quote Originally Posted by SubGothius View Post
    FWIW re: electric pumps, I've long been a fan of the Carter P90091 (and the P60504 and P76438 it superseded) for use with Weber carbs requiring low fuel pressure -- quiet, compact and reliable, and its gerotor pump mechanism provides a smooth, continuous flow, unlike solenoid piston-driven designs. Maybe this tip comes a bit late if you already bought yours, but at least of benefit to others playing along here.

    Thank you for the suggestions, I will consider them. I have not yet gotten an electric fuel pump, but am doing my best to find a good one. I appreciate the suggestions. I didn't know I had new replies to this thread, sorry for the late reply.

  17. #42

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    I'm a bit perplexed as to where the last few parts of the carburetor kit go. These are the parts in question:


    The 8mm aluminium barb as per the instructions is ment to block the water choke hose. Although as suggested by geezer, I replaced it with a straight fitting that I machined out of aluminium, thus eliminating the need for the 8mm aluminium barb. Seeing as the weber instructions that came with the carburetor kit didn't have pictures, I am questioning if this is the water choke they are referring to in the instructions:
    IMG_0022.jpg

  18. #43

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    Spare Parts? I had a lot of them. That boomerang looking bit gets bolted to the top pf the valve cover for the gas cable to mount to.The two big holes are for existing bolts and the little one is for the clip on the cable.

  19. #44

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    The barb you have marked in your pic is the water choke feed described by the Weber instructions. There are parts for a lot of different combinations of install. The bracket is the throttle cable retainer (as 85Ram50 has pointed out). The hose clamps are for fuel hoses. The spring is a throttle return (of some sort...) and the odd bolts and small elongated plate... I got nothing on that The vacuum caps are for the superfluous vacuum connections.

  20. #45

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    Quote Originally Posted by geezer101 View Post
    The barb you have marked in your pic is the water choke feed described by the Weber instructions. There are parts for a lot of different combinations of install. The bracket is the throttle cable retainer (as 85Ram50 has pointed out). The hose clamps are for fuel hoses. The spring is a throttle return (of some sort...) and the odd bolts and small elongated plate... I got nothing on that The vacuum caps are for the superfluous vacuum connections.
    I'll just save them, just in case they are needed or someone needs them. There are two vacuum hose connections on the distributor, which one do I plug and which one do I use?
    IMG_20190814_133459.jpg

    Does the distributor hose connect to this connection on the carburetor:
    IMG_5152.jpg
    Last edited by BJH324JH; 08-14-2019 at 03:04 PM.

  21. #46

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    Ok, you've got one of those distributors... not sure on which vac barb to cap on that one. I'm pretty sure the circled hose barb on the Weber is the correct location to hook up the distributor advance. Vac advance has to be connected from a source above the throttle butterflies or it'll pull continuous vacuum.

  22. #47

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    So am I throwing my money away going with this replacement? https://www.autozone.com/fuel-delive...6615_6626_2425 cause my carb is dumping fuel and flooding

  23. #48

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    Quote Originally Posted by Buckbent View Post
    So am I throwing my money away going with this replacement? https://www.autozone.com/fuel-delive...6615_6626_2425 cause my carb is dumping fuel and flooding
    Not necessarily 'throwing' money away but the stock carbs aren't cheap. This is a simple 'just swap it and you're done' deal - no installing electric fuel pumps, no extra wiring, no coolant line deletes (this particular Mikuni variant has an electric choke anyway so make sure it matches the carb you're replacing) and also no messing with rebuild kits (if carbs aren't a thing you're comfortable stripping down, this isn't the place to start)
    BUT for the same amount of money, you can swap up to a simpler carb that has vastly improved all round performance - not just HP and torque but fuel economy as well. There is some work in installing a Weber but the rewards are worth it, plus there is a ton of info on how to do it, where to get a genuine unit and how to trouble shoot it so it'll run right.

  24. #49

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    Quote Originally Posted by BJH324JH View Post
    I'll just save them, just in case they are needed or someone needs them. There are two vacuum hose connections on the distributor, which one do I plug and which one do I use?
    IMG_20190814_133459.jpg

    Does the distributor hose connect to this connection on the carburetor:
    IMG_5152.jpg
    If memory serves right on the dual vacuum advance units used for Federal High Altitude converted vehicles and California emissions trucks the top port is a secondary advance for the "high altitude compensator" that advances the timing by 5 degrees and the bottom one is the main vacuum advance that is used by the carburetor. hope this helps

  25. #50

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    I learned sumpin' there from Starquest. I wonder if it's worth experimenting with the dual vacuum solenoid on the distributor by trying each one individually with the Weber? Reasoning behind it is the Weber is a vacuum beast and has a tendency to over advance unmodified distributors, possibly causing detonation

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