Replacing a Mikuni Carburetor with a Weber Carburetor

[85Ram50]

A cheap hand held dwell/tach meter will do the job. The dwell isn't much help on an ECM distributor system other than to tell you it's out of spec.

Here's my beef - new school shops can't (or don't understand how to) tune old school engines. There is a subtle art to digging up hidden performance in an old school and every shop I dealt with used the 'factory spec' tune. That's when I started doing my own tune ups and learning how to find that little extra. I had one bunch or muppets undo a good tune I performed on a friends Mazda 808 (40 minutes of dialling in the ignition and resetting the breaker points for optimisation) - when he picked it up from getting something else done to it, it was a slug compared to how it went in.

I usually walk away if they say "we make it like the factory built it" or some version of that. It is a red light warning that they do not know about your rig and may not know about motors in general. Almost every vehicle gets improved and fixed after it has gone into production. Design flaws and other items not built properly show up and need changes. Frequently owners improve them too. If your shop doesn't know this or know to look up Technical Service Bulletins for what has changed on your vehicle they are probably not reliable.

[SubGothius]

I usually walk away if they say "we make it like the factory built it" or some version of that.

Which could also just be tail-covering; they're less liable if they tune everything "by the book". The factory tune may have been nerfed for emissions rather than performance, and doesn't account for upgrades like a better carb, replacing points with electronic ignition, etc.

[BJH324JH]

Should I block this hose? I put my finger on it and its creating vaccum. I intend to put the original air cleaner on when I have the time.


The hose on the valve cover is the one I mean.

[geezer101]

You have 2 options - there is either an elbow under the base of the air filter mount you can install that connects to the breather hose (most likely will make it compliant for emissions) or put a smaller breather element on it. But don't plug it up or delete it as it helps crankcase ventilation and recirculates gas build up back into the engine to be burnt.

[geezer101]

Which could also just be tail-covering; they're less liable if they tune everything "by the book". The factory tune may have been nerfed for emissions rather than performance, and doesn't account for upgrades like a better carb, replacing points with electronic ignition, etc.

Book goes bye bye with a carb swap. The factory tune is a compromise between emissions and worst case scenario cold engine starts. If the tune is in the ball park it 'should' start. I'd encourage anyone who wants to learn sumpin' to buy feeler gauges, a hand held tach/dwell meter and a timing light (you're only going to need the timing light as a diagnostic tool to know what the base timing looks like. There's free performance up for grabs with some patience and trial and error.

[BJH324JH]

You have 2 options - there is either an elbow under the base of the air filter mount you can install that connects to the breather hose (most likely will make it compliant for emissions) or put a smaller breather element on it. But don't plug it up or delete it as it helps crankcase ventilation and recirculates gas build up back into the engine to be burnt.

Got it. Thank you very much.

[SaxMachine]

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.

Do you know what size threads the water barb has? I am doing this in my driveway and would like to purchase the single barb before I remove the one with the "T." Also, is that something I can just purchase at an auto parts store? Thank you

[geezer101]

I can't recall what the thread type was, but I did use an off the shelf manifold barb for a Ford to replace the 'T' barb that was on my manifold.

[SubGothius]

FWIW I couldn't get that stock T-barb to budge at all, had some hardened goopy white residue around the base indicating a PO must have applied some sort of thread sealant. I wound up just capping the small barb with a short length of fuel hose plugged with a short bolt and hose-clamped at both ends, bit of a kludge but seemed more reliable than using a vacuum cap to contain pressurized coolant long-term.

[robertson5347]

Does any of the generic or fake 32/36 dgev carbs. work?

[geezer101]

Does any of the generic or fake 32/36 dgev carbs. work?

It would be near impossible to know which of the 'licensed copies' are any good. The primary fault with them is the internal metering galleries and the way they are machined/manufactured. Genuine Webers have emulsion jets that can be swapped out for tuning. A member recently used an 'EMPI' 38 DGES copy that is working well.

[SubGothius]

Indeed, Webers are designed to manage fuel and air metering with precision-engineered air and fuel passages, so they depend on every passage being finished to exacting tolerances. The clones don't seem to have that finishing step done, or at least not done well and to spec, so it's luck of the draw if any given unit just happens to have them all close enough to work in harmony as designed.

I do wonder if the bright-dip the clones are evidently subjected to (which genuine Webers aren't) could be part of the problem; I'm not entirely clear how that process works, but if it adds or removes any material, that could be throwing tolerances out of range.

I also wonder if EMPI does anything with their clones that may improve matters over units that come direct from the factory.

[geezer101]

They've been making them for long enough to be able to get it right by now. It wouldn't be worth trying to mill the knock off copies to make them operate correctly compared to simply buying a properly designed and manufactured carb like the OG Weber. There must be some info on the crap carbs that goes into depth on why they are so bad

[Chairwolf]

New guy here, subscribed!

[Chairwolf]

Just checking to see if this thread is still alive. I have a 1988 Mighty Max with a 2.0 liter engine. I'm the ORIGINAL OWNER believe it or not!
I've just read the entire thread. I have a Weber 32/36 DGEV carb on my truck. I'm having the "no-power" problem. It will idle like a champ, but it struggles to go over 25 mph, and barely goes up hills. I'm looking at the vacuum/spark advance issue, and possibly the throttle cable. When the carb was put on, I remember the cable being a little too short due to the adapter plate adding about 3/8" to the height of the carb. Has anyone run into an issue with this? I made a little connector out of a piece of aluminum to make a connection. I can post pics later.

Back on the vacuum issue, base on previous comments, did anyone settle which ports to connect to which between the carb and distributor vacuum?

Thanks!

[geezer101]

I found a set up guide for base tuning the 32/36 on another forum (hey, this may already have been covered and posted but it's fun trying to find specific info through all of the threads...)

https://www.yotatech.com/forums/f120...2-36-a-240521/ Step by step guide for mixture and idle adjustment.

When you installed the carb, did you do it with the fuel bowl facing the front of the engine bay or the rear? Facing the rear will cause the fuel float to shut off the needle and starve the engine out. Any other info like has it only just started doing this or has it been like it since installation?

[SubGothius]

When you installed the carb, did you do it with the fuel bowl facing the front of the engine bay or the rear? Facing the rear will cause the fuel float to shut off the needle and starve the engine out.

Just to expand/clarify that point, float bowl in the rear will make it run lean/starve on takeoff/uphill, and rich/flood on braking/downhill, which are the opposite of what's ideal. While you can turn around a Weber DGEV to put the float bowl in front, that makes it so the linkage cable has to come at the carb from the battery side, whereas the mirror-image DFEV model can keep the cable on the exhaust side with the bowl in front.

That said, I'm running a DGEV with the bowl in the rear, and it's not been any major problem as long as I brake gently well in advance, only wants to stall out when I need to brake abruptly.

[Chairwolf]

It's facing the front. Throttle cable is toward the firewall.

[Chairwolf]

I found a set up guide for base tuning the 32/36 on another forum (hey, this may already have been covered and posted but it's fun trying to find specific info through all of the threads...)

https://www.yotatech.com/forums/f120...2-36-a-240521/ Step by step guide for mixture and idle adjustment.

When you installed the carb, did you do it with the fuel bowl facing the front of the engine bay or the rear? Facing the rear will cause the fuel float to shut off the needle and starve the engine out. Any other info like has it only just started doing this or has it been like it since installation?

Thanks for the reply! Let me add that this truck has been sitting for a number of years and not driven. It starts and runs. It will idle and rev like a champ!! It sounds like it wants to win the Indy 500. I mean, it idles a little high, but smooth. I've got the Weber instructions, and have set the mixture and high speed idle so it will start pretty well and idle, and under load (sitting with foot on brake and putting it in gear), it idles ok. It just goes "blah" going up hills.

[geezer101]

This may be a jetting issue. Getting idle and primary jet sizes right can make the difference from it being a slug to running like a freight train.

[Chairwolf]

I'm no expert in the Weber department, but the carb has whatever size came with it from the factory. Is there a "default" size that they normally send, or is it customer specified? I had this carb ordered and installed by a mechanic, so unfortunately I don't know what is in it.

It will drive pretty well in 1st and 2nd gear, but after that, it detonates like crazy, even on flat ground. It's an automatic, BTW. I've ordered a new distributor vacuum advance, which should be here in a few days. If that makes no difference, then at least I know the spark advance is not the problem. We'll see! Any other thoughts? And thanks.

[SubGothius]

It will drive pretty well in 1st and 2nd gear, but after that, it detonates like crazy, even on flat ground. It's an automatic, BTW. I've ordered a new distributor vacuum advance, which should be here in a few days. If that makes no difference, then at least I know the spark advance is not the problem.

Unless the static/base advance is the problem? That could explain the detonation if it's too far advanced.

[geezer101]

There's the missing part of the puzzle. Need to experiment with the tuning. Webers are vacuum sensitive - regap your plugs to 0.85-0.9mm and adjust the distributor timing until the detonation backs off. Also try to avoid using regular gas and go up to the next octane (91+) It'll run better on it.

[Chairwolf]

Unless the static/base advance is the problem? That could explain the detonation if it's too far advanced.

By "static/base" do you mean loosen the distributor and rotate it slightly clockwise a bit? I don't have a timing light, so I'd have to just tweak it and see what happens.

[Chairwolf]

There's the missing part of the puzzle. Need to experiment with the tuning. Webers are vacuum sensitive - regap your plugs to 0.85-0.9mm and adjust the distributor timing until the detonation backs off. Also try to avoid using regular gas and go up to the next octane (91+) It'll run better on it.

Can do on the gap and timing. I'll try that and the gas! Thanks