Author Topic: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --  (Read 26914 times)

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
This was a project that I completed over six years ago to convert an old Mazda B2600 into a more roadworthy vehicle. That included getting rid of the old and rusted non-functioning smog controls.

I changed the fluids, drained the tank and managed to get the 2.6 liter Mitsubishi engine running pretty well at idle, but that was about it. When I started to accelerate, the engine would bog down and smoke like a chimney. Knowing that these engines have notoriously finicky Mikuni Solex carbs, I decided to tackle this "smogger" carb head on.

In 1988, the emission regs were catching up with this design. So to meet specs, Mazda/Mitsubishi squeezed the last bit of emission control out of this carb. These days all this control messaging is handled by a small computer. Yet, even though this truck does have an ECM, it's nothing more than a glorified fuel management system. The bulk of the emission controls are mostly handled by vacuum switches and dashpots. To that end, they wound up with a HUGE mess of vacuum lines that plagued this truck's performance ever since it was first on the road. Thankfully in 1989 Mazda moved to a fuel injection system and much of this hose crap went away.

Here is the "infamous" Mikuni Solex 2bl carburetor -- a design way past its time; even back in 1988.



Since the carb is heated by the cooling system, and the intake manifold sits lower in the engine compartment, I need to drain the radiator to avoid spilling lots of coolant into the intake when removing the carb.



Vacuum line hell --!!!!  billcat







Most of these lines are now solid and cracked from all the heat -- that causes lots of vacuum leaks down deep in these vacuum line manifolds. I don't have a vacuum hose diagram, so I just take pen and paper and label everything that's important.









Success!! It's off -- It doesn't look like much, but just getting to this point is a chore; simply because of all the brittle hoses and corroded clamps that had to be disconnected.



I can see why this thing ran so rich and smoked so much -- just look at all the raw fuel that's dumping down that intake. There's a "lake" of raw gas in that intake manifold.





Once I got the carb on the bench I quickly found the problem. This 2bl carburetor has a progressive secondary that is operated by a vacuum dashpot. So at idle the carb is effectively a single barrel unit. Under acceleration, engine vacuum to the dashpot opens up the secondary; effectively turning this thing into a 2bl carb.

See the dashpot in the upper right corner of the pic? That's the secondary throttle actuator.



Hooking up a vacuum pump to that secondary dashpot shows a little movement, but not enough to fully open the throttle plate under heavy acceleration. That's what was causing my power loss and hesitation when trying to accelerate at speed, and why the damn thing idled pretty well; the primary was working at idle, but the secondary wasn't opening under load. That's probably also why the raw gas wasn't atomized in the secondary and just filled up the manifold.



I could open the secondary manually, but the dashpot was not up to the task by itself.



So, I'm off to eBay to order the parts for a Mikuni Solex rebuild -- stay tuned.  beerdude







« Last Edit: August 29, 2018, 09:59:43 AM by goodfellow »

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 de-smog and Weber carburetor conversion --
« Reply #1 on: August 14, 2018, 08:25:32 PM »
Wow -- I'm impressed!! Look what showed up at the door a few minutes ago.

Weber goodness, and a very nice install kit to go with it.



« Last Edit: August 29, 2018, 09:59:56 AM by goodfellow »

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 de-smog and Weber carburetor conversion --
« Reply #2 on: August 14, 2018, 08:25:51 PM »
Started stripping the engine of "smog" equipment and lines today. Essentially, all the electronic fuel management will be removed, and the Weber will function like a normal manual intake system.

It's amazing how much emission control crap was on this little truck; a wonder that it drove at all. Gulp valves, metering valves, fuel solenoids, vacuum switches; the list is endless and the vacuum lines are never ending. Just look at this mess.







It did clean up the engine compartment pretty well though. Now it actually looks like a normal engine --





The emission recirculation port on the exhaust manifold was removed, and since I didn't have a plug this size, I cut the tube and squeezed the top shut in a vise and welded the seam closed. It makes a good seal and the entire manifold is tight.

ADDITIONAL NOTE: This last step wasn't necessary. The Weber kit did include two large manifold plugs for plugging the two large ports in the exhaust manifold (one on top and the other towards the rear of the manifold). The best way to remove the old lines is to use a cutting wheel or sawz-all to cut the metal tubes right above the fittings, and then heat the fittings with an O/A torch to loosen and remove them. Without that O/A heat, no amount of penetrating oil would budge those rusted fittings.

Alternatively, you cab just cut the tubes above the fittings and install a short piece of rubber hose on the stub, then plug the hose with a large bolt or other makeshift plug.



Don't even need the O2 sensor anymore. I'll just disconnect it at the plug and bundle the wire.



Tomorrow I'll install the Weber --


« Last Edit: August 29, 2018, 10:00:16 AM by goodfellow »

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 de-smog and Weber carburetor conversion --
« Reply #3 on: August 14, 2018, 08:26:34 PM »
Finished this Weber conversion this afternoon. There are many bits and pieces in this generic Weber conversion kit that won't be used on the Mazda 2.6 liter Mitsubishi engine.
The first change required that the throttle linkage that was installed on the Weber carburetor be substituted for a cable guide version that in the kit. This is the original solid linkage piece.....



.....and here is the cable version that is included in the kit. This one will fit the Mazda throttle cable perfectly. A simple nut holds this linkage in place.



Next comes a generic adapter plate and gasket. This is an odd sized gasket and adapter plate that can be used with several different OEM installs; hence the elongated  corner looks a bit odd, but it will fit. Countersink hex screws keep it in place.

NOTE: when installing these gaskets and plates, I used LOTS of gasket sealer to ensure that no vacuum leaks develop in this adapter plate "pancake" stack that must be installed.





Next comes the intermediate plate and gasket. The cap screws must fit below the surface plane of this plate --









Lastly, the carburetor studs and the carburetor base gasket are installed on the intermediate plate





Now before the carburetor is installed I plugged a secondary fuel line and water heater hose that were needed for the old electronic Mikuni/Solex carb. I simply plugged the hoses with a bolt and a hose clamp. You can see the plugged lines on the left and right side of this pic -- simply a bolt with a hose clamp



The carburetor is installed on the studs and the throttle cable is hooked up. The only large mod that I needed to do was to raise the throttle cable mounting clamp that was included in the Weber kit. It is mounted on the back of the carb and was sitting too low thereby binding the throttle cable. I simply welded a piece of 1/8" thick steel on top of the old bracket to lengthen it. Then I drilled another throttle cable mounting hole to accept the cable. This raised the cable to a height that allowed smooth operation.

These pics show the original (unmodified) bracket -- it simply bolts to the two rear carb mounting studs.





After I welded on a piece of 1.5" steel, it raised the bracket to the proper position to allow the cable to move freely.



Last item was finding a switched 12v power source to actuate the electric choke. I simply tapped into the existing Mikuni carb wiring harness connector and found a switched 12v source. A simple wire and spade connectors were furnished in the Weber kit, and was easy to install.









After this last electrical install, I plumbed a new fuel line (also included in the Weber kit) and I was ready to fill the radiator and start the truck.

Voila!!! She runs -- Success!!! The engine sounds much smoother and more responsive. Tomorrow I'll button up all the wiring and a make things tidy -- time to put this thing back on the road.

So this morning I installed the air cleaner, breather, and routed the hoses and wires in a more efficient manner. Lots of zip ties, rubber grommets and tape were used to tidy things up.

First the air cleaner element that came with this Weber kit is top quality. However, because of my breather fitting location I mounted the element in reverse. It fits, but on some applications it may not. The breather fitting is screwed into the bottom, and bolted on the throat of the carb.







A nice thick gasket was included in the kit.





Final routing was accomplished by going straight out the back and over the accelerator cable.





Final routing of the vacuum lines and the electric choke was nicely bundled and secured







Everything is nice and secure and the engine idles at 850RPM -- perfect. The carb doesn't have a run-up circuit that would be triggered when the AC is on, so the RPM does drop to about 700 with AC -- no problem! I can increase the RPM to 950 this becomes a problem.





That's it -- the thing runs well and all the lights/electricals work to pass DMV inspection. Now all I have to work on is the parking brake -- it's totally not functioning from having the truck sit for a decade. 


« Last Edit: August 29, 2018, 10:00:30 AM by goodfellow »

Offline bonneyman

  • Hero Member
  • *****
  • Posts: 3953
Great job!

Looks ALOT like the Toyota 22R fiasco! All those feet (23 last time I replaced it all!) of silicone rubber tubing getting cooked by the heat and rattled by vibration. Just waiting for a chance to crack and leak! Arrgh!
But AZ emissions standards (and yearly smog check) won't let me touch any of that stuff.
But I have seen kits to replace the stock carb and all the tubing in states that don't have emissions checks. or if your vehicle is for off-road use only.

Offline WoodenNickle

  • Newbie
  • *
  • Posts: 7
What a nightmare.  I had a similar problem with a '87 Chevy Vega - really a Toyota with a different body.  Don't remember what make the carb was, but it was varnished up internally from sitting for about a year with half a tank of ethanol laced "gas".  The dealer couldn't fix it, so the owner decided to sell it.  This is one of those "helping out my buddy" deals.  I volunteered to clean the carb for him.  Many an hour searching for multiple vacuum diagrams to straighten out what the dealer's mechanic had done.  We finally got the thing running well enough to put on the road, and I hope I never see it again.
Cheers,
Tom

Keep smiling.  Everyone will wonder what you're up to!

Offline alwaysFlOoReD

  • Newbie
  • *
  • Posts: 4
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #6 on: January 30, 2019, 12:30:31 PM »
Thanks for the write up. It will help me with fixing my 87 b2600. Which carb kit did you use?

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #7 on: January 30, 2019, 01:42:22 PM »
Thanks for the write up. It will help me with fixing my 87 b2600. Which carb kit did you use?

PM sent --

Offline DeadNutz

  • Hero Member
  • *****
  • Posts: 2985
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #8 on: January 30, 2019, 02:06:39 PM »
When I met the wife she had a Subaru Brat and it needed a smog check. I went to the smog place and the guy opened the hood took a look and closed it and said he couldn't help me. The Brat had a built engine with a Weber 2 BBL on it and no one would smog it. We got exemptions for a while and finally got to the point where we had to go to a friend of a friend with extra cash. Finally we couldn't get away with it any longer so we traded it to a neighbor next door to the shop for some work. He had no problem with the smog as he knew just where to take it in the barrio.

The county we live in does not require smog checks while Reno to the north of us does as well as Vegas. Another reason I love where we live.

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #9 on: January 30, 2019, 02:30:01 PM »
In our state (VA) only certain counties require smog checks. It's required mostly in the most populous and densely populated counties . That said, the DMV regulations are such that if the car is 25 years old (or older) and is carrying standard registration plates, it doesn't require a smog check -- only a safety inspection. Vehicles with special antique vehicle plates like my '70 Jaguar don't require the safety nor the smog.

Offline Matt_T

  • Sr. Member
  • ****
  • Posts: 343
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #10 on: January 30, 2019, 02:45:07 PM »
Can you put an antique tag on the Mazda or do they limit them to "collector" vehicles in VA?

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #11 on: January 30, 2019, 03:21:00 PM »
Can you put an antique tag on the Mazda or do they limit them to "collector" vehicles in VA?

You can, but then it can't be used as a daily driver. The law is a bit sketchy, but if you're in an accident with antique plates, the first thing that comes up in the investigation is "why was the vehicle on the road -- car show, weekend outing, going to repair facility, etc.". Everyday drivers, even those over 25 years old, need to have regular plates in this state.

Offline J.A.F.E.

  • Resident Alien
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2611
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #12 on: January 30, 2019, 03:53:38 PM »
In California Historic plates can had for anything over 25yo to 1923 but there are a lot of restrictions to driving it. Basically limited to parades, shows and special events. There is also a Horseless Carriage plate that is for cars made 1922 or earlier but again a lot of restrictions to use. Cars can also use YOM plates and that is a pretty popular option. I've been looking for 71 plates for the little yellow car which are blue/yellow numbers, easy to find, but the number range has to be correct for the year, not so easy.
People who confuse etymology and entomology bug me in ways I can’t put into words.

Offline stokester

  • Hero Member
  • *****
  • Posts: 595
  • Air-cooled!
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #13 on: January 30, 2019, 04:18:06 PM »
Thanks for sharing.

That sounds like quite an expansive kit. 

The real irony of it all is that it now runs better and pollutes less but would not pass a smog test in many areas. :-[
Nick
Yorktown, VA

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #14 on: January 30, 2019, 04:29:56 PM »
Thanks for sharing.

That sounds like quite an expansive kit. 

The real irony of it all is that it now runs better and pollutes less but would not pass a smog test in many areas. :-[

Even if they had a smog check, I can lean that carb out to such an extend that it would easily pass emissions in Virginia. It would run like crap, but after getting the sticker, it can be easily set back to a good running mixture.

I ran a Chevy small block 305 in my 83 Camaro for most of its life with a gutted CAT -- It always passed emissions. You could tune it easily --
« Last Edit: January 30, 2019, 04:33:03 PM by goodfellow »

Offline J.A.F.E.

  • Resident Alien
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2611
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #15 on: January 30, 2019, 04:32:01 PM »
[snip]
The real irony of it all is that it now runs better and pollutes less but would not pass a smog test in many areas. :-[

Almost anywhere it would not pass I believe altering the smog stuff is federal. Pretty short sighted in many ways if it meets or betters the limits and if it increases mileage it's even worse.
People who confuse etymology and entomology bug me in ways I can’t put into words.

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #16 on: January 31, 2019, 07:37:11 AM »
[snip]
The real irony of it all is that it now runs better and pollutes less but would not pass a smog test in many areas. :-[

Almost anywhere it would not pass I believe altering the smog stuff is federal. Pretty short sighted in many ways if it meets or betters the limits and if it increases mileage it's even worse.

The Weber is a good carb for replacing old OEM units - but as you alluded to, the mere
fact that it isn’t OEM is a deal breaker as far as the Feds are concerned.

Thankfully there are not that many vehicles
that use carbs on the road anymore - even older cars can now benefit from a good aftermarket throttle body fuel injection system -




Sent from my iPhone using Tapatalk

Offline stokester

  • Hero Member
  • *****
  • Posts: 595
  • Air-cooled!
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #17 on: January 31, 2019, 03:59:14 PM »
[snip]
The real irony of it all is that it now runs better and pollutes less but would not pass a smog test in many areas. :-[

Almost anywhere it would not pass I believe altering the smog stuff is federal. Pretty short sighted in many ways if it meets or betters the limits and if it increases mileage it's even worse.
Technically in VA it would fail the safety inspection.
Nick
Yorktown, VA

Offline J.A.F.E.

  • Resident Alien
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2611
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #18 on: January 31, 2019, 04:23:02 PM »
No safety inspections here. There is smog testing for cars registered in most of the counties but not all.
People who confuse etymology and entomology bug me in ways I can’t put into words.

Offline DeadNutz

  • Hero Member
  • *****
  • Posts: 2985
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #19 on: January 31, 2019, 04:41:24 PM »
CHP used to set up random roadside inspections. I used to be good at avoiding them until one they set up around the corner from the high school. They pulled me in after I couldn't avoid them. They wrote me up for using a piece of garden hose as a breather hose on the 55 Ford p/u.

Offline muddy

  • Hero Member
  • *****
  • Posts: 3467
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #20 on: January 31, 2019, 06:05:04 PM »
No safety inspections here. There is smog testing for cars registered in most of the counties but not all.
States with out safety inspection scare me.

There are people that never look at a vehicle, ,or ignore any signs of something wrong. That same person in a state that doesn't do inspections, who on Earth knows if that vehicle is anywhere near safe.

Sent from my XT1710-02 using Tapatalk


Offline slip knot

  • Hero Member
  • *****
  • Posts: 2586
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #21 on: January 31, 2019, 08:31:09 PM »
Safety inspections here are a money grab. $7.00 for a 5 minute looksee. Tires, lights, wipers and horn get checked.  But you gotta have the inspection paperwork to get the tags.

A few counties around the bigger cities get emission checks.

They used to have a "smoking vehicle" hotline where you would call and report vehicles that were "polluting"  I don't know what they did to you tho. The boss never said anything and I know he was reported a few times. :D :D

Offline J.A.F.E.

  • Resident Alien
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2611
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #22 on: January 31, 2019, 09:37:18 PM »
[States with out safety inspection scare me.

There are people that never look at a vehicle, ,or ignore any signs of something wrong. That same person in a state that doesn't do inspections, who on Earth knows if that vehicle is anywhere near safe.

Sent from my XT1710-02 using Tapatalk

I understand that. I came from Pennsylvania and at that time they had a very comprehensive inspection program. As a kid I worked for a guy that was an accredited inspector and his shop could do the inspections. He was honest and wouldn't do unneeded work just to draw revenue but also wouldn't pass cars that needed work. So coming out here and seeing no inspections and on top some of the crapboxes on the road. You will get pulled over for worn tires, non working ligts, broken windows or obvious problems. It did take me a while to get used to it.
People who confuse etymology and entomology bug me in ways I can’t put into words.

Offline alwaysFlOoReD

  • Newbie
  • *
  • Posts: 4
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #23 on: January 31, 2019, 10:34:11 PM »
Thanks for sharing.

That sounds like quite an expansive kit. 

The real irony of it all is that it now runs better and pollutes less but would not pass a smog test in many areas. :-[

Even if they had a smog check, I can lean that carb out to such an extend that it would easily pass emissions in Virginia. It would run like crap, but after getting the sticker, it can be easily set back to a good running mixture.

I ran a Chevy small block 305 in my 83 Camaro for most of its life with a gutted CAT -- It always passed emissions. You could tune it easily --

Yeah, just pull the pcv line from the carb and hide the end somewhere, then turn the idle down. You might need to make the hole smaller so there isn't too much  vacuum.

Offline Matt_T

  • Sr. Member
  • ****
  • Posts: 343
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #24 on: January 31, 2019, 11:37:36 PM »
Safety inspections here are a money grab. $7.00 for a 5 minute looksee.

If you get away with $7 and some wasted time you got off light. I've seen inspection stations quote $$$$ to repair vehicles that didn't have a damn thing wrong with them. This mostly happens to women IME. And if the vehicle is a P.O.S. you can find someone who'll slap a sticker on it for a few extra dollars if you know where to look. "Safety inspections" are a huge money grab that have little to do with safety.

And don't ever buy a used vehicle with a fresh sticker without thoroughly inspecting it yourself. That's another way they're used to rip people off.

Offline goodfellow

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 4321
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #25 on: February 01, 2019, 08:30:30 AM »

.........And don't ever buy a used vehicle with a fresh sticker without thoroughly inspecting it yourself. That's another way they're used to rip people off.


THAT is a very good point. Used car dealers have been ripping people with that bogus "QC" trick for decades.

Offline fatfillup

  • Hero Member
  • *****
  • Posts: 2542
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #26 on: February 27, 2019, 07:50:35 AM »
Maryland has a very thorough safety inspection when a car is sold and getting registered.  None after that.  We do have emission inspections in many counties every 2 years but I have only had one fail in quite a number of years.


Offline Barks

  • Newbie
  • *
  • Posts: 41
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #27 on: February 27, 2019, 09:09:54 AM »
"of the states requiring vehicle safety inspections, 12 states plus the District of Columbia had fewer than the national median of crash deaths and seven had more deaths than the national average.

So, there isn’t a clear-cut correlation here between requiring a safety inspection and fewer deaths or lower insurance rates."

Offline alwaysFlOoReD

  • Newbie
  • *
  • Posts: 4
Re: Mazda B2600 2.6L Mitsubishi de-smog and Weber carburetor conversion --
« Reply #28 on: February 28, 2019, 11:22:22 AM »
Just finished installing the weber carb. It's finally running after warm-up. I routed the fuel line different, I removed the piece attached to the head so no need to block off a line. The fuel line now runs up in front of the intake manifold. I had no welder so used a piece of metal bent into a 90* and bolted the old throttle cable bracket to the new cable bracket.