I can't find much info on this easy mod, so I'm posting what I've learned. Feel free to correct me on any details here. I wouldn't try this if I had to pass emissions.

So I bought an 86 d21 with 72,000 miles on it for $250. It did not run, but had perfect compression and a good spark. After lots of time trying to diagnose the fuel injection, I discovered:I had bad injectors - stuck open, very unusualI had burned capacitors in my eccm - the ones that control the injectorsAll these parts, assuming that nothing else was f'ed up, would cost in the ball park of $800 - $1000. Now enter the Redline Weber...

Redline Weber makes several replacement carb kits for the 720 pickup, and the carbureted version of the d21. They do not make a kit for the fuel injected version of the d21. However, all three trucks came with the z24 engine (we're talking about four cylinder here), but the injected z24 is known as the z24i. The differences (that we're concerned with) between the z24 and z24i are: The FI version uses the computer to control the timing on the spark. That thing that looks like a distributor is actually a crank position sensor. On the z24, there is an actual vacuum-advance distributor.The intake manifolds are different.

I've gathered that the easiest way to do this swap on a fuel injected truck is to take the intake manifold and the distributor from a carbureted engine and install them on your FI engine. Then change the fuel pump out for something meant to give the 2-3 psi you will need at the carb. The original fuel pump should be pumping close to 22psi, way too much. It willl just flood the carb till gas comes out of your air filter in about 6 seconds.

OK so sounds great, but there are issues with this plan. Mainly, availability. I had a hell of a time trying to find those parts. I just don't have time to scour junk yards between two jobs and being a full-time student in Automotive Technology. The fuel pump doesn't score high on difficulty, but there is a much easier, better way.

First I took the old TBI unit off, along with the heater (the honey-comb thing) that sits under it. I then test-fitted the new Weber 38 Outlaw that I picked up directly from the company for $338 after shipping. The two studs on the left (left being the drivers side) lined up almost. I widened the the holes in the base of the carb, just a little and it slid down onto the manifold. For some reason, the holes in the adapter plate did not need to be widened.I did end up using the supplied adapter plate because the holes in it line up with some pretty good places to drill and tap some holes.

I stuffed some plastic grocery bags down into the intake to catch any metal shavings. I made a guide for the drill using a block of 2x4 and a square. I made a nice dent with a punch and hammer to start the hole and drilled.

I tapped the holes to match the adapter kit. This is what I ended up with. Looks funny, but I swear it lines up perfectly.

I liberally applied permetex to both sides of the adapter gasket, and used blue threadlock on the bolts. I also ground the top of the bolts a little prior to installation to make sure that they would not stick up. This picture is letting the permetex dry.One of the more difficult parts of this job is tightening the nuts on the carb. Surprising. Btw use some blue threadlock.Throttle cable bracket took a little work with the dremel.

Now the fuel delivery system, here's the good news: you can use the existing pump and the return line. You will need a "T" fitting, made of metal preferably that is 6/16". Now hook up fuel inlet to the "t". You will need some restriction in the return line, so find about 1" of 1/4" fuel hose, lube it up real good with some synthetic oil or something, and shove it into the return line. Now hook up your return line to one of the fittings on the "t". That leaves one fitting to run through a fuel filter, adjustable fuel pressure regulator (available at any major parts store) and then into the carb. I also installed a permanent fuel pressure gauge because I was experimenting and this made things easy. That is of course optional, but for $25 it's pretty handy to know what your fuel pressure is.If you look closely at the return line, you can actually see the bulge where the piece of 1/4" hose is. It's just passed the "T".

Oh and you'll need to filter your PCV air (1/2-3/4" tube coming off the top of the valve cover. Other than that there are many ways to hook up emissions stuff, all detailed in the instructions that come with the carb. I myself plugged all vacuum lines and it runs perfectly. Better than it ever has.
Modified by Frankie Pintado at 12:32 AM 7/5/2009

So... the ignition is unmodified from the TBI setup. Thats cool. It dosen't even know the difference!

That's right. It's still got the old computer. Purrs like it's supposed to. I do have a slight flat spot, like an old volkswagen, when I'm starting in first. I work around it with the clutch. It may be a tuning issue with the carb, but I doubt it. I think it is a timing issue. Still, very minor and more than made up for by the large increase in power. I'll post more on this if I figure out how to eliminate it.

Also I failed to mention that the original TBI had a water choke, and this will have to be bypassed with a piece of rubber hose.

I bet you could even tune the stock computer, (if you want to go through with the hassles, and possible dyno time), for premium gas and get a little more advance, then higher compression, better camshaft, header, exhaust, aluminium flywheel, aluminium driveshaft, posi rear end, fiberglass composite leaf springs, custom torsion bars, poly bushings everywhere, adjustable shocks, dual friction clutch, ram air scoop, gross weight reduction, electric fan, have I forgotton anything? Oh, yeah, all the stuff I just mentioned costs money, maybe a lot.

all the stuff you mentioned costs a lot of money... that's why it may take me years but it will all be done!!!

I can still adjust the timing baseline, I think, by turning the distributor, uh I mean crankshaft sensor. I'll be looking into that shortly here.

Oh, and I wouldn't worry too much about the injection on your ka24. The injection systems on those are pretty good. In fact they were pretty good on the z24i. Mine is a special case. It was owned by an electrician (home electrician). He liked to rig electrical systems on it with bits of extension cord, speaker wire, or whatever else he had available. The injectors were fried in a very unusual way.But I don't know about carbing a ka anyway. If I'm not mistaken, that has multi-port injection. That is a very efficient system, and to change it back to a carb would not really be worth it, in my opinion. Even you could make it work. Besides, there are a lot of pretty fresh ka's sitting in junkyards, easy to take a head or injectors or whatever you need. I've owned a frontier with a ka24. There is a cool little chip that you can buy on ebay for that engine that richens your fuel mixture a little and gives a few horses and lowers your head temp. It was like $30 and installed in seconds by clipping onto the air temp sensor.


Modified by Frankie Pintado at 9:57 AM 7/5/2009

Heh, this is as insane as my turbo "ZiP" (Z. with i.mproved P.erformance) Hardbody, which is coming along slowly, but surely.

i recently completed this swap on my 86 720. it had the tbi setup, i took the intake from an 85 z24 used a 36/36 synchro weber and deleted all the vac lines and emissions stuff, i even blocked off the EGR and welded the bung on the exhaust manifold shut. it made a huge improvement in power through the whole rpm ranger, it is a little cold natured now, but give it five min to warm up and it runs like a champ, however if you do this, you will have to adjust the choke on the carb, which is a little troublesome to find the spot it likes. other than that, it took me a little over a day to complete

I recently answered some questions for someone that found my email. This is the conversation.

On Sat, Nov 14, 2009 at 1:31 AM, BN720

hello, i hope you dont mind but if you would could you answer a couple of questions about swapping my z24 tbi to a weber 36 synchro? i read your post on NICO when you did it on your hardbody. i have an 86 720( hard to find i know), but as far as i can tell the engine is exactly the same. anyway, im using the intake off of a carbed 720 so that isnt an issue. my question is about the ingition and timing, and the ecu. on your swap you said you didnt change the distributor or the ecu and it ran fine? that is what i was thinking because the comp shouldnt know the difference. also i already had an in-line electric pump im using that should be perfect, what fuel pressure did you find worked the best? and as far as jetting goes did you run it rich? and did you keep any of the smog bulls**t or did you cap everything off( thats what im shottin for) thank you so much for your help. i just want to try to get a feel or any of the kinks i might run into thanks

FP:Hey,

Well yes basically the ECU doesn't know the difference. (I'm pretty sure about this next part) When it gets no feedback from the sensors on the tbi, it goes into "safe mode" which bases timing advance simply on rpms. The effect is like having a centrifugal distributor. If you've ever driven a car with a centrifugal-type distributor (like many old vw's are set up), then you will be aware that there is usually a "flat spot". I don't really mind it, but it does take some getting used to in order to drive smoothly. My 72 Karmann ghia has the same issue.

So then you can set and adjust the baseline timing by loosening the distributor and turning it. Mine likes about 5-7 degrees at 700 rpms. Also you will want to adjust the automatic choke so that it barely kicks on, even if you have to rest a toe on the gas to start it. Otherwise it idles too high before the oil pressure comes up. Fuel pressure is about 3 psi. I've put down almost 10k miles and love it.

Also note that weber technical support recommended the larger 38, and that they were the cheapest price, $338 for the kit, including shipping.

BN720:

hey man thanks for all the help, the install was pretty straight forward, but now that ive got the carb on it idles really fast (3000-3200 rpm) ive backed the idle screw all the way and it didnt seem to make much of a differnce if any, all the diagrams and instructions that came with it are very vauge, any advice on what could be causing this? id thought of maybe a vacum leak, but there isnt any vac line running off the intake or carb? thanks for the help man

FP:That's the electric choke, I'd wager. Look for a plastic round thing, mine is white, about 1 inch in diameter, with a single wire going to it, held down but a strange brass clamp with three screws holding it in place. Adjusting the choke:

1. Remove air filter.2. loosen the three screws but do not remove them3. now you should be able to turn the white plastic thing and watch the big butterflies at the top of the carb open and close.4. find a good adjustment, with the butterflies half-way open or more (they were probably completely closed when you started.5. If you do not feel like dealing with finely adjusting the carb, adjust it all the way open and pull the wire off. That'd be disabling it completely. This means you may have to give it a little gas when you start it, but is much better for your engine.

FP:OK so I'm reading what I just wrote to you and I'm hoping it makes sense. I'm going to attempt to elaborate and clarify a few things....

How the electric choke works:there is a thermosensitive coil spring under the white plastic cap. It winds up or unwinds, depending on the ambient temperature. It is attached the end of a shaft which goes through the top of both venturis of the carb. Affixed to this shaft are 2 flat pieces of brass (butterflies) which pivot with the shaft to control how much air is getting into the venturis, which determines how rich the air/fuel mixture is. When it is shut- more fuel and less air(rich) for cold starts. When it is open- it isn't doing anything. that's your basic choke. This choke also has a "throttle step down" feature which is probably causing your problem. This feature is adjusted automatically as you turn the white plastic thing. So you don't need to worry about this part, just understanding it helps with diagnosis.

So why is no electric choke better for the engine and what are the drawbacks if any?

Cold starting is when most engine wear takes place, due to a couple of factors. Oil pressure is 0.0 when you first crank the engine. It takes a second to bring the pressure up. So the only thing that is lubing the internal components on that first crank is whatever oil is still on them from the last time it was run. So the walls of each cylinder have a piston ring riding on a film of oil left over from yesterday. Well gasoline is a powerful solvent... and it takes a much richer mixture to start a cold engine. The added gasoline strips the oil off the cylinder walls. Period. Expect a shorter life on the rings and more wear on the cylinder walls.

Not to mention that with the "throttle step down" feature wants to rev the crap out of engine right when all this other terrible stuff is happening. Good way to spin a main bearing.

Also, electric chokes are famous for flooding the engine so badly that you'll have gas coming out the tailpipe.

Drawbacks of disabling the choke:

You will now be in total control of how rich the fuel mixture is with the gas pedal. Pumping the gas pedal works the "accelerator pump" in the carb which is squirting gas into the manifold like a squirt gun. So pump it a little as you first start to richen it up and get it running. You may have to rest your foot on the gas to keep it running at first on a cold day. Set the idle when the car is fully warmed up. It will idle slowly when cold, and will come up to where you set it as the engine warms up. The car will have less power and just generally run pretty rough until it warms up in about three minutes. Then it will drive perfectly normally. That's it.

BN:i was eager to get my truck running so i messed around with it a little tonight, i adjusted the choke and found that it helped considerably, also the addition of a return spring along with that sloved the problem, now what im curious about is the timing, it seems to run pretty good with a pretty drastic increase in power so im not sure it even needs advanced but, in your first email you mentioned it, would that improve the performance further? or possibly better fuel economy? it was getting 23MPG with the TBI, im guessing thats out the window now, the power increase is well worth it though. just a thought. and thanks again for all the help

FP:Actually most people see an improvement in gas mileage, when they keep they're foot out of it. The technology on the new weber is better than the technology on that 1st gen tbi unit!!!

I'm very glad to know I've helped. I guess not too many people have ever done this. That is why I felt that it was important to document and post it on nico forums. If you don't mind, I would like to cut and paste these emails into that thread in case others would find it useful.

You can drive around with the weber pretty well just on the idle circuit, when you press harder on the gas, it opens up the main jets. So gas mileage really depends on how you're driving.

As for the timing, if it feels good, runs at the proper temperature and gets decent mileage then don't bother. Unless you just want to know where it is set for future reference.

Amazing how much better power these make. The response is way better. The torque is way better. Too bad the EPA would probably have something to say about it... Anyway have fun surprising ricers;-)
Modified by Frankie Pintado at 6:19 AM 1/13/2010

Someone on my favorite vw forum, thesamba.com, said he believed the choke was a government plot to waste gas.
Modified by Frankie Pintado at 4:13 PM 12/17/2009

Where'd you get that adapter plate from? I'm slappin a carb on my vg and I'm gonna try and set it up how you did to save a few bucks.

sorry, haven't checked this thread for awhile.

The adapter plate came with a kit that I purchased new, put together and sold through redline. I would call their tech support and ask them. I've dealt with them and they seem knowledgeable and are pretty easy to get a hold of.

Or, you could probably just make one with a piece of billet and a drill, a rotary tool, a tap and die set ($20 at harborfreight.com). Believe me it doesn't have to be complicated. It doesn't have to be a smooth mating of ports either, but the mating surfaces must be very close to flush, so make sure that they are machined. Overlap is ok, Unless you plan on racing in nascar and really can't live without that extra 2 horses. I'd probably just make the ports match the carb. This method was my original plan, I lucked out when I found out I could use the one supplied in the kit.

Or, you could take the manifold and carburetor down to machine shop and pay someone else to do it. Probably would be pretty cheap. Probably would be a whole lot nicer finish than the one from redline.

And to anyone who might be interested: Chapter 2, Emissions

The next phase is in effect. I'm trying to get mine to pass emissions. I've already disguised my setup as stock. (pics coming)By the way I am not required to pass emissions. I'm doing this for my own sick pleasure.I'll be taking an emissions class and I'll have access to an emissions dyno, a knowledgeable instructor with 30 years in the field, and all the resources I could possibly need at my disposal. If it is possible, I'm gonna make it happen.
Modified by Frankie Pintado at 4:09 PM 12/17/2009

The flat spot was not a timing issue. The timing seems to be rock solid, just like a centrifugal distributor. The problem is actually caused by a lean mixture. Here's the theory:

The accelerator pump squirts gas like a squirt gun every time you push down on the gas pedal. This is to compensate for that first burst of air when you open the throttle. It also gives gas while the carb switches from the idle circuit to the main circuit. If the mixture is too lean, there is a dead spot at this instant, no gas.

The mixture can be adjusted by turning the two adjustment screws. One of them is a total PITA to get to. You will probably end up removing your air filter several times to get it right. I believe that "in" is richer, "out" is leaner. Make sure that the two screws are adjusted equally, for example: 2 turns out.

It's really kind of funny. I've been through all of this before with my 72 VW when I switched it from a vacuum advance distributor to a centrifugal "bosch 009" style. I had to run it rich to get rid of the flat spot. But it runs cooler rich, and since it is air-cooled that's something I keep an eye on. The truck likes running rich too. The coolant temp goes down noticeably, head temp dropped. Everything feels silky smooth. Both of these vehicles probably pump smog (for their size), but they run great.

I guess the flat spot could also be fixed by adding the vacuum advance distributor from an older truck, doing away with the computer. Which I am looking more seriously in to now.

I wonder if I could rig a vacuum actuator into the current distributor? something else I will look into.

Modified by Frankie Pintado at 4:45 PM 12/17/2009
Modified by Frankie Pintado at 6:20 AM 1/13/2010

i have an 86 nissan king cab 4x4 st i change the electronic injection carburator and intake and distributor to do away with the computer system. I read your information about the way to make the carburator fuel system to work but i cannot figure the rewiring that has to be done could you help me with some info on that

If you would have read in the earlier posts, the stock computer controlled ignition doesn't need any modifications, that's what is so cool about it.

You probably wouldn't have to do any of this had you not cut through the whole bundle of wires in the first place.

Takko1988 wrote: I still have the old throttle body to look at with wires hooked up to it but nothing goes or comes from the distributor from the throttle body other than the computer connection for the crank angle sensor which is void because the computer wont use that with the carb.Modified by Takko1988 at 7:26 PM 12/28/2009

Modified by Takko1988 at 7:56 PM 12/28/2009

Wrong. Unless you're using a customdistributor like I am you DO need the crank angle sensor. That's what tells the computer to fire.

Sorry man, it's not just you that gets treated like that, I'm not picking on you. You obviously want to learn, and that's a good thing unworthy of sarcasm.

So yeah, you could put a vacuum advance distributor from a factory carbed naps-z in place of the ECU one. You will still need power to the vacuum advance distributor, but only the power that travels through it from the coil, it would need no crank angle sensor.

The reason I tote not needing to delete the ECU stuff; is because vacuum advance distributors might be hard to find because they are antiquated, redundant parts; and as time goes on there will only be less and less of them. I'm a big fan of getting by on what is already there. It's agricultural to me.

Takko I'm not a mod but if you're going to give us updates can you please made your own thread? I'm sure frankie doesn't like having someone thread jacking his thread. Thanks bud. Good to hear you got it running though.

TJcars2 wrote:Takko I'm not a mod but if you're going to give us updates can you please made your own thread?

One more bone I'll throw you on Frankie's thread here, a Weber downdraft jetting / tuning guide I found in our Datsun Trucks Technical forum: zerothread/376140

So I feel I need to make a correction.

That plastic fuel filter that you see in the pictures above, omit that, or move it to a position after the regulator. There is too much pressure there and it began to fail (bubble out) after about 10k miles. It is not necessary to have a filter there, just replace the stock one.

Here is a diagram showing the simplest way to do this:
Modified by Frankie Pintado at 7:35 AM 1/14/2010

good find. I will add that If there is any substantial amount of vacuum leakage, anywhere after the throttle, then no adjustment will fix it. I finally tracked mine down and now I can make it run rich enough to smooth out completely.

However, if you are buying a kit from Redline, you will not need to change the jetting.

Oh yeah, and here are the pictures I promised.

Pretty stealthy huh?

Modified by Frankie Pintado at 8:45 PM 1/13/2010
Modified by Frankie Pintado at 7:27 AM 1/14/2010

hey i also have a 86.5 nissan throttle body carb that im trying to convert with a weber.its pretty cool you can use the stock manifold to do it.but im wondering if i would need to change the distributor also. or would i be able to use the original one.please let me know thanks

The stock distributor, assuming it was working before, will work just fine with no modification. It will base your timing advance only on engine rpm's, because you are removing all of the sensors for things like: air volume, temperature, throttle position, etc. The computer will do this automatically when you disconnect the sensors. It is already the computer's back up plan, should an important sensor fail. I have mentioned that I run a '72 VW this way (no computer, "but a centrifugal advance distributor", which bases the timing on rpm's). It was originally set up with vacuum/centrifugal but runs cooler now (it's aircooled), and will actually last a little longer between head jobs.

Basically anything that the computer used to do to try to compensate for variables in the running environment, will now be compensated for by your foot.

hey redline said i have to change my stock fuel pump because too much pressure even with a fp regulator it would run for a little while with the stock ones but would only cause to damage the fuel pump is there a carbureted fuel pump that i would be able to switch out with the stock one and how would i hook it up.let me know. Thanks ALOHA

There's a ton. I'm using a mr.gasket blue pump. Google that ish and pick the one that suits your budget.

hey frank that diagram that you have thats the fuel hose so your using the stock filter also and whats that other hose thats going back in the tank is that like a return line that doest go to the weber because of the fuel pressure hows that working out for you on your truck does it still run great let me know thanks.

does that blue fuel pump replaces the stock one.or would i mount it ouside of the tank thanks man

You mount it outside the tank. It replaces the in-tank pump. You need to get which-ever pump matches or more closely matches your carbs pressure requirement

What happened to using the stock fuel pump with a pressure regulator?