3A-SU Won't start

[rhdpat]

Hello all, I bought my first Tercel a few weeks ago. It's a 1986 hatchback from Japan, 3ASU twin carburetor. I know we didn't get this engine here but I've been working at this for a while and don't know where to go from here.

I bought the car from the guy who imported it, knowing it didn't start and likely needed a carb rebuild. He had driven it 3+ hours back from the port and had noticed some sort of skipping so he tried investigating on his own. He somehow came to the conclusion that the "fuel shutoff valve" on each carburetor was the problem and permanently stuck them open. I guess this didn't solve the problem because the car ended up at a shop for a while but they didn't do much because the mechanic was worried about getting parts. They diagnosed it as something stuck in the front carburetor but were unwilling to fix it, which is how I ended up buying it.

After checking the simple things, I pulled the carbs in hopes of finding the blockage but there was nothing. What I know after putting it back together is that I have a fuel issue. It will run as long as I'm spraying starting fluid in both carbs but will die as soon as I stop. Fuel filter has been replaced, and fuel is definitely good. The pump jumps up between 3-4 psi while I crank the motor so that sounds good too. There's no sight glass on the bowl but I can see fuel being sprayed in when I manually open the throttle all the way so I know it's getting there, and after attempting to start I can see wet fuel on the back of the throttle plates. I have extensively checked the vacuum system and even fogged the vacuum lines to be sure there's no leaks.

As it sits the car will not run at all. If I pump the throttle a few times or spray starting fluid in it will attempt to start on that but sputter out after a second or two. More throttle input on startup seems to make it worse, and it also seems to be an issue common to both carburetors. It acts like I'm maybe getting some fuel but not enough. I found a thread on a Land Cruiser forum discussing a similar fuel shutoff valve that was mostly there for emissions and safety and not necessary, although I don't feel great about mine being stuck open. Is there anything obvious I'm missing here common with other Tercels? I did notice the most similarities with the later 90's carburetors although US models still use a single carb. Any help is appreciated and I can post more pictures of my setup.

Patrick

TercelCarb2.jpg

[SirFoxx]

if you pull the fuel cutoff solenoids, you should be able to feel them or see them move when the key is on. I just got done messing with honda's 3bbl cvcc carb and, at least with that, as soon as you unlplug the fuel cutoffs, the engine would die.

You're on your own with these carbs. You're the first to mess with these on the forum, and probably the facebook group as well. It sounds like you arent getting enough gas. Either the cutoffs are faulty, float level is messed up, or they are plugged.

[dlb]

Agreed with SirFoxx. On the North American carbs, the way to test the fuel cutoffs is simply to apply power to them, then take it away. If you can hear them clicking opening and closed, they work. Seems overly simple but that's what the factory service manual says.

[Petros]

Those are a great carb set up, if I could find a complete set up to install in my Tercel4wd I would do it. I have owned and worked on a few imported cars with these Asian SU carbs, but I also have extensive experience with the British SU on many older import cars I have owned and rebuilt, as well as others I have worked on (old volvos, MGs, Trumphs, Austin Healeys, and others all used them). the ASU carb is supposed to be made under license from the British so I think they should work the same way. I do not understand why so many mechanics are afraid of these carbs, even back when they were very common on imported cars in the sixties and seventies. they are simple, rugged and easy to tune and adjust (if you know how). I guess they do not want to bother to learn about them.

Sounds like you narrowed it down to a fuel supply issue, internal to the carb. you should be able to carefully take them apart and reuse the gaskets if you can get them off without damaging them. otherwise you can use fuel resistant form-a-gasket for reassembly. this is what I would do:

1. check the float bowls are working properly, there should be one for each carb. remove the top (3 screws) and remove it to expose the float. check the needle valve that it is clear and free of junk and gunk, clean and working properly (they cut off the fuel supply when you lift the float by hand, I blow on the fuel intake line and lift the float carefully to see if they cut off the fuel). also, remove the float and put them in some gasoline and verify they float. if they are the old hollow brass floats sometimes you can shake them to make sure they are not full of fuel. if the engine floods from too much fuel it will also not run.

2. the bell shaped chamber on top of the carb holds a sliding piston that extends down in to the throat of the carb, it is vacuum operated and has the effect of creating a variable venturi, it opens as the engine speeds up, metering both the air and fuel supply into the engine. on the end of the piston is a brass tapered fuel metering rod that goes into the fuel jet on the under side of the carb throat, as the piston rises with increasing engine demand, it will also adjust the fuel air mixture (they used to make performance metering rods that alter the fuel air ratio, but you will not need those to get it running). the piston assembly should easily slide up and down into the chambers under the bell. with the air filter off, use your finger to gently push up on the piston in the throat of the carb. it should slide up smoothly with little resistance. if there is any gunk or corrosion on any of the parts it will not slide up easily, or at all. if this is the case, unscrew the bell chambers on top and lift out the pistons, clean and polish off all of the surfaces (including inside the bell chambers). be very careful with the fuel metering rod to not damage it. On the top of the bell chamber are thumb screws that hold a dampener that goes into a tube (approx 10 or 12mm dia) in the middle of the piston, it should contain light oil (I always used ATF oil). clean out these tubes of old oil, and if there is corrosion you will need to find a way to polish inside these tubes. these dampeners are important to prevent the piston from slamming to the top if you stomp on the throttle, causing a flat spot.

3. Again, treat the metering rods on the pistons very carefully, it if gets bent you are screwed. set them on a clean table top to work on them so you do not drop the pistons. clean out the venturi and the piston with carb cleaner, as well as the throttle plate and linkage. lubricate the linkage. you should not have to remove the carb from the manifold to do these operations. reassemble and put ATF in the dampener tubes, check the pistons will rise up smoothly in the throat of the carb.

4. that should get it to run, but you will need to check the throttles are matched or balanced (simple way is to put a tube in the throat of the carb, and listen to the other end, adjust each throttle separately until they "hiss" the same amount). there should be a clamp between the throttles or an adjustable linkage to allow you to get the throttles to open the same amount. once you have them synchronized, you than adjust the mixture by turning the large nut under the carb that moves the main jet up and down. adjust them so they match, and than optimize the mixture for best economy/power (screw them both in until it idles rough, than screw them out until it gets rough, than set it half way between).

if you live nearby, bring it by and I can show you everything you need to know about these carbs in less than 30 min, including how to tune and adjust them. do not give up on them. if you search the internet I am sure you can find some good sites and forums, maybe even youtube videos, that will show you how to clean and adjust them.

I have attached a cross section of the simple early SU for reference.

Good luck.

[rhdpat]

Thanks everyone for the replies and fix suggestions. Turns out the "fuel cutoff solenoid" that the previous mechanic stuck open is actually some sort of air valve and needs to be closed to start. He basically had created an internal vacuum leak so fuel was never being pulled into the carbs. Unfortunately between the last guy and myself, just about every adjustment has been messed with and will need to be tuned. But it runs!

Petros your explanation of these carbs is super helpful and will definitely come in handy when I balance them and tune them this weekend! I'm surprised how difficult it was to find any info on these considering how popular they seem to be historically. Even the 88-90 US spec Tercel came with a single version of this same carburetor but all the info for those years seems to focus on the fuel injected models.

Thanks for all the help!

[Petros]

for the sake of keeping a long post not so long I left out some details, if you need more direction than what I wrote up above chime in and I will try to give further guidance.

Here is a decent Youtube video for tuning the SU carbs on a Datsun, that may be similar to your ASU carbs more so than the British type:

https://www.youtube.com/watch?v=0Vadtt-ljfc

here is a Youtube video that walks you through the tuning of a British SU, with more details:

https://www.youtube.com/watch?v=F4JVwqu8dgo

[Petros]

... Turns out the "fuel cutoff solenoid" that the previous mechanic stuck open is actually some sort of air valve and needs to be closed to start. He basically had created an internal vacuum leak so fuel was never being pulled into the carbs. Unfortunately between the last guy and myself, just about every adjustment has been messed with and will need to be tuned. But it runs!

I have seen this before, not just on SU carbed engines, but also on our old carbonated Tercels. A mechanic, rather than turning down the job, and than learning what to do with it, will dive in and start messing around with things they know nothing about, often making it worse. And for this astonishing act of ego driven incompetence, they will also charge their customer to NOT fix the car. Leaving it worse off than if they just left it alone.

I often warn newcomers to this forum to not assume that the previous mechanic got all the vac lines installed properly, or made all the adjustments the correct way. It would be double true for your engine installation. If you work your way though the set up and tuning you should get all of the adjustments sorted out. One complication on yours will have some emissions driven components that may add some complication, it would be great if we can get a Japanese Domenic Market service manual showing how to service the SU carbs in English.

A quick search for the Japanese SUs turned up very little, they are made apparently by Hitachi. the SU has been used on British cars, and Volvos and Saabs, for almost 90 years, it is a simple yet well proven design. When I first learned to work on them on my first Volvo I bought for $100 (a 1956 model 444) when I was in high school about 1975). I found a book about them in a car club book catalog and bought it, and it walked me through all the operation and tuning, plus a section of tweaking it for performance. I have loved that carb ever since. I would often find some of my class mates that had an English can use my help on how to tune them, they all thought I was a genius (ha! fooled them!). It is such a shame you have to own a British car to get a car with that carburetor. Some of the old Japanese and Swedish cars have them, a slight improvement. I would love to get that carb set up for my T4wd daily driver, I have heard of occasionally people who buy a crate engine from Japan will get them, but typically they throw them away not knowing what to do with them.