Hi all, I don't post on here much. Been a bit of a lurker but i thought i'd upload my carb experiences on my 1989 Sierra WT for anyone else who likes to tinker.
I commonly see "get a weber, they are far simpler and more reliable, but don't like hills without mods".
I decided i'd try and reduce the stock Aisin carb in the hope of to the simplicity (and therefore reliability) of a weber, whilst keeping the aisins performance on the steep stuff. Below is a write up i've done. PDF Here:http://www.auszookers.com/forum/download/file.php?mode=view&id=30189
Just consider messing with emissions and carburetors is illegal, so I'm not suggesting you do this on a road registered car/ your daily (or at all, this could be dangerous or harm your engine as everything i've written is my own opinion and may not be correct, i'm no Suzuki engineer!). I've been running this for >10 months, weekend rig. Haven't had to adjust anything since the initial setup.
This write-up might be pretty wordy, I haven't done these before but here goes...
Notes:
• I did not take photos before/during the modifications (I didn’t know if any would work!)
• I recommend completely stripping, cleaning and rebuilding the carburettor before this. Nardek/eBay sell rebuild kits.
• I used some stainless safety locking wire and snips to do all of my temporary fixings. Many of these have ended up permanent.
• Carb: Aisin 90-18(?) found on the SJ50 and SJ70 (G13BA and G13A)
These are the systems removed:
1. EGR
2. Idle up
3. Choke
4. Vacuum assist for secondary throttle.
The EGR on these cars is for emissions and does not have the cruising benefits of newer EGR systems are, I know this because the 4th and 5th gear sensors on the gearbox deactivate EGR. If Suzuki knows the engine doesn't perform well with EGR in 4th and 5th then I don't want it in 1st to 3rd either. The vacuum motor (diaphragm) on the LHS of the intake manifold below the vacuum line going to the brake booster is automatically closed.
I removed the vacuum line from the EGR vacuum motor (1) all the way back to the intake manifold (4). The vacuum line passes through a thermistor below the thermostat (3) and an electronic solenoid on a bracket above it (4) (these two controls deactivate it in 4th and 5th and when the motor is cold as mentioned before).
I left the thermistor in the manifold and just pulled the vac lines off. I took the electric switch and bracket off and tied the cables off (2).
You could make up a plate to replace the vacuum motor (1).
2. The idle up solenoid uses manifold vacuum to pull a vacuum motor, to activate a linkage on the front of the carb which raises idle. The idle up is activated when you use heater fan, headlights or rear window defogger on a hardtop if you would like to test yours to see it work. I was going to reroute mine to a switch on the dash to idle up at my leisure, but the vacuum motor started fluttering so I removed it completely. There is a switch (green wire) which sensors when it is activated, I think it simply relays it back to the ECM but I removed that and snipped the wire back with no issues.
Hopefully you can see from the photo, I literally just removed everything. I took all the linkages off the front side of the shaft, but kept the spring and nuts on it.
I believe the washer on the shaft may help seal the gap between the shaft and the carb housing (feel yours for lateral play) and it also makes it look like the shaft has a purpose and you haven’t just molested the carb (the spring doesn’t add any tension, it’s just sitting there).
3. The choke uses coolant temp to heat a wax motor to control a throttle butterfly in the top of the carb. Even when fully warmed up, the choke butterfly can only open so far, causing a massive restriction to airflow. I changed the coolant hose run so it only runs through the carb base bypassing the wax motor (5) You can bypass this too if you like.
I removed the choke assembly including the throttle butterfly inside the carb and plugged the hole the shaft runs through (6) – you can probably do a neater job than me here. Associated linkages were removed, vacuum lines plugged. I haven't "needed" a choke since. Cold starts are a bit rough, I just start driving and take it easy until she's warmed up. If it runs without a choke, don’t use a choke I say.
4. The vacuum assist for the throttle secondary I removed, like the choke - to see how it would go. Less vacuum lines and motors = less to go wrong. This requires a bit of setting up, tweaking and fiddling. More fun!
I removed the vacuum motor and associated linkages, and all vacuum lines running back from it. These ports where they enter the carb body were plugged (8) (12) (check photos below).
There's a black box on the LHS of the carb with vac lines going into it - I removed this too (It's an air temp sensor to only allow the secondary to open once it's warm).
Once all that was gone, I then got out my stainless safety wire and some pliers and got to work. I added a return spring on the secondary, with two safety wire point so the secondary would open, only at WOT. I played around with this a bit to get the tension correct on everything (so it didn't put too much pressure on the shaft, but still moved properly) This would be the tricky part to all the modifications.
(10) Is your fuel shutoff solenoid. This is for safety, keep it working.
(9) Is a redundant linkage I tied off to stop it rattling. I kept all these redundant linkages as spacers, you could make up some spacers to tidy it up.
(7) Is a spring I relocated to help the throttle return closed completely, I was finding it wasn’t shutting properly and giving me a high idle. There is a kink in the safety wire as I had to get the tension of this spring right so it worked smoothly. If it’s too stiff the throttle will rap shut hard, you can get a feel for what’s right and not abusing this equipment.
(11) is just a screw I added to hold the spring.
(12) is to be blocked off
(13) Is a wire attached to a bracket on the secondary throttle shaft, and the carb body. This is so the secondary can return when throttle is lifted; once again the angle of this rear spring bracket needs to be played around with so there is not too much or too little force.
(14) Is a wire attached to a long spring attached to the base of the throttle to assist it in returning. This spring works in conjunction with spring (7) above. As they are both at different angles, both springs can run at much lower tension yet still ensure the throttle returns properly, minimising wear on the carb body. I will make a bracket to drop this spring even lower one day.
I have also highlighted the ports to be blocked off.
If you are wondering what the small vacuum line is coming from the intake manifold – it is for a vacuum gauge.
Once this is done, in my eyes you have yourself a weber. You should have a vac line (fuel vent) to charcoal canister, (from venturi) to distributor, intake vac to brake booster. You should still have a pair of wires going into the carb, this is the fuel shutoff solenoid to stop fuel leaking anywhere when it's parked up. I’ve added a few more photos below:
Stay safe,
Will.
Choke removed frees up so much airflow!
Will, thanks for sharing
