Installed a wideband on a carb/turbo.....


Well-Known Member
May 24, 2001
A long time ago I had an innovate LM-1. It was hard to read while driving, and cumbersome to record. Then it died. I really like the AEM gauge I have in my '02 GS, so I installed the same gauge in my '83 TR. I didn't want another gauge on the a-pillar, so I can up with this.

It's the gauge mounted in a PVC pipe, painted black and velcroed to the steering column (on top of a steadfast column guard).

Looks better than I expected and its very easy to read. :) Hardest part of the install is welding a bung to the downpipe and that was already done years ago. I used a Bussman "add a circuit" fuse tap for power.

I learned a lot the last couple of years tuning the EFI on the '02 GS. Knowing what proper Air/Fuel Ratios (AFR) should look like, I can see right away the current electronic Quardajet is not doing a great job of maintaining the proper AFR. To begin, at idle, the AFR goes off scale lean and the engine stalls. At WOT, sometimes it goes very lean (bad), other times it goes very rich (good).

I'm going to tackle the idle AFR first. I swapped carbs with the '82 GN, which idles better and doesn't stall. The AFR at idle with this carb is about 16:1. Better, but the ECM should really be able to maintain 14.7:1 (the narrowband oxygen sensor is new by the way).

I did some homework and I believe I need to tweak the Air Bleed Valve. With a scan tool hooked up, the mixture control solenoid is reading a dwell of 6. Recommended is 30 (which would be 50% duty cycle). This is like zeroing out the baseline and having the mixture control solenoid right in the middle of the road, giving it the best chance of a maintaining the right AFR. As a engine gets old & worn, sensors drift, vacuum hoses leak, modifications are made (like changing the air filter box). All of this messes up the factory calibration baseline. An EFI engine uses long term fuel trims (LTFT) to correct the baseline. A carbed ECM doesn' have this. I believe tweaking the Air Bleed Valve is the way to correct the baseline.

I'd say this gauge, along with a boost and knock gauge, is a must have.

Now I just need to find some free time to mess around with it....
Swapped on a third carb just to compare further. This third carb is nearly NOS. Bought it new years ago off ebay (too good of a deal to pass up). This one cycle badly at idle. Bogs a little at tip in, but makes the transition to the secondaries much better than the other two carbs.

I've been doing my homework re-reading the Doug Roe and Cliff Ruggles' books. Idle issues should be easy to work out. There's a throttle stop screw hiding behind the linkage. I may play with that before messing with the Air Bleed Valve.

All three carbs have a hard time maintaining AFR when then seconadaries crack open. Doesn't matter if I mash the gas, or ease into it. When the secondaries first open, the AFR goes lean and the knock meter lights up about 3-6 lights (and pulls a lot of timing). The NOS carb makes the transition best, with only a light or two. The engine pulls hard without having the timing pulled. If I can get the secondaries to open without going lean, it would help greatly. Once they get past the opening transition, they maintain AFR at about 11:1. Seems like to the opening rate of the air valves might need to be tweaked.
The lean condition when the secondaries open can be corrected if you want to take the top off and open the enrichment holes some Rich. Don't forget to open up the feed to the wells at the same time. When you do lighten up the secondary spring so the top plates open faster. You'll still have a slight lean spike but it won't be as bad.
I may need to go that route, but I'm hoping to not pop the top off just yet.

From what I have read, opening the air valves slower will smooth out the transition. And the choke pulls off have something to do with it.
The secondaries open slowly because of the pull off Rich. It's timing controls how fast or slow they open. By lightening the spring they will open easier, but you have to time the pull off to set it up right. If you didn't have it then the butterflies would just pop open every thing you stomped on the gas. The lean spike is the transition from being closed, to opening, so to fix it you need to enrichen it enough to get it flowing more fuel quicker.