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How to: Adjust a first gen(84-87) carburetor (not fix surge)

Got a problem with your stock CRX? This is where you should start.

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How to: Adjust a first gen(84-87) carburetor (not fix surge)

Postby DerRivetBoi » Tue Mar 30, 2010 9:02 pm

Alrighty folks, this is my first write-up on this site in an attempt to make it more 1st gen friendly, or "Allgen" if you will, so feel free to correct me if you feel I am wrong.

So you bought a 1st gen HF/DX crx that can't pass a smog and it's not an surging idle problem? You might not have the funds to make an engine swap at the moment and you need to get it registered to drive it before you can. Or perhaps you like the stock engine in your c-rex?

1.General diagnosis

First things first:

Before You even touch the carb, you need to make sure the idle just needs adjustment, and doesn't have a bigger issue.

Most of the time, idle problems are linked to another part of the car.

Well, as people say, the first thing you wanna do before you try to adjust it is to open up the radiator cap and look to see if the is brownish goo at the surface. If there is, you probably have a blown head gasket. I did.

If you don't, or even if you do you have a blown head gasket might want to take off the air box and have a look at the intake manifold. I did, and found that it wasn't even bolted on all the way :rolleyes1:

-Survey as much as you can before committing money to major repairs. Oil leaks and funky exhaust can be sign

-You want to inspect your vacuum lines for tears and holes. Replace any damaged hoses.

-Check all electrical connections and your dashpot especially before adjustment.

If you cannot find any other possible reason for your car to idle improperly than your carburetor, then it is probably your carb, but, the twist to the crx carb is that it is pretty annoying to diagnose and fix. So we are going to walk through it really quick and inspect it.


Remove the air box by unscrewing the fastener up top. Remove the air filter and gaskets so that you see the gold colored mesh shield. It will have two 10mm nuts that you need to unfasten to lift it up and away.

You should be staring at this:


That is the carb on my '85 HF.
It may look different on earlier 1st gen crx's, but this is generally what you get.

It may need some new diaphragms or solenoids, a rebuild, or it might just be [messed].

Buy a Hand vacuum and a multimeter. and test the power valve, all vacuum connections as well as the wiring harnesses at Control box #1. You might just find your problem.

If you don't have any, then move on.

2.Carburetor Adjustment

Mixture Adjustment:
(Mixture is not idle, Mixture is the actual fuel/air mix that goes to the engine)

Now what I learned from old Honda data, you need this obsolete tool called a Propane Enrichment Kit to properly adjust your mixture (http://www.amazon.com/OTC-7148-Fuel-Propane-Enrichment/dp/B0002SR5N0). The method to do this is sound but, the price of the tool itself is not worth it because it is ONLY USED TO CHECK TO SEE IF YOU NEED TO ADJUST THE ACTUAL MIXTURE AND NOTHING ELSE!!!. Should you need to adjust your mixture, rather than you trying to figure it out and pay for the P.E.K. and risk your carb you might want to have a mechanic do it as it involves dissecting the top vacuum portion of your carby, that is if your are a first timer. But if you are not, and you have a Propane Enrichment Kit, Start up the car. Set up the kit like you normally would. Disconnect the upper vacuum hose where the air box connects to the intake and pinch it shut with a clap. With the hose of the PEK sticking up the intake, slowly depress the trigger to full. Opening it quick will stall the engine and wont give you time to test. As you depress the trigger, the RPMs should slowly rise to about 800 (give or take) and fall back down to normal at full propane volume. If they do not, undo the throttle cable, then undo the screws that hold the upper portion of the carb on, you remove the idle controller bracket, take out the small guard cap and reinstall the controller bracket (there is a small hole on the bracket that you can get into the adjustment hole, re install the upper portion of your carb and the cable and vacuums and air box. Do the PEK test again. if the Propane enriched speed is too low, do 1/4 a turn clockwise and recheck. If it is too high, 1/4 counterclockwise and recheck. Adjust throttle stop to correct rpms. When you get it where you want it, put the guard cap back. (It might seem like a hassle just for a small piece but Honda put it there for some reason, it's a good one).

Throttle stop adjustment:
When adjusting the mixture, if you get excessively high idle, you might want to try adjusting the Throttle stop.
Run the engine till the fan kicks on and grab yourself a carburetor adjustment tool or other flexible screw driver (It's a Philips) and turn the screw till the Tach reads right where you want it to.

3. Idle

On to idle.

There should be a sticker under your hood that tells you what your tach should read. If there isn't:

The HF should be 650 (+ or - 50) for CAL and 49 ST, and Hi Alt should be 700 (+ or - 50)

The DX (Std.) should be 700 (+ or - 50) for CAL and 49 ST, and Hi Alt should be 700 (+ or - 50) (manual) or 650 (+ or - 50) (automatic)

Float level adjustment:
Start the engine. Warm it up and then using the throttle lever, NOT the cable, snap the throttle open to 3,000 rpms and let go to let it idle. Do this several times. When the fuel level is stable, look at the window. If the fuel isn't centered in the window take a large flat-head screwdriver and adjust. Don't turn the screw more than 1/8th every 15 seconds. Paint the screw white.

Idle Control Screw (Pictured above):
Start your Rex and run it till the fan clicks on.Now this is the most messed up, jacked up, horrible screw to get to on the whole car. You need to take things apart to get to it with a normal screw driver and that's not your aim. Using a "carburetor Adjustment Tool" (I call it the wang) or other flexible screw driver, try to push yourself down in there with a a Philips tip and adjust.
Turn on the A/C and check again.

Idle boost Diaphragm:
Easy screw to get to (it is on the idle controller bracket I mentioned above). Run your rex till the fan clicks. Reach down the back of the carb near the firewall and remove the small rubber cap. With the screw exposed, you can adjust the screw by turning it with your hand until you get it where you want it. Siiiimple.

Fast Idle:
Start and warm the car. Turn engine off and plug the vacuum hose of the fast idle unloader.
Open and close the throttle fully while holding the choke valve closed to engage the fast idle cam.
Re-start the engine.

DX (Std.) and HF fast idle should always read 3000 rpms (+ or - 500).

If it doesn't, use the fast idle adjusting screw to adjust.

I hope that helps some people out :-)b
I got a horribly torn up '85 HF stock. Covered in rice and black spray paint.

CRREX wrote:We save the world, one CRX at a time.
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Re: How to: Adjust a first gen(84-87) carburetor (not fix su

Postby James » Sat Mar 08, 2014 10:09 am

Thanks for this very informative post. I have an '85 DX, 5 speed, A/C, all original. Your pics are identical to my setup.

Here is my issue: (First, assume I have allowed the engine to fully warm up.) A fast idle that won't disengage unless I turn the ignition off. Fast idle will step down midway through warm-up by itself, but tapping or punching throttle has no effect. If I turn off the ignition, and restart the engine, I have a proper idle.

Hope you can help. Thanks.
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Re: How to: Adjust a first gen(84-87) carburetor (not fix su

Postby algernon » Mon Apr 10, 2017 12:00 pm

I also have an '85 DX with the same (visually) setup. Your information was exactly what I needed. I've tweaked the screws here and there but never knew that the top (yellow paint) was for float adjustment.

I pulled an identical carburetor and was planning to swap but got a little intimidated. I at least was able to measure the turns on the various screw adjustments.

Thanks for the tutorial. I have a nostalgic affection for the little Honda.
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