Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: Chili Palmer on September 11, 2009, 11:31:59 AM

Title: High HC's on smog test.
Post by: Chili Palmer on September 11, 2009, 11:31:59 AM

A buddy of mine is running a stock rebuilt 401 in his Jeep CJ with a q'jet.

Here's the model number:

Carb is a Qjet, model is 7042210 QE
                                   1262
 
Here are the test results:

**********
2500 rpm test passed
O2 was 3.4
CO%  std is 5.00  test was 2.74
Hydrocarbon  std is 900   test was 403
Dilution CO & CO2   std is 6.00   test was 13.49
RPM was 2402
 
 
Idle test failed
 
O2 was 7.1
CO%  std is 5.00   test was 1.6
HC  std is 900       test was 1155  (this is what failed) (has to be less than 900)
Dilution   std is  6.00   test was 10.68
RPM was at 1130
**********

At first I figured it was old gas, poor timing, old plugs, etc. but here's what he's running..


Plugs look like brand new, gapped at .035, Champion the black ones
Coil is MSD Blaster
gas, is month old at best 6 weeks
temp was at 195*
plug wires are Accel high dollar wires
rotor and cap are clean and appear okay
dist is electronic
and have MSD-6 box on it

So it appears at idle it's not burning all the fuel (or is getting too much?) but at mid throttle it's working just fine. I've poked around some and read the float may need to be adjusted?

Any thoughts...?

Title: Re: High HC's on smog test.
Post by: Schurkey on September 11, 2009, 09:57:58 PM

High hydrocarbon = lean misfire

When the cylinder misfires, the entire load of fuel goes into the exhaust un-burnt.

If you were too rich, your CO would have gone sky-high.  Not enough oxygen to convert to CO2.

Title: Re: High HC's on smog test.
Post by: Chili Palmer on September 13, 2009, 12:36:01 PM

Understood on the HC's; any idea if it could be the carb and if so what could/should be done to fix it?

I personally have not touched it nor heard it run be he thinks it's a carb issue...

Any info would help - thanks.

Title: Re: High HC's on smog test.
Post by: Schurkey on September 13, 2009, 01:41:48 PM

Did you ever adjust the idle mixture screws???

If I had lean misfire at idle--that'd be the first thing I checked.

Title: Re: High HC's on smog test.
Post by: Chili Palmer on September 13, 2009, 03:41:25 PM

As in back in down i.e. lower the idle so less fuel is getting through?

Title: Re: High HC's on smog test.
Post by: 77cruiser on September 14, 2009, 07:28:38 AM

Not the idle speed, the 2 mixture screws in the front of the base plate. Adjust for best idle & turn in/lean about a 1/4 turn might help it out. Don't slow the idle that will make the HC higher.
What's the timing at?

Title: Re: High HC's on smog test.
Post by: Cliff Ruggles on September 15, 2009, 04:12:42 AM

RPM was at 1130

Idle rpm is not that high, it is more than likely on the main system or pulling some fuel from the main system.  The throttle plates would have most of the transfer slots uncovered. 

Why did they do an idle test with the rpm's above the recomended idle speed?.....Cliff

Title: Re: High HC's on smog test.
Post by: Chili Palmer on September 15, 2009, 10:10:04 PM

I can't say for sure why they tested it at such a high RPM was (if 77cruiser's post is correct) because he was trying to adjust stuff to pass the test and that's the closest he could get - if he lowered the RPM's the HC's would go higher.

I just talked to him the other day and he said he's going to join up - I'll try getting him in here so he can answer these questions more directly.