| Passing California Smog Tips [message #235781] |
Sat, 11 January 2014 02:27  |
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MangoMushroom
Messages: 67
Registered: August 2008
Location: Emeryville, CA
Karma: 0
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tried to test today, CO measured 4.5% at idle, 2.5% at approx 2500 rpm so they didn't even try to do full test
I discovered the carburetor had a detached vacuum line, but that didn't solve the problem. It appears the carb is running too rich, so I fooled around with leaning the mixture.
Also tried retarding the timing by rotating distributor cap, but apparently turned it to a less desirable position, as now the timing is clearly quite off... exhaust is producing white smoke (uncombusted fuel) and running engine has a unique smell of off timing that I'd experienced once before many years ago.
So I'm going to take it to a smog shop in town that can tune the engine ($125/hr) while attempting to test and pass smog ($129 with free retest if necessary).
Wish I could do it myself, but I'd need a timing light to get timing accurate. I have a neighbor who is a mechanic whom I may ask first to see if he has a timing light. I like trying to fix things myself first! Of course, sometimes that only causes more problems if I get something wrong!
Question:
What timing setting should I go for in order to have best chance to pass CO test? I know manual says default setting is 8, but what is best setting for smog? And for overall performance in general?
Also, I know how to adjust carburetor fuel mixture screws, but unsure if I can do it right... any tips?
Perhaps I can get things right on my own and save myself two Benjamins or so ($200). Smog test only would be $50 nearby in my neighborhood!
any and all feedback appreciated, and thank you kindly ahead of time!
****MangoMushroom
`76 GMC Birchaven named "Harvey"
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| Re: [GMCnet] Passing California Smog Tips [message #235794 is a reply to message #235790] |
Sat, 11 January 2014 07:21  |
LarryInSanDiego
Messages: 336
Registered: September 2006
Karma: 0
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High CO means a rich mixture. Changing the timing (within reason) primarily affects NOx. The balancer hub may have walked, affecting indicated timing, which you can verify by doing a cold TDC, but I wouldn't waste my time there at this point.
If you leaned out the mixture and it still has high CO, I would suspect a sunk or misadjusted float or grossly high fuel pressure. Carb kits usually don't have floats, but a decent parts store (NAPA, etc.) will carry them, so I would try that first.
Larry Engelbrecht
San Diego, CA
'73 26' ex-Glacier
TZE063V100319 03/07/73
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| Re: Passing California Smog Tips [message #235808 is a reply to message #235781] |
Sat, 11 January 2014 09:10 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Oh boy. Non orthodox but if you are that out if whack this will get you close. Good hearing helps. With engine warm at idle and in park and running, slowly advance timing for max RPM gain and stop advancing as SOON as you start to loose RPM from over advance. Then retard for about 100 RPM retard drop. At least you will be on the right side of ramp. Snug and Carefully test drive and start with light acceleration listening for ping and make minor retard adj of about 50 RPM and retry. You may have to reset idle RPM to 650. It should be running better.
On the Qjet if it is not malfunctioning and choke is wide open, and idle mixture screws are responsive---- you should use 'GM lean drop method' for emissions tuning. Slowly adjust mixture on each side for best idle RPM gain. This will take a couple mins and again you really need a tach at this point. Then lean (CW) each screw just to the point where RPM would start to drop but does not. You are now at max lean idle. Reset idle speed to 650. Recheck the above mixture so you are at best max RPM at the lean edge of RPM drop but still at max. Reset idle to 650. NOW-- slowly lean the left MIXTURE screw in to exactly 625. Go to right screw to lean to exactly 600 RPM. This drop should happen with 1/8 to 1/4 turn in if you are setup right. You now have a balanced 50 RPM total lean drop. Emissions should be way better. After passing test you may want to open mixtures 1/8 each no more. Again my timing guide is to get you back to reasonable if you have really messed it up. Check it to spec after confirming balancer is ok.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Passing California Smog Tips [message #235821 is a reply to message #235808] |
Sat, 11 January 2014 10:52 |
LarryInSanDiego
Messages: 336
Registered: September 2006
Karma: 0
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Snug, not tighten (as in torque to spec), the 9/16" distributor clamp bolt is what I have done on my GM engines. It allows me to quickly adjust the distributor in the event I get a load of bad gas or I have a hot crank problem.
Larry Engelbrecht
San Diego, CA
'73 26' ex-Glacier
TZE063V100319 03/07/73
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| Re: [GMCnet] Passing California Smog Tips [message #235823 is a reply to message #235808] |
Sat, 11 January 2014 10:50 |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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The good side to this is that I'd expect your milage to improve.
I think.
Plato seems wrong to me today.
On Jan 11, 2014 7:10 AM, "John R. Lebetski" <gransport@aol.com> wrote:
>
>
> Oh boy. Non orthodox but if you are that out if whack this will get you
> close. Good hearing helps. With engine warm at idle and in park and
> running, slowly advance timing for max RPM gain and stop advancing as SOON
> as you start to loose RPM from over advance. Then retard for about 100 RPM
> retard drop. At least you will be on the right side of ramp. Snug and
> Carefully test drive and start with light acceleration listening for ping
> and make minor retard adj of about 50 RPM and retry. You may have to reset
> idle RPM to 650. It should be running better.
> On the Qjet if it is not malfunctioning and choke is wide open, and idle
> mixture screws are responsive---- you should use 'GM lean drop method' for
> emissions tuning. Slowly adjust mixture on each side for best idle RPM
> gain. This will take a couple mins and again you really need a tach at this
> point. Then lean (CW) each screw just to the point where RPM would start to
> drop but does not. You are now at max lean idle. Reset idle speed to 650.
> Recheck the above mixture so you are at best max RPM at the lean edge of
> RPM drop but still at max. Reset idle to 650. NOW-- slowly lean the left
> MIXTURE screw in to exactly 625. Go to right screw to lean to exactly 600
> RPM. This drop should happen with 1/8 to 1/4 turn in if you are setup
> right. You now have a balanced 50 RPM total lean drop. Emissions should be
> way better. After passing test you may want to open mixtures 1/8 each no
> more. Again my timing guide is to get you back to reasonable if you have
> really messed it up. Check it to
> spec after confirming balancer is ok.
> --
> John Lebetski
> Chicago, IL
> 77 Eleganza II
> Source America First
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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1973 26' GM outfitted
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| Re: Passing California Smog Tips [message #235838 is a reply to message #235787] |
Sat, 11 January 2014 14:30 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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I finally wired in a cigarette lighter plug on my timing light. (Make sure the polarity is right). Being able to simply plug it into the lighter on the dash saves trying to clip the wires to ground and 12 volts.
I have gotten a smile from more than one GMCer when he saw the plug. We were looking at timing in seconds.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: Passing California Smog Tips [message #235888 is a reply to message #235781] |
Sat, 11 January 2014 21:24 |
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MangoMushroom
Messages: 67
Registered: August 2008
Location: Emeryville, CA
Karma: 0
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Well, I tightened the fuel mixture screws on the carb all the way tight, then loosened them both one half turn. That's the leanest I can set it without risking stalling the engine. I am getting a moderate amount of white smoke from tailpipe even after driving on highway for ten minutes. I have rotated the distributor to be in a relative "sweet spot" between points of stumbling at approx 1/4 turn clockwise and counter clockwise. The engine is just slightly rough at idle at this point.
Why am I getting white smoke even after exhaust is warmed up? Hopefully not a leaky head gasket. Coolant level is low, but I haven't topped it off in several months and drove 6 hours each way to the Nevada desert this summer. I should keep a better eye on that though!
No white smoke when foot on gas, only when idling/sitting at a light. It did rain today though. Also, engine smells a bit more of file than normal... Perhaps my timing is off?
May just take Harvey the RV to Doctor Kanomata's this week for a thorough engine checkup.
All feedback encouraged and appreciated! Thanks everyone
****MangoMushroom
`76 GMC Birchaven named "Harvey"
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| Re: Passing California Smog Tips [message #235897 is a reply to message #235781] |
Sat, 11 January 2014 22:04 |
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MangoMushroom
Messages: 67
Registered: August 2008
Location: Emeryville, CA
Karma: 0
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I think An engine running rich emits too much carbon monoxide (CO) but generally doesn't emit much hydrocarbon (HC). Since carbon monoxide is colorless and odorless, it doesn't burn your eyes. The lack of oxygen prevents the CO from becoming CO2, but the hydrocarbon does oxidize.
An engine running too LEAN can misfire, then the entire cylinder load of fuel (HC) goes out the tailpipe
, it's more likely to be too lean than too rich right now
****MangoMushroom
`76 GMC Birchaven named "Harvey"
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| Re: Passing California Smog Tips [message #235899 is a reply to message #235781] |
Sat, 11 January 2014 22:16 |
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MangoMushroom
Messages: 67
Registered: August 2008
Location: Emeryville, CA
Karma: 0
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I'm also getting some engine pinging on acceleration. May be due to lean mix. Or, the following:
"
Pinging or spark knock is properly called "pre-ignition" and is often incorrectly called "valve noise" because it sounds similar to loose valves that need adjusting. The difference is that loose valves will make noise all the time, whereas pre-ignition happens on acceleration or under a load. You might hear it when going up a hill on the interstate: a rattling sound that goes away when you downshift or get off the gas.
Pre-ignition can be caused by too much spark advance or too low octane gas.
"
****MangoMushroom
`76 GMC Birchaven named "Harvey"
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| Re: Passing California Smog Tips [message #235923 is a reply to message #235838] |
Sun, 12 January 2014 07:29 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| George Beckman wrote on Sat, 11 January 2014 14:30 |
I finally wired in a cigarette lighter plug on my timing light. (Make sure the polarity is right). Being able to simply plug it into the lighter on the dash saves trying to clip the wires to ground and 12 volts.
I have gotten a smile from more than one GMCer when he saw the plug. We were looking at timing in seconds.
|
Great idea!
Add this to you timing light and you will be able to use the light powered both ways:
http://www.o-digital.com/uploads/2179/2195-1/Cigarette_Lighter_Socket_YK_B01_1_361.jpg
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Passing California Smog Tips [message #235927 is a reply to message #235781] |
Sun, 12 January 2014 09:19 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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White smoke is usually coolant in combustion chamber. Also sounds like you are over advanced and over lean. You didn't follow my get out of jail step by step did you. Idle screws are probably too far in and this has little to do with part throttle mixture once you are above the idle circuit.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Passing California Smog Tips [message #235929 is a reply to message #235781] |
Sun, 12 January 2014 09:21 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Also before setting timing check for free advance mechanism function on weights and vacuum. Also good vac hoses and correct patching.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Passing California Smog Tips [message #235931 is a reply to message #235781] |
Sun, 12 January 2014 09:51 |
Chr$
Messages: 2690
Registered: January 2004
Location: Scottsdale, AZ
Karma: 1
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Pull out the air filter just before the test and up the idle to 1000 if they will allow it. I did this in mine several times to pass.
W/O the air filter, you will get more air and a better mixture without screwing up a good running carb.
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.
Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"
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| Re: Passing California Smog Tips [message #235961 is a reply to message #235947] |
Sun, 12 January 2014 15:08 |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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I have a California Smog story that proves truth is stranger than fiction.
Miguel took my coach to be smogged. This is the coach with Jasper motor # 3 that I had dyno tuned in 2010, from which I picked up an amazing HP and TQ gain. (191 hp at 3239 rpm to 235.6 hp at 3209 rpm, 311.3 TQ at 3232 rpm to 439.3 TQ at 2698 rpm) The carb and distributor have remained untouched since 2010.
True story - the smog machine kicked it back as TOO CLEAN. In CA it is hooked to a computer that goes straight to DMV/AQMD They made the smog guy run the test several times and then HOLD THE COACH THERE till they sent a roving inspector to make sure it wasn't a scam. It wasn't.
Poor Miguel. A half hour trip to the smog shop as a sort of favor turned into a 3 hour ordeal.
But - my point is that a well running 455 ought to pass CA smog no problem at all.
Neil
76 Eleganza now sold
Los Angeles
[Updated on: Sun, 12 January 2014 15:09] Report message to a moderator |
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| Re: Passing California Smog Tips [message #235969 is a reply to message #235781] |
Sun, 12 January 2014 16:09 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
Karma: 0
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Is it me, or only California could have problems with a coach being too clean?
I imagine that putting a catalytic converter on your coach would also cause a fail as you're obviously trying to modify the 'as built' condition of the vehicle. Never mind the positive effects it may have. Ever heard of 'zero tolerance'?
George Rudawsky
Chicago, IL
75 Palm Beach
[Updated on: Sun, 12 January 2014 16:09] Report message to a moderator |
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