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dja
Forum Newbie
Posts: 22
Reg: 06-30-12
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06-30-12 09:41 AM - Post#2242944
my 84 has a 305 in it.failed emmissions cuz hc to high,changed eldobrock back to holly and still no pass.timing seems to off and can not get it rite,when its where its supppose to be it wont start.
was told i may need hotter spark plug any suggestions help.
Edited by dja on 06-30-12 09:43 AM. Reason for edit: No reason given.
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 Vaughn
"11th Year" Gold Supporting Member
Posts: 13558
Loc: Colorado Springs, CO
Reg: 08-08-04
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06-30-12 12:19 PM - Post#2242990
In response to dja
Your damper might have slipped it's outer ring, which will cause your timing to be off.
You also may be using an incorrect timing mark. A 305 has a bullet timing mark that is in the center of the motor on the center of the timing cover, behind the water pump. If you aren't using that reference mark your timing will be way off. Timing should be 4 degrees BTDC.
HC, or hydrocarbons, are usually either a too rich mixture or the timing is off. I'd switch back to the original carb OR I would have the jets and metering rods changed on your carb to get the correct mixture (this requires a gas analyzer or a dyno to get the jetting right).
Timing has to be EXACT in order to pass emissions.
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chengny
Forum Newbie
Posts: 35
Reg: 01-15-12
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06-30-12 02:52 PM - Post#2243032
In response to Vaughn
You might want to retard your timing a bit - at least until you pass emissions. The following is excerpted from a post by John Hinckley (Retired GM engineer):
The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.
Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
Full text:
http://chevellestuff.net/tech/articles/vacuum/ port...
Edited by chengny on 06-30-12 02:54 PM. Reason for edit: No reason given.
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75gmck25
Contributor
Posts: 345
Loc: Alexandria, VA
Reg: 12-25-07
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07-01-12 08:37 PM - Post#2243531
In response to chengny
Question for dja - What state are you in that still requires an emissions sniffer check for a 1984? Many states stop that making that a requirement when a vehicle is 25 years old, and only do a visual inspection for emissions equipment.
Bruce
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 gchemist
Senior Chevytalk Moderator
Posts: 20827
Loc: Austin, TX 78748
Reg: 05-09-00
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07-02-12 07:56 AM - Post#2243598
In response to 75gmck25
Probably California. The 25 year rule recently changed. Cali is the only state that I know still requires stock year emissions to be met. 
Another thing to check is your cat. Catalyst converters fail too. Tap on it with a hammer. Does it sound like it's full of sand? If so, it is time to replace it. You can find good replacements online. Now if you are from Cali, you can't buy one online, or have it shipped to you.
Can you post a picture of the engine bay? What is the condition of the engine? Overtime, these engines also require new valve stem seals. Oil can seap down the valves into the combustion chamber. The extra oil will increase HC output. How many miles are on the engine? The more details you can provide, the more we can help you with emissions testing.
Welcome to the site.
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS |
Edited by gchemist on 07-02-12 07:56 AM. Reason for edit: No reason given.
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dja
Forum Newbie
Posts: 22
Reg: 06-30-12
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07-02-12 05:02 PM - Post#2243739
In response to gchemist
thanx for all the help we set time rite and every thing and it is that come to find out the idiots who soldf me the truck had a holly out board motor and an intake for short track but i have the orignal intake on it this is my first vehicle im 13 so imma need all the help i can get
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