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timeing a carburated engine


TonyHi's Avatar
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03-09-02, 12:07 AM   #1  
TonyHi
timeing a carburated engine

When I was heavy into engine work I used a method to time engines that I am not sure of anymore. Correct me if I am wrong.
With a vacuum gage on the carb, bring engine rpm to about 2500.
Adjust timeing to get Max vacuum, and then, retard the timing one inch of intake maniford pressure.

 
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03-09-02, 08:07 AM   #2  
Joe_F
Perhaps.

You should time as per the procedure and spec on the emission decal under the hood and do not deviate from that for a stock engine. Best way.

 
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03-10-02, 12:46 PM   #3  
This is one method that Holley Carbs recommended for getting your carb right. On older non computer engines I still go by ear, for timing, like tuning a raido. The problem with using a strobe on older engines is like anything, the mark and timing plate may not be perfect from one engine to the next.

Back when I was in the shop. Many Mechanics tuned and tweaked by ear & results. I don't remember using a Vac gauge for ingnition timing. Sorry maybe someone else did and will post their methods.

 
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03-11-02, 08:53 AM   #4  
Joe_F
I still say start with the factory procedure and work from there.

If the vehicle has to meet any emission test standards, the timing is critical and will yield the best performance if right.

Timing by ear is an old time scenario that doesn't apply to anything emission controlled (but works on really old stuff).

As I recall, we're talking about a 77 pickup truck, which has not passed California inspection, correct?

With those guys, you have to cross your T's and dot your I's or you won't pass .

Stick with stock timing and procedures and go from there .

 
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03-11-02, 10:26 AM   #5  
I totaly agree with Joe.

When I was in the shop was 1970. Now It the year 2001 and I still work at Home for a few select individuals who know that that I only work on 1967 to 1972 Chevrolet cars & trucks.

I am not in Cal. so I don't have to meet all of emission standards for those years. Take my 1969 C/10, well buy it if you can, but it has a place in the Owners manual that covers Cal. emmisions standards.

The order of the day in 1969 in Cal for my 69 C/10 was a PCV valve, and I run one on each engine I build today, because I believe it is more responsible. If you are my age you remember that oil line down the middle of each lane on our roads, from not using a PCV. Used oil causes Cancer.

I will still stick by my guns on this! A 1970, 350, V8 with todays modern parts and the special Holleys tuned by a Profesional today. Are less pouluting than a modern let's say, a 1994 that has not been matained by compentant owners and/ or Mechanics. Or a brand new 1970 with the old oils and leaded gas of yester year.

I put 4,000 miles on my 1969 C/10 as do many of the folks that have the older cars and trucks. With as many cars and trucks as we have today. Many who put 20,000 or more miles on a year. I am in total aggreement with the Standards of today.

 
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03-11-02, 01:36 PM   #6  
Joe_F
Well said Marturo.

You were in the shop before I was even born, so I take that advice with good authority !

Fact is an old car well maintained will outperform and outrun a poorly maintained newer car. I go out for walks at night. You should hear all the newer cars puttering and spitting. Many are in poor shape. I hear ones like my Oldsmobile in good shape and they run like a dream.

Newsflash: Cars still need maintenance and upkeep, just in different ways than in the past.

No need to junk your old cars and trucks. They are diamonds and have a place in our American history and should be preserved as such. Most are used quite limited and are restored and run so well that they pollute less than newer cars used 10 times as much. My 80 Trans Am passes the idle emission test with striking ease. It runs virtually the same numbers every year.

Today's products do help older vehicles. Stainless steel brake lines, all the nice restoration parts out there and processes that didn't exist before.

Marturo: There is a big following for those old 67-72 GM/Chevy pickup trucks. I bought old NOS parts (what a find..lol) from a Pontiac dealer in Joplin, MO (I live in the NYC suburbs) and that parts manager calls me every once and a while with "really old stuff I know you can help with". Lol. A dealer calls me. Lol! We used to have one in this neighborhood. We called it the "green monster". It was the fastest, loudest, meanest truck I have seen. I believe it was a 72 C10. It was a beast on four wheels. One day I saw it wiped out in front of the guy's house. Must have gotten carried away. That was one FAST truck!

 
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03-11-02, 08:07 PM   #7  
I'm with Joe F., do what the manual says to do. Are you trying to adjust the timing or the dwell. Electronic ignition???
You can get it close by ear (use a timing light!!!!). If you're too far advanced it will sound like you have a low battery when you try to start the vehicle, acceleration will be great. (just like we used to keep them in high school, right fella's?) If you're too far behind, the engine will turn over normally but will take longer to start. Listen for ping under load will tell you you're off also.

Good Luck

 
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03-11-02, 10:35 PM   #8  
TonyHi
OK U GUYS; now you are picking on my '77 Chero. It passed smog with lots of ZEROS. The problem was that the EGR valve failed. The diaphram was shot. I replaced the EGR and cleaned the carbon out of the carb spacer and intake manifold. It passed the CA smog test with flying colors. Now I am going to tune it so that I get MPG's out of it.

 
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03-12-02, 03:40 AM   #9  
Joe_F
Ahhh, now we know what you are working on! We don't have to guess.

You should keep stock timing on the vehicle. For a 77 pickup like that, expect the best to be around 13 mpg or so. These were not made for economy.

Call up the EPA and get their original ratings from GM on what they tested the truck at. Then shoot for there. You will not likely do much better.

Stick with stock timing and stock procedures and work from there.

 
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03-12-02, 08:56 AM   #10  
TonyHi
HEY; Since I tuned this 400 it is getting 12.97mpg in the city. Will drive up to Vegas and find out the hiway mileage. Am going to search out the EPA site. I think the mileage is a function of the gearing. The C6 has lots of power in high gear. What would be your advice on a two speed differential??

 
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03-12-02, 09:19 AM   #11  
Joe_F
13 mpg is good on an old tank like that.

No C6 in a Chevy. That's Ford. GM knows better and puts a THM400 in something like this. .

If anything swap in an overdrive transmission, but you won't gain much in the way of gas mileage. A 1977 Chevy truck is what it is for gas mileage.

You don't buy such trucks for fuel mileage .

 
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