New to Carbs...where to start?

[CriticalMass]

I'm beginning to prepare my dad's Cobra (recently inherited) for the summer driving season. The problem is that this is the first carbureted car I have ever worked on. To make matters worse, I will have to get emissions testing early in the driving season.

He always had to tweak his setup for emissions and then return it to normal after the car passed. He wrote down the changes he made last year to get under the regulations. Among other things, they include increasing idle speed and running on 25% alcohol (with 91 octane). Any reading that would prep me for the work required to make the proper adjustments?

I've started reading "Super Tuning and Modifying Holley Carburetors" by Dave Emanuel since I found it lying around my dad's garage but the reading makes me think that it will take experience on top of the book smarts to get things right, and I don't have any carbureted cars to practice on.

Beyond the idle speed adjustment, what needs to be done to run on 25% alcohol? How difficult is the work? Any adjustments that could really foul things up if done incorrectly (if not I can just practice on the Cobra)?

Its a Holley carb but I don't have the model off hand (I can get it if its important). And its on a 427 side oiler.

Thanks to anybody who takes the time to read this ridiculously long post

[Ron61]

First that was not a long post. Do you have a smog place near you that can put the car on their machine and test it without going on-line? That way you can adjust until it will pass before taking the test for real. See Pm for rest.

Ron

[SCOBRAC]

Running on ethyl alcohol is not new, If the car were run that way prior to your fathers passing it would have been jetted (the physical size of the jets is larger) for the mixture he intended.

If the carb was never built to run alcohol I do not suggest doing it yourself. It is a trial and error process which is more time consuming than it is worth. (in my opinion) Alcohol burns cooler and has fewer BTU than gasoline and jetting, timing and plug selection are all different.

It sounds like he left you instructions. Follow them. If it doesn't work out come back and we'll discuss alternatives.

One would be using Xylene or similar additives to meet your emissions requirement. I would first get a pre-test performed at a reputable shop right now to use as a base line for any adjustments you decide to make.

Here's some background on ethly alcohol...

http://www.globalhemp.com/Archives/E...uel/fuel.shtml



Regards,

[CriticalMass]

Thanks for the replies, but I didn't get anything by private message, Ron.

Im certain the carb was not modified (but simply tuned) since his notes don't mention anything about changing carb parts. The notes include spark plug gaps and timing changes if I remember correctly. I don't have them off hand, but I'll get them and post the full list of changes.

I've seen the old emissions results where he tried to get the thing to pass with simple adjustments (no alcohol)...they were all well over the limits (I'll look for those too and post if I find them). I'm pretty sure it will take drastic measures to get it to pass.

Once I get more information to you it should be easier to tell if running on alcohol is worth the trouble or there are other alternatives...stay tuned for those details. Thanks.

[Ron61]

CM,

I tried the e-mail this time. If the notes mention timing he most likely retarded it some for the testing. The plug gap I would guess that he put in new plugs and maybe widened the gap a little to get a longer spark. If you are running an aftermarket ignition like MSD or Jacobs, you should run wider gaps than stock anyway. Not sure about the new MSD units, but with my Jacobs Pro Street I have played with gaps and the stock .035 didn't work well at all. I finally settled on a loose .049 and that seems to be the best for mine. Read all of the notes and then post anything that you have questions about. Some of these guys will be able to answer them.

Ron

[CriticalMass]

Alright, here are his notes:

Initial timing -- 12 degrees
Plugs -- .32 (assuming he meant .032"?)
Points -- .20
Alcohol -- 25% with 91 octane
Idle circuit -- 3 1/2 open (each)
Idle RPM -- 1200-1250
Carb idle jet - 2 wires each side

The last three entries are really the ones that I was initially asking about. Don't know what they really refer to but will get to that in my reading I'm sure.

On another note, what does the "points" entry refer to?

[blykins]

Last 3 entries.....

Idle circuit is probably the idle mixture screw....Each corner should have an idle adjustment....rich/lean. Apparently he's showing how many turns these should be set at. Screw each one in, then back them out 3.5 turns.

Idle RPM.....self explanatory. If it idles that high...it must have a big choppy cam in it....

Not for sure about carb idle jet......possibly the idle speed adjustment....again....how many threads are showing....maybe this will give you the 1200-1250 rpm idle....

The points entry refers to the ignition method. Older distributors had points inside where there is electrical contact....I guess he's giving what they should be set at.....again I think he may mean .020" instead of .2".

[CriticalMass]

Thanks blykins. That will get me on the right track and I'll come back if I don't figure things out. Hate it that his notes would make perfect sense to him but I have to work to decipher them.

As far as idling that fast: He mentioned that last time he made these adjustments he had to baby it down to the emissions place as it did not like running under these conditions. Under CO emissions standards maximum idle speed is 1300rpm so I would imaging he wanted to set it as high as possible, thus 1250. Currently, under normal setup, it idles much slower.

Maximum hydrocarbon emissions are 1000ppm. On one of his failing stubs I found 1300ppm (but I don't know what his setup was). Then on his latest passing stub HC emissions were under 400ppm.

Do you think I could drop 300ppm with additives or is it going to take running alcohol?

Thanks again.

[SCOBRAC]

I suggest running Xylene in place of ethly alcohol. Xylene is by nature 114 octane. It is an excellent way of boosting the performance of pump gas as well as burning more efficiently.

Before I did anything I would go get a pre-test to make sure anything needs to be done. It may have been your father simply enjoyed tinkering with the carbs. It is a common ailment here.

[CriticalMass]

I'll try Xylene and get it tested to see if I can get it under standards that way.

As far as tinkering, I have no doubt he did enjoy it, but in this case I know that he did it out of necessity as I talked to him about ways to go about passing emissions several times last year. Plus I have the paper trail of his multiple emissions failures.

Thanks for the input.

[SCOBRAC]

What ignition are you running? Is it a multi spark or high energy ignition? Either stock late model Ford, MDS etc? If so your plugs will work better at .045-.050, enless you are running super high compression.

If you are running standard points .032-.035 is fine. You settings may differ in the idle circut running straight 91 octane or a mix of gasoline and xylene. You may want to get it running and turn the idle screws in until it starts to run rough, ease them back out until it smooths out. 3 1/2 seems like a lot, but with 25% alcohol it isn't surprizing.

Xylene is 114 octane, pump gas is 91 octane. 20% xylene will net you a 96 octane mixture. (2 gallons of xylene 8 gallons of gas). 30% will net you 98 octane. (3 gallons of xylene 7 gallons of gas) Do not exceed 30% xylene as it becomes corrosive to rubber parts over 30%.

Have fun,