Yet Another Emissions Question (YAEC)

[BryanC]

I have a early 1.7 motor in a 75 body and I can't get it past emissions in AZ.

The motor has a (new) single progressive carb and is in resonable shape (leakdown 125, 130, 130, 140psi). It had been sitting for a number of years.
The shop that put to carb on can't get the hydrocarbons at idle to be less than 400ppm. The AZ standard is 250. CO is ok. The engine passed the 'loaded' test at 173ppm HC and 1.3% CO.

The shop that I have looking at it wants to put a catalytic converter on it an hack an already hacked motor. I don't know how much this will help since I was under the impression that the early cats just caused a reaction with the CO, not HC.

I think the problem might be a weak spark at idle; it's got a stock ignition. I just bought new cap, rotor, plugs and wires, but haven't seen if that helps or not. I'm considering a pointless ignition, but don't want to spend more money on this engine without being able to drive it.

Does anyone else have hard numbers for the early motors in emissions tests? I saw a reference to someone with a similar setup and 450ppm, still to high. Am I doomed?

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--bryan

[roadtrp204]

High HC with normal to low CO means it is running lean. If the CO was also high then it would be running rich or weak spark. The idle mixture screw should cure this if the carb is within an adjustable limit. The two best tools for adjusting the idle mixture are a vaccum gauge and a hand-held tachometer. I usually start with a turn and a half from bottom and then go in the direction that gives you the highest vaccum and rpm reading. If the mixture screw doen't seem to do anything, you have a vaccum leak. Check the four boots that connect the plentum to the four runners and the manifold to head (mine was notorious for leaks here, my tin kept getting inbetween the head and runner flange)The single progressive is a horrible setup, but I did have it on my 75 when I bought it and I was able to pass Nevada smog tests with it. Good luck!

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Chris
75 914 2.0L

[pbanders]

Chris is right in theory that a very lean mixture will cause high HC with low CO - but your mixture isn't all that lean at 1.3% at part-load, and unspecified at idle (what is it).

I suggest it may be your ignition timing. Timing has little effect on CO, and a fairly strong effect on HC. Check your timing first to see if it's way off. If it's OK, I'd suggest retarding it by at least 10 degrees for the purpose of passing the test.

Many carb'ed 914's have the timing set improperly, and very few have the vacuum retard that is present on the injected dizzys that retards the timing at idle for low emissions.

Brad Anders

[This message has been edited by pbanders (edited 08-10-2001).]

[Joe Bob]

A properly tuned 1.7 with pass with FI....carbs have a hard time. Tim Hannum has a 1.7 that just passed, he's in Phoenix, AZ. He has it for sale for $600.00, newly rebuilt.

I have a FI 1.7, here in CA....$350, but you have to ship it or pick it up....

[BryanC]

The idle is pretty low when it's cool (tach doesn't read that low). When everything is warm It reads a little less than 1k.

The ignition is set at 34BTDC. It's an 009 dist. I'll try retarding it to 27 and see how that goes.

[bowlsby]

Going from 34BTDC to 27BTDC is advancing the timing if it matters.

[Dave at Pelican Parts]

Also try raising the idle. Low-low idle RPMs can contribute to higher emissions.

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[pbanders]

Originally posted by bowlsby:
Going from 34BTDC to 27BTDC is advancing the timing if it matters.

Nope, it's retarding. Pretty sure about that. It is necessary to ignite the mixture before TDC to assure complete combustion. "Advancing" the timing means to ignite it further in advance of TDC, "retarding" means to move it closer to TDC. Too far, and the engine will knock due to non-uniform combustion. Too close to TDC and the combustion never develops peak combustion pressure, and power is reduced.

Brad Anders



[This message has been edited by pbanders (edited 08-11-2001).]

[BryanC]

Just a followup.... (yeah I know it's been 6 months)

I just passed emissions in this car today. I did several things to cure the problem:

- Installed an MSD unit to clean up the low rpm running. This smoothed out the idle quite a bit. I also backed the timing to 27Deg.

- Leaned the mixture out a lot. The mechanic I had taken the car to had the mixture screen at about _8_ turns (didn't even know it would go that far). The car runs great at about 2 1/2.

- Probably most importantly, I found a vacuum leak on the short plugged vacuum hose that attaches to the carb body. I have an 009 dist, so no vacuum advance

The final numbers were: Idle 145ppm HC and 0.97% CO. Loaded 179ppm and 1.01 %. Very good numbers with no cat.

[roadtrp204]

Congratulations!