theandies

Ever since reinstalling my engine I've got a pungent exhaust smell after the engine warms up. I'm thinking too rich? Primary jets a little too big? I haven't really opened the secondaries yet because I'm still taking it easy on my new clutch for break in. It smells "fine" to me when I first start it and it's cold.
'71 with a Lars rebuilt Q-jet. The Q-Jet runs great as it has always after getting back from Lars when he was using it in his loaner carb program a while back. It did have this after getting it back from him but I don't remember it being so bad that I would think of posting about it.
Thoughts?
Thanks

OMF

Most likely it's running lean when warmed up. At start up the choke is providing a richer mixture and as it warms up the choke opens andthe mixture goes lean. This lean mixture causes unburned hydrocarbons to pass throuh the exhaust system and gives that pungent, eye burning exhaust smell.
Richen the idle mixture a 1/2 each and then test to see if it's better.

lars

The biggest contributor to "rich" exhaust smell is retarded timing. Make sure you're running about 16-18 initial with 10-12 degrees of vacuum advance on top of that to get your actual timing at idle in the 30-degree range.

If the carb is one of the carbs that was used in the loaner program, it has been run a lot on a bunch of different engines. I didn't rebuild the carbs in the loaner program - they were all just tested and verified to run acceptably well, so it could be that the carb could use a good setup - be glad to test it and verify it for you.
Lars

theandies

Thanks,
Lars, I'll check my timing as I didn't mess with it when I took my engine out. I left the the distributor in. I appreciate the offer to look at it and I'll let you know if the timing does the trick or not.

One other bit of info, this is on a stock ZZ4. MSD distributor and 6AL box. The number stamp on my vac advance can in B26. I do have a B1 laying in my pile of stuff.

lars

Don't use the B1 - the B26 is a good match for the engine, but you need to limit it to no more than 12 degrees.
Lars

theandies

Ok here is what I found and adjustments.
I'm using the B26.
Before adjustment:
12 BDC@Idle goes above 50 reved up.
Checked my stop bushing and went up a size (black) which is the largest bushing that came with my distributor.
Adjusted to 18BDC@Idle but it still goes above 50 reved up and the vac advance on.
Removed the vac advance (plugged the vac source) and when reved it tops out at 36BDC. Took it for a ride like that and it seems to like it. Got home and I still have the smell, not sure if it's gotten better but it's definitely still pretty bad.
Anyway, I've got a pot luck to go to so I'm done for today. Please keep any suggestions coming as I want to resolve this because my son has his drivers license now and my Vette is quickly becoming my daily driver!
Lars - I attended one of your "Tuning for Beer" tour events in Northern Virginia a few years ago. I didn't have the good fortune to have you look at my setup. I wish you would still do that and if interested I'd gladly host one and buy you lots of beer!!!!

Tim Ware

Try to find an exhaust gas analyzer. You could have multiple issues affecting the exhaust ( and overall running of the engine ) that you might chase without results. Old racer belief is to change one thing at a time. The analyzer will establish your correct air/fuel ratio at all rpm's. Then, you can begin to adjust timing. The easiest &, in my opinion, best way to cure the problem is to have it dyno-tuned. I pay $350. for a complete tune with HP & Torque figures. Car runs perfectly. Its the best $350 I've spent.
Tim

MotorHead

Did you hook up your charcoal canister ?

lars

So with 18 initial, you get 36 total. That's not a bad setup, and it should run great. However, if you're getting over 50 with the vacuum advance hooked up, it means your vacuum advance is pulling in something over 14 degrees. Most likely (from my observations) the B26 will pull anywhere from 17-18 degrees, and that's too much (they always pull a longer curve than the spec advertised). You need to limit it to no more than 12 so the combined total advance is limited to about 46-48. You can use one of my Vacuum Advance Correctors to do this (e-mail me for info on this). But, overall, your timing is set up pretty close. Why don't you send me the carb back and I'll give it a quick setup and test for you (not a full rebuild - just a setup) for the cost of postage.

Lars
V8FastCars@msn.com

CanadaGrant

What would be the reasons or advantage in running a higher initial and lower mechanical with the total being equal. Lets say you want 36 total without bringing the vacuum can into the equation. Would you want to run 12 initial and 24 mechanical or 18 and 18, or 20 and 16?
How is the ideal percentage of initial vs. mechanical determined?

theandies

e-mail sent.

With 36 total without the vac advance is there any harm in just not running the vac advance at all?

lars

The amount of initial you run is dependent on the cam you're running - a bigger cam with more duration and overlap requires more initial timing in order to idle with a reasonable amount of vacuum, which in turn affects the carb's idle system. I have a guideline for this in my timing paper. Initial timing also has a big effect on emissions at idle, so you need to consider this if you live in an area requiring emissions testing for older cars.

As an example, on my 407 small block '64, I have a pretty big solid roller cam. Best idle quality and off-idle throttle response is achieved with 24 degrees initial and 11 degrees of vacuum advance, giving the engine 35 degrees of timing at idle. I make best power at 32 degrees total (I have some good aftermarket CNC ported aluminum heads), so my centrifugal curve is only 8 degrees long. This was all determined and set up with many hours of dyno testing. These number do not work well with near-stock engines: I have done similar extensive testing on mild and stock engines, and this info is outlined in my paper.


None other than that your fuel mileage will decrease and your engine will run hotter at idle and at light cruise.

Lars

theandies

I don't think my ZZ4 likes this setup as I get pinging at WOT. Could this be because I'm not using the vac can?

OMF

Did you try adjusting the idle mixture screws yet??

theandies

Not yet. I wanted to try the ignition first. I will after AI set my advance back to where it doesn't ping.

resdoggie

A bit confused here but I would try this:
Adjust your idle mix screws to attain highest vac, set idle speed
Plug your vac adv can
Go for test drive all the way to wot
If there was no pinging, reduce vac can advance
If there was pinging, reduce initial adv by 2* increments until pinging stops
Tune carb

lars

The vacuum advance has no effect on engine timing at WOT. Somewhere I missed the fact that this is a ZZ4: The ZZ4 should be limited to no more than 32-34 degrees total timing, so back off the total to 32 as a starting point and limit the vacuum advance as discussed earlier.

Lars

REELAV8R

Where is the pinging occurring at high or low RPM?

The zz4 cam specs as near as I could find are an advertised 316/340 does this sound right? on a 112 LSA. Or a 208/222 @ .050.

Given the slow ramp on that cam with plenty of overlap I would up your initial to maybe 20 or higher and limit the travel of the mechanical advance to achieve your desired total timing travel. This should help with the fuel smell at idle a bit.

The other half of the equation is making sure your mixture is correct. Without an O2 sensor you may want to take a look at a couple of plugs to see how black they are or are not. The plugs on the ends, #7 and #8 typically run the leanest and those are the one you may need to tune to.
Here is an article about plug reading that may be helpful.
http://honda-tech.com/forums/forced-...ug***-3063102/
Lots of carb adjustments to get the mixture just right at various levels of performance.

Your vac advance plays no part in WOT performance. It is only involved when sufficient vacuum is present, IE cruise, part throttle, idle.

Oops I see Lars posted again while I was typing so a little duplicate info.

REELAV8R

Looks like this is the right cam specs.

https://www.summitracing.com/parts/nal-10185071

So 275/280 advertised with a 112 LSA on a roller cam. Still 53.5* of overlap.
On my 52* overlap roller cam I run 19* of initial advance. So 20*,21*,22* may work for you. I'd give it a try. Like Lars says the recommended total timing is 32* for the ZZ4.
http://www.gmhorsepower.com/350-ZZ4-Turn-Key.php

theandies

Thanks everyone. I' m going out to reset the timing now but since this has become my daily driver for the foreseeable future I don't have time to mess with the carb today. I work nights and have to be there tonight. I do have 4 days off coming up so I can get it dialed in. You guys