Zenith help..

[blackbird225]

Ok, I tried with some limited success to tune my 70T's Zeniths. Yes, with SOME success, as the car still runs, but still rough.
Here's what I did per Haynes & 101 Projects
Turn off car,
disconnect linkages
Turn mix screws in, then out 2.5 turns
turn air bypass screws all the way in ( they were all in anyways )
tried to pull the airbox assembly ( some hoses attached, so just moved it aside )
then with my brand new synchro tool,
sync'd No1 with a carb on the other side ( 3.5 on the meter )
then tried with mucho trouble to get all the carbs to sit a 3.5
all did except the very right and deepest carb, which is at 3.0.

The car still pops.
When I tried to do the little trick where you turn each mix screw in 1\4 turns until you hear the idle drop. This never seemed to work right. I was able to get a few of the carbs to drop the idle, but turning 1\8 back didnt seem to correct it. It was very frustrating. I sat there with the car running for over an hour looking for the idle to drop at each 1\4 turn.
This car was last tuned at high altitude, and some of you suggested that the jets might have been changed. I have 101 projects, Haynes, Weber and Zenith Carb books, but I still cant figure out where to just " pull the jet out of the top?" as some have suggested here.

What am I doing right or wrong?

btw the settings on the carbs when they came from up north were 1-1\2 turns out on every carb except the middle two which were 2 turns out.

tia

Michael

[jankemi]

I followed the factory manual & had good luck.

Before I started I removed each screw that was accessible from the outside of the carbs & shot carb cleaner into the hole. I got lots of crud out that way.

Turn mix screws in, then out 2.5 turns

Turn air bypass screws all the way in

Sync #1 with #4 using throttle stop screws.

Sync the rest to #1 & #4 using air bypass screws.

Quote: "Note: The air bypass control screw in the mixing throat with the highest rate of air flow (measured with air bypass screw closed) must remain closed (reference throat) while the other throats of that cylnder bank are adjusted. "

So it sounds like the throat with the highest volume gets left alone, the others are opened up to match it.

Now the interesting part: "Adjust all idle mixture screws to smoothest engine performance. First turn the idle mixture control screws in to 'lean' then gradually out to 'rich' until the engine runs smoothest. "

I had to richen them out to get rid of the popping. I just opened up each one the same amount.

Then readjust idle speed using throttle stops & re-balance #1 & #4 using throttle stops.

The 'correct' way would be to drill a tiny hole in each header & measure the CO of each exhaust witha gas analyzer. You can then set each cylinder to optimal idle mix. We used to do this with our road race bikes. After tuning we'd put a pop rivet in the hole.

--Mike

[blackbird225]

Maybe thats what im doing wrong, i am supposed to open all of the mix screws at once? like all 2.5 turns then all 2.0 turns , etc...?

That actually makes sense.

Michael

[jankemi]

Without some ability to check the fuel/air ratio of each cylinder, I'm not sure how you could adjust the mix for only one cylinder. Plug reading maybe?

Also -- cleaning the crud from the various orifaces and circuits make a huge difference. It wouldn't 'respond' to the adjustments in a rational way until I did that.

--Mike

[blackbird225]

So just crack open every screw and shoot carb cleaner in there? Sounds good to me..
No i mean I would turn each mix screw in waiting for the whole engine to calm down. I think that you are saying to make an adjustment to every mix screw. E.g., back all screws out to 2.5 turns, then turn them all in 1\4 turn at a time untill the idle dips, then turn them all back out 1\8 turn,
right?

Michael

[jankemi]

Originally posted by blackbird225
So just crack open every screw and shoot carb cleaner in there? Sounds good to me..

Yes. I pulled out any screw or plug that looked like it would come out w/o trouble, one at a time, and shot it & the open hole with cleaner. Lots of brown gunk came out. of some of them. It looks like there are at least 4 per throat. Idle jet (up high on the carb), idle mix, air bypass, and a small threaded plug just above the idle mix. There are a couple more on the middle throats that are related to the auxiliary enrichment circuit ( only in effect when decellerating). I'd leave those until you get basic idle set up.

I turn the screws in first & count the turns, so I know where they belong when I put them back., just in case the manual doesn't tell me.

......E.g., back all screws out to 2.5 turns, then turn them all in 1\4 turn at a time untill the idle dips, then turn them all back out 1\8 turn,
right?

Yes, all six the same. I did not try for 'idle dip'. I just opened them up until it quit popping. It may be too rich at idle now, but it runs & idles real nice.

I don't know of a method of objectively determining the idle mix of one cylinder unless you probe that cylinders exhaust, so I don't know that I could adjust one cylinder different than another.

--Mike

[Mukilteo911]

I suggest rebuilding them if it has not been done before. You may find some clogged lines inside there. I just did mine and it was very easy just takes about 8 hours.

Keep your Zeniths, don't sell them.

[si2t3m]

For the Zen on adjusting Webers & Zeniths, this is one of the best!

Weber rebuild

Lookup for a post from T Bird. It's a 2 part post.

Remember, if you turn in one of the idle mixture screws completely in with no effect on the idle, something is wrong in the idle circuit or your initial setting (like 2 1/2 turns) was not enough.

HTH

Marc-André

[blackbird225]

I am gunna try and rebuild.
The carbs are caked with black crud in the recesses, so I have a hunch that the PO and the PO before that never rebuilt them.
Ordered the gasket kits from pelican today.

I hope the board has thier collective fingers crossed for me...

Michael