Carb Tuning


http://209.208.111.198/Topic15205.aspx 		Print Topic | Close Window

By Ys Guy - 17 Years Ago
I'm having a really hard time getting my Y Block running smoothly.  Bear with me - I'm still learning.  I have a 292 in front of a Ford-O-Matic in my '59 Country Sedan.  About 7 or 8 years ago, I had the engine rebuilt to stock specs (but bored .030 over) but it never ran quite right afterwards.  I was always very inconsistent - I'd get it tuned and going well, but once it ran for a while it would sputter.  Then the next time I turned the key it'd run poorly again.  So it mostly sat and now only has maybe 8-10hrs of run time and fewer than 400 miles on it.  Before today, it hadn't been started for any real length of time in over a year.

I recently got a renewed interest in the project though so after a fluids change I decided to try to get her running this afternoon.  Following the shop manual, I started by warming her up and tuning the idle speed on the Autolite 2100 (rebuilt with the engine), then the fast idle.  The idle was slightly lumpy and I had to raise the RPMs to 550 since 450 was too rough.  Then I moved on to the mixture.  The manual says to lean it out until it runs rough, then enrichen the mixture until it "rolls", then turn the screws in until it runs smoothly.  The first step was easy, but backing the screws out would smooth it out immediately and then produce no change no matter how much I turned them.  I finally settled on an arbitrary one full turn from lean but the slight lumpiness remained.

This is where the trouble began.  I gave it a quick rev and got a backfire out of the carb.  The idle then got really rough and it produced a good amount of white exhaust.  I tried playing with the mixture again but it didn't help much.  I haven't double checked the timing yet, but it should be at spec since it was set during the last tune.  Any ideas what the problem could be or what else I can check?  I'm hoping I didn't permanently damage something...

By GREENBIRD56 - 17 Years Ago
Have you ever tried to adjust the valve lash? -  There is a real possibility that when you pull the valve covers off  - you'll be finding a bent pushrod - or two.

What does a vacuum guage show?

By pegleg - 17 Years Ago
Do what Steve said, but add to that a compression test. White often indicates water in the combustion chambers, maybe a head gasket issue.
By Ys Guy - 17 Years Ago
Thanks for the input (and for the justification to buy new tools).  I'll get vacuum and compression readings and check the pushrods tomorrow morning and report back.
By Pete 55Tbird - 17 Years Ago
Hello and welcome to Y block info central. Can you give some more info? You say the engine was rebuilt and then tuned but it never ran right. Is this correct? Who tuned it? What was done? Y block engine fireing order is somewhat unique, is yours correct? You sure? What flavor gas do you have in your tank, is it the stuff from 8 years ago? White smoke suggests water in the cylinders so with a COLD engine take the radiator cap off and check the water for oil. If your area uses E85 your 8 year old NEWLY rebuilt carb may need some attention. Remember YOU must give a lot more quality info if you expect to get the RIGHT ANSWER to "your" problem.
By Ys Guy - 17 Years Ago
It used to run well until fully hot when it would stumble.  When I revisted it recently, it idled okay, just a little lumpy - until the backfire.  NOW the idle is very rough and it puts out white smoke.  The engine was tuned during initial startup by the mechanic who built it.  He's built countless engines but, to my knowledge, didn't have direct Y-block experience.  I can't tell you specifically what he did since I was not there, but I'm fairly sure it was just lash, timing, and mixture.  Enough to get me started.  The firing order is correct.  I am sure.  The gas is fresh.  The carb was removed last weekend, air horn removed, and all thoroughly sprayed with carb cleaner.  Accel pump shoots 2 strong jets of fuel.  There is no oil in the water.  I haven't had time to check vacuum, pushrods and compression yet, but that was good advise and a good place to start.
By Ted - 17 Years Ago
If you have the original Ford two barrel (1959 vintage), then the power valve is likely a good place to start looking.  Carb will have to be removed from the engine and flipped over to gain access to it though.  If you pull the power valve cover off and it’s wet or full of fuel, you’ve at least found a leaky power valve that is at least one issue you can easily address.  Run compression and vacuum checks any way to search out other issues.
By Ys Guy - 17 Years Ago
Okay, I turned her over today and, big surprise, she's running strong again.  Here's what I found:

warm engine idle vacuum in neutral (700 rpm) - 20 in. hg

warm engine idle vacuum in drive (550 rpm) - 17.5 in. hg

I didn't get to checking the pushrods.  There is some muted ticking but I understand some valve noise is normal for a Y?

Here's where it gets interesting.  I went to pull the first spark plug for the compression test and it wobbled in my hand.  6 of 8 spark plugs were only finger tight (or less).  Half of the electrodes were well coated in carbon and almost all plugs were wet around the sides with what appears to be oil.  Needless to say, a new set of plugs is in my future, but what could be the cause?  As for the compression, I took 2 measurements for each cylinder, and both matched within 1 or 2 psi (gauge resolution is low).

From #1 to #8 - 153, 155, 155, 165, 160, 157, 150, 159 psi   Thoughts?

I haven't yet checked the power valve, but that's a good idea too and hopefully I can get to it tomorrow.  Much thanks for the help!

By pegleg - 17 Years Ago
Well, now you know what it isn't and that's a compression problem. Put the set of plugs in, tighten them and see what you have. Still not certain what's causing the white smoke, but fix the obvious  with the plugs and go from there.
By Ys Guy - 17 Years Ago
Well, I got the new plugs in (old ones weren't even consistently gapped), checked the power valve (no gas leak), tweaked the timing, and ran a can of Seafoam through the intake.  Runs like a champ now!  The vacuum reading went way up.  The gauge's tube collapsed around 21 in hg but I know it's at least that much.  I'm going to find a stronger tube so I can adjust the mixture for max. vacuum, then I should be good to go.  Thanks everyone for the insight! 

The only thing that still seems amiss now is that tuning the mixture screws out doesn't cause any change in the idle.  Is this an indication of worn needle and seat?

By pegleg - 17 Years Ago
Usually indicates the throttle blades are too far open. Try setting the idle down a bit and the try again.