Club Cobra SAAC  

Go Back   Club Cobra > Engine Building, Tuning, and Induction > Weber Tuning

Welcome to Club Cobra!  The World's largest non biased Shelby Cobra related site!

  •  » Representation from nearly all Cobra/Daytona/GT40 manufacturers
  •  » Help from all over the world for your questions
  •  » Build logs for you and all members
  •  » Blogs
  •  » Image Gallery
  •  » Many thousands of members and nearly 1 million posts! 

YES! I want to register an account for free right now!  p.s.: For registered members this ad will NOT show

Midwest Classic Insurance
Nevada Classics
Trigo Wheels
Main Menu
Module Jump:
Nevada Classics
Nevada Classics
Midwest Classic Insurance
Advertise at CC
Banner Ad Rates
Midwest Classic Insurance
Midwest Classic Insurance
April 2014
S M T W T F S
    1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30      
  #1 (permalink)  
Old 04-11-2010, 10:42 AM
Gun Doc's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: Nov 2006
Location: Gig Harbor, WA
Cobra Make, Engine: BDR#499 PE351W with Webers
Posts: 189
Not Ranked     
Default Dead Cylinder

I have had this car for going on three years now and it took me most of that time to get my Webers running right! After a long winter here in Middle Tennessee I took the car to work a few weeks ago and promptly fouled a plug. I had to drive the thing about forty miles back home with it popping and backfiring.

A couple of days ago I put some fresh plugs in and cranked it up, but still had the miss. Using my flow meter I quickly determined it to be the rear left (driver’s) cylinder that was not firing. It was reading around 5 while the others cylinders were right at 10. I played with the carb a little, but soon figured it was not the problem.

I changer the plug again and noticed a slight amount of oil on the electrode…Not wet, but slightly discolored. I changed the plug and swapped the plug wires with the plug next to it. No change.

Right after I changed the plug the first time, I dove the car about 10 miles and it seemed that the offending cylinder would fire every once in a while, as the RPMs would climb some and the engine would smooth out.

This engine only has about 5000 miles on it and was professionally built by Performance Engineering, so it is hard for me to believe it is a serious engine problem (At least I am keeping my fingers crossed!) that is causing this problem.

I am running an MSD ignition and distributor/cap with Taylor wires and Autolite Platinum Plugs (AP3924) . I am somewhat concerned about the oil film on the plug.

Any thoughts??

Thanks,

Gun Doc
Reply With Quote
Sponsored Links
Sponsored Links
  #2 (permalink)  
Old 04-11-2010, 11:00 AM
Rick Parker's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: May 2001
Location: California, Ca
Cobra Make, Engine: NAF 289 Slabside Early Comp Car with 289 Webers and all the goodies. Cancelling the efforts of several Priuses
Posts: 6,334
Not Ranked     
Default

The problem is in the idle circuit.
__________________
Rick

As you slide down the Banister of Life, may the splinters never be pointing the wrong way
Reply With Quote
  #3 (permalink)  
Old 04-11-2010, 02:10 PM
CobraEd's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: May 2000
Location: Northern VA, VA
Cobra Make, Engine: Classic Roadsters
Posts: 2,708
Not Ranked     
Default

if the webers were set wrong, and that weber stack was washing that cylinder with gas, the rings could be trashed.


.
__________________
LIFE IS TOO SHORT TO WORRY ABOUT GOOD GAS MILEAGE
________
Utinam logica falsa tuam philosophiam totam suffodiant!
________
Those in life who offer the least, . . . demand the most
________
The good are getting better, . . . The bad are getting worse
________
If God is a good and just God, . . . I fear for our nation
_______
It is not about working very hard in un-smart ways, . . It is about working easily in very smart ways
Reply With Quote
  #4 (permalink)  
Old 04-11-2010, 02:59 PM
PatBuckley's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: Jan 2003
Location: Atlanta, GA
Cobra Make, Engine: CAV GT40 with 331 KC
Posts: 2,132
Not Ranked     
Default

Perhaps some sort of insect plugged up a circuit?
Reply With Quote
  #5 (permalink)  
Old 04-12-2010, 12:37 AM
Gaz64's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: May 2008
Location: Brisbane, QLD
Cobra Make, Engine:
Posts: 804
Not Ranked     
Default

I'd be doing a compression test first to rule out the engine.

Then I'd swap two carbs around to prove the fault to one barrel of the suspect carb.

Airflow of 5 compared to 10 of the rest does not sound good, could be a twisted throttle shaft or idle air issue.
__________________
Regards

Gary

Last edited by Gaz64; 04-12-2010 at 12:40 AM..
Reply With Quote
  #6 (permalink)  
Old 04-12-2010, 03:19 AM
Registered User
Visit my Photo Gallery

 
Join Date: Mar 2001
Location: E BRUNSWICK N.J. USA,
Posts: 3,600
Not Ranked     
Default sounds like no spark problem

Gun Doc If the spark plug is wet, I would n't start with the carbs. Start with the cap and rotor on the MSD. REPLACE both. MSD has had cap failures and burnt holes in the rotors. Make sure you have good light in that cylinder.
Next You may have to do a little search on this forum and the FE forum but running Platinum plugs is no good for MSD systems. Running just 3924 with a wider gap of .044" Is what I believe is to be run with stock plugs.
As Gaz said the easy thing is to swap carbs and retest. If you have poping and back fires, this is more ignition than carb. Get a spark tester and make sure you have a good large blue or yellow spark. If not the coil could be going. Lets try the basics first, Check for good spark in all cylinders and see if you can shoot a picture of inside the cap and rotor. Rick L.
Reply With Quote
  #7 (permalink)  
Old 04-12-2010, 05:23 AM
CobraEd's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: May 2000
Location: Northern VA, VA
Cobra Make, Engine: Classic Roadsters
Posts: 2,708
Not Ranked     
Default

I guess the big question is, what is fouling the plug, gas or oil. He mentioned oil.


.
__________________
LIFE IS TOO SHORT TO WORRY ABOUT GOOD GAS MILEAGE
________
Utinam logica falsa tuam philosophiam totam suffodiant!
________
Those in life who offer the least, . . . demand the most
________
The good are getting better, . . . The bad are getting worse
________
If God is a good and just God, . . . I fear for our nation
_______
It is not about working very hard in un-smart ways, . . It is about working easily in very smart ways
Reply With Quote
  #8 (permalink)  
Old 04-12-2010, 03:37 PM
Gun Doc's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: Nov 2006
Location: Gig Harbor, WA
Cobra Make, Engine: BDR#499 PE351W with Webers
Posts: 189
Not Ranked     
Default

Thanks for all the replies…I have not had the time to do any more testing, but I think I’ll start by blowing out the idle circuit on the offending barrel.

I did say there was some residual oil on the plug. It is NOT wet, but has a slight film on the electrode. I smelled both plugs that were recently in the cylinder and neither has an odor of gas. I really don’t think that plug was firing at all. The original plug I took out HAD been firing and looked to be fuel fouled (black and sooty).

The last drive I took in the late fall I remember the car running pretty well. The problems started with this first spring drive.

If the carb doesn’t fix it, I guess my next step is to run a compression test on that and a couple other cylinders.

If I have destroyed the rings in that cylinder, what are my options? Is it as simple as honing and replacing the rings with oversized, or is it a complete overhaul of the engine? I have just over 4300 total miles on the engine.

Thanks,

Gun Doc
Reply With Quote
  #9 (permalink)  
Old 04-12-2010, 06:44 PM
Rick Parker's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: May 2001
Location: California, Ca
Cobra Make, Engine: NAF 289 Slabside Early Comp Car with 289 Webers and all the goodies. Cancelling the efforts of several Priuses
Posts: 6,334
Not Ranked     
Default

You'll find the problem without going to that extreme.
__________________
Rick

As you slide down the Banister of Life, may the splinters never be pointing the wrong way
Reply With Quote
  #10 (permalink)  
Old 04-13-2010, 03:47 AM
Registered User
Visit my Photo Gallery

 
Join Date: Mar 2001
Location: E BRUNSWICK N.J. USA,
Posts: 3,600
Not Ranked     
Default Easy big GUY

Gun Doc Doc you are helping to fill in some things. First off, last fall, did you empty the fuel system and run the carbs out of gas?? Did you replace the gas filter and open it up, this is to see if there is any debry in there? Here's the mean question, If the fuel system was not emptied, did you fill and run some gas stablizer through the system? How did the MSD system check out?? Before you start disassembling the motor, leak down test and compression test will tell you if that cylinder is fuel washed.
Is there any change that you red lined the motor? bent some pushrods? Using a vacuum gauge might help. You all ready know the bad cylinder, Check out theses parts too. The motor will run with a bent pushrod. The other question, does the motor run better ot worse when hot or cold? This is also important. What hoses are you running on the Webers? There are starting to be problems with running rubber hoses. The rubber is breaking down because of the 10% ethonal ( spelling is off ). I have had to replace all the rubber hoses in my chain saws, and now the fuel system in my car for the fi system. The rubber turns into little balls of goo. The one carb could also have tarnish in the bowl and causing this problem. Keeps us posted. Rick L.
Reply With Quote
  #11 (permalink)  
Old 04-13-2010, 06:08 PM
Gun Doc's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: Nov 2006
Location: Gig Harbor, WA
Cobra Make, Engine: BDR#499 PE351W with Webers
Posts: 189
Not Ranked     
Default

Did a little more troubleshooting after work today... I started by blowing out the idle circuit (mains, too) with my blow gun. I then changed the idle jet in that barrel from a .60 to a .65 and started the engine.

I only let it run for a couple of minutes then shut it down. It wasn’t missing too badly at idle, but after I rev’ed it up a couple of times, it did start to miss. I shut it down and pulled the plug.

I could now smell fuel on the plug and when I wiped it off with a shop towel, the electrode wiped clean – white. The gas cleaned off the slight oil film.

I am beginning to think this may be an ignition problem. The plug is obviously not firing at all. I don’t think there was enough oil on the thing to foul it. Before I changed out the idle jets a couple of years ago the plugs would come out black and covered in soot, but would still fire. I guess the cap and new, non platinum plugs are my next step…

MTF

Gun Doc
Reply With Quote
  #12 (permalink)  
Old 04-19-2010, 05:34 AM
Caprimaniac's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: Sep 2006
Location: Skjetten, No
Cobra Make, Engine: Unfortunataly ; none
Posts: 331
Not Ranked     
Default

I am confident that Rick is close to the solution; fouled idle curcuit. And to check if the plug is firing or not is quite easy; put it close to ground and crank. Although, a combination of faults is also possible...

hope you get it running.
Reply With Quote
  #13 (permalink)  
Old 04-19-2010, 03:46 PM
Gun Doc's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: Nov 2006
Location: Gig Harbor, WA
Cobra Make, Engine: BDR#499 PE351W with Webers
Posts: 189
Not Ranked     
Default

I took a little break from the car to get my head right…I have two bikes that I have been neglecting since I got the Cobra. One of the bikes has been sitting since I got transferred to Tennessee a couple of years ago; the other has sat since I got divorced four years ago…So I spent some time on them and got both running. I just now started back on the Cobra.

I did a cold cranking (throttle closed) compression check of the dead cylinder and got just over 150 psi. I have not checked the other cylinders yet, frankly because it is a real pain to get the tester started in the spark plug holes!!

I am not sure how much compression I should have, because of cam, etc, but I am pretty sure 150psi cold with starter motor only should be plenty for that cylinder to fire if it has fuel and spark.

I am now debating whether to pull the carb, or just go out and buy a new cap and rotor. I did look at the cap and rotor and they both look okay…Nothing obvious, like a visible crack, or burn.

Gun Doc
Reply With Quote
  #14 (permalink)  
Old 04-19-2010, 05:18 PM
Rick Parker's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: May 2001
Location: California, Ca
Cobra Make, Engine: NAF 289 Slabside Early Comp Car with 289 Webers and all the goodies. Cancelling the efforts of several Priuses
Posts: 6,334
Not Ranked     
Default

Suggestion: Try this before you drop the cash for new ignition parts. On a cold engine, drain the fuel from the suspect carb. remove the idle and main jet holders. Spray some carb cleaner in the holes where the jets screw into. Then disassemble the jets and holders and spray THEM with carb cleaner, pay close attention to the small hole in the end of the idle jet. THEN when you reassemble the idle jet in its holder do not fully bottom the parts out when you insert one in the other. Then mark the taperd face of the idle jet with a felt marker or machinists dye, do the same with the tapered face of the main jet. When you screw them into the carb body the jets will first bottom out in the wells, marking the faces of the jets, pull them out and inspect the markings. They must seal in the bottom of the wells or fuel will not flow correctly. Sometimes over the winter some of the fuel can go bad and plug very small passageways. Check it out and report back.
__________________
Rick

As you slide down the Banister of Life, may the splinters never be pointing the wrong way
Reply With Quote
  #15 (permalink)  
Old 04-19-2010, 06:25 PM
CobraEd's Avatar
Registered User
Visit my Photo Gallery

 
Join Date: May 2000
Location: Northern VA, VA
Cobra Make, Engine: Classic Roadsters
Posts: 2,708
Not Ranked     
Default

Did u check the plug wire? Put an ohm meter on it, it could be open.


.
__________________
LIFE IS TOO SHORT TO WORRY ABOUT GOOD GAS MILEAGE
________
Utinam logica falsa tuam philosophiam totam suffodiant!
________
Those in life who offer the least, . . . demand the most
________
The good are getting better, . . . The bad are getting worse
________
If God is a good and just God, . . . I fear for our nation
_______
It is not about working very hard in un-smart ways, . . It is about working easily in very smart ways
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 06:07 PM.


Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
The representations expressed are the representations and opinions of the clubcobra.com forum members and do not necessarily reflect the opinions and viewpoints of the site owners, moderators, Shelby American, any other replica manufacturer, Ford Motor Company. This website has been planned and developed by clubcobra.com and its forum members and should not be construed as being endorsed by Ford Motor Company, or Shelby American or any other manufacturer unless expressly noted by that entity. "Cobra" and the Cobra logo are registered trademarks for Ford Motor Co., Inc. clubcobra.com forum members agree not to post any copyrighted material unless the copyrighted material is owned by you. Although we do not and cannot review the messages posted and are not responsible for the content of any of these messages, we reserve the right to delete any message for any reason whatsoever. You remain solely responsible for the content of your messages, and you agree to indemnify and hold us harmless with respect to any claim based upon transmission of your message(s). Thank you for visiting clubcobra.com. For full policy documentation refer to the following link: CC Policy
Links monetized by VigLink