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Hi Robert, backfiring is Frequently caused by unburnt fuel in the exhaust getting oxygen to burn, and usually with a bang!
On deceleration, there is a lot of vacuum in the intake manifold, and this pulls a lot of fuel through the idle jets which are below [intake manifold side] of the throttle plate. With the throttle plate closed, there is not al lot of air/oxygen to burn all this fuel, so the mixture is rich, and it is still able to burn when it leaves the engine, but there is no oxygen in the exhaust system..
UNLESS there is a leak in the system. A loose muffler clamp, or loose exhaust manifold bolt, or flange can allow air into the exhaust, especially under deceleration, then the exhaust burns off the remaining fuel and usually in the form of significant backfiring.
So look over your exhaust, check clamps and flanges. You might find your culprit.
Greg Long
Yes Ed as you say drive it etc. Did 1200 kms the weekend before last in our ’29. Great fun after you forget the fuel bill—- & that was just for me!! Jak.
Greg – Thanks, I will put check for leaks in the exhaust system on my “to do”” list.
Robert”
Problem solved!
And the winner is……Greg Long
Ed Minnie told me to check the lower radiator hose to be sure is was not collapsing. Funny how you don’t notice things until someone tells you to look at it. My lower radiator “hose” was not a hose but a pipe with very short pieces of hose connecting it to the radiator at one end and the water pump at the other. So that was not likely the cause.
Then I checked the torque on the cylinder head bolt. With my torque wrench set at 40 ft/lbs the nuts were tightening. Reading the article “A Tale of Two Heads, Cylinder heads that is by Chris Diekamn in the Featured article section, he refers to the PAS service bulletin 95-2 for the torque specifications. They listed them as 65-70 fl/lbs and showed the recommended order of torqueing the head bolts. I first torqued the bolts to 60ft/lbs. Drove the car for a short while (also working on trying to sort the car and get it to run smoothly, currently have a lot of back firing and lack of power, but that is for another topic on the forum), let it cool down, and then re-torqued the bolts to 70ft/lbs. I drove the car again for another short trip and checked the torque on all the bolts. The coolant level did not change. Today I went for a longer drive, about 45 minutes and when I checked the level of the coolant it was about the same as yesterday.
So, one problem solved! Thanks all for your comments. Now I will decide on anti-freeze/water/anticorrosive additive.
Robert
Robert, that is why I recommended inserting an exhaust probe in the radiator to check for exhaust gases. I must admit I thought it would be a lower house issue or restricted radiator before the combustion gas pushing past the head gasket. Interesting it was only a one way leak. Now on to the next issue! One step at a time, you will get it to 100 percent. Drive on……..Ed
Ed, thanks for all your help and continued encouragement. I am methodically working through the running issues. There are only so many things it can be, we will check them one by one. I am confident we will get it sorted out. Life is full of many truly frustrating and serious issues, this is definitely not one of them. I am learning so much about my car and having a great time doing it! The PAS community is outstanding. I have been very lucky and enjoyed the cars I have had, but this has been one of the best automotive moves I have made.
Robert
By way of indirect contribution to this subject, I have recently been made aware of the potential problems caused by the use of permanent antifreeze in veteran cooling systems. The following is taken from an AACA Forum on the subject:
Exclamation URGENT WARNING–EXTENDED LIFE ANTI-FREEZE
Hi,
Information was just published in the Auburn Cord Duesenberg Club Newsletter concerning the use of “extended life” antifreeze in cars over 10 years old.
In a nutshell–don’t do it!
Under NO CIRCUMSTANCES should an “Extended Life” antifreeze, which utilizes Organic Additive Technology (OAT, H-OAT, or N-OAT) as one of its chemicals, ever be used in our cars over 10 years old. It attacks the gaskets and gasket cements in our cars, causing major leaks and forcing ultra-expensive repairs. The “Silver Ghost Association” Rolls Royce people have documented massive cooling system failures apparently caused by this anti-freeze product.
Antifreeze that can be used safely in our cars uses older-fashioned Inorganic Additive Technology (IAT) additive.
You cannot tell by the color of the antifreeze if it’s safe to use. Also, the product may be labelled “Safe for Older Cars”–meaning 10 years old at most. Brands to be AVOIDED are all Prestone lines and Zerex’s G-05 in the Gold-color container. Avoid any “extended-life” antifreeze. None of us wants to pull and rebuild our cars’ engines.
Acceptable brands are Peak, Peak’s HD Product “Sierra,” and Zerex Original Green in the WHITE container.
If any of the OAT, H-OAT, or N-OAT products are in your car the cooling system should promptly be drained–radiator and block– the system flushed thoroughly, and IAT antifreeze installed. I am checking to see what’s in my 37 Buick and 40 LaSalle.
The article is in Newsletter LVII Number 8 2010. It will be posted on the ACDCLUB.ORG site in a few days in the newsletters section of the forum.
Forewarned is forearmed.
This is an older posting and the Peak product I had used in my 836A is described as “Long Life” which may have been introduced after this brand was described in the AACA Post as “acceptable”. For that reason and since my engine has recently experienced some weeping around the head bolts, I will take the precaution of removing this Peak “Long Life” product from my cooling system.
Joe