Replace Holley 6280 Feedback Carburetor: backfire at idle, fuel smell in exhaust

[mrtaylor]

Hi my name is Mark  after reading everything I can stand I have finally decided to ask a question.

In my 1973 RV I have a dodge 318 engine with a Holley 6280 carburetor.  The Holley 6280 carb is of course a feedback carb with the wires on the carb hooked to nothing.  The 6280 default to full rich if not hooked up.  The engine runs good, gets about 10 mpg, but the exhaust smells like unburned fuel and it back fires if idling going down hil (I live in Colorado Springs, CO, its all mountains).  Now for my question would you change out the carb for a non-feedback one (Holley 2280, I believe the original was a carter bbd) or leave it a alone?  Thanks
 

[JDxeper]

You have one of the best guys ever on Dodges stuff, in your backyard in CO Springs, try to hook up with retireddodgeguy2, search the members list and send him an e-mail.

[RV Mech Tech]

Mark - first thing to do is check you States emission laws before discarding anything- you may have to keep it connected (see "Anyone familiar with the 454 AIR system? " in the Chev chassis section)  - the computer controlled carb ( CCC) that anyone installed on their vehicles no matter what type of vehicles was a temporary measure at best to reduce what was coming out of the tailpipe and we started to see the GM Rochester CCC carbs in the late 70' s and anytime we knew one was coming in for problems at the GM dealer I worked at you never saw so many techs disappear so fast!!  - the computer basically controlled the power enrichment circuit, the accelerator circuit (depending on the make of carb) and  in some cases the choke circuit - when they were new most worked o.k. but when there was a little bit of wear in any of the mechanical parts that the computer controlled they would pollute more than a non-CCC carb- what other emission devices are on your MH?  at that early stage your RV may have been manufactured for California since it has the CCC - I could not find a replacement on the Holley website and at this time I do not have access to my old catalogs ( I remember seeing a few of those) so if you have to keep that carb on it then Holley will probably have a kit for it - did you ever have it connected? - since you live in CO you may not have to keep it on the MH but  what else does the computer control?  - possibilities are the ignition system, cooling fan operation etc. so check this first - if the computer only controles the carb and you do not have to keep it then it will not be a problem to remove it but on any computer controlled engine management system there will be oxygen sensors and the computer will control the ignition as well - another possibility is that being a motorhome with a GVW  (gross vehicle weight ) over  a certain amount you will be exempt from any emission equipment  in CO and/or it will only have the CCC carb and oxygen sensors  and  disconnecting the carb and replacing it will not cause any other problems - let us know what you have on the MH- thanks!

[DaveVA78Chieftain]

Someone has replaced your original carburetor.
The original carb on your rig was indeed a Carter BBD. Given that Winnebago typically placed the current year house on a chassis from the previous year you could have either a 72 or 73 chassis.
For 72 the Carter number was BBD-6225S.
For 73 the Carter number was BBD-6367S.
Different jet sizes due to emissions changes.
Both had an electric Choke which was the only electric connection.
Far as I know, none of the Dodge Class A motor home chassis ever used computer controlled carburetion.  They stopped making the Dodge Class A chassis before that happened (bankruptcy requirement).
Do yourself a favor and get a copy of the Dodge chassis service manual for the CW store.  Will answer almost all your questions and save tons of grief.

Dave

[mrtaylor]

DaveVA78Chieftain:   How do I tell which chassis year it is? VIN said it a 1973. I have a Service manual, used it to find what original carb was.

RV Mech Tech:  I do not think this RV ever had a computer control anything and I doubt it could pass emission test for the space shuttle, thank god it does not have to. The current carb is definitely not stock equipment

Back to my original question, it not a matter if I can replace the carb, it a matter of should I and what with.  A good reason to would be better gas mileage or just a better running engine, engine will last longer, etc...

Thank you for all the replies.

[RV Mech Tech]

Mark - as Dave has pointed out the original carbs on that application were not computer controlled - the reason I had mentioned all that is that I have seen a 1975 Ford  vehicle with a CCC system on it and it was factory installed -found out later it was one of the first destined for California at that time - if you are smelling raw gas out the tailpipe you could over a long period of time cause engine damage as an excess of fuel can and will wash the lubrication off of the cylinder walls -  your cylinder walls and piston(s)  are lubricated from the oil throw-off from the connecting rods and an excess of fuel can dilute/wash this oil film off- take your oil level stick out and smell the oil- you will smell gas as well - you can check the local parts store for the correct carb or maybe one of the members may have a carb that you can rebuild  if you want the stock carb- or if you want to do some fine tuning yourself you can get an aftermarket carb such as a Holley or an Edelbrock that will allow you to make adjustments and fine tune your system - other members who have done this conversion can give you  the part numbers or you can go to your local auto high-performance shop and see what they have for your application.

[Oz]

As to the question if you should replace it or rebuild it, that's totally a matter of personal preference, only you can make that choice.  Same applies to the question of, if you decide to replace it, what should you replace it with?... use the Message Search.  Plenty of advice from experience and observations on brands, cfm sizes, etc already on the boards.

[DaveVA78Chieftain]

If the VIN you used was in the form of R39CG3S000001 or M39CG3S000001 then the 6th digit (3) is year.

If the Holley carb that is currently installed was from a Computer controlled system, then you will never make it work correctly.

You are only going to need something like a 350cfm 2bbl carb like the holley 0-7448K shown on this link:
http://www.jegs.com/webapp/wcs/stores/servlet/KeywordSearchCmd?storeId=10001&catalogId=10002&langId=-1&N=0&Ntk=all&Jnar=0&Ne=1%2B2%2B3%2B1147708&searchTerm=2+bbl+carb

That one has a manual choke but you might be able to find an electric one.

Dave

[mrtaylor]

Thank You