Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
73MidgetLigon
Senior Member
Offline
I recently put in a used DCOE Weber carb in my 73 midget and it backfires quite a bit i had a local shop tune the carb and now its runnig better but still backfiring any ideas?
-
Hi Guest!
You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
There are some perks with a member upgrade!**Upgrade Now**
(PS: Subscribers don't see this gawd-aweful banner
mg backfire dcoe
- Thread starter 73MidgetLigon
- Start date
Share this page
Offline
First: Welcome to the forum!
Second: Is this "shop" conversant in DCOE Weber? Can you give us a "baseline" rundown on the jetting?
The thing is dumping gas (I assume by "backfire" you mean throught the tailpipe), the "choke" mechanism on the DCOE is a set of barrel-looking valves at the rear of the unit... they can allow fuel to pass by them if not seated and the actuating lever not "tied down" (pushed "home") with the cable. I'd start with those as a likely culprit.
Second: Is this "shop" conversant in DCOE Weber? Can you give us a "baseline" rundown on the jetting?
The thing is dumping gas (I assume by "backfire" you mean throught the tailpipe), the "choke" mechanism on the DCOE is a set of barrel-looking valves at the rear of the unit... they can allow fuel to pass by them if not seated and the actuating lever not "tied down" (pushed "home") with the cable. I'd start with those as a likely culprit.
Offline
If it's "popping" or "chuffing" thru the carb, it's a lean condition... and yes, fire is a possibility.
I'm making several ~assumptions~ here: The shop checked/set the timing per spec... They've checked the HV side of the ignition... checked the jetting and float level against *something* as a guide... It's a "kit" install with proper mountings... The aforementioned "backfire" is from the exhaust, not thru/from the carb throats.
Now we wait...
I'm making several ~assumptions~ here: The shop checked/set the timing per spec... They've checked the HV side of the ignition... checked the jetting and float level against *something* as a guide... It's a "kit" install with proper mountings... The aforementioned "backfire" is from the exhaust, not thru/from the carb throats.
Now we wait...
Offline
[ QUOTE ]
If the carb is backfiring and you have a foam air filter on the car take it off immediately. An unwanted fire could occur easily.
[/ QUOTE ]
I've run "foam" air filters on two Lotus Elans (40 DCOE 18's on both) for over thirty years... so far no fires... The S-3 will snarl, crakle and pop sometimes. Am I just LUCKY or should I go out and rip 'em off now? /ubbthreads/images/graemlins/confused.gif
If the carb is backfiring and you have a foam air filter on the car take it off immediately. An unwanted fire could occur easily.
[/ QUOTE ]
I've run "foam" air filters on two Lotus Elans (40 DCOE 18's on both) for over thirty years... so far no fires... The S-3 will snarl, crakle and pop sometimes. Am I just LUCKY or should I go out and rip 'em off now? /ubbthreads/images/graemlins/confused.gif
Joe Reed
Jedi Warrior
Offline
Lots of people run 'em for years and problems may be rare - but possible. If it floods and fuel gets in the foam a backfire can ignite it. That's how Tom Bedenbaugh here in Memphis nearly melted down his Midget a while back. I use an EMPI filter on mine, since it fits an RB car nicely.
As for the backfire....try advancing the timing a little at a time. Mine doesn't like the factory specs at all - but runs just fine with it advanced. If it pings under acceleration or diesels, you've advanced it too far. I think I'm at about 15 BTDC now...
Also, by "tuning the carb" did they properly jet it, or just adjust the idle mixture and idle speed? Those are the only two things that can be adjusted on a DCOE without swapping parts. If whoever did it isn't familiar with the DCOE, they won't have a clue what to do.
Did you buy the carb used (like off of Ebay), or did you buy it new from someone who knew the state of tune of the engine it was going on?
Duhh....ignore the last paragraph - I need to improve either my reading skills or my memory! Since you bought it used, do you know what kind of engine it was on previously? If it wasn't very similar to yours, you might have to completely change the primary and secondary venturis, main jets, idle jets...pretty much everything! These carbs are VERY tunable... and that's both a blessing and a curse...
As for the backfire....try advancing the timing a little at a time. Mine doesn't like the factory specs at all - but runs just fine with it advanced. If it pings under acceleration or diesels, you've advanced it too far. I think I'm at about 15 BTDC now...
Also, by "tuning the carb" did they properly jet it, or just adjust the idle mixture and idle speed? Those are the only two things that can be adjusted on a DCOE without swapping parts. If whoever did it isn't familiar with the DCOE, they won't have a clue what to do.
Did you buy the carb used (like off of Ebay), or did you buy it new from someone who knew the state of tune of the engine it was going on?
Duhh....ignore the last paragraph - I need to improve either my reading skills or my memory! Since you bought it used, do you know what kind of engine it was on previously? If it wasn't very similar to yours, you might have to completely change the primary and secondary venturis, main jets, idle jets...pretty much everything! These carbs are VERY tunable... and that's both a blessing and a curse...
Offline
I ~suspect~ the shop may not have DCOE experience and only see the throttle adjustment and idle mix screws.
I'm fishing for the facts here to get some info to try and help this guy... It could be a 45 DCOE on a 1275!!! No info to speak of yet, so again: we wait.
Oh... and gas-soaked ANYTHING will ignite, given the right conditions. Even that EMPI.
I'm fishing for the facts here to get some info to try and help this guy... It could be a 45 DCOE on a 1275!!! No info to speak of yet, so again: we wait.
Oh... and gas-soaked ANYTHING will ignite, given the right conditions. Even that EMPI.
Joe Reed
Jedi Warrior
Offline
Agreed, but the EMPI filter is a metal screen. That somewhat reduces the risk (which is probably minimal anyway) since only the fuel would burn, not the filter medium...
Maybe I should expand on that a little. I had a stuck needle valve once, so fuel was flowing into the carb throats...and then into the filter. It drained out the bottom side of the filter, so only a small amount remained on the filter itself. The problem with a foam filter in the same situation is that the filter is simply a sponge...and can soak up quite a volume of fuel.
Maybe I should expand on that a little. I had a stuck needle valve once, so fuel was flowing into the carb throats...and then into the filter. It drained out the bottom side of the filter, so only a small amount remained on the filter itself. The problem with a foam filter in the same situation is that the filter is simply a sponge...and can soak up quite a volume of fuel.
Offline
Compare the "medium" with afterbirth... baby's already out.
Fuel fire is FIRE. The charred smoking foam is small stuff after the blaze. I get the physics, the EMPI screen doesn't HOLD as much fuel... but *all other conditions* being the same, i.e.: fuel leak, errant spark or high enough under-hood temp to create vapor ignition, it'll still be a lump of smoldering (s)crap.
I figure I have another fifteen or twenty years before I can't drive anymore... I'll announce any on-board conflagration... oh, and the Alfa and the MGB are also sportin' Weber DCOE's, BTW. My chances are skewed even further to the "red".
Fuel fire is FIRE. The charred smoking foam is small stuff after the blaze. I get the physics, the EMPI screen doesn't HOLD as much fuel... but *all other conditions* being the same, i.e.: fuel leak, errant spark or high enough under-hood temp to create vapor ignition, it'll still be a lump of smoldering (s)crap.
I figure I have another fifteen or twenty years before I can't drive anymore... I'll announce any on-board conflagration... oh, and the Alfa and the MGB are also sportin' Weber DCOE's, BTW. My chances are skewed even further to the "red".
Offline
I had a racing Ferrari catch fire with me that was fitted with those foam filters. /ubbthreads/images/graemlins/nonono.gif Buy a K&N, cut down the stacks, ream out the holes on the filter base, fit the stacks and then the filter assembly.
Your carb is too lean. It would probably be best if you find a shop in your area to tune the carb...cheaper than buying all of those jets and tubes. /ubbthreads/images/graemlins/driving.gif
Cheers, David.
Your carb is too lean. It would probably be best if you find a shop in your area to tune the carb...cheaper than buying all of those jets and tubes. /ubbthreads/images/graemlins/driving.gif
Cheers, David.
Offline
For all we know this guy has a 45 DCOE strapped to a 1275! "Backfiring" can mean a number of things. It may HAVE a K&N, an EMPI, the dreaded foam or nothing at all for a filter... If it leaks there's concern, but instead of skewing it into an issue of whether to fob it off to a shop (apparently he tried that already) to save money on "all of those jets and tubes," start hacking ~tuned~ trumpet$ to accomodate cheap filters or run screaming from a potential flaming death trap, let's wait and learn some of the FACTS? We may actually be able to HELP him get it right.
Again..... we wait.....
Again..... we wait.....
Offline
Sorry for writing. The only problem is that I have worked most every car on this list...I guess that I will just go back to my work shop. And yes, a 45 dcoe can be fitted to a tuned 1275.
Cheers.
Cheers.
OP
73MidgetLigon
Senior Member
Offline
Ok well im sorry it has taken me so long to reply it is a DCOE 45 and it is backfiring out the throats the shop i took it to said they new how to adjust DCOE but who knows im not sure what the setup is as far as jetting i bought it used it was jetted for california. for a 1275 mini cooper The car runs great with this carb other then the backfires I would asume from what i have read so far that i need to get it rejetted and check the chokes? Or do i need to just find someone that knows dcoe to tune it thanx for the help guys
OP
73MidgetLigon
Senior Member
Offline
Can anyone come up with an estiment of what my horsepower should be with 1275cc DCOE 45
Offline
Yup, not gonna get carb change alone to return gobs of power increase.
You've got classic Weber lean pop, or "chuff". The ~best~ way to deal with it would be to find a Weber guru locally, but I'm not so sure there's one of those in Provo Utah. Stranger things have happened, tho. /ubbthreads/images/graemlins/wink.gif
Since you understand "process" we need to have some baseline info. When it pops are you accelerating, decelerating, or at "neutral throttle"? Where (what RPM) does it idle and is that smooth? And, naturally the jets/venturi/emulsion tubes/metering and idle jets' numbers would be necessary info. They are complex beasties and a change of one thing affects about everything else.
Joe Reed Wrote above:
[ QUOTE ]
These carbs are VERY tunable... and that's both a blessing and a curse...
[/ QUOTE ]
It takes time and patience to get 'em right, but worth it after that.
EDIT: The float height is also of interest.
You've got classic Weber lean pop, or "chuff". The ~best~ way to deal with it would be to find a Weber guru locally, but I'm not so sure there's one of those in Provo Utah. Stranger things have happened, tho. /ubbthreads/images/graemlins/wink.gif
Since you understand "process" we need to have some baseline info. When it pops are you accelerating, decelerating, or at "neutral throttle"? Where (what RPM) does it idle and is that smooth? And, naturally the jets/venturi/emulsion tubes/metering and idle jets' numbers would be necessary info. They are complex beasties and a change of one thing affects about everything else.
Joe Reed Wrote above:
[ QUOTE ]
These carbs are VERY tunable... and that's both a blessing and a curse...
[/ QUOTE ]
It takes time and patience to get 'em right, but worth it after that.
EDIT: The float height is also of interest.