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Registered:
May 2002
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18RC & Weber 32/36 hesitiation and Backfiring.
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Sat, 07 December 2002 13:27
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Hi people,
Have recently fitted the webber carb into my stock 18rc. Had to take pollution some pollution gear out due to the conversion... I know naughty .. but the old carb is dead and since I have this one lying around I might as well use it.
Now the problem is a huge hesitation whenever I quickly mash the throttle down from near idle rpm (800rpm). Sometimes it backfires back up through the carby intake as well.
I've also replaced the spark plugs, correctly gapped the cams, replaced the intake and exhaust header gasket, corrected the timing and made sure all the hoses are connected correctly. The carby has been rebuilt to standard DGV 32/36 specs ie. jets etc.
It seems there is no problem when I gradually accelerate (press the accelerator gradually) though sometimeses I feel it bog down at around 2000-3000RPM.
What I notice though when I look in the carby intake whilst yanking on the accelerator linkage... a crapload of fuel is kinda dribbled down through some outlet... and looks very uncontrolled... The outlet is high up the carby just after the choke mechanism.
Now any help would be greatly aprreciated to get this thing running smoothly.
If you are one of the people who are runnung a 32/36 DGV, DGEV etc. carby on a stock 18rc what jets / carby settings are you using.
I have a feeling that it's bogging down running extremely rich for that instant due to this seemingly uncontrolled dribbling of fuel down the carby. I swear I have looked the carby over many times and am sure it is rebuilt properly. I'm hoping it's the jets or other changable parts that care doing this... as the rest of the car is in running order.
Any help at all please guys as I really don't want to spend another day of the already 3 days I haven't had the car.
I'm still waiting on auto one to get an air filter for me... said it will be in friday and guess what... nada.. the bloke I talked to before wasn't even there.... Talk about crappy service or what.. the guy promised it will be in.... REally pissed me off more than the carby problems I'm having .. oh well.. what can you do??
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sun, 08 December 2002 03:20
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Either its the carbs fuel pump working, or just the way the carb works.
Look down the thoat, and pump the throttle (while car isnt running), you should see it squirt a fair amount of fuel down the throat. If it doesnt, the carb prolly needs a recon.
If it does, well the carbs working as it should be. I also cant just plant the foot with my carb at low RPMs. I have to wait until ~2500 RPM before i can.
Its somthing you get used to.
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Location:
adelaide
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sun, 08 December 2002 08:36
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Yeh ive experienced this carby backfire and hesitation before too on my 18rc, running stock carb tho. Its the same deal, when u plant the right foot at low rpm it mite hesitate for a sec or even splutter a little, then once above ~2500 engine opens up lot smoother. This only happens when its pretty cold, or not been run for a while, but nothing seems to work at its best until warmed up a little.
I too have gotten used to gradually letting my pedal get to the floor to counteract this, it may be frustrating but its effective. it also sounds good going from half pedal to full once the engine is up past the 3grand mark.
Just food for thought.. On average how many k's do guys think you get from say 10 litres of petty in your 18Rc's? running stock at the moment i get about 100k's/10 L, but way more if its freeway driving.
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Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sun, 08 December 2002 12:19
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Hi Guys,
Thanks for the reply's....
This is happening even when the car is warmed up... I definitely didn't have these hesitation problems when I had the old carby (when it was working properly). Either that or I couldn't really notice as the engine would bog down like that anyway when I drop the clutch  .
The engine and carb setup does definitely sing when I gradually accelerate and totally changes note when have full throttle at higher rpms.
I do see a very vair amount of fuel being squirted down the throat and I did just fully rebuild the carby so I know it it isn't a mechanical problem with the carb itself.
If it's something I have to live with... so be it... but it would be nice if I can just hammer down the accelerator whenever I want...
I found this regarding weber carbys and MGB's which seems liek the exact problem ...
........Found this info............
WEBER 32/36 DGV (all MGB's 1963-1980)
While a very reliable carb/manifold set up, a disadvantage with this carburetor is the fact that the primary venturi accounts for two thirds of the throttle open position (no CFM* figures are given for this position) with the secondary venturi becoming active in the final one third of throttle movement. This carburetor requires excessive initial ignition timing advance to avoid stumble on take off (if the ignition timing was retarded, we would have to open the primary throttle plate to obtain the necessary idle; this would expose the progression bleed holes which in turn would require that the idle mixture be leaned to compensate for this richer mixture condition. The end result being very little progressive richening upon further throttle opening, especially at snap throttle and so the stumble). Carburetor can be modified to allow the primary & secondary throttle plates to open simultaneously plus modifications to the progression circuit and accelerator pump. Unfortunately, the company that used to provide this service no longer offers this modification. Maybe a search on the web will turn up a company that can help you.
.........End...........
Maybe this can shed a light on what is happening???
I think it's exactly what is happening on my car.
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sun, 08 December 2002 15:02
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The old carb would have had a system that stopped the second butterfly from opening until there was enough vacuum (high rpm).
The hesitation happens when you open the second butterfly too early.
My 18R (not RC) stock carb had a vacuum system which was inactive for a long time (meaning no second throat). I chucked the vacuum system away and replaced it with a spring, so it now opens from about 70% throttle onwards. If i go past this before about 2500RPM the engine will struggle. The cool thing is i can feel the new spring on the pedal, so i know when im going to open it.
I get about 120KM/10L on the open road on ULP + valve lube.
Im running ULP98 all the time now, i havnt check mileage around the city yet.
Remeber this is a 4spd manual Corona... no 5th gear crusing for me 
Gotta love the 18R in my Corona (RT104). Top end is a little noisy (prolly timing chain), but it runs damn well for over 275,000 on the clock.
I love taking it out to 120Km/hr in 3rd... thats about 5500RPM.
Ill be needing a new project to keep me busy soon, so im gonna try building my own DIY ignition timing and fueling ECU along with inlet manifold, throttle body and injectors.
Will be interesting. With any luck i should be able to get it to run better than on the carb, and if things go well i should get quite a bit more power out of it as well.
[Updated on: Sun, 08 December 2002 15:10]
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Location:
adelaide
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sun, 08 December 2002 15:10
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that article says:
" ...This carburetor requires excessive initial ignition timing advance to avoid stumble on take off... "
What is your ignition timing set to? Did you mention it had been set recently, if so have you tried fiddling with the timing to see if it has any effect? a couple of weeks ago for no reason i clicked the timing over just 1 degree advance and took the car for a drive, and i seriously almost felt a difference in drivability.. cos the same problem was annoying me that day shitloads..
just a thought.
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sun, 08 December 2002 15:13
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| blackRA28 wrote on Mon, 09 December 2002 01:40 |
that article says:
" ...This carburetor requires excessive initial ignition timing advance to avoid stumble on take off... "
What is your ignition timing set to? Did you mention it had been set recently, if so have you tried fiddling with the timing to see if it has any effect? a couple of weeks ago for no reason i clicked the timing over just 1 degree advance and took the car for a drive, and i seriously almost felt a difference in drivability.. cos the same problem was annoying me that day shitloads..
just a thought.
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For this, rip apart your distributor, and move the limiting screw on the vaccum advance unit back a few mm. This will give that ign adv on take off.
It still wont help when you just floor it tho. Im thinking, its just somthing youll have to live with (as most poeple with high end carbs do).
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Location:
adelaide
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sun, 08 December 2002 15:46
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Yeh i thought somewhere on this board i read that all decent carbies are only tuneable to certain rev ranges, and that this is one of the great issues in the batle between carbies and EFI..
Carbies set up right on a good motor are truly awesome and i wont argue with that, but they are only tuned 100% perfectly for a certain part of the powerband, because thats what they are and they do the job. Would be wicked for a race car that stays between say..6 and 8500 RPM.
And with EFI the ecu adjusts the fuel/air mixture and timing according to the engine temp, the oxygen flow, throttle pos, and a whole heaps other stuff to give it the edge to get good driveability all across the rev range.. There may be a loss or flattening of poke or torque higher up(where the carbies would usually sing) but i dont think this is really noticeable in fairly standard engines, correct? Anyway, you sacrifice a little grunt for a much more consistent and smooth flow of power. And also you can turbo a whole heap easier(hehe).
maybe this is could be a very vague answer to the question..
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Location:
Mornington Peninsula
Registered:
September 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Mon, 09 December 2002 21:45
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I've got an 18RC with just the stock carb on it. Mine keeps doing the back fire thing through the carb. I can let it sit there for 5 minutes to warm up and then go to drive but it will backfire one after the other. I've had about 8 in a row. The timing is all correct and the dissy has been replaced but it just won't run properly. I've got huge burn marks under my bonet and worried something will go really wrong one day. Even when it's warm i'll be crusing along and it will back fire for no reason. It always bogs down. I only get about 250km to the 42 litre tank around town. This is really bad. I've done about 900km in her since Thursday night, majority long country drives and ran well, but I only got about 350km to a tank. I think all my petrol is burning up in the carbie through the back firing.
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Tue, 10 December 2002 05:44
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| ra23celicachick wrote on Tue, 10 December 2002 08:15 |
I've got an 18RC with just the stock carb on it. Mine keeps doing the back fire thing through the carb. I can let it sit there for 5 minutes to warm up and then go to drive but it will backfire one after the other. I've had about 8 in a row....
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Doesnt the answer seem kinda obvious?
Take it to a carb specialist to have it fixed.
Tuning carbs is thought by a lot of poeple to be an art, so taking it to someonw with experience is a must.
Or you could just buy a new carb for it.
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Registered:
May 2002
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Location:
Mornington Peninsula
Registered:
September 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Tue, 10 December 2002 21:37
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All the gasket's have been replaced, the carby has been rebuilt on it. It's only started since we put the new head on it since the last one cracked. I have been planning to book it into a mechanics for a while. I need time off work to take it there as everyone else refuses to drive her.
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sat, 31 July 2004 08:57
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Strange... I used to run a Weber 34/34 ADM on my 18R and now the carb is on my 21R.
Works fine with both.
No hesitation at all... can mash the pedal and away it goes.
The auto-choke is a dream too.
It did take a while to tune though, and is still running a bit rich.
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Location:
ballarat
Registered:
April 2003
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sat, 31 July 2004 12:54
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running a weber 32/36 dgv on my 18rc too
finding this exact same problem. but in a couple of days putting 2x dellortos on so havnt done anything permanaent about this hesitation problem. BUT
since i heal and toe all the time, the engine would hesitate, as you say, as i blip the throttle to downshift. i found that if my manual choke is ALWAYS about half on, the hesittation is not there, which lead me to belive that there was a problem with the accelerator pump on the carby, just never got to do anything about about it.
so i dont have a permanent solution, but i always thought it was running a bit lean under sudden go-pedal usage.
hope this give ya some ideas 
cheers
evan
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Location:
tallahassee FL usOFa
Registered:
May 2002
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Re: 18RC & Weber 32/36 hesitiation and Backfiring.
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Sat, 31 July 2004 22:22
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accel. pump jetting -inlet, outlet bypass & oneway valve-, and/or linkage, and ign. timing and/or mechanical and/or vacuum advance problem.
maybe the mechanical or vacuum operation of the secondary throttle.
sorry, i've got to to say this, but this carb was not rebuilt, it was taken apart and put back together, and even that is impossible to do correctly if you don't know what an accelerator pump is.
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. I definitely like the change in tune of the engine when the second throat opens up!!
Re: 18RC & Weber 32/36 hesitiation and Backfiring.
