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Author Topic: Spluttering under acceleration on Carb Saloon  (Read 3759 times)
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« on: January 25, 2009, 09:36:35 PM »

The old saloon is almost ready to visit the man from the ministry, other from a dodgy headlight she could go tomorrow.
She runs ok but when you accelerate there seems to be a splutter or hesitation but the will power on through this when more gas is added, or seems to.
I changed the cam belt, also rebuilt the carb so maybe have i not dne something correctly.
Could i be a notch out on the belt?
Could i have swapped the jets when i rebuilt the carb?

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« Reply #1 on: January 25, 2009, 11:20:37 PM »

Mark, Take the air cleaner cover off and have a look to see if the accelerator jet (its on the primary - left - side looking from the drivers side) is squirting a nice clean "healthy" jet of fuel down the barrel.

Do this with the engine hot -  so you don't have to wedge the choke flap open.
Just open the throttle with your right hand and have a good look - you should see the jet as described above.

Flat spots as you describe - where the engine eventually pulls through -  are usually caused by this "injector" either being fully or partially blocked or the "o" ring that seals it to the carb body allowing fuel to leak out - not giving the engine the full measure it requires to richen up when the throttle is snapped open.
Sometimes the pump diaphragm perishes but you have changed it i assume when you rebuilt the carb with a kit.

If the jet is blocked, poke it out with a wire bristle from a wire brush - so long as its fine enough.
Probably have to remove the top of the carb to do so and carefully "pluck" the jet out with a pair of pliers

If the above checks out - hope it does not! - make sure the float level is correct (Haynes manual covers this)

Timing belt being a notch out usually results in a lack of power, not a flat spot - the same with the jets being fitted the wrong way round.

As a rule of thumb - the smaller main jet (119 factory) F30 tube and 240 air corrector goes on the primary, furthest away from you looking from the drivers/belt side.
The larger main jet (150) F30 tube and 240 air corrector goes on the secondary, closest to you.

The tick over jets follow the same rule - smallest, "50" furthest , Larger "80" closest.     

Get the tick over jet wrong and it wont idle properly, get the mains wrong and again you have a lack of power as mentioned above.
Remember that if the jets are a different size from what i mention, chances are they have been replaced with larger ones by somebody previously - it does happen!

Check the belt if it makes you feel better and check the distributor timing with a timing light - 10 degrees before TDC with the vacuum pipe removed and blocked (If early Bosch that is) idling around 900 rpm.

Personally i would put my money on the accelerator jet.

Hope you find the problem.
Lancia Beta 2000
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« Reply #2 on: June 06, 2010, 02:31:03 PM »

Any news Mark?
I've a similar problem of stumbling with my DATRA 34 carb'd 2000 beta coupe..
The carburettor is renewed with new gaskets, 'oring, accelerator pump diaphragm, choke etc...
But sometimes, under heavy acceleration, the engine stumbling..
I've seen the nice and clean fuel squirting of the accelerator pump, so I can't understand where the problem is..

The contact breaker and ignition is ok..
Maybe spark plugs??
 Roll Eyes
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« Reply #3 on: June 09, 2010, 09:15:24 AM »

Don't know if this helps.  Had the opposite problem, stumbling under light acceleration.  Rebuilt Carb, new fuel filter, petrol pipes etc.  I actually changed the Timing (CAM) Belt, and found to be 1 tooth out on each cam.  When corrected cured the supposed Carb problem??  cheers Joe
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« Reply #4 on: June 10, 2010, 04:18:05 PM »

Hi joe,
my beta does this stumbling under light acceleration too...maybe more with light acceleration than harder..
Timing belt is ok with the marks at their place..
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« Reply #5 on: June 10, 2010, 05:26:37 PM »

Had this many years ago on Fiat 132 which I think is similar set-up. Turned out to be the mechanical fuel pump on the way out. It started as light stumbling, then would loose power under hard acceleration and eventually would only allow the car to idle. Aso, check and see if any of the exposed steel fuel lines under the car have been damaged and partially closed off by a stone or piece of road debris.

Rust never sleeps
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« Reply #6 on: July 15, 2010, 02:48:26 PM »

Be sure to change one thing at a time otherwise you won't know what the cause was.
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