I'm the lucky new owner of a Fulvia S3 74 model. I just have two issues. It "hesitates" during acceleration. It starts fine, when it's cold, but it stops after a second. Then I have to repeat the starting procedure 3-5 times before it's running. I have to pump the throttle each time. When it's cold I use full choke, and half choke in scandinavian summer temperature. I have adjusted the ignition, and the carbs, to the best of my ability, and the car runs fine, exept for the "hesitation" during acceleration.
The only visible strange thing I have observed is air bubbles in the inlet hose to the petrol pump. It's more than bubbles, it's 50/50 air and petrol. The return hose is old and not so transparent, but it looks like surplus petrol is pumped back into the tank. I don't have any petrol leakage, but I have not done a check of the tube or the joints. If it sucks air, I guess the leak must be above the tank level.
Is the symptom pointing at a worn out petrol pump, or is it normal that I should see air in the inlet hose? The pump is the origin mechanical pump.
Air in the petrol inlet tube
Re: Air in the petrol inlet tube
First, the hoses have to be changed to ethanol resistant hoses. If still original they are not even unleaded resistant.
Air bubbles may remain in the hoses. No problem. Air bubbles move from bottom to top. The routing may be such that flow is not always up.
2nd series Fulvia's have a return for the fuel. The carbs got more sensitive float needles from about 1969. So there is either a pressure regulator (on the series one) or a return with a calibrated hole (1mm) in the banjo (series 2).
If it hesitates during acceleration I would first check the jets of the acceleration pumps. Take off the cover of the air filter housing and the flame killer. Look into a barrel. Spot the acceleration jet. It is sticking out of the "ceiling" just before the butterfly valves. Flip the throttle and check if the jet squirts fuel. If not, take out the screw above the jet and use drill bit 0,4 mm to clean the jet. The flow rate of the pumps is important. The flow rate decreases over time due to wear.
I don't know where you are. We do have the tools to measure and adjust the acceleration pumps. If necessary we do also have the parts to restore the acceleration pumps.
Air bubbles may remain in the hoses. No problem. Air bubbles move from bottom to top. The routing may be such that flow is not always up.
2nd series Fulvia's have a return for the fuel. The carbs got more sensitive float needles from about 1969. So there is either a pressure regulator (on the series one) or a return with a calibrated hole (1mm) in the banjo (series 2).
If it hesitates during acceleration I would first check the jets of the acceleration pumps. Take off the cover of the air filter housing and the flame killer. Look into a barrel. Spot the acceleration jet. It is sticking out of the "ceiling" just before the butterfly valves. Flip the throttle and check if the jet squirts fuel. If not, take out the screw above the jet and use drill bit 0,4 mm to clean the jet. The flow rate of the pumps is important. The flow rate decreases over time due to wear.
I don't know where you are. We do have the tools to measure and adjust the acceleration pumps. If necessary we do also have the parts to restore the acceleration pumps.
Re: Air in the petrol inlet tube
Thank's for your quick reply. I'm located in Sweden, 50 km south of Gothenburg.
All the fuel hoses are new, except for the return hose. I will replace it.
All four jets squirts fuel, but it's hard to say if it's sufficient. I will try to find a 0,4 mm drill bit, and check.
All the fuel hoses are new, except for the return hose. I will replace it.
All four jets squirts fuel, but it's hard to say if it's sufficient. I will try to find a 0,4 mm drill bit, and check.
Re: Air in the petrol inlet tube
If all 4 acceleration jets squirt fuel, it is ok for now.
Next step, the spark plugs. Can you put NGK plugs type BPR7ES and make sure the gap is set to 0,6mm? The Fulvia engine is sensitive to the gap. Or, if your engine is healthy put the expensive iridium NGK BPR7EIX. Don't touch the electrodes. The gap set by the factory is ok. If you prefer another make of spark plugs you can put those again when the problem is solved.
Try to start without choke. The surfaces of the choke mechanism wear quickly resulting in so much false air that you cannot set the idle under 1000 rpm. Instead pump the throttle. Small strokes as the accelerations pumps only work during the first part of the throttle opening.
It is normal to use the right foot to keep the engine from stalling during the first few dozens of seconds. After half a minute or a full minute or so (I never timed it) the engine suddenly spins better. Some might say that if you start by pumping the throttle, the spindle, zamac and butterflies may wear instead of the choke. That is mostly true for 1st series carbs. Series 2 carbs are better.
Next step, the spark plugs. Can you put NGK plugs type BPR7ES and make sure the gap is set to 0,6mm? The Fulvia engine is sensitive to the gap. Or, if your engine is healthy put the expensive iridium NGK BPR7EIX. Don't touch the electrodes. The gap set by the factory is ok. If you prefer another make of spark plugs you can put those again when the problem is solved.
Try to start without choke. The surfaces of the choke mechanism wear quickly resulting in so much false air that you cannot set the idle under 1000 rpm. Instead pump the throttle. Small strokes as the accelerations pumps only work during the first part of the throttle opening.
It is normal to use the right foot to keep the engine from stalling during the first few dozens of seconds. After half a minute or a full minute or so (I never timed it) the engine suddenly spins better. Some might say that if you start by pumping the throttle, the spindle, zamac and butterflies may wear instead of the choke. That is mostly true for 1st series carbs. Series 2 carbs are better.
Re: Air in the petrol inlet tube
I have the NGK BP7E S, without the resistor. The plugs are new, and I reduced the gap to 0,6 mm, as I read in one of your earlier posts.
I have also tried a cold start, without choke, and it works fine. The choke is functioning, but if you have time to let the engine get warm before you drive, you don't need to choke it. (My opinion.)
I have calibrated the idle mixture screws, and the balance screw once again today. The engine runs very smooth on idle speed, almost no vibration, and quick throttle response.
The contact breaker points are adjusted with a gauge, and the ignition timing point with a stroboscope lamp. The timing point is set to be in the middle of the red marked field on the flywheel. I have tested, earlier and later ignition points, but ended up in the middle of the red marked field. I run it on 95 octane, and there is no "ignition knock". The ignition advance function on the distributor looks to be working well. The springs look fresh and OK, and the surface is well lubricated, and I don't suspect any friction.
I have checked the various invoices from previous ownership. There is an invoice for a carburetor gasket set, from 2023. So, i guess something was fixed at that time. I just hope the float levels are not messed with.
I have also tried a cold start, without choke, and it works fine. The choke is functioning, but if you have time to let the engine get warm before you drive, you don't need to choke it. (My opinion.)
I have calibrated the idle mixture screws, and the balance screw once again today. The engine runs very smooth on idle speed, almost no vibration, and quick throttle response.
The contact breaker points are adjusted with a gauge, and the ignition timing point with a stroboscope lamp. The timing point is set to be in the middle of the red marked field on the flywheel. I have tested, earlier and later ignition points, but ended up in the middle of the red marked field. I run it on 95 octane, and there is no "ignition knock". The ignition advance function on the distributor looks to be working well. The springs look fresh and OK, and the surface is well lubricated, and I don't suspect any friction.
I have checked the various invoices from previous ownership. There is an invoice for a carburetor gasket set, from 2023. So, i guess something was fixed at that time. I just hope the float levels are not messed with.
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lancia7550
- Posts: 77
- Joined: 10 Nov 2012, 22:26
Re: Air in the petrol inlet tube
Check for air leaks as well. It is not that easy to identify but spraying some carb cleaner around the cab mount and brake vacuum connection might show a leak if the idle changes. I had a slight hessitation between light throttle and then accelerating which dissapeared after I remounted the carbs using a little gasket sealer on the paper gaskets.