Engine hesitation- Mechanical fuel pump issue? 1500 engine
- Thread starter eng622
- Start date
No luck with the new condenser (although sent the wrong one but all the nearly the same electrically). Looked at the rotor arm looks almost new and distributor cap looks fine. Fitted another coil (one of another car I know works), hot wired to battery still no joy. Took each spark plug out in turn and grounded, cranked over and getting a spark on all four (not under load I know).
For a short time the engine would idle at around 900 rpm but most of the time dies and on occasion difficult to run under 2000 rpm.
Next I inserted a colour tune into cylinder NO1. Results interesting. Because the engine would not idle a put a brick on the accelerator pedal. Started and engine ran at 2000 rpm. The colour tune was orange so running very rich then after a short time turned blue with orange hints, correct mixture. Then I let the revs drop to see if it would idle and it did , colour now blue/colourless with just the odd orange flash, correct again for idle mixture. Even the exhaust had an almost an even beat but suddenly it started to misfire again.
Not put the colour tune in place of other plugs, big job as needed a mirror to see results, as in no1.
I'm now thinking there is a fuel and not electrical problem.
It has a Weber carb with manual choke. The choke appears not to work as need to pump the throttle to start from cold. When you pull out the control knob the choke butterfly does not rotate but stays in vertical position.
So thinking to much fuel/not enough air but the problem seems to be intermittent.
It is odd when I purchased the car the plugs were all very pale indicating a lean mixture and after no more than 200 miles the plugs are now black with soot plus there is the misfire.
Further help needed
For a short time the engine would idle at around 900 rpm but most of the time dies and on occasion difficult to run under 2000 rpm.
Next I inserted a colour tune into cylinder NO1. Results interesting. Because the engine would not idle a put a brick on the accelerator pedal. Started and engine ran at 2000 rpm. The colour tune was orange so running very rich then after a short time turned blue with orange hints, correct mixture. Then I let the revs drop to see if it would idle and it did , colour now blue/colourless with just the odd orange flash, correct again for idle mixture. Even the exhaust had an almost an even beat but suddenly it started to misfire again.
Not put the colour tune in place of other plugs, big job as needed a mirror to see results, as in no1.
I'm now thinking there is a fuel and not electrical problem.
It has a Weber carb with manual choke. The choke appears not to work as need to pump the throttle to start from cold. When you pull out the control knob the choke butterfly does not rotate but stays in vertical position.
So thinking to much fuel/not enough air but the problem seems to be intermittent.
It is odd when I purchased the car the plugs were all very pale indicating a lean mixture and after no more than 200 miles the plugs are now black with soot plus there is the misfire.
Further help needed
Ics19
belle macchine!
As mentioned previously, have you checked the carb bowl float height and the inlet valve needle for grooves? Both these could be allowing excess fuel in and causing flooding.
You've not mentioned checking the ignition timing at all - might be worth doing with a timing light the next time it feels like idling, if only to verify it's not widely out or jumping around for reason unknown...
Ics19
belle macchine!
There's a section on float level in the workshop manual here:
https://xwebforums.com/wiki/images/f/fd/WrokshopManual_25.pdf
I've used a 7mm drill bit to measure the gap in the past.
As mentioned, check the needle valve point to see if it has a worn groove where it seats - if it has, it's not going to seal and continually let fuel past.
ignition (distributor) timing is a mechanical thing and shouldn't change once set so always worth doing early on. First though, use a dwell meter to set the point gaps as it then caters for wear, 55 degrees +-3, - when correct, check the timing with a light (7 BTDC seems good on mine, the spec is 5 BTDC iirc)
https://xwebforums.com/wiki/images/f/fd/WrokshopManual_25.pdf
I've used a 7mm drill bit to measure the gap in the past.
As mentioned, check the needle valve point to see if it has a worn groove where it seats - if it has, it's not going to seal and continually let fuel past.
ignition (distributor) timing is a mechanical thing and shouldn't change once set so always worth doing early on. First though, use a dwell meter to set the point gaps as it then caters for wear, 55 degrees +-3, - when correct, check the timing with a light (7 BTDC seems good on mine, the spec is 5 BTDC iirc)
Thanks for carb info/pics. Have checked the float dimensions and valve for seating/leaking and all ok. Checked float for leaks and ok. Blew out the jets and other passages again. Started engine and ran in drive, once warmed up big surprise no misfire and it would idle. Exhaust smoke minimal and normal colour. The colour tune tells me the mixture is weaker than before, idle a little erratic at 850 so turned the idle speed screw inwards a fraction and set to around 950 which was about that when purchased. So do not know what the problem was but clearly over fueling. So now it appears to be running lean again as purchased. So was going to reset the idle mixture. Now the problem as cannot find the screw. All the holes around where the pic shows the screw are blanked off. And my carb has a big boss with electrical connections where the pic shows the idle mixture screw.
Is the pic a 34DATR. I ask as assumed mine is a EU spec car with that carb but cannot find any number on it to verify.
Is the pic a 34DATR. I ask as assumed mine is a EU spec car with that carb but cannot find any number on it to verify.
NEG
True Classic
Mixture screw is on the very bottom right corner of the carb facing the right hand side of the car auto choke side. You now need to check for an induction leak. Spray carb cleaner at the base of the carb if the idle picks up noticeably you have a leak. The carb bases warp when tightened down too much and you have to flatten them out to get a good seal.
Ics19
belle macchine!
Yeah, the workshop manual is not showing your carb type. Yours will likely be a 34 DATR 7/250 - there's pictures here (turn on that French translation in your browser!):
https://x19forum.1fr1.net/t1873-donnees-de-reglage-de-carburateur-weber-34datr7-250
As NEG says, it's rear bottom right as pictured here and the (1500 / 34DATR) screw should be a pointed and not chewed (the one in the picture does look like it has a ridge TBH which may upset the flow/adjustment) and there's also meant to be an o-ring seal in the groove at the outer end of the screw (obscured by thumbs in this picture)..
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Thanks for pics/link. Now getting to grips with this carb, or maybe.
Mixture screw being at the bottom must be a volume/fuel one so need to screw out (ACW) to richen. Turned the screw 1/2 a turn ACW and the idle increased 100/150 rpm indicating the original setting was too lean. Problem however as it would not turn out much more, did not want to force it so left it at half . The engine would idle and was not erratic, just set the the idle to 950 rpm.
Now for the road test. First 3 miles to petrol pump fine no hesitation or black smoke. Put 6 gall in drove half a mile and at the first junction would not idle. Did not give up carried on and at around 25 miles a couple of misfires (almost same spot when I first had the problem), carried on but it was clear at junctions it would not idle. Then after 50 miles the throttle response improved and it would idle. This lasted for around 10 miles before more misfiring which gradually got worse. Got home after 90 miles engine stalled as expected and would no restart. The inline fuel filter was empty. After a few minutes rest the engine started and would idle but at 850 rpm and a bit erratic.
Let the engine cool and removed plug no 1. Ground tip pale straw but nose cone/insulator white still suggesting a lean mixture.
It was a very hot day and the engine temp did run for most of the time lower than previous (leaner higher temp so guess not so lean after adjusting the idle mixture).
So not finding the original problem ( the recent black smoke issue did not occur) so thinking it is a fuel problem and lack of it. Wondering if fuel filling , which I did slowly, is disturbing the tank contents. The inline filter looks clean but as said empty after the run when it would not start. The tank to pump to carb hoses look new and on cranking the pump squirts fuel a with ease.
All the carb jets are the sizes in the data.
Mixture screw being at the bottom must be a volume/fuel one so need to screw out (ACW) to richen. Turned the screw 1/2 a turn ACW and the idle increased 100/150 rpm indicating the original setting was too lean. Problem however as it would not turn out much more, did not want to force it so left it at half . The engine would idle and was not erratic, just set the the idle to 950 rpm.
Now for the road test. First 3 miles to petrol pump fine no hesitation or black smoke. Put 6 gall in drove half a mile and at the first junction would not idle. Did not give up carried on and at around 25 miles a couple of misfires (almost same spot when I first had the problem), carried on but it was clear at junctions it would not idle. Then after 50 miles the throttle response improved and it would idle. This lasted for around 10 miles before more misfiring which gradually got worse. Got home after 90 miles engine stalled as expected and would no restart. The inline fuel filter was empty. After a few minutes rest the engine started and would idle but at 850 rpm and a bit erratic.
Let the engine cool and removed plug no 1. Ground tip pale straw but nose cone/insulator white still suggesting a lean mixture.
It was a very hot day and the engine temp did run for most of the time lower than previous (leaner higher temp so guess not so lean after adjusting the idle mixture).
So not finding the original problem ( the recent black smoke issue did not occur) so thinking it is a fuel problem and lack of it. Wondering if fuel filling , which I did slowly, is disturbing the tank contents. The inline filter looks clean but as said empty after the run when it would not start. The tank to pump to carb hoses look new and on cranking the pump squirts fuel a with ease.
All the carb jets are the sizes in the data.
Float settings. Mine held vertically float parallel to body is 7 mm . The manual here, which is not for a 34DATR, gives 6 and 9 for drop giving travel of only 3. This does not look right on the diagram. Haynes gives 6 and 15 giving travel of 9 which looks more correct. Found a reference of 7 for mine but drop not stated. If the drop/travel is wrong could this cause running lean.
Anyone know the correct settings are.
Anyone know the correct settings are.
NEG
True Classic
I set 7 / 15mm on my carb. If the drop is too great the float can get stuck, got the T-shirt on that one 
Is the float needle valve ok? Can’t recall if you checked all the jets are clear, no blockages and did you blow through all the galleries in the carb with a tin of compressed air?
Is the float needle valve ok? Can’t recall if you checked all the jets are clear, no blockages and did you blow through all the galleries in the carb with a tin of compressed air?Update, the float drop was huge, tab had never been bent (suspect new float installed at some point). Now drop set to 15 mm. Idle mixture screw will now unscrew more and set to max rpm about 1 turn out from original setting. Car started fine and the smoothest idle and even exhaust beat so far. Now the road test. Drove fine with even idle when needing to stop. Went 30 miles and then the usual hesitation came back, that's the longest trouble free run so far beating 23 miles. So had to limp home 30 miles, really bad hesitation (no popping in exhaust) would not run at all below 2000 rpm. Got home took no 1 plug out and normal colour, maybe a little weak. Still will not idle and you can hear the misfire at any constant rpm up to 2000.
So where to go from here. Is it a fuel or electrical issue, thinking it is still fuel maybe petrol pump or fuel contamination in the tank but need to be sure as replacing the pump looks to be a nightmare with respect to access.
So where to go from here. Is it a fuel or electrical issue, thinking it is still fuel maybe petrol pump or fuel contamination in the tank but need to be sure as replacing the pump looks to be a nightmare with respect to access.
Stared this morning but still wont idle. So took carb top off and pleased to see fuel in the bowls (having set the float drop). Took the idle jets out and blew out with compressed air. Put all back started and now a smooth idle. No road test this time as seeking opinions on what is happening. If the idle jets are the problem why are they getting clogged up. There is an inline fuel filter (new) and one at the carb inlet (clean but blown out) so the clogging appears to be from something already in the carb.
Any suggestions?
Any suggestions?
kmead
Old enough to know better
Have you ever tanked the carb, blown cleaner through every orifice and galley to really clean it?
How old are your gas lines and are the compatible with ethanol fuels?
Never just blow out a fuel filter, it will induce holes or tear the media off of what it is attached to. A new filter is not expensive.