Engine hesitation- Mechanical fuel pump issue? 1500 engine

eng622

Daily Driver
First decent drive since buying. First thing I noticed the temp gauge go well above 90 C after about 10 miles (warm day here 21C). Continued and then lost power a sort of hesitation that started to get worse. Switching off and leaving a few minutes and then starting would run ok for a few miles until repeat of problem. Got it home took two plugs out and electrodes very white suggesting lean mixture and which maybe caused the overheating. No coolant loss. Took air cleaner off to look into carb and did not see a quirt of petrol when moving the throttle cable suggesting lack of fuel. It has the sealed non cleanable mechanical pump but the hoses have been renewed. Despite new the hose from the pump to carb has a kink where it tries to turn 90 deg so thinking causing fuel blockage. There is no in line filter but have one to fit. Any suggestions on problem?
 
Some suggestions, in no particular order but this is what I would be looking at doing: Fit an in-line fuel filter, Eurosport uk sell them. Change the fuel line so it doesn’t kink, longer maybe. Flush the cooling system if you’ve not done this already, drop the rad flush it and the pipes and the engine block. refill with 50/50 antifreeze and water. Bleed properly. Check the jets, air correctors etc have been replaced in the correct order. If no fuel is being squirted in when pumping the throttle you will need to check the accelerator pump diaphragm and also the feed to it from the float bowel, this will mean removing the top of the carb and cleaning out all the galleries and the feed to the accelerator pump. You can check the pump by removing the plugs and fuel feed hose from the pump to carb and spinning the engine over collecting the fuel in a container, get somebody to turn the engine while you check the flow, it will probably be ok, if it’s a dribble then…..

Whilst you have the top of the carb off check the float height and inlet valve operation.

Check ignition timing!
 
I had two different mechanical fuel pumps that eventually could not pump enough fuel because the return spring had rusted to a point where the stroke was too short. The key symptom was that you could only go so fast before the engine started to sputter. Going slow, it operated normally.
 
I had two different mechanical fuel pumps that eventually could not pump enough fuel because the return spring had rusted to a point where the stroke was too short. The key symptom was that you could only go so fast before the engine started to sputter. Going slow, it operated normally.
Did either one make a ticking sound which sped up as you accelerated before they went bad?
 
I did disconnect the fuel hose from the carb to relieve the kink and turned the engine over. Nothing to start with then fuel spurted out in pulses as you would expect. Will change the hose for a longer one to route without kinking and re test. Thinking the new hoses (fitted in the previous ownership) maybe of poor quality like so many rubber based components,
 
Update. Made a spiral round the pipe with copper wire and it relieved the kink (like some brake hoses have). Now a further road test. All went better to start with (around 30 miles) temp reading still high above 90 but lower than last drive (another hot day). Then suddenly started to hesitate and the temp rose quickly to bottom of red sector so coasted to stop noting that the engine would still idle. Have fitted an inline fuel filter just before the carb inlet. The filter was full of fuel on stopping then after a minute or so bubbles appeared in the fuel, looked to be from the inlet and the filter gradually emptied itself assume into the carb. So thinking still a fuel blockage. Is there a carb filter, mine has the Weber I think. After cooling down drove off with no problem and no hesitation but after some miles it was clear that the engine would not idle but ironic that the temp stayed around 90 for 30 miles (longest so far). Got home would not idle just stalled, left a few minutes started again and idle fine. This all seems like a lack of fuel problem/blockage. Any clues?
Putting some more posts as now have other issues.
 
Did either one make a ticking sound which sped up as you accelerated before they went bad?
No unusual sounds. Everything appears normal until you require more gas than the pump can provide. The original pump started acting up at about 30K. I went on the freeway and could not get over 50 mph. The replacement did the same thing at about 60K. The return springs on both had rusted to a fraction of their original length. A stainless steel spring would have been a better solution.
 
Thinking the new hoses (fitted in the previous ownership) maybe of poor quality like so many rubber based components,
You definitely need decent brand hose these days - the additives and increasing E ratings just eat away internally. Beware that unbranded "R9" hose on your favourite auction site and fit proper low permeable stuff. Any debris from the hoses will do the carb no good.

Sounds like you've got (at least) two issues, cooling and fuel. As mentioned above, flush the cooling and more importantly make sure all the air is bled out. If the radiator is 10 years old or more than consider getting it re-cored in my book, it'll make a world of difference to always running at over 90 and running at 75 even on hot days. The random temperature rise could be a stuck shut thermostat - is the radiator fan coming on when it hits the red? If not then it would imply there's no flow through to the rad (or the fan/fan sensor switch is faulty!).

On the fuel front, also check the needle valve (in the brass holder at the fuel line inlet) isn't grooved or jammed as that can cause flooding - there's also a fine filter in the holder too - perhaps get a genuine weber carb overhaul kit and replace the needle/inlet filter/float/mixture screw/accelerator pump diaphragm etc. Buy a couple of cans of injection cleaner and go through all the passages 'til there's none left :)
 
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Can you remove the brass plug on the inlet with the carb still on. As its on the underside (looks to be 19 mm AF) finding ring spanner too thick and socket too long.
 
You can remove the top of the carb while leaving the body still attached to the manifold.
 
Problem getting worse. Blew out the carb fuel filter (was clean anyway) and the 4 jets once removed. Engine started ok, went to put fuel in and then would not idle. Anyway continued to do around 30 miles and ran fine, until decided to stumble as on previous test runs. Would restart but difficult to rev up just kept misfiring so had to limp home (35 miles). Now and then the stumble cleared just for a few seconds but after about half way back a misfire (loud pop) developed in the exhaust, around 8 in 15 miles. It would not idle at all and had to keep revs up at junctions/lights to prevent stalling. At times there was almost no power. On arrival home took out spark plug no 1 and it was very sooty (dry no oil). When I first reported the problem the plugs were very white suggesting under fueling. Still hot it will start, blipping the throttle it misfires and releasing it it just stalls. Pops in the exhaust are usually a sign of unburnt fuel. Now on this 70 mile run reckon it used over 4 galls suggesting this, whereas previous more like 30/35 mpg.
So thinking the problem is now electrical. Plugs new but nothing else checked, any ideas?
 
I had a '77 that had much the same symptoms when I first bought it. The PO fought the problem for a long time, and I'm sure was a major factor in letting the car go. It took me a day to find it, but it turned out to be a faulty ignition switch. It would momentarily loose contact. On that car you had to keep the revs up around 4,000 or it would stall. Sometimes it was hard to start, and other times it would start and idle normally. What gave it away was when it stalled or was hard to start the dash indicator lamps went dark. If it stalls, at the very least your alternator lamp should still be on. Replaced the switch and never had another issue. Don't know if this is where you're problem might be, but it might be worth a shot to check.
 
Maybe a case of eliminating all the obvious things, have you checked the carb fuel float height, is it sticking, does the inlet valve seal correctly?
 
Update. Started from cold, difficult to rev, can hear misfire in exhaust. Stinks of unburnt fuel but no smell of fuel. Had all the plugs out, all just sooty which wiped off. Dist. is Marelli points gap correct at 15 thou, all HT leads resistance checked out ok, rotor arm looks good. Checked coil P & S resistance readings look normal. Put all back and put an inline spark tester in plug 1 lead. Ran with less hesitation but still misfire in exhaust, spark tester flashing ok. But then at around 2000 rpm the engine suddenly died and would not restart. On cranking the tester did not flash indicating no spark. Tried a different coil and would start but still running rough. Then put back the original coil and would run. This tells me it is not likely to be the coil. I can only think it is the condenser which is supposed to be around 0.22mF but I checked and got a massive reading of 9mF.
Any suggestions, thinking it is a failing condenser, cannot see it is a fuel issue but did have the top off the carb to check the filter, the float looked fine.
 
Update. Started from cold, difficult to rev, can hear misfire in exhaust. Stinks of unburnt fuel but no smell of fuel. Had all the plugs out, all just sooty which wiped off. Dist. is Marelli points gap correct at 15 thou, all HT leads resistance checked out ok, rotor arm looks good. Checked coil P & S resistance readings look normal. Put all back and put an inline spark tester in plug 1 lead. Ran with less hesitation but still misfire in exhaust, spark tester flashing ok. But then at around 2000 rpm the engine suddenly died and would not restart. On cranking the tester did not flash indicating no spark. Tried a different coil and would start but still running rough. Then put back the original coil and would run. This tells me it is not likely to be the coil. I can only think it is the condenser which is supposed to be around 0.22mF but I checked and got a massive reading of 9mF.
Any suggestions, thinking it is a failing condenser, cannot see it is a fuel issue but did have the top off the carb to check the filter, the float looked fine.
The 9uF reading sounds bogus and could be caused by leakage affecting the reading. If the condenser is bad, the waveform on the coil primary will not be as designed which means the high voltage on the secondary won't be as intended.
 
Put all back and put an inline spark tester in plug 1 lead. Ran with less hesitation but still misfire in exhaust, spark tester flashing ok. But then at around 2000 rpm the engine suddenly died and would not restart. On cranking the tester did not flash indicating no spark.
Missed this on the 1st go around. The lack of spark at #1 is just that; no spark at #1. To verify an actual no spark condition the tester needs to go on the coil lead at the cap. You may very well have spark, but it's not getting where it needs to go. You indicated you checked the rotor. Did you check the length of the brass contact against a new rotor? Rotors can look fine, but are actually quite worn. How about the length and spring tension on the center contact of the cap, as well as the brass lugs? If the condenser doesn't solve the problem, this is where you might want to go next. Hopefully you'll get this sorted soon.
 
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