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Poor Performance

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Bobbee44

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This weekend, I experienced a recurrent problem, this time in spades. The car, after being warmed up does well in first gear, but after shifting into scond, I get the stumble and backfire through the carbs and then all seems smooth. The smooth running gets rough when the car hits 180 degrees, and it sounds like I am running on three to four cylinders. When I press the excellerator hard, I do not get any appreciable increase in engine speed, but a lot of noise and popping. My first inclination is a carb issue; however the rule of thumb is check everything else before touching the carbs. I do not thik timing is the issue, since the car starts well and runs cool. Any ideas?

Thanks,

Bob
 

EV2239

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I can't be sure from a few thousand miles and not hearing it, but with everything replaced mine did that and in desperation I put it on a rolling road and found it was running weak with current fuel.

I repeat everything in it was set to the book with rebuilt carbs, distributor, plugs, leads, caps everything.

Modern fuel seems to run weak in old cars, so bear this in mind if all else fails

Ash
 

TimK

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Coil?
 

stretchit2

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What do your plugs look like?
 

pkmh

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Sounds similar to what happened to me and two thoughts come to my mind as possible causes.

1. Check the center underside of your distributor cap (that center black carbon spring coil) for positive and continuous contact with the rotor. That caused my coil wire to burn, resulting in poor acceleration and popping, and not always from a cold start. I would try replacing the coil wiring (or clip the ends and inspect for burning and pull out the spring coil enough (being careful not to disengage completely though it can be reinserted) to provide a more positive contact with the rotor.

2. Another possible cause, maybe some of your male/female connections have severed enough, but may not be visible from view. If possible, let your engine idle and then gently play with your electrical connections, especially at the ignition coil, to see if noticing a difference in idle. Generally, I feel this would result in engine either running or not, but stranger things can happen.
 

Jeepster

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I recently cured an issue where my car was running rough and wouldn't drive over 2000 revs.
I changed ALL of the ignition but no improvement so started to look at the carbs.

Turned out it was the jet/diaphram that had stuck and perished in one of the carbs.
 

BoyRacer

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Check the condenser. An easy way to check is to clip on a second condenser to the ground side of the coil.
 

RAC68

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Hi All,

This condition seems to be getting common.

A few weeks ago I reported my Healey, that has usually revved freely to my common 5K rpm shifting, started to have difficulty moving to 4K rpms. It also started to backfire through the carbs when not quite hot and plugs 2 & 3 began to burned black. Finding the timing (Crane CD ignition and 40K coil) on the money at 15 BTDC, with smooth mechanical and vacuum advance movement, I addressed the carburetors and found a non-consequential amount of sediment in the bowls. After resetting the carburetors and adding 93 octane from another station, the car seemed to run better but not as before.

A few days ago, the idle seemed unstable after a drive and decided to reset the mix. Pulling the plugs again, plugs 2 & 3 again were much darker then the others. Pulling the pistons to establish a starting point by having both seats at bridge level, I pushed both choke (separately) to assure both seats moved freely. Although the rear carb seat dropped, the front seat did not move and I used a plastic punch required excessive force but the seat moved.

Since Jeepster and others seem to be experiencing similar surprise (seemingly non-developing) conditions, I am beginning to wonder if their is a common cause in play. We are experiencing this condition over geographic areas but can not rule out a common fuel additive that is reacting with the spring, diaphragm, or seat and causing higher resistances in seat movement or even causing them to frozen in place. I appreciate that it is just a suspicion with little to base it up but I thought I would extend the suspission.

Ray (64BJ8P1)
 

EV2239

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Hi All,

This condition seems to be getting common.

A few weeks ago I reported my Healey, that has usually revved freely to my common 5K rpm shifting, started to have difficulty moving to 4K rpms. It also started to backfire through the carbs when not quite hot and plugs 2 & 3 began to burned black. Finding the timing (Crane CD ignition and 40K coil) on the money at 15 BTDC, with smooth mechanical and vacuum advance movement, I addressed the carburetors and found a non-consequential amount of sediment in the bowls. After resetting the carburetors and adding 93 octane from another station, the car seemed to run better but not as before.

A few days ago, the idle seemed unstable after a drive and decided to reset the mix. Pulling the plugs again, plugs 2 & 3 again were much darker then the others. Pulling the pistons to establish a starting point by having both seats at bridge level, I pushed both choke (separately) to assure both seats moved freely. Although the rear carb seat dropped, the front seat did not move and I used a plastic punch required excessive force but the seat moved.

Since Jeepster and others seem to be experiencing similar surprise (seemingly non-developing) conditions, I am beginning to wonder if their is a common cause in play. We are experiencing this condition over geographic areas but can not rule out a common fuel additive that is reacting with the spring, diaphragm, or seat and causing higher resistances in seat movement or even causing them to frozen in place. I appreciate that it is just a suspicion with little to base it up but I thought I would extend the suspission.

Ray (64BJ8P1)


i think it is common because both my Bentley and the Healey had the same symptoms and others are reporting them on other forums. I'm pretty sure it's modern fuel and that it burns weak in old engines. Therefore I keep suggesting that the cars affected go on a rolling road, which will save a considerable amount of time and possible engine damage. Whatever is wrong is quickly diagnosed on one and my money is on a weak mixture even though the carbs will have the correct orginal needles. They need a fuel/air ratio at the top end of the scale to run right and make power.
 

RA_Healey

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You may want to look at the intake/exhaust manifold gasket. There may be an air leak on one of the intake ports and it needs replacing. Just a thought.
 
OP
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Bobbee44

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Thanks to all for excellent input. I did check the center probe in the distributor cap and the carbon was completely worn so that an arc was required to close the connection between the coil and the rotor. In fact the top of the rotor was blackened from the arc, and the center of the cap was visibly burned. I replaced the distributor cap, but my problem persists. I will change the points and condenser this weekend. Hopefully this will end my saga.

Bob
 

EV2239

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As I said I had it with my Healey and my Bentley and others are reporting similar. I really thing a rolling road is the quick way to sort it because both my cars were set to the book with everything new.

One theory is that old fashioned combustion chambers don't burn modern fuel very well and run weak as a result, because richer needles seem to be the answer.
 
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Something else to consider, and will certainly cause the same symptoms; any chance that you've recently serviced the distributor, with a few too many drops of oil down the spindle? An oil mist/film whirling about, and contaminating the contact point surfaces will allow you to acheive lowish RPMs, but won't tolerate anything much over 2-3k, or when under a load.
 

pkmh

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Thanks to all for excellent input. I did check the center probe in the distributor cap and the carbon was completely worn so that an arc was required to close the connection between the coil and the rotor. In fact the top of the rotor was blackened from the arc, and the center of the cap was visibly burned. I replaced the distributor cap, but my problem persists. I will change the points and condenser this weekend. Hopefully this will end my saga.

Bob
Hi, I don't know if you also checked your plug wires at the distributor, but they too might have become damaged as well and because of what happened to your distributor. I would investigate the condition of those wires by clipping a small piece and cut open to reveal and see if powdery, signifying they too, became burnt. Let us know and thanks!

Paul
 

Brinkerhoff

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This is why I think you need to carry a known good coil. Cover enough miles and you'll need one eventually and no , you won't be able to find one when you need one. Sub it out in 5 minutes then you know for sure.
 

Bob Hughes

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To get my fuel/air ratio somewhat right I am using a couple of colour tunes.

Give your dizzy a check over, I have never been able to get a good tick over and recently if you stopped the engine when it was hot, it would not restart. The moving plate on mine was found to be very wobbly, the earth lead to the condenser was broken, the low tension wire inside the dizzy was in a poor condition and it turned out that the wobble was due to a broken spring clamp against the fixed plate, also the advance and retard mechanism was worn enabling the moving plate to move with out the aid of the advance and retard arm. We are all fine and dandy now.

This may not be the cause of your problem but it is worth checking through.

:cheers:

Bob
 
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Bobbee44

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Well, Inan and Bruce at Healey Surgeons in Maryland hit the proverbial nail on the head. Bruce suggested the rear carb was acting up and causing the problem(s) because of crud in the bowl. He was spot on. I cleaned out the bowl (it did contain a bit of foreign matter), took the carb apart, cleaned it out, refilled the damper, and the car runs exceptionally well. The center contact that had disintegrated in the distributer cap and left carbon residue was not the culprit, although I am sure a new distributer cap was in order.

Again, thanks to all for your input. I do add a bit of octane boost to the tank because the 10% corn "squeezens" and a 54 year old automobile are not all that compatible.

Bob
 
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