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engine cranks, but won't start  Rate Topic 
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 Posted: 02-26-2007 03:14 am
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Ben Cecilia
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A couple of days ago I was driving around  in SF bay area. The next  day when I tried to start the Jensen to do some routine maintenance the engine would not start. So, I checked the following;
1.carb gets gas
2.replaced coil with known working coil
3.checked #1 spark plug for spark
 

Thanks in advance  for  any info

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 Posted: 02-26-2007 07:47 am
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Harkes
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Hi Ben, assuming you have checked for spark and you indeed get a spark. Then all I can think of is your distributor and advance... Check your distributor to see if it the clamp/screw isn't loose and changed your advance.

Do you run an MSD? I encountered a problem once. Engine cranked but wouldn't fire up. Turned out my white trigger line was poorly connected to the black wire (pertronix) in the distributor. Fixed the wire...and she started right up.

So do check all ignition parts and check advance.

good luck

erik

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 Posted: 02-26-2007 10:24 pm
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Ben Cecilia
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Hi Erik,

This engine does  not have the msd,I have checked the distributor cap for worn out
parts and have found that's it's ok. I will pull out the spark plugs to see if they are
fouled.



Thanks again
Ben

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 Posted: 02-28-2007 03:00 am
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LambandAndy
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Ben,

The ignition system has a "bypass" circuit for the ballast resistor that supplies a full 12V to the coil during starting.  Should be a white/yellow wire running from the starter to the coil.  Could have come loose.

Andy 15223

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 Posted: 03-07-2007 02:31 am
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Ben Cecilia
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Hi Andy,

Here are the following tasks the that I have done so far:

1.I pulled each spark plug to check for spark and they all produce a spark
2.I checked the carbs (stromberg's) and I can see fuel eventhough the back carb has a sticky  needle

Do I need to change the coil? , for bigger spark

Thanks again in advance
Ben

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 Posted: 03-07-2007 03:13 am
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Mark Rosenbaum
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For an engine to run, you need:
  • Sufficient compression
  • Sufficient spark, at the right time
  • Proper fuel-air mix
Since the engine was running, lack of compression is not very likely to be the cause of your problem, and I'll ignore this area for the moment.  Which brings us to the following possible problem causes:

Sufficient spark, at the right time.
Verify that the spark occurs at the right time -- ideally about 8° to 12° BTDC though the engine should run (perhaps very poorly) if it's anywhere between 0° BTDC and 28°BTDC.   The distributor mounting can sometime get loose and allow the distributor to jump free for half a turn before it re-engages.  Also, certain distributor internal faults can give sudden timing changes.

Try a replacement distributor cap.  Try a replacement rotor -- and if you have one of the rpm-limiting rotors, make sure its sliding weight isn't sticking in or near the spark-disable position.  Check the points gap and ensure it's about 0.015" -- too small, or too wide, and you end up with a weak spark that may light up a plug in free air, but which will not fire a compressed charge in the cylinder.  Try a replacement condenser -- again, a fault here gives a spark that won't fire a charge in the cylinder.

Proper fuel-air mix.
You mentioned that the rear carb had a "sticky needle."  If its piston-like vacuum valve isn't free to rise and fall, you'll have an uncontrolled fuel-air mix which is unlikely to support combustion.  If you can see fuel dribbling into the carb throat, you have a leaking fuel inlet valve or sinking float, which in addition to messing up the fuel-air mix is also a major safety hazard.  Both of these conditions, if they exist, would have to be fixed before you could expect the engine to run properly.  A severe vacuum leak could also result in a bad fuel-air mix.

From what you've described, it would be prudent to presume that you have several problems at once.  If so, you will probably have to go through the whole troubleshooting process several times in order to be certain you've found them all.  Please do let us know your results.  Further advice and suggestions are available if needed.

 

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 Posted: 03-07-2007 02:21 pm
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Dan (Florida)
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I've had an unusual no start situation before and it may pay you to check if the distributor hasn't jumped out of its drive on the oil pump.  There is a spring between the distributor drive on the oil pump and the distributor shaft that over time causes wear between the distributor shaft and the distributor housing causing the drive  to move apart.  Eventually the drive may just hop out of the oil pump end of the drive.  If there is end play in the distributor shaft or the distributor isn't seated completely in it's drive housing you may jump time and stop.   I fixed mine with an appropriately sized flat washer behind the distributor drive end and a close look at the seating of the distributor in the housing. 

HTH  Dan

Last edited on 03-07-2007 02:24 pm by Dan (Florida)

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