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Author Topic: 32 DATRA idle circuit  (Read 382 times)
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mwredit
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« on: March 24, 2017, 07:49:17 PM »

I have a problem with the idle circuit on my 32 DATRA 101 carb. The idle circuit seems to be acting as though a passage is restricted, but when I disassemble the carb to blow out the passages and jets, everything is clear and I see barely any sediment.  I do have sediment in the tank that the filter is picking up, but very little seems to be getting to the carb.  I also went to the extreme of extracting the lead plug that is near the idle jet on the top to verify that the passage was clear and it is.  During the cleaning process, I remove the mixture needle and the idle stop solenoid and use carb cleaner and compressed air and blow it both directions, even from the idle jet hole. 

Months ago, I cleared the clogged return line to the tank and reconnected it, along with reinstallation of the stock fuel regulator.  As the car is warming up from a cold start, it sounds normal, but when it reaches operating temperature and the choke fully kicks off, the idle is rough and lopes.  If you gently put two fingers over the carb throat, the idle smooths out, until I took my fingers off and the roughness and loping continues, which indicates to me a problem with the idle circuit.  Also, when you unscrew the idle jet 1/4-1/2 turn while it's running, the idle smooths out and increases slightly.  Once I tighten it back, the idling continues as before. This would indicate, I think, a restricted idle jet, but it's clear as can be.  I verified the function of the idle stop solenoid and when I unplug the red wire leading to it, it will stall after 2 seconds, so that is working.  The float is slightly lower than stock height, by 1/32" or so. The Haynes manual is vague on what the level should be.  I've been told the float needs to be level with the carb top mounting surface with a light contact on the float needle.  Is that correct?  Both emulsion tubes and main jets are also clear.  I had assumed earlier that the emulsion tubes were plugged, but seem to have a division wall in the lower section, 1/4" from the main jet, assuming they were free flowing bottom to top.

When I drive the car, it will sputter and cough on moderate acceleration, especially from 1st to 2nd.  Beyond that, it goes like a bat out of hell when I floor it and the secondary kicks in.  I'm stumped to what it could be and haven't found the smoking gun yet.  Any suggestions?

Thanks,
Mike
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Mike R.

1968 Mercury Cougar XR7
1961 MG Midget
1974 Ford Mustang II Ghia
1977 Lancia Beta HPE
peteracs
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« Reply #1 on: March 24, 2017, 11:54:48 PM »

Excuse my ignorance, but you mention the idle jet, do you mean an adjustable screw which needs to be adjusted to give smooth idling?

First thing to check is that you do not have any air leaks. USe carb cleaner or other and spray around the the spindles and manifold to see if the revs change.

Not convinced that the following is the cause this time, but it has been noted more than once that latest fuels work better if you go up on main jet size by one to two increments.

Peter
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« Reply #2 on: March 25, 2017, 04:10:25 AM »

Peter,

No, not the idle metering screw, the primary idle jet, the one that resides with the other 3 jets on the top section of the carb body.  There doesnt seem to be any intake leak of any kind.  Everything within the carb checks out, that's why I'm stumped. The primary throttle shaft is a little wobbly, but it was prior to what I have going on now.  The thing is, it ran fine up until a week or so ago.  The idle circuit is leaning out, indicating a plugged idle jet, but the jet is clear. This is what's baffling me.  Maybe I should go up on the float setting?  Also, since I live in California where the gas is the most tainted gas you'll find in the US, I guess anything is possible.  I'm trying to get the car ready for the second round of emissions testing and the carb acting up is a new development I wasn't expecting.
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Mike R.

1968 Mercury Cougar XR7
1961 MG Midget
1974 Ford Mustang II Ghia
1977 Lancia Beta HPE
Neil-yaj396
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« Reply #3 on: March 25, 2017, 09:08:25 AM »

These carbs are so old now that they have a life of their own. My car went through a period of poor running last year then cleared itself after a week of hard use. The only true cure is a rebuild including an ultrasonic cleaning bath for the carb body. Particles not visible to the eye can totally mess things up.

I don't think the float setting will have anything to do with it. All that controls is how much fuel is in the chamber ready for delivery, so always enough at idle speed.

You mention that the idle improves when you turn the adjustment screw. Why not just leave it there?
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« Reply #4 on: March 26, 2017, 12:45:16 AM »

Neil-yaj396- Turning the mixture adjusting screw makes little if no difference in idle quality, unless you turn it almost all the way in until it wants to stall.  Originally, I was referring to the IDLE JET (one of the 4 jets that mount vertically) uppermost on the carb that I was turning (turning to remove, theoretically speaking).  Believe me, if I was able to obtain a proper "tickover speed" and smooth idle, I would definitely leave the mixture screw where it is indeed.  However, I am unable to obtain such results due to the nature of my problem.
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Mike R.

1968 Mercury Cougar XR7
1961 MG Midget
1974 Ford Mustang II Ghia
1977 Lancia Beta HPE
Neil-yaj396
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« Reply #5 on: March 26, 2017, 08:38:21 AM »

I'm almost certain that it will be due to an invisible piece of crud somewhere in the slow running circuit then.
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« Reply #6 on: March 26, 2017, 10:44:13 PM »

Neil-yaj396-  You couldn't have been more correct.  I finally rectified the problem with the carb today.  It was a blockage in the idle circuit that evaded typical cleaning.  What I did is that I disassembled the top section of the carb, extracted the lead plug next to the idle jet (adjacent to the idle jet) and flushed the passages with carb cleaner and compressed air.  I then resealed with a new lead plug and reassembled the carb.  The engine now runs like a Swiss watch.  I wanted to share the outcome and recommend that if anyone that has problems clearing the idle circuit, you need to extract this lead plug for extensive cleaning and replug after cleaning for best results.
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Mike R.

1968 Mercury Cougar XR7
1961 MG Midget
1974 Ford Mustang II Ghia
1977 Lancia Beta HPE
Neil-yaj396
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1979 1300 Coupe


« Reply #7 on: March 27, 2017, 06:59:10 AM »

Not sure what the lead plug is?
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HFStuart
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« Reply #8 on: March 27, 2017, 12:14:02 PM »

Lead as in soft dense metal.

Lead balls are often used to seal galleries or drillings on carbs
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« Reply #9 on: April 20, 2017, 05:30:05 PM »

Update-

The engine is still running like a swiss watch after super cleaning the idle circuit after I extracted that lead (soft silver like metal, like what HF Stuart described) plug on top.  I also replaced the fuel filter with a larger plastic generic see thru type so I can monitor if there's crap getting into the system.  So far, so good.  What I have learned on this if you have idle circuit problems like what I've had and with a vehicle that sat for over 20+ years,  that plug needs to be removed for proper access to completely clean the idle circuit. There's too many sharp bends in the circuit that standard cleaning, especially with lousy California grade carburetor cleaner, can't completely clean.
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Mike R.

1968 Mercury Cougar XR7
1961 MG Midget
1974 Ford Mustang II Ghia
1977 Lancia Beta HPE
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