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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
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If the Carbtune now doesn't read #3 (ie, the problem followed the hose), then the vacuum hose is plugged... clean it out.
However, if the Carbtune still doesn't read #4, then the throttle shaft is probably twisted such that the #4 butter fly is still closed while #3 is open at idle. Remove the progression hole covers, look in and you'll see the progression holes drilled through the bottom of the passage into the carb throat. Look through the drillings while operating the throttle and you'll see the edges of the butterflies sweeping past the drillings.
With the throttle closed, do both #3 & #4 butterflies align with their drilled holes in the same way... ie, are they equally open? If not, then the throttle shaft is twisted. The shaft is weak. If you ever put a wrench on the nut on one end of the shaft in order to hold the shaft from turning while you tighten the nut on the other end of the shaft, then you will twist the shaft. NEVER do that.
If the shaft is twisted, then the 'book' fix is to replace it. However, at this point, you have nothing to loose by attempting to twist it back to straight. With the Carbtune hooked up, and with wrenches on the front and rear nuts, twist the shaft a little in the direction that would open #4. Just a little twist, then release it to see if #4's Carbtune reading improves. Nudge it in little steps, checking readings in between. If you're lucky, you might get #4 back into balance with #3. If not, you tried, now replace the shaft with a new one.
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Are your carbs just 40, or is there a letter after it, like 40E or 40N ?
Plain 40 carbs have Idle Mixture screws with coarse threads and blunt taper needles. They only have a couple of turns available before the needle fully retracts from the orifice and more turns do no additional good. Settings in the 2.0-2.5 range are common.
40E & 45E carbs have Idle Mixture screws with fine threads and long taper needles. They have about 4.5-4.75 turns of total adjustment available before the needle fully retracts from the orifice. Normal running settings in the 3.5-3.75 are typical.
For either idle mixture screw, after the needle fully retracts from the orifice, further turning of the screw produces no further meaningful change.
If you feel the need to turn the mixture screw out further than normal (3.5-3.75 for 'E' needle) in order to get the mixture rich enough, then the idle circuit is jetted too lean to begin with, and you're trying to compensate in a big way with the screw. No!! The jetting needs to be 'right' in the first place! Then only small tweeks are made with the mixture screws.
You report Mixture Screw settings of 5.75, 4.5, 4.0 & 3 25. 1 thru 3 are too many turns for 'correct' jetting. The idle circuit needs to be jetted richer before the mixture screw settings will become 'right'.
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Dirt Road Dyno --
When you get #4 figured out, and sorted (new shaft), start the engine and let it warm up to normal operating temp. Adjust the idle speed as slow as possible consistent with smooth running... no missing.
Open the throttle slowly enough that the accelerator pump isn't much of a factor. If the engine hesitates off-idle, then the Idle Jet Holder (aka, Idle Air Corrector) is too lean. If it does not hesitate, then you don't know where it is, but it's probably too rich. Go with progressively leaner Idle Jet Holders until the engine just begins to hesitate off-idle. Then go back one step richer until the hesitation just disappears.
With the Idle Jet Holder set, go find a quiet bit of road where you can make full throttle runs without attracting attention. From a rolling start, short-shift into a higher gear and accelerate at full throttle. The Idle circuit hands off to t he Main circuit at 3200 rpm. During the full throttle run, if the engine stumbles approaching 3200 rpm, then the Idle Jets are too lean, and the Idle Circuit runs out of capacity before the Main Circuit takes over. Go a couple of steps richer on the idle jets and repeat until the stumble disappears.
If there is no stumble during full throttle acceleration, then you don't know where you are... but probably too rich. Go a couple of steps leaner with the Idle Jets and make another run. Repeat until the engine just picks up a new stumble. Then go back richer one jet size at a time until the stumble disappears..
When adjusting the Idle Jet Holders and Idle Jets, each one also affects the other. So after the initial round of the above adjustment routine, go back and start over. Repeat & repeat until no further change results.
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The 34mm chokes are not standard J-H, so what car are the carbs originally from? Or are you playing with smaller chokes in hopes of improving low-end driveability?
................................ Paul ....... Jensen-Healey Factory
Dellorto DHLA Specs ... Reese .... Emissions ... Non-Emissions
Model ......................... __ ......... 40E ............. 40
Choke ........................ 34mm .... 35mm .......... 35mm ... 34mm chokes are not stock JH or Lotus.
Main Jet ..................... 145 ........ 130 ............. 130
Main Air Corrector Jet ... 190 ........ 160 ............. 160
Main Emulsion Tube ...... 7772.5 ... 7772-5 ........ 7772.5
Idle Jet........................ 55 .......... 55L, 4-spd ... 50
Idle Jet ........................ __ ......... 52L, 5-spd .... __
Idle Jet Holder .............. __ ......... 7850.5 ......... 7850.1
Float Weight, grams. ...... __ ......... 8.5 gr .......... 8.5 gr
Float Height, mm .......... __ .......... 16.5-17.0 .... 16.5-17.0
Float Needle Valve ........ 170 ........ 170 .............. 170
Pump Jet ..................... 45 .......... 45 ............... 45
Starter Jet ................... 60 .......... 70 ............... 70
Starter Emulsion Tube ... ____-_ ... 7482-1 ......... 7482.1
Regards,
Tim Engel
Last edited on 12-20-2021 10:42 pm by Esprit2