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Idle Jet Re-sizing

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Does anyone have any advice on resizing idle jets.

The idle jets on my dellorto 45's are size 55 (standard). However I experience the common hesitation on acceleration which I believe is due to the idle circuit running too lean. I have read that people have had success in overcoming this by installing larger jets such as size 58.

I have tried installing size 58 jets but on hard acceleration the engine splutters quite bad with back fire on overrun - mixture too rich??

This suggests 58's are too big, but before I refit the original jets am I missing anything or can anyone recommend a better set up to the standard.

Thanks

Graham

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Graham,

I am currently doing some re-jetting on my 83 (USA) Esprit utilizing the Innovate Technologies LM-2 AFR data logger. In my opinion this thing has saved me lots of time and money in guessing with its ability to see the AFR throughout the RPM range. Stuff you could only guess at with seat of the pants driving or plug reading.

My carbs are of a different spec and if you have your carb information you can compare with mine. In your search for the correct idle jet you also need to take the idle jet holder in account as it works as an emulsion tube. Using the LM-2 you will see the transition from idle circuit to main circuit and be able to more accurately determine which one needs to be changed.

I found that most of your driving is done on the idle circuit, so in order to have good drivability and gas mileage you want to get this one right.

On my car someone had changed the idle jets to the 60's and the stock holder is a -9 (lean). It too had a stumble on normal acceleration and the exhaust tip and spark plugs had black soot. With the LM-2 what I saw was a long length of time that the low revs range stayed extremely rich, leading me to suspect the accel pump jet was dumping to much raw fuel. I took the stock 38 pump jet and went down to the smallest pump jet (33) and found a noticible improvement on acceleration and no bog or flat spot. Next I went to a 58 pilot and got the AFR closer to 13.5 at cruising speed and the plugs and exhaust soot was gone. Best of all mileage is improving and I am not washing down my cylinders with raw fuel.

Other than that I am currently staying with the -12 emulsion tubes, reduced the main jet from a 165 to a 160 and dropped the air corrector from a 230 to 210, all doing to equalize the AFR throughout the rev range with emphasis on not allowing it to be to lean at max boost. Still more to do but it is all looking good and running great.

Next step will be to utilize the 4 extra analog inputs of the LM-2 to monitor fuel pressure, IAT, boost and water temp.

Good luck,

Jeff

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Jeff

Many thanks for the info, much appreciated. Apologies for not replying sooner as I've been doing much head scratching but have now solved the problem.

On rechecking the carbs the float levels where too low. Have reset and its now running like a dream with the 58 idle jets having eliminated the stumble under acceleration completely.

Thanks again

Graham

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Your welcome. The float level is tricky to get right. I ended up machining aluminum dowels at 15mm and 14.5mm in order to place between the cover and float. The old "eye ball" method failed me. I ended up at 15mm due to the car flooding in hard right corners.

Good luck,

Jeff

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Your welcome. The float level is tricky to get right. I ended up machining aluminum dowels at 15mm and 14.5mm in order to place between the cover and float. The old "eye ball" method failed me. I ended up at 15mm due to the car flooding in hard right corners.

Good luck,

Jeff

Jeff

Interested that you sorted the hard right hander problem with float level, I've got the same problem. Did you have to change the float levelby much to stop the problem?

cheers

Mike

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Mike,

If you are familiar with the proper float setting procedure of having the cover vertical and the float just touching and not compressing the tiny spring in the needle valve, you know first hand how hard it is to do accurately by holding and eyeballing it with a measuring device (scale, ruler, etc)

I used a small bench vise with made up wood jaws to gently hold the cover stationary (with gasket). I rolled my aluminum dowels under the floats to get the proper clearance. This is the only way I could get the floats NOT to be pushing in on the needle. You will need to adjust the floats but not by very much.

Having a machine shop make you up some machined dowels should be relatively easy and inexpensive. I am fortunate to have a small shop lathe and did my own. Make sure they are long enough to extend the length of the cover. I made a 14.5mm and 15mm. Ended up with 15mm working.

Tedious but the results worked. The right hand bog is awful annoying.

Cheers,

jeff

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Thanks for that,I'll strip them back down and have another try, It's quite an embaressment stalling when you come off a fast roundabout.

cheers

Mike

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