Lotus Elan

Some progress

PostPost by: types26/36 » Fri Jul 09, 2010 9:07 am

Robbie, the way I understand the operation of the accelerator pump on Delloto's is that the size of the jet varies the "time" the fuel is delivered and adjusting the rod changes the "amount" of fuel delivered.
I also believe adjusting the nut further down the rod increases the amount of fuel and lessens with the nut screwed off although I am prepared to be wrong here but before you start adjusting take out the pump jets and make sure they are not blocked, I usually take a strand of wire from a wire brush (brass if possible) and poke it in the jet hole then blow through it.....a word of warning DONT snap off the strand of wire in the jet hole :roll:
Here is an Alfa forum with a discussion that you may find relevant.
http://www.alfabb.com/bb/forums/carbure ... shaft.html
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PostPost by: billwill » Fri Jul 09, 2010 2:48 pm

>How do I adjust the pump settings? In other words what happens
>when I turn the nut and do I tighten it or loosen?

Ironically I don't really know. :shock:

And not having a Dellorto in my hand right now, I can't remember. I do remember thinking "That is a weird arrangement" :lol:

The screwed adjusting rod is not FIXED to the pump lever, there is a certain amount of 'dead travel' of the screwed rod, so I think it rather determines the quantity of fuel in the pump chamber, more than it determines the exact timing. Unfortunately the book I bought, just says "Do not alter these from the factory settings", which wasn't any help as I doubt that mine are still at the original factory settings. Alas I have not been able to do any further trial adjustments since, because on firing up my engine after carefully cleaning & new bits in the carbs, it started fine for the first time in years, but alas the repaired cylinder head cracked immediately and I haven't had the heart or money to do anything about that yet.

If you find out how to adjust the accelerator pump, please let us know. :roll:

PS: I hope whoever cleaned your carbs remembered to check & free up the little ball valve inside the pump.
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PostPost by: billwill » Fri Jul 09, 2010 2:52 pm

Poking wires into a jet is never a good idea it is best to use a compressed air jet.

You can buy a tin of compressed gas nowadays, to do such a job.

=============
Re the comment above about the timing of the squirt.

Though the jet size will affect this in part, my assessment is that the timing is determined by the spring inside the accelerator pump. As far as I can tell the pump works the opposite way to what I expected. Pressing the accelerator foot pedal does not force the diaphragm to cause a squirt, instead it releases the lever position so that the internal spring moves the diaphragm, so it moves evenly under the effect of the spring. When your foot comes off the pedal, the screwed rod then moves the lever & hence the diaphragm to draw a measured amount of fuel into the pump chamber, ready for the next time.
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PostPost by: billwill » Fri Jul 09, 2010 3:22 pm

Buy a copy of the Hammill book
http://www.amazon.co.uk/Build-Power-Del ... 805&sr=8-1


It's not expensive and well worth the money

I've just had a look at it again and on pages 101 102 it does sort of say how to chose jets and adjust the pump settings.
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PostPost by: types26/36 » Fri Jul 09, 2010 3:27 pm

[quote="billwill"]Poking wires into a jet is never a good idea it is best to use a compressed air jet.quote]

Yes that is why I suggested a brass wire strand, I've had occasions where compressed air will just not do it alone and a combination of the two worked.
I also dont believe that useing a brass wire once in a jets life can possibly make the silghtest difference to its size which I presume is what you are referring to.
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PostPost by: Robbie693 » Mon Jul 12, 2010 3:06 pm

Thanks guys for the advice, I have to admit I'm feeling a bit wary of messing with it especially as I'm not sure if I need more or less fuel to cure the problem!

With this and the other high rev problem I'm considering taking it to a rolling road place to see if they can iron out all the problems in one go. I'm also running out of time to fiddle with it.

I'll let you know how I get on and what the fix was (hopefully)

Cheers

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