| fozworth |
Sun Feb 18, 2018 11:08 am |
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Hello fellow members ,I wonder if any of you would be able to shed some light on what might be wrong if anything at all with my dizzy following instructions to replace it after a rolling road session.
My bus has a 1641 type 1 motor with vintage speed exhaust,with Std internals and I've just fitted a pair of DRLA 36 carbs that have been totally restored to a factory fresh condition.
I initially had the following jet sizes fitted as per dellorto uk recommend.
115 main
55 idle
180 air
35 pump
28 ventures
9164.2 emulation
150 needle
I proceeded to set the carbs up and balance them according to the dellorto book .It idled well and pickup was good but i couldn't seem to loose the flat spot rolling off idle .I tried 58 idle jets and 118 mains but still had the same issue So I decided to take it to a rolling road .After the technician had done a couple passes and used the timing gun he said I was running way to lean and that my dizzy was not advancing early on then spiking at 42 degrees with vac off and 53 with the van on at about 3500rpm causing it to lean out across the Rev range . He upped my jet size to 128 main and 60 pump .The larger main solved the lean issue and the 60 pump cured the flat spot ,but he said once I've sorted my dizzy he would down size the main and pump accordingly.
As my Bosch svda was a very clean unit (later Mexican bosch unit) I thought it best to get it refurbed .So I sent it off and upon bench testing it they could not find anything wrong .They ran it up yo 10000 rpm and it still would not advance over 32 degrees with vac off .
I then tried it in a friends 1600 type 2 and the figures on the strobe gun showed that with timing set at 8 degrees btdc at 900 rpm the dizzy would reach a max advance of 32 degrees at 3300 rpm vac blocked or 42 vac connected. We tried it on my bus and had the same result.
I reported back my findings to the rolling road chap and he's said that my dizzy is still defective as he says it's advancing to 42 when under load like going up a hill and shouldn't be .he says if you were just cruising and it was advanced to 42 that would be ok .
I'm fully confused as what my friend and I found along with the bench testing results something doesn't seem right.
I really need to find a known working dizzy to try in my bus to see if the figures are the same on the strobe gun ,but not having any joy with that yet .
I don't want to buy another dizzy if I really don't need one .
Any suggestions? |
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| UK Luke 72 |
Sun Feb 18, 2018 11:27 am |
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I still suspect your vac plumbing if it is as your RR man says and advancing 42ยบ under full load.
But like you said earlier, the vac is all setup right, therefore your RR chap is talking out of his arse.
Will be interesting to see what others say :) |
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| Bugsy61 |
Sun Feb 18, 2018 2:10 pm |
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The vacuum can on your distributor should be plumbed to ported vacuum. It sounds like you have it plumbed to manifold vacuum. They are not the same thing. Do a search for "ported carburetor vacuum" and you should get some good diagrams to explain the difference. Your dual barrel Dellortos may not have a ported vacuum passage cast into them. If not, you will not be able to use the vacuum can on the distributor.
Here is a statement I plagiarized from an article on the subject. This is basically what you should shoot for at cruise speed, 55 mph, 1/3 throttle opening.
if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
50 degrees total may be a little extreme for our old cars, but you get the idea. |
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| fozworth |
Sun Feb 18, 2018 3:05 pm |
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