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Replace or leave? Carb&Dizzy


Jeffds1360
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Car is running great (when I dare go out!)

I have fitted a new 45D dizzy but have the old 25D, which seems a 'solider' unit but has no advance springs. :( my fault, I knacked them!

I've set the mixture at tickover and it is fine there. Solid 650rpm, smooth, no bother at all, but it runs rich all through the rev range.

I have a spare decent 150 CD , and new jet and needle.

Should I fit the jet and needle in the spare carb or in the existing one?

I also have my original 25D4 dizzy, but only have spare 45D springs. Cannot find definite 25D springs to match anywhere. ( no idea if the curve will be right) So... should I try the 25 back in with 45 springs?

Such a nightmare doing road tests :) my mother in law needs so much medicine:)

ramble ramble...???

 

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Why not try making the mixture leaner 1/4 turn of the jet each road test? You'll know when its too weak when you feel hesitancy at cruising speed.

Setting mixture at tickover is a pretty hit n miss affair so final tuning should done be driving. Do make sure your dash pot oil is topped up....

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Will do Johny. It's just that I'm sat doing nothing with a carb and new bits for it and a dizzy with some wrong springs in and I am fed up just looking at them and want to go out and test.

Think I'll put the new jet and needle in the carb on the car and try it out. I'll polish up the spare one later. I'll maybe try the 25 with 45 springs in and see how it runs later on too. Staying local ha!

 

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unless you can define the 45 springs are the ones you need to rebuild the 25 then whats the point you end up with a dizzy with a completely unknown curve 

and do as jonny suggest 

makes sure the air filter and gaskets are not obstructing the ports on the filter face of the carb 

in fact  when hot adjust  the mixture to get the best fastest idle and lean off to drop the revs by 50rpm  

have you advanced the timing by ear to the fastest and back it off  a  good bit 

if retarded at idle you use more throttle than is needed and always get a rich overfueled    result 

back to chicken and egg mode 

and regardless of what needle you have the idle start on the needle profile remains the same for every needle of its type /spec.

Pete

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Ha! Yes Pete, up, down, in, out!!

Timing is set very near book, quite a few degrees back from 'ear setting'

Carb is set using the 'tickle stick' and is sound at tickover and revs without a stutter. I just feel it is a bit rich.

I'll fit the new jet and needle on the installed carb.  Need something to do :)

so bored. Rambling. Thanks.

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lifting pins must have the filter fitted or you waste your effort it will be rich when you refit the filters 

always test and set in a road running condition , nothing left off 

lift to just touch the piston then raise piston 2mm   if it rises 50rpm its rich  if nothing it just right if you get a 50rpm falter its lean

your are listening for a hint of change , blink and you will miss it , its a very touchy feely exercise 

Pete

 

 

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Yes Pete, it's a couple of mm to engage the piston and a couple more. A 2p is permanently sitting under the master cylinders, I am deft at not burning my knuckles on the exhaust!! It is set right.

Think my needle is worn. New one will tell. Thanks.

20 degrees tomorrow :)

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On 30/03/2021 at 18:39, Pete Lewis said:

lift to just touch the piston then raise piston 2mm   if it rises 50rpm its rich  if nothing it just right if you get a 50rpm falter its lean

your are listening for a hint of change , blink and you will miss it , its a very touchy feely exercise

I was taught slight RPM rise but falling back to 'pre-lift' RPM in a couple of seconds for correct mixture.

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