I have a Blackjack induction system fitted to my standard 602cc M28 engine. It works fine except for some fluffing/hestinancy around 2,800 to 3,200 rpm approx. I currently have either a AZZ or AZR needle (its difficult to make out which) with a K+N cone filter as supplied by Blackjack.
Does anyone have a similar set up and if so is there a more suitable needle?
Any advice appreciated
Thanks, Nick 1933J
Needle for a SU HIF38 carb
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Geoff Ryall-Harvey
- Posts: 568
- Joined: Sun Aug 19, 2012 5:47 pm
- Country: UK
- Region: Cheshire
Re: Needle for a SU HIF38 carb
I helped Richard Oakes develop this kit and I have set them up on many Avions.
Start with an ABC. Then try AAC if it is running rich and ABB if it is running lean. Be aware that it is easy to mistake lean for rich and vice versa.
The needles you have are not those usually successful in a HIF 38 in this application. It is worth noting that because of the design of the SU carb any engine will idle well with almost any needle and will also work passably at WOT. It is how it works through the rev range and under acceleration that is the difficult bit. The needles referred to above were arrived at following a lot of development. I would be surprised if the ABC is not the one you settle on after having fiddled with the oil viscosity.
Another thing that helps, and is easier than changing springs, is to introduce a weight into the dashpot. Richard had some great big "washers" (like M38) cut in 1mm stainless and these are put into the dashpot under the spring. They serve to slow the rise of the piston (in the same way as a stronger spring does), keeping the mixture rich and not allowing it to lean out and stutter. I put two in the carb on my Avion when I rebuilt it recently and went over to a custom made version of the Avion manifold made in stainless tubing of a smaller diameter with a much smaller plenum chamber (designed to increase gas speed). He may have some left. If not I might have one or two.
You will need to set the idle first - see this article;
http://www.team.net/sol/tech/su-tune.html
You also need to ensure that there is oil in the dashpot - LHM is a good starting point. The spring in the dashpot is also an important factor (but try experimenting with different grades of oil first)
Make sure that the carb is in excellent condition and thoroughly cleaned. There should be no air leaks after the carb. Use narrow hose clips to ensure a good seal on between the large diameter rubber hose connecting the Blackjack manifold and the Citroen inlet stubs. Check for cracks in that hose. It is very important to check the tiny filter housed under the float needle. This becomes blocked with fibreglass particles and resin residue from the tanks - best to remove it altogether. Burlens have any parts you need for a rebuild. Replace all gaskets in the inlet manifold assembly.
Contact me if you have any issues.
Start with an ABC. Then try AAC if it is running rich and ABB if it is running lean. Be aware that it is easy to mistake lean for rich and vice versa.
The needles you have are not those usually successful in a HIF 38 in this application. It is worth noting that because of the design of the SU carb any engine will idle well with almost any needle and will also work passably at WOT. It is how it works through the rev range and under acceleration that is the difficult bit. The needles referred to above were arrived at following a lot of development. I would be surprised if the ABC is not the one you settle on after having fiddled with the oil viscosity.
Another thing that helps, and is easier than changing springs, is to introduce a weight into the dashpot. Richard had some great big "washers" (like M38) cut in 1mm stainless and these are put into the dashpot under the spring. They serve to slow the rise of the piston (in the same way as a stronger spring does), keeping the mixture rich and not allowing it to lean out and stutter. I put two in the carb on my Avion when I rebuilt it recently and went over to a custom made version of the Avion manifold made in stainless tubing of a smaller diameter with a much smaller plenum chamber (designed to increase gas speed). He may have some left. If not I might have one or two.
You will need to set the idle first - see this article;
http://www.team.net/sol/tech/su-tune.html
You also need to ensure that there is oil in the dashpot - LHM is a good starting point. The spring in the dashpot is also an important factor (but try experimenting with different grades of oil first)
Make sure that the carb is in excellent condition and thoroughly cleaned. There should be no air leaks after the carb. Use narrow hose clips to ensure a good seal on between the large diameter rubber hose connecting the Blackjack manifold and the Citroen inlet stubs. Check for cracks in that hose. It is very important to check the tiny filter housed under the float needle. This becomes blocked with fibreglass particles and resin residue from the tanks - best to remove it altogether. Burlens have any parts you need for a rebuild. Replace all gaskets in the inlet manifold assembly.
Contact me if you have any issues.
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woodsy99
- Posts: 26
- Joined: Sat Aug 25, 2012 2:11 pm
- CSC Membership Number: 1933
- Country: UK
- Region: south
Re: Needle for a SU HIF38 carb
Geoff, Thanks for the reply and info - pls can you let me have your phone nbr as I'd like to discuss further with you. Regards, Nick
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Geoff Ryall-Harvey
- Posts: 568
- Joined: Sun Aug 19, 2012 5:47 pm
- Country: UK
- Region: Cheshire
Re: Needle for a SU HIF38 carb
Have just PM'd you with numberwoodsy99 wrote:Geoff, Thanks for the reply and info - pls can you let me have your phone nbr as I'd like to discuss further with you. Regards, Nick
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Geoff Ryall-Harvey
- Posts: 568
- Joined: Sun Aug 19, 2012 5:47 pm
- Country: UK
- Region: Cheshire
Re: Needle for a SU HIF38 carb
If you want to compare needle profiles graphically then try here;
http://www.mintylamb.co.uk/suneedle/
http://www.mintylamb.co.uk/suneedle/