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Carb setup jet loctions etc

gtmatt

Well-Known Member
Hi team
I've got an afr,t28 piper 285, want to run around 18psi of boost.

Standard carb at the moment , need to know what jets to change and location of the jets on the carb , pictures if any one has them ,ive got a spare carb which I can take pictures of and show what I think needs changing, and the process of changing the jets ive never done this before lol.


thanks matthew
 
Air corrector jet is the brass jet sitting in the middle of the carb (screwed into the emulsion tube).

2nd stage bush is on the left hand side (from the pictures), where the triangular block screws on to.

Take a picture of that side of the carb, and I'll highlight which one is the bush.
 
The jet in the triangular block is the 1st stage enrichment jet. No need to drill that out - If anything, it'll need reducing in size.

2nd stage jet/bush is located where that block screws onto.
 
Yo....I've used drill bits on main jets in the past... From maplin....about a tenner I've evan bought the kits from the market for about 3 quid...but they are not accurate enough...the best way to do any but mostly the main jet is to buy the manufactured size jets from southern carbs (webcon dont seem to stock them) stamped with 130/1.3 mm for a bar/ 15 psi of boost or 135 /1.35 mm for 18 psi...but as your using a t28 hybrid maybe a 140/1.4 mm...I've just bought 2 jets from Mike @ gt spares for the mainjet...135 and a 130... For a smaller turbo at 15- 18 psi not not sure which im going to use ... The simplest thing to do on any original gtturbo carb is to swap the air corrector 1 mm or 1.1 mm for the 0.9 mm first enrichment circuit. The smaller air corrector allows less air into the mixture and the first enrichment allows more fuel through, this basic mod added to a drilling out of the fixed bush 2nd enrichment circuit to 1.2 mm is the start of a simple carb upgrade for higher boost, add a 140/1.4 mm main or a 145 /1.45 main jet and you could turn you boost up to 21 ish, add water injection and or a mess about with the position of the T D C sensor and you Might be able to run 2 bar/30 psi with this level of set up a 230- 240 bhp will frighten all your mates, but I must add if your heading for over 18psi you'll need the later type fuel pump that is the size of a can of beer as opposed to the earlier red bull size. Theres loads more that can be done to a carb to upgrade its performance...all this stuff is well troden by most members on the other place:-O:T(<3
 
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Increasing the main jet is an old skool way of increasing fuelling, and completely messes up the fuelling throughout the rev range. If anything the main jet needs reducing in size to lean off the cruising/off-boost fuelling, as it runs fairly rich with a 120 in situ. This is assuming a standard 25mm venturi is present. If you fit a larger 'grp A' (sic) venturi (which isn't worthwhile either), then yes, the main jet will need increasing in size to compensate for the reduced venturi effect.

Likewise, swapping the air corrector & 1st stage jet is unwise, as although a 0.9/1mm a/c jet will work ok, an o.e 120/125 a/c jet in the 1st stage will cause over-fuelling on spool-up. Again, if anything, you want a slightly smaller 1st stage jet (than o.e) to aid lean spool-up.

2nd stage enrichment mod's (not just drilling out the bush) are all that's needed for on-boost fuelling, and obviously good fuelling-supply (eg, ph1 fuel pump, possibly an increase in base fuel pressure (~6psi), larger needle valve, etc).

Water injection isn't needed unless you're running a more-advanced ignition and/or a higher comp' ratio.
 
So true... Old skool and unwise now...the carb set up will never be able to compete at modern fuel management levels.. But well proven and tested to turn the cars into a relativelly reliable pocket rocket... Many a member have used this simple set up to expand their understanding of the carb and build a fast car...

Now is the time to start a page or section In this club forum on all the modifications available and used by members on carb fueling and ignition and their effectiveness... So there's no confusion

We could start with as you said ,

Venturi size and adjustment
Main jets
Air corrector
Emulsion tube mods
1st stage enrichment
2nd stage enrichment
2nd stage enrichment boost pressure activation adjustments
Float hight adjustments
Needle valve changes
Choke flap removed
Spiral inserts
Fuel pressure
Fuel pumps and filters
Fuels pump/race
Fuel pressure regulators
Advanced ignition wire swap
Ignition adjustment on the T D C
Renault's own R11 turbo group A carbs
Carb kit self rebuild
Detonation sensor removal and upgrade
Charge temperature
Idle jet drilling out
Compression ratios
And my favorite ...Water injection

Etc etc etc...:acute.gif::read.gif:
 
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So true... Old skool and unwise now...the carb set up will never be able to compete at modern fuel management levels.. But well proven and tested to turn the cars into a relativelly reliable pocket rocket... Many a member have used this simple set up to expand their understanding of the carb and build a fast car...

Now is the time to start a page or section In this club forum on all the modifications available and used by members on carb fueling and ignition and their effectiveness... So there's no confusion

We could start with as you said ,

Venturi size and adjustment
Main jets
Air corrector
Emulsion tube mods
1st stage enrichment
2nd stage enrichment
2nd stage enrichment boost pressure activation adjustments
Float hight adjustments
Needle valve changes
Choke flap removed
Spiral inserts
Fuel pressure
Fuel pumps and filters
Fuels pump/race
Fuel pressure regulators
Advanced ignition wire swap
Ignition adjustment on the T D C
Renault's own R11 turbo group A carbs
Carb kit self rebuild
Detonation sensor removal and upgrade
Charge temperature
Idle jet drilling out
Compression ratios
And my favorite ...Water injection

Etc etc etc...:acute.gif::read.gif:
Start an article then bud, we'll get [someone else] to review it and sense check and stick it on the guides forum. I'd sure appreciate it, my carb knowledge doesnt go much beyond the basics.
 
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