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TR2/3/3A When to use R [Rich] needles in my SU's?
- Thread starter karls59tr
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STeve 1958
Jedi Hopeful
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A rich mixture produces more horse power, however it does not take a special needle to get a rich mixture. just turn the nut.
Thickening you damper oil will also richen your mixture when you first hit the gas.
Someone else may know of an advantage, but I don't.
Thickening you damper oil will also richen your mixture when you first hit the gas.
Someone else may know of an advantage, but I don't.
martx-5
Yoda
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I have 87mm pistons & liners, a 282 deg cam tubular headers and have the head milled 0.085". I needed to change the needles. I don't remember what I wound up with (I'd have to look in the carbs), but I think they are RG. I have a wide band O2 sensor in the exhaust, so I can easily see what the air fuel ratios are with the different needles. I experimented with RA, RB, RG, and RH.
BTW, not all "R" needles happen to be richer than the stock SM needle. It's just coincidence that the needles generally used with modified TR engines happen to be "R" needles."R" does not stand for "R"ich.
Edit: Here's a link to an SU needle program where you can put in various needles and see how they compare.
http://www.mintylamb.co.uk/suneedle/
BTW, not all "R" needles happen to be richer than the stock SM needle. It's just coincidence that the needles generally used with modified TR engines happen to be "R" needles."R" does not stand for "R"ich.
Edit: Here's a link to an SU needle program where you can put in various needles and see how they compare.
http://www.mintylamb.co.uk/suneedle/
Hi,
I have a similar set up as martx-5. with a TR-4a intake on my TR-3a. I also ended up with the RG metering rod. I started off with a stock 1 7/8" exhaust and the Moss RH "rich" metering rod. A/F as typically 12. I went to a 2" straight exhaust, with two glass packs, and it leaned it out to 14:1. The RG rod brought it back to 12:1. I run the SAE 20wt 3 in1 oil in the dampers. The set up runs well, no hesitation and 29 MPG at 65.
As a note, Kastner suggested the RG for strong running street engines in his website.
RG
I have a similar set up as martx-5. with a TR-4a intake on my TR-3a. I also ended up with the RG metering rod. I started off with a stock 1 7/8" exhaust and the Moss RH "rich" metering rod. A/F as typically 12. I went to a 2" straight exhaust, with two glass packs, and it leaned it out to 14:1. The RG rod brought it back to 12:1. I run the SAE 20wt 3 in1 oil in the dampers. The set up runs well, no hesitation and 29 MPG at 65.
As a note, Kastner suggested the RG for strong running street engines in his website.
RG
Hi,
I put mine on the collector, just upstream of the reduce flange. I welded it about 2 o'clock if looking from the rear, forward. It does not hit anything. I have a Autometer Wide Band Sport Comp A/F Meter. It uses a Bosch sensor. It came with a bung to weld on the header. I also have a Sport Comp vacuum gauge next to it. I get vacuum from the old PVC port on the TR-4a intake. Watching the two at the same time tells a lot.
Shop Summit, Jegs, Speedway, etc for a sale.
Roy
I put mine on the collector, just upstream of the reduce flange. I welded it about 2 o'clock if looking from the rear, forward. It does not hit anything. I have a Autometer Wide Band Sport Comp A/F Meter. It uses a Bosch sensor. It came with a bung to weld on the header. I also have a Sport Comp vacuum gauge next to it. I get vacuum from the old PVC port on the TR-4a intake. Watching the two at the same time tells a lot.
Shop Summit, Jegs, Speedway, etc for a sale.
Roy
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Regarding using the adjusting nut to provide a rich or leean mixture, this only applies to the mixture at idle. The SU needle has 10 different taper positions on it and the last 4 positions are what controls the mixture at speed.
If you look in the needle chart you can see the differences in the R series needles and the stock SW needle.
I am sure there is literature out there as to what needles should be used with specific modifications
If you look in the needle chart you can see the differences in the R series needles and the stock SW needle.
I am sure there is literature out there as to what needles should be used with specific modifications
martx-5
Yoda
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How do you know they are mixing equally without an O2 sensor??
In a perfect world, two sensors would be great. But, having one O2 sensor will still yield more than enough info for selecting the proper needles for whatever mods have been done to the engine. Take a look at the spark plugs if you want to see if the two carbs are working together.
Mine is in the tubular header measuring cylinders 1 & 4.
poolboy
Yoda
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It changes the mixture ( the annular space between needle and jet) thru out the entire range of the air valve movement.
Putting it another way, if the jet is lowered, the annular space will be greater for any given position of the air valve than it was before lowering the jet.
Putting it another way, if the jet is lowered, the annular space will be greater for any given position of the air valve than it was before lowering the jet.
Nelson Riedel wrote some great articles on O2 monitors. They pertain to the ZS carbs and the TR6, but the principle also applies to SU carbs. The bottom line is that the adjusting nut effect on mixture strength is mainly at idle and diminishes with piston lift. As piston lift increases, the needle profile has a greater effect on mixture strength.
A good explanation is found near the top of page 4/5.
Berry
https://static1.squarespace.com/sta...a2d9/1560383918525/Using+Air_Fuel+Monitor.pdf
Last edited:
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Then why are there so many SU needles, over 100. The needle has to be correct for the specific setup. Dropping the jet may richen the mixture a bit but if it is the wrong needle then the mixture will be wrong for the entire RPM range.
When you play with cams/intakes/headers/ compression or anything that changes the quantity of air going through the engine then the needle needs to be different across its entire range.
When you play with cams/intakes/headers/ compression or anything that changes the quantity of air going through the engine then the needle needs to be different across its entire range.
poolboy
Yoda
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There may be no perfect needle profile for all driving conditions and engine modifications, but which ever you choose to try out there will be an adjustment range available to you...
.My suggestion is to set the mixture for what rpms you tend to drive the most.
If you find yourself driving in the 2200 to 3000 rpm range more than 1500 or 4000 rpms, then check the plugs immediately following a nice long drive at those rpms.
If you want to race and redline do the same thing.
.My suggestion is to set the mixture for what rpms you tend to drive the most.
If you find yourself driving in the 2200 to 3000 rpm range more than 1500 or 4000 rpms, then check the plugs immediately following a nice long drive at those rpms.
If you want to race and redline do the same thing.