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Discussion Starter #1
Ok trying to fine tune the Ultima 131 a bit. I put on an AFR gauge so I got a little data.

First, carb is a bored G with thunderjet. Current jetting is:
Main - 0.82
Inter - 0.33
T Jet - 135

First question, what determines which jet is being used, RPM or throttle? Meaning, if Im in high gear putting away at 3k rpm but barley 1/4 throttle is that running off the main jet or interm?

Second question, related to the first, if barley on the throttle cruising on the freeway, not bogging the motor above 2500 RPM but maybe 1/4 throttle, the AFR gauge shows in the 10-11 range, hell going up to Tahoe it even got in the 9s a bit and I think caused the motor to sputter? But if I crack the throttle all the way open it goes up in the 13s and 14s.
Would that mean Im running too rich on the main jet?

I had it tuned beginning of the spring but had to swap out the Ultima carb for a real S&S and had Scott at Hillside bore it out while I was at it. Also planning to have head work done over the winter so don't want to pay another $450 for dyno tuning if I can dial it in close myself for now.
 

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I'll toss in my opinion but keep in mind although I have tuned EFI cycles and carbed autos, I haven't tuned a carbed cycle. Sounds like you're a bit rich down low (10-11, even 9 parts of air to 1 part of fuel) and getting lean when you open it up (13-14 air to 1 fuel). My EFI Road King is around 13-13.5 to 1 at lower RPM, 13.5-14 cruise at light throttle and 12.5-12.8 at higher RPM open throttle. That's just a general view but you get the picture. 9 to 1 is rich, 14 to 1 getting pretty lean on an air cooled motor.
 

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you may be 1 size rich on the main,,, with a t-jet,, the low speed jet should be close,,,

what size is the air bleed on the thunderjet? it should come I at around 4500rpm,,,
a large engine can use a 190-200 air bleed,,, bringing the t jet in later..
did the folks who did your thunderjet,,, do the full package? or just bore it and add the t jet..
I sometimes send a new G carb to zippers,, cost is in the $300 range for the full package,,,

as an example or 2
my modified S&S 113,, uses an 80 main, 35 intermediate with 3/4 turn out on the af screw,, and a 165 t-jet with a 200 or bleed.. it rolls like a CV no stutters sputters, just acceleration
another 117 S&S,, I also modified used a 32 low speed, 78 high speed, 165 tjet and a 175 air bleed

the 113 makes 137hp the 117 is in the 145hp range,,, and is just like mine,, smooth as glass and wicked quick.
 

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Discussion Starter #6
Thanks guys

How do I check the air bleed on the T jet?

Not sure what the full package would include but I sent him the G carb he board the throat and bored in the T jet, then put in rough guess of jetting.
 

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Discussion Starter #7
I had a couple hours between jobs yesterday so I watched a video from s&s on jetting and tuning which helped a bit but didn’t cover the thunder jet piece.

I also put on the larger filter Scott sent with the worked G. I’ve been putting it off looking for a backing plate to run the external breather kit I have plus I need an end cap. But I said F it and slapped it on. Looks like 10#s of sh*t in a 5# sac with that cover but it works. Hopefully it doesn’t leak between the filter and backing plate.

Anyway. Adjusted the AF mixture some and marked the screw so I can MSN’s sure it’s not turning in it’s own. This seems to have helped some but I think I need to spend more time and swap some jetting still.
 

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not sober all the time
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I watched a S&S video on tuning the Super E & G carburetor this morning. Tuning those isn't that much different in principle than the automobile carbs in the past. The A/F ratios they used are in the ballpark with what I did on my Road King except I'm a little leaner while cruising at light throttle. Interesting video.
 

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Discussion Starter #11
Jake you figure your air bleed size yet, should be on the left side of the carb above S&S Super.
No haha. I been looking at the dam thunder jet wondering what else there could be for air bleed size. What’s funny is I just watched that video again and the mentioned an air bleed in the spot to look st once the bowl is off. Some are fixed and some are replaceable ?

I think my G is the older style or it at least has the older style choke “T” handle not the arm lever you pull up so not sure if mine is a fixed size but I’ll pull the bowl this week. Took her on a 9 hour ride up the coast so letting her catch her breathe and my a$$ relax haha
 

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see the pdf I posted above tuning a tjet is not the same as a regular S&S carb, disregard that video. The original location you described above should now have a screw plugging that hole. The air jet is external in the location I described above. look at top left of S&S Super printed on side of carb, clearly visible if you look there.
 

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Thanks guys

How do I check the air bleed on the T jet?

Not sure what the full package would include but I sent him the G carb he board the throat and bored in the T jet, then put in rough guess of jetting.
The air bleed for the T-Jet is on the base of the jets main body. Look at the base, regardless of what color the body is, there will be a raw aluminum slice at its very base. There is at least one very small hole, that is the air bleed for the T-Jet. To change its size requires a set of very small drill bits.

Depending on your Super carb, the bleed for the main jet is either internal/fixed, internal/replaceable or external replaceable.

If the main jet air bleed is external, it will be on the rear portion (towards the back of the bike) of the carb looking at it from the side. The air bleed for the main jet uses jets with the same thread pitch as the T-Jet. Be careful as there are two very different types of jets that will screw into those holes and work, but they have very different numbering conventions. Some will easily get the too confused.
 

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get the instruction sheet for the thunder jet from zippers,,, it thoroughly explains how the tjet,, and the rest of the carb circuits work once the tjet is installed... read it nd understand it before you try tuning it like an unmodified super G.

my zippers carb had these mods..
throat bored
a bowl vent machined into the carb body,, the original vent plugged.
a
an air bleed installed,, and the original plugged.
a high flow needle and seat installed
thunder jet installed and bowl drilled for the fuel supply.
a few other mods but I dont remember..
I used a 5/16 fuel line and petcock..
 

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Discussion Starter #18

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basically
the low speed jet is 8ncreased in size and the a/f screw may only he less than 1 turn out,, as the low speed now supplies fuel to a higher rpm than a stock G

the main jet is brought in later,, by increasing the air bleed jet to a point where all the fuel from the main can be used

the thunderjet starts feeding by vacuum at around 4500 rpm.

the reason for all this is,, literally as soon as the throttle is opened on a stock G it begins pulling fuel through the main jet due to the small fixed air bleed,, and on large engines, to assure smooth running across the entire rpm range,, the low and mid range jetting is adjusted to feed the engine from idle through about 4500-5000rpm the thunderjet adds fuel above these rpm levels up to the redline of the engine...

the thunderjet and the air bleed are not connected in any way, in the carbs internal plumbing..

with only 2 jets you can tune for low to 4500,, but these large performance engines will go lean up on the big end,, seriously detrimental to long happy engine life,,, or, conversely if you tune for the big end the engine will run rich until it gets in the upper rpm range.. neither is conducive to having a quick revving powerful engine that pulls hard throughout the entire rpm range..

I hope this is helpful to you..
 

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Tune it completely off you AFR gauge. It's better to tune running down the road in real world time. Than it is to put it on some guys dyno with a set water grain. Altitude, air pressure. All of these things are a set number on a dyno. In the real world they are every changing. If you want to take your bike to a Dyno shoot out. Have it tuned on a Dyno. If you want to tune it for every day riding. Leave the AFR gauge on your bike and tune it by that gauge & that gauge alone!

The real question is. Do you still want the lock up pressure plate. I'm doing much better. I'm finally up & running after my Corotted arterie surgery.
Let me know Jake.
Lee
 
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