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Discussion Starter #1
I am sure everyone has totally opposite opinions on this. I haven been finally able to start sorting out the tune on my Evo BigTwin with a CV40 on it but I am kind of lost with some jetting suggestions. It seems people run really wacky jet combos or jetting that seems rather insane such as 50 pilot with a 165 main jet or a 42-195...

I have a 46 pilot with a 180 main jet. It seems totally solid down low but I don’t know if the top end is that good or if I’m getting a placebo effect or if I am interpreting the tune well enough but it feels pretty right on without any surging or popping/pinging

Running a Tear drop air cleaner, Ev27, with stock exhaust, rest of it is stock as well. I know when I had the XL it seemed like it was pretty cut and dry on what to use but with the Evo big twins the suggestions are all over the place, even from the manufactures books from what I understand. What is a solid main jet to run with an I modified carb?
Thanks,


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What needle, and is the rest of the carb stock?

And remember, they jet from the bottom up. Add fuel with the mix screw adds fuel for the whole range. Adding slow jet adds fuel from off idle all the way up. Fast jet adds fuel on the upper end only. The needle trims fuel through the mid range.

On carbs that wont jet in the normal range, the needle is usually the cause or the slide has been drilled. or the emulsion tube does not match the needle.

OEM needle range is 180 fast 42>45>48 slow depending on what oem needle it is. And you can trim on the needle with shims, up to about .o6o max. No Cali needles allowed.

The hot over the moco counter set up was the 27094-88 (N65) needle and 165 fast, and the 45>48 slow jets. Then cut one coil off of the slide spring.

All of theses asumne that the float is set corectly, and the slide is free to move. And the pet cock will deliver a steady stream of fuel. No filters in the hose.

If you think it might have aftermarket needles emulsion tubes, springs, etc and you don't know exactly what they are. Throw them out and start over. This little kit from CVP will be money well spent.

https://cv-performance.com/cvp-harley-carb-deluxe-tuners-kit

When you have it close, the mix screw should be about 3 turns out from lightly seated. And it should change idle speed with a turn in or out. If it wont, then something is wrong. Vacuum leak, plugged transfer port. or needing too much idle speed screw to idle. At idle the blade should not uncover the first transfer port. If it does, you'll need to drill the bypass hole in the blade to a larger size.
 

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Discussion Starter #3
What needle, and is the rest of the carb stock?

And remember, they jet from the bottom up. Add fuel with the mix screw adds fuel for the whole range. Adding slow jet adds fuel from off idle all the way up. Fast jet adds fuel on the upper end only. The needle trims fuel through the mid range.

On carbs that wont jet in the normal range, the needle is usually the cause or the slide has been drilled. or the emulsion tube does not match the needle.

OEM needle range is 180 fast 42>45>48 slow depending on what oem needle it is. And you can trim on the needle with shims, up to about .o6o max. No Cali needles allowed.

The hot over the moco counter set up was the 27094-88 (N65) needle and 165 fast, and the 45>48 slow jets. Then cut one coil off of the slide spring.

All of theses asumne that the float is set corectly, and the slide is free to move. And the pet cock will deliver a steady stream of fuel. No filters in the hose.

If you think it might have aftermarket needles emulsion tubes, springs, etc and you don't know exactly what they are. Throw them out and start over. This little kit from CVP will be money well spent.

https://cv-performance.com/cvp-harley-carb-deluxe-tuners-kit

When you have it close, the mix screw should be about 3 turns out from lightly seated. And it should change idle speed with a turn in or out. If it wont, then something is wrong. Vacuum leak, plugged transfer port. or needing too much idle speed screw to idle. At idle the blade should not uncover the first transfer port. If it does, you'll need to drill the bypass hole in the blade to a larger size.


Yeah the whole carb is stock except the pilot (46) and main jet (180). It seems pretty flawless in operation. It had a 42 in it when I bought it and that made it really really cold blooded... as well as spark plugs with really narrow gaps, I regapped them to what my manual said .040 inch... Was looking for more validation that it seems in line with what is normal, as well the plugs seem okay but I haven’t chopped one to see the main jet ring. It is Kind of hard to stomach the cost of a Dyno Tune... maybe one day I will. Just hard to pay for one while feeling like a year from now I might change something. I feel pretty okay After finding a Dyno tuner who said that my main jet seems okay for the setup I have.


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Biggest improvement on my 1991 was changing to the N65 needle. It was then easy to jet from there. Was able to get almost all the low rpm farting out of the carb which was my biggest problem with the stock needle. Was able to drop my low speed jet from a 48 down to a 45. Believe my high speed jet ended up being a 180. Was running a 190 or 195 with the stock needle. 2 3/4 turns on the air fuel mixture adjustment. Could probably drop the main a little more (put in smallest I had) but sparkplugs are cheap compared to a hole in a piston.
 

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Yeah the whole carb is stock except the pilot (46) and main jet (180). It seems pretty flawless in operation. It had a 42 in it when I bought it and that made it really really cold blooded... as well as spark plugs with really narrow gaps, I regapped them to what my manual said .040 inch... Was looking for more validation that it seems in line with what is normal, as well the plugs seem okay but I haven’t chopped one to see the main jet ring. It is Kind of hard to stomach the cost of a Dyno Tune... maybe one day I will. Just hard to pay for one while feeling like a year from now I might change something. I feel pretty okay After finding a Dyno tuner who said that my main jet seems okay for the setup I have.


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If you're looking for more out of than EV 27, then a good spark box would be next up. Only so much you can do with jetting when running that lazy spark curve.
 

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Discussion Starter #6
If you're looking for more out of than EV 27, then a good spark box would be next up. Only so much you can do with jetting when running that lazy spark curve.


Haha. I think everything about the Evo big twin was lazy; low compression, I honestly laughed at the n-grind cam when I pulled it out, duel fire ignitions, and many others.

I honestly don’t have any information on the timing on Evo Big Twins other than if it is like anything else with the bike then it is most likely very lazy as well. What’s the recommendation?


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