Lore of the #20 Pilot

Maintenance, repair, troubleshooting, etc.
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radare
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Tue May 30, 2017 8:45 am

I appreciate the information, Sleek. My bike actually runs great through the entire range except for an off-idle bog which I am still diagnosing. We have such a varied elevation profile here in the US that understanding the jet sizing for stock XJ's is important so that we stop making the blanket #20 pilot jet recommendation. I have my Wideband A/F set up to data log while riding and I plan to take it out on the Scrambler over the next few weeks and better understand the fueling in the inner-cylinder carbs. I suspect I have a transition issue where the mixture is changing drastically when the butterfly opens. Still understanding the root of the problem.
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draco751
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Sun Feb 25, 2018 1:03 am

radare wrote:
Tue May 30, 2017 8:45 am
I plan to take it out on the Scrambler over the next few weeks and better understand the fueling in the inner-cylinder carbs. I suspect I have a transition issue where the mixture is changing drastically when the butterfly opens. Still understanding the root of the problem.
Did your testing ever yield any results? Since spring is right around the corner here I've been gearing up to put the XJ back on the road as it's been too long. The thread here is great and quite informational. I'm now trying to factor what settings I should be running myself here in Orlando.

The rack of carbs I have currently on the bike have the DynoJet Stage 1. (Mikuni #20 Pilot, DynoJet #98 Main, and a recommended clip position of #3 per the instructions.) Reading this thread here really has me second guessing the DynoJet #98 mains that came with the kit along with the clip position. DynoJet numbers from what I've researched are not the same as Mikuni. DynoJet uses diameter sizes where as Mikuni uses flow rate numbers and I've yet to find a crossover chart that's accurate enough to tell me if where I sit is right or not so I'm simply going off what the instructions say.

Given I'm at 98ft above sea level and temperatures here in Orlando range from 75-95 degrees Fahrenheit on average I feel I should move back to Mikuni 102.5 on the main jets but I'm really not sure about the needle clip position and hole the kit had me drill on the slide to widen per the instructions. As for modifications I have only installed a K&N air filter, the exhaust is still factory with no plans to change that. I have a spare rack of carbs with all factory parts on it but if you were to suggest a second opinion what would you do in this situation?

I'm still awaiting a response from DynoJet that I proposed to them regarding jet sizing and needle information. The package this kit came with along with the instructions seen below are quite old. As it stands right now the bike runs okay, but there's a bit of hesitation in a spot or two I'm still trying to figure out how to define better. I have a feeling I'll need to pull the diaphragms and needles to compare stock vs DynoJet's #3 position on their needle.

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Slartibartfast
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Sun Feb 25, 2018 2:46 am

found this interesting to read, I'm not sure how I missed this thread before.

my XJ is currently running stock carbs as far as I'm aware; I live (and work) virtually at sea level, to within a couple of hundred feet at most.

so I'm guessing that I should probably be running #20 and #102.5 jets? Vs standard of #17.5 and #100?

I got a spare set of carbs that are almost fully assembled, I think I should use these as a project. I've never dismantled carbs so have the ideal opportunity to have a go at no risk.
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mikee112
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Sun Feb 25, 2018 1:10 pm

Slartibartfast wrote:
Sun Feb 25, 2018 2:46 am
found this interesting to read, I'm not sure how I missed this thread before.

my XJ is currently running stock carbs as far as I'm aware; I live (and work) virtually at sea level, to within a couple of hundred feet at most.

so I'm guessing that I should probably be running #20 and #102.5 jets? Vs standard of #17.5 and #100?

I got a spare set of carbs that are almost fully assembled, I think I should use these as a project. I've never dismantled carbs so have the ideal opportunity to have a go at no risk.
This whole thread is for the American spec carbs Jim, Euro carbs are fine with the stock setup :)
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radare
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Sun Feb 25, 2018 2:06 pm

Sorry I never followed up, Draco. I installed 17.5 pilots in both of my XJ's. That gives #100 mains and #17.5 pilots. I left stock needles and set the pilot screws using the A/F gauge, running them slightly rich at idle.,

The results were quite positive for the Scrambler (which has a stock induction system). With some tweaking of the pilot jets, I was able to lean out the plugs to where they were clean and also eliminate completely the horrible off-idle bog.

The results were less positive on the Black/Red one. It has an aftermarket exhaust. I noticed that the bike feels like it's lean at speed with a noticeable reduction in power during acceleration. To be fair, I didn't tune its pilot jets since I don't have O2 bungs on that exhaust. I plan to swap over the exhaust with those bungs, tune the carbs and see if the results improve.

Bear in mind, my bike is always at or above 5000' in elevation so this impacts its performance and fueling requirements.
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Slartibartfast
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Tue Feb 27, 2018 9:59 am

mikee112 wrote:
Sun Feb 25, 2018 1:10 pm
This whole thread is for the American spec carbs Jim, Euro carbs are fine with the stock setup :)
Sweeeeet, one less job to do!
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