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Jet identification help

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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I am diagnosing what seems to be a lean condition on my 82 Katana. It pops on deceleration, takes a long time to warm up, and sometimes the idle will take a while to settle down when coming to a stop. The motor is all stock and has the CV carbs, individual K&N pods, and a Kerker pipe with a new baffle. I think the carbs are all stock, don't see any notches on the needle for adjustment a la Dynojet (many years ago I put a kit in an 1100E).

I am trying to determine if any work has been done to the jetting though, I see that the main jet size is 107.5 stock. I see on my jet a letter R and number 145. It can be seen in the pic:


jet.jpg
 
For pod's/pipe, you have to re-jet all three circuits.
The size of your main jets looks about right.
The slow warm up and decel' popping means you need to go up on the pilot jets, but you may be lucky and only have to adjust your mixture screws out an additional turn or two. If the pilots jets/mixture screws settings have been increased correctly, then your pilot circuit is dirty. Popping can also be caused by loose exhaust gaskets.
Your stock jet needle will make the bike run very lean just off idle to 3/4 throttle position. If you don't install the adjustable needles, you need to shim up the needle with spacer(s). Don't overlook the needle circuit. You spend the most time riding on this circuit. It's actually the most important.
Jet kits also will tell you to drill out the vacuum orifices to the diaphragm chambers to increase throttle response. Also, remove the two floatbowl vent lines for better venting.
 
Not to hyjack this tread but Kieth, what is a good pilot jet size for pods and pipe to work well? I have a 138.5 main and a 40 pilot. I think the air jet is 180. Isn't the 40 pilot a stock size?
 
Jethro said:
Not to hyjack this tread but Kieth, what is a good pilot jet size for pods and pipe to work well? I have a 138.5 main and a 40 pilot. I think the air jet is 180. Isn't the 40 pilot a stock size?
Click to expand...
I'm not positive about your stock pilot jet size. 40 sounds right.
Re-jetting all depends on how it's performing. You could try just mixture screw adjustments (not likely), a step up (2.5) with mixture screw adjustments, or a full size (5). Depends on the brand of pods/pipe.
 
I've got a Mac 4 into 2 into 1 canister and K&N pod filters. It's a little slow to respond off the line and I don't think I have air leaks.
 
For jet identification we've always relied on "Jane's".
:lol:
 
Jethro said:
I've got a Mac 4 into 2 into 1 canister and K&N pod filters. It's a little slow to respond off the line and I don't think I have air leaks.
Click to expand...
Regarding your pilot jet question, I'd probably try a full size up on the pilots and tinker with the mixture screws if needed.
"A little slow to respond off the line" is opening the throttle. So this involves the jet needle too. From slightly opened to nearly 1/4 throttle, both circuits overlap each other. If your carbs/filters are clean and carbs synched, then slow warm ups and idle/lower speed problems are probably because of your stock pilots. If "slow to respond..." means opening up the throttle closer to 1/4, then any mixture problems is most likely the jet needle position. CV carbs are supposed to have their vacuum orifices to the diaphragm chambers drilled out larger to improve throttle response also.
 
Thanks Keith and others, good info. I have exhaust gaskets on order- the ones in there are shot, I found out. Carbs will get a good clean and I'll look into the pilot jet size. I tried backing out mixture screws before to little avail. I don't think the needles I have are adjustable but may be wrong.
 
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