Do I need to go up or down a Jet Size on 82 Xs400 Seca?

[flutterball]

Have a 82' Seca XS400, just changed the exhaust from the originals (rusted out dual pipes) to a new 2-into-1 MAG exhaust. At the same time I completed cleaned out my carbs and increased my jet size on both carbs up one number to account for the new exhaust.

Now since I added the exhauset while the bike runs fine, when I get to the 6000 RPM level it hesitates, and does not have the same pull as before.

My question is, should I go back to the original jets? or do I need to go up even higher? Not sure about others but I find it very hard to get the carbs out (rubber boots make moving it in and out very hard), so I would like to get it right versus trial and error.

(Other info that may be important: The Airfilter is the orginal, not changed but cleaned, this is the 12E version of the engine, not the older XS400 engine, the orginal jets were a different size for each side, so I just went up one size for each, therefor they are still different.)

Thanks in advance for any help, (Going to be taking a long trip next week 2000+km, so would like it to be running at tip top shape )

Mark

[johnsnownw]

Are you sure you have the mixture screws adjusted properly?

[dtmf]

does it just fall flat on it's face @ 6k and pick back up ? sputter and backfire ? any surging . have you cheaked the plug's for to lean or to rich?

[flutterball]

At 6k the bike bogs down then picks up after a couple of seconds, then it does pick up RPM's and speed but not the same power as before. Before the exhaust and jet change, the bike pulled strong after 4k and followed strong all the way to red line if needed.

Right after the change the bike did sputter and backfire, but that has all gone away after the initial day/ride, only have issues when the rpm's get to around 6k in any gear, not just 6th.

Going to recheck the plugs tomorrow (not home right now), what should I be looking for exactly (too rich would be black deposit I think, too lean would be?) Once that is determined what is next, is re-jetting the next step, or how else would I re-set the fuel air mixture on this bike.

Thanks again for all your help,

Mark

[johnsnownw]

If you haven't fiddled with the mixture screws on the carbs (top of the carbs) then I would say that is the culprit. However, checking your spark plugs is the best method to see exactly what's going on. Here's a chart to diagnose spark plug deposits:

http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm

[Ficky]

If you haven't fiddled with the mixture screws on the carbs (top of the carbs) then I would say that is the culprit. However, checking your spark plugs is the best method to see exactly what's going on. Here's a chart to diagnose spark plug deposits:

http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm

I would be trying a bit more air (slip the air cleaner boots off), it sounds like it is starving low preformance at high revs (free flowing exhaust, larger jets ,needs lots out more air in) if this makes sence. The way to check the plug is by doing a plug chop as its known, take the bike out warm it up get to the point it stars to choke up and kill the motor, stop bike rip out plug (take a glove hot) and look at plug if wet/black/sooty plenty of fuel, not burning due to lake of air,if dry and tan refer to Johnsnonw plug chart.

The fact it has differant size jets in each carhy sound strange I am no mot guru but this seems wrong did ya check a manual ?

Cheers Chris

[flutterball]

Chris, I will try to check the plugs as you stated, and see what that tells,

As for the jets the actual shop manual states it should be 115 right and 125 left, and that is what I had before changing my exhaust, so with the new exhaust I went up to 117.5 right and 127.5 left. In past forum topics (did a search) this was not really clarified why this engine has this, so I'm wondering if I should have gone to 127.5 on each side, or 125 right and 127.5 left (since right now I have only a limited selection of jets to work with, 1-115, 2-117.5, 1-125, 2-127.5 wont have time to get anymore since I'm heading out on my trip in a couple of days.)

Thanks again everyone for your help (thanks John for the chart on plugs), going to get this right eventually.

Mark

[dtmf]

Chris, I will try to check the plugs as you stated, and see what that tells,

As for the jets the actual shop manual states it should be 115 right and 125 left, and that is what I had before changing my exhaust, so with the new exhaust I went up to 117.5 right and 127.5 left. In past forum topics (did a search) this was not really clarified why this engine has this, so I'm wondering if I should have gone to 127.5 on each side, or 125 right and 127.5 left (since right now I have only a limited selection of jets to work with, 1-115, 2-117.5, 1-125, 2-127.5 wont have time to get anymore since I'm heading out on my trip in a couple of days.)

Thanks again everyone for your help (thanks John for the chart on plugs), going to get this right eventually.

Mark

i changed to same size for both carb's when i did my mod's "straght pipe's and podfilter's" after the change to a bigger jet size the side with the smaller jet's was way to lean. i then went to same size for both side's as i went up in size . i think the reason for the offset jet size was for emission's. ive got a bit of lag in the low rpm's cuz of the pipe's but it pull's up to 115 mph from 65mph fast

[akronevan2]

I have the same problem with mine with a few exceptions. I have stock everything, just had the carbs cleaned, air filter needs to be replaced (but isnt terrible yet), my hesitation begins at 4K and goes away at 5k. I've read that it is one of 2 problems, either the Air Filter or it is running too lean. When you figure yours out let me know so that I can do the same to mine. Thanks!