Pilot Jets?????

[tweeleft]

Ok So when is the need to change pilot sizes? 79SF,mac 4/1 exhaust,drilled airbox,142.5 mains. Back fires running off idle

[WMarshy]

After you run out of adjustment with your pilot needle screws. They control your mix at idle. If your poping at idle you could turn them out 1/2 a turn at first and see how that does. From there I wouldnt make more than a 1/4 turn adjustmen. If its been idling for a while, pull you plugs and check the color. Your going for a light brown / tan color on the insulator. If making adjustments doesnt seem to be doing anything, shut the bike off and take the pilot adjustment screw out to see if the tip is missing. Sometimes people tighten them too much and it breaks the tip off into the carb body and adjustments will not be affective...

Assuming the tip isnt broken, if you adjust the screw out to the point where they are about falling out, then its time to go up one pilot size. The '79 carbs had 42.5s in them, going to 45 would probably take care of it.

[tweeleft]

I sycned and colortuned, she doesn't pop at idle. Pops giving her gas after idle. More noticeable when riding. after a bit of coughing seem to clear towards wot

[TopCatGr58]

It does sound like it's still a bit lean, but what do the plugs look like??

ALso what are your floats set to....if stock 79 carbs...25.7mm but they stated +/- 1.00mm....you can richen it up a little with lowering the floats.

Even though you've colortuned it, thats just for idle! The pilots to contribute some to the throttle in the low to midrange throttle position before the mains start kicking in. That's why it was suggested to try turning the pilot jet screws OUT another 1/2 turn DESPITE what they colortuned to.

IF the screws are close or more than ~3.5 turns out then it's suggested to go up another pilot jet size.

T.C.

[motoman]

It does sound like it's still a bit lean, but what do the plugs look like??

ALso what are your floats set to....if stock 79 carbs...25.7mm but they stated +/- 1.00mm....you can richen it up a little with lowering the floats.

Even though you've colortuned it, thats just for idle! The pilots to contribute some to the throttle in the low to midrange throttle position before the mains start kicking in. That's why it was suggested to try turning the pilot jet screws OUT another 1/2 turn DESPITE what they colortuned to.

IF the screws are close or more than ~3.5 turns out then it's suggested to go up another pilot jet size.

T.C.

Hmmm........guess it would be lowering with carbs upside down.........otherwise .5mm raised, if that is the issue when checking them.

[tweeleft]

Thx guys I'll give that a try(idle screws) before I pull the carbs and do a wet float level check. The plugs were dry black and sooted so I'm thinking too rich? Will let you know

[TopCatGr58]

Aha...the plot thickens!

Black and sooty! Sounds familiar! You haven't specified WHAT type of Pilot jets you have. This bike is NEW to you, so you may not know what the PO did or put in the carbs. We have found that some aftermarket..ie. K&L brand pilot jets....non-Mikuni are the wrong style/size....the metering orifice is way too large vs. what is actually stamped on the jet...and they WILL cause excessive richness. Another identifying item for these jets aside from the fact that do NOT have the Mikuni diamond mark, is that they have 8 vent side holes instead of 6. Would suggest IF you don't know for sure what Pilot jets are in there to pull the carbs and inspect, and change to Mikuni.

Thanks Motoman....yeah...UPSIDE down view for lowering float=raising them which will richen....but suggest he investigate the pilots first with this new finding=plug color!

T.C.

[tweeleft]

Ok carbs coming out soon, and i thought it was suppose to be 6 holes not 8 thx

**Edit...you're right, my CRS getting to me...I editted my post above to correct info.! T.C. **

[WMarshy]

There are a lot of resources for reading plugs, just google it. There is a nice detailed on from a small engine aircraft web site thats floating around here somewhere but I cannot find it... here is one I came across that seems to have good info (probably more than the average person needs).

http://i577.photobucket.com/albums/s...eadingJPEG.jpg

[TopCatGr58]

Or even on our site: http://www.xs11.com/forum/showthread.php?t=2712

[WMarshy]

Or even on our site: http://www.xs11.com/forum/showthread.php?t=2712

Thanks TC, didnt realize we had one. Should have checked... take a look at the link I posted. It might be worth addimg to our tech tip..? I got it from a racing forum where a guy took tech info from a few good sources and combined it into one visual... the only dowbside is its on photobucket so if it ever went away we'd never be able ro recover it. JAT

[tweeleft]

Thx Guys I'm hoping to get to work on it today. We'll see. That 61 wife may have other ideas lol. Will tell of the outcome

[tweeleft]

Ok PO has 45 pilot jets. Going shopping Monday for 42.5 mikini BS30/96's

[spayne83]

Sorry to threadjack, but I just tried to sync my carbs and screwing out the idle mixture screws didn't change the vacuum at all. I did not have a tach hooked up but I had the idle set so the bike would run without stumbling. I was able to sync using the sync screws on the butterflys. My question from reading this thread is does the lack of change from the idle mixture screws indicate that I need bigger pilot jets? I have pod filters and a 4-2 exhaust.

[WMarshy]

Sorry to threadjack, but I just tried to sync my carbs and screwing out the idle mixture screws didn't change the vacuum at all. I did not have a tach hooked up but I had the idle set so the bike would run without stumbling. I was able to sync using the sync screws on the butterflys. My question from reading this thread is does the lack of change from the idle mixture screws indicate that I need bigger pilot jets? I have pod filters and a 4-2 exhaust.

More likely that your pilot screw tips are broken off in the carb body... Take the screws out and look at the tip to see if its still intact. If/when you tighten the screws, only go lightly seated as the tips are fragile.