Page 1 of 2 12 LastLast
Results 1 to 10 of 13

Thread: Pilot jets are 1 size larger than spec on new-to-me bike - replace w/'correct'?

  1. #1
    Join Date
    Jun 2021
    Location
    St. Petersburg, FL
    Posts
    44

    Default Pilot jets are 1 size larger than spec on new-to-me bike - replace w/'correct'?

    Background:
    I just got what is (best I can tell) an '81 GS1100E. Seemed in need of a good tank flush and carb clean, which I am tackling now. Other than 40 years of crud and debris that has since been cleaned, everything looks in pretty great shape. I did however notice that the pilot jets were all marked 47.5, whereas per the factory service manual, and everything I can find online, the factory spec for these carbs is a 45 pilot jet. The motor and intake setup seems mostly stock, though exhaust may be aftermarket (?), the factory airbox/filter setup is used (no pod filters). Though some of the inlet holes in the airbox dont look factory, so maybe some were added? not sure what an original one looks like.

    Question:
    Short version: Is there any reason I should bother getting the "correct" 45 pilot jets, or should I just re-assemble with the (perfectly fine looking) 47.5 jets that were in there (since it seemingly ran fine before, and its not a big difference anyways)?

    Longer version: I know the pilot circuit controls at idle and just off idle, and my gut tells me that being one size larger is probably not going to make much of a difference, and if it did, it could be adjusted out using the air screw. But I don't have much experience with 4-gang carbs on inline 4s (mostly messed with thumper enduro/dirtbikes up to now) so maybe I'm off base. Was told bike ran/drove fine before sitting (friend of family who gifted me the bike, no reason not to believe him), is in overall good shape, just lots of scale/rust/debris in tank and carbs, junked up petcock etc. The carbs look like nobody has been inside them before too, screw heads were clean OE JIS screws, no signs any of the jets had been removed before, factory plugs were still in place over the air screws, etc. Really seems like this rack of carbs came assembled with the 47.5 jet. The carb body code matches what the book says is correct for this bike (49200), but maybe they came from a different bike at some point? But other than being curious of how it got this way, my guess is theres not going to be any issues running with the pilot jets that I pulled out of there.

  2. #2
    Join Date
    Dec 2014
    Location
    In the doghouse, usually.
    Posts
    467

    Default

    Usually, there is no reason to increase the size of the pilot jets. Even if you remove the airbox and install pods, the throttles are the limiters at low speed, so there is no increase in air volume that needs to be compensated with larger pilot jets.

    The only thing to consider is that you might need to turn the pilot screws (NOT "air screws") in a bit more. What you are calling "air screws" actually control a mixture that is pre-set by the pilot air jet and the pilot fuel jet. The screw controls how much of that mixture is added to the air stream at low throttle openings. Some here call it a "mixture screw", but Suzuki calls it a "pilot screw". Turning it OUT (anti-clockwise) will richen the mixture, turning it IN will lean the mixture.

  3. #3
    Join Date
    Jun 2005
    Location
    Norene TN
    Posts
    4,189

    Default

    These bikes were pretty cold natured, in my neck of the woods we would install a size or 2 larger pilot, just to get it started & going a little quicker. Have since been told we weren't accomplishing anything, but it sure seemed to start & get going better with less choke. One size larger pilot sure ain't going to hurt anything.
    1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

  4. #4
    Join Date
    Feb 2018
    Location
    Davis,CA.95616
    Posts
    651

    Default

    I would leave the 47.5's in for now and if needed,fine tune the mixture screws a bit leaner,imo.

  5. #5
    Join Date
    Jul 2011
    Location
    Oklahoma
    Posts
    2,821

    Default

    IME, most Japanese bikes of that era were jetted on the lean side, particularly in the low speed circuits, for emissions reasons. One step up on the pilot jets was the standard fix.

    Disclaimer: I have no experience with that exact model.
    Rich Desmond
    1980 GS1000S
    2007 V-Strom 650
    2008 Ducati 848
    2002 DR-Z400S
    1999 SV650 (race bike)

  6. #6
    Join Date
    Jul 2009
    Location
    New Zealand
    Posts
    3,442

    Default

    Quote Originally Posted by RichDesmond View Post
    IME, most Japanese bikes of that era were jetted on the lean side, particularly in the low speed circuits, for emissions reasons. One step up on the pilot jets was the standard fix.

    Disclaimer: I have no experience with that exact model.
    Correct. And an aftermarket pipe usually made things worse. Leave it as is until you've put some miles on it.

  7. #7
    Join Date
    Jun 2005
    Location
    Norene TN
    Posts
    4,189

    Default

    Just noticed this is your 1st post... Congrats, Welcome, & "WE REQUIRE (or enjoy) PICTURES.
    1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

  8. #8
    Join Date
    Nov 2019
    Location
    spring hill florida
    Posts
    1,298

    Default

    In my experience with my bike, I upped the pilots from 42.5 to 45 and i noticed that the bike was louder at idle and my plugs would be fuel fouled with any amount of turns on the mixture screws. But I guess since the bike isnt done I cant say it was directly because of the jets sizes.

    If you have a smooth idle, reaction, and not a huge difference of power when the pilot circuit switches to its next circuit, I'd say its fine. I know with my bike it was running like complete crap and then would send you off when it hit the next set of jets. Terrible for stop and go stuff lol.

    An exhaust should never affect the jetting on a bike since the amount of air flowing in doesnt change.
    Ian

    1982 GS650GLZ

    Want a "twin" for my bike

  9. #9
    Join Date
    Jul 2011
    Location
    Oklahoma
    Posts
    2,821

    Default

    Quote Originally Posted by timebombprod View Post
    ...An exhaust should never affect the jetting on a bike since the amount of air flowing in doesnt change.
    ?? A good aftermarket exhaust will usually flow a bit more more air than the stock exhaust. Not a big difference typically, but often enough to require a small jetting change.
    Rich Desmond
    1980 GS1000S
    2007 V-Strom 650
    2008 Ducati 848
    2002 DR-Z400S
    1999 SV650 (race bike)

  10. #10
    Join Date
    Jun 2021
    Location
    St. Petersburg, FL
    Posts
    44

    Default

    Quote Originally Posted by rphillips View Post
    Just noticed this is your 1st post... Congrats, Welcome, & "WE REQUIRE (or enjoy) PICTURES.
    Thanks for the welcome. Didn't think to snap any pics of the bike before pulling her apart, so here's how she looks now. Please forgive the mess of a garage, I am in the process of moving in, and of course garage is staging point for most of the junk:

    PXL_20210621_153027538-a.jpg

    Not much to look at right now, but she actually is pretty nice looking when assembled. Generic "cafe" style with clubman bars, round headlight, 'rocket' style mono seat (you can see it resting on the table behind the bike there) with a pretty nice red paintjob on frt fender, tank side covers & seat. The wiring/electric looks mostly factory at a glance, so likely going to do the charging system checkout/fixes while I have it apart, and address any other suspect areas. Otherwise she is in pretty good shape for a 40-yr-old bike. Everything seems to work as it should, and while its not pristine the wear/tear/corrosion is less than I'd expect on a bike this age. The 'custom' work to install the seat isn't the most elegant, but its not terrible or some unsafe hackjob. All in all I'm excited to get her on the road.
    Last edited by RocketScientist; 06-21-2021 at 11:49 AM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •