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Has anyone tried tuning slow jet circuit?
So, now that I've got the bike running at I would say 97% perfect...I'm starting to think about these carbs and setup and the possibility for improving drivability.

All bikes seem to be set up lean for emissions purposes. On my previous bike I had tons of lean problems with the new ethanol gas and all. So I remember going through the carb on that bike (yes that was a single carb bike). And I found upping the slow jet on that bike from stock to just one size bigger made a huge improvement on mid range (driving around town) drivability. It actually improved the gas milage on that bike too.

SO now getting back on track on the GL1200 :-@

I know the slow jet is a #40. I also know the mid range on my gl1200 is very "per-snickaty". LOL! I tune it in and within 3000 miles I need to tune it in again because you can tell it's getting out with lean pops though the carbs and lugging. As soon as I reset the carbs I'm good again for a while. I'm not sure if this is unexpected as I see in the service manual syncing and checks are expected every 5000 miles? HOWEVER, I've been thinking of my success on the midrange with a slow jet change out. Has ANYONE tried this on the GL1200?
The #42 slow jet is available from Honda.
I'm thinking of giving it a whirl but thought I'd ask here to see what others might of tired?

I've already improved acceleration with a tinny shim on the Main Jet Needle. However, I'm thinking the better way to do this is remove the shim and then change the slow jet because the slow jet has more overlap from idle to mid than shimming actually touches...(when reading the Kleihn Carb website tuning instructions and circuit diagram LINK: <!-- m --><a class="postlink" href=""></a><!-- m --> )

What's your opinion? I'd like to know... :YMBRINGITON:


P.S. on another topic what is the expected Pressure one wants to see Dry and Wet on a compression test on a GL1200?
#1 07-30-2010, 08:14 AM,
Maintenance: Compression Test GL1200

NOTE: The engine must be warm for accurate readings.

1. Disconnect plug caps and remove all four spark plugs.
2. Install a comp. gauge in the No1 cyl plug hole.
3. Turn the engine stop switch OFF, push the choke lever OFF.
4. Open throttle completely and crank the engine until the psi reading stops rising
5. Record the cyl number and psi, repeat for other 3 cyl
6. Compare to normal compressiom of 155-215 psi.

If compression is below 142
if there is a 14psi variation between cyl, there is a leakage at the valves, piston rings, or cyl head gasket
#2 07-30-2010, 01:54 PM,
THANKS for the Test Process!
#3 07-31-2010, 05:34 AM,
First off. What year is your wing? 84 and 85 had a #35 jet and 86-87 had a #40. I tried going to the web site you posted, but it says account deactivated. I am having problems with my 84 gl1200 staying in tune as well. I reset the floats after work and put the carbs back in. I got the old girl hot and began setting the idle drop. She ran like a dream for the first mile or so. After taking off from a stop sign I opened her up and she took off like a rocket. But then at the next sign she died and ran like crap! Now when I left at 7 am I had to keep a touch of choke on her or there was missing backfireing and no accel. When I left work at 3:30pm she ran a little rough but after a mile or so she ran better. I would not be aposed to upping the jet or jets one size from a 35 to a 36 or 40 to a 41. You would have to drill them out, I don't think they make those sizes. I have had a post on here for awhile but I am getting no replies or any suggestions!! I am also on 2 other sites with the same questions and get no answers. I thought here being a GL 1200 site it would be better.
If you try drilling them out, use fractinal drill bits. Find the one that fits in the jet, then use the next one up. I would have extra jets on hand incase you make a mistake. I still have my old ones so I would be covered. Let me kow what you decide.
#4 09-21-2010, 01:44 PM,
have you checked for vacuum leaks? i.e. propane method
#5 09-21-2010, 02:42 PM,
Carb tuning is an art and it takes a guy that has a lot of know how to do it right as in richening the slow jet will affect the main jet fuel delivery as well. Might be best if you leave the jets stock and work at making sure none of the jets are dirty, there are no vacuum leaks and the floats are set correctly. Even a dirty air filter will affect fuel mixing. If you can really make a difference in power with carb tuning and actually feel it without a dynomometer and an air/fuel meter then you are really special. At the least if you are going to play with the carbs you should do full throttle acceleration tests and read your plugs right after the run to see what color they are. Shoot for light tan, black is too rich, white is too lean. Good luck.
Ed (Vic) Belanger - 1954-2015
Founder of

#6 09-21-2010, 02:55 PM,
Shim your carbs.

That means installing a washer under all four main jets.

This will make the bike run much better at idle and is great for parking lot type riding.

Most common quote from a cager after killing a motorcyclist.

"I never saw him" instead of "I never looked for him".
#7 09-22-2010, 06:22 AM,
unionjack Wrote:Shim your carbs.

That means installing a washer under all four main jets.

This will make the bike run much better at idle and is great for parking lot type riding.

Yep, I did the shims. They do help. I might play with jetting over the winter when I don't mind if the bike is down for weeks on end. This is the first bike I've owned with multiple carbs so I'm thinking it will be alot harder to play with jetting than any of my previous motorcycles.

Shimming seemed to take away a lag that was there and the bike really is snappy off the line now. I just know on my last honda (A shadow - single carb). When I upped the slow jet it made a huge difference in a positive way how the bike handled. Now that tuning was done with the help of a forum and about 15 different people one who had access to a dyno. I still maintain the spreadsheet we made of the whole process (<!-- m --><a class="postlink" href=""></a><!-- m -->)

I was just curious if people have done any experimentation on the Wing. On most bikes upping the slow jet is always a plus because for emissions out of the factory the bikes are set up lean. Opening the slow jet helps both the main and idle circuits as well, I think someone mentioned that already. Might be worth playing with when I have time...

#8 09-22-2010, 07:06 AM,

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