Carb Questions

[chef1366]

I have a 1980 GS 1100 L, 4-1 kerker pipes, stock air box without lid, windshield and a 300 pound rider. The bike starts great, has good midrange but not very clean with higher rpms. I'm getting about thirty miles a gallon. The bike pops on deceleration and I have blue pipes which tells me I'm running a bit lean but my plugs look good. The bike does not run unusually hot because I don't get the cool down ticks and pops but I do have an oil cooler. Have not torn the carbs apart yet so I don't know if it has been rejetted. I have purchased a filter box lid and a k&n filter for the air box. I have read prior posts on jetting and have figured I need to go with a 112.5 main jet. I have used this site for suggestions and methods for many repair jobs and respect the insight of the members that have already been through this situation and I would appreciate any now.

[SqDancerLynn1]

4 into one Kerker pipe should work fine, it is thin walled tubing, some Blueing is normal. Have you checked the spark plugs ??? In the upper RPM range what happenes if you add a little choke does it get better or worse

[chef1366]

It smooths out a little with the choke on, but not a real noticable difference (except for braking The plugs are fine. I'm happy with the low and mid range so I think there might be a problem with the main needle adjustment or the main jet size. Is my gas milege normal?

[chef1366]

Am I getting little response because I'm on the right track?

[Road_Clam]

Re: Carb Questions

I have a 1980 GS 1100 L, 4-1 kerker pipes, stock air box without lid, windshield and a 300 pound rider. The bike starts great, has good midrange but not very clean with higher rpms. I'm getting about thirty miles a gallon. The bike pops on deceleration and I have blue pipes which tells me I'm running a bit lean but my plugs look good. The bike does not run unusually hot because I don't get the cool down ticks and pops but I do have an oil cooler. Have not torn the carbs apart yet so I don't know if it has been rejetted. I have purchased a filter box lid and a k&n filter for the air box. I have read prior posts on jetting and have figured I need to go with a 112.5 main jet. I have used this site for suggestions and methods for many repair jobs and respect the insight of the members that have already been through this situation and I would appreciate any now.

A few comments, bluing of you pipes, can mean a lean condition, OR it can also indicate an overly rich condition. Your main jet is only a factor at 3/4 throttle and above. The most impactive adjustment you can make for average driving and accelerating is your needle clip position. This affects 1/3-3/4 throttle behavior. Maybe your main jet is right on target, but your needle clip position is set too lean. You need to pay close attention to exactly where in the powerband, and exactly how the engine is behaving to make the proper carb adjustment. Lean conditions the engine will hold back and buck like its needs more fuel. Rich will yield smooth, but real slow acceleration (like leaving your choke on) Good luck,
Rich

[chef1366]

K&L Carb Kit

I purchased 4 K&L carb kits. It came with 2 main jets (107.5 and 115). 2 air jets (160 and 170). 2 pilot jets (45 and 50). I did purchase 112.5 main jets from Dennis Kirk. I was planning on going with the configuration I stated earlier. (4-1 kerker, K&N filter in air box) The 112.5 main jets came from the "Jetting Recommendations by Denny Zander". Now I'm interested in drilling the air box and putting in the 115 main jets. It also stated I had to step up one size pilot jet. Do I have the right Pilot jet in the kit for this? If 45 is the stock pilot do I need to purchase a 47.5 pilot jet? Also does anyone have a pictutre of a drilled air box or a good explanation of how to do this? 160 is the stock air jet do I keep this the same? I also purchased the o-ring kit I found thanks to this site.

[chef1366]

Quick directions on how to drill an airbox for a 1980 gs 1100 LT. Please

[chef1366]

The carbs are apart and I have a 117.5 main jet, 47.5 pilot jet and a 170 air jet. For a stock motor and running with no air box lid and 4-1 Kerker pipes does this look like too big a main jet? Could this explain my high end troubles. Can you repair pinholes in the diaphramg without spending eighty dollars apiece for new ones? Should I keep the same setup because the diaphragms could of been my trouble? I also bought 47.5 pilot jets just in case.

[chef1366]

Bought some used carbs and used the diaphragms. Put the carbs together with the 47.5 pilot jets, 117.5 main jets and 170 air jets. Put them on the bike and fouled the plugs at idle while adjusting the air screw. The bike was running rich, all plugs were black and dry. I could hit the throttle and clean the plugs enough to idle smooth for few minutes and then it would run rough. The air screws made little or no difference when adjusting. I am going to try 45 pilot jet, 112.5 main and 160 air jet. Why would it foul plugs after the rebuild of carbs and not before with the same set up? It idled fine with the 47.5 jets. With the rebuild including the o-rings could this increase the gas flow enough to cause this?

[KEITH KRAUSE]

I wouldn't drill holes in the airbox. If you must modify it, removing the lid will be best.
I suggest you install the lid and then re-jet for the pipe and K&N filter.
Reading back, you have more than one problem. Decel' popping is a lean condition, possibly an intake leak or lean jetting. 30 mpg is poor though and suggests a rich mixture as do the sooty plugs. Poor top end can be either. You can have both lean and rich problems. It also depends on throttle position and which jetting circuit you're using. You could also have other things contributing to the problems. Poor valve adjustment, weak spark, incorrect timing, carbs not cleaned correctly, float levels off...
I'm not sure what you've done so far to fix it. You say you've rebuilt the carbs and replaced diaphragms. Are the o-rings new? Are the manifold o-rings new? Are the manifolds in good condition? Did you check/adjust float levels? You should also check the entire diaphragm/piston assembly for correct assembly order. No missing/incorrectly assembled spacers, etc, when compared to an illustration? What are the stock jet sizes for this model?
Have you checked the timing and spark quality? Valves adjusted? 5/16" fuel line? Floatbowl vent lines clear and not kinked? Plug leads in good condition? Basics need checking before trouble shooting.
Also, did the bike just start having problems or did you get the bike this way? Any other symptoms? Idling at about 1,000 rpm's cold AND hot? Dark exhaust during acceleration? Pinging?
Let us know what has been done correctly and we can focus on what remains. Really need stock jet sizes to suggest re-jetting for your mods.

[chef1366]

Thank you for responding. Stock jet sizes "main 107.5" "pilot 45" "air 160". I do have a 5/16 fuel hose, float adjustment is good, timing and ignition are good, did valve adjustment, new o-rings, intake and airbox boots, dipped carbs and blew out with air, used stock jet needle with diaphragms and all parts are present, 140# compression on all cynlinders, k&n air box filter with lid and 4-1 kerker pipes. Carbs had 117.5 main jet, 47.5 pilot jet and 170 air jet. Was running stock air box with no lid. Do you think with the increase in jet sizes that the bike might have been modded in some other way "cam, bored cylinder ect..."

[KEITH KRAUSE]

Don't know about any other mod's but those jetting changes would be "ballpark" for that pipe and NO LID. I would probably have tried the same pilot jet and air jet but actually larger on the main.
With the LID ON and the filter the only mod to the airbox... and the pipe, I would try the 117.5 mains and test.
I would try the stock 45 pilot jet in combination with richer mixture screw adjustment before going up on the pilot jet. Don't know where the screws were but I'd try an additional 1/2 to 1 full turn from where they were or try adjusting using the highest rpm method. They are generally 1 1/2 to 2 turns out on a stock bike.
As for the air jet(s), there's two. A primary air jet and a pilot air jet. Your kit supplies the primary air jet. Going up to 170 would be to match the 117.5 mains. You need more air to better atomize the extra fuel. On paper it seems the sensible change for the main circuit and to a lesser degree, the jet needle.
The pilot air jet needs to be checked to be sure it's clean.
Are you SURE you measured the floats at the correct point??? Where did you measure? I have to wonder if the PO could have changed jet needles or needle jets, though that's not as common as the other jetting changes. Were there any "shims" to raise the jet needles?
Stock heat range plugs?
If everything (basics) has been done right, I would try the stock 45 pilots with mixture screw adjustments. As for the main/jet needle circuits, I'd stay with the 117.5 mains and 170 air jets and test/chop the bike at full throttle and 1/3 throttle positions and check the performance/plug reads. You need to separate the circuits to see what each is doing. Mark the throttle housing and grip to be sure. Can you do high speed tests?
Be sure to answer all questions to help fix your problems.
Not sure how much this helps but I'm just saying where I'd start if the bike were here.

[chef1366]

Got the bike running and synched the carbs. Had trouble with the pilot air screws. They are 1/2 turn to 1 turn out to obtain optimal idle. Went with the 47.5 pilot jet, 117.5 main jet and 170 air jet. Runs great mid thru high but now I'm running rich on the idle. I think I'm going to try the 45 pilot jet but man I've had these carbs on and off at least eight times. I'm going to ride it a few days and see if the plugs hold up. It's like having a new bike, smooth acceleration from start to finish, strong throttle even after 85 mph. I think I'm going to purchase a color tune. Do you know the best place online to get one?

[KEITH KRAUSE]

Glad it's running better.
I don't know why you left the 47.5 pilot jets in though. Your previous post said it fouled the plugs while idling with the 47.5's The stock 45's should fix this, along with some mixture screw adjustments.
Also, I'm not sure why the bike is running better mid to high speeds now. Same jetting but maybe the diaphragms you replaced?
Like you say, take some time off from the carbs, if they'll let you.
I still suggest the throttle tests/plug reads though. It may not be what you want to hear but you may be lean on the jet needle circuit because you've done nothing to richen the jet needles...unless the PO made changes we don't know about. You spend the most time riding on this circuit so it's important to get it right. It depends on how that Kerker effects mid-range though.
Let us know how it goes and if you need help.

[KEITH KRAUSE]

Oh, and I've never looked for the Colortune product. Some members here own it.
Maybe make a new topic requesting info?