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Gs 450l pilot screw help

  • Thread starter Thread starter Swim_fan02
  • Start date Start date
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Swim_fan02

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Hey guys. I'm have a little issue with the carbs still. I'm running straight through pipes and stock airbox. I'm not really getting the throttle response I should be getting at half throttle. Carbs are clean and everything is is great running order. The bike runs good but not great. I'm pretty sure I need to back out the pilot screws a hair to increase the fuel a touch but I'm not exactly sure where they are located and don't want to drill out something that isnt it. If someone could please explain in detail where these damn screws are I would aprreciate it greatly. Pictures would help a lot too. Thanks in advance.
 
I don't believe the pilot screws have any effect at half throttle.
 
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you run the risk of burning up valves or otherwise destroying your engine by running a modified exhaust without properly adjusting your carburetors.

Properly figure out the circuits on your specific carb and adjust them. Don't try to run the bike witout making the necessary adjustments.

Edit: In other words what I am saying is that you aren't approaching the problem correctly. Changing the exhaust typically isn't a small adjustment on the pilot circuit and you are risking your engine by thinking it is. Somebody else with your bike will have to give guidance on the specifics of what you will need to adjust.
 
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What year 450?

I'm going to assume you have CV carbs, and you need to get some idea of how the jetting is.

You'll need to do plug chops at the various throttle openings to work it out.

CV carbs need to be jetted from the mains down, ie. make sure mains are good at WOT, then check needles at 1/8, 1/4, 1/2, 3/4 throttle, then check pilots and mixtures screws at idle.
 
It runs great at wot. What do I look for when I do a plug chop and what adjustment should be made? Btw it's an 81 450L. And if I have to re jet what is a good ballpark to start at?
 
Hi,

Look at the carb information on my website. There's pictures and everything.

Note: "Pilot" screw is the wrong term. CV carbs (Mikuni BS34SS, in your case) have an "idle mixture" screw but that has little effect on carb operation and fuel delivery once you get above idle.

Thank you for your indulgence,

BassCliff
 
So after doing a plug chop I noticed on one cylinder that the plug is black while the other is a light tan color. What gives?
 
You probably know this, Black is rich, more fuel than air, Light Tan is usually pretty good. Both these colors are better than white, white is lean, and lean is bad.
I have a gs450T, same carbs I think, and It has a modified exhaust and pods, and it runs great. The downside to having a modified exhaust is that it took me many, many, ....many hours to tune this bike correctly. There are no magic ballpark settings as every bike is different , even withing the same model and year, but I have main jets around 145, pilots around 120-125 (cant remember exactly) I have different needle jets, and shimmed needles. My carbs have float bowls from a completely different set of carbs, as my originals were defective. It becomes a series of deductive reasoning and testing.
I know this message gets monotonous, but Before you do any of these mods, please clean the carbs thoroughly, and replace the rubber bits. You need to sync the carbs as well. Get your plugs the same color, did you do the plug chops at different throttle settings?
 
Swim_fan02 said:
So after doing a plug chop I noticed on one cylinder that the plug is black while the other is a light tan color. What gives?
Click to expand...

Simple answer: your bike needs maintenance and some mufflers.:p
 
All this info about YOUR bikes is great. But the question is how do I correct the one cylinder running rich compared to the other running good?
 
Hi,

Have your carbs been propely cleaned? Do you need to replace intake boots and O-rings? What maintenance have you done? Unless the carbs and intake system are in proper working order no adjustments will help. How does the spark look?

Sorry, I can't remember, have you seen the "mega-welcome" package?

Thank you for your indulgence,

BassCliff
 
Swim_fan02 said:
All this info about YOUR bikes is great. But the question is how do I correct the one cylinder running rich compared to the other running good?
Click to expand...
you are asking for a very simple solution to a problem that has numerous and unknown variables. These kind and knowledgeable people will help you but you have to help yourself first.

Start by performing all of the appropriate maintenance. It is easy to do.

Once you have done the work that the bike needs then you can worry about adjusting the carbs.

No matter how you ask it the nice people here will ask you the same things over and over because those things matter. Have you checked your valves? Have you stripped and rebuilt your carbs replacing the rubber bits? Have you inspected the carb boots and replaced the o-rings? Have you sealed the airbox? etc etc.
 
Yet again I say the carb is clean. It is spotless. Entirely rebuilt. Everything is in great working order as if it was new. I have spent almost a grand in replacing and fixing and repairing parts in this bike. This bike has received a total overhaul. Carb rebuild cables checked timing checked oil changed valves checked tires replaced front and rear brakes replaced stator and r/r replaced wheel bearings head bearings repacked new chain and sprockets. I have gone over this bike extensively. And yes I am askin a simple question and for opinions on to what could cause that issue. I'm not trying to be an ******* but it's absolutely rediculous that people clearly don't read the whole thread before commenting because you are asking the same question as someone else has and I have to repeat again with the same answer. so again I ask what could cause a cylinder to run more rich than the other?
 
Hi,

Swim_fan02 said:
so again I ask what could cause a cylinder to run more rich than the other?
Click to expand...

A few suggestions:

Too much fuel in that cylinder.(Bad petcock? Missing pilot jet plug? Jet fallen out?)
Insufficient spark in that cylinder. (Bad plug? Bad plug cap? Bad coil? Bad igniter?)
Not enough air in that cylinder. (Bad valves? Ripped diaphragm in that carb?)

Have you looked at the carb tutorials to figure out how to get to and adjust the "idle mixture adjustment" screws?


Thank you for your indulgence,

BassCliff
 
I'm gonna take the carb out again today and go over everything an make sure it is all in the proper place and set right. The plugs and wires and igniters are all good. Didn't even think of the petcock. I'll check that also. Other than that I'm at a loss as to what it is.
 
Hey Joe, just replied to your PM. If you haven't sync'd your carbs yet, that will definitely make a difference.

If one butterfly is opening before the other, that's gonna make a huge difference between carbs.
 
Hi,

Yep, a leaky petcock can cause a plug to foul. On the 4 cylinder engines with CV carbs it's usually the #2 plug that fouls because gas leaks down the vacuum line or the vacuum cutoff doesn't work, which can allow gas past a weak float valve/spring, into the cylinder, and eventually the crankcase which dilutes the oil.


Thank you for your indulgence,

BassCliff
 
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Swim_fan02 said:
Yet again I say the carb is clean. It is spotless. Entirely rebuilt. Everything is in great working order as if it was new. I have spent almost a grand in replacing and fixing and repairing parts in this bike. This bike has received a total overhaul. Carb rebuild cables checked timing checked oil changed valves checked tires replaced front and rear brakes replaced stator and r/r replaced wheel bearings head bearings repacked new chain and sprockets. I have gone over this bike extensively. And yes I am askin a simple question and for opinions on to what could cause that issue. I'm not trying to be an ******* but it's absolutely rediculous that people clearly don't read the whole thread before commenting because you are asking the same question as someone else has and I have to repeat again with the same answer. so again I ask what could cause a cylinder to run more rich than the other?
Click to expand...
Sorry for trying to help. You never said you checked your valves, rebuilt the carburetor, replaced the carburetor o-rings, replaced the boot o-rings, checked the boots, or sealed your airbox.

I guess it is ridiculous that I read what you wrote in a literal sense. :)

Good luck with your problem.
 
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