Transition mixture screws

[carzxl]

I have a gs 1100 L that I got a really good deal on. I love the bike and it runs great except when you are coming off of idle giving just a little throttle there is a slow response right between idle and cruise. Its almost feels like the bike is taking off in second everytime. I have went through the checklist in your greeting and the only thing that I haven't been through is the mixture screws because they have brass caps over them. I am an automotive technician and in my world that means it wasn't meant to be messed with. At the point I am at it is the only thing that makes sense because I am definatly having a transition problem but when they are capped off it gives me the intention they are not to be f**ked with. The bike idles perfectly and cruises perfectly. How do you remove these caps? Am I barking up the wrong tree?

 

[twr1776]

Carzxl, the caps were put on there for EPA purposes and need to be removed to adjust the fuel/air mixture. Some drill them out and some use a sheet metal screw to remove them. Either way be careful the screws are not far under the caps and you do not want to damage them while removing the caps. If they have never been off you also might want to get the Robert Barr o-ring kit and replace the little o-ring under the mixture screws. It will be hard to get a consistant air/fuel mix unless they are in good shape which after 25+ years is not too likely.

 

[Turtleface]

+1 on the o-ring kit. Buy a gallon can of Berryman's carb dip too, and do it right the first time, so you don't end up doing it more than once. The mixture screws shouldn't have too much effect on the off-idle transition. That's usually the realm of the pilot circuit. My best guess would be a possible clogged pilot jet. Either way, none of your o-rings have any elasticity in them anymore, and they all NEED to be changed before you can do any sort of real trouble shooting or tuning. I thought mine were ok on my 15k mile stocker, but they were all completely brittle.

 

[carzxl]

turtle, nice spot on diagnosis. weirdest thing ever though. When I removed the rubber caps from the pilot jets the bottoms instantly like within 5 seconds of me removing the caps it would turn green and had like almost a corrosion consistency. The same thing had happened to the jets all green. They did not appear clogged but after seeing the green stuff I cleaned them. Put it back together and fired it up. It runs perfect from 1000 rpm to 8000 rpm (I never take it higher than that) in every gear. I started to fully disassemble the carbs but when I got into the first two I realized some one was in here and recently did a bunch of seal work. Carbs are almost spotless. A little bit of sediment in the bottom of the float bowl. Do you know the cause of the green stuff? I am going to run premium non ethnol fuel and continue with my seafoam regiment for a couple more tanks.

 

[Steve]

I am going to run premium non ethnol fuel and continue with my seafoam regiment for a couple more tanks.

If you like your bike please DON'T use "premium" gas. It is no better than "regular", it does NOT give you any more power (how can it, it has fewer BTUs per gallon) it only costs more.

Unless, of course, your engine has higher compression than stock and requires the ANTI-KNOCK additives that make it "premium".

Oh, the "non-ethanol" is a good idea, though. See if you can find that in a "regular" grade, 87 octane.

.

 

[centeno711]

? really 87? what is the compression on these motors? 9:1? ii would think with an air cooled aluminum motor heat and predetonation would be issues. the higher octane rating alleviates predet right? thats is why people started running propane drip ....to increase octane in the fuel.

My bbrother inlaw just burnt a hole in the piston on his yamaha and the consensus was from cheap gas

Hopefully this is untrue and i can buy the cheap stuff for my gs!!!

 

[trippivot]

?

My bbrother inlaw just burnt a hole in the piston on his yamaha and the consensus was from cheap gas

the "consensus" is WRONG. a pluged pilot jet will burn a hole in a piston due to lean misfire. heat range of a spark plug will do the same thing points set wrong will too. I can go on because there are more causes.


CARZXL- transfer or bypass circuit you are describing is controled by the pilot jet you still need to drill the mixture screw caps out for fine tuning-- 1 step larger pilot jet and re-adjust your idle mixture. the bypass circuit will cover the off idle leanness by doing this.- IF,- that is, IF the symptoms are being identifed and described accurately. I respect mechanical people and I like that you didnot just start drilling and hacking your carbies.

a idle mix adjustment might just cure your issue if your bike noticeably responds to a little enrichment on each cylinder -- re adjust the idle speed down to 1000~1100 and know you are going the right direction.
a needle position change will do the same thing but after 1/4 throttle

the transfer are most noticed 1/10-1/8 throttle

 

[Steve]

Yessir, trippivot has it nailed. :clap: :clap:

However, just to keep it easy, I might try turning out the mixture screws before changing the pilot jets.

The stock setting on the mixture screws tended to be about 1 to 1 1/8 turns out from lightly seated.
Most of us have found that it works best between 2 and 3 turns, depending on your bike, location, etc.

Start by removing the caps, see if your screws turn easily. If they do, turn them in slowly, counting the turns (record that number), then backk each one out to 3 turns for a starting point. Start the bike, warm it up, set the idle to about 1100. Slowly turn each screw IN, listening for any change in engine speed. If it goes up, leave it at the highest speed. If it goes down, back off 1/4 turn. Repeat for each carb. Go for a ride, enjoy your "new" bike.

If you don't get any improvement after turning the screws out over 4 turns, it's definitely time for new pilot jets. Less than 4 turns, keep the stock jetting.

.

 

[Steve]

?My bbrother inlaw just burnt a hole in the piston on his yamaha and the consensus was from cheap gas

the "consensus" is WRONG. a pluged pilot jet will burn a hole in a piston due to lean misfire.

After thinking about it, I am going to have to disagree slightly.

Yes, the "cheap gas" probably caused the problem, but not due to low octane numbers. :-\\\

There might have been some water or other crud in the gas, and that is what plugged the pilot circuit in the carb,
causing the lean condition that burnt the hole.

Yes, the compression ratio is up a bit on these bikes. In fact, my KZ1300 was over 10:1 and still only required 87 octane.
There is more to consider than just compression ratio when you look at octane requirements.

.

 

[FlyingSteve]

The smallest amount of water in your gas can cause you to blow a hole through a valve like a laser beam. I've seen it happen before on a fuel injected car engine from "cheap" gas.

After thinking about it, I am going to have to disagree slightly.

Yes, the "cheap gas" probably caused the problem, but not due to low octane numbers. :-\\\

There might have been some water or other crud in the gas, and that is what plugged the pilot circuit in the carb,
causing the lean condition that burnt the hole.

Yes, the compression ratio is up a bit on these bikes. In fact, my KZ1300 was over 10:1 and still only required 87 octane.
There is more to consider than just compression ratio when you look at octane requirements.

.

 

[ddaniels]

I've never run anything except 87 octane in any bike I've owned. Never ever had a problem with it.

Have you checked the syncronization of the carbs?

 

[koolaid_kid]

The green was most likely copper oxidation, nothing to worry about.
Something most are not aware of - when a fuel truck fills the tanks at a service station, it stirs up water and sediment lying on the bottom of the tank. It takes quite a while for it to settle back down. You can easily pump that junk right into your tank.
If I see a truck filling up the tanks at the local service station/convenience store, I pass it by.

 

[carzxl]

Very good information from all of you. This forum is one of the greatest services I have ever used. I have the highest regards for all of you. Unfortunately here in madison wi the only available non ethanol fuel is premium and thats sometimes a chore to find.

 

[FlyingSteve]

It's really tough to find non-ethanol here in eastern PA. The corn industry is really a bunch of BS, but this ain't the place to get into that

 

[FlyingSteve]

The green was most likely copper oxidation, nothing to worry about.
Something most are not aware of - when a fuel truck fills the tanks at a service station, it stirs up water and sediment lying on the bottom of the tank. It takes quite a while for it to settle back down. You can easily pump that junk right into your tank.
If I see a truck filling up the tanks at the local service station/convenience store, I pass it by.

I was thinking copper oxidation, but I couldn't come up with an area on the carbs where copper would be used. All the jets are brass... Copper and bare aluminum is a bad mix...

 

[carzxl]

the green oxidation also happened on the bottom of the rubber caps. ???

 

[koolaid_kid]

Brass is an alloy of copper and zinc. Just an fyi.

 

[Steve]

Unfortunately here in madison wi the only available non ethanol fuel is premium and thats sometimes a chore to find.

As long as it's less than 10%, don't worry about it. You will use a little more of it to travel each and every mile, but you will spend a LOT less money and will not harm your bike in the process.

.

 

[Turtleface]

The smallest amount of water in your gas can cause you to blow a hole through a valve like a laser beam. I've seen it happen before on a fuel injected car engine from "cheap" gas.

Had a buddy develop a water jacket/cylinder wall crack on a 1/4 mile track duty 383 he had in his Firebird. Of course, it was at WOT, and during a run. The cylinder in question didn't have any holes in the pistons, but it did bend the crap out of his expensive Eagle H-beam rod. Turns out water doesn't compress very well. I've never seen any piston damage from water, I would have thought water in the cylinder would lower combustion chamber temps. At least, that's the idea behind a water-injection system.

 

[Steve]

I would have thought water in the cylinder would lower combustion chamber temps. At least, that's the idea behind a water-injection system.

Yes, WATER will reduce the temperature, depending on how it's introduced.

Water injection involves spraying some water into the intake. Usually it is done as a very fine mist and far enough upstream so that it can evaporate. The physics behind theh evaporation process tell you that it loses a LOT of heat in the process, that cools the mixture.

However, if you have raw (unevaporated) water that gets into the cylinder, the temperatures there will change it to steam. Steam tries to occupy 1200 times the volume of water. Since there is only so much volume available in the cylinder, the pressure goes up, WAY UP. That is what bent your buddy's rod.

.