1981 GS1100E Idles ok. Turn throttle instant death.

[Donaldderby]

C&c i hadn't seen where you mentioned your manifolds. I had the same problem and just replaced my manifolds and o rings $140 and now the bike starts cold no problem. Just something to check

 

[Steve]

I have my screws at ~1.5 turns. How low can I go before having to change jets?

It's not a matter of "how low can I go", it should be "where should I set them?" For cold starting the first time, set them at three turns out. After the bike is warmed up, use the Colortune on them, but good luck. Some of us have not had good luck with the Colortune on the BS-series carbs. We have seen the blue flame start to sputter a bit, then go out, but never change color.

Using other methods of mixture tuning, you may find that your screws may end up about 2 to 2 1/2 turns out, but I feel that 1.5 turns is not enough. It is much easier to start the engine with them too rich, it acts a little like a choke to richen the mixture for the cold start.

I also read to adjust the mixture between 2000 and 2500 rpm. Apparently that is the range mostly used.

Actually, there is not a whole lot of running in that range. Besides, the mixture does not depend on engine speed, it depends on throttle opening. The throttle opening necessary to maintain 2500 RPM in fifth gear on the highway is going to be larger than the opening necessary to maintain the same engine speed in neutral on the centerstand.

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[c&c]

C&c i hadn't seen where you mentioned your manifolds. I had the same problem and just replaced my manifolds and o rings $140 and now the bike starts cold no problem. Just something to check

The short rubber tube that connects and holds the carbs?
My modle does not have o-rings and they are almost new, there are no cracks.
I made sure they are in good condition.

 

[c&c]

It's not a matter of "how low can I go", it should be "where should I set them?" For cold starting the first time, set them at three turns out. After the bike is warmed up, use the Colortune on them, but good luck. Some of us have not had good luck with the Colortune on the BS-series carbs. We have seen the blue flame start to sputter a bit, then go out, but never change color.

Using other methods of mixture tuning, you may find that your screws may end up about 2 to 2 1/2 turns out, but I feel that 1.5 turns is not enough. It is much easier to start the engine with them too rich, it acts a little like a choke to richen the mixture for the cold start.

Actually, there is not a whole lot of running in that range. Besides, the mixture does not depend on engine speed, it depends on throttle opening. The throttle opening necessary to maintain 2500 RPM in fifth gear on the highway is going to be larger than the opening necessary to maintain the same engine speed in neutral on the centerstand.
.

I thought turn left for rich and right for lean? It's the other way
Damn no wonder nothing works, cold starts are hell and from the get go it keeps burping like a carbonated addict!

That would also explain why the colourtune colour change was nonexistent was always pale blue almost white.

I'll be adjusting them tomorrow night.

I'll report back.

 

[c&c]

Well the tomorrow night turned into a couple of days.

I turned the idle screw right 3x360 turns.
With choke on and bike on the side stand. Startes then dies. At least now it starts. When I sit on it and put it level then start it it turns with more intensity then dies. Now with the front break on I start jerking the front suspension up and down to get the float bowls moving to allow more fule in the bowls. Push the start button it starts , revs high then back down to about 900rpm and stays there just bearly alive. I start jerking it agan and it revs up to 2000rpm.

So please correct me if I'm wrong but there is just not enough gas in the float bols. they are jetted using the recommended jets, DJ138s and the float bowl are set to the recommended hight and I did a level test with transparent tubs and they are at the same level.

I think I will play with the float hight and get more gas in them. Ill add 2.5mm

The carb is squeaky clean and the gas needle plugs are in excellent condition.
Petcock is new and no problems what so ever when in prime.

Am I missing something or this is the correct route to take?

Thank you

 

[c&c]

I fixed the cold start issue.

I lowered the floats 2mm ( when carbs are upside down ).
I had not installed the choke leaver on the carb correctly. Fixed that.
Had the pilot screws turned out 3 turns which is to lean.
With choke on it starts up almost instantly. YEA BABY!

Not to self turn the air screw in for rich and out for lean.
Not the other way like I thought in my last post.

Tried to colour tune it but never got it yellow or pale blue. I'll try again tomorrow night. If it does not work I will thy the Idle Drop method.

Verdict
There was not enough gas in the float bowls thats why it would startup and die just after and when I finally got it running it would burp like crazy in the first quarter, under load, and would pull very strong when the jet needle would go up which is above the quarter turn.

I'm taking her for a ride tomorrow. Forecast is sunny with a max of 10 degrees Celsius. BRrrrrrr!

 

[tkent02]

Not to self turn the air screw in for rich and out for lean.
Not the other way like I thought in my last post.

This is incorrect. The mixture screw turned farther out gives a richer mixture.

 

[Nessism]

I fixed the cold start issue.

I lowered the floats 2mm ( when carbs are upside down ).
I had not installed the choke leaver on the carb correctly. Fixed that.
Had the pilot screws turned out 3 turns which is to lean.
With choke on it starts up almost instantly. YEA BABY!

Not to self turn the air screw in for rich and out for lean.
Not the other way like I thought in my last post.

Tried to colour tune it but never got it yellow or pale blue. I'll try again tomorrow night. If it does not work I will thy the Idle Drop method.

Verdict
There was not enough gas in the float bowls thats why it would startup and die just after and when I finally got it running it would burp like crazy in the first quarter, under load, and would pull very strong when the jet needle would go up which is above the quarter turn.

I'm taking her for a ride tomorrow. Forecast is sunny with a max of 10 degrees Celsius. BRrrrrrr!

This is incorrect. The mixture screw turned farther out gives a richer mixture.

Agree. And you don't set floats by randomly setting the height, you adjust the height until it's within the factory specification range. Carb rebuild tutorial linked in my signature.

 

[Steve]

I turned the idle screw right 3x360 turns.

Hopefully you are talking about the idle SPEED knob that is below the carbs, between #2 and #3.

So please correct me if I'm wrong but there is just not enough gas in the float bols. they are jetted using the recommended jets, DJ138s and the float bowl are set to the recommended hight and I did a level test with transparent tubs and they are at the same level.

I think I will play with the float hight and get more gas in them. Ill add 2.5mm

Jetting will not affect the amount of gas in the carbs.

If you have the proper float height that is verified by a transparent tube, why do you want to "play with it"? It's already the correct level, something else must be the problem.

The carb is squeaky clean and the gas needle plugs are in excellent condition.

It does not matter how noisy they are ("squeaky" clean), what matters is whether they really ARE clean. I saw in post #18 that you dipped the bodies in Pinesol. I have never used it, so I don't know how well it works. Any particular reason you did not get the stuff that we KNOW will work? I know you said you used what you had on hand, but come on, for $20 or so to get the proper stuff, you might not be having all this aggravation now. By the way, when you dipped the carbs, how long did you leave the carbs in the Pinesol?

I lowered the floats 2mm ( when carbs are upside down ).

What you really mean is "I applied a Band-Aid to the system by messing up the proper fuel level."

Had the pilot screws turned out 3 turns which is to lean.
With choke on it starts up almost instantly. YEA BABY!

Not to self turn the air screw in for rich and out for lean.
Not the other way like I thought in my last post.

What you are calling "pilot screws" are "idle MIXTURE adjustment screws". They control the amount of a pre-set MIXTURE that is admitted to the engine. Turning them OUT from a lightly-seated position will RICHEN the mixture, not lean it out.

Using the "choke" is normal to start a cold engine.

Tried to colour tune it but never got it yellow or pale blue. I'll try again tomorrow night. If it does not work I will thy the Idle Drop method.

I mentioned that possibility back in post #22. That does not mean that something is not working right, just shows that the Colortune is not the perfect tool in all situations.

Verdict
There was not enough gas in the float bowls thats why it would startup and die just after and when I finally got it running it would burp like crazy in the first quarter, under load, and would pull very strong when the jet needle would go up which is above the quarter turn.

I would suspect that your verdict is not quite correct. Because of your questionable cleaning fluid (Pinesol), my personal opinion is that your pilot mixture passages are STILL clogged up with gunk. Raising the float level 2mm above the recommended level merely enabled the needle circuit to kick in a bit earlier (becaue it's running richer), making you think that your problem is solved.

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[c&c]

Ok I got your hints... I'm a noob

I'll go back and recheck everything.

 

[c&c]

Thank you for your response. Much appreciated.

Found this diagram of the BS34 carb. It's the closest I found. Final I see what the hell is happening in there!

My cold start problems was my own doing. I installed the choke leaver on the carb the wrong way.
Reinstalled it the correct way. Now in works like a charm. I now see where the choke is getting the fuel from.

If I understand, you are saying that my idle jet passage is still clogged. (thanks diagram) That would explain why the throttles first 1/4 is erratic/burps with hesitation.

Ok so I'll set the floats back the way they are suppose to be and I will make sure the idle jet passages are free of debris/junk.

The idle MIXTURE adjustment screw, which they call Pilot screw on the diagram, when unscrewing does not add more fuel, it allows more pre-set mixed air and fuel to enter the engine. Like you mentioned it's a "pre-set MIXTURE" dictated by the pilot jet and air pilot. Which would also explain why the ColourTune stays the same colour no matter what position the Idle Mixture adjustment screw is in.


So maestro do I finally "get it"?

 

[Steve]

Found this diagram of the BS34 carb. It's the closest I found. Final I see what the hell is happening in there!

That is a rather generic diagram, try this one; (if it wasn't identified as an 850 carb, you would not know the difference. This is a BS32, yours are BS34.)

This picture was doctored up some time ago to show the location of the rubber plug, but is a better shot to show the pilot mixture passages.

When you get to (re-)cleaning the carbs, pay special atttention to the transition ports at the top of the throttle blade.

Some bikes have two, others have three, but there is always one that is open all the time. When the throttle is closed, it will admit as much mixture as it can, but it's not quite enough, which is why you can add more with the mixture (pilot) screw. As the throttle is just barely cracked open, another port is opened, now you have three places where gas is being added to the incoming air. By the time the throttle is opened a bit past the last transition port, the overall vacuum level will drop a bit, reducing the pull through the transition ports, reducing the amount of gas that comes through them. That is when the air flow is sufficient for the needle circuit to start flowing enough to handle the mid-range throttle settings.

The idle MIXTURE adjustment screw, which they call Pilot screw on the diagram, when unscrewing does not add more fuel, it allows more pre-set mixed air and fuel to enter the engine. Like you mentioned it's a "pre-set MIXTURE" dictated by the pilot jet and air pilot. Which would also explain why the ColourTune stays the same colour no matter what position the Idle Mixture adjustment screw is in.

I would think that the Colortune should show some differences, because, even though you are adding a pre-set mixture, you are adding that mixture to plain AIR, so you are still changing the overall mixture. However, on the three bikes with CV-type carbs that I tried it on, I never saw any change in the burn color. The flame simply started to flicker a bit, then went OUT as I turned the mixture screws in. The flame came back as I turned the mixture screws out, so I went for "steady flame" rather than "bunsen burner blue". On the one bike with VM carbs that I used the Colortune on, it was GREAT to see the flame change color. That was the first one that I did, and it got me all excited to use the Colortune on the other bikes.

So, yeah, the Colortune does work, just not for all bikes.

.

 

[c&c]

WOW! Thanks for the much better cut outs. Makes even more sense and much easier to understand the internal workings. Without that it's pretty hard to know why an adjustment does what it does or does not do.

I will recheck the transition ports for sure.

I also noticed the flame going out but did not make sense of it. I did notice a change in idle speed/sound when adjusting the screw. I'll also use the "steady flame" while adjusting.

A good chance you guys are here. With out this help it would be practically impossible for us mere mortals to get our bikes up and running properly.

 

[Steve]

A good chance you guys are here. With out this help it would be practically impossible for us mere mortals to get our bikes up and running properly.

Thanks.

We have seen more than a few new guys that were rather adamant about how "clean" their carbs were or how meticulously something else was done,
but we kept reading what they had done and kept trying to convince them that it wasn't right. Thanks for seeing the light.

Resistance is futile. You WILL be assimilated.

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