78 GS1K Carb Rejet? Bad Fuel Economy - KEITH KRAUSE!

[KEITH KRAUSE]

OK. First of all, this bike should idle all day at 1,000 to 1,100 rpm's.
When tuning for highest rpm's, the idle MUST be set initially in this rpm range. 1,500 rpm's is beyond the side air screws range with most intake/exhaust mods.
The reason your bike is idling too high without the idle adjuster even contacting the throttle pulley, is the vacuum synch has been done wrong.
You kept adjusting the vacuum levels and gaining rpm's at the same time. This forced you to keep lowering the idle adjuster knob. Eventually, the bike will idle high "off the adjuster".
This happened to me a couple of times when I did my first synch. To avoid over-heating the bike, I've found it's best to start over.
This means taking the carbs off and doing the best possible bench synch you can as I described earlier. Don't forget to turn the idle adjuster in several turns after the carbs are bench synched, so the bike will start. Follow the procedure exactly. If you do, the vacuum synch will be easy.
After the carbs/filters are back on and all clamps tight and throttle cable slack is good, set the side air screws to 1 5/8 (my best guess at the "sweet spot"). Start the bike (turn in the idle adjuster a little more if needed) and warm it up completely on the centerstand. Set the idle at 1,000 to 1,100 rpm's, no more. Now fine tune the side air screws for highest rpm's. You should find the sweet spot somewhere between 1 1/2 to 2 turns out. If the air jet and passage to each screw is clear, the idle WILL respond as it should.
Now hook up your vacuum tool and fans. Observe initial levels at 2,500 rpm's. I like to set them at 3,000/3,500 rpm's, but because you're new to synching, 2,500 rpm's will create less heat and not "rush" you, so to speak. Also, 2,500 rpm's is still a lot closer to where you actually ride at. I've always thought setting the levels at normal idle speeds is a waste of time. So set them at 2,500 rpm's.
Now lower the higher vacuum level(s) you initially see to closely match the lower ones. If you find a BIG difference between the highest and the lowest levels, you may compromise and instead of bringing the high one all the way down to match the lowest, make the two levels meet each other "half way", by turning the high one down some and turning the low one up some. It doesn't have to be perfect. Set all 4 so the difference is about a 1/2" from the highest level to the lowest one. This will be fine.
After a little tweaking of the throttle valve screws, tighten their holder nuts to 3 or 4 ft/lb, no more. You should now be able to adjust the idle to about 1,100 rpm's easily, if needed.
Let me know how it goes.

[Hoomgar]

Rock on Keith. Back on the bench it is then. I am going to get this right.

I am eager to play with my colortune. What do you suggest there?

Wait until after I do everything you say here or use it to get initial fuel/air settings right then proceed?

[Detman101]

You can do it man!! I know you can!!!
You will soon be a master of carbs along with everything else you know loads about!!!

Rock on buddy!!
(Proud of ya!!!)

[Hoomgar]

You can do it man!! I know you can!!!
You will soon be a master of carbs along with everything else you know loads about!!!

Rock on buddy!!
(Proud of ya!!!)

Thx dood

[KEITH KRAUSE]

Mark, I've never used the colortune and can't comment on it. Remember, it depends on the spark quality being good and the general motor condition being good too. Not just the carburetion.
I just know what I'd do after your re-synch problem, because I've done the same thing myself and I understand these carbs.
As for the highest rpm's method, this method has been used for decades on all kinds of carbureted motors. It works fine. If the rpm's don't respond as they should, you have other problems or didn't follow procedure.

[Hoomgar]

Mark, I've never used the colortune and can't comment on it. Remember, it depends on the spark quality being good and the general motor condition being good too. Not just the carburetion.
I just know what I'd do after your re-synch problem, because I've done the same thing myself and I understand these carbs.
As for the highest rpm's method, this method has been used for decades on all kinds of carbureted motors. It works fine. If the rpm's don't respond as they should, you have other problems or didn't follow procedure.

Well that was what happened. I know I screwed something up because it wasn't working out and then ran like crap. I'll get it right


With your help!

[Hoomgar]

Keith. I am missing something. Or this bike is screwed up. Or I am OK and just need to be more patient.

Here is my list for tonight.

Recheck points to make sure gap and timing are right. Spot on.

Pull plugs, wipe clean with dry clean rag. Recheck gap. Way off. Was set at like 40. I set them back to 28.

Check spark. Looks good on all four plugs. Some maybe a bit stronger than others but all of them plenty strong to fire an engine.

Pull carbs. Bench sync. Reset screws.

Pop carbs back in, adjust cables, put on air filters.

Make a tune up tank. Tired of sitting my bike tank on the seat.

Try to adjust for max idle like you said. Nothing happens dood. Only a very very marginal barely noticeable change. I can turn the screws the whole dang way in and out 4 turns and the idle may change about 50 to 100 rpm. I am not kidding you.

So I did another vacuum sync on it. Way off. Number 3 was bottomed out. I brought them all down to meet it and took it up just a hair to meet them along the way. Now it looks good. Nice and even across the board at 2500 to 3500 rpm. Not bad at idle either.

Sounds to be running a bit smoother. It's 11:30 PM, I am worried that the neighbors may be getting annoyed so I stop for the night. Here I am.

I am going to check for max idle again tomorrow. And then I may just pop the colortune in to see what is going on. I was reading that earlier and it looks pretty easy and accurate.

Anyway. Do you think I am on the right path now or is there something else you can see that I am missing? The max idle adjustment thing has me bothered.

[KEITH KRAUSE]

Everything you did sounds fine to me, except the problem with the side air screw adjustments. You ARE adjusting the correct screws? The ones on the side pointing up at about a 30 degree angle?
If the engine was idling at 1,000 to 1,100 rpm's as you started this adjustment attempt, the bike should respond by a good 300 rpm's or even more. The only way it would not is if the air jet or its passage, that's regulated by the side air screw, was not completely clear.
The air jet allows air into the pilot circuit and also the needle jet/bleed pipe. This air helps atomize the fuel as it enters the carb throat/main bore. If not enough air enters, the mixture will be rich and poor fuel mileage is the result.
On the filter side of the carbs, lower right, you can see the air jet/orifice. If I plug mine with a plug or finger tip (at correct idle speed), that cylinder drops very obviously. If I turn my side air screw from the sweet spot (about 1 5/8 to 1 3/4) to just 1 full turn, the engine drops about 300 rpm's. All 4 of my screws will effect idle this way.

[Hoomgar]

Keith. I played with this all weekend and only got marginal results. It still runs way worse than it was. I am going to try to set it back up the way I had it before I started to mess with it again ad see if I can get it leaned out then from there.

It was running darn near perfect and was just passing fuel. Now it runs like crap. And I mean crap! I Don't even want to ride it the way it is. *sigh* this is very discouraging.

I know the sweat spot is there. I just need to be more patient to find it I guess.

[Hoomgar]

Keith, as if you don't get enough of them already, I just sent you a PM.
:roll: 8-[

[KEITH KRAUSE]

Keith. I played with this all weekend and only got marginal results. It still runs way worse than it was. I am going to try to set it back up the way I had it before I started to mess with it again ad see if I can get it leaned out then from there.

It was running darn near perfect and was just passing fuel. Now it runs like crap. And I mean crap! I Don't even want to ride it the way it is. *sigh* this is very discouraging.

I know the sweat spot is there. I just need to be more patient to find it I guess.

Your carb synch problem, I've seen before. But your side air screws not operating as they should, creates a problem. If the bike is idling at the factory recommended idle, the screws will effect the rpm's as I said. If you can't get the idle down because of a synch problem, you have to re-do the bench synch.
The side air screw allows air into the mixture. It atomizes the fuel entering the carb throat. If it's not operating right, you'll pass unburned fuel. You may think the bike is running great, but you would be surprised at how much better it can run.
The air jet or passage to the air screw or between the air screw and carb throat/needle jet must be clogged. If not, then a high fuel level in the float bowl can cause a problem trying to adjust the screws.

[Hoomgar]

Well after reading that I pulled the air screws out of 3 and 4 and discovered that there is shiny brass fragments stuck to the needle. I am sure they have found they're way into the pilot needle seats as well so I will pull these carbs and get that out. It is really fine and so much so that it crumbles in your fingers. I think it is from the threads of the new needles. I didn't check them as I now know I should have.

I am going to blow these carbs back out and make sure the needles are all clean as well as their passages.

Getting good at taking these off and putting them back on

Thx Keith.

Edited for the added bold text correction above

[KEITH KRAUSE]

OK. And don't forget to turn over those choke brackets we discussed.
Be sure all 4 of those plungers are completely seated just before the choke lever is fully off. One less thing to think about, regarding the raw fuel smell/dark exhaust.
If any doubt about which way they go, send a pic.

[Hoomgar]

OK. And don't forget to turn over those choke brackets we discussed.
Be sure all 4 of those plungers are completely seated just before the choke lever is fully off. One less thing to think about, regarding the raw fuel smell/dark exhaust.
If any doubt about which way they go, send a pic.

That is also on the "To Do" list.

Thx again Keith. Third time's a charm

[Jethro]

Oh boy! Another one who has had a HELL of a time rejetting!

I feel for you Mark, there were a few times when I was about to throw in the towel and call up my credit union for a loan on a brand new machine. But I stuck with it, and man did it pay off. My bike idles like a charm at a spot on 1050rpms, has not one flat spot, god only knows what the top speed is (120 is as fast as I have the cajones for) and gets a good 40-44mpg. Granted, I'll bet I have a few hundred hours in the rejetting and synching and taking the tank off and...... well, you know what I am talking about. Stick with it man, you'll get it.

I really wanted to comment on the colortune. Pano, one of my local GS buddies recently bought one of them, in hopes to get the mixture screws right. On our CV carbs, the mixture screws are really tough to set. Everyone says to adjust for the highest idle, but most of us have found that the screw settings are extremely subtle, almost undetectable unless you ride the bike. If you figure that the settings will be between 1/2 turn out to 6 turns out and every 1/4 turn in between and that all the carbs could be different, you have thousands of possible combinations of settings. The colortune was bought in hopes for him to get that right, without road testing between every 1/4 turn of the screws. I was pshyched to have him call me back and tell me how well it worked. Unfortunately he said the thing wasn't as accurate as we hoped. He said that the idea is to get it to burn a certain color (blue maybe?) and that he put it on and it burned blue (or whatever color it's supposed to be) pretty much no matter what he did, unless he bottomed out the screws, which you don't need a colortune to tell you is bad news, cause the engine bogs really bad.

If you want more info on it, PM Pano, I'm sure he'll fill you in, but I'm sorry to say he was not impressed by it. Pano knows his stuff too, he slotted his camshaft gears recently, jetted his bike and everything.

Anyway, keep up with it, you are on the right track- I know it!!!