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

[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!!!

 

[Anonymous]

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.

I found nothing less than 1/2 a turn was noticeable when I was jetting for pods. I never went for the highest idle method, I went on plug readings, start up/idle, and throttle response. At 2.25 turns the throttle response was very abrupt (a sure sign of a lean condition) and the plugs were reading a very light tan/dark grey color. At 2.5 turns everything improved a bit and at 3 turns throttle response is sharp but not at all abrupt and the plugs show a nice medium tan color. You should never turn out the mixture screws more than about 3.5 turns, at that point you are wide open on the adjuster and you really need to step up one size on the pilot jet and start over. At least setting the mixture screws is a 5 minute job. You can get a lot of testing done in an afternoon with a screwdriver bit and some time...

Mark

 

[Hoomgar]

I played with my colortune a bit and saw the same thing Jethro. What I noticed is that there is a base blue color to it all the time. What I think goes on is you have to read the color of it the instant it fires. I played with the air adjustment screw with it in and the blue color never changed. However the color around the rim and inside post everytime it fired was changing colors. Just like they show in the chart. I am sure that this is what your to be looking at. I haven't used it beyond that though yet.

The Carbtune II tool rocks though. I can't give it enough of a good word. It seems to be just as good as a mercury one would be but you never ever have to worry about sucking mercury into your engine and it will never fog up like the mercury ones do. I am not saying it is better than a mercury tool. I am simply saying that I think it is every bit as good.

I am going to get this, no worries

I actually spoke with Keith K. on the phone about this last night and I am glad I did. Getting to pick his brain a bit in a more time reative situation like a call was way faster and more informative than a hundred posts.

And I can tell you another thing, he is all business. Very serious about tunning these bikes. If you guys are ever asking him questions about something be sure to follow EVERY thing he says. There are little tid bits of info that he gives that if over looked can turn your entire project into a waist of yours and his time.

And that's all I have to say about that... <--- Forrest Gump :lol:


This bike will run right before the southern rally.

 

[Hoomgar]

Keith. We have made some major progress here tonight.
This is by far and hands down the best the bike has ever run.

It is still not perfect but it has a snap to it now that it never had.
It is running so smooth after tonights sync that the speed you
generate is deceptive. At one spot I looked down just to see where
I was as I was swapping along through the night air on a mildly windy
road and the speedo said 110! 8O 8O

I verified what gear I was in. It has a 0 to 60 right now that is smooth
and fast.

Anyway, that said, it was for sure that brass shrapnel I found in them last
night. I got all that blown out tonight.

Here is what I have done and where I'm at. Pics included:

I took the carbs off and pulled all needles and screws, floats, etc...

Blew it all out with 180 PSI and then verified with light and air that all
passages were clean open.

I checked the float levels, they were still spot on so I did them right the
first time.

Buttoned it all back up. Set both pilot and air screws at 1.5 turns out
each.

Did a really meticulous bench sync and popped the carbs back in.

Low and behold the air screws actually have an affect on the idle now
So I set them all for max idle. I should have written them down but I
didn't think to do it. None of them went over two turns out. They are all
somewhere between 1.5 and 2 turns on the air screws.

I have not touched the pilot screws, they are all still at the starting point
of 1.5 turns out.

After I got that all done I did my best sync yet. They really were not far
off. Maybe 3/4 from each other. Here is a pick of the sync for you
Keith. Note the RPM's

After all that I put the tank, seat and side covers on and went for gas.
That is when I got to see how good it is running.

I did my best 1/3 throttle chop test. It ain't perfect as it was hard to see
my marks in the dark but it is still very close to a good 1/3 throttle chop
test Keith. Here it is:

One thing I found that maybe I was doing wrong before too. The vacuum
hose for the petcock has always been open when trying to tweak it
before. This time I plugged it shut while using my tune tank and the
results were way better. Maybe this was the most of my issue?

What do I do from here to get rid of the lean on that 2 and 3 cylinders?

 

[KEITH KRAUSE]

I never went for the highest idle method, I went on plug readings, start up/idle, and throttle response.

If the plug reads at all 3 circuits are their best, your start up and idle is good, and the throttle response is it's best, then your bike is running its most efficient. When the bike is running its most efficient, it's also running at the highest rpm. They're one and the same.
You may not have made a deliberate attempt to adjust for highest rpm, but if the above is true, you'll find the mixture screws (CV) or air screws/pilot fuel screws (VM) are at a point that just happens to be the highest rpm achievable on that bike.
When your bike was new, it came set this way too.

 

[KEITH KRAUSE]

Mark, I just read your last post and I'm glad you're getting there.
It's way late and I'm getting the evil eye from the wardon. I'll think about those plug reads and do my best to reply after work tomorrow.
As before, I can't see them like you can, but 2 and 3 are lean as you said. Exactly how lean? Is the insulator whitish/gray, or bone white? Are 1 and 4 pretty good?
One quick thought, are you POSITIVE the timing for 2/3 is the same as 1/4? Talk to you soon.

 

[Hoomgar]

Mark, I just read your last post and I'm glad you're getting there.
It's way late and I'm getting the evil eye from the wardon. I'll think about those plug reads and do my best to reply after work tomorrow.
As before, I can't see them like you can, but 2 and 3 are lean as you said. Exactly how lean? Is the insulator whitish/gray, or bone white? Are 1 and 4 pretty good?
One quick thought, are you POSITIVE the timing for 2/3 is the same as 1/4? Talk to you soon.

Yeah being up posting after midnight can generate those looks :lol:

I am 100% positive that the timing is smack on in both the 1 and 4 and 2 and 3 sets. They both idle right on the f mark and when you crack it to 3k they both sit right on the higher mark. The gaps are also perfect. They are spot on.

Yeah the photos are always deceptive. Makes things look lighter than it is. Here is what I would say about the plugs by comparing them to the color chart.

Plug 1 is just a little on the rich side. It is too dark and is carbing up a bit.
Plug 2 is just a tad lean. It could stand to be a bit darker.
Plug 3 is lean with both the tab and the insulator being pretty whitish/tan
Plug 4 is almost perfect. Maybe just the slightest hair on the lean side.

I rode it to work this morning and boy is it running strong. You crack the throttle and you?re gone! When down in the idle circuit and the early part on the needle circuit it runs a tad rough and sporadic until you give it a little more gas. Then it runs near perfect.

WOT is exhilarating!

What is next? Pilot screw adjustments?

 

[Jethro]

One thing I found that maybe I was doing wrong before too. The vacuum
hose for the petcock has always been open when trying to tweak it
before. This time I plugged it shut while using my tune tank and the
results were way better. Maybe this was the most of my issue?

:lol: :lol: :lol: :lol:

Sorry to laugh Mark, I do it WITH you, not at you becasue I have made that mistake more than once! I finally came up with a solution for me- I made a little plug for the vaccum nipple and now velcro it to the end of the hoses on my synch gauge! Now I have to take it off and put it somewhere when I attach the hoses. It does make a difference- a huge difference!

 

[Hoomgar]

Yeah it supposed to be plugged huh? That little bit of info was missing. It isn't in my manuals that I saw and no one mentioned it. There is a 500 to 700 RPM difference in the idle with it plugged or unplugged! 8O


:? :? :? :?

 

[KEITH KRAUSE]

I'm gonna start mentioning to cap the vacuum nipple if you're using a seperate fuel reservoir. You're the second person I've tried to help this year that's done that. I finally mentioned it to the other guy. I didn't before because I didn't want him to think I thought he was stupid. It just seemed so obvious to me. This info is supposed to be included with your synch tool instructions. I know it is with the Motion Pro tool.
With a vacuum leak that big dragging down the motor, each cylinder air screw will have little effect on the rpm's. I do suggest to use the tank for a fuel source during synching, by using longer fuel/vacuum lines. Pingel owners don't have this "problem".
As usual, I gotta get to work. As for the leaner 2 and 3, If everything else has been done the same regarding jetting, cleaning, timing, etc, then make some pilot fuel screw adjustments. Be sure to keep a record. Be sure you turn them the right direction. Some people don't because they're upside down. Also, be sure you didn't go past the sweet spot on those two carbs when you adjusted the side air screws. A combination of smaller mistakes can cause a larger problem.
Try an ADDITIONAL 1/4 turn out on #2. Try an additional 3/8 turn out on #3. Try 1/8 turn IN on #1. Test again.

 

[Hoomgar]

I'm gonna start mentioning to cap the vacuum nipple if you're using a seperate fuel reservoir. You're the second person I've tried to help this year that's done that. I finally mentioned it to the other guy. I didn't before because I didn't want him to think I thought he was stupid. It just seemed so obvious to me. This info is supposed to be included with your synch tool instructions. I know it is with the Motion Pro tool.

Never under estimate the impact that the ignorance of your pupil can have on your advice Keith! 8O :lol: :lol: :lol:

With a vacuum leak that big dragging down the motor, each cylinder air screw will have little effect on the rpm's.

Ding! Ding! Ding! Ding! We have a winner! :lol: :lol:
Now we know why my air screws were not affecting the idle.
I told you I wasn't going crazy. I knew I had to be missing something!

I do suggest to use the tank for a fuel source during synching, by using longer fuel/vacuum lines. Pingel owners don't have this "problem".

But plugging that hose and using the tune tank should be fine too right?

As usual, I gotta get to work. As for the leaner 2 and 3, If everything else has been done the same regarding jetting, cleaning, timing, etc, then make some pilot fuel screw adjustments. Be sure to keep a record. Be sure you turn them the right direction. Some people don't because they're upside down. Also, be sure you didn't go past the sweet spot on those two carbs when you adjusted the side air screws. A combination of smaller mistakes can cause a larger problem.
Try an ADDITIONAL 1/4 turn out on #2. Try an additional 3/8 turn out on #3. Try 1/8 turn IN on #1. Test again.

Exactly what I was thinking believe it or not. But I wanted to hear it from you first. I'll recheck the air adjustments first just to be sure.