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

[Anonymous]

Hey Mark,
I have been following this thread, learning what I can.
Great to hear you have it so close on the first try!
It always takes me at least 3 times to get anything right.
And that is when I am lucky.
Looking forward to the ride!
Charlie

 

[KEITH KRAUSE]

Glad it's running good for you! You had some previous questions, before your latest post.
Yes, with pods, the float bowl vent lines should be removed. Permanently.
Yes, I said to use the stock #15 Mikuni pilot jets instead of the cheaper brand you get in a rebuild kit. If they don't work, get 17.5 Mikuni's. I was just trying to tell you to stay with Mikuni brand.
I can't really see the plug reads too well, but if you say 1 and 4 look good and 2 and 3 are a little lean, (I can see those two) then I suggest the vacuum synch needs to be done to get uniform and more accurate readings. I still think the needles will need to be raised one position more.
Just a note of caution, lean mixtures can be very deceiving. They tend to make more power and make you think the bike is carbureted correctly. Synch the carbs and get more reads is my suggestion.

 

[rek]

carb synch tool

carb synch tool

in the post earlier you asked about the sych tool and the possibility of making one. i posted this earlier but here is the link to one that is supposedly more accurate than the ones you buy while costing only 4 bucks to make!
i will try to make one and try it out this w/e on the yamaha and see how it does.

http://www.airheads.org/index.php?Technical Tips+$4 Carburetor Synchronizer

 

[Hoomgar]

Glad it's running good for you! You had some previous questions, before your latest post.
Yes, with pods, the float bowl vent lines should be removed. Permanently.
Yes, I said to use the stock #15 Mikuni pilot jets instead of the cheaper brand you get in a rebuild kit. If they don't work, get 17.5 Mikuni's. I was just trying to tell you to stay with Mikuni brand.
I can't really see the plug reads too well, but if you say 1 and 4 look good and 2 and 3 are a little lean, (I can see those two) then I suggest the vacuum synch needs to be done to get uniform and more accurate readings. I still think the needles will need to be raised one position more.
Just a note of caution, lean mixtures can be very deceiving. They tend to make more power and make you think the bike is carbureted correctly. Synch the carbs and get more reads is my suggestion.

That's where I have to go next then. I will stay with all Mikuni parts then. Joe has drawers full of them so this is good. It looks like 'll be set if my tool comes in this afternoon then. If not, I have an offer from another forum friend here to come out and use his. What a pal

It isn't lean enough to worry about at this point. It could be ridden the way it is so a sync job should help bring it up a bit more for me. According to the color chart none of them are lean and 1 and 4 are called "Ideal" while 2 and 3 are close to it. I was really pleased with that.

I do need to get a heavier return spring on it. I went too light




rek, thanks for that info. I saw that when you posted it but had already commited my funds to a sync tool from Morgan. I am waiting for it to arrive.

 

[KEITH KRAUSE]

OK Mark. You can see the plugs better than I can. #3 is quite lean from what I see. The others are harder to see.
I can tell you this: During the synch, if you see an initially low vacuum level at #3, and also #2 to a lesser degree, as compared to the others, then there's a better chance that correct vacuum adjustments will fix you up. If the levels don't start off looking that way, then the jet needles will have to be raised a position.
I suppose you can go on your ride. I know you're going to regardless. I'm just trying to warn you about lean mixtures and the problems they create. I'm a perfectionist about this stuff. I can't help it. :roll:

 

[Hoomgar]

OK Mark. You can see the plugs better than I can. #3 is quite lean from what I see. The others are harder to see.
I can tell you this: During the synch, if you see an initially low vacuum level at #3, and also #2 to a lesser degree, as compared to the others, then there's a better chance that correct vacuum adjustments will fix you up. If the levels don't start off looking that way, then the jet needles will have to be raised a position.
I suppose you can go on your ride. I know you're going to regardless. I'm just trying to warn you about lean mixtures and the problems they create. I'm a perfectionist about this stuff. I can't help it. :roll:

And I am going to follow your advice to the letter buddy

I only ride once the time comes because I have to. But then it is back to tweaking. I have an offer from someone to come over tonight with his sync tool regardless if mine comes in or not and we are going to sync it up so were golden

They really are not that lean. At least according to the plug color chart which says a light brownish tan color is optimal. That's what they are. There are no white plugs this time.

If I must raise those needles I WILL be doing that. No worries

One thing that is playing into this is that newly repacked baffle. I packed it fairly tight and I know it is making a reduction in flow so I may be getting the results I am due to that. I think they jetted the bike with no packing before and that was why the big mains.

Were almost there now

 

[Hoomgar]

All right. I believe we are about 90%+ there. It is running very good this morning. Last night a forum friend came over with his Motion Pro manometer and we got the carb sync done and the points set. It runs a lot better! The sync positively made the engine a lot smoother. Thx Duane

Here are the manometer shots:

Before

After

It came up with just a little tweaking and we were there. It took longer to set the timing :lol:

I took a plug read then when I got back from my burn last night and although I can see the need for more tweaking it is way better! At least it isn't lean!

I need to walk that in now so it will be a matter of learning to master the pilot and air screw adjustments I believe?

I did get another spring for the throttle and although it is still much lighter than the stock spring it returns the throttle a lot better than that last one I put on and I can ride the bike normally now.

Over all, I am very pleased. I rode it to work this morning and I can tell you, it was making me proud to be riding my vintage GS sports bike. Man does it ever sound good. The pipe is much quieter now. It is still a loud bike by my definition but it is half of what it was before I repacked that baffle.

Keith, those plug reads always look lighter in the photo than they do in real life. The lightest one there is actually on the dark or rich side according to the plug color chart. That said, the others are darker and have a bit of a carbon buildup on them. What do you suggest from here? I am going to resume working on this after this weekends ride.

 

[KEITH KRAUSE]

Mark, I'm betting you have a lot of overlap from the pilot circuit in those reads. That would mean some fine tuning of the pilot fuel screws underneath. Just 1/8 turn can change the color/performance. Remember, they are for fine tuning each cylinder. It's common to set them a little different from each other. I get reads for the pilot circuit by running the bike in 4th gear at about 35 mph for a few miles. The side air screws have been adjusted for highest rpm I hope. Do that too if you didn't.
To get true/accurate reads, if I had your bike here, I'd find a safe place to do a solid 1/3 throttle position run for a few miles. The "chop test" should always be done. This would give you a true jet needle read.
For the main jet, you have to do the same thing, except at full throttle.
I would do the main test first, then needle, then pilot, just my habit.

 

[KEITH KRAUSE]

Also, what rpm's are those pic's at?
As I said earlier, I was interested in the initial vacuum reads and how they compared to the first plug reads. Your #3 plug was leaner than the others and #2 to a lesser degree. If strictly vacuum related, you would have seen a lower initial vacuum level at #3 and #2 as compared to 1 and 4.
3 was not lower, and 2 was equal with 1. Also, 4 was also equal to 3.
As long as the tool was attached without leaks, this suggests the slides are not operating smoothly/predictably all the time, or something else is effecting the mixture reads.
If all other work is done exactly the same and correctly, then the initial vacuum levels you saw would have reflected the first plug reads you showed.
Your needle circuit plug reads still surprise me a little. I have to assume you tested as I suggested. Raising the stock jet needles just one position from stock, isn't much for the K&N's. I have to think the K&N's flowing ability has been compromised by cleaning them wrong in the past. They can't be cleaned with gas or rinsed in the wrong direction (outside- in) without damaging the fibers. They could be flowing like cheaper pods, or even less. K&N's usually require richer adjustment of the needles, especially with a quality pipe.
Your choice of pipe packing material may also be effecting things.
I'm not trying to be negative, just saying what I believe. If you're happy with things, that's great.

 

[Hoomgar]

No I am not happy yet Keith.

These K&N Pod's were never cleaned incorrectly to my knowledge? They look good buddy and the only cleaning I have even done on them was with the K&N filter recharge kit. They are good to the best of my knowledge.

If I follow what your saying on the initial sync read vs the initial plug read then yes these need some tweaking of the pilots.

What I am getting now is a bike that is running really good. It has nice throttle response and a good rolling on torque band from what I can tell. It is waking up at around 4.5k and lives up to red line. No perceivable flat spots. Not backfiring, no sputtering. But it is smoking like crasy! And everyone following me says it smells gassy.

I am guessing my pilots are off and that I am maybe a bit rich?

I tried to adjust for highest idle? Not sure I know what I am doing there? Can you go over that briefly for me?

Aside from the highest idle, where should I go from here?

 

[KEITH KRAUSE]

K&N filter oil, who would have thought it? I thought they were dry filters? I have been using them for over 14 years and never did or knew that. Learn something everyday I always just cleaned them out with gas, polished the chrome with chrome cleaner and put them back on. I will get some of this oil.

At first, I thought I confused your topic with another one. (I answer too many. :roll: ) But noooo, it was you allright. K&N pods breath better than just one position up on the jet needles. But that's water under the bridge now.
I gotta go, I'll answer your questions after work.
Under acceleration or even just idling, is the "smoking" exhaust dark or blackish?

 

[Hoomgar]

K&N filter oil, who would have thought it? I thought they were dry filters? I have been using them for over 14 years and never did or knew that. Learn something everyday I always just cleaned them out with gas, polished the chrome with chrome cleaner and put them back on. I will get some of this oil.

At first, I thought I confused your topic with another one. (I answer too many. :roll: ) But noooo, it was you allright. K&N pods breath better than just one position up on the jet needles. But that's water under the bridge now.
I gotta go, I'll answer your questions after work.
Under acceleration or even just idling, is the "smoking" exhaust dark or blackish?

You made me read back Keith, I was talking about the pods on my "other" GS before LOL! There I go again. Sorry buddy :| These pods came with the bike and were oiled with a red oil. I assume they are good and I cleaned and oiled them correctly.


Anywho, yes, it is VERY black and like soot.

 

[KEITH KRAUSE]

Hi Mark. So it runs great but there's obviously unburned fuel passing. :? The two don't mix, but lets chip away and find the problem.
What's bothering me is that you say everything I asked about has been done correctly. The carbs are clean and rebuilt, floats set, identical jetting in each carb, carbs synched, no intake leaks, timing set and great spark, good compression...but you're still getting varied plug reads and passing unburned fuel.
The side air screws should have been adjusted for the highest idle before the vacuum synch. Also, the pilot fuel screws sound like we should lean them some. From what you're telling me, your bike runs richer than any I've seen with similar settings. Your flow restriction seems high for K&N's and a good pipe, though I don't know about that exhaust packing you've installed.
I still have to know what throttle position you're typically riding at to give better advice. The throttle position is the most important thing. Right now, I'm assuming you're just puttin' around town?
First thing, permanently remove the two floatbowl vent tubes, if you haven't already. Now turn the pilot fuel screws in so they are all 1 turn out. Use a mirror and be sure you turn them the right way, clockwise.
Now set the side air screws for highest rpm.
The side air screws should be about 1 1/2 turns out to begin. The bike should be on the centerstand or as level as you can get it. Warm it up completely first. Set the idle to 1,100 rpm's, not any higher. Starting with any carb, SLOWLY turn the side air screw out, c-c-w, until you hear the rpm's max out. The "sweet spot" is usually around 1 3/4 to 2 turns out. Just slowly turn the screw, in either direction if necessary. Fine tune so you stop turning just when the rpm's stop rising. Now re-set the idle to 1,100 rpm's by adjusting the idle adjuster knob. Repeat this same procedure to the next carb. After all 4 are done like this, you're done. Don't touch them anymore.
Be sure the plugs are gapped correctly and they're NGK B8ES.
If possible, can you hook up your vacuum tool and re-check the vacuum levels?
Go test. If you can, I'd really like to see some solid/steady 1/3 throttle position plug reads followed by some minimal/steady throttle position reads as I've described earlier. Always chop the bike off. Do the 1/3 throttle run first, then the lower speed run.
There are a lot of things that can cause the bike to run rich/pass unburned fuel. Try the above and we'll go from there.

 

[Hoomgar]

Will do Keith. I have all the time in the world now and my carbtune and colortune came last night

I'll will do the above and report back. The plugs are correct but I will recheck the gap. I will recheck the points/timing/dwell and I'll redo the pilot and air screws as you said.

I didn't know how to adjust for max idle before so now I'll get that done.

I hope my baffle packing is OK? I can't see it being a problem as I used the really course stuff and it seems to flow well.

I'll post back when done.

 

[Hoomgar]

OK Keith, here is where I am at :|

Last night I rechecked my points. I made sure I did a solid gap on both sets and timing job on both 1&4 and 2&3. It is spot on the marks and the gap is right-o by the specs in the manual.

I turned all my pilot and air screws back in the whole way. I turned each pilot out 1 complete turn out as you said and then I set each air screw at 1.5 turn out. I then started the bike and adjusted the air screws for max idle. That proves to be almost impossible.
I really cannot tell a difference in most cases with several complete turns in either direction? What am I doing wrong? Only if I turn them in too far will it chug out. Otherwise it seems all the same. Am I maybe doing it at too high an RPM?

Once I got the air screws where I thought they should be I hooked up my carbtune and tweaked the sync in a bit more. It wasn?t off by much at all but I set them all even across the board. I have a picture of it, just didn?t get time to post it. I then rechecked the max idle adjustment and actually had better success that time. It now idles at almost 1500 rpm on it?s own without the idle adjustment screw touching at all.

I took it for a run and it runs like crap. This is the worst it has ever run. It is bogging, sounds wrong? It seems like it isn?t hitting on all 4 but it is. It?s just rough. Nothing smooth about it. I was really mad because I put all evening into it with a hurt back only to end up with a midnight run that proved to simply crap out the bikes performance.

I didn?t do something right, that?s for sure. :|

 

[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.