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

[Anonymous]

78 GS1K Carb Rejet ? Bad Fuel Economy

78 GS1K Carb Rejet ? Bad Fuel Economy

Does your bike bog ? Does it seem to have more power when you first start out ? If you have not done any work on your carbs for a long time they may need to be cleaned and new O-rings . I had one hell of a time with my intake boots . Had to change all the intake boots . The O-rings were so flat and dry they fell off the old boots. Hope this can help you

 

[Hoomgar]

Keith. I am not sure what it may be but there must be something else wrong with this engine?

I now have the DJ 122 mains in and it runs good. Needles are at the fifth position (highest setting). Carbs are in sync. Pilots are 1 turn out on 1 & 4 and 1&1/4 on 2 and 1&1/2 on 3. Air screws adjusted for max idle.

Before I did that I recleaned all the openings in the carbs with carb cleaner then put all the needles back in. I then balanced the float levels with clear plastic tubes in the bowl drain holes so that all four are at the same level. They were actually good except the fuel level in carb 1 was low. Now they are good. I put brand new o-rings in the carb intake boots and helped seal them with hi-temp grease. The valves are all adjusted. That measurment I was looking for was .0015 to .003 inches that was confusing me earlier. It's from the manual. It is right. They all fall right between the two.

It doesn't seem to have quite as much top end/WOT power now but runs pretty good. Midrange is near perfect now and low end is a lot smoother while using a little throttle but still eratic when just cruising.

The kicker is, it still smokes and gets 24 MPG. No matter what we have tried it always gets 24 MPG and smokes.

What else do you think I should check at this point?

 

[Hoomgar]

OK I have dropped the main jet clear down to a 120 and I think I may be getting there. It seems I may have been going about this all wrong. I was talking with a local vintage UJM carb guru and he said to start with the main circuit first and get your main jet right. Then do your needle and then any idle adjustments that may still need done.

So my question is this. What is the prefered method for doing a WOT main jet plug read test? Just find a nice long open cop free road or what?

Any replies are welcome and wanted.

 

[Anonymous]

It seems I may have been going about this all wrong. I was talking with a local vintage UJM carb guru and he said to start with the main circuit first and get your main jet right. Then do your needle and then any idle adjustments that may still need done.

I might as well reply, since Keith K hasn't yet...

It is better to start at the bottom and work your way up (ie. pilots, then needles, then mains) than starting with your mains. The biggest reason is that what you do to your pilot and needle circuits affects running on the mains, but the mains do not affect running on the lower circuits. You could REMOVE your main jets and still toodle around town (and at legal highway speeds, for that matter) with no problems at all. Especially on a litre bike you will spend almost no time at WOT and most of your time barely off the pilot circuit. So sort those first and then worry about your mains after it runs well at small throttle settings. Actually, once you get the pilot and needle circuits set, it is a piece of cake to size the mains. I do feel your pain on getting the lower circuits set, they can be a bear to sort really well, as you have been showing here.


Mark

 

[Hoomgar]

Thx Mark. I believe that is the path Keith had me on. I just wanted to see what others thought as well since Keith isn't around right now and I was being told this.

I am getting closer I know. Time to get back to this now. It is running better now on the needle and WOT seems OK too but I get some coughing at idle at times.

Is there a place where I can see how to do all three plug read tests that are recommended?

 

[Anonymous]

I believe that is the path Keith had me on.

I believe you will find that Keith and myself agree on this point and that many others disagree. Many jet kits will tell you to sort the main jet and then the pilot/needle settings, but that is a situation where you have mostly well sorted carbs and are fine tuning the settings from EPA lean to smooth running. You are trying to find baseline settings with no well sorted starting point. That requires a different method to work it out.

Is there a place where I can see how to do all three plug read tests that are recommended?

Not that I know of, but someone else may have seen one.

One point to remember on plug readings - they are most important on the pilot and needle circuits and less so on the mains, as the mains are easier to figure out. Keith mentioned that he gets the pilot and needle set and then simply goes up to the biggest main he can run that won't affect the needle. This is possible because it is not important if you are somewhat rich on the mains. The plug reads are important on the lower circuits because you want them to be as lean as possible for sharp throttle response, good fuel mileage and no plug fouling, while not being so lean as to damage the motor. Ideally, you want the pilot and initial needle to be slightly lean of optimum (assuming no driveablilty issues), then have it transition to slightly rich as the needles raise and transition to the mains. As RacingJake noted, the engine will just pull harder and harder at WOT as the mains get bigger until it blubbers from too much fuel. You want to be at the last jet size that pulled hard before it blubbers. That way you will not cook your motor from a lean condition at WOT. The lean settings on the pilot and needle will not cook the motor because it does not generate much heat at low power settings and there is little danger of damage while running there.


Mark

 

[Hoomgar]

All makes sense to me Mark. Thx again.

 

[KEITH KRAUSE]

Hey Mark. I'm back. Let me try to catch up here.
I personally jet the needle circuit before the main which appears to be the opposite of the majority. It works for me though. I believe in a perfect running needle circuit and I then run the largest main I can without creating a bog during top gear roll ons. That's the simplest way I can put it. I will sacrifice a couple of mph's top speed if I have to, I will not accept a bike that won't roll on (typical high speed passing) without bogging.
I test/plug read the main at full throttle on a level or uphill road. I test/plug read the needle at 1/3 throttle. I test/plug read the pilot at the very mimimum amount of throttle opening needed to just cruise at about 35 mph in a higher gear such as 4th. The pilot takes more fine tuning because of the overlap with the needle.
I don't know exactly what you mean by "coughing", but it sounds like you're doing something to lean it out too much. It still depends at what throttle position the problem, or any other problem occurs.
Your worst problem by far is the bad mileage which is directly related to the heavy exhaust. I feel this is a carburetion problem. You say the compression is good and you've checked everything you can related to good spark. A poor spark and 24 mpg would absolutely cause the plugs to run very sooty. Your plugs are good or if anything, a bit lean with the bad gas mileage. So you're simply passing unburned fuel and the plugs are staying clean. Either too much fuel is entering the cylinder(s) or the fuel isn't being atomized (vaporized) correctly. You say the carbs are clean and all basic carb adjustments have been done.
Going by your messages and our phone conversations, these carbs have had butchers working on them. That means anything is possible.
I'm positive your main jet is not the cause of the problem. You would have to be at 3/4 throttle and above for it to be the problem. I have yet to see a pipe/K&N pod equipped 1000 run rich with the STOCK needle in the 5th position. So what's causing the 24 mpg and heavy exhaust?
I'm suspecting the pilot jet or pilot circuit at this time. Also the needle jet/bleed pipe. I know you say the circuits are clean. The pilot fuel screws turned out at 1 full turn is certainly not too rich and lean if anything for your mod's.
So I'm thinking the pilot jets may have been drilled out or the tiny holes in the needle jet could be clogged. What are your side air screws set at? If they are still not adjusting "normally", about 1 1/2 turns out, this is a sign of a too large pilot jet or too rich a mixture. Are your pilots #15? Are they genuine Mikuni or from a rebuild kit? Can you show a good picture of them next to a ruler or measure them? Can you hold yours up to another #15 pilot jet and compare the holes? Can you see a size stamped on the needle jet? Are the new needle jet o-rings you installed seated corrrectly?

 

[Hoomgar]

So I'm thinking the pilot jets may have been drilled out or the tiny holes in the needle jet could be clogged. What are your side air screws set at? If they are still not adjusting "normally", about 1 1/2 turns out, this is a sign of a too large pilot jet or too rich a mixture. Are your pilots #15? Are they genuine Mikuni or from a rebuild kit? Can you show a good picture of them next to a ruler or measure them? Can you hold yours up to another #15 pilot jet and compare the holes? Can you see a size stamped on the needle jet? Are the new needle jet o-rings you installed seated corrrectly?

Pilot jets are stock #15 according to the stamp on them. The ones that came in the rebuild kits were much shorter in lenth? The o-rings are seated correctly. What are the needle jet's you speak of? The mains? Right now, they are brand new Mikuni 120's if that is what you mean. All my main jets have been new in the bags.

Right now the bike is running good like always but is still passing fuel although not quite as bad. All I changed was the mains. I removed the 125's and put in 120's.

I am putting the ball back into your court if you have time. What would you like me to do next? I am out of and open to ideas. So far nothing has made a "real" change.

 

[KEITH KRAUSE]

Wow. The longer this thread goes on, the more possibilities.
Also, I read a small part of your other post about black/heavy exhaust.
The pilot jets MUST be the same length as original. Though shorter pilots should cause fuel starvation while on the pilot circuit (and you're experiencing rich problems) replace the pilot jets with MIKUNI ONLY #15 jets. The original pilot jets have an exact amount of holes in them. The replacements must be identical. If you don't replace them, the bike will always have a problem. This just goes to show how many things could be wrong with the bike.
As for the needle jet, it's the brass jet the jet needle slides up and down through. It has little holes that need to be completely clean. The main jet screws into it. These jets could be the wrong size or worn.
I'm even wondering about other parts in your rebuild kits. The needle jet o-ring could be a little smaller. This would absolutely cause your problem. If they supplied the wrong pilot jets, anything's possible.
And then reading your other topic, you say the plugs only burn clean at about 1/3 throttle. Otherwise, they're black and sooty and fouling out. This topic you only mention and show pic's of fairly decent looking plug reads, though a bit lean at two cylinders. The plug reads you show and the poor mileage simply contradict each other. But then the other topic says something that at least makes sense. I need to know everything that's happening.
When you were on your trip, you spent the most time riding on the needle and pilot circuits. Your previous solid 1/3 throttle tests show the needle is set as good as the stock needle can be set. Those reads were good or a little lean. Any black/fouling plugs at lower speeds would then be caused by the pilot circuit overlap at lower speeds/throttle positions.
If your plugs are cleaning up as the bike runs more on the needle circuit/main circuits, then your pilot circuit is probably causing the problem.
If you also get heavy exhaust at full throttle, then this would suggest the mains are too big. But your bike should be able to handle 120 mains unless there's an unknown problem. With the smaller mains you say you're losing a little top end but the bike still has heavy exhaust. Another contradiction. This also suggests an unknown problem.
At this point, I have to say I doubt too many things. I would install the correct pilot jets and check the needle jet sizes and clean the holes out if needed. We may have to go through every part that can cause your problem. Eliminate things one at a time. Without looking at the carbs myself, it's difficult. Maybe if you show part pic's and describe your adjustments in detail, such as float adjustment, needle clip/spacer assembly, slide cut away size (should be 1.5), etc, something will appear.

 

[Hoomgar]

That's what I will do then Keith. I'll pull these suckers after this tank full and see about getting you some parts pics. The pilot jets I am betting are right because they really look like the stock Mikuni jets and I didn't swap them with the ones in the rebuild kit because those looked wrong to me. I know all the holes in them were clean and looked good but I'll get you some pics of them.

One thing to note about the trip. We spent most of the time on that ride on the needle and main circuits. Very little riding was done on the pilot. Especially the ride down and back. Most of that was well into the needle as it was all highway and at high speeds. But the fouling did always happen at idle right after starting the bike. I think I had turned the pilot out too far on 3. I had put a new plug in it and gave it 1/4 turn back in and that never happened again.

All the plug reads in this thread were done at 1/3 throttle yes so that is all we have eve seen. But when pulling plugs down at the rally they were seriouly rich.

I need to service the bike anyway after the trip. I did put new sprockets and chain on it since then and changed oil/filter but nothing else. I need to find some time and I'll pull that rack off again and get you some pictures.

One thing I see right now is that on this tank of gas since I put the 120's in it I am getting better MPG. I'll get a read when I fill up. But it coughs a good bit at idle. Never while moving but at ilde it will cough through the carbs. That means lean from what you have told me and I believe it because I have the pilots turned back right now.

Let me get those pics.

 

[Anonymous]

One thing I see right now is that on this tank of gas since I put the 120's in it I am getting better MPG. I'll get a read when I fill up. But it coughs a good bit at idle.

I find that strange that smaller mains would affect your mileage much at all. Unless you are doing a lot of cruising above 3/4 throttle, that is. I would have some serious issues with the local cops if I spent much time on the mains, though.

Does the coughing go away with choke? Does it cough if you cruise on the pilot circuit? Does choke help it there?

I have to agree with Keith, there is something unusual happening with your carbs. Normally, jetting is not this complicated. You have to be very methodical and take it one step at a time, but you should not chase it all over like you have been. Once you set your pilot circuit, you are done with it, then you set your needle and leave it alone, then the mains. After that, it should only be small changes to fine tune the overlap points and maybe compensate for a slightly leaner or richer needle taper than you need. With a set of stock carbs it should always be possible to get pretty close on all the circuits, maybe not perfect, but certainly rideable with no real issues like your fouling problems. From the sound of it, your carbs have been treated badly by a PO, whcihc certainly complicates the whole process...


Mark

 

[Hoomgar]

One thing I see right now is that on this tank of gas since I put the 120's in it I am getting better MPG. I'll get a read when I fill up. But it coughs a good bit at idle.

I find that strange that smaller mains would affect your mileage much at all. Unless you are doing a lot of cruising above 3/4 throttle, that is. I would have some serious issues with the local cops if I spent much time on the mains, though.

Does the coughing go away with choke? Does it cough if you cruise on the pilot circuit? Does choke help it there?

I have to agree with Keith, there is something unusual happening with your carbs. Normally, jetting is not this complicated. You have to be very methodical and take it one step at a time, but you should not chase it all over like you have been. Once you set your pilot circuit, you are done with it, then you set your needle and leave it alone, then the mains. After that, it should only be small changes to fine tune the overlap points and maybe compensate for a slightly leaner or richer needle taper than you need. With a set of stock carbs it should always be possible to get pretty close on all the circuits, maybe not perfect, but certainly rideable with no real issues like your fouling problems. From the sound of it, your carbs have been treated badly by a PO, whcihc certainly complicates the whole process...


Mark

Yeah it is weird Mark. But that is all I did was put a smaller main in it and the MPG are noticably better. I'll know tonight how much better.

Admitedly, I spend a LOT of time on the "high" end of the needle and the main.

What is being done in this thread is mostly what Keith has been telling me to with few exceptions from times when he was not around so your critiquing his trouble shooting there :lol:

I agree that something is screwed up. It doesn't seem to matter what we try, this bike smokes and is passing fuel. I'll be posting pictures of the parts he asked for soon as time permits. I really don't think were going to find anything like drilled pilot holes or anything because they look identicle to my other set of stockers. It's something else. I just wish I knew what so I could fix it. This thing gets about the same fuel economy that my wife's Focus does :?

 

[KEITH KRAUSE]

(Mark, read the bottom line before tearing things apart, if you would. )
Yes, this re-jetting over the internet has been fun. And yes, the bike is not getting the results that other 1000's with similar mods do.
This bike started out with bad gas mileage and still gets bad gas mileage.
As for the jetting, in my defense, I said from the beginning the stock needle doesn't work many times, especially with K&N's and I prefer jet kits. I also said to put the stock needle in the 5th position, if it had any chance to work at all. I still stick to my main jet selection because it's certainly "ballpark" by past experience and wouldn't cause these problems on any other 1000 I've jetted or helped jet. The pilot circuit SHOULD work well with just pilot screw adjustments and the air screws adjusted for highest rpm.
Everything else... spark, compression, valves, clean/correctly adjusted carbs, etc, Mark says is good.
But what we have is a bike that's passing fuel, though the most commonly used circuit, the needle circuit, is fairly close according to the plug photos.
However, now the bike is giving rich reads on the plugs?? With no needle change and only a leaner main change?? Makes NO sense. He has played with the valve clearances since the leaner reads though.
All I know is if the bike was here I'd go through everything and suspect everything.
Last I saw, the needle was as close as the stock needle will get and was lean at 2/3 if anything.
The main, as Mark just said, is now too small and the bike's top end is suffering. The smaller main will help MPG when on the main but when the top end is suffering this is an obvious sign you've gone too far. On a properly running bike, the main is not the cure for these problems.
With a pipe and K&N pods, the stock pilot circuit works fine almost every time after screw adjustments. Sometimes a 17.5 pilot jet helps with decel' pop and cold start "spitting" out the pods, but the larger pilot sometimes creates rich related problems and you just live with the less troublesome decel' pop.
As I said earlier, at this point I would start the inspection with the pilot circuit and the needle jet. Pic's with the parts next to a ruler would help. I'd like to see how the float levels were set, etc, etc.
PS:Mark, if you now chop tested the plugs at full throttle, 1/3 throttle, and at a steady 35 in 4th gear (in that order), that would help too. And, where is the sweet spot on your air screws now?

 

[Hoomgar]

(Mark, read the bottom line before tearing things apart, if you would. )

PS:Mark, if you now chop tested the plugs at full throttle, 1/3 throttle, and at a steady 35 in 4th gear (in that order), that would help too. And, where is the sweet spot on your air screws now?

Well were in luck because as time would have it I didn't get to do anything yet

I'll get chop tests then. How do I do that though for WOT? I mean, how long should I let it run to get a good read? Speeds that high have limited roads where I can do it so I want to get it right in one shot if I can.

The only running symptom right now Keith is that spitting at idle. Top end is in no way suffering. It is running strong right now on both needle and mains but at idle it spits a lot out the filters. And I mean a lot. If I raise the choke it dies immediately at idle. Yet I can't start it cold without the choke now. This is a first for that! Once moving and on the needle it is fine as well as at WOT.

Oh, BTW, I topped off the tank and got MPG reading. Just shy of 30 MPG! And that is city miles. It has never been that good before. That is the best I could do highway prior to this setup.

I'll leave everything as it is until I get those plug reads.

 

[KEITH KRAUSE]

OK. I was going by your June 14 post (while I was gone) where you said you tried some DJ 122 mains, which are about the same as 115 Mikuni's, and you said the bike was losing some top end but running pretty well.
Going back and seeing that the previous top end loss was due to the smaller mains at least makes sense. I just didn't notice that we were using different brands of jets here. DJ and Mikuni jets aren't the same. If you now have Mikuni 120 mains, you actually increased the size from the DJ 122 mains. Of course, what's funny is you say the gas milege is improving by installing larger mains. I'm beginning to think this is an exorcism instead of a re-jet. :lol:
Actually, despite some odd stuff happening, you haven't really worked on this as much as many others have. I read here all the time how a member says he's had the tank off maybe 10 times messing with the jetting.
As for main testing, wide open is the only way I know of without a Dyno to get accurate reads. I know it's not safe if you live in certain areas and I try to mention that. I make sure the plugs are clean and after being sure the bike is completely warmed up, I go 2 to 3 miles, usually split up by two seperate wide open runs of about a mile each. In between, something a little slower, say 3/4 throttle. I then do some acceleration tests to check for any bogging, etc.
If your pilot circuit is spitting, that's a lean condition. If it just started happening, with no other parts changes or carb problems such as dirt, then adjusting the pilot fuel screws or the air screws should help. If the air screws are adjusted the way they should be, then I would go with pilot fuel screw adjustments. Problem here is I think you say richening them was causing fouling??
Another thought...if you messed up the valve clearance adjustment, this can cause spitting too.

 

[Hoomgar]

The valves are good Keith. I set them at Paparo's under his direction using his tools, gauges and shims.

I don't know when I am going to get a chance to do those plug reads but I'll post when I do.

 

[mike J]

Guys, been trying to read this thread. I just got a problem solved on my 1150 that has been driving me crazy. It has Dynojet Stg III jetting , K&N pods and a 4into1 pipe. Long story short my needle and seats were leaking on two cylinders. No matter what I did it made no difference. The way I found the problem was like this. Take the float bowls off the carbs and turn them upside down on a work bench. Hook up a piece of fuel line to the carbs. I used a product called Snoop leak detector but probably soapy water would work also. Drip some on the needles and blow into the fuel line with just normal breath pressure. If you get bubbles replace the needle and seat. I had one leaking pretty good and the other was just minor. It cleared up all my jetting problems. Worth a try Mike J

 

[Hoomgar]

Thx for the tips Mike. It may come to that. I have a feeling that the next thing we'll be doing is a rejet kit to get new needles. I can see Keith leaning that way since the start of the thread. I believe this is one of the bikes that just isn't going to come right with the stock needle. This may be it.

 

[mike J]

Yea, I didn't realize that your needles were stock. The whole time I was blaming my problems on the Dynojet kit and it wasn't the problem. Mike J