A Keith Krause carb jetting question!

[jonr]

Keith,

Back when I had that big oil leak on my 750 before the E/SE rally, I had mentioned that my re-jetting project was not going well and I went back to my factory jets. Well, I think it may be time to try this project again and I was going to take you up on your offer for some advice.

To give you some background, my current stock setup is:
#15 pilot jets
#100 mains
1 turn out on the pilot mixture screw
1 turn out on the air screw

With my V&H pipe, they recommend the following:
17.5 pilots
115 mains
raise the needle one notch

I know you mentioned that raising the needle was not a good idea, so I am curious about your thoughts on all this. I also just acquired a Morgan colortune, so I should be able to adjust the fuel mixture screws a lot more accurately.

Thanks!
Jon

[KEITH KRAUSE]

Hey Jon. Almost didn't see this.
I'm assuming the jet needles are also at their factory position, which is with the e-clip in the 3rd/middle position.
I'm not necessarily against raising the needles, but you should test at 1/3 throttle FIRST to see how performance/plug reads are. By far the most work when re-jetting your carbs is changing the needle positions. Many times, a pipe only mod doesn't effect the jet needle circuit enough to make changes, but I do what the plugs/performance say.
Interesting how V&H has changed their jetting recommendation info over the years. They used to claim their pipe (street megaphone) didn't require any jet change but somehow increased power. Kerker claimed the same. Then they said 1 size up on the main only. Now they say 3 full sizes AND jet needle and pilot jet changes? Hmmm. Their street megaphone looks the same to me after all these years.
I think an increase of 15 is too much for a pipe only mod. One full position richer on the needles is also too much, based on my experience. The 17.5 pilots are not that much of an increase but very often all that's needed are richer pilot fuel screw adjustments (underneath).
If you read any of my past posts, I've always been out front and said I have much more experience re-jetting for intake and exhaust mods than just exhaust mods. A freer flowing pipe that's restricted by the stock airbox is a poor match. Poor matches can make jetting more difficult. I don't want people to think I'm the "last word" in jetting and run out and buy jets based only on what I say. I always do my best but it's not easy to get jetting right the first time. If you do get it right the first time, most will say it was a lucky guess.
As always, the bike must be ready to jet. All basic tuning/maintanance must be done first.
This assumes you DO have the street megaphone and not the competition pipe and you run the stock air filter element with the airbox lid on...
I typically allow a 7.5 to 10 main jet increase for that pipe. Between the two, I recommend the 110. Test at full throttle.
I'd test the jet needles at solid 1/3 throttle first. Do what the plugs say.
If the plugs do look lean, I'd imagine that a 1/2 position change would be enough but it depends on the reads. A 1/2 position change is done by taking the e-clip from the 3rd position and lowering it down to the 4th position from the top. Then you place an approx' .022" jetting spacer directly on top the e-clip. Re-install the two factory plastic spacers in factory order...thicker above the e-clip and any jetting spacer needed, and the thinner spacer under the clip. V&H should sell you some jetting spacers if you contact them. But test first.
Remember, every time the jet needles are disturbed, you must re-synch.
As for the pilot circuit, I'd first try testing at minimal throttle (steady cruise around at approx' 35 in 4th/5th gear) and get reads. If lean, try a solid additional 1/2 turn out on the pilot fuel screws underneath and re-set the side air screws using the highest rpm method after that. If the pilot circuit is still lean with the pilot fuel screws as much as 3 turns out, then the screws have reached their effectiveness range and you would need to go to the 17.5 and return the screws to something close to factory (about 1 turn out from lightly seated) and re-test.
Remember, to accurately check the performance and plug reads, the carbs must be bench synched followed by a vacuum tool synch. The carbs should be synched before any initial testing/reads too. Before the synch can be considered accurate, the valve clearances and ignition timing must be correct. You also must fully warm up the bike and then set the side air screws using the highest rpm method before the synch. I initially set the air screws to 1 1/2 turns and then fine tune. Whenever the carbs are taken off and it's been awhile, it's usually a good time to change the manifold o-rings too. More work, but worth it.

[jonr]

Keith,

Thanks for the lengthy and detailed post. Here's is what I can tell you about my setup:

Intake boots: soft and supple
Intake orings: new -spring 2007
Stock airbox with K&N element
Carbs: cleaned, new orings, synced -spring 2007
Needles currently in 3rd position
V&H street megaphone
Valve shim job -spring 2007

I, like you, thought the main jet jump was rather large, but I guess there is one way to find out. If so, I'll get some 110's as my dealer is selling them to me for $8 a set (mikuni). I've never checked the timing since I put on my dyna S ignition 7-8 years ago as I have never removed the pickup plate since then.

My goal is to have a few shots at it this week. We've got rain right now and so the most I'll be doing today is checking the timing. I will report as soon as I get some results.

Thanks so much for your time.
Jon

[KEITH KRAUSE]

OK. Be careful when high speed testing. Without a Dyno, there's really no other way to see what the separate jetting circuits are doing unless you operate the bike at the throttle positions required.
Sounds like the bike is ready. However, I have seen the Dyna sensors "creep" a little with time and the bike may benefit from checking the full advance with a gun. Don't over-tighten the sensors small allen screws either if they must be moved. I've found that after verifying correct timing and snugging the screws properly, a small dab of silicone on each end of each sensor will permanently stop any possible movement.
I'd install the 110's. If you have decent finger dexterity, it's easier to swap the mains without removing the carbs. Just be sure to use the right tool and don't over-tighten the main into the needle jet/bleed pipe. Be careful of loosening the needle jet and forgetting to snug it properly too. Depending on how old your bowl gaskets are, be aware of possible leaking when you disturb them. The bowls are a bit easier to install "tilted" if you aren't careful. Just mentioning things that can happen when you work with the carbs still on the bike.
You also have the option of leaving the stock mains in and simply testing the jet needles at 1/3 throttle. The mains will have no effect on 1/3 throttle position reads/performance. If solid 1/3 plug reads say you're lean, then you can save changing the mains for carb removal/needle change. Up to you as to what's better.
Regardless of how you proceed, I'd first adjust the pilot fuel screws to 1 1/2 turns out initially, or 1/2 turn further out than where they have been (if the pilot circuit was working well). This would be followed by adjusting the side air screws using the highest rpm method. Now you can go test both the pilot and jet needle circuits.

[jonr]

Keith,

I got a chance to do my first test this evening... kind of a quickie. I turned out the pilot fuel screws a half turn (1.5 turns total) and then used my colortune to adjust the air mixture screws. I don't know how you guys do it by listening for the highest RPM, but thankfully the bunsen blue flame was easy to dial in. I ended up turning out my air screws another 3/4 turn to get the constant blue flame. Then it was out to test...

So far so good. The plugs looked very normal and tan and I wonder if I should try another half turn out on the pilot fuel screws to see if I can milk some more. To be honest, the plug read was not much different from when I had the pilot screws at 1 and the air screws at 1. Is this oK? Also it performed nicely - no lag and no popping of any kind.

I have yet to mess with the mains or the needle circuit and I'm going to wait for the bike to cool off anyway before I drain and tear off the fuel bowls. I am also able to change the needles with removing the carbs - only the tank. It just requires pulling out the throttle rod. Gotta re-synch anyway right?

Thanks for your time.
Jon

[KEITH KRAUSE]

Keith,

I got a chance to do my first test this evening... kind of a quickie. I turned out the pilot fuel screws a half turn (1.5 turns total) and then used my colortune to adjust the air mixture screws. I don't know how you guys do it by listening for the highest RPM, but thankfully the bunsen blue flame was easy to dial in. I ended up turning out my air screws another 3/4 turn to get the constant blue flame. Then it was out to test...

So far so good. The plugs looked very normal and tan and I wonder if I should try another half turn out on the pilot fuel screws to see if I can milk some more. To be honest, the plug read was not much different from when I had the pilot screws at 1 and the air screws at 1. Is this oK? Also it performed nicely - no lag and no popping of any kind.

I have yet to mess with the mains or the needle circuit and I'm going to wait for the bike to cool off anyway before I drain and tear off the fuel bowls. I am also able to change the needles with removing the carbs - only the tank. It just requires pulling out the throttle rod. Gotta re-synch anyway right?

Thanks for your time.
Jon

Your pilot fuel and air screws are at very typical settings. The bike should be running a little better while on the pilot circuit since the air screws were too far in initially. Depends on exactly what plug color change you see when you say "the plug reads were not much different". They would figure to be similar since you increased both the pilot fuel screw adjustment (more fuel/air mixture= richer) and air screw adjustment (more air). The main difference now is the mixture is being better atomized. 1 turn out is simply too little for VM carbs with your mods or almost always even a stock bike.
I did say it was up to you how you want to change mains, etc, and when.
You said the carbs were synched well. If solid 1/3 throttle test show good performance AND acceptable plug reads, there's no reason to think about synching. Only if you see lean reads will you have to re-synch because of necessary needle changes. If that happens, I'd suggest removing the carbs but I know you have a harder time with the stock airbox boots.
It may seem easier to you keep the carbs on and delete the bench synch but you can't accurately synch the carbs for both the fully closed and fully opened positions with the carbs on the bike. The bench synch, when done correctly, will allow the bike to start easily in preparation for the air screws highest rpm method adjustment followed by the vacuum tool synch. You run the risk that the bike may not start easily or at all. Many owners kill the battery trying to start a bike with poorly bench synched carbs. If it does start, the vacuum tool synch may take longer because the carbs are not as close initially as desired and you can over-heat the motor by taking more time to get the levels close.
You also can't bench synch the slides for the fully opened position when on the bike. You can't see if the bottom of the slides are within the required .5mm to 1mm range above the top of the main bore. If not, full throttle performance will suffer, something you don't want or need when testing main jet performance.
Hopefully, your 1/3 throttle performance and mixture will be good and you won't need to make jet needle changes, or re-synch.

I meant to mention this before. Have you considered some pod filters? You'll get more high rpm power. I don't know if it appeals to you or not. There's always a risk that that there may be "driveability issues" when you get deeper into jetting. In your case, the stock jet needles may or may not be able to supply a rich enough mixture if you run pods, especially K&N's. This is a problem because there are no jet kits for your model anymore. Changing jet needle and/or needle jets can get very complicated too. If the stock needles do work, paired with the larger mains, it's worth doing unless you don't care for extra high rpm power, right around 7,000 to 8,500 rpm's.

[jonr]

Keith-

Thanks again for the detailed info. Firstly, I have never benched synch with the bores wide open - only when they were mostly closed using the gap listed in my service manual. I'm guessing that when adjusting for wide open that you are only adjusting the throttle stop so they will go high enough to clear the bore?

Secondly, I actually have some pod filters that will fit on these carbs. When I picked up my KZ1000, the guy had pods on it and I plan on returning it to stock airbox because he could never get it jetted correctly. I just went to look for them and could not find them, but they are most likely Emgo's or equivalent. Anyway, the carbs on the KZ are the same Mikuni VM's sans the air screw. I'm guessing that's why it might have been hard to jet since he had stock pilots, needles and mains in it. Must have been super lean.

In the mean time, I'm going to go another half turn out on the pilot fuel screws and check the plugs to see if all the fuel being burned. One of your previous posts indicated that once the pilot fuels screws are approaching three turns, I would assume it's time to change the pilot jets?

Thanks-
Jon

[KEITH KRAUSE]

Whenever the slides are re-synched, their fully open position can change. The factory states to have their bottom from .5mm to 1 mm above the top of the carb bore. I always set them as stated. I often have found adjustment necessary during rebuilds. I can't say how critical it is because I've never directly tested for it. At least one member here said he had a full throttle issue (lack of top end power) that was fixed after he noticed the slides were too far above that 1mm limit. It seems to me that slides too far up would cause at least some turbulence/swirling and compromise optimum streaming/flow into the head.
As for the fully closed position, I would set the slides to their lowest seating by eyesight, not a recommended gap from a manual. I suppose your manual method may give close enough results, but I can set the slides so low that the remaining "gap" can't be easily measured. In many cases, the nick or opening remaining is nearly nothing. The smaller the opening, the easier it is to match them. I set them to their true lowest possible seating. If you have decent eyesight, this method will give the very best bench synch results.
Your 8/10 post said the plugs were looking a nice tan color and no running problems and I assumed you meant this was after a minimal throttle position test. If so, I wouldn't touch the pilot fuel or air screws unless other changes make it necessary.
It's true that by the time the pilot fuel screws are backed out about 3 turns, the secondary pilot fuel passage these screws regulate is opened fully or very close to in my opinion. So if you had lean plugs while operating on the pilot circuit and the screws reached this setting, you'd almost certainly need larger pilot jets. But your plug colors and performance are good, so I don't know why you want to continue richening the pilot fuel screws.
Let me know if you want to continue as planned, or if you want to see if the stock jet needles will allow you to run pods.
I'm going on vacation for about 10 days starting this Friday. I always try to stick with someone when they ask for my help. Others here may help you but I just want you to know in case it effects your testing/jetting plans.

[jonr]

Keith-

Ok, I'm going to leave the pilot circuit well enough alone then. As for the pods, I think I'll hold off since I don't actually have them. After I made my last post, I went to look for them again and gave up. I called the guy I got the KZ from and he told me that I never had them to begin with because they were in his garage and falling apart.

I can't say that I want to drop $ into pods right now and I also like the look of the factory box. I am thinking about acquiring another airbox down the road and cutting some sizable holes in it to experiment with some higher airflow.

I think the next step is to experiment with the needles and the mains. I think I'll go ahead and pull the carbs, move the needles a half notch with some washers (I've got everything down to 0-80 in my shop), and swap out those mains while they are out. Then do the bench sync, carb sync and then go do a plug chop.

I can't thank you enough for all your attention to my project. I'll try to get this wrapped up in the next few days.

-Jon

[KEITH KRAUSE]

OK. Sounds good. But...
I wouldn't just assume the jet needle circuit is leaned out enough to make jet needle changes. It may very well be, but I'd test before going through the extra work. Doesn't take much time to test and check. If you're thinking about "pre-setting" the jet needles because it's inconvenient or unsafe/difficult to make 1/3 throttle tests, I can understand the reasoning, but at some time this bike will be operating at those higher speeds and it needs to be verified before any changes can be made with confidence. Even if you need to plan and take a longer ride to find a good test site, it should be done. Along with a plug removal tool, you can take along a rag and a piece of tubing to help with hot plugs. The tubing should fit very snug over the plug end and you use it to remove and start the last/first few plug threads. Careful of cross threading. A plug socket with a rubber inner lining is even better. A little 1 mile dash at 1/3 throttle and chop off, should give an honest plug read.
Since it's your time and your bike, I'm sure you've got a reason if you want to do things a little differently than I might. We all have our own ways. There's always the chance the bike will need the jet needles raised.
If it is lean, my past experience says that a 1/2 jet needle position change should do it, but, I always test and see HOW the plugs look first. On these carbs, a 1/2 position change is accomplished with an approx' .022" jetting spacer. Just in case you aren't sure, you will need to lower the jet needle e-clip from position 3 to position 4 from the top of the needle. Be sure you pull the e-clip away from the needle, straight out, without twisting or upward/downward movements. Pop the clip back in the same way...straight in. Using a small socket facing up, I put the needle over it and carefully press on the clip with needle nose pliers. Avoid spinning/turning the e-clip to verify it's seated because it can damage the softer needle and lead to further damage from vibrations. Then, you place the jetting spacer directly on top the e-clip. You of course must replace the two factory plastic needle spacers in correct factory order...thicker on top that new jetting spacer, and the thinner plastic spacer goes under the e-clip. If you've never done it before, the needle assembly/throttle arm can take some finger dexterity to re-install. Use a very good fitting tool during dis-assembly/re-assembly because the small factory phillips screws in the slide assembly are easily stripped. Be sure everything is in correct order. During dis-assembly, note the small dimple on the thin brass plate that sits under the throttle arm base and be sure the plate goes back right side up...things like that. During re-assembly, I use a very small dab of grease, just enough to hold the thin plate to the base, and I drop the small phillips screws into position. I lower the whole assembly down and carefully start the screws, the whole time pulling the spring loaded needle assembly down enough to allow straight threading of the phillips screws. Don't pull the needle down too far or the spacer(s) will come off the top. Maybe you've done it before and this advice is not needed?
Then you'll need to test again. The plugs are the window to the engine. They don't lie.
If you do eventually try adding holes to the airbox, that will significantly change the jetting you do now. Most people just run the box with the lid removed. You still won't gain as much power as you would with pods, but you can feel the difference if re-jetted right. The real difference is still at higher rpm's, same as with pods.
Talk to you later.

[retrex]

New to rejetting, a couple of quickies if you would Keith

Hi Keith and jonr I have read the above and find it interesting and informative. Due to a slight leak, I have removed the carbs on my stock 81 1100 and I am in the process of doing a quick clean and trouble shoot to solve the problem.

After reading the above I am now tempted to do a slight upgrade. I have, but do not run, a new V&H 4-1 street pipe. I also have a set of parts carbs that I can scavenge the mains (115s), the pilots(170s) and accompanying needles off of if need be. In looking at the scavenge carb springs I noticed that they are longer than the stock units. Are these something I need to use?

I am thinking that I have the pieces needed to do the upgrade and I thought I'd run it by you two and see what you think.

[KEITH KRAUSE]

Back from my vacation. What's up?

[jonr]

Keith,

Thanks for checking in. While you were gone, I blew insulation into my house and got ready for the new semester (the students started back yesterday).

I may get a chance to work on it this week again and I will most certainly keep you updated.

best,
Jon

[jonr]

Keith,

I just got a nice deal from a GS member for another airbox for my 750. I'm going to have a little surgery on it and open up the bottom quite a bit. I figure as long as I can keep the covers secured and keep it structurally sound, I'm going to remove as much as I can on the filter side to increase some airflow.

Aside from the expense of pods, I like the look of the factory airbox on these models, especially with the chrome covers and not the black. When I get it out of the O.R., on the bike and run some tests, I'll report in.

thanks-
Jon

[KEITH KRAUSE]

OK. I'll be around.
Since you've decided to add what sounds like sizeable holes to the stock box and a V&H pipe, you WILL have to raise the jet needles in addition to even larger mains than what we discussed before.
The stock pilot jets MAY still work with richer adjustments to the pilot fuel screws.
I generally don't think modding the box is the way to go since you don't pick up as much of the top end power as you would with pods. My thinking is that since you go through the trouble of jetting, you might as well get all you can from the intake and exhaust.
But I understand your choice and it will increase the power. It will be a compromise. You WILL feel the difference but only at higher rpm's.
Let us know the size of the holes so we can help you determine the right jetting. Avoid cutting holes where it looks like water, etc, may enter too easily. As you can imagine, it may take some guess work when jetting for this mod.