I'm in Maine. Never seen another SH around here ever.

Well, I moved the needle to the last clip. Made absolutely no difference. How can that be!? I am questioning whether the diaphragm is actually opening the slide/needle. That would explain why it idles fine but wouldn't account why there's no problem when you're hard on the gas. The problem occurs only when there's a constant throttle at any rpm above idle. The line that runs from the air cut off to the brass nipple had a crack in it. I was ecstatic - thought I'd found the problem. So much for that. I tried what was suggested above - pushing the slide assembly up - it comes down like it's supposed to.

Where does the vac signal come from that opens the slide? Is it possible that syncing the carbs could eliminate this issue? Could the front cylinder be 'pulling' the rear along and making the rear draw the same amount of air but not the same fuel as the front causing the lean condition? Obviously I'm grasping here. I am literally ready to trade it in. I hate being beaten and I don't like to give up. So far the bike is winning and I'm out of ideas.

The manual lists several causes for a lean condition. I've checked them all. The only one I wasn't sure on was 'vacuum piston failure'. Are they referring to the diaphragm on top of the carb?

One final piece of info I don't think I mentioned... The problem goes away with the choke on. Looking at the ports underneath the diaphragm where the choke (enrichener...whatever it's called) goes, it appears that pulling the **** opens those ports and allows the slide to raise up a little at idle? Throttle is still closed restricting air so the mixture is rich at that point, correct?

My last resort is the dealer. I trust the techs at my local Honda dealer - well, most of them. Wonder what they charge to sync the carbs? I hate dragging this thread out like this but I'm really hoping someone has a brainstorm!

 

I'm a firm believer in buying the tool if the dealer with the tool is going to charge me three times its value to use it. I priced these not long ago and IIRC - two-tube synchonizers were about $50 and 4-tube were around $100+. You sound like you're inclined to be able to use it so instead of a leap of faith you are potentially still unbeaten!

 

Any harm in running it with the tank propped up and the airbox cover and filter off? Then I could see if the slide is opening or not...

 

I don't think that is possible because all those elements are essential to the tuning of the intake. The choke thing has me puzzled as I still think you have an air leak. Did you see Greg's post about seating the carbs properly and in the right order. I think this is critical to confirm.

 

driven;

I don't see how it would hurt to start engine and blip throttle with tank up and air box lid and filter off, not just to see that slide is moving, but moving in concert with front carb slide.

I think we're assuming you carefully checked the rubber diaphram attached to carb slide, but in re reading your posts, you don't say.

Also, especially because it is a two cylinder bike, you can make your own carb sync tool with a couple of wide mouth glass bottles, a couple of rubber stoppers, some plastic tubing and some H2O. Shouldn't cost more than $5 or $6.

 

I just reread this entire thread. I want you to check a few things before going on to the next step here. First, (and I can't believe nobody has mentioned this yet) check that the petcock vacuum line is going to the nipple on the rear of the petcock, NOT the bottom nipple. If that's fine then we'll go on to what I think is the next probable cause. You mention in other posts checking mains, pilot jets, and needle height but I see no mention of mixture screw position. You need to get them to between 2 and 2.5 turns out, so check the current position of these and adjust as necessary. These carbs will run on mixture and pilot jets until about 1/8 throttle, then the slides start to open (depending on vacuum/load of course). At about 7500 rpm WOT the slides are all the way open and the mains provide all the fueling. If you're having steady state cruising problems then the problem is most definitely the mixture screws.

If neither of these are a solution then we will move on to other things. Now go start wrenching!

 

I think people discounted the petcock vacuum line 'cause he says it is a one cylinder problem. Should check it anyhow. I mentioned 2.5 turns out on the pilot screws in my first post but I don't know if it has been checked.

 

I think it's usually the front cylinder that runs out of gas first in a situation like this, or a vacuum lock scenario when the tank vent gets clogged/filled with gas.

 

driven says bike idles OK and accelerates Ok but stumbles at steady state partial throttle.

Front cylinder spark plug looks OK but rear plug is white, even though rear needle is full rich and rear carb main jet is the richest in the kit.

driven says he's looked and can't fine any air leak.

Question, 'cause I don't know the answer.

If the carbs were way out of sync- the front manifold vacuum pulling way more than the rear, could the rear vacuum (which sucks on the petcock) be weak enough that it wouldn't keep the petcock flowing fuel at partial throttle?

And/or

Could that imbalance reduce the flow of mixture through the rear carb or make it excessively lean?

 

Petcock is fine. I even checked it by looking in at the diaphragm and applying vacuum. It opens all the way. Screws are both 2.5 out. Carbs were carefully fitted per Greg's instructions. I have checked every line and every connection and there is no vac leak. I rode it to work this morning (about 50 degrees) with the choke on and it ran like a new bike. I would keep it if it ran like that all the time! In response to an above post, I will say that the K&N doesn't appear to be as oily as others I have seen. I will oil it. Not sure how much of an effect that has on airflow.

RK, I had those same thoughts. I am convinced there's no vac leak, but I'm not ruling out something vacuum related - mainly the opening of the rear slide.

My manual is at home and I don't recall...to richen the mix do the screws go in or out?

I am checking with the dealer this morning to see what they get to sync the carbs and do the idle drop test to set the pilots. Seems like those things need to be addressed before I bother with anything else. I have spent the last few nights in the garage and the wife has been more than patient. At this point I'd rather pay a couple of hours labor and hopefully get this taken care of. Time for me to step back and let the pros take over - maybe I'll learn something.

 

Pilot screws go out-counter clockwise- to rich.

If I was in your place and had a Honda tech I trusted, I'd go that way.

Good luck and let us know what happens.

 

Dealer can't look at it until Monday. Ugh!

Greg, screws are already at 2.5 out. Should I try 3? I have the weekend to try and fix it before the dealer gets a shot.

 

You can try 3, but that's unusually high. I was running 2.5 at sea level with the K&N and Hindle non-chambered pipes. Only a full system would require the use of larger pilots and/or more turns on the mixture screws. You are 100% sure that these carbs are thoroughly clean, right? Even the pilot jets and under the mixture screws? All those tiny holes on the emulsion tubes are completely clean and they are not switched? If everything is in order there then I'm going to recommend you go back to the stock air filter. Some bikes, dunno why, just can't be tuned with the K&N.

You've got a Dynojet kit, right? Have you verified that the holes are drilled in the slides?

A severely out of sync pair of carbs would not idle correctly. One would not fire, the other would take all the load.

 

I was thinking of ditching the K&N too. I was wondering if I could block off part of the filter that's on there somehow and see if the situation gets better before I order an oem filter. As I stated, there isn't much oil on the K&N so there's basically no resriction. Holes are drilled in the slides. I cleaned the pilots but not under the mix screws. Where are the emulsion tubes? I didn't touch those either. Are they in the bowl?

I stopped by the dealer to make an appointment and my tech friend was outside. I told him my story and he said all that's really left to do is a leakdown test on that cylinder, though it's not likely the problem since it idles perfect and there is no backfiring. Otherwise he said I checked all that he would have checked. He said synching the carbs is a good idea, but won't make a difference above idle. Basically he was stumped too.

 

Mine would never run right with a K&N so I went back to stock. Also have you replaced the plugs? If they came with the bike, you never know what their history is. I wouldn't normally suggest you change them but with all the problems you've been having it might be worth it to put a new set in.

 

The emulsion tubes are basically the pilot jets. They are the ones with the tiny holes in them. See pages 5-11 and 5-12 of the Service Manual. One other thing, ensure the needle holders in the slides are firmly seated. The needles should be able to spring in when pushed upon.

Oil the filter and lets see what happens. Don't OVER-oil it.

 

Someone else will have to figure it out. Trading it in today...2008 YZF-R6S. My friend is the sales manager and gave me a deal I couldn't pass up. Thanx for all your suggestions and input!