Old member been gone awhile but BACK!

Has anyone ever posted a video of an XJ carb cleaning? I am obviously missing something as the right-most pipe is only warm and the bike running badly except under heavy throttle. This after a full carb cleaning. Would love to see a pro do this.

 

It might be the spark, swop the plug & lead from 1 to 4 & see if the problem moves to # 1.

 

This can come from your pilot circuit being clogged-or the o-ring is toast-so LEAN. Double check the cleanliness and function of the pilot circuit. Low float level possible too, or a dirty nozzle (even a tiny bit of "does not belong in there" can clog these micro passages). Make a short list and check off what it's not till you only have one thing left it can be. You can start with Wizards idea about spark. If it's getting fat spark your missing fuel or compression. Valves in spec?

True video would be helpful- I would love to watch an experts technique , but if you follow the advice you can find here-and follow it religiously as in clean Clean CLEAN and carefully assembled you should be fine. Don't feel bad or get too frustrated as most/many people repeat a carb job more than once to get it right. I did.

 

Might want to start there.

Then get a compression test. Can't adjust the carbs correctly until the valves are in spec; the compression test will give you an idea of what's going on.

 

+1 to the above advise,

The Pilot passage has a couple "sisters" that also need to be clean.
A fine guitar string and carb cleaner and patience will clear 'em out.

 

Same thing (same header) when I first got my bike. I used the carb cleaning post and problem solved :wink: ...

skillet

 

There are those that make money cleaning and setting up carbs, so for them to create a video showing us how to do it would reduce the demand for their services. just sayin'.

 

Hopefully, hopefully, this website will put all those swindlers out of business.

 

Just so everyone knows, I have been meticulous with tuning, valve adjustments, etc. Positive this is carb. This inability to come off of idle seems to happen every year after the bike sets unused for a long period of time. Has always gone away after a carb clean but, in the past, I have found a small piece of something in a jet. No such luck this time so pretty sure I missed something. How do I locate the best instructions on this site?

 

Use the search tool and try a variety of terms to get what you want.

ie. carbs AND clean, or Mikunis AND clean, or Hitachi AND clean, etc.

You can also go to FAQ suggestions-there's several good posts in there. the www. has some useful articles as well-just gotta dig around.

Here's some links Smuckaholic posted recently: (check out the Mikuni one)
http://xjbikes.com/Forums/viewtopic/t=34781.html

If you're sure about it being your carb-then I vote for clogged pilot circuit, low float level, or a clogged nozzle. If it happens often after sitting for a while, then 1)-quality of the gas hanging out isn't good (use Seafoam/Stabil etc. & steer clear of gas w/ethanol) 2)-carbs aren't as clean as they need to be (varnish is still there and building). 3)-Your tank is polluting your carbs (in-line filter?) 4)-There's a small rodent in your airbox. Sounds crazy but it's happened.

 

The writeup by Chacal is very good, as is everything he does. What would really help would be knowing what jet/port/passage, etc., causes the symptoms of good idle, great acceleration and high speed running, but will hardly get from a dead stop to 10 mph. What components are in play in that transition from idle to main jet? I will just have to try again and double-check everything. Just have the feeling there is a component I have missed. By the way, bike will pull from zero just fine if the enrichment circuit is on about half way so I must be lean with the EC off, yet idles fine. Float levels were adjusted years ago and never touched. And, no pure gas around Dallas for 200 miles in any direction.

 

Strongly suggest you check float level - I'll put money on that

 

Don't base your diagnosis on how it idles. 3 cylinders can limp the fourth along and it's not easy to notice in neutral with no load. Hesitation getting out of the hole and cold pipe are telling you not enough fuel before your mains kick in.

Pilot must be providing enough fuel to both idle and just a bit more to provide that transition when you open the throttle and air rushes in-so your lean-yes and critically so when you go throttle on. You don't notice it as much when your rolling and the engine gets an assist from inertia. If your acceleration is good as you go up in rpm with no problems then your main is fine, but could still be lean.

Do check your float levels and floats for that matter-make sure the cold pipe's float isn't stuck. Must check your float level with carbs level in both planes and with gas. I would clean that pilot circuit as well. Have you tried to adjust the mixture?

I just went through similar problems and my floats were 1mm low and 2 of 4 pilot circuits were clogged with what looked like tiny bits of rubber or plastic. Now floats right, pilots clean and flowing-engine is purring in steady rhythm. All 4 pipes hot.

I can get non-ethanol gas here if I buy premium. You can buy an ethanol mediator at the Auto parts store. Or use Seafoam in your tank. Somebody mentioned Marina's as having pure gas. Don't use that ethanol blend w/o doing something to stop its evil deposits. It's screwing up cars intakes even though they use fuel injection and can adjust ignition-so you can only imagine what it's doing to our CV fixed ignition setup.

 

Did you do a compression test and if so what were the results?

How recently were the valves adjusted?

 

I truly appreciate the suggestions but trust me. Bike has had valves maintained, carbs synched, color tuned, best oil I can get, etc. It is a fuel problem. Mercman, define what constitutes the pilot circuit. That is what I think the problem is, too.

 

Below is a post of Mikuni BS28's that bigfitz kindly posted. It shows it very clearly and you can see the components (pilot screw, spring, washer, o-ring, pilot jet, pilot air jet) and passages (look at the first pic to the left of the main jet and right of the enrichment plunger-they must all be clean and functional.

http://xjbikes.com/Forums/viewtopic/t=31061.html

There was a great link on here for Hitachi's but it isn't working now try this one:
http://cycles.evanfell.com/2008/09/how- ... right-way/

Pilot screw screwed down all the way means no air flowing into pilot air jet because it's cut-off from the vacuum which stops fuel being drawn up through the pilot jet-Factory settings are generally 2-3 turns out depending on model and year. The o-ring and washer at the bottom of that screw must be present and good. It helps me to think of it like a mini-throttle that you set at the precise point and there it stays. 4-5 turns out is max richness, down below 2.5 (again model, carbs, years) is increasing lean.

Since you will have the carbs off to do this you should check your float levels as well. just a mm can make a difference.
Like I said two of mine were clogged with little black chunks (tiny) but big enough to screw it up-adjusting my screw on those two did nothing until I got it clean. After dis-assembly I used carb cleaner, thin wire, & compressed air to blow out passages and made sure it was all clear and clean. New o-rings. All good. If your pilot screws have never been touched they may still have the factory plugs on top-those will have to go-just be careful not to damage your little brass screws underneath.

Rick is your best advisor on these CV carbs. So any advice he gives you I would follow. He is the reason I was able to tackle my problem and understand what little I do. Obviously bigfitz has extensively worked on the Mikunis and there are others here who can help you if you get stuck. Go for it - you can fix it.

 

Tip - spray water on your pipes at idle, see if the water evaporates uniformly, or is a pipe cold.

 

Merc,
Thanks for that link! Even though the 750 carbs are a bit different, that will be a major help. I need to pay more attention to The enrichment tube and circuit and I have never pulled the Pilot screws and cleaned those circuits. Big help.