Pilot jets, mixture screws and MPG

[Capn Ron]

Don't try to confuse him with "Turn it one way, then the other until it is better"...........................He wants to know exactly what it does when you turn it in, or turn it out.

Go back and read the original post.  There's no need to try to confuse anyone, the information that's already out there is contradictory and confusing enough.

I was trying to focus him on the solution rather than trying to straighten out whether in or out is lean or rich or RPM hanging is lean or rich. 

That video was about a fuel screw. The FJ carbs do not have a "fuel" screw.

Hooligan,

Thanks and you are quite right...there's plenty of contradictory info out there!  Thus my confusion.   

In changing the pilot jets to larger, I changed the way the engine returns to idle.  I've read the bits about turning the screws whichever way improves the condition, but I'm digging further into this to see if I'm overlooking something important...such as also replacing the air pilot jet to match the larger opening in the #40 fuel pilot jet.

I did pick up at some point that it's not either a fuel screw or an air screw...but in fact a mixture screw.  That's VERY helpful! 

[Capn Ron]

Oh...yeah, I assumed all four emulsion tubes would wear about evenly.  I was asking if the needle and tube in each carburetor are typically replaced as a set?

Honestly, it really depends on the air filter type, confirmed sealing and maintenance intervals.

It also depends if someone cut the index tab from the plastic needle holder.

Mike's emulsion tubes were worn but the needle did not show any wear. Those were a new set of carbs he installed several years ago and many, many miles. He used RPM pod filters exclusively.

You'll need to inspect to know for sure.

Randy  - RPM

Ahhh...that's excellent!  It never occurred to me that the wear of the emulsion tubes (and needles) would be related to air filtration...but of course it would!  Things are essentially being sand-blasted with poor filtration.

I've seen pictures of the wear on emulsion tubes...and it's pretty easy to see the oval wear pattern.  Are the needles something you can spot by eye or would I put a micrometer on them at all points?

[Capn Ron]

Hey Ron. I find it strange that the worn emulsion tubes would show up at exactly the same time you changed the pilot jets. When you changed out the pilot jets, did you fully disassemble the carbs or only remove the bowls. Is it possible that the needles are set higher than they were before? Perhaps the plastic washer is below the clip?

Derek

Hey Derek!

I find it strange too and I'm obviously digging deeper into this.  I *suppose* I could have missed the gradual drop in MPG since the big trip.  I've done mostly local rides and "spirited" riding at rallys for the last 9,000 miles.

I didn't tear the carbs down...I just removed the bowls and replaced the pilot jets.  The seeming correlation with an MPG drop may be just that I started paying attention to it again because I made a change.  I have two more things I'm going to test:

1. Going for a ~200 mile ride today to check MPG after the mixture adjustments I made yesterday.  Well, I am going to ride Angeles Crest Highway (don't hate me), so it's not just about the MPG! 

2. Put the 37.5 pilot jets back in...reset the mixture screws to where they were and ride the Santa Monica Mountains tomorrow!

I just found two more excuses to ride...not that I needed them!   

[FJmonkey]

1. Going for a ~200 mile ride today to check MPG after the mixture adjustments I made yesterday.  Well, I am going to ride Angeles Crest Highway (don't hate me), so it's not just about the MPG! 

Very windy today near my house, the Crest may be quite challenging.

[Capn Ron]

Very windy today near my house, the Crest may be quite challenging.

Did you mean that the wind is blowing or the roads are windy?  



If you're talking about highway 2 by your house, it's ALWAYS windy!   

Had the roads to myself today!!  

[Capn Ron]

I have two more things I'm going to test:

1. Going for a ~200 mile ride today to check MPG after the mixture adjustments I made yesterday.  Well, I am going to ride Angeles Crest Highway (don't hate me), so it's not just about the MPG! 

2. Put the 37.5 pilot jets back in...reset the mixture screws to where they were and ride the Santa Monica Mountains tomorrow!

Alright then...I just came back from a nice 130 mile loop up into the mountains.  Wasn't pushing it hard, just a nice 35-45 MPH run through the twisties and taking the freeway home.  This completes #1 above...and the result?

33.5 MPG.  Ug.  I'm now going to put the 37.5 pilot jets back in and go for another ride.   

[Firehawk068]

The carbs are original to the bike.  At 20,000 miles, I had them cleaned and rebuilt by WiredGeorge.  There were no changes required...he asked me about pods and exhaust...and as I'm still stock in both of those areas, I don't imagine he changed anything.  I bolted them up two years ago and all ran well.  There are now 46,000 miles on the bike.

According to info that is posted on the Factory Pro website (the link I posted yesterday) The emulsion tubes could start to show wear in as little as 5,000 miles............................
To me that seems overly excessive, and I am sure that could only possibly happen in an extreme case of mis-use...............

However, with your mileage, it is probably certain that yours are worn.........

When I bought my FJ, it wasn't running, so I pulled the carbs and cleaned them all inside and out. When I looked at my emulsion tubes, they were visibly worn into an oval shape.......
Having researched the cost of 4 emulsion tubes, and 4 diaphragm/slide assemblies (mine had pinholes in them) along with the other various needles, seats, and O-rings, I deemed it more cost effective (at the time) to just buy a brand-new rack of XJR carbs...................(This is not the case anymore, as the price of said rack of carbs has TRIPLED since I purchased mine)

I would start thinking about the cost of the tubes and a new set of needles to go with them......................Also, you might want to pull the tops off and check the condition of your diaphragms.. Inspect them carefully against a bright light to see if there are any pinholes. This would possibly cause the carbs not to operate properly also..

[Firehawk068]

Don't try to confuse him with "Turn it one way, then the other until it is better"...........................He wants to know exactly what it does when you turn it in, or turn it out.

Go back and read the original post.  There's no need to try to confuse anyone, the information that's already out there is contradictory and confusing enough.

I was trying to focus him on the solution rather than trying to straighten out whether in or out is lean or rich or RPM hanging is lean or rich. 

That video was about a fuel screw. The FJ carbs do not have a "fuel" screw.

Sorry.....
For me, "Focusing on the solution" means understanding exactly what happens when I turn the screw one way or the other.................
I am not happy with simply "Turn it one way until it is better.............If it makes it worse, turn it the other way"

When there are certain symptoms exhibited during idle that would lead me to believe my carbs are not operating properly..........(as Ron stated: Dips well below idle and almost stalls, then returns back up to idle speed.) or (Hangs up around 2000 rpm, and doesn't return to idle speed) Understanding those symptoms, and understanding what exactly is happening when I turn the screw, should lead you to the proper solution.............

Whether you want to call it a "Fuel" screw, or a "Fuel/Air" screw, or an "Idle Mixture" screw, it still does the same thing......................
On the Mikuni BS36 carburetor, turning it out richens the overall idle mixture, and turning it in leans the overall idle mixture..........

When I say "Overall idle mixture" , I'm referring to the air that enters the engine past the throttle blades COMBINED with the fuel/air mixture that comes out of the little orifice that is adjusted with the idle mixture screw...........
I really have no idea what ratio of fuel to air is mixed in the pilot circuit, but I am certain that the engine would not run on that alone.(turn the idle speed screw all the way in to completely close the throttle blades, and see what happens)................Only when it mixes with the air that goes past the throttle blades does it combine to somewhere around a 14:1 ratio of air to fuel......................Give or take a couple of points.......

I have studied mechanical things, and have been a mechanic all my life....................To me these carburetors are very simple and easy to understand.................To others, they are this magic device where voodoo happens inside, and somehow gets the fuel to my engine......................Some people understand electronics, and web servers.......To them it's really simple........
I certainly don't know every detail about the mechanical stuff in/around the FJ. There are some (like Randy) who are familiar with almost all of it.

Ron, the video that you posted that shows the operation of a CV carburetor is pretty easy to understand, for someone who wants to learn about them..............

Hooligan, I know you are trying to help as well, or you wouldn't have posted.......................But there are some people who might require just a bit more detailed information..........

Not only are we trying to help Ron here, but I am sure down the line there will be someone else with "Hey, I have that same symptom. What should I do about it?"
I am hoping some of our knowledge will help them too..............

[movenon]

When I rebuilt mine a few years ago I had Randy ship me a complete rebuild kit including all the jets, emulsion tubes and the adjustable needles. Has ran great ever since.  RPM is a great source for all the parts required.

To add to the emulsion tube/needle info I ran across a Suzuki's site and the poster claimed that the Suzuki factory estimated the life expectency of the needles and emulsion tubes to be 60,000 miles. At any rate they do wear out.

Randy mentioned the "index tab from on plastic needle holder".  My index tabs were gone, I asked about it at the time and am under the impression that it did no harm so I just reused them.  Someone with more in depth experience will have to weigh in on that. Seems no matter what the needle will move around.

Ron your cv carburetor video looks correct to me. I am envious of your weather....  
George

"Whether you want to call it a "Fuel" screw, or a "Fuel/Air" screw, or an "Idle Mixture" screw, it still does the same thing......................
On the Mikuni BS36 carburetor, turning it out richens the overall idle mixture, and turning it in leans the overall idle mixture.........." 
+1 That's how I see it Alan  .

[FJ_Hooligan]

For me, "Focusing on the solution" means understanding exactly what happens when I turn the screw one way or the other.................
I am not happy with simply "Turn it one way until it is better.............If it makes it worse, turn it the other way

So, what was the basic conclusion of that video?  Same as I proposed, turn the mixture screw(s) BOTH ways to find the sweet spot.  Does it matter whether you're going lean or rich?  Not really! Following the technique is what really matters.  That will get you to the ultimate solution. 

[FJ_Hooligan]

Not only are we trying to help Ron here, but I am sure down the line there will be someone else with "Hey, I have that same symptom. What should I do about it?"
I am hoping some of our knowledge will help them too..............

I think Randy already answered that; if it's a mileage problem, it's probably a needle issue.

[Capn Ron]

I've got the carbs torn down now and just running all the brass bits through the ultrasonic cleaner.  I pulled the emulsion tubes (nozzles) and needles and I'm hard pressed to see the wear.  I can see ONE needle with a burnished look on one side that is definitely more worn than the others, but wow...it's hard to spot!  I took some macro shots with the camera to get a closer look, but it's not easy to light those close ups.  Even with that, I *guess* I can see that two of the nozzles aren't perfectly round.  Part of this might just be that it's my first time looking at them.  Randy could likely spot the wear straight away.

I have a fresh set of OEM needles and nozzles in my spares stock...BUT, I'm stubbornly going to do a test ride tomorrow with everything like it is...but with the 37.5 pilot jets.

I'll report back my findings and if the mileage still sucks, I'll use up my spares and report my findings there as well.

[simi_ed]

Ron, what happened with this?  Did you do the Crest run?  Or were you rained out? 

[Capn Ron]

Ed,

Yep, I did the crest run with the 40's but had adjusted the idle mixture screws a bit.  Mileage sucked, but the ride was fantastic!

I put the 37.5's back in...While doing this, I removed and cleaned the needles and nozzles and all the other brass bits.  The bike now runs badly.  It's got a huge hesitation off-idle.  I was going to ride it again to see if the mileage was improved, but we've had a bit of rain, I had a huge tree fall across my driveway...spent a couple of days clearing that.  I'll likely get out this weekend, even with the stumble off-idle.

After that, I'm going to put in new needles and nozzles and the 40's and see what I get.

[Bones]

My bike has always gotten around the low 40's to the gallon and I've been pretty happy with that because it ran well and was on par with what I've read. When I stripped the carbs to install the ss screw and o ring kit I took note of the jet sizes and settings, and they were: 42.5 pilots, main jet 110, needle on the middle groove, and mixtures were between 4 1/2 to 4 3/4 turns out.

Since installing the kit I'm now getting 46 mpg which I think can be bettered still with slower riding, so what I'm trying to say Ron, is it can't be your pilot jets because mine are bigger and I'm now getting great mileage. Put an o ring kit through it, put the 40 pilots in, tune your mixtures in, and go from there. Btw my bike has 110,000 km on it and still running the same jets etc.. only difference is unipods.

                                                             Tony.