I need carb tuning suggestons

85 XJ700N - After doing everything twice, I'm still getting about 33 mpg. I have the carbs off again and I'm looking for any suggestion or advice as to what to look for or do. you can see on the carb picture the mark I have scribed to measure the float level. The XJ700 has Hitachi 33's and the float level should be 1mm +/-1. Am I measuring from the wrong place? The plugs were removed after about 20 miles and no idle. the pilot screws are set at anywhere from 1-1 3/4 open which seems odd since the starting point is 2 1/2. I have no idea what the po might have done, but I'm going to try to see if I can measure the jets in case he enlarged them. All the jet numbers are stock. the air filter and exhaust is stock. I have cleaned the carbs three times and I am convinced they are very clean and all passages are clear. Everything seems to point to the float level, which I'm going to check for the fourth time. I'm thinking of actually setting it at 2 mm this time. Valves were adjusted and carbs were sync'ed. By the way, the bike starts, idles and runs well, --just gets 33 mpg. I'll appreciate any
suggestions and nothing is too simple, since I may have missed something very simple.
Update--I just did a float check and 1 & 2 are very low--probably 5-6 mm. 3 & 4 are perfect.

 

Well, it is certainly running rich. If you haven't tried already, turn your mixture screws out to 2 1/2 turns and check your plugs again (if you don't have a color tune plug kit) You should have a paper bag brown color on the plug insulators when it is right.

 

Looks like you are on the right track with checking jet sizes. Unless you have access to measuring equipement it will be difficult, numbered dirlls will get close but are not exact. It would be just as easy to replace them, I get mine from Amazon for less that 15$ for a set of 4 shipped. Don't forget the pilot jets, they are equally imporntant.
Is the air filter in good shape?
I see some buildup on the carb slides, are they free sliding in the bore(clunk test)?

 

the carb slides drop like a rock. I thought about polishing them but got the idea from others that if they dropped freely to leave them alone. By pilot jets, are you referring to the ones under the diaphragm? Which jets did you get from Amazon? I have a friend that worked in a m/c shop and he says he can measure them. Although the needle valves seem to be working fine, they are old and I'm wondering if anyone has ever had problems with them leaking while running and causing richness?

 

The pilot jets are the ones just forward of the main jets inside the fuel bowl. They have a much smaller orifice(hole) in them. The jets under the slides are the air jets for the main and pilot circuit. Most folks don't ever mess with them. Hopefully your friend can measure them accuratly. By the looks of the plugs I think the pilots have been enlarged at some time. Pilot jets can suffer orifice dammage from cleaning with drill bits and wires making the hole larger. Even a few thousands of a inch change will cause problems.

Here is some Mikuni jets on Amazon, Your carbs are not Mikunis though.
http://www.amazon.com/s/ref=sr_nr_scat_ ... c0f8b42b7b
You can also PM Chacal for jets.

Slide needles do wear out but usually only on high mileage bikes(100K miles). Or from dammaging when cleaning.

 

From the looks of those Plugs, ... investigate the MAIN Jets.

Some PO's "UP" the Main Jets to compensate for XL and XXL sized owners.

The Bike PULLS better for a larger rider with a Oversized (or doctored) Main Jet set-up.

READ the Size of the Jet engraved on the face of the Jet.
Use the Jet Size / Drill Bit Size Chart to measure the I-D of the Jet Orifice.
The Shank of the Drill Bit will fit the Orifice when correct.

 

The two outer carb hats are installed backwards, although that won't make any difference.........the slope should face the rear (towards the airbox).

The two outer carbs..........did you paint them black or did they come that way?

Make sure the AIR jets (under the vac piston diaphrams) are not reversed.....the larger air jet (should be size 210) is the PILOT air jet and goes in the forward-most of the three holes up thar'.......i.e. directly above the pilot FUEL jet.

Since all 4 plugs are sooty, then it's an issue that is common to all the carbs. Choke is hanging open a bit? Fuel levels too high? Main jet needles wrong size, or, not "seated" properly on their plastic head caps (the top of the shaft "ledge" should seat completely against the bottom of the platic head cap; needles that get stuck, in carbs that sat for a while, can have the needle shaft pulled "out" of their head caps by a not insignificant amount). Needle retaining springs (under the plastic hex nut inside the vac pistons) correct and seated properly? Incorrect or modified vac piston springs (if they've been modified, cut, or replaced as part of a "dyno-tune" effort they'll allow the vac piston to rise way too quickly in a stock configuration):

HCP3810
OEM Hitachi HSC33 vacuum piston SPRING
29R-14933-00-00
much longer than the HSC32 spring, and less tightly wound
20.70mm OD
0.68mm wire thickness
104.60mm tall (relaxed)

700 all non-X
750RL (44X)


Also, inspect the air bleed holes in the bottom of the vac pistons....do they show any sign of being drilled (re-drilled, that is) by a tinkerer?


If the float level in carbs #1/2 was that low (measured from the "joining surface" of the bowl to the body) and all the plugs were still the same amount of sooty, then I would suspect some other issue is at play that, again, is common to all the carbs............chokes hanging or gouges on the choke plunger valves or their seating area in the carb bodies, reversed air jets, incorrect main jet needles, or modified fuel jets/modified vac pistons/springs/main needles (i.e. someone installed a "dyno jet" kit or similar).

Did the bike used to have pods or anything on it? Know it's history at all? Was this problem NOT a problem at some point in past time? If so, what changed between then and now?

 

I have a friend that has the proper bits to measure the jets so that will be done as soon as I can hook up with him.

 

I had just removed the outer hat to check the position of the air jets and apparently put it back on backwards.

the outer carbs were black with I got the bike. Looks like they came that way and not painted later.

The air jets under the diaphragm are in the correct position and are numbered correctly.

can't find any evidence of the choke plungers hanging up. All seat well.

I have noticed that the main jet needle does not move up and down smoothly in the slide. The springs and plastic caps are good, but sometimes the needle catches if I depress it against the spring. I took it apart and can't see any obstruction. Should it be smooth snap back?

I'll check everything else you mentioned and repost.

One thouht I had was that perhaps the float valves might be leaking while running and it is causing the high fuel level and richness, and maybe even dumping fuel out the over flow tubes. Anyway to check that?

I appreciate everyone's comments and suggestions. This has now become a mission and a mystery, and I love both.

 

Just measured the main jets and they are all 107mm. The pilot air jets are 226 mm, even though they are stamped 207. Did not have anything small enough to measure the mail air jet (marked 70) or the pilot jet (marked 36.5) but they don't show any sign of having been enlarged. The main jet needle is the y-20. The spring appears to be correct although perhaps a tad longer than 104.6.

However, while checking these we noticed that if the jet needle was depressed it was sticking. We inspected each and while they are clean, it appears taht the sticking is caused by the plastic end sticking. Since there is a spring in there I assume that they should move freely. What should I do to free them up? Would that have anything to do with making them run rich?

 

Well it appears that the pilot jet is the right size (Yamaha air jet numbers do not = mm, while the fuel jets do! [per Chacal] Go figure.) and there are no comments on the main jet needle, so as far as I can tell I've done everything possible to the carbs. Therefore, I'm going to lower the float setting a tad and see what happens. If there is anything outside of the carbs and valves that I should be looking at, electronics, timing, etc. let me know.

 

After following through with all the suggestions and ruling out any modifications to jets, etc, I decided to start over with the floats. I checked and all were less than the specified .63 inches, so I reset them to that height. The wet check was within the tolerance of 1 mm +/- 1, so I have re-sync'ed, colortuned, and will see what happens.

MPG increased from 33mpg to 40 mpg, but the plugs are still a little smooty, so I'm going to run it for a couple of hundred miles, check again, and perhaps tweak the floats again. It has occurred to me that perhaps the float needles have been replace and the replacement needles may be 1mm taller.