Rebuilt and bench synced carbs still wont run.

Took my carbs all the way apart so I could change the throttle shaft seals and soak the carb bodies in parts cleaning solvent. Soaked then for 5 days in the gallon paint can container you get at the auto parts store. Blew out the passages with 100 psi. Carb cleaner spray goes through all passages and blow out again. Get rid of old gas in tank and get new gas. Install clear inline gas filter. Float levels set at 5/8" as measured from carb body gasket surface to the flat part of the float at the bottom of the fuel bowl. It starts on starting fluid, runs bad and has no response to trottle input at all.
I found missing washers in 3 of the idle mixture adjusters. Got new o-rings and washers from xj4ever and installed them o-ring first, washer second and spring last as they go into the carb. I put everything on the screw and held the carb upside down to make sure the o-ring and washer didn't just fall down the hole. Set them 3 turns out. I used a .020 wire to set the butterfly openings all the same. Tightened the rack bolts using a flat granite plate from a tool room shop and another flat square bar on the engine side of the carbs being carefull of the throttle linkage. What could be wrong? EVERYTHING was apart and cleaned. There was a backfire about 10 seconds after I gave up on cranking the starter one time.

 

You either have very low compression, or didn't clean out the idle enrichment circuits well enough. In the float bowls, there is a port with a small oriface to meter fuel for the "choke" circuit. If they are blocked, the engine just won't start worth a damn. To verify that they are open, stick the straw from the carb cleaner in the small hole on the inside of the bowl and try to spray cleaner through it. It should spray out rather well. The other way is to stick it in the larger hole and seal it by pressing your finger over the straw. The carb cleaner should litterally shoot out of the hole. Be mindful not to get any in your eyes, it hurts like hell.

 

Is it the pin size hole at the bottom of the bowl and it leads up through the wall of the bowl? Trying to remember. I believe carb spray went through there ok. The bike has 5800 (fifty eight hundred) miles on the odometer. The valve clearances are all .006 inches. The bike had to be in fifth gear for me to be able to turn rear wheel to turn the engine over while checking clearances on the valves.

 

Where did you get the information for setting the float levels at 5/8"? My Haynes manual says .700", which is almost 3/4". After checking the fuel level in all 4 carbs I wound up resetting the float levels for #1 and #4 at .750 (3/4" and the #2 & 3 at .800 to get the fuel level in the float bowls at the 3mm level. It could be that my floats are a bit heavy, I don't know. I do know that the carbs were a pain in the butt to set the level in.
I have literally built hundreds of carbs on all kinds of different engines and this was about as difficult to do as I could have imagined. I have never had to set the fuel level like this on anything. Everything else was very easy. I only had to remove the fuel bowls about 12 times to get it right.

Ed

 

Ed's right, setting the float levels on XJ carbs is a total pain in the butt.
I found a way to check the float levels that's very accurate in british mag called Classic Motorcycle Mechanics. Definitely worth subscribing to for old Jap bike nuts.

Set your float levels using depth gauge end of Vernier caliper. If you don't have one, get one, they're very useful measuring tools and are something like $20 for a decent one.
After setting levels, put the float bowls back on the carbs.
Now put the entire carb set in a vice - softly with some rags as padding.
Use a level to make sure they are in there nice and straight.
Insert a small funnel in the gas line.
Now very slowly and carefully pour fuel into the funnel, until the carbs fill up and fuel reaches the bottom of the funnel.
Now get an assistant to hold the funnel so it doesn't pour out.
Next you very carefully undo the screws on float bowl #1. Carefully lower the float bowl away from the carbs, making sure you don't spill any gas.
Now you can see exactly how much fuel gets into the float bowl before the floats rise and close off the valve. On my XJ650, the fuel level should be 1mm to 3mm below the top edge of the float bowl body. If it's under or over, you know you have to re-adjust your floats.
According to the mag, this is the most precise way of knowing exactly what your float levels are.
I can tell you it's a time consuming, finicky, nerve racking, major pain the rear but I've never had to set my float levels since.

Oh, and to do the middle 2 float bowls, you have to put vice around carb #1 or #4 so you can access the two middle bowls. Remember to use the level again. Also according to the article, it's better to drain all the gas out of the float bowls each time you check one. Then refill them all through the funnel and gas line again before checking the next float bowl. As I said, a real pain, but clearly worth the hassle. If you want to check out the magazine's website, they have lots of good info. It's at classicmechanics.com
Good luck.
baz

 

Yep, that's where I'm at with this bike. If I spent this much time on my mustang, I'd be sick of it running nines by now. I have a clear line that fits the drain spout and all the fuel heights are just below where the gasket meets the bowl execept for #3 counting from left to right while sitting on the bike. Seems like the drain is clogged on #3 eventhough carb cleaner was leaking all over when I cleaned the bowl with the plud removed. I suspect the drain plug is clogged on #3 because #4 fuel height looks just like #1. #3 has to fill up before #4 gets fuel right? As for the jets that go under the rubber boots or the top part or the carbs, when looking down at them, does the one marked 205 go closer to the engine? I thought I read there was a mistake with the book and they got it reversed. I found them with 205 closer to the engine. Thats how I found them and thats how I put them back.
Is 17mm about .625 or 5/8?

 

Don't use GAS to set the Float Heights. Use Windshield Washer Solvent.
You don't have to dial 9-1-1 if you spill Washer Fluid!

I'd guess you have something wrong with the Ignition if you have all your ducks in a row with the Carbs ... which it sounds like you do.

Charge-up the Battery and make SURE you are getting Spark.
Clean the Ignition Pick-ups with Q-Tips and alcohol.
Make sure the Connections to the Igniter Box are clean and tight.

Try starting the Bike using some Starter Fluid.
If it pops and runs on Starter Fluid there's something (Probably Pilot Mixture Settings) wrong and you aren't getting enough or are getting too much Fuel to fire the bike.

The other Post regarding Starter Jets is almost an A+. Yon need the Float Bowl Jets cleaned and free flowing AND you need the small Brass Siphon Tube which extends down into the well cleaned, probed and free flowing, too!

 

Yes, that is correct. The larger AIR jet is the PILOT air jet and is located in the forward-most hole both under diaphram cover.

Easy way to remember it is that the air jets are REVERSED in relative size compared to the fiel jets. Main FUEL jet is the larger of the two fuel jets, and thus the main AIR jet is the smaller of the two air jets.

Positioning is easy to remember since the pilot jets (fuel and air) line up above each other, as well as the main jets (pilot and fuel) also line up, one directly above (or below) the other.

17mm is .6693".

5/8" = .6250"

 

The .700/.850 measurement they are referring to it the float drop, not the float height. Do not get these confused. When it comes to setting the float level, the float drop directly influences the float level. The Haynes manual is not accurate and even states many time to set the carbs to the factory specs. Unfortunately, Yamaha does not release those specs to the general public, so you have to bring your bike in to the dealership.

The factory, off the assembly line does not waste their time using the bubble level technique to set float levels. As any of you know from doing this, it takes a bit of time to so and gets messy. The factory set the float level by mechanical measurement.

It’s easier then you think. All float levels are adjusted by bending the main tab located at the center of the floats. The tab off to the right side is for the float height. Do not adjust the float height. This will make the carbs to constantly flood and possibly hang the float up.

All you need is a 6” steel bench rule found at most hardware stores. There are 4 scales on the bench rule. Use 1/16” You measure from the carb base, with no gasket, to the live on the float where the side and radius corner transition to the bottom of the float. This is a mold line from the manufacturing process and make a good reference point.

My nephew, who is a bike mechanic, got this information for me. The float drop is about 13/16” or .8125” = 20.64mm. This will give you the 3mm float level required. Trust me it works. See my very rough sketch below.

A word of caution. Use small, gentle adjustment to bend the main tab or you can inadvertently bend the main support structure where the floats and the structure connect. This will affect the needle shut off to the seat which is not a good thing.

You can verify the float level when you are through using the bubble level if you want, but if you do. Use gas. The washer fluid technique sounds nice, but will damage your carbs. The solvents and ammonia left behind in the carbs will react to the gas and corrode the brass parts in the carbs, including jet, needles, seats, etc….

You would still have to disassembly the carbs to do a complete flush anyway. There are ways to use gas and be clean about it. If you drain screws work, you should not have an issue. Just take you time and drain the gas from the float bowls into a gas can.

Good luck and may the force be with you.

Dodger62

 

Dodger62,

All of this makes sense and I can see it taking forever to set the floats at the factory as it is described in the Haynes manual. In the past I have always been impressed with the Haynes manual but this time I am not. It is very confusing. It did not say "Float Drop", it said float height.
According to your information, what is the float level supposed to be? I had to set it at .750 and .800 to get the desired fuel level in the carbs. What a pain. I still have one cylinder that is not hitting right. I am beginning to question other areas that I felt was fine. You can chase this all over the place if you aren't careful. But, at the .750 and .800 I have the desired fuel level in the bowls.

Ed

 

Could it be the throttle cable that's caught up on the recess the outer sits on ? That had me for a good half-hour,even with 'choke' it wasn't rich enough to start.

 

Dodger,

I am interested in your method for setting the floats. You mentioned a rudimentary drawing, but I didn't see one. Perhaps you could repost it.

 

I had the carbs completely disassembled so I could replace the throttleshaft seals. The wire I used to bench sync the carbs was too thin. I needed to turn the idle screw up to get the thing to idle on starting fluid. The cable was installed right.

 

Wire too thin?
I use a strip of paper and Bench them practically closed.

Maybe your Pilot Mixture Screws are in need of being adjusted.
You could have them too Rich and the Bike can't get the over-rich Mixture to Ignite.

Conversely, you might be too Lean and there's not enough Fuel in the Mixture to even Idle the bike.
Too lean and you'd probably hear an occasional Pop or backfire.

Too Rich and the Bike just won't fire at all. The Plugs would foul and be wet with Fuel.

 

Removed the bowls and threw them in the partscleaner to soak for 2 days. Blew them out with air and put everything back together. Did the same thing like before. I kept up with the starting fluid to keep it running and after about a minute the left 2 cyclinders fired up and it ran on its own and the idle went up to 5k so I adjusted it back down. There was tons of blue smoke and the smell of raw gas for another minute or two. After that it ran ok. Slightly rough idle at 1000 or so. Great throttle response now. Thanks for the help.

 

You more than likely need to get the Pilot Mixture Screws adjusted for the right Mixture and smooth-out the whole picture.

It can be tricky dialing-in the Mixtures.
Do several Plug Reads and NUDGE the adjustments Rich or Lean as need be.

But, if you are running ... you can't be too far out ... so, don't get carried away and adjust them too far all at once.

The width of a Nickel will make a HUGE difference in the Mixture.
Tweak!
Don't Turn!