Over rev when first started.

So i have a 1982 yamaha xj 650 with the YICS motor. I have been slowly working on this bike over the last winter. I rebuilt the carburetor and changed the oil and the rear end oil. However I cant seem to figure out why the bike immediately goes to 5k or better rpm when I first start it. I am getting very frustrated with this. I am part of the generation that didnt grow up with carburetor or even the likes of it. When I rebuilt the carburetor I did so with the Haynes manual. All of my float levels are perfect, my slides are in great shape, all jets are looking great cleaned them multiple times over. All of my idle air screws are set to 2.5 turns out due impart to having all stock jets. I broke the rack apart all of my seals are brand new. I am really at a complete loss as far as why this is happening. If someone could please help me. I would greatly appreciate it.

 

You do know about the mis-print in the Hayes manual don't you?

 

1. The idle are screws are not idle air screws. They are idle mixture screws (yes it's pedantic, but common language is vital when working solely with the written word. I stopped trying to turn the tide years ago and call them what Yamaha calls them)
2. Did you loosely fit the throttle plates and make sure they were centered before tightening the screws?
3. Have you inspected the intake boots, vacuum line, and vacuum port caps for cracks or splits?
4. Did you bench synch the carbs?
5. When you set the fuel levels did you just set the measured height of the float, or did you check the actual fuel level using clear tubing on the drains?
6. Did you put the air jets back exactly where they came from (the error mentioned above has to do with their location. All of the manuals have errors).
These are the correct locations


7. Are the choke cable and throttle cable hooked up properly (a common error is to swap them for each other at the carb).
8. Did you check valve clearance? This isn't the cause of your problem, but if they haven't been done then getting the carbs tuned correctly will be somewhat pointless.

 

When you state you rebuilt carbs, did you break the rack and replace butterfly seals? If you soak a carb with the rubber seals in place seals will start to dissolve and a vacuum leak is something that can cause erratic idle.

 

No I do not know of the mis print. What is the mis print in regards to?

 

See my reply above.

There are other errors in the manuals (yes, all of them), but they don't pertain to your particular issue.

 

From another thread.

Throttle shaft seals and all other parts that are currenly available can be bought from XJ4Ever. The link to the catalog is in the upper right corner of every page. Start a conversation with @chacal for service.

Leaving the petcock in the on position will not cause the fuel to flow into the crankcase unless the vacuum valve in the petcock is faulty, and one or more float needles is not sealing. I leave my petcock in the on position all the time as Yamaha intended. Fuel will only flow with the engine turning or an ouside vacuum source applied to the vacuum line.

Homework time.
Read This First
IN THE CHURCH OF CLEAN
THE SECRET LIFE OF CARBURETORS
Inside your Carbs
Replacing your Hitachi throttle shaft seals
Setting the fuel levels


Pleas keep us apprised of any work you are doing and what the results are. We can't help if we don't know what you've been doing.

 

Small update, just got a hold of a dealership that has a fossil for a tech. He has done a little work for me, not the master mechanic that worked on it previously... They are going to take a look at the bike to let me know what they believe the problem is with this bike. That might be a good starting point for me... I am just stressed and need the help with this bike. I will continue to update everyone on the status of my bike.

 

Hey @Jonathon Kent I noticed you're in Rochester as well. I'm heading to the Carb Clinic tomorrow, but am generally around if needed.
I had my carbs re-built by @hogfiddles in 2016. They've been flawless since!
I can say that if you have have a sync or mixture issue, it's not impossible for one carb to bring the revs up for the entire engine since once one cylinder starts getting more gas/air, it will cause the others to pump more air through the carbs, which will happily adjust to deliver more fuel/air as well. (because of the slides that respond to air movement).

 

That's really good to know. I may look up @hogfiddles. I since found the butterfly valve on carbs 2 and 3 were just slightly open compared to carbs 1 and 4, I adjusted them and now I am around 2k for rpm, but that fluctuates. So clearly not the entire problem. But all the same, thanks for the input; this weekend I am going to be building a jig to set the carbs on to get them wet set, and making absolutely certain that everything is exactly as it should be.

 

cool. I did a simple jig with 4 deck screws into a block of wood, supporting 4 corners of the carb rack. Nothing too fancy.

 

Do you still have it? Perhaps you could send some photos... for some food for thought.

 

Found it! I had a chunk of 4x6 post I cut off from another project. A 2x6 would be plenty big, or some plywood.

 

That's pretty genius! Sometimes the simplicity should not be overlooked.

 

This is what i ca me up with.

 

I however keep having a particular problem. After I did a float height set and 17.00 mm and then went after setting the fuel level in the bowls. I started with one then worked my way down the rack. Upon the 3 rd carb I overadjusted and ended up with no fuel in the line when checking the fuel level. And carb number one began overflowing. This has happened on 4 separate occasions. Each time I would readjust the float not getting fuel and then another bowl would overflow. This grew very tiresome. I finally called it a might after working on this for 4 hours after work. Any suggestions would be appreciated.

 

1.If you're going to measure with calipers you have to physically register them on the lower lip of the carb body or paralax will throw the measurement off.

2. Have you replaced any of the original parts yet? Particualrly the float needles.

 

Yes i replaced the original needles and seats. With the steel after market options that are available. The size on the seat and needle claim to be the correct size. And what is paralax?

 

Paralax is the difference between what you see (based on the angle of view) and the actual measurement. Think it as if you were looking down a line of fence posts (no fence). Standing direclty in front of the fitst post you would only see a singel post, but step just a tad to either side and you begin to see more of them.
IMO it's better to scribe marks onto the carb and bowl and use that as your scale.

You might have a float that's hanging up, or a needle that isn't perfectly mated to the seat. You can use a bit of jewler's rouge or valve lapping compound to mate the needles to the seats. Just a tiny bit of the aforementioned polishing compound on the needle, and just a few spins of the needle against the seat (by hand).

I'd wager that the float is more likely the culprit than the needles and seats. Inspect the #1 float, float tower, and float pin carefully. Polish out any roughness that you might find on the pin, the float hanger, and the inner portion of the towers where the float hanger can contact them. Also make certain that you have the floats in rightside up.

 

And just to be sure, new washers were used when you installed the seats?

 

No, new washers were not used on the seats. Would old,washers make that much of a difference? As far as the float towers they look good pretty clean. No burs on the small pin going through the towers I can spin the pin freely from the towers and from the float. The floats have very small pin holes that do not appear to penetrate the shell of the float they actually float.. I tried with with a small bucket and gasoline to,make sure that the floats all "floated" and then slightly shook them around, I could not hear any fluid sloshing around in them.

 

By the way really good,idea to index the bowl instead of trying to use the caliper. Fewer things to hold in place. Is there any reason, when I refilled the rack I wouldn't get any fuel in one of the bowls when it was totally empty, and then another one would overflow?

 

empty bowl would happen because a float and needle keep fuel from flowing into carb bowl.
stuck needle, stuck float, or float set incorrectly

other options would be because screen cap on needle valve body assembly is clogged or carb is clogged at the fuel rail(tubes and tee that connect carb bodies )


over flow

would happen because a float and needle do not keep fuel from flowing into carb bowl.
stuck needle, stuck float, or float set incorrectly

other options would be crap in assembly keeping it from sealing​

 

just a thought on your photo of wet set you want to use a little more tubing yours is bent at quite an angle which could be compressing or restricting fuel flow into the tube .

see photo page 8 and how long tube and routing. when I set fuel levels after the tube fills I lower tube and let it fill back to level incase the initial flow over filled the tube with an incorrect height.

Setting the fuel levels

 

Reusing a brass washer is usually fine, but if your carbs used the dense fiber washers (usually redish color) then they have to be replaced with new. My prefrence is to use new washers when rebuilding new-to-me carbs, since there is no way to know how often the washer has been used, and the brass will only compress so many times before it can no longer provide a seal.

The floats are made of a plastic foam, so the pinholes are normal.
Sounds like the floats are free to move in the carbs.

 

Would brand new float needles for a xj 750 work on this carburetor?

 

Yes. the XJ650 and XJ750 have the same carbs, but with slightly different jetting.

 

Awesome, i found some brand new ones on eBay. Perhaps the softer tip may help solve the flooding problem. As per your recommendation i looked and re-evaluated all posts and floats and there isn't any reason for the flooding other than the float needles. I even came across an opportunity where the carb was flooding I shook the entire thing and suddenly it stopped overflowing.

 

Another thing that can prevent the float valve from working is that when you tip the carbs over and back, sometimes the needle can get stuck, so just rap on the bowl a couple of times with a screwdriver handle to get it unstuck. That said, quality replacement parts are important first.

 

Finally got the new needles, for the fuel inlet. Hoping to get them in on Friday, I am wondering if very small washers may help to keep the floats in perfectly straight between the towers. Any thoughts on this?

 

if you read the xj4ever catalog you will see they sell little washers to help keep the floats from hanging up on the float posts


HCP18328 Aftermarket float pin tube SHIMMING WASHER, for use with all Hitachi original floats. Each stainless steel shim measures 0.0254mm thickness. Use as required or in conjunction with other size shimming washers to take up the proper amount of slop. Each:

there are different thickness washers listed

its not just a catalog...……..

 

Thats good to know I really havent had a full opportunity to look at the xj 4ever catalog a lot.

 

it is a very long read

 

I started reading it 7 years ago, and am still not done.

 

Holy cow

 

It's a good reference. Some of the information in the catalog is better than what the official shop manual provides.

 

I am at my wits end.... I put the new needles in for the fuel inlet to the bowls. They are still flooding out, they are actually 19 mm for the float height. I honestly have no idea why this is happening. I really have absolutely no idea why this is happening. The floats all move freely from the posts, the needles are in good shape, they arent sticking when I put them in. Flip the carburetor over and wala they flood almost immediately. Any good recommendations for someone who can figure out whats wrong with the carbs being wet set, or aka setting the fuel height in the bowls? This problem is infuriating, I feel just about ready to walk away from the bike altogether because of this problem. Please help if possible.

 

float height is the starting point then you have to do an actual wet set.
19 is to high 17 to 18 is correct

Setting the fuel levels

contact hogfiddles he is in your state and does carbs

 

When starting off when doing the float height set, how important is it to have the carb rack tilted at an angle? Or is it not really important?

 

When wet-setting the float height (on the stand you built), the carbs should be level.

 

...in all directions. front/back and left/right.