83 Seca 900 bogs down.

Sure sounds like a wonky float level to me...

 

Float level looks good. If a possible problem could be the float level is too low how could it be coming out of the overflow tube? In any case, I'm taking apart the engine to fix a faulty starter clutch and I'll be able to check the valves and everything else for that matter.

 

If the FLOAT is too LOW or stuck down, then valve doesn’t seal and EXCESSIVE FUEL flows into the bowl, creating a possible/likely overflow and a HIGH FUEL LEVEL. If the FLOAT is too HIGH, the valve seals too soon, causing a LOW FUEL level.

float low = fuel high
Float high = fuel low

Having valves out of spec can create back/excessive pressure which can cause fuel to blow various incorrect ways.

dfox

 

You don't have to disassemble the top end of the motor to fix the starter clutch. You do need a factory service manual, splitting the cases is not a minor task. There are a number of critical details that must be adhered to or you can wreck the motor.

Valve clearances are a maintenance item requiring removal of only the valve cover.

 

Would this be the correct manual?: https://www.xjcd.org/node/1301
I also have the Haynes for the XJ900 '83-'94

 

Hi guys. I'm working on my carburetors and I changed the slide needle on one of the slides and compared to the old slide needle it is just a slight bit longer. Is this a problem? Should I just stick with the old slide needle? Does the older slide needle look worn out to you?

 

First time I’ve seen a brass needle. Usually they’re aluminum, as far as I recall. You’d have to measure to see if they’ve worn. Also, check the holes in the tops of the emulsion tubes, too. If they have worn to egg shapes or ovals, then you’ll consume extra fuel too

 

Aftermarket, possibly Dynojet. Is the shaft inscribed with a series of letters/numbers?

 

I replied to our conversation but just to let you know here, the number stamped on the needle that came with the bike is 4HZ22. However, according to the Haynes manual it should read 4Hz26-3. The one that came with the kit says Y278

 

Question: When I'm on the freeway and I quickly crack open the throttle, the bike bogs for a second before taking off. Am I running too rich or is this typical of liter bikes at higher speeds?

 

Weak.
Someone has been at your carbs. Have a good look inside them again - post a pic of the bottoms of the slides. What about your needles - did you sort this, or are we to guess?

 

I've been at my carbs!! LOL. I did a carb rebuild. Broke the rack and everything. Kept the original needles but changed the emulsion tubes. I ultrasonic cleaned AND chemical dipped the carbs. Replaced jets. Everything is stock. Balanced the carbs and kept the original mixture screw settings from the PO. I'm not good at tuning the mixture screws and a Colortune did not really help me.

 

Can you explain this in a bit more detail?

 

When I would try the Colortune it would stay blue the entire time I would turn out the mixture screws until I was 5+ turns out and then it started turning orange. I've tried many times and I could never figure it out.

 

I'm with you - never had success with a colortune.
Adjust the mixture screws in to soft seat and log where they were, then one at a time adjust for fastest idle, listening fot a rhythmic or uneven misfire - rhythmic is rich, uneven is weak, then adjust to between the two. Then it's down to starting performance, listening for pops back when cold, and plug cuts.
I'm guessing they've been out, since youve cleaned these carbs? If so you should have logged the settings? I'm sure someone will know where they need to be for an all standard setup on a 900, will get you close, or tell you if you have another issue if you're a long way away from there?

 

I have the mixture screw settings at where the PO had them. They are currently at 1) 2 1/8 (turns out), 2) 2 1/8, 3) 2 1/4, 4) 1 3/4 Can this issue be solved simply by turning the mixture screws? Would it be worth a try to turn them all in a quarter or half a turn? I also have the original jets. I've heard that some companies get the jets wrong on the sizes even though they are labled correctly but I had this issue originally on the bike before the carb rebuild.

 

This situation almost 100% of the time is due to the pilot jet fuel passage (within the carb body) being partially or completely clogged......the lack of fuel flow thru the clogged passage means that adjusting the mixture screw results in no additional fuel coming thru the mixture screw, since the flow is being restricted way before the mixture screw (with a clear internal passage and clear jet, then the adjustment occurs at the mixture screw).

This could explain the hesitation you are experiencing; you are running a bit lean (but still within the "blue" range), and quickly cracking the throttle results in no extra fuel flow thru the pilot circuit (which should occur immediately), and it takes a few moments for the vac piston to respond (and raise the main jet needle) bringing the fuel mixture back to what's needed.

A test you could try to confirm this is to take the bike back out again, and crack the CHOKE open just a little bit.......the choke supplies fuel to the carbs thru a completely separate passage within the carbs......and the extra fuel coming in thru that circuit (which is also instantaneous in response to throttle position) will richen up the mixture sufficiently to avoid the lag in response (due to insufficient fuel flow thru the pilot fuel system, due to passage clogging) until the main fuel circuit takes over.

 

Chacal, I understand what you're saying but if it was the pilot jet passage being partially blocked wouldn't the bog down occur whenever I opened the throttle at any speed? It seems to only really happen at the higher speeds. If it's any indication, I also get poor gas mileage on my xj900. 35-38mpg. 40 on a good day and I'm hearing people get 45+ on these bikes.

 

Chacal is correct.
The difference in fuel flow will not always be notacable at lower speeds, especially if you're in a lower gear than the speed requires.
Your additional fuel useage could be due to a number of factors not related to the carbs, but if the carbs aren't 100% (and your's clearly aren't) then you'll never see better fuel mieage than you are getting now.

As for the idle mixture screws: none of them are set to the factory baseline. They are easy to change, so start there and see if you get better results.
Baseline is 2 1/2 turns out, then slowly add 2 degrees of turn until you it the sweet spot. Most of us end up at 2 3/4 turns out, with some going to 3 turns out.

 

What k-moe says is absolutely correct, but again with the reminder that if screwing the mixture screws in-or-out results in no changes to the mixture "color" as seen thru a Colortune, that points to a deeper issue that must be resolved.....with your mixture screws being at 5 turns out (!) there is definitely some type of major issue in play: you simply are not getting enough fuel thru the pilot fuel circuit (for whatever reason(s); typically, it is due to plugged internal passages, but it could be any number of other issues that would restrict fuel flow thru that circuit: incorrectly size jets, plugged fuel jet, incorrectly sized AIR jet, incorrect mixture screws, etc.

But.......the most common issue (by far) is internal clogging, those passages are tiny and any fuel residue that has set in the carbs for a period of time will gum-up (if you're lucky) or crystalize into a rock hard substance (if unlucky).

http://www.xj4ever.com/inside your carbs.pdf