Re-Re-Doing my carbs

First I would like to say hello! Hello! I'm new to the forum and have already learned TONS from this forum. Thanks!

I was given an 83 XJ650 Maxim from my father in law about 2 weeks ago and I have been working diligently to make sure I don't make any wrong moves with the process of getting this thing running. It was previously owned by a man in his church and hasn't run for about 3 years.

I have already taken the carbs out once to clean them, then again because I didn't bench synch them correctly (duh!), and now I think I need to take them out again.

Here's the situation and question:

I can't get the bike to start very well when it's cold, it just turns and turns and turns. Eventually with much patience and determination I can get it started but it's rough at best. Usually if I try to blip the throttle it backfires or races and sticks to the extreme. So I'm going to take them out for the third time and hope this will make it a charm.

First, do you have any idea off hand what would make it backfire or race every time I try to blip the throttle? Or why I'm having a hard time getting it to start for that matter?

Second, looking around the forum I have realized I never adjusted the float level. (Double Duh!) What height in mm am I looking for on an 83 XJ650 Maxim?

Thanks ahead of time!

 

Sounds like they are out of sync to me. Try reseting the idle mixture and then search the forum for how to make and use a homemade sync gage. The hard starts are most likely due to you not getting the enrichment circuit clean when you were in there last time. Make sure the cleaning fluid flows easy from the little hole in the bowl out of the brass tube coming up out of the bowl. You can remove them with out taking the carbs off the bike but its a b!T$%.

 

Running too rich, out of sync possibler for backfires..

Hard starts, double check the enrichment circuit/pilot jet be sure all is clear and install an inline filter...

 

Thanks for your suggestions so far. I will definitely take them off again.

I took Rick's advise and returned the idle screws to where they originally were before cleaning, but two of them where bottomed out, should I set them at two and a half turns like the threads suggest?

Still can't find what depth to adjust my floats. Help with that would be appreciated!

 

I'd start at 2 turns out from the bottom and adjust from there. The float levels need to be at the flange where the bowl hold down screws mount using the wet clear tube method. Until you have the float levels correct you will never get it tuned correctly. It sounds like you are close if it will pull all the way to red line and is not dumping fuel into the airbox.

 

It never ceases to amaze me how much stuff you can find on this forum if you just keep digging.

I answered my question about float height. Dry measurement is 17.5mm to the top of the float opposite the hinge. That is for HSC32 carbs.

See the post here: http://www.xjbikes.com/Forums/viewtopic ... t+dry.html

 

Ziggy that's still just a ball park to get you started. The clear tube method will let you see where they really are and show you if the neeldle are sealing.

 

I took the carbs back off and checked the enrichment circuit, which I thought I had cleaned previously. Apparently I hadn't or at least not well. 1 of 4 worked properly. Now I have them all working, bench synched and put them back on. Still just turning over and over, now it seems like it doesn't want to catch at all. So I came back inside to take a break, gather some thoughts, and get some food in my belly, and I realized when I checked this thread, I never adjusted the idle mixture screws, could this be the issue? I'm going to go check on that.

Could you better explain the wet clear tube method to me? I'm very visual and I can't figure it out from threads. Can this be done when the carbs are mounted?

 

Ok, here is a simple check - make sure you have enough fuel in the tank. A problem after a carb rebuild is to be so anxious to check the carbs out that you only put a little fuel in the tank and it is not enough to fill the float bowls. I've witnessed this three times so far. As far as the float height goes, I have been rebuilding carbs for over thirty years and I have never seen the dry measurement NOT work. The float level only has to do with making sure there is fuel in the bowl when there is a demand (that is, when you crank on the throttle). The amount of gas that the bowl will hold is enough to propel you at FULL throttle for a considerable distance (like far enough to get you in deep trouble with the local law enforcement). As long as you are at that 17.5mm level it will have no effect on carb tuning.

 

Well I have put it up for the night, but I will definately look into the fuel tomorrow.....that would be only slightly embarassing!

 

I do not believe that is quite right.

The fuel level in the bowl is there for a purpose besides making sure you don't run out of gas at full throttle........which, given that the float valve opening (at least in HSC32 carbs) is about 2.0mm, and the main fuel jet is only 1.10 to 1.20mm (depending on model), the "intake valve" is much greater than the "exhaust valve" as far as fluid flow is concerned.

Remember, the area of a circle (and that's what jet openings are) is determined by the formula pi x radius-squared, so small changes in the radius of a circle results in an exponential increase is the area of a circle (of fuel jet, or float valve inlet), and the area of the circle is what allows and determines the maximum amount of fluid flow thru it.

The fuel level determines how much "work effort" has to be performed by something.....in the case of carbs, by the engine vacuum signal.....in order to raise that fuel up into the jet, intake charge, and hence into the cylinder.

A low fuel level in the bowl will result in a lean fuel mixture, and a high fuel level will result in a rich condition, for a given amount of vacuum signal.

The amount of vacuum signal depends on your engine size, ring/piston/cylinder condition, valve clearances, etc.....but, basically, for any single engine, is a "fixed" amount for that cylinder, on that engine. Altering the fuel level will produce a change in the fuel mixture setting for that carb.


The proper "float height" is whatever float height achieves the proper fuel level in the carb bowl. For most moels using the HSC32 carbs, that fuel level (as measured via the clear tube method) is 3mm +/- 1mm.

For HSC33 series (on the XJ700 air cooled engines), the proper fuel level.....even though both carbs use the same floats, bowls, float valves, etc.......is 1mm +/- 1mm, while on the XJ750E-II models (also using HSC33 carbs), the proper fuel level is 5mm +/- 1mm.

 

i take it if i were to, say, hook up a clear tube while the carbs were on the bike, then start the bike up, and - while it was running - open the drain screw on the carb and see where the fuel level goes - nothing catastrophic would happen? would this be a good way to check for obstructed fuel flow? i.e. the bowls fill to the correct level - but they don't fill fast enough to match the demand from the engine?

 

Really need to be careful with fuel dripping on hot or even warm engine, random spark can ignight as well. If you have old carb holders they can be mounted to plywood at the proper spacing, put the plywood in a bench vise making sure the ply is level, mount carbs and do your testing. If carbs are clean flow rate shouldn't be an issue.


Not my idea...can't take credit, works well tho.

 

Thanks for passing that on. That looks t be the easiest way to set the Float hight. Now to get some old carb holders.

 

this thread got real deep real quick - even though I love it and learned something new (as usual) maybe we should ask some more basics.

while the carbs are off have you fully inspected the intake manifold boots for cracks? I thought mine weren't cracked for a LONG time before I found one around the vacume nipple. Is there an air filter? Hows your spark? maybe even the TCI. Are you sure the wires are going to the correct plugs? that's just my 2 cents.

and oh, here's the clear tube method:
http://xjbikes.com/Forums/viewtopic/t=1 ... ethod.html

May the force be with you

 

Wait, something just clicked. With the clear tube method you are measuring 'wet' volume. So it's acutally 3mm cubed +/- 1mm. For what ever reason I was thinking linear and I couldn't figure it out! See breaks are a good thing! So what do you use to measure your mm's?

Also, I have a very good feeling someone else took these carbs off and may have messed around with them prior with my ownership.

**ROOKIE ALERT, ROOKIE ALERT**
Could someone please tell me where gas line is supposed to hook up to the carb? Mine is currently between 4 and 3, but that is where it was when I started. I'm pretty sure I just saw a picture of it between 3 and 2.

Also, I never completely broke them apart. Could something in the connection between the individual carbs be leaking?

Aaaaaand one more question. Once I get the carbs back onto the bike what should I do before I press the start button? I have small engine experience but a lot of those machines need to be primed in some way. Do you just choke and press go on a bike i.e. self priming?

 

Rubber plumbing couplers from Home Depot/Lowes can be made to work as well. Also, spraying WD-40 around suspected air leaks (carb holders)while motor is running is a good way to find leaks. If the RPM's go up the spot is sucking air and needs to be addressed.

 

fuel inlet is between 1 & 2. one of my fuel rails was completely clogged and took me a while to clean with Qtips. when the carbs are returned to the bike, turn the petcock to Prime and wait for the bowls to fill up by watching the flow in the fuel filter, when it stops, they're full

 

Between 1&2? Is that on the left or right when you are sitting on the bike? I thought it went 4-3-2-1 from left to right when mounted to the bike. Will try the petcock thing. Maybe that's my issue I think it's on 'Reserve' right now.

It's always the simple things isn't it? Like when I stalled out today four-wheeling and couldn't figure out why, then I remembered I turned the petcock 'Off' when I stopped for lunch! DUH!

 

Checked the petcock. It was off.....hmmm. Added a little more gas to the tank, and turned it to 'pri'. Let it sit for a bit, because I still haven't installed an inline fuel filter (I am ashamed) and tried to get it started. Just turned and turned. Turned the petcock to 'res' and tried to start it. Again, just turned and turned.

So in a last ditch effort I decided to see if I could get it to start if I just let it turn until I could at least get a sputter. Drove the front of the car into the bay, hooked up jumper cables to the battery and sat there for about 15 seconds letting it turn over and over. Then finally, a sputter! And then another! And then VROOM!!! And guess what, it didn't sound half bad. Blipped the throttle and it behaved (didn't rev to the sky). There is still a little bit of a hitch in the idle. I can hear it on the right side exhaust. But I'm sure I can synch those.

I guess the bigger issue at this point is getting it to start from cold. But thanks for the suggestions so far! Maybe I'll start a thread of my rebuilding adventure to keep the forum updated on what's going on.

 

Step in the right direction...nice work.

 

yeah it's the other way, 1 is on left when sitting on the bike. you'll be surprised at how many things you'll want and need to replace once you get into them. I'm guessing your fuel rails could use a cleaning and throttle shaft seals could use replacing. and I thought replacing the butterfly screws w/ allen heads was Real cool, like the extended allen head screws for the bowl drain. This site is so damn good you should get a diploma from self schooling lol

 

I thought it ws over! I came home from work today and there was a big puddle of gas under the bike. It was leaking from the center two headers. This must be a semi-common issue since there are bolts (drain holes?) located on the bottom of the header pipe. Is the a product of last night, i.e. turning over and over and over before starting?

Any ideas would be appreciated.

 

your fuel valve is leaking, put some gas in it, take off the fuel line and see how much it drips, any is too much, this is a good way to blow your garage up
those bolts in the header pipes are what dealers used to use for exhaust gas analyzers
if gas was coming out there your motor is likely full of gas and the oil needs changed
don't run the starter for more than a 5 count, when the starter gets hot quit for a while
don't give it any throttle while starting with the choke
if you smell gas while trying to start it take the choke off twist the throttle all the way and give it a 5 count if it was flooded that should clear it out and get a sputter out of it

 

Thanks for the heads up Polock, so now what do I do?