Need troubleshooting suggestions

[Take Warning15]

This is my first bike and I finally got it back together, but now it won't run. It has spark, so I suspected that it was not getting fuel. However, to troubleshoot, I sprayed fuel directly into the intake and still got no fire. Also sprayed right into the cylinder after that failed and still nothing. Now, I will say right now, that carbs are not my strong point. What is my next step? Could it be a carburetor issue?

 

[Paulrxs650]

Hi,

If you are getting a spark (double check its strong and continuous) I would start with the following:

1. Strip carbs, clean, check jets and sizes, floats and float heights (check out the carb guide in the tech section - Brilliant)
2. Check timing is set correctly (use search and there are good threads detailing this)
3. Check and set cam chain
4. Check and set valve clearances

Paul

 

[Scrambled]

Was your bike running before you took it apart ? When you say "took apart " just what was taken apart (engine ?) There are a few things to look at before you start taking your carbs apart (espesially if ,like you say, carbs are not your thing.) Start with the basics , look at the plugs , dry them off and clean them (they will be wet from you spraying fuel in ),then try starting procedure. Keep in mind that your XS will not start if you try to use the throttle while starting. Use choke only . Have you done a compression test ? Did you replace any ignition parts ? Sometimes non starting can be as simple as a blown fuse, so my suggestion is to start looking at the simple things first . A dead or weak battery could also cause your bike non starting. Keep it simple, that usually works for me. Another suggestion, turn your petcocks to prime and turn it over a few times (to fill the bowls ) then turn them back to run.

 

[XSLeo]

If your bike is a 70-79 and still has the points it could be when you put it back together you crossed the wires at the points. Try swapping the plug wires, just unplug them from the plugs and plug the left wire to the right plug.
Leo

 

[Take Warning15]

Could my timing be so far off that it isn't firing at all? Possibly sparking on the wrong stroke altogether?

Also, found something curious. Though fuel is running out the petcock, the filters are clean, when I took the bowls down there was no fuel in them. I took it apart and I can easily blow through the fuel passageways on the carb. The floats also move freely. What could I be missing here?

But, like I said before, it still doesn't fire when I spray fuel directly through the carbs.

 

[Take Warning15]

Oh, and I did turn the petcocks to res... don't think I have prime, and cranked it to fill the bowls, but it looks like they still didnt fill. Also checked the plugs. I don't have a compression tester here but I'm fairly certain it has compression. I'll check that when I get a tester. Thanks for the replies

 

[5twins]

If you're not getting fuel into the bowls, it's not gonna run. Fix that problem and maybe you'll get somewhere.

 

[trance]

If you aren't getting a pop with starting fluid you either are firing on the wrong stroke or the spark is really weak. Fill up the fuel too, you probably don't have enough pressure to get it into the bowls.

also, check your compression. if it's non-existent or very low, it won't run regardless.

1) spark
2) fuel
3) compression
4) air
5) electricity

that what the bike needs to work

 

[Take Warning15]

Thanks guys! Got it running, but not great. With the choke it idles around 3000-3100. When I turn the choke off it either quits or idles around 1000 then quits. I waited for it to get hot etc. Also, without the choke it won't take throttle without quitting. Carb problem? Could this just be mixture or something else?

 

[weekendrider]

A through cleaning should clear up the problems.

 

[Take Warning15]

Okay, I did check the needles, jets, diaphrams, choke plunger, bowls and floats. All looked clean to me. I'm afraid to get more into it than that.

 

[jchrisk1]

Don't be afraid. Follow this guide. It's easy.

http://www.amckayltd.com/carbguide.pdf

 

[5twins]

You have to insure that the idle circuit is clear. The fuel/air mix from the pilot jet passes through the carb body and exits into the main bore through 4 tiny holes. If any or all of them are plugged, the idle circuit won't function properly .....

You'll need to provide the year of your carb set in order for me to be more specific. The cleaning technique, or at least the preparation for cleaning, differs slightly between the 38s and the 34s.

 

[Take Warning15]

I believe the carbs are original. 1975 xs650b

 

[Scrambled]

Oh, and I did turn the petcocks to res... don't think I have prime, and cranked it to fill the bowls, but it looks like they still didnt fill. Also checked the plugs. I don't have a compression tester here but I'm fairly certain it has compression. I'll check that when I get a tester. Thanks for the replies

Do you have stock petcocks ? Stock petcocks are vacum controlled. There is no "off" position, when they are on "run" the motor has to be creating vacum in order to suck fuel. The "prime" setting allows fuel to flow, but if you leave it in that position your bike may flood. What year is your bike ? Do you have bs38 or 34 mm carbs ? The more info you give the Gurus the better. Now, you say you got it to run, so now it quits when you shut off the choke. Your bike should idle at around 1200 rpm so it sounds like that is set low to start with. If you can get it to idle and run so you can open the throttle without stalling ( warning ! do not let your bike idle for more than 5 mins at a time ! You have an air cooled engine and excessive idling can cause severe damage . At least put an electric fan in front of it when you are trying to set it up. ) So, if you get it to where you can rev it , try blocking off the intake on one carb at a time with the palm of your hand, just for half a second at a time while alternating between carbs. It will feel like sticking your hand over a vacum hose . Some times this will work to clear minor clogs .

 

[Take Warning15]

If any of the holes are clogged up, would it idle okay on choke because the mixture is already richer, but not without the choke? I'm trying to picture where they are. its hard to tell from that picture, but I'm suspecting that is my problem now. Again, thanks for the help, guys.

 

[5twins]

The holes are in the main bore of the carb where the upper half of the butterfly plate closes. You'll need to flip the plate open to see them. Dribble some carb cleaner in the pilot inlet on the carb bottom and blow it through with compressed air .....

Watch for the cleaner to come out those 4 holes. One is from the mix screw. You should remove that and cover the screw hole with a finger while blowing the cleaner through. You can also put cleaner in the screw hole, cover the 4 holes in the bore, and blow it back through. It should come out the pilot inlet hole on the carb bottom. Work back and forth like this until you have the 4 holes cleared. Blow WD40 or kerosene through when done to flush the carb cleaner out.

 

[jacob]

hey guys just wondering if someone could tell me what are supposed to be put here ...they were blocked off with a bolt and jb weld before i cleaned it off ... just wondering if it is supposed to be blocked off with a bolt...

 

[XSLeo]

That hole, if the same as the 78-79 carb I have in my hand, is a blind hole in the enrichener body.
If it is then it doesn't need a bolt or JB Weld.
I might remove the body and look at that hole from the other side. It shouldn't go all the way through.
Leo

 

[DogBunny]

It's not supposed to be a bolt and JB Weld, it's supposed to be a screw with a flat tip screwdriver slot, with an aluminum sealing washer under it. There should be a similar screw on the outboard side of the left-side carb body. Those two screws both get removed and temporarily replaced with screw-in barb fittings so that you can attach a manometer for carb syncing (assuming that you don't have vacuum fittings on the rubber carb boots).