starting issues...

I'm new to this project and mechanical stuff in general. I've tried to read up on this site and others to get as much info and knowledge as possible. I have an '82 xs400j. Now, on to my issues.

I was having troubles getting her to start and when she did, it was a battle to keep her running. I checked the plugs, wires, coils, connector harnesses, for both cylinders. All wires and coils checked out just fine. Plugs were black-n-sooty (rich mix), tried to lean it up, no luck. Checked plugs again and noticed the right-side plug was still black and a little wet with fuel indicating no spark (or flooding?). Checked the coils and wires again to make sure I didn't miss anything and everything was still good. Now I can't seem to get started at all.

SO questions:
One idea I'm having is could the timing be off? Maybe missed a tooth? How would I go about checking it when I can't get the bike started? Or am I barking up the wrong tree on this one?

Thank you for any help and advice in advance.

 

Sounds more like you need to remove/COMPLETELY disassemble/clean your carbs (& check the carb diaphragms for holes). Then check the fuel levels in the bowls, bench-sync the carbs and set the idle mix screws to whatever is right for the XS400s (1 - 1 1/4 turns out I believe).
Edit: also check out the info at www.xs400.com

 

zap, thanks for the info. Awesome site, I actually found that just this morning! Looks like I'm in for another cleaning. I'll try it out and keep things posted. Probably be a while (gotta buy new rubbers and such).

 

ok, so removed and completely cleaned carbs. Replaced all o-rings, gaskets, etc. Bench synced, checked and corrected float levels, pilot screws set. Still not starting. Checked for spark at plugs, left is beautiful, bright blue. Right not as strong. Checked voltage and resistance, both within specs on both coils/plug wires/plugs. Still not starting and getting frustrated now :x

I'm at a loss here, any help would be appreciated. Thanks for taking the time to help a guy out.

If you need more details just let me know and I will do my best to provide...

 

Have you checked compression yet? How about valve adjustment?

 

@waldo - checked compression, 142-143 both cylinders. Haven't checked valve clearance since compression check was good, at this point looks like I should. I won't get to the valves for a couple days so if there is anything else I could/should look at instead I'd appreciate the heads up.

 

When you checked for spark did you have plugs installed in the engine or did you remove plugs and lay them on the heads and crank the engine over? Here is why I ask , now I dont have or have ever turned a wrench on a 400 so I dont even know if this applies to you, but, some bikes will turn over but not spark when the battery gets low all the juice goes to the starter and there is nothing left over for the coils to fire but if the plugs are removed the starter draws less current and then there is juice to fire the coils giving the impression that there is fire when all is put together. It sounds like you have everything for your bike to at least fire up, good compression, spark and fuel . That leads me to wonder how old is your fuel and why would you think the timing is off. Charge the battery put in new plugs and give her a try and / or give her a shot of starting fluid and see if she busts off for you.

 

Waldo - thank you very much for your help. I checked the spark by grounding the plug on the engine. It definitely seems like the starter is sucking up all the juice. I cleaned the starter brushes, but did not replace it. I put the battery on a trickle charger overnight before attempting to start. P/O said battery was new when I got the bike. It checks out at 12.5v at full charge. I've tried starting fluid to no avail. However, a few times she sputtered for a turn, but ultimately nothing. I'm stumped at this point and definitly thank you for all your help. If there is anything else you think of please post or pm me. I'll keep at it and let you know if anything happens.

 

PM sent

 

Install a BRAND NEW set of spark plugs, and with the petcock on PRI, fresh gas and a fully charged battery see what happens.

Unless the air filter is completely plugged or the carbs completely hosed it will probably fire up.

You'll never get saturated plugs to fire, even if you "clean" them.

 

Fitz - I'll try the brand new plugs and new fuel tonight and post the results.

Waldo - sorry, didn't get your pm.

 

Is the "choke" full on at the carbs when trying to start?

 

Adrain - I've tried choke at various points (full, 1/2, 1/4, off). No luck.

 

ok, so an update. I rechecked timing (make sure the auto-adjuster wasn't slipping), tried starting again. Nothing yet. Tried a little shot of starter fluid in the carbs, still nothing. Decided to pull the carbs and shoot a touch of starter fluid into the chambers...it puttered. Tried again (no added fluid), puttered. So my conclusion is the carbs are still clogged somewhere. Now, I have options. I can dunk'em in the chem-dip (rubbers removed), or I read on another site (can't remember which one) about "boiling" the carbs. Has anyone tried this? If so, any advice to make sure I don't mess anything up and end up with a cool paper-weight? Thank you all for the follow-up and help in trouble shooting this headache.

 

You are better off stripping them down as far as reasonably possible - probably don't need to separate the main carb bodies from the rack. Soak all metal bits in real strong carb cleaner; soak bodies in PineSol or the Yamaha carb cleaner mix. Rinse off & dry all parts; reassemble; check float bowl fuel levels; do "bench sync"; set idle mix jets at prescribed initial setting; reinstall rack; do final idle mixture setting and sync.

 

It also souns to me like your problem is in your carbs. cold start on on my xj it starts best full choke full or half throttle. and yeah i would try also putting ur petcok on "PRI" once it fires back to ON or RES. hopefully the problem isnt as serious as you are thinking.

 

zap - Thanks for the advice. I decided to go with boiling the carbs since I could do it inside without "fuming" everyone out of the house (including myself). If it doesn't work, I will do the chem-dip again once it warms up a bit more outside.

I won't get to testing the carbs for a couple days, but I will post whatever results I get when I can.

 

If by "boiling" you literally mean boiling the carb rack in water, you will do far better soaking with PineSol or the Yamaha carb cleaner. FWIW - there was an "unofficial" use of the Yamaha carb cleaner by adding it to water (vs gas) and heating the mix until it was warm (not boiling) and placing carb racks in heated mix.

I would strongly advise NOT soaking the carb bodies in anything stronger than PineSol or the Yamaha carb cleaner (i.e., chem dip) as they may have internal "O" rings that will dissolve.

 

The reason not to submerge whole carbs is the throttle shaft seals. If you don't plan on breaking the rack, removing the butterflies and shafts and replacing the seals, don't "dunk" the carbs in anything; you'll trap it in the throttle shaft seals and can cause damage that wasn't there before.

 

Everyone, thanks for the warnings and advice. I completely disassembled the carbs, broke the rack apart, went through everything with a fine, fine, fine tooth comb and put it all back together. Bench synced, checked and rechecked float levels then reinstalled.

Put new, fresh fuel in her. Freshly charged battery said some hail Mary's and pushed the start button...VOILA!! SHE'S ALIVE!!! Ok, so not so much. It's more like she's HALF alive. Got her started and idling, but only on the left side. I'm stumped at this point on what's going on. I've posted before (back in October or so) about this issue. Runs on left side, misses on right. Any ideas on a remedy I'm all ears.

Thanks for the help. I can almost see the light at the end of the tunnel (if I were riding through one...)

 

Misses like doesn't run at all, or sputtering? How does the right-side plug look? Since it is a twin, you could swap the ignition wires at the plugs to see if the left side now runs poorly. Did you get around to checking the valve clearance?

 

Zap - from what I can tell it misses like sputtering so it kind of pulses. I haven't check valve clearance yet, plugs look like a sooty black. Too rich? I was thinking next to check valve clearance and also compression again to see if I got a fluke reading last time. Any other thoughts would be much appreciated.

 

I'd check the valves just to make sure that all of the right-side set are closing properly (not enough clearance will cause the cylinder to run poorly and burn the exhaust valve if run too long). You can also switch the spark plug leads to see if the right side problem moves to the left side.

 

Hello Everyone!!!

So it's been quite a while since I posted. A month and a half, too long. In that time I've been able to get the bike started and idling fairly well. I got a rebuilt tci unit, replaced piston rings, all appropriate gaskets, have solid compression of 125psi on both cylinders, new plugs and fuel.

Now, I tried to give a little throttle (less than 1/8 turn) and she sputters, coughs, and backfires out the carbs/airbox. Checked valve clearances and they were all too small.

-Would this be an indicator as to why these problems would happen? (I'm guessing so from what zap said, just want a confirmation)
-Do the shims only come in intervals of 5? (that's what I'm finding)
-Could the timing be off 180? (would it even run?)

And that's where I'm at now. Just throwing out some ideas of what I think are possibilities. Again, this is all really new to me and all the help everyone's provided has been immeasurable in it's value. Thank you again for the help and patience.

 

I'm pasting some carb jetting guidance I picked up a while back for your future use:

Generally speaking, jetting can be quickly diagnosed by the following questions:
1) Low end performance
A) A lean condition is typified by surging and popping back thru the carb when steady light throttle is applied. It will cause popping during high rpm deceleration thru the exhaust (quicker when moderately lean, rapid when very lean, once every now and then when correct), once the rpm has dropped enough that the air speed thru the idle circuit is slow enough for it to pick fuel up that is. It can be quickly diagnosed by adding a slight application of the choke or starter enricher (if the popping stops, it’s lean). The intake will have a “droning” sound at steady throttle or under light acceleration loads in low gears when it is too lean. So, the question is; “Does it pop out the exhaust during deceleration with a closed throttle from high rpm to idle, while in 4th gear or above?”

B) A rich condition can also cause surging but will more than likely be very sluggish to respond to throttle inputs too. A quick diagnosis is to run the machine up to high rpm and listen for the occasional (once every now and then) pop out the exhaust, if no popping is heard, it is too rich on the idle circuit or fuel screw. If turning the fuel screw in does not remedy the richness, take a step down on the pilot jet and try again. So, the question is; “Does it pop out the exhaust during deceleration with a closed throttle from high rpm to idle, while in 4th gear or above?”

2) Midrange performance
A) A lean condition in the midrange is somewhat hard to diagnose. The biggest single giveaway is the sound of the engine. Usually when the engine is lean in the mid, it stutters and stammers and just doesn’t want to run right when it is VERY lean. When it is a little lean, it will cause the engine to labor slightly to run (it won’t sound happy), the engine will sound strained to maintain rpm, and the droning sound from above is easily heard thru the intake. It will also most certainly have a hesitation during sudden throttle application. This triggers a sound to be generated from the carb like the engine is sucking for air right before the engine starts to accelerate. A light popping will also be heard from the exhaust during steady throttle. When the jetting in the midrange is correct, you can accelerate thru the midrange with light throttle application or rapid throttle application and no hiccup or hesitation will be felt or heard. A method of diagnosis for a lean hesitator is to pull the choke on just for an instant and then stab the throttle the instant the choke is closed. If it takes off, the needle may be too lean or the pilot jet too small. Start with the needle, by lowering the clip one notch and feeling for the result. So, the question is; “Does the machine accelerate slowly through the midrange without any hesitation or hiccups?” Listen to what he says closely and go from there.

B) Rich conditions in the midrange are easy to diagnose. Under normal circumstances, a richly jetted midrange will make the machine very slow revving and unresponsive to small throttle position changes. If it’s the size of the pilot jet causing it, you will get no popping during deceleration no matter where the fuel screw is set. If it’s the needle causing it, you will be able to get it to pop during decel by adjusting the fuel screw. So, the questions to ask are: “Does it pop out the exhaust during deceleration with a closed throttle from high rpm to idle, while in 4th gear or above?” And “Does the engine react instantly with acceleration to small throttle changes when applying the throttle lightly?” (works best when in 2nd gear so the throttle changes can be felt immediately). If those 2 questions are answered with “No” and “No”, it’s most likely rich on the pilot circuit first, one step down on pilot jet size then repeat the test. If the answers change to “Yes” and “No”, lower the needle (raise the clip one position). Keep changing until you run out of clip positions. If it’s still needle rich, go to a leaner needle.

3) Top end performance
A) Lean condition on top is a little harder than the midrange. If it’s VERY lean, it just won’t take throttle. If it’s a little lean it will most likely rev quite good but, may SEEM to struggle to rev all the way out. Typically speaking, in a 4 stroke, it’s pretty hard to discern the differences from a little lean, just right, and a little rich. About the only way is to learn how to read spark plugs or find a lambda sensor to use. The question to ask is; “Will it take throttle past 1/2 throttle to ¾ throttle?” If the answer is “No”, it’s lean.

B) Rich conditions are fairly easy to discern. If it won’t accelerate or accelerates very slowly between ¾ throttle and WOT it’s rich. The question is obvious.

 

Zap! Wow, an amazing amount of information!! Thank you very much for this. I'm not sure if my situation fits into this, but I can definitely use it once I get her to take some throttle. Right now she idles, but if I try to rev past idle she shows the above symptoms (spit, sputter, pop out carbs). I will re-read and think through this more thoroughly in case I missed something.