starting issues (Won't start once engine warm)

[pIatipus]

I'm pretty new to bikes and am learning as I go.

Bought the bike at the end of December and haven't had the opportunity to get it going until now, with the warm weather and all. It was running in December when I got it and I could start it with the kick start. When I replaced the spark plugs, the right plug was dark, suggesting it was running rich. Also, it idled at low rpms, to the point that it would shut off idling. A friend helped me adjust the idle rpms and the fuel/air mixture so that it was running leaner. From that point, the bike was running and would start when warmed or from a cold start. I didn't have a battery tender, so I removed the battery and kept it inside from mid January until late February.

The bike floods easily. When the bike was starting "normally", it would start on the first kick or two. Any thing past 4 kicks and the engine would flood. (Vacuum petcock is set to on)

Now, its hard to start with kick start (xs400-2e, so no electric start). I can get a running start, and the engine will turn.
Yesterday it started with the running start. Today, it turned over, but didn't quite start. One kick and it started easily.

This is where it gets interesting. Took it for a short spin, maybe a mile or two, 5 minutes.
Once warmed (10 minutes), then turned off, it won't start again, both running start or kick start. This happened today and yesterday.

Yesterday, after the short run, I checked out the spark plugs, and the right plug was dark again. I cleaned up the plug with emory cloth.
Its worth noting that since its replacement in December, the bike really hasn't been run (as it was winter). Maybe a few hours of running time, tops.

Battery has sufficient CCAs and appropriate 12 volts available.

I'm looking for two things. The first (and biggest) is why won't it start when its warm?
Second, why can't I get it to kick start as easily. I'm not really into run starting it all the time, which I'm sure you all can appreciate.

 

[PEPXS400]

Do you have good fuel?
Does the fuel flow from the tank good?
Are the plugs wet with fuel when you can't start after warm up?
Are you running the recommended plugs?
Are the coils original?

It sounds like a carb issue, but just to make sure.

 

[Gramatron]

I've seen this before. And only on carbureted bikes where there's no computer regulating the mixtures. If the last time you tuned it was in cold weather, pull the carbs and set them again. Try to blow them out with compressed air too. (After you pull the diaphragms) While you're working, put the battery on a tender.

You're either getting too little air or a weak spark on that right cylinder. So after you get it together, pull out that spark plug and do a check by plugging it into the wire and holding the other side to the block as your buddy kicks the starter. It's probably not gonna be this but better to be safe.

When your engine warms up the fuel air mixture changes a bit which is probably knocking one of your cylinders out. That would explain the weird behavior. Good luck!

 

[pIatipus]

Do you have good fuel?
Does the fuel flow from the tank good?
Are the plugs wet with fuel when you can't start after warm up?
Are you running the recommended plugs?
Are the coils original?

It sounds like a carb issue, but just to make sure.

Fuel from late December was in the tank
Fuel flows well, unimpeded.
The plugs are NOT wet when I can't start.
Running on recommended plugs.
Coils are original.

I drained the float bowls... some sediment... so
I pulled the petcock to inspect the fuel filter, looks good.
Have pulled the carbs to clean em. Figured any sediment is NOT good. The air jet on the left side looked a little beat up, but mostly like someone hadn't been careful with a brass screw. Both gaskets on the choke were broken. All other seals, jets & various other parts looked in great condition. Working on putting em back together, only having trouble with rebuild kits. It looks like many of the rebuild kits include main jets that aren't the same as the stock one. Kits have 132.5 and the manual has them listed as 137.5. I haven't found sizes listed for the air jets, but the manual lists them as #45. I tried ordering the few pieces I needed individually, but that seems rather impossible for the air jets.

Any suggestions? Just looking for two new float bowl gaskets, air jets, & washers for the panhead screws (they were intact, but old. figured i should replace em). (Oh, and the gaskets for the choke.) Will reassemble and try again. Next step, if this doesn't resolve it....?

Local bike mechanic (mounting my new tires) suggested I looked resetting the points, that as they warmed, the gap was getting larger. This sound viable?

 

[pIatipus]

I've seen this before. And only on carbureted bikes where there's no computer regulating the mixtures. If the last time you tuned it was in cold weather, pull the carbs and set them again. Try to blow them out with compressed air too. (After you pull the diaphragms) While you're working, put the battery on a tender.

You're either getting too little air or a weak spark on that right cylinder. So after you get it together, pull out that spark plug and do a check by plugging it into the wire and holding the other side to the block as your buddy kicks the starter. It's probably not gonna be this but better to be safe.

When your engine warms up the fuel air mixture changes a bit which is probably knocking one of your cylinders out. That would explain the weird behavior. Good luck!

When you say "pull the carbs & set them", can you explain this a little. I have them taken apart to clean (after finding some sediment in the float bowls). This is all pretty new to me, but I'm just going slow & steady, watching a lot of videos and researching like a mad person.

Also, checked the sparks as one of my preliminary options. Seemed fine.

 

[PEPXS400]

One more question, do you have any rust in the gas tank? large sediment in the bowls should have been picked up by the filter if you have rust in the tank. I have seen rust in a tank with a inline filter still put sediment in the bowls. From what I have read, this can get in every wear and cause issues. A good clean tank and rebuilt carbs should do the trick.
I was able to get a lot of the carb rebuild parts of mikesxs.com and they look like good replacements. They have the correct size jets too. I ordered everything that was a wear item or items that could be damaged by the PO. Waiting on the last few parts and them mine are getting rebuilt.
As for the points, you should most definitely reset them or replace them if they are out of spec.. I would do the valves adjustment too, just to make sure. Have you tried to ohm out the coils and see if they are in spec.?
Something that also helps on some of this, is pictures, take a lot of pictures. It helps with reassembly and if you need to post for questions.

 

[pIatipus]

One more question, do you have any rust in the gas tank? large sediment in the bowls should have been picked up by the filter if you have rust in the tank. I have seen rust in a tank with a inline filter still put sediment in the bowls. From what I have read, this can get in every wear and cause issues. A good clean tank and rebuilt carbs should do the trick.
I was able to get a lot of the carb rebuild parts of mikesxs.com and they look like good replacements. They have the correct size jets too. I ordered everything that was a wear item or items that could be damaged by the PO. Waiting on the last few parts and them mine are getting rebuilt.
As for the points, you should most definitely reset them or replace them if they are out of spec.. I would do the valves adjustment too, just to make sure. Have you tried to ohm out the coils and see if they are in spec.?
Something that also helps on some of this, is pictures, take a lot of pictures. It helps with reassembly and if you need to post for questions.

Tank is pretty dang clean, especially with the age in mind. I did use some filtered old fuel to rinse it out. Thanks for the tips on the photos. I did just that while breaking down the carbs. After that, I'll take a look at the points, valves & ohm out the coils.

 

[PEPXS400]

Good luck! PM me when you find out what it may be. Curiosity will get to me

 

[arfstrom]

My guess is you have a hole-ly float. That is my first guess. 2nd guess, I always recommend to trim 1 half inch off both sides of the coil to plug wire. (1 inch total) That will get both your coil, and your sparkplug cap some new fresh wire to bite into.
3rd guess, your gas cap vent hole has been painted over, or worse. I had sealed my fuel tank, and I just rolled the tank with the fuel cap on. That materiel seal the vent. So I would get about 2 miles down the road, and it would stop, and act like I am out of gas. Then when I looked into the tank, the seal was pulling away from the walls. (redo) We strongly recommend a filter. paper is better than copper screen. (it limits the size of the particles that make it though it. One fall season, I had red dust in there when I cleaned it out in the winter time. (it was rust from my tank)

guess number 3, is that the pilot isn't set right. we recommend a 3 turn out, for starters.You can always adjust later when you are ready to fine tune it. (initial setting from 1980's was 1.5 turns, too hard to ensure it will start, and it limits speed (i think))

You are higher up in the atmosphere, but I don't think that is a major change. perhaps someone with jeting experience will chime in.

 

[DanD]

I'm not saying this is your problem, but it is worth considering.
I had an old 78 Honda CB125, I had a very "similar" issue with it. Not starting hot, and also dying on me when hot, like it was out of gas. Fouled plug. I tried everything with the carb and fuel and tank. Messed with the points and ignition. In the end, I found it was a weak coil. When it got hot it didn't work. I replaced the coil and everything was great.

 

[Gramatron]

When you say "pull the carbs & set them", can you explain this a little. I have them taken apart to clean (after finding some sediment in the float bowls). This is all pretty new to me, but I'm just going slow & steady, watching a lot of videos and researching like a mad person.

Also, checked the sparks as one of my preliminary options. Seemed fine.

I'm sorry my phone autocorrected the word "set". What I meant is to dip them in a can of Gunk Carburettor Parts Cleaner. But if you've already pulled them then I'd investigate elsewhere.

 

[pIatipus]

Good luck! PM me when you find out what it may be. Curiosity will get to me

Oh the saga continues...
So far, have cleaned the carbs, set the points, checked ignition timing, replaced coils & condenser. I've checked the gas cap vent hole; seems to be venting appropriately.

After setting the points and checking the timing & prior to replacing the coils, it would start fine, but die after about 20 minutes when the engine was warmed (as previously described). Since replacing the coils & condenser, I have successfully started the bike a few times, but with starting fluid only. Granted the weather has turned pretty lousy, cool & damp. When the bike would start, the right side was coughing pretty substantially. I drained the fuel & added StarTron enzyme fuel treatment to regular gas (fuel additive recommended by a number of bike owners, specifically local bike mechanic when dealing with older bikes.) Started without a problem. Unfortunately didn't have a lot of time to take it for a longer test run that day.
I set the bike in the sun today, pretty warm & dry out, pulled the choke out and it started with a light kick. Dreamy. Took it for a 10 minute spin on the usual route. Didn't die & ran beautifully, no stuttering, no coughing. Got home. Turned it off and tried starting it with the engine hot, previously a problem. Started immediately.
Later this evening, went to see if it would start after NOT sitting in the warm sun. No luck.

I work with tractors from the 60s and know how fussy they can be in the cold, both gas & diesel. This bike seems crazy sensitive. I mean, i can't start it with starting fluid and appropriately choked. Left in the warm sun, not a problem.

I would really like to take the bike on a longer spin when it is running to see if it dies when it gets warm, like a 30-40 ride, but am struggling with getting the bike to reliably start. Its a xs400-2e, so kick start only.

Something to note, the kick start seems to have resistance sometimes, feeling like its just locked in place. When pressure is taken off the kick start and retried, it is normal. When the engine is warm, this doesn't happen.

 

[DanD]

Sounds like you might have a choke problem, meaning it is not really working when you turn it on.

For my machine (an xs360), I got it with completely seized carbs, full of green gummy crap. Slides did not move. Choke did not move. I completely disassembled it, and needed to really clean out the float bowls, remove the jets, clean everything really well (I soaked everything in some kind of yamaha combustion chamber cleaner, it is just what a yamaha mechanic recommended - expensive for the can, but it did the trick - MUCH better than brake cleaner - it did not evaporate quickly, and I don't think it was not as hard on rubber and plastics).

Anyway, after a thorough cleaning or two (and finally three), it worked. Now, after sitting over winter there are times when it is hard to start and I have to rock the choke on and off as I turn the engine over. It seems to get it running. This is now getting better as I run new gas through it. I only run premium in it.

This is a pretty good thread on the issue: http://www.xs400.com/threads/yet-another-cold-start-problem.10764/#post-111350

But this doesn't explain your problem after the coil change. The only other issue that I can think of is to be sure your coils are grounded properly, that everything is super clean where they meet up with the bike - and I guess you have new plugs with the new coils - I don't know how much this will affect things, but I always put in new plugs when I start on an old machine...

Anyway, you probably already know all this, but it is where I would start.

 

[pIatipus]

Sounds like you might have a choke problem, meaning it is not really working when you turn it on.
For my machine (an xs360), I got it with completely seized carbs, full of green gummy crap. Slides did not move. Choke did not move. I completely disassembled it, and needed to really clean out the float bowls, remove the jets, clean everything really well (I soaked everything in some kind of yamaha combustion chamber cleaner, it is just what a yamaha mechanic recommended - expensive for the can, but it did the trick - MUCH better than brake cleaner - it did not evaporate quickly, and I don't think it was not as hard on rubber and plastics).

I had thought similarly, but when i took apart the carbs, I checked it the choke over too. It does mechanically work. When it does get started, the choke does seem to be running normally. When at the full choke, idle is high, half choke lowers it, and off it sits at normal idle.

I can't even bump start it when cold. The bike comes to a skidding stop.

 

[DanD]

Hmmm. I don't know. Maybe someone else can chime in here that has more experience/theory in the carb area on this one. It sounds to me like the choke is working from what you describe. Could there still be a carb issue? Anyone?

There is the basic fuel-air-spark triangle of what an engine needs to run. I try to work through these by process of elimination and (limited!) experience.

Have you pulled the plugs (after some time trying to start) and looked at them? Are they all wet? Dry?

In the second part of my post, I mentioned the ground on the coils (I know it is reaching, but on my CB125, it was an issue I had). Are you getting a good spark when it is cold?

Ever try starting it cold with the air filters off?

These are the kinds of things I would check when diagnosing some issue like this. But the real question in my mind is why did it change when you changed the coils? What could old coils "hide", and what could new coils exacerbate? Or are the new coils a red herring?

Sorry - more questions than answers!

 

[xschris]

Have you done a compression test?