Engine sometimes starts, always cranks, never runs

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blink5625

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Hi guys,

I'm hoping that you can help me out. I enjoyed riding all summer on my 81 xs400 Special. But, I haven't been able to start it lately.

I can get the thing to crank, but it won't turn over. What would work before was when put my hands over the carbs. It would crank right up. I replaced the intake boots. I cleaned the carbs. The petcock works as it should. The spark plugs were replaced in the spring.

The battery was low, so I charged it up. I can get it to turn over, but it never fully catches. The mechanic looked at it and said that all the electrical connections were clean. Any suggestions?
 
I'll give a diagnostic procedure to narrow it down, and then without waiting to hear the results, give you a diagnosis. It's the American way.

The first thing you want to know is whether you are missing spark or fuel. Chances are you are missing one or the other, possibly both, but probably not.

1) Check for spark. Out of direct sunlight, pull the spark plugs, then plug them back in and lay them so the electrode end is touching the head, to ground them. Crank it over. Do you see blue spark on both? I don't care about how big the spark is, only if there is one. If there is, move on to checking for fuel.

2) Check for fuel. take the air filters off. While cranking it over spray starting fluid in the carbs. It should start or at least fire a few times. If it does and runs more than it has, not only do you have spark, but you know the issue is fuel delivery.

Now, don't waste your time. Skip step 1, go directly to step 2. When the bike inevitably starts, take the carbs off and clean them. Add an inline fuel filter when you reassemble. The T-shirt doesn't say this for no reason:

xs400_a_back.jpg
 
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I'm having similar issues. The bikes actually started with the starter, cranked over but both idled really high. I took carbs out. Cleaned them. Tried to sync best I could. New spark plugs. Now. They won't turn over. Starters won't work. I get one decent kick over and that's it.
Wtf? What did I do wrong?? I made them worse lol.
I will try your suggestion HoughMade. Sounds good advice.
 
Tate said:
I'm having similar issues. The bikes actually started with the starter, cranked over but both idled really high. I took carbs out. Cleaned them. Tried to sync best I could. New spark plugs. Now. They won't turn over. Starters won't work. I get one decent kick over and that's it.
Wtf? What did I do wrong?? I made them worse lol.
I will try your suggestion HoughMade. Sounds good advice.
Click to expand...

I was having problems with high idle, too, but when I replaced the intake boots, that helped. Seems like we're having very similar issues though... Also-- what does the inline fuel filter do?
 
Where would the inline filter attach to?
Would this be necessary as the Petcock has one....or is just bonus filter?
I'm hoping I got the rust out of my tanks. I do have a kit called Kreem it's a 3 step process for $80. I haven't used it yet.
If I have rusty gas would that cause these issues?
 
awesome. thanks
someone suggested I soak my carbs in diesel fuel for a week, 1 to clean them well, 2 to get the valve cove plate screws to loosen.
is this right? I'm assuming ill need new seals then...order a kit perhaps from Partsnmore?
appreciate all the feeedback
 
DON'T soak the assembled carbs in Diesel! Or ANYTHING else for that matter. Do NOT spray carb cleaner, or anything else, into the throats of the assembled carbs. The diaphragms will be ruined and cause all kinds of performance issues.

If you need to loosen screws, first buy the correct screwdrivers. Japanese Industrial Standard - JIS. None of the cross screws on our bikes are "Phillips" or "Posi-Drive" or any other such cross design. They are JIS. Similar in appearance, but different enough to cause problems. Unless you have worked on older Japanese bikes before, you DON'T have the correct screwdrivers. Take a look at http://gofastinnovations.com (a company located in London, Ontario, Canada). I've been using their screwdrivers for 1.5 years and they work as advertised.

If you need a good penetrating oil, get some Dexron II ATF and Acetone and mix a small amount 1:1. Apply, wait about 5 minutes for it to penetrate, and then try loosening the fastener. The Acetone thins the ATF and makes it wick through rust. Once it evaporates, the ATF lubricates very well.
 
Thanks Dave. Good to know and they ship the screw drivers free....though ill just drive there and pick up. Thanks
do you know anyone who likes to tinker and knows what they are doing with these bikes? I am in no rush but need some help to rebuild/restore these bikes. I live in Komoka.
 
I'm not sure how much you want to spend but I'm running the carbs from mikes xs. Some have had bad experiences but the work well on my bike. I had to use the gasket as a template to mill them to fit though.
 
Tate said:
Thanks Dave. Good to know and they ship the screw drivers free....though ill just drive there and pick up. Thanks
do you know anyone who likes to tinker and knows what they are doing with these bikes? I am in no rush but need some help to rebuild/restore these bikes. I live in Komoka.
Click to expand...
I know where Komoka is without looking at a map! I'm on the other side of London from you, about an hour away.

I can help. Shoot me a PM.
 

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