No power......couldn't pull skin off rice pudding

Ivant1066

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Hi all,

Need help, my 1982 xs400 has very little power, I think a 50cc would beat me off the line & it is just gutless, it starts fine & ticks over no problem, had the carbs cleaned, new plugs, new leads, new rec/reg, it's with my local bike mechanic but I think he needs ideas......any thoughts appreciated
 
Welcome to the forum!

I guess I would start with the very basics. What sort of compression do you have in the cylinders? Does it smoke under acceleration? How does it rev in neutral? What does the bike sound like under load? Is the bike stock, or have there been changes to the air intake and header/muffler? Does the fuel tap flow a lot of fuel or just dribble?
 
Thankyou for the welcome.

Thanks for all the suggestions, it doesn't smoke but that's the only thing in the list that's definite. It isn't stock.....it has cone air filters & the header & silencers have been changed. Compression is a definite to check, when revved in neutral the pick up to me doesn't feel responsive.
 

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After seeing your picture (nice looking bike BTW!), I am thinking you probably have an issue with the carb tuning given the pod filters and the shorty exhaust. The CV carbs used on these bikes have a reputation of being hard to get tuned properly with pod intake filters. Some builders claim that they can get them to work, but I have never seen a good "recipe" for jetting and tuning. Longer intake stacks seem to be one solution that might be promising. You might search the forum here for jetting/tuning tips for pod filters. The engine will probably do better with slide valve carbs, but that is a pretty big expense.

However, do the easy to check stuff anyway. Then worry about the carbs.
 
Thanks again CaptChrome for the feedback. I had heard before about pod filters being a pain & not being easy to jet/tune easily, the shorty pipes as you said won't help either. As you say I will get the easy stuff checked first, but I have a feeling your hunch about the carbs will be right.
 
I would start to see if it it running on both cylinders. Are both exhaust pipes heating up? (near each cylinder) If they are not I would start investigating why the cylinder isn't firing.
check compression
check to see if you have Good spark.
look at the spark plug. Is it wet? I yes it might be over fueling causing a spark plug fouled.
If it is only running on 1 cylinder you may have to check the resistance on the pickup coils along with primary and secondary of the ignition coils.

These bikes are pretty simple it dose not take much for them to run.


I just went though this on my on my 81 xs400. I found 2 issues
1. my tci box was defective (I was able to fix it)
2 that same cylinder the carb needle seal was bypassing.So I rebuilt both carbs.
 
Had an 80 and well ended up running the H pipe with unis........... worked out great......... both SOHC builds I did I used the H pipe and unis........ even my latest uses the unis...... not sure what it is but the regular pod filters you see I think are junk......
 
Thanks for the info guys........sorry please forgive my ignorance, but can you explain "the H pipes" & "unis" in lamens terms please. Thanks.
 
on the stock exhaust if you look under the motor there will be a pipe connecting both exhaust pipes together. that is what is called a "h pipe". If you look at it it is in the shape of an H.

I not sure what Spectra means by unis
 
I think Spectra is referring to the intake manifold here. Here is a pic of what that looks like and why it gets called an H-pipe...
Carb Intake boots2.JPG


The unis are pod filters make by Uni Filter. Search for "uni pod filter" and you will find out what they are. However, I will let Spectra correct me if I misspeak (which I seem to do a lot, just ask my wife.)
 
Update.....bikes pulling off OK now upto half throttle, after that it's misfiring, jets have been changed but going to check them again. Left plug is fine, but right plug is black.......any ideas?
 
Change the plugs it might be misfiring under load. if it still dose it try this.
At night or in a dark place start your bike and give it a few revs while taking a peek at your spark plug lead to see if it is arching to ground.
that would defiantly cause a misfire.
the black right plug might have been fouled by too rich condition.
if the electrical checks out check to see if the right carb is over fueling (too much fuel in the float bowl).
if the fuel level is not right and the float height is correct than the float is not buoyant enough( if it is copper give it a shake and listen for any fuel inside)
, the needle isn't seating correctly, and/or the "o"ring on the needle seat is no good.
 
Hi guys - another update, I have Cone filters on the carbs......on the inlet of the carb where these attach, it looks like there are a number of holes that are being fouled (my limited knowledge to describe), has anyone come across this when fitting cone/pod filters & do I need to fit some kind of sleeve to allow the holes to do what they should, sorry for being so vague.
 
If you are saying that raw fuel is coming out of the holes in the front of the carbs than you most likely either have your float height not adjusted or the float needle valve O ring is bypassing or the seat isn't shutting off.the carbs will have to be removed and the float bowls taken off to inspect the float and needle valve.
 
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