XENclam Posted June 13, 2010 Posted June 13, 2010 Hello everyone, I'm sorry to bother you all with my issues but I've been watching the forum for quite some time and I could really use some help. Several weeks ago I was gifted a 1981 XS 400 Special. I don't know much about bikes but with some help from my friend we have since done the following: Replaced clutch springs & friction plates (shifts like a pro now) Repaired the kick-start (easy fix and it's fun to use) changed the headlamp assembly to a high end halogen (mmm light) Rebuilt and cleaned the carb Replaced the battery And that's about all I can think of... Well today me and my friend thought we finally had it! It seemed like it was running great until I tried to run it up a hill near my house and the engine started dogging. It seemed to drop rpm with more throttle. We came to find out that the engine is only firing on one side. We checked out the carb again and noticed the main jet on the one side was clogged. After clearing it out it continued to perform the same. Thinking that the issue might be electrical we reversed the sides in which the spark-plug cables were on. Swapping cables did nothing. So we decided to swap the ignition coil along with the cables in order to see if we could get a change. I'm unsure if this was incorrect in the first place as this is the first time I've worked on a bike, but this resulted in the bike failing to start but backfiring quite a bit. If anyone has any insight into why this could be happening I'd greatly appreciated it. Thanks, -Ken
DCornelius Posted June 13, 2010 Posted June 13, 2010 Sorry for the captain obvious suggestion but.... have you checked the spark plug?
Moderator drewpy Posted June 13, 2010 Moderator Posted June 13, 2010 Xen I'd check the timing, especially if you have contact ignition (also check the contacts for pitting) you really need a xenon strobe lamp so it can be done when running. swapping over the coils also swapped the timming if you didn't swap over the feed wires. that will mean they will fire with the pistons at BDC. also sounds initailly like you have carb issues as, if you cleaned them properly, you would'nt get any crud in the mains. do you have an inline filter between tank and carbs? its poss that the tank is rusty inside, this will also affect the petcock. drewps
Ebola Monkey Posted June 13, 2010 Posted June 13, 2010 I just went through this with my wifes bike a few weeks ago. We did a basic carb clean, new plugs, etc. We got it to run, but only fired on 1 cylinder. Then it ran OK, then only 1 cylinder again. It was fouling plugs after only about 2 minutes also. You need Spark/Air/Fuel to run. I'm assuming air is covered. Do you have spark on that side? Pull the plug, put the wire on it, hold the threads against the case and push the starter button. You should see a spark jumping the gap. If not, try a good plug. If you still don't have spark we'll move on, but I think it's going to be a carb problem since you already mentioned the main jet being clogged. Also, Drewpy is right. You need to do a thorough carb cleaning before you do anything else, and you need a fuel filter. You'll clog up the carbs over and over again if you don't because you're churning up whatever is in the tank, and you probably already have crap in the carbs. When we did the basic cleaning we thought it was good, but when I tore into it again I did everything. I found the needle jet was all gummed up with crap. It looked like seaweed in there, and the rest of the carb was nowhere near that bad. Download This Guide, it's the most thorough guide to your carbs out there. I knew how to clean the carbs, but still learned from it. Once you have spark, do a good carb cleaning, and add a fuel filter you should be good. You should be able to do a complete tear down, and cleaning in about an hour. Then you know you have a good starting point. Just made sure to put a filter on so you don't get more crap in there, and have to do it again.
XENclam Posted June 13, 2010 Author Posted June 13, 2010 Xen I'd check the timing, especially if you have contact ignition (also check the contacts for pitting) you really need a xenon strobe lamp so it can be done when running. swapping over the coils also swapped the timming if you didn't swap over the feed wires. that will mean they will fire with the pistons at BDC. also sounds initailly like you have carb issues as, if you cleaned them properly, you would'nt get any crud in the mains. do you have an inline filter between tank and carbs? its poss that the tank is rusty inside, this will also affect the petcock. drewps I think our main problem with that bad jet was a failure of knowledge when it came to the full assembly. We simply overlooked it the first time. Even after immediately cleaning it we received a throatier sound from the bike which was telling us more so that the bike was sucking more air but I could be wrong of course. I'm going to test that plug on that side right now and if that isn't the problem I will move onto a deeper carb cleaning like suggested. One quick question though since I'm sure you're correct about the tank having a bunch of junk in it regardless of any other problems going on... Are we talking about the fuel filter on the petcock? or are we talking about an in-line filter between the carb and the petcock? If in-line, where can I get one of those. Thank you very much Monkey and Drewpy! I'll keep ya updated.
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