BALLERJ Posted August 16, 2010 Share Posted August 16, 2010 Hello everyone, I apoligize if I posted this in the wrong section but I just finished my 1981 yamaha xs400 and it won't start. It ran before I tore it down from stock. I'm getting fire, getting fuel, guess ill try to do a compression test today but it should be ok. I have pulled the plugs, cleaned, regapped. Tried full choke, half, and none. I'm not having any luck. Any tips or advice would be much appreciated. Thanks Link to comment Share on other sites More sharing options...
johnsnownw Posted August 16, 2010 Share Posted August 16, 2010 Check mixture screws. If you have them turned out less than 3.5 times, that's probably the issue. Link to comment Share on other sites More sharing options...
BALLERJ Posted August 21, 2010 Author Share Posted August 21, 2010 Thanks for the reply. After you said that I remembered not seeing any mixture screws on my carb like another thread talked about. Mine were sunkin in screws. One was pretty boogered up and they were all the way in, so I thought that had to have been my problem. So I pulled them out and went ahead and bought new ones from mikesxs. They came in yesterday so this morning I threw those bad boys in there. Set at 3.5 turns out. No luck, turned them in half a turn at a time. No luck, then tried out no luck. This is becoming a nightmare. Anything else you guys can think to try? Link to comment Share on other sites More sharing options...
neversaydie Posted August 21, 2010 Share Posted August 21, 2010 How did the compression test go? You have fire, you have fuel, what about air? Is it making any attempt to start ie spluttering, or no sign of firing at all. Is timing set correctly? If youve had the bike down for a while, how old is the fuel? Link to comment Share on other sites More sharing options...
BALLERJ Posted August 21, 2010 Author Share Posted August 21, 2010 Well I did the compression test and it looks like around 127psi on the left side and 149psi on the right side. I will get light signs of fire maybe a pop or backfire pop. I'm starting think its gotta be something with my carbs. Fuel is new. Bike has been totally redone cosmetically. New tank, etc. It ran before I started customizing it. Link to comment Share on other sites More sharing options...
johnsnownw Posted August 22, 2010 Share Posted August 22, 2010 Thanks for the reply. After you said that I remembered not seeing any mixture screws on my carb like another thread talked about. Mine were sunkin in screws. One was pretty boogered up and they were all the way in, so I thought that had to have been my problem. So I pulled them out and went ahead and bought new ones from mikesxs. They came in yesterday so this morning I threw those bad boys in there. Set at 3.5 turns out. No luck, turned them in half a turn at a time. No luck, then tried out no luck. This is becoming a nightmare. Anything else you guys can think to try? Did you purchase the o-ring for the mixture screws? Those are, so says MikesXS, needed for the bike to idle properly. Link to comment Share on other sites More sharing options...
BALLERJ Posted August 24, 2010 Author Share Posted August 24, 2010 Yeah they came with the screws but wasn't sure how they should go on so I referenced a picture on google. Said screw, spring, washer, oring. My buddy says he runs his xs at 1.5 turned out. I told him the book calls for 3.5. But eitherway it was flooding and plugs were wet. So I pulled the plugs, pulled the carb, drain the oil. Before I drained the oil I cleaned the jets and tried again. Still getting wet plugs so I figured the floats had to be set to high maybe. So I drained oil, pulled carbs again. Reset floats, new oil. Still nothing. No love and I'm crushed. Lol. I'm ready to throw my hands up. Any other ideas would be much appreciated. Link to comment Share on other sites More sharing options...
johnsnownw Posted August 24, 2010 Share Posted August 24, 2010 What does the engine do when you press the start button? In other words, what does it sound like? Link to comment Share on other sites More sharing options...
BALLERJ Posted August 24, 2010 Author Share Posted August 24, 2010 Just turns over and sometimes when choked I get a loud backfire. Link to comment Share on other sites More sharing options...
johnsnownw Posted August 24, 2010 Share Posted August 24, 2010 Just turns over and sometimes when choked I get a loud backfire. Can you tell me exactly what you replaced in the rebuild. Also, what spark plugs are you using? What grade fuel, and if the battery fully charged? I mean fully charged, these bikes are tricky to start without the battery being completely charged. Link to comment Share on other sites More sharing options...
BALLERJ Posted August 24, 2010 Author Share Posted August 24, 2010 Sure, as far as the motor nothing. Just cleaned it and painted it. Gas I believe is super unleaded, plugs are BP7ES NGK gapped at .75 mm. Battery was brand new. I drained it pretty good trying to start it for the last few days. But I am getting very good spark. Link to comment Share on other sites More sharing options...
BALLERJ Posted August 24, 2010 Author Share Posted August 24, 2010 Hey thanks bud for taking the time to try and help me. I have had the worst luck with bikes lately. I have been doing everything I could think of. Link to comment Share on other sites More sharing options...
johnsnownw Posted August 24, 2010 Share Posted August 24, 2010 Hey thanks bud for taking the time to try and help me. I have had the worst luck with bikes lately. I have been doing everything I could think of. Not a problem. Even if you think you're getting a good spark, you should recharge that battery. It needs to be full to turn that engine over. Well, it seems as though the bike is running rich, if indeed the wetness on the spark plug is gas. With that in mind, it will be easier to deduce the issue. Several things will cause the bike to run rich. What air filters are you using? Also, why did you change the oil so many times? I'm going to go into chat, if that would make it easier for you to explain the situation. If you have time, meet me in chat. Link to comment Share on other sites More sharing options...
BALLERJ Posted August 24, 2010 Author Share Posted August 24, 2010 Sorry I'm on my phone no chat option. I will put the battery on charge. I only changed the oil twice. Drained cleaned painted. Then I put oil in. Tried like hell to start it. My buddy then said it was flooding and that I should change the oil. So I did one time and that's where I'm at now. Oh the airfilters I took off but they are some cone k&n lookalikes I got off ebay. Link to comment Share on other sites More sharing options...
johnsnownw Posted August 24, 2010 Share Posted August 24, 2010 Sorry I'm on my phone no chat option. I will put the battery on charge. I only changed the oil twice. Drained cleaned painted. Then I put oil in. Tried like hell to start it. My buddy then said it was flooding and that I should change the oil. So I did one time and that's where I'm at now. Oh the airfilters I took off but they are some cone k&n lookalikes I got off ebay. If you put on aftermarket filters, you have to re-jet the carbs for it to work properly. You will also have a difficult time starting the bike if you don't have the filters attached, as it will give you too rich of a mixture. If you're trying to start it with the filters off, then that is probably your problem. Also, when you changed the tank did you also change the petcock? Secondly, if you didn't change the petcock is it vacuum operated or manual? Link to comment Share on other sites More sharing options...
BALLERJ Posted August 24, 2010 Author Share Posted August 24, 2010 Its manual petcock. Not sure what jets to get. My buddy told me to take off filters cuz to restrictive. Ill do some searchin on jets. Thanks Link to comment Share on other sites More sharing options...
BALLERJ Posted August 24, 2010 Author Share Posted August 24, 2010 Hey I was brainstorming with my boss. What if I wired the coils to the wrong sides? Would that make it not run do to firing wrong? Hints the loud backfire I'm getting. Link to comment Share on other sites More sharing options...
johnsnownw Posted August 24, 2010 Share Posted August 24, 2010 I doubt it's a coil issue, but if you want to try switching, go for it. As for the filters, those pod filters are less restrictive than the stock filters, hence the need to re-jet. Pulling the filters off, however, will not help with starting the bike. If you have a manual petcock on that bike, make sure that you have a rubber barb over both vacuum ports on the boot of the carbs. This will also not allow the bike to start properly. Link to comment Share on other sites More sharing options...
BALLERJ Posted August 25, 2010 Author Share Posted August 25, 2010 Hell yeah I got her running. I swapped the spark plug wires and bam she started right up. Thanks for all your help. No I have to adjust it all to run right. Thanks again Link to comment Share on other sites More sharing options...
johnsnownw Posted August 25, 2010 Share Posted August 25, 2010 Hell yeah I got her running. I swapped the spark plug wires and bam she started right up. Thanks for all your help. No I have to adjust it all to run right. Thanks again Glad to hear it, mate. Though it seems you were able to figure it out on your own, you're welcome. Link to comment Share on other sites More sharing options...
Recommended Posts