No power below 2500 RPMS

thlillyr

thlillyr

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My bike runs great above 2800 rpms. It seems to idle fine aswell however when i put it in gear and try to accelerate i get zero power. bike just seems to sputter and very very gradualy accelrates. Probably takes a good 10 seconds to go from 1200 rpm to 2500 then the bike takes off. Giving in more or less throttle makes no difference.

I've tried adjusting the idle screws. from 2 turns all the way up to 4 1/2 turns no difference at all. I don't know if im adjusting the right screw. Is it the 2 screws on top front of the carb. 1 screw per carb. Gotta lift the gas tank to reach them. could someone point out the screw in a picture? I've got a clean air filter k&n and the carbs a perfectly clean by a professional.

This is my first bike so if this is normal behavior let me know.
 
sound like you have a fuel problem. maybe to rich where it is bogging down. remove the carbs, clean check the float hight, syncronize, then ride.
 
OK, I just road about 14 miles to work. I don't really pay attention to the rpm as I am leaving from a dead stop, but i did this morning. Normally, it seems as though I'm revved up close to 3,000 rpm as I start to release the clutch and and the engine speed never dips below 2,000 rpm. This bogging from 1200 rpm to 2500 rpm, is that while feathering the clutch or with the clutch all the way released? I never fall below 2,500 rpm out of 1st gear with the clutch released. If I even fall that low, the bike bucks...but there's nothing wrong. A 400 does make very little power below 2,500 rpm so it should spend very, very little time there in gear with the clutch released. In fact, below around 2,500 rpm, I don't even think I could keep the bike running in gear without feathering the clutch.

If you are talking about under 2,500 rpm when you are feathering the clutch, yep, sounds like a fuel issue.
 
Both. Its when i'm fething the clutch to get it in gear. For a good launch i've got to keep it about 4000 and feather the clutch for much longer than i'd like. Also i can replicate it this way. Get it in gear and then brake or let it coast all the way down to your idle speed around 1500. My bike doesn't stall it just keeps me rolling. Then while rolling under idle power give it gas. And i get the same bogging shuddering till i get about 2500. I do belive it's running rich as a mechanic tride to fix an earlier issue of not reving above 4000.

Heres the background this should clear up whats going on.
Bike wouldn't rev passt 4000rpm in or out of gear. Mechanic pulled carbs cleaned them and said he messed with stuff to make it much richer. Fixed power in low end but still not reving past 4000. I pulled it myself and found the main jets wer only 95s. Put 125s in and poof fixed problem lots of power but now my bottom end is boggy. So i belive it's just to rich so i've tried adjusting the idle screws. I the idle screws from 2 -41/2 turns but made zero difference. Don't know if i even turned the right screws. ISn't it the 2 screws on top front of each carb?

So I'm gussing theres another part of the carb i need to adjust to lean it out but I don't know enough about bikes to figure out what needs adjusting.
 
So I've got 125 jets should I go to 135 or what do you think? I've played somemore with the idles mix screws. At 2 1/2 turns its terrible. and it is definitly better but not resolved at 3.5 turns
 
its the pilot system so a bigger pilot or more probable, a thorough clean of the pilot system is in hand
 
I've turned it 4 turns and its all but gone gonna try 5 or six. Sounds like i need bigger jets. Wheres a good source to get them for cheap.
 
Also seems the carbs need a proper syncing have you tried doing this?My bike idles 900 cold and 1200 warm.I rev up to about 18k rpms fether the clutch and go no problems with power or bogging down.
 
M0nkeycheese - This thread is from 2011, so I am willing to bet he figured it out or sold the bike lol

You should start a new thread of your own and you would get more help.


But on topic i really think its a clogged pilot circuit or a problem with the vacuum on the petcock. It wouldn't be a main jet issue as they don't do much/anything until like 7k RPM+ and 3-4K would be close to where the needle jet comes in which would explain the power coming on around there.

If it was the vacuum on the petcock i can maybe see that if its leaky and until it gets a lot of suction it doesn't seal properly and limits fuel, when it hits that threshold it seals and fuels flows and it takes off...

Both would have about the same symptoms, although the pilot circuit issue would get better with the choke on, and the petcock issue would not.
 
Hey guys thanks for the replies I love how active this forum is its awesome! I knew it was from 2011 so hopefully it had been resolved as the OP still seems to be active I thought I'd ask and also shoot him a PM. had a dig to see what other threads he has made and found another similar
http://www.xs400.com/forum/showthread.php?t=5972
Which he explains that the choke was a little open. I did adjust that the other day before I started having problems. I never thought it could be that so I'll check after work today.
 
MC - I think perhaps its time to take the carbs out and clean them, and take apart the petcock and make sure that has no leaks either.

I would check your lines first, you may just have an air leak, or a clogged line, but if not it could be petcock, or carb issues...
 
I'm also having this problem. Time to revive this thread again...

I'll check my petcock etc, and I suppose at some point I should probably take the carbs off and clean them... I did notice that when I was turning the crank over by hand when I was making sure my stator mods didn't contact the rotor that there was bubbles being pulled into the fuel line as the engine went through it's cycle.

Fuel line 'looks' clear and I have an inline metal filter.

I know for sure that when I have the enricher on, the problem is still there...
 

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