So I was given a 2004 Magnum 330 4x4 by my dad that was not running due to a spun bearing. I had it rebuilt and now it runs but very poorly. It idles fine but once you try to accelerate the engine boggs down.
Here is the problem I am finding- with the muffler/ silencer on it runs like crap. I take the muffler off the bike (just the muffler) and it runs like a scalded-***-ape. So I purchased a new muffler ($189) but it did not help the problem.

I am wrench savy but this has really got me to the point of grabbing some tanerite and seeing how high I can make this b@#% fly. After a FREE bike turns into a $2300 bike this is getting old.

I have replaced-
new carb
new motor rebuild
new plug
new oil filter
new air filter
new tires
new muffler
new stator

any help would be appreciated.

 

Just to make sure,you always need to have the air box and filter installed.If you bought one of those Chinese knock off carbs,I'd tear it down and clean and make sure all passage ways are clean and open.Check that it has the same jetting as the oem Mikuni. Parts lists shows a 122.5 main jet,42.5 pilot jet. Sounds like it's rich if you have to take the muffler off to run right.My two cents is if you still have the oem Mikuni,I'd rebuild it and see how it does.https://www.ebay.com/sch/i.html?_odk...hindy&_sacat=0 Also pull the black wire from the reverse limiter first and see if that helps. If it faults it can cause limiting in forward range. Item#28.

 

Air Box and Filter are installed with the cover on. I have ordered the rebuild kit for the Mikuni carb. I will check the reverse limiter switch this evening.

What bothers me the most is it will run fantastic without the muffler. I was leaning toward an exhaust issue but maybe it is the intake side of things with the carb.

I will keep you updated and thanks for the direction to look.

 

Well. I realised I should try something that i should have done a while back. I have another magnum 330 that works just 2 years newer so I swapped the carbs and now the bike in question runs so clearly it is on the carb side of things.

I can get it up to about 30mph but it still feels a little sluggish but not nothing anymore. I don't think the guy that overhauled the motor bored it out but he may have being that it is a little slow to accelerate. Is there something I can do to try to change the fuel mix without changing the jets?

 

Problem may not be all carb related. Rebuild the carb and see how it does. If it still seems to limit,could be clutch related. 2 different drive and driven clutches on the 2004 Magnum. If you have the ebs clutch,there is a plastic jam nut(#17) that can back off and cause limiting. If you have the non ebs clutch,rear ramp buttons could be worn.