help! engine idles fine ,bust up at throttle

[bdydrppup]

so ive been riding my 650 for about a year. ran great. last ride while going about 55 it lost power. it will idle fine for days but as soon as you give it any throttle it bust up real bad and wont rev. thought it may be the coil but i replaced it and no difference.

little back ground. 1980. new coil plugs and wires. new carbs. also my buddy was riding it that day and layed it down about 40 miles before it started acting up. dont know it it had any effect but figured id throw it in there. any help?

 

[angus67]

ruptured diaphram? when it laid down, maybe some crud dislodged in the carbs and bodged the pilot circuit.

 

[gmiller217]

pinched off the exhaust when it laid down? ever drive a car with a plugged convertor? acts just like you described could have kinked the pipe or dislodged the baffle and plugged up the exhaust. ... there are several possibilities including Angus' ideas

Fuel ... plugged filter, dirt or sediment in carbs, ruptured diaphram, damaged petcock damaged or dislodged vacuum line to petcock.

exhaust ... could be plugged in one way or another

 

[CDNTX650]

CDI problem?

 

[bdydrppup]

btw this is a bobber hardtail. you know it did flatten out the pipe a little bit, has a 2 into the 1 and it has a dent right before the muffler. has a sporster tank so no vaccum petcock. i checked the petcock and after the filter and had good fuel flow. put a spark tester on it and it jumps the gap great at idle but if you try to rev it it has blanks out and kinda looks weak but im not sure if its actually ignition or jus cuz the engine cant keep up. it has good compression. im not ruling out damaged or dirty carbs either. still gota check em . maybe vaccum leaks or cracked boot on intake? thanks again for the ideas and help. is there a way to check the black box?

 

[bdydrppup]

o and it has the mikuni 34s from 650 central

 

[xjwmx]

Creative, subtle, and crafty use of a timing light might help you decide if it's spark or fuel.

 

[bdydrppup]

i do have a timing light. any ideas?

 

[gentlemanjim]

I'd say torn diapharam - easy to check

 

[gmiller217]

are you running stock ignition? could be the igniter box or possibly something loosened up in the left case where your crank trigger is located?

 

[bdydrppup]

yeh still has stock ignition

 

[gmiller217]

could be the "spider egg diodes" in the tci box I read something about that here somewhere

 

[pumps]

I had something that sounds similar happen. My bike would idle fine like yours but as I would wind it out between gears it would cut out. I traced it to crud/water in my carb bowls and bad gas. Drained the float bowls and it stopped. Hope this helps.

 

[bdydrppup]

thanks again guys. ill be checking it again tommorrow. like to have a list of things i can check haha

 

[rhkansas]

I had a similar problem with my '81 a couple of years ago - was running fine, and suddenly refused to go over 2800 rpm. It turned out to be a weak ignition trigger magnet in the alternator rotor. I had installed a new rotor from Mike's XS a few weeks before as the original had shorted internally and was no longer charging. The bike ran fine for a couple of weeks. I suspect the magnet was installed at the factory with the wrong pole facing inward and was weakened over time by the field of the outer rotor half. Anyway, the weak magnet was about as strong as something you would use to stick up notes on the refrigerator door - original (strong) magnet will suck a .015 feeler gauge down to it and hold on tight! I installed the original (not charging) rotor just to be sure, and bike ran great - just wouldn't charge. - Don't know if that's your problem, but might be worth checking out. You'll need to take off the left cover and remove the stator - look for the round (about 3/8") trigger magnet just outside of the outer slip ring - you can use a feeler gauge or a small flat blade screwdriver to feel how strong the magnet is - should be pretty powerful. If it seems weak - could be the problem.
Good luck!
rhkansas

 

[vagabond]

I had the same problem with my 1979 Special II this week actually. It was stuck in the garage until I cleaned out the gas tank, petcock, and pilots on both carbs with a good skin-burning dose of B12 carb cleaner and adjusted the BS 38 floats to 27mm. BS 34 will be different, but check to make sure they line up evenly and are at the right height from the carb body inside the little ridge on which the gasket seats. Are you having the same problem from both cylinders or only one? Once I did all of the above, the bike was out of the garage and made it 2 hours up the highway and up a 6000ft mountain the very same day.

Check out my post from a couple days ago for more details and a more thorough checklist: http://www.xs650.com/forum/showthread.php?t=6219&highlight=acceleration