rpms bouncing at 80 mph

[97Blade]

Well, i searched the forumsve this problem when i get around 80 mph,the rpms bounce from 7k or whatever down to zero the back up to 7k over and over.Sometimes it will not even do it,do you guys think i need new spark plug wires?Oh, and it either afterfires or backfires extremly bad.Up untill 80 or so,it runs great.

[kevin2502000]

So does the tach accurately represent the engine rpms? If so sounds like you are running out of fuel at that speed.

[HexKrak]

I'd pull your plugs and see if they're fouled anyway, but it sounds like a fuel delivery issue. Poorly synched carbs/dirty carbs/ugly carbs/ I hate carbs sometims/pinched fuel line/dirty petcock filter.

[mather_builders]

Possible electrical short(ignition, kill switch, side stand, ect).

[Cheriff]

So it only does it when it is going 80? Not at the same RPM in a different gear, or over bigger bumps? Just trying to pull out some more clues...

[97Blade]

just when im going around 80 or so,i was thinking that maybe i have a loose spark plug wire,engine vibration and all?i doesnt do it any gear but last and i have to be cruisin pretty fastlike the kickstand switch is being made,but i know thats not it,i think ill check the plugs and wires,i hope its just wires

[quik89Kat]

I'd pull your plugs and see if they're fouled anyway, but it sounds like a fuel delivery issue. Poorly synched carbs/dirty carbs/ugly carbs/ I hate carbs sometims/pinched fuel line/dirty petcock filter.

Yep if your carbs are ugly they wont run right..lol Just Kiddin HK

everyones right sounds like fuel to me....is it at 80 no matter what? like I mean is it repetitive with 80 mph exactly? if it is then it may be electrical My friends kat did that and it was the sidestand switch you hit even a lil bump at 80 and thats enough to make the stand drop a smidge and cut out ...I'd ziptie it up and do 80 and see that will rule out it moving then move onto lookin at your fuel filter/carbs

[md86]

No , if the tach goes down to 0 and up again , it ain't fuel . And yeah , likely them plugs will be rough-looking . Hell , SOMETHING'S apparently cutting spark momentarily ..... Like the 2 guys up there said earlier , short , kickstand switch , things that may cut ignition ...... Even if fuel's faulty , RPM's ain't gonna dip like that . While the engine's turning , RPM's stay up REGARDLESS .... 'Lectrical

[coggs]

I agree electrical
Around 80 seems to me to be the speed at which you get the most vibration from the engine - possibly a link? this could possibly cause an electrical connection to break/short or maybe a faulty coil that shorting with the vibration. Another place to check is ignition switch - from personal experience!

[97Blade]

Ok,ill check out those-thanks

[the_shayne]

i have about thae same issue. i have a kat service book and its troubleshooter is leaning towards fouled plugs....possibly valve adjustment. fouled plugs could also be the culprit for a rolling idle which is somethin i'm dealing with.