Analyze This

[btdtdan]

Have just cleaned the carbs on my 81 special. Starts,Runs and idles smooth as silk. Took it for a test ride and it was smooth but sluggish until 5k then it will not go any more. Just like a gov. kicked in.
Pulled the sidecover and the vaccum advance will only let it go so far when you rev the beast up. If you manually overide then it will red line with no problem. What do you guys think? I have read several other threads on similar problems but none quite like this. It has after market 2 into 1 exhaust with no crossover. Are my jets to big or to small. It has a K and N stage three jet kit installed. Don't know how it ran before, this is a back from the grave restoration project.
Thanks for any help or suggestions,
Dan

[xssiveone]

When you cleaned your carbs, did you remove the idle mixture screws and clean the passageways underneath? The manual will tell you not to remove the plug over these, but it's the only way to ensure they are clean. Also, when you put the carbs back on, did you reconnect the vacuum advance line to #2 carb, and not the rubber intake boot? The nipple on #2 has a restriction in it, the carb boot does not, resulting in too much vacuum being applied to the advance mechanism.

Clean and lube the advance mechanism. When you say

the vaccum advance will only let it go so far when you rev the beast

does it rev to the same RPM in a no load situatiion as it would under load? (ie driving?) Usually not difficult to get to redline without a load on it.

While you're cleaning/lubing the advance, check the wiring harness for breaks. Pickup wire fix This doesn't normally cause sluggish performance until after the advance mechanism moves but it won't hurt to check while you're there.

[btdtdan]

It revs to the same RPM with or without load. Will go to redline when you manually override. Is smooth and without hesitation when you overide. No problem with pickup line. Yes the caps were removed and cleaned.

[btdtdan]

Yes vaccum line was also connected to the #2 carb. So far cleaning and lubing the vaccum advance did nothing to improve performance

[ratbyk]

Won't Rev Over 5000

Are your K&N's true K&N's or the cheap after market copies? Remove the filters and try reving with them off. If they are not true K&N's and have the big rubber collar where they attach to the carb air horn it can block off some of the balancing ports to various circuits in the carb. The large rubber collar also has a smaller hole through the throat than the carb air horn and starts to act like a choke at higher RPM.
If the air filters prove to be OK (true K&N) then I would very quickly blame your stage 3 jet kit. Pull plugs and see if you are running too rich. Compare the actual hole in the jet to the original jets. After market jets even though they may have the same number stamped on them as the original mikuni's often have a fuel flow away higher than the original carbs.
Ken/Sooke
78E Ratbyk
82 FT500 "lilRat"

[strom]

Might be the TCI... or the carbs.... check the tech tips for the diagram/explanation. You will learn there which jets control which rpm range.

LP

PS: Pick up wires?

[TopCatGr58]

Okay, think folks missed this line: When you manually override the vacuum advance! So I think you mean that you turn the vacuum advance plate in the advanced direction with your hand while operating the throttle, since the plate will only go so far under vacuum control?!?!?

With engine off, pull off vacuum hose from carb, and have timing cover off. Apply vacuum to hose and watch advance, see how far it travels. While applying vacuum, fold/pinch the hose, does the advance mechanism slowly return to NO advance=leak in the vacuum diaphragm/module!?

When you manually advance the timing plate, is it very smooth, not sticking anywhere?? I remember seeing a post/reply from a fellow Xsive, the screw/pin that the vacuum advance plunger attached to the timing plate was loose, and so wasn't getting the most from the range of travel on the vacuum advance plunger, he replaced it with a screw/nut/bolt type combo and that fixed it!?
HTH.?

[btdtdan]

TC,
You are exactly right!! Will let you know how your suggestions turn out. Need to also pull the plugs and see if they have a story.
Don't know if has run long enough to tell much. Perhaps I may expect to much. I have a 78 with a jet kit and 4 into 1 supertrap that just is scary fast and screams. Don't know if this 81 will ever run like that.
Thanks to everyone for suggestions /input. Will get this thing going one way or another.
Dan

[btdtdan]

I wonder if my diaphrams have pin holes and if they do, could that cause the symptoms/problem I have?