stumbling, stalling, backfiring

[YellowJacket!]

Check your spark plugs too.  Even if the mix or sync is off (and the cause of the problem), they will most likely be fouled too.

Just some more thoughts.

David

[Rikugun]

My last post was rather lengthy so let me restate - there appears to be vacuum leaks at the throttle shafts.

[Re-Vision]

I'm certainly no carburetor expert but seeing as how the vacuum is taken off of the upper throat of the carb,it would appear to me that any leak from around the throttle shafts would have little or no bearing on proper engine operation. I may well be wrong on this but synching ain't gonna hurt anything.     BDC

The more I think about this the clearer I see that I am wrong about the vacuum and its takeoff point. My first mistake for the day Ha Ha.

[Rikugun]

Yellow Jacket - When I had the valve covers off I took the opportunity to change the plugs. I will check them and hope to see them dry.

QBS - I would agree and just because my filter looks clean that's no guarantee the pilots haven't become fouled.

Has anyone used the technique I described to locate vaccum leaks? Should I be concerned over what I've found or is that normal?

[pat sullivan]

Rikugun.  I wouldn't give up on the fuel pump being the problem.  I had similar symptoms and overhauling the fuel pump corrected the problem.  See my post on the main board. 

I used to think that as long as there was enough gas in the tank that the bike would run OK even if the pump was bad.  I'm not sure that I believe that any more.  If the outlet valve on the pump is not opening properly then it looks like it's possible that no fuel gets through.

Pat S.

[Rikugun]

Pat, I read your post and still don't think that's my problem. After the last ride with a hot engine, I ran the bike and captured the pumped fuel into a catch can. Now I don't have a spec for litres/hour flow rate but the volume seemed sufficient for a half litre engine to my quasi-trained eye. I then ran the rest of the tests from a test tank just to completely eliminate the pump, regulator and their respective vacuum feeds from the equation. The erratic, high idle persisted under these conditions. Spraying carb cleaner around the ends of the throttle shaft caused a temporary and immediate increase in engine speed.

I believe that the symptoms I first wrote about were a combination of general poor running due to high ambient temperatures as reported by many Vision riders. In addition, I think there may be vaccum leaks at the throttle shafts -  the symptoms of which I have been in denial over. These have been present from the first time I ran the engine but due to my lack of familiarity with this model, combined with anecdotal reports of Visions having quirky carburation, I took it to be normal.

I have never been satisfied with the idle. It always seemed a bit rough. I could never get it to idle at the speed suggested in the manual but rather a couple hundred RPM higher. The mixture screws seemed to require more turns out than normal to achieve the smoothest idle it was cabable of. It would surge ever so slightly at steady rpms down low to midrange. The throttle response and mid to high rpm performance was good and my excitement over wanting to ride the bike clouded my judgement re these problems. I didn't want to admit these things and initially they were easy to explain away. Over the course of 1500+ miles, the symptoms have worsened to the point where they can no longer be ignored.

Sorry for the long post (again) but if nothing else it helps me sort things out by writing about it. Anyone willing to put in the time to read this  :) I welcome your critique of my diagnosis so far. I'd love to be prooven wrong - especially if it turns out to be something easy to fix!  :laugh: :laugh:

[Tiger]

 :) RE: Spraying carb cleaner around the ends of the throttle shaft caused a temporary and immediate increase in engine speed.

I think...for what its worth...that the butterfly seals are KAPUT mate and need replacing...A complete strip down, clean and rebuild of your carbs is, IMHO, (if not done recently), also needed.

          8).......TIGER....... 8)

[Night Vision]

OR... try fattening up your carbs... nice thing about these carbs is you can fiddle with the jets pretty easy...

I can tip the carbs and change the fuel pilots and mains in about 15 min.

before you give up and have to go for a major tear down, play with the jets..

I'm running 127.5 / 130 mains and some #64 fuel pilots I made... got rid of a pesky 4.5-5k rpm surge that was driving me coconuts..

if you send me a spare set of #60s I can drill them out for you.

[Rick G]

They won't run right IF the butterfly shaft seals are toast. DO NOT try to replace them . The screws that locate and afix the butterflys are staked and are not reusable. The factory must have some sort of fixture to support the whole thing during the staking process.
First relocating the butterfly is impossable , in the field  and if the screws do  come loose you will have , either a stuck throttle , or they will go into the engine , or , more likely both.

[Rikugun]

Tiger, are the seals still available for these carbs and from where? I understand Rick G's concerns but I'm not ready to trash the carbs just yet. If seals are available I would think there must be a way to replace them, yes?

Night Vision, jetting the problem away is not my first choice but I'm considering all options. What size drill did you use ? I have .0135"-.039" (80-61) available. Also, how did you determine you ended up equivalent to #64 pilot jet?

[Tiger]

Tiger, are the seals still available for these carbs and from where? I understand Rick G's concerns but I'm not ready to trash the carbs just yet. If seals are available I would think there must be a way to replace them, yes?

:) P M Canadian_Lou, who does the Canadian crews carbs. He will be able to answer your questions regarding cost and availability... ;)

              8).......TIGER....... 8)

[Lucky]

actually, pm Rick G. he once mentioned that throttle shaft seals from a Polaris will fit...

[Re-Vision]

Would it perhaps be simpler to just get a new carburetor and not have all the hassle? At least get  your bike running and then see about rebuilding the old carb. JMT 
BDC

[Lucky]

throttle shaft seal dimentions:
in inches:
.455 x .313 x .195

or in mm, roughly:
0.115 x 0.75 x 0.2

now i can find referances to Mikuni throttle shaft seals on the web, but nothing that states their size, only part numbers.  my search skills aren't the best, so someone else may be able to find them.

Jason says slightly undersize #6 orings will work, i find the ones my store sells are tight.

the seals i have out on a junk carb are loose on the o.d., some sealer will would fix that, a tiny garter spring would help against the throttle shaft except if you look at the seals with a jewlers loop, you can see the edges are cracked & dry (rotted)

just thinking out loud:
a garter spring could be made from a turn or two of the right size spring...

[Raj1988]

hey folks, What seals are these. ??? i cannot figure out what it is you folks are speaking of. is this the seal that "seals" when the throttle plate closes?

[Lucky]

throttle shaft seals are the the seals where the throttle shaft passes thru the body of the carb. there are 2 on each shaft

[Rikugun]

Lucky, I'm guessing your metric conversion decimal points are off? Are the inch measurements actual? i.e. you've physically measured seals to arrive at those numbers?

just thinking out loud:
a garter spring could be made from a turn or two of the right size spring.

Maybe with steadier hands than mine brother!

So Rick is advising me against this but has experience with Polaris parts as replacements!?  ???

[Lucky]

Rick & I (at least) have years of experience as mechanics, technicians, AC techs, small & large engines, etc.  we will do some things most people are skittish about (or should be):
--R & R'ing butterfly valve screws,
--taking an engine down to it's crankshaft
--Rick had modded his upper tripple to take regular bars (which has to be done right or you could lose control of the bike)
I & a few others here have actually drilled & taped into our engines oil gallerys to install oil coolers...

we are not telling anyone not to do these things, we are also not taking responsibility if you grenade your engine...  what we are saying, is that you MUST have the experience to be aware of the fatal possabiliys before you begin a jot that has that potential..

if Rick advised you not to do somnething, it was because he percieved a certain skill level from your posts.  for your own safety, or the health of your bike.  he would be the first to admit that you can only tell so much about someone from posts on a website, & if you feel you have the ability to perform a task, go fo it! we are here to help & answer question if you wish too.

--Lucky

[Lucky]

the mesurements are with a micrometer on the bore, shaft & actual seal thickness.  the micrometer reads inches but also has a mm scale, so i estimated.  i (obvously) haven't used one in quite a while, lol

just rechecked, my inch measurements are accurate...

[Night Vision]

Night Vision, jetting the problem away is not my first choice but I'm considering all options. What size drill did you use ? I have .0135"-.039" (80-61) available. Also, how did you determine you ended up equivalent to #64 pilot jet?

ok, I pulled my stuff and correct myself... I made several sizes but ended up using #62.5 fuel pilots, and 127.5/135 mains with 130/135 air pilots and the vacc flapper box.

a #60 pilot jet is (to me) .60mm = 0.02362198"
thus a #62.5 would be .625mm = 0.02460623"

Grainger has wire gauge drill bits.. a 72 wire gauge bit is equivilant to .0250 = close enough
the bits are cheap so you can get an assortment and keep going bigger if you need.. you just can't go backwards  ;)

I got 72,71,70,69 wire gauge bits that equal .025, .026, .028, .0292 (yes the lower the gauge bit #, the larger the size)... and used an old fashioned hand drill to drill the jets... pilot jets turned upside down and placed in the top of an old carb top makes a handy holder


I estimated (proportioned) those sizes to be #62.5, #65, #70,  and #72.5 pilot sizes....

my "theory" is that leaking butterfly seals is just some extra air in the mix that can be compensated for by adding additional fuel,,, ie bigger mains and bigger fuel pilots...

my mpg did go down.. around 43-45mpg.. and she doesn't like choke at startup (never did) but she doesn't run stinky rich