Engine Stumble 4000-5200rpm

[Cdnlouie]

I am working my way through the 21 pages of posts and learning a great deal from the experts here. ?I are resurrecting a Vision I bought in August (first one), and I am working out the carburetion right now. ?I have a few things not quite up to specs and need to complete the YICS repair next. ?I am leaking internally so I blocked off the rear cylinder and capped the inlet temporarily to avoid some major running problems.

I have a wired open air flapper (which I will shortly reconnect to some specs mentioned in a previous post). ?I will get these items fixed shortly to narrow down my problem of a significant engine stumble between 4000 & 5200 rpm. ?Engine pulls fine coming up slowly, but any sudden accleration in this range and it falls on its face only to get up and get going with gusto at about 5500rpm.

Is this the infamous "vision stumble"? Everything works great other than this issue. ?Carbs need a good going over this winter, they were well cleaned, but not checked for float level during my initial "let's just see if this thing will run."

I am closing the gap on my understanding of this little gem, so looking forward to a couple of hints that may get me going in the right direction.

Sincerely,

Not Far From Perfection. :)

[Lucky]

CLEAN & TUNE, CLEAN & TUNE, CLEAN & TUNE, CLEAN & TUNE, CLEAN & TUNE, CLEAN & TUNE, etc [/color]
I have rebuilt well over a dozen now and the mantra is the same for every single one[/b]: CLEAN & TUNE,

all things being equil (valve adjustment, compression, flapper doors, etc)  a clean carb that has been accuratly synced, and had the pilots properly adjusted SHOULD NOT have a stumble, except when very cold.  the factory updated worked.  no coins on the flapper door should be needed either.
--Lucky

and i'm finally learning to use code here... now i can be REALLY annoying...

[Cdnlouie]

Thanks for your patience with a neophyte.  I know this is old news, but us new Vision owners will all need to hear it again & again & again....

You need to generate a button for us to press and hear something to the tune of "You are an idiot".

[Lucky]

I didn't mean to imply anyone is an idiot, i was just playng with the pretty buttons... :)

[Cdnlouie]

I have a few more quick bothersome questions.  I released the flapper from being wired wide open from my initial start-up of the bike.  It did cure the stumble of 4000-5200 but it really breaks down after 5500 and up.

So I am on the clean & tune phase (only the 2nd time)  I have too high a fuel level on the rear carb (only 5mm from the top of the gasket) and a bit too low on the front (24mm from the top of the gasket).  Do you guys recommend the 20mm level form the top (using a clear hose and releasing drain screw test - Haynes)?

I am on the hunt today for some "O-rings" for my needle and seat.  I am trying to find a source here in Toronto for some of my seal needs.  These may be leaking in the rear as the float level is at 36mm.

Interestingly, the secondary venturi on my front card looked to be dislodged from its seat so I am hopeful that this will help my cause.

Also, anybody got a couple of 135 pilot air jets or a source?  I have 120's in both front and rear.  I wonder if my bike missed the recall on that one.  I appreciated the discussion of your trials with the 135 air jets and the discussion on the richness of the 82's.

Thanks for the input always,

Louie

[Cdnlouie]

Narrowed this problem down to rear carburetor, but wondering about the right solution to it. ???

I got some nice o-rings for the needle and seats.  Anyone need some drop me an address.  The measurement is 7mm by 10mm by 1.5mm.  Vitron is a nice flurocarbon rubber which is better than the original (or so they say).

[Lucky]

The Venturi's sit in a little recess with a fiber gasket, and are held in place with a set screw, so they may look "dislodged" from the fuel pump side.

Also I have found that not all the overflow tubes in these carbs were installed properly, so i tend to go 2mm lower on the float hight.  no lower though.

[Dave T.]

I assume Canadianlouie, now, that your problem is that your V burbles at any rpm over 5500. Check out the previous post Easiest way for more power on your '82 Here we discussed some issues of the V's stumble and carb problems. I found this to be the best post in a long time.

My "off the cuff" advice is to get more air and less fuel into your carbs at high rpm's. Remove the air filter and leave the flapper "unwired". If this helps, get a new AF.
Does your V run better at high rpm in cold weather? I.E. below 60 degrees? Do you have stock exhaust or a less restrictive one? If you have an '82 with Mac exhaust LOUD then you want to rejet so both carbs have the same jets. Also, the main jets are the same as the air jets. What's this G in a green circle for?
[shadow=red,left,300]Wow this html stuff is neato![/shadow]

Keep on keepin' on..... 8)
http://www.93x.com

Code Select Expand

What's this? Whoa, cool...

[Cdnlouie]

Okay, I've gone over this baby with a microscope now and I have a bit more info for you guys to plug into your awesome databanks.

I have a strange combination of jets. ?I do have a Mac (loud) exhaust. ?I noted that I have 120 pilot air jets (Haynes seems to suggest 130 although they may be confused on that spec) on the top of both front and rear.

I also have 145 main jets below (Haynes says I should have 122.5 front and 127.5 rear).

Now is this combo likely to work or work like it is at the moment (dying over half throttle). ?This requires some expert advice here.

I removed the air box and watched it kick fuel back when going over half throttle much like a situation with valve timing off (although I do not think this is the case). ?Both cylinders seem to be affected although it seems a bit worst on the rear.

This may be a sabotage issue of previous owners to address.

Any suggestions on recommended jets and where to get them.

[Dave T.]

Get all your jets figured out first. Is your bike a 1982 or 3?? If you have the 1983 model, my advice might not mean much, but if you have the 1982 carbs with the vacuum operated flapper, and you have 145 main jets in, dude, this is WAYYY rich.

Here is my 82 vacuum operated setup. Pilot jets, stock. Pilot air jets, 132.5 F, 135 R. Main jets: 120F, 120R. My V rips at temps below 70 (all rpm's, a little stumble once in a while), and burbles a little on top above 70 degrees F. Oh yeah, I have MAC exhaust and a UNI foam filter.

I know those little numbers are hard to read on the jets so make sure that was the right numbers you gave. You should be able to get Mikuni jets at your local Yamaha dealer for about $3-$4. Bring one in to them.

[shadow=red,left,300]EAT AT JOE'S[/shadow]

Good luck!  :o

[Lucky]

I agree, get your jetting back to stock before you go much further.

[Cdnlouie]

Redline City!!!

Okay guys, thanks to all for the interaction.  I have learned most of the Vision's "character" these past 3 weeks.  Last night one of the previous posts kicked in and gave me the thought to switch the jets as someone in a past life (rest his weary soul) had done so.

The 120's went down to the mains and the 145 went up to the air.  I enriched the pilot screw to about 7 turns but it runs like it has never run.

I look forward to finding a couple of stock air jets as you have suggested and things should be pretty peachy.

In this process I have completed all restorations and my Vision lives.

Louie   ;D

[Rick G]

Hi Louie, MAC suggests the stock jetting is fine with thier exaust. Mine has MAC pipes and stock jets. I monkeyed around with the jetting at first but clean carbs and  and a properly adjusted flapper door are the solution! Whats all this code stuff?

[Cdnlouie]

Hello Rick. ?Pray tell what is stock jetting for an 82? ?You guys take a lot for granted with us newbies. ?I have not read any two guys on this forum in combo with my Haynes manual that agree on stock jetting.

However, for the record a plug reading on the combo of 120 main and 145 air (which is all I have at the moment other than sticking dubble bubble in them), gives a very lean mixture. ?Certainly not the best idea from what I am beginning to understand.

At least I have some real top end now and a stumble between 3500-4500 rpm. ?I am really learning how to move that stumble around lately. ?I will get to the flapper and fine tune when I have the jetting stabilized.

I plan to go with the 135 air recommendation that you guys seem to be having success with as soon as I can get out to my dealer who does have a few kicking around.

If anyone wants some extra jetting sizes I can probably lay my hands on some next week.

I am really enjoying this bike. ?Had a nice ride today to work and back. ?She only has 17,000km (10,000 miles) on it so someone really messed things up early in her life and I have them to thank for getting the bike to me.

Louie ? 8)

[jasonm.]

Go to the stock sized main jets also! And set the pilot screws to about 4-5 turns out. One more turn out and you'll lose them.