Author Topic: Carburator Jets for Visions  (Read 850 times)

artbone

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Carburator Jets for Visions
« on: February 28, 2018, 08:45:57 PM »
My 83 is running so good now I can't believe it but I still need to fine tune the carbs. I just looked at it in the shop and it's got 130 jets in the pilot air, front carb, and rear carb. I just changed it to 120 in the front because that's the only jet I had in my huge collection.
Yesterday I took it on a ride up to Xichu, a little town in the Sierra Gorda mountains, going from 6500' to just over 9000' before dropping down to Xichu at about 7000'.
I want to change it to about 122.5 front and 125 rear but I'm going to try it with what I have for the time being.
My question is: where can I buy jets for a reasonable price. I know I've seen an address on ROV for a place that sells jets but I can't seem to find it.

By the way, what my bike is doing now is: in 5th at about 4500 rpm to 5500 rpm it just stalls. It just quits pulling. If I happen to hit a downhill it picks up until the rpms hit 6000 then pulls like a freight train to redline. In the lower gears it goes through that range so fast that I don't notice it.

As always, thanks for any suggestions.
Art Bone

'83 Yamaha Vision in the Classic Black and Gold  Running
'82 Yamaha Vision Running
'74 Norton Fastback - Colorado Norton Works #26  Running
'73 Norton Interstate  Running
'75 Triumph T 160  Running
'62 Harley Davidson Vintage Racer
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Walt_M.

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Re: Carburator Jets for Visions
« Reply #1 on: March 01, 2018, 12:25:09 PM »
The site I use is jetsrus.com sad to say reasonably priced is a relative term as they are 5-7 bucks each. And I don't think they will do exchanges. Your problem sounds like an extreme case of Vision-stumble. There are a multitude of causes on the '82s but fewer on '83s. Mine was poor carb synch which I was able to fix and it ran fine for a long time but my carb swap got rid of it. Since your carbs are still in good shape you can fix them and I agree that leaner jetting should help. Good luck.
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Prophet Of Doom

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Re: Carburator Jets for Visions
« Reply #2 on: March 02, 2018, 04:28:11 PM »
I've only worked on 82 carbs but 83s should be similar.   7000ft altitudes will richen your mixtures considerably, but won't do your engine any harm.  Much better than jetting (leaner) for altitude and then descending to sea level.  Since yours is pulling to redline (I'm assuming also OK at low throttle opening), then don't touch the jetting.  It's probably fine.

I'd go for a good sync first, then float level, then valve clearances, then cleanliness.  If you still have a bog especially at those RPMs then look at your round grey air bleed filter to make sure it's clear then check your accelerator pump. 

Does it happen most when you whack on the throttle, but not when you increase throttle ever so gently?  On my bike, when I cracked open the throttle I got a  massive bog - enough to make the bike dive through engine braking and this took 2-5 seconds to clear, then it took off. 

Using a hydrocarbon meter I found it was dispensing far too much (unatomised) fuel so made sure the accelerator pump was spraying properly and not hitting the butterfly.  I screwed out to grub screw a couple of turns and shortened the rod by about 1.5cm.   Bog nearly gone.  Widening the pilot air to 120/120 gave me a stumble free bike.

Semi synth oil and iridium spark plugs also helps incredibly for a smooth running and happy bike.

QBS

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Re: Carburator Jets for Visions
« Reply #3 on: March 02, 2018, 11:50:34 PM »
Pod, thank you for the timely and concise carb tutorial.

Prophet Of Doom

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Re: Carburator Jets for Visions
« Reply #4 on: March 03, 2018, 03:20:02 AM »
:-) There's more to it of course.


I've just added to the resources page a Mikuni Pocket Tuner.   It should be equally good on our carbs.  If you do live at altitude, or hot places this will help with jetting adjustments.

artbone

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Re: Carburator Jets for Visions
« Reply #5 on: March 04, 2018, 11:04:51 AM »
Thanks for the advice. I should have said in my first post that I have gone through the valves and they are adjusted correctly, installed aftermarket coils, and cleaned the carbs in my ultrasonic cleaner. The accelerator pumps are spraying correctly and I'm using the stock airbox with flapper door and it works correctly. And I've got a MAC exhaust.
The problem happens at wide-open throttle and gets worse the higher up I go. I live at 6500 Ft. and it gets much worse at above 9000 ft. I tested it on a long up hill by opening the throttle at about 3000RPMs. The bike pulled strong until 4500, then struggled up to about 5000. I backed off the throttle just a bit (not over 1/16) and the bike surged forward for a second then pulled better than with full throttle. If I dropped down a gear and got out of that range (above 6000RPMs) then dropped it back in 5th, it would pull up to redline.
My thought is that at that RPM the only circuit operating should be the main jet and I've ordered some new jets from Niche Cycle in Florida ($3.50 each) What I don't understand is why is it running so good below say 4500 and above 5500 but so crappy in between.
Is it actually too rich everywhere and just gets so rich in that range under load that it won't pull?
Maybe air flow hits some sort of harmonic in that range and changes the breathing?
Anyway, I'll get the new jets next week and report back.
One other question. The venturi on the rear carb of my bike is loose. I didn't notice it until I had the top of the air box off with the engine running and it was vibrating. I couldn't find anything to tighten it. The one in the front it is fine.
Art Bone

'83 Yamaha Vision in the Classic Black and Gold  Running
'82 Yamaha Vision Running
'74 Norton Fastback - Colorado Norton Works #26  Running
'73 Norton Interstate  Running
'75 Triumph T 160  Running
'62 Harley Davidson Vintage Racer
'61 Sears Puch  Running
'15 Triumph Scrambler
'17 Honda Africa Twin
94 Kawasaki KLR 650

jefferson

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Re: Carburator Jets for Visions
« Reply #6 on: March 04, 2018, 12:09:19 PM »
There is a set screw just to the right of the idle air mixture screws that holds the venturi's tight. They will have loctite on them. Sounds like one of them needs to be snugged up.

artbone

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Re: Carburator Jets for Visions
« Reply #7 on: March 09, 2018, 02:11:15 PM »
Thanks Jefferson. I've got the bike on the bench and I'll check that today.
My jets are still not here. They were delivered to my mail service in Laredo TX about noon last Monday but my local mail service still doesn't have them. One of the joys of living in Mexico. You get to pay 17% plus handling charges for everything you ship in and still get crappy service.
Art Bone

'83 Yamaha Vision in the Classic Black and Gold  Running
'82 Yamaha Vision Running
'74 Norton Fastback - Colorado Norton Works #26  Running
'73 Norton Interstate  Running
'75 Triumph T 160  Running
'62 Harley Davidson Vintage Racer
'61 Sears Puch  Running
'15 Triumph Scrambler
'17 Honda Africa Twin
94 Kawasaki KLR 650