Author Topic: Carburation Question  (Read 256 times)

artbone

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Carburation Question
« on: April 11, 2018, 05:36:48 PM »
To make the pilot system leaner do you increase or decrease the size of the pilot air jet (the one in the top of the carb?) Stock is 130 so to lean it out I would go to 135 I think. If anyone knows for sure, please enlighten me.
Art Bone

'83 Yamaha Vision in the Classic Black and Gold  Running
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ProphetOfDoom

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Re: Carburation Question
« Reply #1 on: April 12, 2018, 02:42:50 AM »
Not sure why you would want to make an overly lean bike leaner, but bigger numbers on the pilot air jet passes more air and so makes it leaner.
Euro spec for the 11U and 16R models (1982) is F120/R120 and I found that significantly better overall than the 130 and 135 that I've also tried.



artbone

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Re: Carburation Question
« Reply #2 on: April 13, 2018, 09:17:17 AM »
As to why I want it leaner, I live at 6500 Ft and regularly ride up to 9500 Ft. The bike pulls strong and doesnít have a flat spot or the famous Vision Stumble but I still think it feels a little rich. Iím going to try one or two sizes at the time until it feel right to me.
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

ProphetOfDoom

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Re: Carburation Question
« Reply #3 on: April 13, 2018, 05:27:01 PM »
Sorry, I'd forgotten that. Presumably it's hotter in mexico than the rest of the world also - that will have a similar effect to increased altitude.   Hot air is less dense and has less oxygen.
Pilot air will only adjust up to about 1/3 throttle.  The main air jet is hard to swap out, but perhaps think about reducing the main fuel jets as well to get leaner across the board. 



artbone

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Re: Carburation Question
« Reply #4 on: April 15, 2018, 05:51:42 PM »
I went down to 122.5 on the main jets and 140 on the pilot air jet. I think the bike runs better than it ever has. I might order a couple sized smaller, maybe 120 and 117.5 but I'll probably leave it alone. I forget to mention that Iíve got MAC pipes on it. It has no hesitation, no Vision Stumble, just pulls like a freight train to 10K.

It does have one other problem thatís just turned up in the last couple of weeks. Sometimes, when the bike has been ridden long enough to get completely warm, then let sit for 30 or 45 minutes, it will crank on one cylinder and act as if one spark plug is disconnected. It will run like that a few minutes then suddenly start running on two cylinders. I canít determine if itís fuel related or electrical. It did it today as I was riding out in the country and I putted along until I got to a place I could pull well off the road. I lifted the seat and pulled each of the fuses out. They all looked good so I put them back and tried it again and it fired right up and ran perfect the rest of the way home.

I had replaced the diaphragm in the fuel pump and looked at the diaphragm in the petcock and it looked fine. I replace both the fuel and the return lines. As I said, when itís running itís running the best itís ever ran.

I have intermediate problems.
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

cvincer

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Re: Carburation Question
« Reply #5 on: April 16, 2018, 03:10:52 AM »

Out of interest.......after the bike has been ridden long enough to get completely warm,  let sit for

30 to 45 minutes & then drain each float bowl into a measuring cup & see how much comes out of

 each.

Walt_M.

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Re: Carburation Question
« Reply #6 on: April 16, 2018, 05:43:39 AM »
That sounds a lot like a failing rev limiter. Have you disconnected yours?
Whale oil beef hooked!

artbone

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Re: Carburation Question
« Reply #7 on: April 16, 2018, 09:44:45 AM »
You are right Walt! Thatís exactly what it sounds like. I didnít know there was a rev limiter on this bike. I take it up to 10K once in a while just to see if it will do it but normally I never shift at over 9K. Where is the rev limiter and how do I disconnect it?
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

fiat-doctor

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Re: Carburation Question
« Reply #8 on: April 16, 2018, 11:13:04 AM »
At the TCI there is a Yellow/Black wire.   This grounds the TCI when the tach senses an over rev and kills one cylinder.  I use a small probe and release the wire from the connector block at the TCI.  This way you can always put it back to stock if you want to.

I have had a couple of TCI's fail where it would quit running on one cylinder when it got warm.
If you have access to a spare it's a 5 minute swap for testing.

Steve

artbone

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Re: Carburation Question
« Reply #9 on: April 16, 2018, 12:11:46 PM »
When the problem started in the past was after the bike was warmed up and then shut down. When it started running correctly again it was like a switch was thrown. Yesterday I was riding about 60 mph and it started running on one cylinder again, like a switch was thrown. Because I was messing with the carbs I forgot the old rule of thumb - ďMost Carburator Problems Are Electrical.Ē I was all set to pull the carbs and go through the fuel pump, change all the hoses, etc.

I did a search on ďRev LimiterĒ and found that the yellow and black wire is the one to cut and tape up to disconnect the offending device. I think for me the easiest place to do that is right at the TCI unit. I canít face taking that fairing off again. Now I see that fiat-doctor has posted the same info with the suggestion that I release the wire from the connector block so I can put it back to stock if I want to but I donít know why I would want to do that. As I said, I never turn it over 10K and I didnít even know it had a rev limiter.

I donít see how anyone gets or keeps one of these running without being a member of this group. Thanks everyone for the advice.
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