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XV920 Bogging

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XV920 Bogging

PostAuthor: k.huang402 » Tue Apr 06, 2021 9:51 pm

Hello everyone.

I got my 83 xv920 back from the dyno and its been up and running again. I noticed that in first and second gear that the bike boggs at around 4100rpms and it just stays there until it shift into another gear. Most of the time I can get the bike to 6000rpms in 3rd gear and on. Any reason why my bike is doing this? I checked/cleaned the jets just before taking it on a ride and although it ran better, the first two gears topped out at 4100rpms. I have two in line fuel filters so its not bad or old gas. The only aftermarket parts on the bike are; a mesh cover over the side of the frame where the air box usually goes, 2 into 1 exhaust, and 2 Mikuni Vm34 carburetors but the dyno tune should've corrected the air/fuel ratio. Thoughts?

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Re: XV920 Bogging

PostAuthor: mark75 » Wed Apr 07, 2021 6:24 am

was it doing this before the "dyno tune"?

I would look at the fuel filters 1st thing.
& make sure the slides move easily and freely

JIC - check your battery is fully charged, spark plug cables / caps and maybe some new plugs?
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies --- whether you're having fun __ :bike: or not --- :fan:

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely ---> Semper Vigilans --- always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
... Mark Twain

“THESE are the times that try men's souls. The summer soldier and the sunshine patriot will, in this crisis, shrink from the service of their country; but he that stands by it now, deserves the love and thanks of man and woman.
Tyranny, like hell, is not easily conquered; yet we have this consolation with us, that the harder the conflict, the more glorious the triumph. What we obtain too cheap, we esteem too lightly: it is dearness only that gives every thing its value.
Heaven knows how to put a proper price upon its goods; and it would be strange indeed if so celestial an article as FREEDOM should not be highly rated”


Thomas Paine --- 1776 December 23


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Re: XV920 Bogging

PostAuthor: Hellgate » Wed Apr 07, 2021 1:14 pm

I agree with what Mark said. What changes were made during the tune? Typically bogging indicates it is too rich. Check the basics first, usually it's the simple things.
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Re: XV920 Bogging

PostAuthor: k.huang402 » Fri Apr 09, 2021 6:10 pm

mark75 wrote:was it doing this before the "dyno tune"?

I would look at the fuel filters 1st thing.
& make sure the slides move easily and freely

JIC - check your battery is fully charged, spark plug cables / caps and maybe some new plugs?


Before the tune it was able to run but it had idling issues. The guy at the shop put in a bigger main jet and pilot jet and said that he dialed it perfectly. It's definitely ride-able now but I cant get it over 4100rpms in 1st or second. I check the fuel filters and it's all good and clean. Took off the float bowl and checked the jets for clogs and it's all clean. 3rd gear seems to bogg at 4100 as well but I was able to throttle until it got over that hump.

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Re: XV920 Bogging

PostAuthor: k.huang402 » Fri Apr 09, 2021 10:42 pm

mark75 wrote:was it doing this before the "dyno tune"?

I would look at the fuel filters 1st thing.
& make sure the slides move easily and freely

JIC - check your battery is fully charged, spark plug cables / caps and maybe some new plugs?


To be more precise. It's more of a flutter than a bog. When I open up the throttle it reaches 4100rpms and then it feels like it's hitting a rev limiter and will not go any higher.

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Re: XV920 Bogging

PostAuthor: mark75 » Sat Apr 10, 2021 6:36 pm

:yup: @ that rpm range you would be on main jet ... either too rich or dropping a cylinder? :con:
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies --- whether you're having fun __ :bike: or not --- :fan:

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely ---> Semper Vigilans --- always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
... Mark Twain

“THESE are the times that try men's souls. The summer soldier and the sunshine patriot will, in this crisis, shrink from the service of their country; but he that stands by it now, deserves the love and thanks of man and woman.
Tyranny, like hell, is not easily conquered; yet we have this consolation with us, that the harder the conflict, the more glorious the triumph. What we obtain too cheap, we esteem too lightly: it is dearness only that gives every thing its value.
Heaven knows how to put a proper price upon its goods; and it would be strange indeed if so celestial an article as FREEDOM should not be highly rated”


Thomas Paine --- 1776 December 23


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The views, opinions, and experiences expressed in this post are mine and may not necessarily represent views and opinions of other VTF members, so feel free to agree, disagree, or ignore them.
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Re: XV920 Bogging

PostAuthor: Flyingdog » Sun Apr 11, 2021 10:55 am

k.huang402 wrote:It's more of a flutter than a bog. When I open up the throttle it reaches 4100rpms and then it feels like it's hitting a rev limiter and will not go any higher.


Be helpful to know if this happens in every gear. This 4100rpm wall, so to speak. If so..good indication your manifolds are leak'n. Specially if they're show'n signs of cracks. As the rpm build, so does the pressures. Hence, those tiny little cracks open up like the Grand Canyon. That..and cracks in the piston's diaphragms will do the same thing.
Last edited by Flyingdog on Sun Apr 11, 2021 4:46 pm, edited 1 time in total.
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Re: XV920 Bogging

PostAuthor: k.huang402 » Sun Apr 11, 2021 1:08 pm

Flyingdog wrote:
k.huang402 wrote:I noticed that in first and second gear that the bike boggs at around 4100rpms and it just stays there until it shift into another gear. Most of the time I can get the bike to 6000rpms in 3rd gear and on.


Be helpful to know if this happens in every gear. This 4100rpm wall, so to speak. If so..good indication your manifolds are lean'n. Specially if they're show'n signs of cracks. As the rpm build, so does the pressures. Hence, those tiny little cracks open up like the Grand Canyon. That..and cracks in the piston's diaphragms will do the same thing.




The manifolds are new which came with the 2 in 1 MAC exhaust. Can you explain what a piston's diaphragm is? I was not aware that my bike had this. Thanks for taking the time to help me out.

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Re: XV920 Bogging

PostAuthor: Flyingdog » Sun Apr 11, 2021 4:26 pm

Just so we're all on the same page...when I mentioned manifolds, I was talking bout the rubber carb joints between carbs and heads. Just curious as you mention they "came" with your exhaust. Manufacturers/parts houses wouldn't normally send them too, unless they were also ordered.

I probly could have explain it little better. Inside the carb, it will be the rubber membrane that, thru throttle/rpm/vacuum lifts the piston/jet needle outta the needle jet/main jet to let in the metered air/fuel mix. What distinguishes CV vs. Mechanical carbs. Item 2C--> https://www.yamahapartshouse.com/oempar ... carburetor I only mention this cuz, your bike being 37 yrs old, they do crack, get thin, pin holes etc. Plus, if the tops of the carbs have ever been removed, sometimes those diaphragms can get folded, crunched/pinched between the carb body groove and tops, and you loose vacuum..aka: just don't lift as they should.
Nother thing: if you look here---> https://www.yamahapartshouse.com/oempar ... air-filter items, 22/23 are air vents for these diaphragms to work. Those little black bulb things, contain "foam" filter elements, that "will" break down, and the pieces start float'n throughout the carbs..causing havoc. Specially the diaphragms. Oh yea, they also should be piped to still air. Item #11 MCV/gulp valve.. is another thing that screws up alot. Best to just 86 that thing and plug of the vacuum sources.
Does this happen in every gear? I mean hitting that flutter'n wall (4100rpm). Be also curious, if the transition from gear to gear is smooth? Whelp, that few things that might help ya get a handle on this.

inside view of hitachi carb - Copy.PNG
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Re: XV920 Bogging

PostAuthor: k.huang402 » Mon Apr 12, 2021 2:48 pm

Flyingdog wrote:Just so we're all on the same page...when I mentioned manifolds, I was talking bout the rubber carb joints between carbs and heads. Just curious as you mention they "came" with your exhaust. Manufacturers/parts houses wouldn't normally send them too, unless they were also ordered.

I probly could have explain it little better. Inside the carb, it will be the rubber membrane that, thru throttle/rpm/vacuum lifts the piston/jet needle outta the needle jet/main jet to let in the metered air/fuel mix. What distinguishes CV vs. Mechanical carbs. Item 2C--> https://www.yamahapartshouse.com/oempar ... carburetor I only mention this cuz, your bike being 37 yrs old, they do crack, get thin, pin holes etc. Plus, if the tops of the carbs have ever been removed, sometimes those diaphragms can get folded, crunched/pinched between the carb body groove and tops, and you loose vacuum..aka: just don't lift as they should.
Nother thing: if you look here---> https://www.yamahapartshouse.com/oempar ... air-filter items, 22/23 are air vents for these diaphragms to work. Those little black bulb things, contain "foam" filter elements, that "will" break down, and the pieces start float'n throughout the carbs..causing havoc. Specially the diaphragms. Oh yea, they also should be piped to still air. Item #11 MCV/gulp valve.. is another thing that screws up alot. Best to just 86 that thing and plug of the vacuum sources.
Does this happen in every gear? I mean hitting that flutter'n wall (4100rpm). Be also curious, if the transition from gear to gear is smooth? Whelp, that few things that might help ya get a handle on this.

inside view of hitachi carb - Copy.PNG


Thanks for the explanation. The manifold joints are brand new and I've checked them for cracks and leaks. They're in good condition. I also swapped the stock carburetors with two mikuni VM34 round slides so they don't have that membrane that you speak of. I recently tightened up and checked all the lines, swapped new spark plugs in, cleaned out the mains and pilot jets, adjusted the throttle cable and assembly and it ran a bit better.

So to better explain what is happening, when I Open the throttle a quarter turn up to 3,000 RPMs, and then open 3/4 throttle it can go beyond 4,100. But if I keep a quarter turn up to 4,100 RPMs, that's when it starts to flutter. It does seem to happen in every gear. More distinctly in first second and third gear. So it seems to be only happening during mid-range power. Does that mean that a certain jet needs to be adjusted on my carbs? I know the main jet controls 50-100 percent throttle. Should I look into adjusting the needle jet?

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Re: XV920 Bogging

PostAuthor: Flyingdog » Tue Apr 13, 2021 3:08 am

Rodger on the new manifold/joints.

k.huang402 wrote: I also swapped the stock carburetors with two mikuni VM34 round slides


Oooh Mann..I'm not sure how I missed that swap..since you did mentioned it in your first post. Really had a mental gap go'n here. :;:

I'm going to bow-out on this one, as I'm not familiar with TMs or VM Mikuni. Other than it "maybe" those carbs are a tad small. But for a 920? Not sure. I'm sure someone more in-tune to these will step in here. Kinda odd that your mechanic, who re-jetted the thing, didn't notice something didn't work. No wonder you didn't know what I was talk'n about mentioning the diaphragms..sorry bout that.
Hope ya get it sorted out.
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Re: XV920 Bogging

PostAuthor: k.huang402 » Tue Apr 13, 2021 7:15 pm

Flyingdog wrote:Rodger on the new manifold/joints.

k.huang402 wrote: I also swapped the stock carburetors with two mikuni VM34 round slides


Oooh Mann..I'm not sure how I missed that swap..since you did mentioned it in your first post. Really had a mental gap go'n here. :;:

I'm going to bow-out on this one, as I'm not familiar with TMs or VM Mikuni. Other than it "maybe" those carbs are a tad small. But for a 920? Not sure. I'm sure someone more in-tune to these will step in here. Kinda odd that your mechanic, who re-jetted the thing, didn't notice something didn't work. No wonder you didn't know what I was talk'n about mentioning the diaphragms..sorry bout that.
Hope ya get it sorted out.


Thanks Flyingdog! I'm going to try to raise the jet needle a couple of clicks to make the mid range mixture more rich and see if that makes a difference. I appreciate you getting back to me.

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Re: XV920 Bogging

PostAuthor: chrismalm » Fri Apr 16, 2021 8:40 pm

Sounds like your shop tuned for WOT, not the whole throttle range. I don't know Mikunis either, but if they have a fuel enrichment circuit (choke), try operating the choke lever when you hit your flat spot (1/4 throttle @ 4,100 rpm) and see if it improves.
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