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Discussion Starter #1
Not sure what is happening. On a flat road with no wind, my TW tops out at 55 mph. I am running 15/50 sprockets and weigh 175 lbs. At 8000 ft with stock jetting and fuel screw out 2 turns. Bike feels great up to 45 mph. I live in a small town and don't see speeds much more than that. My plug looks like it could be lean or rich and i'm not sure how to tell. I was running a pod filter but just got the parts and got my air box back together and reinstalled on the bike. Any suggestions would be great.
 

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I'd be willing to bet it's related to your air intake somehow. Maybe you had a rag stuffed in there and forgot to take it out when you put the filter back on, or the filter is really dirty or plugged up somehow, or something like that. I'd take a good look at all the intake stuff (including the rubber boots and their clamps, and the box and all that).
 

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Discussion Starter #3
The intake boot is less than a year old and the UNI air filter is brand new. There are no vacuum leaks. The throttle is crisp with good response. I would't even know there was an issue but I have been becoming more confident in my riding and decided to see how fast I could go.
 

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How does it run at 55mph? Does it sputter or run smoothly? I definitely have experienced a lower top speed at altitude with the factory main jet. I'm not the best at reading a spark plug - but my understanding is that black is too rich,
'whitish" is too lean, and somewhere in the tan/light brown area is just about right. I would try a leaner main jet and see what happens.
 
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Discussion Starter #5
How does it run at 55mph? Does it sputter or run smoothly? I definitely have experienced a lower top speed at altitude with the factory main jet. I'm not the best at reading a spark plug - but my understanding is that black is too rich,
'whitish" is too lean, and somewhere in the tan/light brown area is just about right. I would try a leaner main jet and see what happens.
Smooth I guess but the throttle is pinned and it took a long time to get from 50 to 55. A black plug can mean too hot / lean also.

207334
 

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A black plug can mean too hot / lean also.
That is true, Errtu. I must admit that I'm making the assumption that your bike would unlikey be running too lean at 8000ft with the factory jet.
 
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Discussion Starter #7
That is true, Errtu. I must admit that I'm making the assumption that your bike would unlikey be running too lean at 8000ft with the factory jet.
It may have been lean before with the pod filter but now back to the stock air box I am unsure. I think I should buy a new plug so I can test the color better.
 

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If no access to a new plug right away, clean the old one good as you can. Carry plug wrench with you and take the bike out on the road where you can run high gear wide open for a mile or so. Preferably somewhat of an uphill grade if possible so the bike us under load. When safe to do so, close the throttle, pull in the clutch and hit the kill switch simultaneously and coast to the side of the road. Take out the plug and have a look then. I feel pretty certain at that altitude if you are running stock jetting you are running quite a bit rich. Too big of a main jet.

Marty
 

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Discussion Starter #9
If no access to a new plug right away, clean the old one good as you can. Carry plug wrench with you and take the bike out on the road where you can run high gear wide open for a mile or so. Preferably somewhat of an uphill grade if possible so the bike us under load. When safe to do so, close the throttle, pull in the clutch and hit the kill switch simultaneously and coast to the side of the road. Take out the plug and have a look then. I feel pretty certain at that altitude if you are running stock jetting you are running quite a bit rich. Too big of a main jet.

Marty
I tried cleaning the plug but it didn't do much. I plan to go get a new plug tomorrow.
 

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If you do the test, take a picture of the plug if possible.

Marty
 
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Not sure what is happening. On a flat road with no wind, my TW tops out at 55 mph. I am running 15/50 sprockets and weigh 175 lbs. At 8000 ft with stock jetting and fuel screw out 2 turns. parts
Did it run over 55 when you had the pod filter on it? My guess is that you have too high of a gear for 8,000 feet. The torque curve peaks at 7,000 RPM and the HP curve peaks at 8,000 RPM. At 55 with your gearing you are about 1,000 RPM below the average of the two. 7,500 to 8,000 RPM should provide the most power the TW engine is capable of.

My gearing is 13/50, so I'm at 7,500 RPM at 55 mph. I can't go any faster either and the slightest hill slows me to 50. I think you should go back to stock or even my gearing for 8,000 and up. You should also put a 124 or 122 main jet in there. I took my filter off for a short run to test airflow restrictions but besides being real loud I went maybe 1 mph faster. You can try that to eliminate any abnormal airflow restrictions, but I doubt there is anything wrong with the bike.....You are just asking it to do the impossible.

Have a look at : Gearing Commander - Motorcycle Speed and Drive Train Calculator v7 Remember that the speeds listed are real speeds, not speedometer speeds, and the TW speedo with stock tires is 7% faster than reality. Use a GPS for actual speed. So our 55 is really only 52.5 and I have checked that hundreds of times against a radar trailer. Also, try pumping up the tires to 20 psi. You might gain 2 mph. :confused:
 

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TK MV28 carb?
The altitude compensating slide diaphragm could be an issue:
1. If apart recently, not fully seated (putting in freezer for 1/2 hour before installing helps)
2. Pinhole leak

If the above is an issue, the slide will not fully lift.
 
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Discussion Starter #14
TK MV28 carb?
The altitude compensating slide diaphragm could be an issue:
1. If apart recently, not fully seated (putting in freezer for 1/2 hour before installing helps)
2. Pinhole leak

If the above is an issue, the slide will not fully lift.
I have no idea if that is an issue or not. The carb hasn't been apart. Pinhole leak where?
 

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If original, diaphragm could be cracked
It is under the top cover of the carb, if you have the MV28.
Vacuum lifts the slide to control the needle position
There are some very good photos on this forum.
Jbfla?

Yep
 

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Posted Jan 2017 for my stock (other than pilot screw setting) 2017:

Corn Creek Springs, Alamo Road on Desert Wild Life Refuge, Cold Creek Road and Lee Canyon ride:

The TW is now one month old, 496 miles on the clock (114 today) and behaves fully broken-in, but I will continue to not hold WOT for another 200-300 more miles.

1. Up a 6% grade, even at ~5,000 feet, it will pull 50-55 (trying to not yet sustain WOT) MPH in 5th gear.

2. Up an 8% grade, at over 5,000 feet, it will only pull 45 MPH in 5th gear at ~90% throttle.

3. On the level, or even up a mild grade, at 3,000 to 4,000 feet, it will pull 65 MPH with some throttle left.

4. With a slight down grade, I saw 77 MPH on the speedo a few times, sitting up straight. If speedo is optimistic by 6%, that would be 73 MPH, true. Did not hold WOT more than a few seconds, each time. On Highway 95, returning to Las Vegas, a steady cruise at 65 MPH was comfortable (excluding seat).
 

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Not sure what is happening. On a flat road with no wind, my TW tops out at 55 mph. I am running 15/50 sprockets and weigh 175 lbs. At 8000 ft with stock jetting and fuel screw out 2 turns. Bike feels great up to 45 mph. I live in a small town and don't see speeds much more than that. My plug looks like it could be lean or rich and i'm not sure how to tell. I was running a pod filter but just got the parts and got my air box back together and reinstalled on the bike. Any suggestions would be great.
Sounds like you need to move to a big town.
 

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Just a couple of comments: first, rule of thumb is 3% power loss per 1000' elevation, at standard temp, barometric pressure, humidity (air density). You've lost 24% of power on a standard 59 degree F day. Up the temp to summer temps and you lost more. You may have lost 30% right there.

You've changed the gearing "taller" which lost some torque which is just compounding the power loss from altitude. That's about 7% torque loss over stock gearing. Now your getting close 35-40% power loss total.

Carburated engines run richer as they go up in elevation because there are less air molecules per cu ft. The tw has a CV carb so it does compensate a bit for altitude, temp, and air density in general, to a point. You might be above "that point" but I don't know where "that point" is on those carbs.

To try to get more speed, I'd drop that 15 back to a 14 tooth front and keep the 50 rear to get that 7% torque back. I'd check the plug reading to see if you are rich or lean.

I've never experienced a black plug on lean, only on oil fouled or carboned-too rich running. Brown or tan is good. I shoot for light tan when I setup a carb. White to very light gray is lean and or hot, darker gray is OK but I'd richen it to tan. Black chunks building up can be too rich or too cold.

I rode my 01 last night at 4800' and 94F here on WY. I have stock gearing and it hit 70 mph, albeit the engine was screaming. I have a Chinese carb as that came on the bike as the PO threw the oem carb away instead of cleaning it. My sparkplug is tan.

My $. 02.
Jay Dub
 

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My 2 cents...take it or leave it.
The "2 turns" on the mixture screw is a guideline...it should be adjusted for each individual bike; I found that mine works best between 1 ½ and 1 ¾.
Using a 15T counter sprocket immediately lowers your available torque.
The "rule of thumb" regarding elevation and HP loss is a valid concern.

Try the "burble test"...it will give you an idea if your problem is carb related:
Find a fairly long stretch (1-2 miles) of road that is lightly used.
With the bike at operating temp, start out slowly and shift through the gears until you get to 4th (you should be BELOW 20 mph at this point).
Once you get to 20 mph in 4th gear...crack the throttle WIDE OPEN.
While it won't snap your neck...the acceleration should be smooth and linear, with no hesitation, surging, "burbling" or missing.
If you pass this test, you can be confident that your jetting is close to perfect.
 
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