Replace the throttle diaphragm

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Replace the throttle diaphragm

Postby global_mz » Fri Feb 12, 2010 15:42 15

Because a few folks have had an issue where their Majesty would not rev above 4500rpm (see http://majestyusa.com/forums/viewtopic.php?t=5189)

My bike is a 2006. This should apply at least to years 2005 - 2007.

Make sure you have:

- a flashlight
- a decent allen wrench set (metric)
- a couple magnetic phillips head screwdrivers
- adjustable pliers
- a few plastic pop rivets from Yamaha
- a ziploc bag for all the screws, bolts, and rivets
- a good friend
- some cold beer for that good friend
- a majesty maintenance manual
- a digital camera

First, buy a maintenance manual from Yamaha *or* ask your 12 year old nephew to get one from the internet. Don't ask how, he will just know. The diagrams will come in handy.

Second, disassembly. The throttle body is buried under many many plastic pieces. The engineers had a good sense of spatial awareness (or just a good sense of humour). To get to your target you first must remove or loosen the following:

Passenger Seat and Side Covers
Rider Seat and Storage Box
Air Filter Cases
Throttle Body and Fuel Injector

Don't be intimidated, it's not that bad. See my pics:

Image

The rear cover may seem tricky at first. It is fastened by two black plastic pop rivets accessed from inside the storage box. Yes, you will probably break some pop rivets while removing them. That is why you have a few spares. Take photos to help remember which bolt goes where.

The Japanese factory workers used 22 ft pounds of torque to install bolts. If you have taken your Majesty to the dealer for any reason, they will have reinstalled any bolts with approximately 450 ft pounds of torque. This is why you have adjustable pliers like the red one shown in the photo. Use it to grip the end of an allen wrench for leverage. It really helps. And it works better than the adjustable wrench that we tried first.

The air filter covers and throttle body do NOT need to be completely removed. Remember, your goal is simply to replace a rubber diaphragm thingy.

On the throttle body, carefully remove the vacuum chamber cover because 1) there is a big spring in there and 2) you do not want to get dirt, grit, and grime in the engine. Take a few seconds to brush or wipe off accumulated dirt first.

Do not be shocked at how good the old diaphragm looks. It's been sitting in a sealed chamber for most of its life. Notice in the last photo that there are hairline rips around the edge of the inner ring. After disassembling my bike I was very happy to see those rips!

Third, test. Keep everything clear of the rear tire and start your Majesty after reattaching the throttle body and air filter cases. Rev it past 4500rpm. Good? If not, then check any cables, screws, and bolts that you may have removed. Best not to wait until you have reassembled everything. Stop the rear tire with the handbrake.

Fourth, reinstallation. Reinstalling parts should go more quickly than the disassembly, as you are now familiar with the internal workings of your ride. Make sure you have secured electrical cables and plugged them back in. Some side panels take a few minutes of patience to correctly line them up. What's your hurry, anyways?

Fifth, take your bike for a test ride. Prove it on the road.

Sixth, wash your bike. It has grimy hand prints on it.

And last, buy your buddy some pizza for the invaluable help.
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Postby BA_LoKo » Fri Feb 12, 2010 18:22 18

Outstanding write up and picture tutorial.

Thank you!
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Re: Replace the throttle diaphragm

Postby cwim1 » Tue Jul 09, 2013 9:49 09

not seeing any pictures here. My system says the link is bad.
Sure would help.
I suppose the passenger seat he is speaking of is the one I have outlined in red?

I don't see how that gets me anywhere near the engine where I would think the throttle body would be?
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scootpasseat.jpg
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Re: Replace the throttle diaphragm

Postby ScooterDuende » Sun Jul 14, 2013 7:11 07

I replaced my throttle body diaphragm yesterday.
You have to remove the seat to remove the grab rail. The grab rail must be removed to remove the side panels. I did not remove the air boxes.
I stripped one of the screws, and had to cut a slot with a hacksaw blade to get it out. I applied some pressure to the diaphragm housing to tilt it so I could get at that screw with the screwdriver. I replaced both screws with hex key head screws and used a small L-shaped hex key. In another thread, one poster drilled holes to get at the screws.

People report a sudden loss of power, but I experienced a somewhat gradual decay. I noticed harder starting in the spring, even after I replaced the spark plug. It just took a few more turns then last year. Acceleration has been getting worse. And last week it got to the point it was a lot slower at take off, and took longer to get to 50.
1998 Suzuki VZ800 Marauder
2006 Majesty 400
2002 Ramirez FL2
2003 Honda Metropolitan *sold*
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Re: Replace the throttle diaphragm

Postby ScooterDuende » Sun Jul 14, 2013 7:28 07

And I found the seat bolt I dropped a few years ago!

Cwim1, if you haven't removed your passenger seat, you could end up losing the seat bolt...a lot of people do.
1998 Suzuki VZ800 Marauder
2006 Majesty 400
2002 Ramirez FL2
2003 Honda Metropolitan *sold*
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Re: Replace the throttle diaphragm

Postby cwim1 » Sun Jul 14, 2013 8:37 08

Thanks very much! I am not even sure where or what the throttle body even looks like.
I saw where another drilled holes to access the screws and another tilted the body to access the screws. I like the idea of the allen screws. I guess I will see which is best for me when I get to it. I am still waiting on the part to come in. They said it may be in around july 17. I got it:
1 of 5RU-14368-01-00 - Yamaha - DIAPHRAGM ASSY 1 @$21.19ea.

Subtotal: $21.19
Shipping: $17.48 via UPS Ground
Estimated Delivery: 7/17/13 - 7/26/13
Sales Tax: $3.19
Total Amt: $41.86

Power Parts Plus
2450 Veterans Blvd Po Box 420834
Del Rio, TX 78840
830-775-2323
parts@powerpartsplus.com

I am interested in any and all help, especially with pictures.
Shane the rancher preacher texas man.
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Re: Replace the throttle diaphragm

Postby ScooterDuende » Sun Jul 14, 2013 9:45 09

It's right in the middle where the seat would be. As mentioned, take time to clean the area well.

http://s1282.photobucket.com/user/Papir ... 9.jpg.html
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2002 Ramirez FL2
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Re: Replace the throttle diaphragm

Postby cwim1 » Mon Jul 15, 2013 1:58 01

Thanks! I see that I am going to have to take the whole seat off. Any thing I need to know about that?
Shane the rancher preacher texas man.
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Re: Replace the throttle diaphragm

Postby ScooterDuende » Mon Jul 15, 2013 17:46 17

Nothing to note with the seat. Pages 3-4, 3-5, 3-6 in the service manual cover the removal of all the body parts.
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2002 Ramirez FL2
2003 Honda Metropolitan *sold*
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Re: Replace the throttle diaphragm

Postby cwim1 » Fri Jul 19, 2013 2:28 02

I haven't been able to find the owners manual since I moved.
Shane the rancher preacher texas man.
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Re: Replace the throttle diaphragm

Postby cwim1 » Mon Jul 22, 2013 23:59 23

I started this AM in changing out the diaphram. I didn't have a manual so had to use this post as a guide. Thanks guys! In the AM I hope to finish it. I fot it installed and the rider seat back on. I plan to post a step by step in a day or two of the process I used on mh maj. 400 2006.
Shane the rancher preacher texas man.
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Re: Replace the throttle diaphragm

Postby cwim1 » Mon Aug 05, 2013 11:13 11

OK guys, sorry, it has taken me longer than I planned to get back on here with the step by step throttle body diaphragm replace/repair/install.
It took me about 5 hours to figure it all out the first time when I made the below with pictures that I hope I can upload in there proper place. The entire process took me about 2 hours including my test ride and getting gas the second time. It is really quite simple just a lot of stuff to take off. I put all of my bolts, etc.. into a big zip lock bag.
Bike the work was done on is 2006 400 Majesty with 32k miles.
2006 Majesty 400.jpg
2006 Majesty 400.jpg (66.31 KiB) Viewed 2945 times


1) Removed my "flatbed" (for others it may be the trunk):
2-12mm bolts (+ 6" extension)
2-6mm hexhead socket bolts
(reason is to get to the one 5mm socket hexhead passenger seat bolt).
2006 Majesty 400 flat bed.jpg
2006 Majesty 400 flat bed.jpg (68.99 KiB) Viewed 2945 times


2) Remove Passenger seat
1-5mm allen screw (socket hexhead bolt)
Seat has hook like clips on each side. Slide towards handle bars & lift off.
2006 Majesty 400 Passenger seat screw .jpg
2006 Majesty 400 Passenger seat screw .jpg (58.25 KiB) Viewed 2945 times

2006 Majesty 400 Passenger seat hook .jpg
2006 Majesty 400 Passenger seat hook .jpg (42.9 KiB) Viewed 2945 times


3) Removed Rider seat:
4-4mm hexhead bolts (seat adjustment bolts)
remove seat skirt 6- #2 Phillips screws
discount storage light wiring (2 wires snap connectors)
remove cotter pin from seat opener (shock absorber looking thing)
remove 2 6mm allen bolts
2006 Majesty 400 Rider seat removed .jpg
2006 Majesty 400 Rider seat removed .jpg (61.48 KiB) Viewed 2945 times

2006 Majesty 400 Rider seat removed .jpg
2006 Majesty 400 Rider seat removed .jpg (61.48 KiB) Viewed 2945 times


4) Remove grab rails
4-6mm (allen) socket hexhead bolts


5) Remove side Tupperware (both sides)
6-#2 phillip screws
(2 are hidden: one is underneath and the second is inside the tupperware that snaps off at the License plate. There is actually a third one hidden behind the black plug toward the front of where the seat used to be.)


6) Removed the petrol access panel and door
2-#2 phillip screws

7) Remove storage assembly
4-10mm bolts
4-phillip tupperware screws
both grab rails brackets 2-12mm bolts on each
lift out the entire storage box


8) Remove Throttle body cover
2-#2 phillip screws
(you can tilt the throttle body to be able to reach the screws but you do take a litle risk in striping the phillip head portion; the screw is tight. I did it the first time that way. Tilting may also have been the cause of the replaced diaphragm not seating properly when I reassembled. It is not much more to simply drill a hole through the frame to access the screw. I did that the second time, since I knew what I was doing.)


9) remove the rubber diaphragm with its plastic throat. I stuck my finger in the hole and pull out the whole unit.

10) Remove the diaphragm: it simply pulls off from around the plastic piece it surrounds.

11) gently stretch the new one on over the plastic (throat) thing.

12) replace unit into throttle body: ensure that the edges of the diaphragm is in the seat around the throttle body and ensure it stays there while you tighten the 2 cover screws.

put everything back together in reverse order. The Rider Seat opener assist shock absorber is put back on by ensuring the seat is in the fully open position.
(sorry guys 5 is the maximum pictures).
Shane the rancher preacher texas man.
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Re: Replace the throttle diaphragm

Postby jimshorts » Mon Aug 05, 2013 21:59 21

I replaced my diaphragm today. I used the "drill a hole in the cross beam" method to access the hidden screw. I also suggest carefully using a few spots of silicone adhesive around the new piece to secure it to the grove in the throttle body. Otherwise, when you fiddle the cover into place, you can fail to seat it into the groove properly, it will leak, and you'll have to repeat the process. As I did the first time! The top edge of the diaphragm MUST fit completely into the groove.

Another suggestion: Before you put all of that plastic back on, find a small cushion, or anything else that will work (I used a small block of ridged foam), place it on top of the cross beam, and carefully (it's a little awkward) take it for a test ride on an empty stretch of road. You need to put the engine under a load to insure that the diaphragm has seated, and is working properly. Putting it on the stand and revving the engine won't do it.
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Re: Replace the throttle diaphragm

Postby cwim1 » Mon Aug 05, 2013 23:53 23

I would agree somewhat. I too did the throttle rpm test the first time so thought it was good; it failed the loaded test. However the second time i did the throttle test again and notice that the reaction time to rpm was much faster. So if you note the climb wnd response time of the rpm it is possible to properly test but riding is the best test.
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Re: Replace the throttle diaphragm

Postby Vlad » Sun Jun 01, 2014 9:28 09

I know I'm reviving an old thread and I appologize for that, but i just wanted to say big thanks to everyone who worked on diagnosing, fixing and sharing this issue. You saved me a lot of time and grief.

Here's my story: I was in the left lane on the 401 express (one of the most congested highways on the planet) full throttle at about 135km/h (~85mph) when the bike suddenly started to act like it hit a rev limiter or something severely restricted the air/fuel supply. It wasn't extremely abrupt and there was no sound or sound change, but it got me down to about 80km/hr in less than a minute. I expected the engine to stall, but it didn't. I managed to pull over and stop on the shoulder safely. Listened to the engine for a while, shot it down, started again, no problems. No smoke in the exhaust or any other indication that there's something wrong with the engine. No warning lights were on either, and I have checked the oil level the previous day. I was thinking that maybe oil blew into the air filter housing, but that would burn away very quickly and wouldn't produce the symptoms I was experiencing.

I couldn't notice any difference whatsoever with the way engine and transmission were behaving, except that everything - acceleration, throttle response, top speed and power - was reduced by about 50%. It acted like a 200cc scooter and I couldn't get it above 75km/h (BTW, all speeds are read from GPS, Majesty speedo would read about 10km/hr more) . At that point I concluded that something is either choking the air supply, fuel supply or the exhaust. Exhaust was quickly eliminated because the engine was revving relatively well and high on the center-stand, without load. I had no idea what could have choked the air/fuel intake, but I suspected that one or both of the DIY UNI foam OEM retrofit air filters got sucked into the intake manifold. Took both air filters off, but they were in perfect shape. Put some SeaFoam in the tank in case the injector was clogged (the only other culprit I could think of) and called it a night. I've heard about the speed sensor issues before and eliminated that option right away because speedo was working just fine.

That's how I exhausted my expertise before I decided to look the problem up here. Thank you all one more time!
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Re: Replace the throttle diaphragm

Postby wadboy73 » Thu Jun 26, 2014 13:59 13

Well how bout that...............I too am experiencing the same symptoms as everyone is describing. :roll:

My question is: can the diaphragm be cleaned and reinstalled or should it just be replaced?
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(='.'=) 1984 Honda Aero 125 (The Gold Ghost)
(")_(") 1987 Honda Elite 50 (R.I.P)
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Re: Replace the throttle diaphragm

Postby tonymarchman » Thu Jun 26, 2014 17:40 17

It is a rupture, however some have glued it (superglue?). I would order one before dismantle it.
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Re: Replace the throttle diaphragm

Postby jimshorts » Mon Jun 30, 2014 17:51 17

Having replaced mine, I wouldn't even consider trying to repair and re-use a diaphragm. As I recall, a new one was only about $25 or so. And it is a hassle removing all of the plastic, especially the first time you do it. This is no place to save a few bucks.
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Re: Replace the throttle diaphragm

Postby Pnanna » Sat Sep 13, 2014 19:05 19

My Turn!!!
Got 'r done....
All I can say is it's a good thing I built a lot of model kits when a kid.
After 50K+ miles and 9 years of road, it was dirty and grimy and I still can't figure out where the rubber sheet stuff goes back.
Yep, little tears along the bottom edge of the cup.
We shall see.....
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Re: Replace the throttle diaphragm

Postby vintage red matthew » Thu Sep 18, 2014 14:08 14

The symptoms described are exactly what I am experiencing. I was thinking it was the variator but not now. I am reasonably confident that this is my problem. I doubt that i would have ever figured this out on my own. As soon as I finish posting here I am going to see about getting a new diaphragm. Isn't the internet great?
Ride it like you stole it from your ex wifes new husband.

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Re: Replace the throttle diaphragm

Postby Wald » Fri Sep 19, 2014 12:05 12

vintage red matthew wrote:The symptoms described are exactly what I am experiencing. I was thinking it was the variator but not now. I am reasonably confident that this is my problem. I doubt that i would have ever figured this out on my own. As soon as I finish posting here I am going to see about getting a new diaphragm. Isn't the internet great?



yes, u are in luck; this problem is well documented
2005 EU Majesty 400. Malossi variator. 50l Topcase. Gerbing Clothing. 66.000km. 23km/l
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