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TOPIC: Hello from Texas. New DT400b owner here.

Hello from Texas. New DT400b owner here. 08 Jul 2019 11:57 #1

  • hookembevo
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Always wanted a big bore 2 stroke, and one finally found it's way to me!

About a month ago, I picked up a 1975 DT400B with low miles. Was helping a buddy pick up a motorcycle lift he found on Craigslist, and saw a motorcycle cover in the corner of the driveway. The owner was out of town and on the phone, while a neighbor provided access to his garage. I told my buddy to "ask him If I can peek under the motorcycle cover," and the rest is history.

The bike:

The good -
Super clean with pillion accommodations for plus size passengers.
Low miles
Clean title and had been registered in 2017 by current owner.
Seemed to have good spark and compression.
Carb had reportedly been serviced and no fuel added since.
The Bad:
Had been sitting outside for a year.
Tank was a disaster. A total repeat of my Honda project last year. Failed liner, varnish, and rust. UGH!! I will never understand why people line good tanks.
No battery.
Dry rot in rear tire.
Owner said it was leaking oil, but included a full gasket set.
-I parked bike on cardboard and noticed oil was blue and tasted like Yamalube. Removed Oil pump cover and found that the clip was not seated over the nipple on the intake side and it was weeping slightly. Snugged clip and cleaned up and nothing since.
Front braking is virtually non-existent.
Current State & work completed:
I tried to be gentle with the tank cleaning. Tank is very straight/ clean outside.
-Powerwashed
-Filled with Evaporust for 2 weeks. Yeilded some rust and a few chunks of liner but tank was still a mess.
-Added a couple of cups of WD40 and sloshed it around. Started shopping for replacement tanks.
-Right before I went with the nuclear option (muriatic acid), I decided to try the old tumble dry trick. I cannot BELIEVE it took me 40 years to try this. Results were amazing. Removed WD40, added a pound of 1.5" galvanized nails, wrapped in a blanket, placed inside of sleeping bag, then placed into another sleeping bag. Stuffed the big ball into the dryer for 2 hours, rotating the "ball" every 15 minutes or so. Looked to be working very well, so I added another pound or so of trim nails and repeated the process. Tank came out shiny and new. Not ONE TRACE of the failed RedKote liner or rust.
Filled bike with fuel, installed new inline fuel filter, and Duracell AGM battery from an emergency exit sign (onto which I had soldered leads), and bike started on the first kick!
Replacing Tires and installing new brake shoes this week. Also installing headlight from twisted spoke, as it currently only has hi beam. All signals, horn, and light work great. Should be able to get inspection/ plates after this.

Current problem:
Bike seems to run GREAT and pulls well between 1500 to ~ 5000 rpm. It will pull the front wheel up easily with throttle alone in first and 2nd, and cruises effortlessly up to ~80mph (indicated). At high RPMs, bike begins to "break up" a bit and does not provide any more power at all. Could be coincidence, but I noticed that when it starts to break up, tach gets very erratic. I've played a little with the mixture but haven't gotten into the carb otherwise. Prior owner was running B9ES spark plug for 3K miles and it was black but not really sooty. I replaced with recommended hotter plug, B8ES and bike seems to run a little better. Haven't pulled carb yet, but I've got it set pretty rich at less than 1/2 turn out. If I lean it out, it's slow to return to idle and sounds lean. I'll likely remove side covers and check crank seals and have a look inside the carb. Open to suggestions on other things to look at.

So far, the board has been very helpful an I look forward to contributing where I can help. Been riding and wrenching for a long time, but this is the my first Yamaha.

I'm middle aged, but showing no signs of growing up. Spend the majority of my time working in tech and being a dad, sneaking in rides wherever I can. I've owned and loved a BMW for the last 12 years and enjoy doing camping trips/ commuting on it, but I'm looking forward to getting back to the trails.
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Last Edit: by hookembevo.

Hello from Texas. New DT400b owner here. 08 Jul 2019 14:49 #2

  • MarkT
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Wow great find and nice write up!!

I can really relate to this statement you made: " I will never understand why people line good tanks."

Maybe the tank lining industry has an exceptional marketing program? :)

The 400 is a torque monster that really doesn't like to rev past 4,500 ~ 5,000 rpm... so the "fix" for the erratic running is easy. Don't rev it that high! :)

You might consider adding a good voltage regulator (from DEET or OEM Yamaha) as a preventative measure against future headlight burning out problems...

Nice work!

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

Hello from Texas. New DT400b owner here. 08 Jul 2019 16:48 #3

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hookembevo wrote: Always wanted a big bore 2 stroke, and one finally found it's way to me!

About a month ago, I picked up a 1975 DT400B with low miles. Was helping a buddy pick up a motorcycle lift he found on Craigslist, and saw a motorcycle cover in the corner of the driveway. The owner was out of town and on the phone, while a neighbor provided access to his garage. I told my buddy to "ask him If I can peek under the motorcycle cover," and the rest is history.

I'm middle aged, but showing no signs of growing up. .


I've also scored a few prizes by "peeking and snooping". And I'm also not growing up.
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The hours spent riding my Enduros is not deducted from my life span.

Hello from Texas. New DT400b owner here. 08 Jul 2019 17:12 #4

  • KennyV
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Welcome and same here, I'm never growing up!

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Hello from Texas. New DT400b owner here. 08 Jul 2019 23:56 #5

  • Gr8uncleal
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How big are your freaking tumble dryers over there?!

I read somewhere recently of someone doing the same trick, but using a cement mixer.

Welcome from the UK by the way!

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Hello from Texas. New DT400b owner here. 09 Jul 2019 09:11 #6

  • darinm
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Texas sized drier! Great first post, never thought of that as a way to clean a tank.

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1972 Yamaha CT2 175
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Hello from Texas. New DT400b owner here. 09 Jul 2019 10:30 #7

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Haha. I'm married to a Spaniard and spend plenty of time in Europe as well. Our dryers over here are indeed very different. I'd have to get creative in Europe but the concept is the same. Fill with stuff, spin and shake. Might be fun to make a green alternative, using old bicycles and such.

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Hello from Texas. New DT400b owner here. 09 Jul 2019 11:04 #8

  • Gr8uncleal
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Just think, with that buddy seat and if you fitted a sidecar as well, you wouldn't need a car!

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Hello from Texas. New DT400b owner here. 11 Jul 2019 06:29 #9

  • hookembevo
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Hah. A guy I worked with was from India and said that his dad had the same model BMW that I do. They would ride 3 on the seat, and one kid sitting on each of the panniers.

You could tell he was genuinely confused as to why you would need a motorcycle that big for a single person.

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Hello from Texas. New DT400b owner here. 11 Jul 2019 10:02 #10

  • run103
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Let it breathe make sure the filter is cleaned or replace it with a very free flowing one and lightly oil it. Also i have found if you remove the tool tray which has the inverted airbox cover integrated with it you will pick up some RPM . Or just leave it andf be happy at the 5 to 6 k RPM range and last a long time
Doug
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