I have a '78 dt175 that struggles to hold 50 on a flat road with no wind. I have been trying to make it faster for almost 2 years now. Everyone I meet keeps telling me the bike should go much faster. A wheelie is impossible even from a stand still. But I am 210lbs and 6'3 so I'm heavy and catch wind like a kite. If this is normal I'll stop my search for speed.

One thing is odd for mine at least. in the first 4 gears I can red line and get good rpms. However when I go to 5th the bike struggles to hold 5,000 and kind of shudders. Feels like a governor is on the bike because when it drops in speed it will get a speed boost for a second then slow back down.

Wyatt, what you described in your bike revving fine through the first four gears, then bogging down around 5,000 RPM in 5th is exactly what was happening on mine, when I first got it running a month ago. In fact I started a thread about it. It turned out the main jet was dirty. Once I cleaned that out it winds out just fine, and it easily gets up to 60. I put a 17 tooth sprocket on the front, so I actually think that limits my top speed a little bit, especially in wind. However I prefer it for cruising around town, because it does great at 45 to 50 without winding out, and makes first gear a little bit taller.

With the CT1 I had back in high school in the early seventies, I used to pull wheelies all the time. 50 years later, I'm not about to even try a wheelie, but I really think I could easily with this one, at least in first, second and third gears. I'm about 5' 9" and 180, so I'm a little bit lighter and shorter.

I have cleaned it before and didn't notice a difference but I might not have gotten it perfectly clean. Any tips or tricks to make sure it is completely clean and open?

I just used some good carburetor spray, and put a single brass bristle of a brush through the opening as well. Blew through it to dry it out with some compressed air, and put it back in. However if it's really varnished internally, it might be better just to get a new jet. I was just about to order one, but when it worked after I cleaned it I decided not to.

I had the exact same symptoms, in fact I think I described it in the thread as it seemed like it had a governor on it only in 5th gear. Mine would start bogging out at 5,500 RPM. Even though it would wind out pretty well in the other gears.

I had a '78 DT175MX back in 1986 when I was fifteen and probably weighed 135 lbs and whilst my memory isn't what it used to be, it was quick.
My neigbour was a few years older and had owned the same bike and was renowned as the wheelie guy.
I'll never forget him asking for a go a few days after I bought the bike, he went down the lane then came back up it on the back wheel for a good 100 yard wheelie.
Some guys and girls just have that skill, I certainly don't.
I tried but never got the hang of wheelies and managed to lose it trying on that bike and stuffed it into my neighbour's fence whilst my neigbours kids were watching, fat lip thanks to the open face helmet and a very dented pride  .
Agop  and I got 70 out of my CT1-C and his AT1 (175) a few months back.
We were ragging them down "The Straight Mile" (country road about a mile long ) and then like a couple of teenagers we ducked down and tucked in side by side until the speedo hit 70.
Couple of idiots who should know better.

 

If it wasn’t suppose to go so fast… why did Yamaha give us so much throttle?
Sneezles61

Third gear wheelies - so it’s not an urban myth!
Clutch it up or off the throttle?
What fun!
I’m just pottering mainly - but I feel egged on do give it some real beans and see what happens!
Hopefully I won’t end up in a fence….

Wyatt H: re: your question about carb cleaning... Best sure fire way to ensure your getting the best cleaning is to use an ultrasonic cleaner AND clean each jet individually as TomP mentioned.  Using micro drill bits works well for larger jets to make sure you're clearing them to the spec'd hole size.  But like I said, in my experience, taking your time to do a super thorough ultrasonic cleaning of all parts is best.  It really gets into the passageways of the body that you can't otherwise efficiently manually clean.  I use a cheap Harbor Freight cleaner and it's worked wonders with HD simple green (the purple stuff) which is safe to use with plastics and even rubbers.

I cleaned the carb by completely taking it apart and cleaning each piece to perfection this morning and had every hole open as it should be. I just got back from a ride with it and the same symptoms persist. Any other things I can try?

Unfortunately...  You like others (and me) are discovering the difference of being a lithe youth, probably brought up on a diet of small two strokes from a fizzy, through various 125s and then the 175.  You were a spotty youth weighing 10 stone, wet through to your underwear.

​​​​​​The average family car had had 50 - 60bhp and the average bike in the late 70s was around 400cc and 37bhp.  You being the spotty lithe youth tried the latter, as did I, lovely Honda 400/4F2 in canary yellow, put down a deposit on the bike and the insurance company laughed in your face.  Back to square one.  Enter the fire breathing beast of the DT175mx.  Wow that was a fast bike...at the time.

Years pass and you have a variety of faster and bigger bikes, the average family car now weighs in at 160bhp at 100bhp a litre, something only highly tuned sports bikes could achieve in the 1980s....

You have had a variety of bigger and faster bikes and also put on the pounds, perhaps by more than 50% of your teenage years.  You have filled out and more resemble  a wombat, rather than the racing snake you once  were..

You decide you want the bike that you remember as a fire breathing monster from your youth, it was a DT175mx, it pulled wheelies off the throttle in the first three gears, it did 75mph and had a vicious powerband.

You restore it to almost new condition, slinging a middle age, somewhat more portly leg over it and are disappointed with the performance.  Remember what a performance hit carrying your girlfriend on the back in early 80s was like?  Unfortunately no slim young thing on the back now, just your middle age frame giving the same effect.

So you remember 75mph from your 175 with 16bhp as do I.  Removing the rose tinted glasses, I can remember my 250 superdream barely hitting 80mph with 27bhp, almost twice as much power and only hitting 5mph more.  Difference being a overly "enthusiastic" teenage, apprentice memory with not a care in the world, to a young man's memory, just out of apprenticeship, is now a skilled tradesman and is suddenly realising that he is saddled with real responsibilities.  He has to keep it real.

Memory is a strange thing.