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dt175 won't rev above 7k

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i'm trying to get my 81 dt175 going 100% , but i'm having some issues . you can give it as much gas as you want and it does fine untill you hit 6k , then it just flutters there . i checked the float height and it was off so i set it to factory spec . the slide needle isn't adjustable , the autolube pump seems to be adjusted right (peg lines up with the dot) , all jets clean . once i'd done all that i could get it to go to 6.5k rpm and sometimes a little higher but it would start gurgling . then i thought hey , maybe the air cleaner isn't as clean as it looked , so i took it out and found the back side of it sopping with oil and pretty much falling apart . i removed it and i took it for a spin up the street and now i could get it up to 7k maybe a little higher but not up to the 8k red line so i'm guessing the clogged up old air filter had something to do with it (i have a new one on order) . but shouldn't i be able to get her up into the red (not that i plan on riding in the red , but theroetically shouldn't it be able to get there ? atleast to the 8 ? ) and if so what could be holding it up ? there's nothing else adjustable on here . compression is good and she starts first kick , idles great , the plug looks a little wet but the tip is somewhat tan .

i just noticed that in the diagram for my air box there's a small snorkel that you set into the box before screwing the cover down and mine doesn't seem to have that ...that couldn't cause this could it ? i wouldn't think that an inch long plastic snorkel would make that much of a difference tho . anyone else have any ideas ?

tomorrow i guess i'll check the reeds and make sure they're good . and i'll try running it with the fuel off to see if once the fuel level gets lower if it'll rev all the way up . if neither of those pan out i'll run it wide open up a hill and hit the kill switch and then check the plug . i know it's something dumb but i'm running out of ideas .

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i have a '74 dt 175 maybe the exhaust maybe plugged? does it hit the powerband alright mine shoots to 9k wen the band first kicks in, that or try pre mixing ur gas just unplug the autolube and put a pint of 32:1 in see if that works

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it hits the powerband but it gets about half way thru and hits a brick wall , does it under load or in neutral . basically the engine is 100% untill it hits the 6-7k range then thats all you got . you can hold it wide open as long as you want , it won't go past 6-7k . there's no other bogging or hesitation , and it's got plenty of power , i can even grab a hand full of throttle and it lifts up , even with my fat ass on it .the bike is low miles and possibly the cleanest looking dt i've ever seen . i just don't get why it won't rev past 7k

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ok , well i just tried running it with the fuel off to see if it was still float height , it ran as usual untill it didn't have enough gas to keep going , so i don't think it's float height . then i came down the street as fast as i could , hit the kill switch and pulled the clutch and rolled back to my house , pulled the plug . it was a little wet but the tip was slightly tan . i haven't checked the reeds yet , i'm going to let the engine cool down some first . i think i'll also pull the exhaust off and make sure it isn't all blocked up near the head .

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i just pulled the muffler off and besides being loud as hell i can now get it up to 7.5k rpm . i think i'm going to pull the whole exhaust and make sure it's clean ....i really hope this is it.

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just for the hell of it i fired it up with the entire exhaust off , same deal , it would get to 7.5 and that was that , the exhaust port is fairly clean and the pipe doesn't seem to be blocked up ...i don't think the exhaust is the problem . ehhh , i'm really starting to get tired of this , every single bike i've ever had has always worked 90% because of some undiagnosable mystery problem that bugs the hell out of me untill i give up and sell it .

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i just put everything back on and took it for a spin , it still only wants to pull 7k , tho when i pulled up back at the house for the hell of it i turned the gas off but left it running again . i kept revving it wide open , the first 2 or 3 times it got to 7 , the third and fourth time it got to 7.5 , and on the last rev before it ran out of gas i got it to 8 , maybe i should try lowering the float a little more and see if that does it . when i have the carb off i'll check the reeds , but i dunno why it would run prefectly up to 7k if there was a problem with the reeds but i've seen weirder stuff before . if anyone else has any other ideas feel free to chime in .

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i pulled the carb and pulled the reed block out , they look brand new and they're the metal kind , no missing hunks and they all flap back just fine so i rebuilt the carb again ,i'm running the stock 22.5 pilot and the stock 150 main , i reset the float height again just to see . went out and fired it up again .....still tops out at 7 . i don't think there's anything else i can check . the bike is 100% yet it's not 100% and thus is my off road bike curse , a problem that can't exist because everything is correct , yet it still exists . not one out of the 50 or more dirt bikes i've owned has ever worked right , it's always something . i'm starting to think i should swear off anything that's not meant for the road and just be done with it .

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My first suggestion would be to make certain that the exhaust is flowing as it should. And from the scanning your previous posts, you already looked into that.

Aside from a jetting problem / carb adjustment, the next thing that I would be looking at is the ignition system.

You obviously have spark so that is not the issue. But ignition components can and do weaken with age. You may have plenty of spark for the lower RPMs, but your coil may be weakening a bit and unable to keep up with the higher revs.

Just something to consider.

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sir, I'll have to say that is the cleanest DT I've ever seen, we have a 1978 DT175 that has been converted to a "dirtbike" you can imagine what it looks like, nothing like yours...remember it is a two-stroke and there is no rev limiter on it unlike a 4-stroke...not sure what the problem is but my dt has been sitting for a year now b/c we can't figure out *** is wrong with the kick starter

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tomorrow i'm removing the restrictor from the exhaust , everyone on the dt forum suggested it , yamaha welded in a cone right at the front of the pipe to keep it epa friendly ....screw the epa . then i'm going to clean out the whole exhaust . then i'm going to check the timing , which shouldn't be adjustable , but the lines are there to check it so what the hell . if that doesn't do it i'll test the coil . i'm getting this stupid thing running right one way or another .

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Has it ever ran better than this for you?

The engine does not sound bad at all. I have one odd thought. Suppose the 30 year old tach is not too accurate anymore?

Most of the enduro bikes from that time period had a very hard time hitting "red line" and the power band basically ended 2000 prm's before redline as they were tuned for low end and midrange power...smooth was the key.

If you have to try and get the extra 1000 rpm's, try a 1 size smaller main jet. The stock jetting back then was always rich and very safe. It had to be. One person used it as a dirtbike. The next guy used it as a freeway commuter.

The exhaust pipe was typically what held them back. You might check with DG and see if they still offer a pipe for it. The airfilter was also restrictive as was the air intake. For the most part, enjoy it for what it is. A 30 year old bike in incredible condition. Based on whats available today, you could spend thousands and never equal the performance of a modern yz 125. Not that the bike should be able to do that. See if the yz 125 will keep a piston and rings for 10,000 miles like the dt can.

This bike uses basically the same engine as yours. Notice where it hits it power and torque peak.

http://www.bikez.com/motorcycles/yamaha_dt_175_mx_1980.php

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yeah , there's a few more things i still have to check , but i have the exhaust off right now and that epa restrictor is comin out . that should help some . i got the bike this way so i dunno if it's ever revved higher , but it sucks , right as you hit the power band BLEHHHHHHHHH no more power , i'm sure there's atleast 1000rpm's worth more powerband , i just can't get to it yet .

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The bikes back them really were not built like that in stock form. Many of the IT and yz parts will bolt on. To get much more power, you'll have to start going that way. Yamaha also made a yz 175 for a few years so those parts might be an option . They were only rated for 22 hp in stock form. Thats about what a modern , stock CR 85 puts out. What they did have was low end and torque. Dont try to make a race bike out of it. That really destroys the charm it has as it is right now. Compression is low, porting is mild, the carb is small, and the bike is very restricted as it sits right now.

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Hey Rockso,

Guess Who ? haha.

Anyway, after watching that YouTube video, I'd tend to agree with the last couple posts. The bike is pretty old and if I remember correctly they weren't very top-end oriented or powerful, compared to what we are used to these days. And maybe the tach is off also.

👍

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i've had many of these old dt's , i've just never had one with this problem , once i get this restrictor out of the exhaust then i can start playing with the tuning , as it sits it's almost unridable , these bikes don't have anything until the powerband kicks in , and right now i can be in the powerband for about half a second then i gotta shift ....no good .

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You HAVE to report back on the findings. I wish we could still buy new DT's. Imagine the shock people are in for now when going to a shop for a basic motorcycle to save on fuel costs.

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ok , well today i got that restricter out of the exhaust , without a rotary tool . there was alot of chiseling and the plasma cutter took care of the bulk of the cutting . even tho it's badly out of tune i can already feel more oomph . i also checked the timing and it was dead on . it still doesn't rev up tho .

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