I just picked up my first dt . I want to get this thing to be reliable . When she gets hot she would rev up and stay stuck revving so I would have to shut the engine off . First work today replace carb entire unit . But then I was told to pick up a mikuni 36mm well the size compared to 32 mm original is the 36mm can’t fit in the stock air box . So do you get rid of all that and do a uni flow air in take or what ? Does the 36mm give u more hp? Or do I just do a carb rebuild on the original carb and call it a day ? What’s gonna get me more hp? And reliability guys ? Thanks for your time and advice . As I am a newbie even with tinkering . Also what are some things I can do to this bike to make a bad ass reliable 2 stroke ?

Raise the barrel 2 or 3 mm, widen the exhaust, drop the intake, shave the top deck. Close the squish clearance. Bring compression to 145 lbs. Get a pipe and carb for extra oomph. RacerClam ports these as well here on the forum. Just pm him.

For reliability you're probably best to leave it alone & run the original carb & just give the exhaust a burn out especially in the spark arrester in the tail section. You could spend quite a lot of money to get 'go fast' results including a new chamber exhaust & muffler so keep 'that' in mind. First thing 'is' what caused the original problem, so best sort that first. Is it a major air leak, or throttle slide not returning--things like that--base gasket sucked in under the cylinder etc. As FrankC says above 'Rich' here on the forum does modifying work. just doing a bit of a search--here's a link to a page sort of relating to what you might want.

www.yamaha-enduros.com/index.php/forums/...porting-dt400#104254

Man the pics look good. Way beyond me but i could look at those pics all night lol.

If you want it reliable, staying with stock carb and no modifications is best.

If revving is not a throttle cable issue, it sounds like you might have an air leak. Reed valve gaskets and crank seals are common sources. Finding and repairing air leaks is also important for reliability.

What do u mean raise the barrel ? And when u drop the intake what do u replace it wit ? Sorry I’m greener then ya grass outside . Thanks btw the stuck revving I’m assuming was the main jet getting stuck when I opened up the original carb had twigs and sand in it .

Make a spacer gasket under the cylinder or barrel be to raise port timings. This increases torque up the Rev range at the expense of lower end torque. Porting takes special skills, tools, and patience to get out of it what you want. As I was told by a wise man I leave to you- better to leave with professionals. I ported my cylinder for my 78 dt400 and I did it by taking a leap of faith with what I saw different builders do. Added up it worked. I like the results, but really I don't fill comfortable sharing because I only ported one cylinder, but will if you really want to know what I would do to get more power. Also, look under "78 dt400 performance improvements" with the search feature for improvements other than full porting. RacerClam does these cylinders too. Gary Braun is making an expansion chamber pipe for my 78 dt400 with silencer right now. Should be ready soon! Give him a call. 1-612-913-241 Tell him Frank Crawford sent you. It may add 10 horsepower and increase the spread of power both low and high end by 1500 rpm. In other words more low end torque as well. Even though my cylinder is ported I asked him to make a pipe that would work all on a stock Dt ports keeping the massive low end power. As far as I have seen there is no credible evedense anyone in the United States has ever gotten an upswept aftermarket expansion chamber for a 77 or 78 Dt400 other than modded aftermarket pipes- Even then less than a handful. How cool to finally have one for these old bikes.

More HP = Less reliability.

Sand & twigs in the carb aint good. Don't want that in 'Any' orifices lol. Just run it as an original & do the best you can with what you have--& be happy--before you spend lots of money.

Wondering if you got your bike sorted and if you are going to port it?

Frank , I got it running today . So the problem was in the throttle cable not operating properly . It was leaving the slide wide open in the carb . I just lube up the cable spraying inside of it . Now it retracts open and close properly . But what I learn now from finally inspecting the whole thing while I’ve got it running is . Top part of the engine need new gasket . Due to smoke coming out of it . I cranked down all the bolts on the engine and the smoke did stop from coming out of there . Then I noticed that where the engine meets with the start of the exhaust pipe there rusted out holes in the exhaust . So that a lost of some power there . It would be nice to find whole new exhaust system but I’m sure that is pricey . Also I need to get a new clutch , clutch gasket , springs in clutch ,new clutch plates , friction plates , also need new brake shoes , front and back . Seems like the guy who owned this just put whatever bolts he had to put this thing back together . Spacer where the fork and brake meet also . How do I find all these thing is the real question? I just ordered a coil off eBay last week and it listed for dt400 but it didn’t fit . Do you guys have a place you know about for what I need ? Thanks so much for your time . This project is going be so sick when I get it all running right . I post some photos so u can even see what’s going on with what I need new .