Jump to content
Sign in to follow this  
Peter Campbell

DT400e jetting

Recommended Posts

Trying to eliminate carburetion gremlins in an old DT400E: I remember reading a few months ago about a service bulletin which

detailed changes in the suggested main jets, pilot jets etc for this bike. Can't seem to find that info anymore. Anyone have any info on this bulletin?

Share this post


Link to post
Share on other sites

Hi peter " what problems you got ? has is leaned out ? or just starting probs,, :eusa_think:

Share this post


Link to post
Share on other sites
  • The bike afaik is completely stock and unmolested. It has 3300mi showing and is in excellent overall condition Starts and runs great when cold -but after riding for a mile or two it just doesn't run right (light pinging sounds at partial throttle, piston rattle among other problems). I've already replaced the CDI box with a new one from rex, put a new ignition coil and plug wire on it. The carb has been gone through several times -it has the stock 180 main jet and stock pilot jet, needle settings etc. I've also ordered a nos pulser coil just in case that is the problem (even though my coil tested fine). I've tried colder heat range plugs, replaced the main seals, checked the rotor and keyway and key, Pulled off the head-piston was ok except for what looked like orange peel appearance on top (detonation?). Checked the gas cap vent it is fine. Running premium unleaded,

So after spending a ton of money on this wretched bike I can now ride it for about a mile before it starts to run like sh*t and I have to park it. And it's not like I'm a noob-some previous bikes I've owned: ds7, r5, rd250,350,400, rz350, H1, kh400, dt360, dt250, ts400 among others.

So I remember reading about a factory bulletin which suggested changes in the carb jets but cant seem to find that bulletin anywhere.

Still not convinced it is a carb problem but once the pulser coil is installed the entire ignition system will have been replaced......

Share this post


Link to post
Share on other sites

Pwew " thats a good reply. When you say runs like shit, is it when warmed up, When rolling off throttle, it kangaroo"s ,like gang gang, how does the engine idle, diference hot/cold,

Share this post


Link to post
Share on other sites

You mention piston rattle after a mile or two. Just wondering if it's getting enough two stroke oil ? Have you made sure the pump is working ok and bled through. If you look on the side of the oil pump you should see a small cross head screw with a fibre washer underneath. Make sure the two stroke tank is topped up then remove the bleed screw for a couple of minutes and watch to see if any air bubbles come out. Replace screw then run engine on tickover with the pump cable pulled out of the oil pump adjuster for a few minutes to bleed the oil line between pump and carb. What grade of plug are you running at the moment ?

Share this post


Link to post
Share on other sites

I find that what was a standard jet size back in the 70's should be increased a little with todays crap petrol even if the rest of the bike remains at stock settings and equipment, why not try a 190 195 or 200, genuine jets are cheap as chips

Maybe even retard the ignition by 0.2mm or so

Share this post


Link to post
Share on other sites

And before somebody says " they"re all like that" :eusa_snooty: Listen to how smooth the Dt400 is , especialy on over-run,,

Share this post


Link to post
Share on other sites

Thanks for all the replies:

Oil pump has been bled, also tried running premix with no difference

Plug is NGK B9es. plug is dark. also tried B8es. Idles perfectly hot or cold

Will run cleanly without choke after a minute or so. Surely if the mixture was too lean it would run worse when cold?

Does kangaroo (sometimes spectacularly) on the overrun after it warms up.

It's still a blast to ride for the first mile or so-maybe I should just be happy with that...

Share this post


Link to post
Share on other sites
Does kangaroo (sometimes spectacularly) on the overrun after it warms up.

.

Aha " :eusa_think: thats what mine used to do, after it sits for a night, I think you should pull the head & barrel , then spin the crank, an see if thers gear oil on the bottom of crank, i suspect R/h crank seal sucking thru , i know it will burn it off , but if its as bad as mine was, it will be half up the crank, talking up swept volume in the case, resulting in that kangaroo effect, see how smooth that DT in video is,

Share this post


Link to post
Share on other sites

Having the same bike, I also have the same problems!

Mine has done 4,800 miles and was imported from America a year or so ago.

I thought it might be carburation so stripped the carb and found that it only had 150 main yet (guess it had been located high up in the mountains in its early life) and that the floats were stuck. Fitted a 190 jet and cleaned it all out and it felt a bit better, but still not right.

From other posts it would seem that the crank seals are the likely culprits. Are they are an easy fit?

I have the Clymer, Haynes and Yamaha service manuals but haven't checked yet. Also, are there any other tasks worth doing at the same time as the crank seals?

Share this post


Link to post
Share on other sites

If the crank seals have gone then for the money you may as well do them all.

They all work at their limits in their own way. Although i really dont get changing one crank seal...?

Share this post


Link to post
Share on other sites
From other posts it would seem that the crank seals are the likely culprits. Are they are an easy fit?

Yeh, R.h = off with magnito, L/h = off with clutch basket& primary gear, Screw two self tapping screws into old seal, and pull out,

When intalling new seal" a litttle lube on edge, as its a tight fit, be gentle with tap in with big socket ,, dont bash bash, as seal might get damaged, :thumb: , As for Main jet size, 150 was standard, upping a size is a fine safety measure when on full throttle,

Share this post


Link to post
Share on other sites
Yeh, R.h = off with magnito, L/h = off with clutch basket& primary gear, Screw two self tapping screws into old seal, and pull out,

When intalling new seal" a litttle lube on edge, as its a tight fit, be gentle with tap in with big socket ,, dont bash bash, as seal might get damaged, :thumb: , As for Main jet size, 150 was standard, upping a size is a fine safety measure when on full throttle,

Thanks for the info. Know all about caution with oil seals - once did a mini clutch and replaced the output shaft oil seal at the same time. Noticed oil dribbling onto drive way from clutch housing during the following week and then spent the next weekend doing the job properly :eusa_doh:

150 main jet is standard on the 250's, 190 on the 400's.

Update: Just noticed that the jet I took out was either a 155 or a 165 - the middle number is a bit difficult to decipher - so not quite as small as I originally thought.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

  • Who's Online (See full list)

    There are no registered users currently online

  • Recently Browsing

    No registered users viewing this page.

×
×
  • Create New...