Peter Campbell

Good point. I did change the left but not the right. Suppose I'll have to add that to the project list (sigh)...

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...

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......

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?

Newbie here. Just bought a 78 DT400 sight unseen on CL. PO said it ran fine. When I ride it it runs good for about a mile then starts pinging and knocking and becomes unrideable. I've cleaned the carb three times and have ensured that the bike is stock (80 pilot jet, 180 main jet, main nozzle I am not sure of did not see any markings) I have two questions: First is are the main nozzles marked? Second is can the air jet be seen from the rear of the carb? I can't see one on mine and I'm wondering if it got shot out during the many carb cleanings it had. Do they even have an air jet? Any help would be appreciated thanks...