Tdr250 hard cold start

[RD350NL]

I am the proud owner of a stock TDR250 since a couple of weeks. Bike came as a non-runner but I went through it and it now drives perfect.

The problem I am having is present when the engine is cold: It will start very hand and once it starts it only runs for like 2 or 3 seconds and dies as soon as I hit the throttle. If I dont hit the throttle it will run for a couple of seconds more but eventually will also die. It just wont get going, also not with the choke on. As soon as I spray some carb cleaner in the intake it fires up straight away and there are no more issues, it responds to throttle perfectly and it will idle/run forever. The bike runs like a champ at all throttle inputs and throughout the entire rpm range. It idles perfectly, picks up throttle perfectly and storms to 10k rpm easily.

It sounds like a fuel delivery problem but you would expect this to be present even after introducing carb cleaner, which is not the case as it does keep running.

What I did already to the bike (im not sure if the issue existed before I did these things as I didnt got it to run):

- Compression test (115psi both cylinders)
- New NGK spark plugs
- New OEM petcock
- New fuel lines
- Rebuild both carbs with yambits rebuild kits
- New exhaust gaskets
- New stock air filter

I did notice an intermittent fuel sweat/leak from the left side carb where this hose connects. See red circle on picture.

Thanks for any ideas here

[m in sc]

well thats a the power jet tube. i wouldnt worry about that. 

when you get it to fire up, does it smoke a lot then clear out?  my guess is its flooding the motor due to a petcock seep issue. the carb cleaner will allow it to fire then its ok.

vacuum petocks IMHO are always eventually trouble. id look there.

[RD350NL]

Thanks for the suggestion. A new oem petcock is on the bike and it aint leaking.

It does smoke yes and the first miles its not reviving up throughout the entire rev range (with lot of smoke), after that it runs perfect.

[m in sc]

yeah  . one flake of rust or dirt in the petcock diaphragm from the tank and it can lean/seep. ask how i know. I would strongly recommend pulling the line off the petcock and putting it into a bottle over night see if drips any. ypusure the choke is working?

[RD350NL]

Choke is working on both carbs (at least the plungers are retracting fully) and I tested the petcock, its really not leaking.

[m in sc]

might want to take the carbs off and make sure the choke passages are clear.

[1976RD400C]

You might want to check if the carb bowls are empty after sitting for a day or so, before trying to start it. If so, the lag time for vacuum to get the petcock open and fuel flowing is a problem and the carb cleaner spray helps that. 

[pdxjim]

#20 stock pilot jets are too small. They generally run better and are less prone to blockage with #22.5

Also make sure the inline fuel filters at the carb fuel inlets are clean.

Neither may fix your problem, but both are known troublemakers and easy to address while you're in there.

[RD350NL]

might want to take the carbs off and make sure the choke passages are clear.

Good one ill give that a try

[RD350NL]

might want to take the carbs off and make sure the choke passages are clear.

This actually solved the problem! The choke pickup in the fuel bowl was blocked, thanks a lot for this tip!

[m in sc]

awesome 👌