rd400 service for misfire in perth

[tarjla]

Just imported an rd400F from uk.Got it to start fine,motor just been rebuilt,it idles fine and revs in neutral but when i try and ride it feels like its running on one cylinder,does anyone now of any mechanics in perth that know about the old 2 strokes,thanks

[Jeram]

have you tried the obvious things first?

(dont want to sound like Im calling you stupid or anything like that. I just have no idea if you've experienced and have tried the obvious or whether your new to this stuff)

fresh fuel? (few bucks for gas)
new plugs? (few bucks each)
charged battery?
choke stuck on?
compression test? (guages on ebay and are very cheap) (may be worn rings or a worn bore)
blockages in the exhaust? built up crud over the years may need cleaning out
carb clean? (10-15 bucks for a can of carb clean and a few hours)
plug chop? (quick ride down the road at WOT, pull clutch, kill engine, stop, check plugs to see jetting.

the above I always do when buying a 2T bike even if the engine is thought to be in good condition. that is if I dont tare it to peices first.

even if this doesnt fix the issue for you, it will save paying a mechanic 100 bucks an hour to do it for you.

Id say its most likely something very simple. If you've got money to burn by all means just get a mechanic to do it. but it could cost you 30 bucks to fix instead of 300 if you do it yourself.

so of the gurus on here might have some more specific info for you relating to the RD400.

[Jeram]

oh and if you cant get an answer on this forum within a week, try perthstreetbikes

but there are a few perth guys on here who can hopefully find you a mechanic if you chose to go down that path.

[EPApolice]

Is it a coffin tank or a Daytona shape bike. If its a Daytona is it a 2V0 or 3M4 prefix. If its a 2VO does it still have the anti pollution gear on the carbs if not then it has to be all set up again. The coffin tank shape and the 3M4 should have 2R9 carbs and pipes, clean the carbs fully an ultra sonic clean is a suggestion and check the slides are in the right way around. A 2VO has points and needs a strong battery but the electronic ignition will run without a battery like an LC.

[Stankflapper]

^ Now there is a guy who knows his stuff!!!!

[tarjla]

thanks for the replies.Its a 400f coffin with the 2R9 set up.It will idle fine and runs clear on full throttle,its between 3500 and 6000 where it just bogs down and feels like it is running on one cylinder.The seller had the carbs sonic cleaned not long ago

[EPApolice]

I would pull them down anyway that way you know for sure. Make sure you have the correct mains 145 and float height is correct 23mm. You will get a slight stumble around 4500 anyway. See if the needles are genuine Mikunis if not toss them away and get genuine. If you can find out if the carbs were rebuilt with Keyster kits if they were thats your problem those needles are no good. They should be 5J6 and on position 3 is standard.

[tarjla]

Thanks that is very useful info,I will contact the seller,pardon my ignorance but what is 5J6,cheers

[EPApolice]

5J6 are the needle numbers that the E/F/G run. The C/D have different needles and it wont run right if they are wrong. The needles in the Keyster kits for the air cooled bikes are no good but the rest of the kit is ok. A lot of people fit a Keyster kit when they rebuild the carbs for no real reason and then they all have running issues that are chased back to the needles. I dont know what number is on the Keyster needles but if you pull yours out and have a look you will know for sure, an easy job. If you dont have 5J6 needles you will have a big problem getting some I'm afraid.

[tarjla]

Checked the carbs,floats bang on 23,main is 145.The needles have Y246 on them so I will try and get a pair of 5J6,anyone reading this got any for sale

[Jeram]

are you guys talking mikuni part numbers or yamaha part numbers.

don't get them confused!

this thread may or maynot be useful... seems like many have asked a similar question previously... GOOGLE IS YOUR FRIEND> TOOK ME 5 SECS TO FIND THIS

http://www.2strokeworld.com/forum/index ... ic=11515.0

[tarjla]

The 5J6 is the mikuni number on the needle,the Y246number is what is written on my needles which I believe are Keyster ones.The thread link is useful but USA Rd400s have different needles to uk ones which mine is,cheers

[tarjla]

Managed to get some 5j6 needles from usa and fitted them today.WHAT A DIFFERENCE,cannot believe such a small change could alter so much.I reckon the bike runs about 95% right now.I will change the other jets to mikunis and set up the carbs.On setting up the carbs the book says to pull off the left plug lead,when I do this the motor cuts out on my 400F,I believe this is normal,how can I syncro the carbs when this happens as I need to adjust the rh carb first,cheers

[hybrid]

I have a vacuum carb sync tool that I used to sync my 500. Works pretty good.

[EPApolice]

Its always the Keyster needles that cause the problems in the AC bikes.
All I do is look in the back of the carb with the airbox rubbers off to see they are both rising at the same time, sync the slides via the windows at the top of the carb body. To set the idle I just put my hand at the rear of each pipe. Every time you unscrew the carb top you will need to check it.