RD400 NO start condition....???

folks..my 1977 RD400 does have spark on the plugs but won't start. In fact it died on Hwy .. Now only 1 cylinder fires up & dies out. Any one have comments what to look for..I hope that cyl is not seized. By the way it does leak few drop of oil after a ride. I did top up the oil mixer reservoir. Thanks.

 

Check compression, check timing. There's a lot of info needed to further diagnose a problem like this.

 

Two strokes of this era are simple beasts - air, fuel and spark. Need to check each of these. A two stroke always drips oil as it burns oil in the combustion process, that's what causes the blue smoke. A by product is also the burnt oil residue which is black. This is different from your engine oil pre mix which will be clean and clear and colour depending on brand. If it's a newly purchased bike I'd change the spark plugs anyway - surprising how what you see as a spark may not be strong enough to kick the bike. Check you're plug condition too as it can tell you what's going on in the engine. On my H1 I had an issue that tank rust was clogging my carbs so the fuel/oil mixture was wrong and I was getting fouled plugs on one cylinder from too much oil not enough fuel - worked it out from the oiled up plug. Also eliminates and issue cheaply and check the gap on insertion. Then look at the airbox and filter to make sure proper air flow - don't run it without the air filter though despite temptation as you'll mess up the tune. But make sure it's clean and there are no obstructions. Once you've done the easy ones it's fuel time. I presume your carbs are nice and clean and the cables are good and carbs are in balance. You do the balance with the bubble in the sight glass on these I think - follow the manual it's easy. Pull the fuel line off the each carb and open the tap - if OK that eliminates tank vacuum and fuel tap delivery issues (and don't forget the bucket). Do it for both carbs. Then take off your float bowls to make sure it's all good and clean in there - again doesn't take long so an easy check. Check your cables have good tension so that they open the carbs properly. Now you get down to fiddly bits of mixture. General rule of thumb for stock set up should be 1.5 - 2.5 turns from full in - check the manual. So screw the mixture needle all the way the in turn it out the stated number of turns. And then see how you go. Once it's running set your idle speed when warm.

One other thing you may want to check is that baffles in the exhaust are clear. Because of the way exhaust pressure works in a 2 stroke if the baffles are clogged the exhaust will not work and the burnt gas will not get away from the cylinder, As a result new mixture will not enter the cylinder as the blockage affects the induction cycle. You check this by removing the baffles at the back of the muffler and checking that the holes are not clogged with carbon and gunk. Wear gloves as its one messy job. They are usually held in with one screw for each side.

RD's are simple cause the reed induction takes away all the issues with crank seal and stuff that you had on early two strokes. Good luck!!

 

BTW it's a two stroke so there is no timing like on a 4 stroke.......

 

No cam timing but there is ignition timing on an Rd if the points are out of spec ignition will be out of sorts ! Point gap will affect timing.

 

Yup, been through it before. Not certain about the RDs if the timing is adjustable, on some two strokes you can retard or advance the spark by adjusting the magneto.

 

Owned a 1973 RD350 many years ago, and it looks like things have not changed all that much when checking service data online. Point gap is set from .3 to .4mm (.012 to .018). Ignition timing is set at 2.3 +/- .15mm before TDC. If things have not changed, you would first set the gap and then use a dial gauge in the spark plug hole to set the ignition (points opening) at 2.3 mm BTDC. With ignition timing and carb sync done to perfection the 350 was almost vibration free.

Compression is a good place to start as suggested and if OK then:

Get the points cleaned / replaced, gap and timing set, and get the carbs thoroughly cleaned and go from there.

 

Electronic ignition...........