1973 Yamaha RD350

cancb550

Active Member
Hello everyone
My first 2 stroke bike I got myself few days ago. Looks good and clean, waiting for snow and cold to show some mercy so I can work on it.

PO has disconnected oil pump and rode with premix. I would like to put it back in service. Would appreciate help in doing so.

Not familiar with 2 strokes only 4 strokes CBs and GLs I have worked on previously.

Tried but couldn’t get a pdf copy of shop manual online, would be nice to know of a link to download.

Will keep updating this post as it progresses. Would like to have usual help from 2 strokers knowledge and experience.

Thanks


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2_DONE_THE_TON

Over 1,000 Posts
DTT BOTM WINNER
Welcome on board Sir!

A beauty you scored there I restored a RD250F (last aircooled model) over the course of the last years,very rewarding and nice to ride!

As for the things to do for this specific model:
When the engine was not serviced a few years back I strongly advise you to do so.
The crank is sealed up by crank seals made out of rubber that harden and shrink over time which can cause terrible motor damage,working on this engine is super easy and even with beginners skills you can remove the engine and change all seals quite easily.

Make sure the timing is spot on and carbs are clean.

As for the oil pump, I never rode premix (only when I started the bike for the first time to make sure all is working correctly.I didnt tke the pump apart (there are tiny balls inside that can stick).
The oil pump is actuated by a steel rope (the gas grip splits up into 3 separate ropes).
Fill the gas tank with premix, install the oil pump, make sure there are no bends in the oil hoses to the carbs, start the engine pull the oil pump rope all the way and watch if oil is pumping up trough the oil hoses (you are simulating full throttle).

This was my RD I sold it last summer.

If you have any questions feel free ask!
 

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Pete12

Been Around the Block
This should help you, scroll down to the manual's section and download from there...

http://www.aircooledrdclub.com/tech.html

I built an RD350 flat tracker, there's lots of little engine and carb tricks that we can help you with when the time comes.
 

cancb550

Active Member
Pete and Ryan, thank you very much for warm welcome and assistance.

I bought this one without seeing. Was for sale at a distance that I didn’t want drive in this weather (over 1300 kms). Little information in addition to three photos I got from seller, “rode it last summer,runs fine. New spark plugs, new battery, oil pump is disconnected, one fork dust cap is damaged, runs on premix”.

Got the bike, charged battery, connected it but nothing. Found out kills witch is not working (has cracked and doesn’t make firm contact) will have to fix or replace it. Managed to bring and hold it to a contacting spot, kicked it, fired up on2nd kick but noticed only on right cylinder.

Few seconds later, black gunky stuff started to drip out of left muffler (drain point where muffler meets header)

Turned it off. And started to do search and reading.

Another kind member from my 4stroke forums suggested few steps.

Removed both plugs, wire brush cleaned them (right plug was more fouled than left but ran fine).

Spark on both plugs, big fat healthy spark.

Put the plugs back in, 1/4 of kick with my hand and it fired up on both cylinders. Within very short time, left muffler dripping started and left cylinder stoped.

Is it possible that fouled muffler can prevent cylinder from firing in order ?

Planning to remove both mufflers and clean all the stuff. It seems like unburnt gas deposited there.

Would appreciate any thoughts.
Cheers


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2_DONE_THE_TON

Over 1,000 Posts
DTT BOTM WINNER
The stock exhausts have baffles mounted inside them, that will slowly overtime gunk up with the unburnt fuel.You will have problems removing them.I removed the exhaust from the bike (both sides).Removed the downpipes and used a wooden broomstick and a rubber mallet from the inside (where the downpipe is connected) to slowly tap out the baffle,be sure to remove the LOCKING SCREW on the bottom.
Before you remove the mufflers (which is hard work) check the following-->

For me it sounds more like a ignition or carb related problem.
Clean the carbs thoroughly and be careful to assemble the float bowls on the right side of the carbs (the choke only works if you mount the bowls on the right carbs, if you switch them the bike won´t be "chokeable").
There are tiny drillings in the carb throat which need to be super clean to work properly.
Best would be total dissassembly and ultrasonic cleaning.
My guess is dirt in the carb, probably gunked up idle jets,which have very fine holes...
Check if your gas tank has rust-->is there dirt in the carburettor?
Clean the ignition contacts,lube the advancing mechanism.
 

CarbsAndCylinders

Careful With That Axe Eugene
Welcome and good luck with your bike, there are some expert "Smokers" here. Was there old gas left in the tank? That could be your problem and you will have to disassemble the carbs and clean them it so.
 

stroker crazy

crazy as a fox
cancb550 said:
black gunky stuff started to drip out of left muffler …

It's amazing how much unburnt oil and carbon can build up in a 2T muffler!

(Especially if the PO was a bit heavy handed with the pre-mix)

Crazy
 

stroker crazy

crazy as a fox
Ryan Stecken said:
The crank is sealed up by crank seals made out of rubber that harden and shrink over time which can cause terrible motor damage,working on this engine is super easy and even with beginners skills you can remove the engine and change all seals quite easily.

This can't be over emphasized!

The time and effort involved in fitting new seals can avoid having to replace the motor.

Crazy
 

jpmobius

where does this go?
DTT BOTM WINNER
Sav0r said:
You can do the seals without splitting the cases. Definitely worth it.
It is definitely worth it, but while possible to replace the seals without splitting the cases, please do not do it. It will be far more difficult to remove the seals (as they have a very pronounced ridge along their perimeter specifically intended to prevent the seal from moving with the cases together), than it will be to take the engine apart. It is absolutely NOT possible to install the correct seals without removing this ridge first, which is a VERY bad idea as this could allow the seal to move possibly creating the very problem you are wishing to solve. I believe (?) that earlier versions of this engine (the R-5 and DS-7) had different seals which Yamaha changed in the '73 350 which is the first year of the reed valve design which may be what the very knowledgable mr. Sav0r is thinking of. Regardless, your 350 is exceptionally easy to take apart, so if you wish to change out the seals - and I recommend that you do - split the cases. You can perform a crankcase pressure test, but personally I would not consider that a long term solution as your bike is old, and presuming it seals now, that is not a reason to expect things will be fine down the road. The very nature of 2-cycle engines make them very susceptible to catastrophic damage (compared to 4-cycle) with either too much spark advance or too lean a fuel mixture when you run them hard. This can happen VERY quickly and even the very experienced may not suspect that trouble is afoot until it is too late. For that reason, it is important to ensure your ignition timing is correct and you don't suffer a lean fuel condition which the extra air leaking into the crankcase past old crusty seals does. Fortunately, these things are very easy to maintain (seals very rarely need to be replaced so long as the engine is used regularly).

Your RD has famously weak ignition coils, and presuming yours are original, age has very likely made them worse. There are aftermarket options, including replicas that are much better than the oem units. The points and condenser ignition is fine and works great with the normal tune ups. It is very possibly that you will have a lot of trouble keeping the plugs clean enough to run reliably with the oem coils, which will make getting it to run right pretty difficult.

You will absolutely have to take your carbs apart and clean them. This is not hard or complex, but you have to be super careful to use exact fitting tools (precise fitting flat blade driver for the pilot jets for example) plus great care and patience to avoid damaging some of the very soft brass parts. Heating the carb body with a hair dryer (hot as you can - hair dryers don't get that hot) may help a lot if you have trouble. Ryan is very correct about the importance of cleaning the tiny passages 100%. As a rule, I never need anything except spray carb cleaner and compressed air (and I have "rebuilt" many hundreds of carbs) to achieve flawless operation, so resist the urge to poke anything into the tiny passages. You may do more harm than good. It does happen that passages get clogged with some pretty hard goo, but it is rare.

Don't worry at all about your pipes. They can and do collect an astonishing amount of oil, and this can often drip out once the pipes warm up and even smoke enormously when you take it out on very fast hard rides and get the pipes really hot and burn off accumulated oil. There is virtually no chance that the baffles have carboned up enough to be significant at this point, but usually they are not to hard to remove once you get the little screw out which holds them in. There is a hole at the very back on the bottom of the pipe that lets you place a screwdriver through it to remove the screw. Once that is out the baffle simply slides out the back, though if it is crusty it may be a pain. If you have drips at the muffler-header connection try tightening the big nut that screws the muffler to the header. You will have to get an appropriate spanner wrench. There is a gasket in there which gets compressed when you tighten this nut. If it still leaks, you will need a new gasket, which are long discontinued, but you can find them if you look. Looks like your pipes are pretty nice. Really nice original pipes are very rare so if yours are take care of them! There are lots of aftermarket pipes available if you want more power. It is extremely unlikely the pipes are causing you any problems at all.

Cleaning your plugs with a wire brush is commonly a last ditch. Commonly (mostly?) plugs don't foul, they short. This happens because it is too hard to make an arc across the electrodes due to too much fuel and/or oil in the combustion chamber. Your likely very anemic coils probably make this a real problem. Although there may not be enough energy to bridge the too saturated gap, it is still a lot of energy, and the result is that it finds its way to "ground" by traveling along the insulator back to the base of the plug and the rest of the electrical system. If this happens a lot, a sort of carbon track results on the insulator which is a far easier path for the electricity to follow than jumping even even super clean electrodes in clean air. So the plug is trash and only a new plug is the solution. Not saying you can't clean plugs at all, but once the insulator shorts they are pretty much impossible to revive. And weak ignitions on 2 strokes do this A LOT! Once you get everything sorted out, plugs have a fair lifespan - even on an RD!

That looks like a really nice complete bike. If you decide to alter it, take care of all the parts you take off. There's lots of people out there looking for them! I have several of these things, but I ride my totally stock one most of the time.
 

adventurco

Nick Ol' Eye
DTT BOTM WINNER
When reinstalling the oil pump it is quite easy and very important to bleed the lines of all air. The main line from the oil tank can be bled with the bleeder screw on the pump, and the two hard lines to the cylinders need to have oil forced through them with an oil can (unless they are full already).
 

Pete12

Been Around the Block
Good advice on the bleeding.
You can also use the oil pump to bleed the system. Open the metering valve full (where the cable connects) and then rotate the thumbwheel on the end of the pump with your finger. It's a little slow this way but gets oil through the whole system.
Edit: Forget to mention, there's a little bleed screw on the side of the pump that you remove when bleeding the pump. It goes back in when you bleed the lines to the carbies (after you disconnect them, of course).
 

sav0r

Coast to Coast
I guess it depends on what seals you use, but yes, I had forgotten about the the locating rings on the seals. Splitting the cases is really quite easy, so that's definitely the best way. I did my last engine rebuild in less than four hours, that included removing the engine from the bike, cleaning the engine before disassembly, bore/hone, new pistons, new crank, all new seals, and reassembly. So taking your time and giving it a proper going through really isn't even hard.
 

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