Yamaha RD350LC carbs

1980 Yamaha RD350 LC 4L0 Restoration – Part 10 – Carbs

Project Elsie part 10 – Told my Wife I would have to forget her – time to put on the two carburettor(s)

Yamaha RD350LC carb float bowlI have to admit that I have had what can only be described as a proper bastard of a day. The problems started before I had even got up when I had a dream that the RD wouldn’t start because I had put one of the pistons in the wrong way round. Now even though I knew I hadn’t the doubts set in. It was no good I had to go find my old endoscope and check it out before I could put it out of my mind. That was an adventure itself because first I couldn’t find it then the phone it works with had a flat battery and then I couldn’t remember how to use it – it has been a while. With all that sorted I was able to confirm that both pistons were fitted correctly anyway.

So after delivering a bike that took most of the morning I got on with the job I wanted to do which was cleaning the carbs -they were filthy. Both were missing their mixture screws and springs, which was a bloody serious nuisance as I don’t have any for Mikuni crabs, only Kei Hin, so they will have to be ordered. Turns out we need a new throttle cable too the one on there is very stiff.

Both carbs cleaned up nicely with carb cleaner, petrol and a Dremel with various wire brush attachments. The inside of one was particulary nasty as some 10 year old fuel was still in it but it had turned to varnish over the years and the float was totally gummed up as was the needle valve. 

The outsides were cleaned first – not because I wanted them to look pretty but because I didn’t want any crap from the outside getting to the inside.

Yamaha RD350LC carbsThe clean one was so shiny the photo looks totally crap, sorry about that I can’t take it again because both carbs are now fully fettled and fitted to the bike.

The fitting of the carbs was a whole new adventure, one that caused me to lose nearly 2 hours of my life, quite a lot of blood and a sore throat from some world record breaking shouting and swearing. Even I didn’t know I knew some of those words. The problem was that you have a really tight space to work in and 40 year old rubber components that don’t seem to want to fit or give any more. In the end I removed the rubber adapters that go from the carbs to the air box and warmed them up until they were a lot more supple, I then fitted them to the carbs with them off the bike – this  made life a hell of a lot easier. I then warmed up the inlet rubbers and man handled the carbs in to place. It was still hard but I got there in the end.

While I was at it I fitted the left hand side engine cover and fitted the new Venhill clutch cable, everything was well greased and lubed, it works beautifully now. They have PTFE liners and they really do work so much smoother than lesser cables – well worth the money in my opinion and they match the rather nice brake pipes we fitted too.

Yamaha RD350LC carb installationSadly the throttle cable is the original item and now everything is connected up the throttle is horribly stiff. A new cable is on order, it’s a weird one as it splits in to 3 – one cable to each of the two carbs and then one to the automix oil pump. Not looking forward to fitting that as the carb balancing on these bikes is primitive to say the least. Instead of having the usual vacuum ports on the inlet side that you can connect a gauge to you have to rey on lining up the throttle slides through 2 tiny windows on the carb bodies. It’s a ridiculous idea, which is probably why nobody does it like that any more.

Another handy hint at this stage for anybody embarking on a similar project – before both carbs are installed fit the tacho cable. It’s easily forgotten and much easier to do when you don’ have a carb in the way.

Yamaha RD350LC throttle cable installationThe right hand side panel was next in line for attention – fit the gasket to the engine first is the advice here – it hangs quite nicely on the two dowls and the top water pipe. The oil seals for the water pump, oil pump and kick starter were fitted while it was on the bench, as was the oil pump and it’s new gasket. It was tremendous fun fitting the new water pump gasket – God alone knows what the old one was made of but it took quite some effort to remove the plate that seals it and then even more time to get the remains of the old gasket off. Reassembly was, thankfully, a far easier task.

I found it easier to fit the radiator bottom hose to the pump before putting the side cover on, it’s quite short and not terribly easy to manipulate.

Other minor jobs were to replace the sump drain bolt with a new ally washer and to connect the two oil pipes up to the carbs. I need to get a joiner for the oil pipe from the tank or fit a new length of pipe if I can get one – when the bike came to me it had a joiner in the pipe but it broke when I tried to remove it. Once I have that sorted I will bleed the pump, the first run will be on premixed petrol as the pipes from the pump to the carb will have air in them.

Next job having sorted the carbs as far as I could with what I have it is time to get started on the things that let the burnt stuff out – the exhausts.

Ian had procured these from some mystical source unbeknown to lesser humans and they were in pretty good nick for 40 year old pipes. There were a few bashes and scrapes but the only major things I spotted was that one was missing a baffle and the other one had a chunk missing from the flange that forms the seal with the engine. First job was to tackle that so it was out with the trusty arc welder.

This is the broken bit looking very broken, nothing will make that seal without some serious intervention.

Yamaha RD350LC exhaust flange repairSo I built it back up with weld and then got out my trusty old friend the angle grinder. Only trouble was the unreliable worthless piece of shit decided not to work so I had to file it down by hand.

It was an iterative process but the end result was pretty good.

I’m quite pleased with the result, it will be fine and dandy and nobody will ever know. Unless I go and tell them all about it on some well known motorcycling centric web site of course.

Yamaha RD350LC exhaust flange repaired - NICE JOB!So now after much fannying about it was time to fit the pipe. At first I had a brain fade moment and attempted to fit the right hand pipe to the left hand side of the bike. Surprisingly that didn’t go at all to plan so I had to remove it and attempt to fit the correct one. That didn’t go a lot better to be honest. I just couldn’t get the thing to bolt up snugly at the engine end, things got so desperate I had to come in, have a cuppa and look up the parts diagrams. I then realised that the ends of the exhaust have like a collar in them that is supposed to mate up with the exhaust port. These pipes didn’t have that. I could not find them as a separate part so guess somebody must have removed them at some time or other. It’s all very odd. I attempted to make a couple but that didn’t go so well. The only lump of metal I could find to make them out of was a big old lump of stainless which is a bitch of biblical proportions to machine. I made one but wasn’t happy with it.

In the end the solution I have come up with is to use a double gasket, I have trialled it on one side of the bike and think it will be ok, I have a second pair of gaskets on order so I can do the other side.

Both exhausts have been sprayed with high temperature barbeque paint, I just need the other baffle now.

So that’s it for this thrilling episode, I need to wait for a parts delivery now – front tyre, rear tyre, chain, sprockets, carb idle mixture screws, throttle cable, exhaust baffle and a front brake light switch – I will then have everything I need to complete the project. So stand by, get the popcorn in, next time I hope to be attempting to start the old girl. Tata for now, Dave.

Article sponsored by Wemoto.

Article provided by David Powell of Boston Bike Bits.

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