It’s alive!
Scoop’s early RD350 is making smoke and screaming like a banshee… but why?
Following on from last time the dial gauge and timing light were pressed into service and a pleasant hour (not) was spent tweaking the RD’S points and back plates until we had a firing point of 1.85mm BTDC. And before every air-cooled Yamaha owner writes in, fighting off fits of apoplexy there’s a good reason why I’ve strayed from the supposedly sacrosanct figure of 2.0mm. With the advent of ethanol based fuel, two-strokes have been doing strange things and detonation has been taking out pistons, cylinder heads and, on occasions, even entire motors. My contacts in the industry are now strongly recommending that timing is retarded just a touch. Seemingly it’s even more crucial with some of the earlier Japanese classics such as my RD350. Apparently the early 1970s cylinder head profile the engine runs is simply wrong for what now flows out of the pump nozzles in 2016. The compression ratio is too high, igniting the fuel too early and generating too much combustion pressure. So with timing suitably tweaked and everything else theoretically sussed there wasn’t really too much left to do hopefully. With the carbs back at their official residence the tank was now ready for fitting. It’d been derusted, had the metal balance pipes relieved of a vile black intractable mass, been given a total tap overhaul and had its filler cap rebuilt. Yamaha’s disproportionately annoying, below-the-top-frame-rail link pipe has been replaced with an easily and readily demountable link pipe once again supplied by the ever patient Yambits. Given all the attention the tank has received I fully expect it to repay me by doing the dirty at some point in the near future! However, and entirely against CMM reader expectations, I’m actually not quite as stupid as I look. Okay, hard to believe I know but on this occasion I was genuinely planning ahead. I’d worked out that it’d be a whole lot easier to access the carbs and their fittings when the bike was first fired up if the tank wasn’t obscuring everything. So removing the freshly fitted tank, digging out the Sealey remote fuel tank and rigging twin outlets meant I was dangerously close to being ready for the auspicious moment.
Now a salutary word of caution here about these devices. They are incredibly useful and convenient but as flagged up on social media recently there are a couple of caveats. Firstly the pipework attached to them needs to be on tight and secure, ditto any additional lines you rig up to feed multiple carburettors. Secondly if the reservoir is filled to the top and then mounted high up there’s a real likelihood of the float valve struggling to stem the flow of fuel. Check out the opening picture and you can see residue where the RD’S float valves cried enough, embarrassing stains etc. Lowering the reservoir to the level of the top rail solved the issue. So with some ethanol free Aspen fuel and 50:1 premix just to be sure, it was time to bite the bullet and see if the bike would run. Fuel into the carbs, several priming kicks, ignition on and… nothing. Repeated ad nausea but not a vestige of life. Move the kill switch to on and amazingly the bike soared into life like it had never been interfered with by a 60-year-old numpty. The yard filled with smoke, the choke came off ASAP and even Mrs Cooper looked duly impressed. With my eyes full of tears, from the smoke and not the emotion of the moment, I then allowed the bike to idle ensuring both pipes were getting equally warm. Satisfied all was well I stopped the engine for a quick sanity check and then fired the bike up again. What happened next scared me witless. The bike fired instantly, idled at three grand then rocketed to seven. Even though my synapses aren’t what they once were, basic instinct took over and the kill switch and ignition were both flicked to OFF. At times like these you think you act rationally but in retrospect you probably don’t. It was apparent that the slides which had previously been returning fine no longer did; especially the left hand one. No amount of fiddling or cajoling had
the desired effect even when the carb tops were popped off to double check everything. Crawling all over the bike revealed several things I’d not spotted before. There was lumpy corrosion on the upper extremities of the oil pump cable, the splitter box was cracked and the lower cables had kinks on the inner wire; none of this was exactly conducive to perfect running. And strangely neither of the two carb securing clips were tight, though I remain adamant they were! So sticking cables and massive air leaks… yes that should do it. A throttle cable kit from the ever patient Yambits arrived but revealed that my bike takes a different lower cable to the one that normally works. Duly supplied and with everything crossed the bike was once more fired up and, blessed relief, it ran sweet as a nut responding as expected to opening and closing throttles. Sorted, or almost! Just going over the bike while it was running led me to yet another reminder that you should never assume anything with old bikes, regardless of apparent condition. A cursory glance of a hand across plug cap had me doing a strange wriggly dance across the yard. Old plug caps are not worth bothering with; black NGK replacements are the obvious thing to fit and so they were. Such things ought to be obvious, second nature, automatic etc. but of course the gift of hindsight is a peculiarly useless talent. So there we are; an old Yamaha RD350 ready for its MOT after I’ve been around it just once more time to make sure everything is as it should be. Nothing has been overlooked, all fixings are secure, fluid levels are correct etc. Given the, ah hum, small oversight of the carb clips I’ve resolved to do the pre-flight check on a quiet day when I have nothing else going on in my addled old brain. It’d be near criminal at this juncture to make another schoolboy error!