The X(J600S) Files - Battery Special

Custom XJ builds, restorations, major modifications or just a topic dedicted to your own bike. Look here for long term cool projects.
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One of the Regulars
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Joined: Thu Apr 19, 2018 5:36 pm
Location: Essex, England.

As you are probably well aware batteries are one of the custom builders biggest headaches. Lithium Ion is normally the weapon of choice, but they are expensive (particularly this side of the pond) & somewhat fickle requiring more modern & expensive regulators than those fitted on our bikes. So if you're on a bit of a budget or tight like me this will probably be out of the question.

So you're left with the OEM YTX9BS house brick. One of the ideal places to put this on an XJ is in that nice big space taken up by the air box under the tank, after all you can easily remove the airbox, fit pod filters and fettle a cradle for the battery in that cavern. Problem is Yamaha like all the other manufacturers have spent many hours & a lot of Yen on this monstrosity so that the carbs get a nice smooth airflow, fitting pods directly to the carbs effectively turns what was a pleasant summer breeze into a blustery autumn blow, CV carbs hate this & all hell breaks loose – flat spots, rough running etc. etc. etc. So you go and spend fortunes on Dynos, Colourtunes, new jets & it still has flat spots, rough running et all. If you are still unsure about this see other posts on this forum & elsewhere.

However it appears that the key to the pleasant summer breeze effect is down to the velocity stacks within the standard airbox. These are the iron hard rubber boot part that clamps onto the carb & gives everyone a real headache when trying to refit the airbox:


New items are available at ridiculous prices as are cheaper Chinese knock off's, but I have heard that these fall to pieces after a short while. A better bet if they are sound is to pop these out & soak them in a mixture of 25% Wintergreen Oil & 75% IPA (isopropyl alcohol not the beer) for about a week to make them pliable again & a damn sight easier to fit back on. Word of warning though, Wintergreen Oil smells like surgical spirit on steroids & you & your garage will smell like a hospital for the next few weeks & be mistaken for some kind of Brain Surgeon.

So bearing all this theory in mind, I decided to remove the air filter section from the airbox & try to fit the battery in this space & keep the OEM velocity stacks. Blimey, this might work:


If the airbox is going to be off the carbs for any length of time, its prudent to shove some 43mm solvent weld waste pipe fittings coated with a thin smear of silicone grease into the boots to keep their shape:


The air filter section was carfully cut away & a 6mm thick sheet of Nylon was cut to fit the opening in front of the velocity stacks, glued in place using a hybrid polymer construction adhesive (CT1 or similar) which is (allegedly) fuel resistant. The diameter of the primary air intake is 40mm which gives an opening area of 1256mm. 2x 34mm Ramair foam filters would give a total opening area of 1802mm. The original idea was to fit these on to a short length of 34mm 2mm thick stainless pipe which would have taken the opening area to 1412mm. However I found that they protruded too much & cut holes so they would push in & could sleeve these down should the need arise. They do a smaller 28mm which would have given a total area of 1230mm. but since fitting Black Widow GP pipes the engine has run a little rich (I know it don't make sense, but others have reported the same problems) & there was a slight flat spot around the 6K mark. Ramair are a lot cheaper than K&N's but either should work:


Unfortunately the battery was now struggling to fit. I could have tried to find a flat filter & made a bracket to support the front of the airbox, but after some lengthy research I found that a Motobat MBTX7U battery would fit as it is smaller in length & width but slightly taller. Its a standard AGM 8AH battery (which meams I can still use the original regulator) & is the same AH rating as the original Yuasa, but slightly lower rated at 115CCA as against the Yuasas 135CCA. Most of the standard alternative batteries are rated between 110-150CCA. It just means I wont be able to keep my thumb on the start button for so long. The bottom of the airbox was filled with layers of 15mm closed cell polyethylene cut out to accommodate the battery & starter solenoid:


Everything in place & raring to go:


The battery had more than enough oomph to start the bike (its been off the road since last year) I have done a few runs totalling 71 miles at the time of writing. Very pleased to report that it all seems to be working as before, spark plugs look good & the slight flat spot has dissapeared. So far, so tickedy-boo. I will endeavour to keep you posted should any problems arise.
1992 Yamaha XJ600S (modified)
2011 Triumph Tiger 800
2016 Lexmoto Valiant
2018 Triumph Street Twin

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