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Building a Better Dominator

Article by Ron Grant, "SideTrack" – Motorcycle Adventure Magazine, Australia. August – September 1998, Issue 20.

What works, what doesn't on the way to eight extra horses and a vastly improved suspension package.

Ron Grant from Shogun Honda in Brisbane has spent the last 18months making an already good bike that much better.

Working at a large motorcycle dealership has it's advantages, like getting to ride the latest and greatest whenever you like. One day a couple of years ago it was time to go home, all the bikes were put away and the only thing I could get out without shuffling a dozen bikes around was a near new Honda Dominator. You're kidding, a damned trail bike! I begrudgingly dragged it out and headed home. A few kms down the road I remembered the Honda Riders Club was having a ride day at a small, local, road race circuit, so I swung off to have a look.

Everyone was having a ball. The thrill of going for a fang around the track was really tempting, but I only had a trail bike to ride… What the heck, I was there and it was all I had so onto the track I went. The coarse was winding with about seven real tight corners and only one short straight, and it came as a surprise to realise that the Dominator was capable of mixing it with the best of them. In fact it was an absolute bag of fun!

A couple of weeks later my club had a run to Woodenbong. We'd been there so many times that frankly it was getting boring – the same beautiful twisty bitumen road, same great views and scenery, but it had been done a few times too many. I decided the Dominator would be my chosen transport and again, it was a blast. More fun than any other bike I had ridden in years.

That was it, goodbye road bikes.

Within a few days I had bought a new dominator and have enjoyed every one of the 30,000km on it since. But it needed more power, less weight and better suspension for real serious off road work.

Getting Started

I read in Sidetrack about the Long Term Dominator and the chosen path for modifications was weight saving first and then handling. As it had been quite a few years since I had ridden dirt bikes the Honda handled well enough for me so after the weight loss program I concentrated mainly on finding more horsepower.

We did an initial dyno run in standard trim after a full service and tune at 3000kms and recorded 32 hp at the rear wheel – with so little it shouldn't be hard to find more! The first mod was to ditch that heavy twin muffler system for a modified XR600 header with a laser pro D'or muffler. After six weeks of mucking about with the importer, and heaps of money, the new pipe was on and looking good. To my dismay though, the dyno showed a loss of 3 hp in the mid-range and nothing on the top end. This was due to a change in exhaust back pressure, which affected the carburation, but as the needle jet is unadjustable, we couldn't match the pipe to the bike.

The choice was clear, either scrap the new exhaust or change to a different type of carburettor. We chose the latter and a 41mm Mikuni flat side to suit an XR600 was the eventual choice for replacement. The carb fitted beautifully but with extremely limited room to make adjustments – to change the needle position meant the carb had to be removed from the bike. The quickest way is to remove the sidecovers, tank, battery and carrier then lift up the rear mud guard, unbolt the air box and out comes the carb. After about twenty jet and needle position changes I can now do it in 1 hour and 40 minutes!

So after a number of weeks and many more hours of fiddling the bike was now really strong but was difficult to ride under 4000rpm. If we had increased the compression ratio the modified cam would have been more effective but we avoided this because of the possibility the higher compression may have adversely affected the starter motor operation. The dyno showed we were now up to 40hp. That's a genuine 40hp, 25% up from standard, but at a real price.

Heaps of experimentation and development time had gone in, but we now had a bike that was a bitch to ride unless the gear change got a good work out. 1500kms later a rattle developed in the top end and inspection of the cam showed severe lobe wear due to incorrect hardening. This time I thought I would go for a stage 1 cam to make the bike that much easier to ride – it was a little better at low revs and not much different at high revs, but that cam only lasted 300kms before the hardening fell off it too.

The next decision was easy, go back to a standard cam! I could not believe how smooth the bike was and easy and enjoyable it was to ride again. A number of people warned me that hot cams were a pain in the arse but sometimes one has to learn the hard way.

Power Pipes

At this stage we turned to the exhaust set-up. The single sided muffler caused a fair bit of grief until we started experimenting with different baffle diameters and discovered that the original Laser outlet was too big and therefor wasn't creating enough back pressure. When this was rectified the pipe worked exceptionally well.

Still not satisfied we decided to try a twin exhaust and eventually made up another system using the original headers but running them into a pair of carbon fibre mufflers, extended to finish them level with the rear of the tail light. The theory here being that the longer the overall length, the more torque would be produced. And amazingly enough, it worked too. The proof was on the dyno; standard cam, flat side carb, ported head and twin carbon muffler system and still 40hp on the top with quite a bit fatter mid range than the original efforts had produced. After 28 dyno runs and a whole heap of time and money and experimentation, the following are my conclusions.

Lessons Learnt

1. As a general rule standard exhausts seem quite efficient if somewhat weighty. Caution should be used before forking out heaps for something that may end up providing less power and merely increase noise. Staintune is one company that does its homework before putting something on the market and its products are usually well worth the money.
2. Flat side carburettors can make a real difference, but unless one has experience at jetting this step could be the beginning of a long, expensive drama.
3. Camshafts. Ugh! Stick to standard. The supplier of the two cams that self destructed is renowned as Australia's no. 1 cam man. The cams were installed and run in properly. For reliability stick with standard. In the end when all was set up correctly hp was about the same but the bike was more enjoyable to ride with a standard cam.
4. Port jobs. If I could do it all again, I wouldn't bother with this step. I don't believe the gain was relative to the cost outlayed, especially running a standard cam and compression. Once upon a time companies churned out bikes what weren't overly efficient in the above areas, but companies like Honda obviously put many hours of research and development into each model and it really is hard to beat them at their own field of expertise.

Suspension

Rave tech Gold valves were fitted in the forks making the suspension more compliant over small bumps and helping reduce dive under braking. 15w fork oil seems to work the best. The forks still bottom out on big hits under brakes and although sag is about right, heavier springs would make it great. To date I'd rate it about a seven out of ten for improvement.

On the rear the shock was under damped and under sprung so we had a remote canister with adjustable compression damping and Gold Valve fitted – the canister increased the oil capacity which contributed to reduction in shock fade. The shock works better everywhere but the improvement is especially noticeable when sliding the back on smooth dirt roads. Before it would wallow quite a bit and a hangside would have been easy to manage. Now the back end sits where requested. It's great.

The only problem with fitting the remote canister was clearance between the shock body and the frame. We have finally got mine set at 1/2mm clearance – any wear in the top shock bush and the connector will probably get broken off. The spring is too soft so even with maximum spring preload we still have too much initial sag. In fact the standard item is a real piece of junk.

We modified the shock because at the time we couldn't buy an Ohlins or similar. Retail price to do the shock work was around $600, so I believe it would be better to put the money towards an Ohlins.

Loose Hints

We repadded the seat by fitting a foam wedge 30mm thick at the front and tapering it to zero at the back. This made the seat less like a ski slope and far more comfortable on long trips. We fitted an Acerbis 24 litre tank. It is so good now to have a decent fuel range, managing 500kms on the road if we stick to the speed limit. Doesn't quite fit perfectly but definitely a good thing.

The XR600 front mudguard was fitted the same day we changed exhaust systems and when we were down about 15hp on top speed and the bike felt gutless we blamed the exhaust. In fact the problem was the high guard blocking the air from the channel under the tank to the air box. Off came the guard and the bike went like a rocket again. High front guards are not suitable for Dominators.

An automatic chain oiler proved a good move. I tried the lube point in several different positions and found oiling through the top of the front sprocket cover works extremely well. After 12,500kms of real abuse the chain has had its first adjustment and is still like new. The rear sprocket too is like new although I have had to change one front sprocket. The oil used on the chain is just cheap engine oil, which works a treat! I turn up the flow rate for dirt work then down for bitumen.

Shaping Up

Overall the Dom has been ridden fairly hard for the past 30,000kms but has been serviced and maintained at a high standard. The bike still runs exceptionally well and nothing has broken or required changing. It still has the original cam chain, rings and the rest.

It's a top bike, really hard to beat for those who want a mount that can handle both dirt and bitumen. If only there was just another five horsepower, and about 8kgs less weight, and just a bit more compliant suspension, and, and…

Thanks to Tony Boggart for the use of his Dyno facilities, to John Hill from JHH Engineering for the excellent head work, and to Noel Rogers from Motorcycle Exhaust Professionals for that great pipe. And a big thanks to my manager, Bruce Tinlin of Shogun Honda for allowing many hours of which he and his staff provided.

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