Nitrous Oxide Suzuki GT250 X7.
Nitrous Oxide Suzuki GT250 X7.
In response to John Randalls letter in your August issue, I thought to bore you with the tale of my Suzuki X7s. An X7 was the first bike I owned after passing my test. It was a three year old bike bought for the princely sum of 150. As I recall It had 12,000 miles on the clock. The Bike was cheap because of the impending 125cc learner restriction. Had I waited for a further 6 months I am sure I could have bought an even cheaper one. That machine was a dream come true after years on Honda CJs and Yamaha XSs. It did 40 - 50 miles to each gallon, /indicated a hundred miles per hour, and left most Jap middleweights for dead if the road had anything worthy of the description bend in it. After owning it for a week, it began to rattle so I took it back to the shop I had bought it from and had it diagnosed as Paranoia. It continued to rattle, It continued to go very rapidly and so I continued to ride it. I kept it for a year putting oil and petrol in it and did approx 7000 miles on it. In that time I replaced the plugs once and the rear Roadrunner for another Roadrunner. I also tried bolting on a pair of Suzuki racing expansion chambers that a friend had. They lasted 30 seconds after I started the engine. Lots of noise for no appreciable gain in performance. I let him have them back. Then I made a big mistake, I sold the X7 (At a profit mind, 175 I got for it), in order to finance a larger bike. There followed a period of 3 years, in which learned some more about motorcycles, owned a variety of machines, including a Suzuki GT38O which I refuse to talk about, and finally sold the last bike, a Kawa Z550 to finance passing my car test.
(Interim period where nothing interesting happens)
Then I came to my senses again and decided that to cure my withdrawal symptoms I had to have another bike. Cash was a problem (cash always is !), with only 100 to spend I couldnt afford the GPz55O that I wanted, so it was time to reassess the situation. My faithful X7 came to mind. After two weeks of scanning the ads I found one a short 30 miles away. It was priced at 150 with no tax but MOTd for 3 months. I decided to go and see it. It was almost all there. It looked like It had been abused for a long time by a man with a big hammer, It had obviously been down the road on both sides more than once, the wiring was hanging out from under the tank in big lumps of insulating tape and the standard exhausts were all but worn through. miraculously, it started. I resolved not to let appearances distract me from the mechanics of the beast and took her out for a test ride. Fortunately for the vendor, the roads around his house were very twisty and I never got the speedo to indicate more than 60 mph. It felt O.K. so I beat him down to 15O and rode it home. On reaching the motorway I cracked the throttle open expecting the exhausts to wail and the bike to hit the powerband and take off. What happened was that plumes of smoke trailed from the exhausts making me look like a low flying Red Arrow and the bike droned up to a maximum indicated 80 mph. Sfunny, I thought, My previous X7 was much faster than this. Nonetheless, the machine accelerated up to 60 ish fairly tepidly and after being without a bike for 12 months I was in seventh heaven. A complete bike with wrecked engine was procured for spares for a meagre 30 including delivery, and this payed for itself within 2 months as small items on the bike gave up the ghost, Like the exhausts (blew out where they had worn almost through), like the headlamp, (fell out and smashed), the Brake light switch, (stopped working), The clutch cable (snapped). It all seemed to point towards a bike that had not been used for some time.After all these minor niggles had been sorted out It was a fairly smart machine, But it still only did 80 mph. It was on one of the frequent visits up the speedo dial to see if anything had improved, that the first disaster struck. The engine seized solid and the GS550 that I was, er, following away from the lights disappeared into the distance. Fortunately it was only a 3 mile push home. On disassembly of the engine It was found that excessive bore wear had caused the poor performance and probably the seizure too, the machine had done 23,000 miles on its original bores if the mileometer reading was anything to go by. If I had to pay for a rebore and new pistons anyway, I reasoned, Why not have a little tuning work done at the same time. Financial considerations precluded going the whole hog so a modest stage one was procured from Terry Beckett tuning, Who did an excellent job and is always very helpful and patient on the telephone to jokers like me. The package arrived at 8:30 one morning and the day was taken off work to build the engine up. The reed blocks were bolted back to the barrels with standard reeds and the top end bolted back together, carbs on and off we go. She started first kick, would I feel the difference even at running in speeds ? I revved it up and started off down the road. No dice .. Tickover no problem, any sort of load on the engine and it died. Two desperate days and two rebuilds later I phoned Terry Beckett, who as I have explained before is very patient with idiots like me who cant put a simple piece of machinery back together in the correct way. Be patiently listened to the problem and then patiently, with the voice of an infinitely wise and patient man, explained that engines run best when the throttle slide cutaways in the carbs face in the correct direction, Try swapping them over, left and right was his advice. perfect.
I rode everywhere I could think of for two weeks, I followed random cars to their destination, anything to relieve the boredom of running in a small two stroke, then 500 miles came up and I cracked the throttle open.This was better! 100 mph came up 101, 102, 103, 104, 105 ... not bad for an old 250. all was well for 12 months, I put oil and petrol in it with the occasional NGK B9ES spark plug. Then for no reason at all she holed a piston, broke a ring and scored the bore. Back off to Terry Beckett went the top end with instructions for a stage two tune with the rebore and requisite new pistons. The parts came back, the traditional day off work was had and the engine was reassembled, taking care to place the correct throttle slide in the correct carburetter. .. And off we went down the road, not really any appreciable difference thought to myself, until I noticed that the bikes original reluctance to rev into the red had been replaced with the interesting habit of not wanting to spend any time out of it. Heh heh. !
About this time a number of things happened. Firstly, it was decided that a stage two tune ought to prove itself on the track. Forms were sent off to compete in an Amateur streetbike Drag racing competition, Secondly a rolling chassis was offered to me with good tyres and a Dream Machine paint job and fairing. Thirdly I decided to increase my chances of a good showing with a nitrous oxide injection kit. The bike was stripped down rubbed down and wheel and head bearings replaced. It arose from the ashes with fresh bodywork fresh paintwork new bushes and bearings throughout and a stage two motor with K and Ns and Micron micralloy expansion chambers after the required 500 mile running in period, the bike hit the Motorway on the way to Santa Pod and its first meeting, The nitrous kit had been bolted on but not used because the bottle had ruptured in transit (sic) and no one would sell me any gas. On the motorway the bike averaged 70 mph on slightly higher Gearing than normal (15/38 for those interested), with occasional forays up to 110 (indicated) which it managed with ease. When we stopped for petrol we found that the highly tuned 250cc two stroke had averaged 68 mpg. I was astounded. Ive never yet been able to better that figure but I have got close. Saturday morning dawned bright and sunny and I went off in search of somebody to sell me some gas. A supply was found at 4.00 to fill my 2 pound (avoirdupois) bottle, and we bolted it on and queued up to race. The feeling of butterflies attempting to dig their way out of my stomach with jack hammers is indescribable. The light goes green and with a big breath I gas it and sky the front wheel, off the throttle, front wheel comes down with a bang. Snick it into second and... wheres the bike I was alongside, Christ hes finished.. I know, hit the nitrous button, whooooooaaaaaaaaaaeey Whoooooooaaaaaaaaaeey, fourth, whoooooooooaaaaey, oh! finished lemnedoitagainpleasepleaseplease Queue up again while my chief mechanic goes to fetch the time ticket, 14.6 seconds at 85 mph. I dont know why, but I was expecting great things of the nitrous oxide. The truth is it does make a big difference, but on a drag strip that only translates into half to three quarters of a second. Anyway the whole point of using nitrous is for the incredible feeling it gives you. To cut a long story short the engine blew up that day with a neat hole melted in the piston crown. The fault was traced to a split in the rubber inlet manifold where it had been punched to take the nitrous injector. This was my first time racing, Id brought no spares, few tools and had ridden the bike there. The afternoon was spent driving around the surrounding towns in the Support car (girlfriends escort), collecting the parts needed. piston kit from one shop, inlet rubber from a breakers in Northampton, gaskets from yet another shop, we drove 60 miles to get everything I needed. Then, all that was needed was a top end rebuild in the dark, in a field, with drunk people falling over me, my chief mechanic and assistant, and the bike. To our credit it only took 5 hours and 18 cans of beer. three of those hours were spent looking for the small end bearing which had gone missing and could have been almost anywhere, It was found seconds before the search was going to be called off by dint of it slipping on to my little finger as I was crawling around behind some tents. At one point we had a number of complete strangers crawling around with us. Thanks for your efforts lads.
With the bike back together and running we claimed some well earned sleep and looked forward to the morrow, which dawned with a wet track and black clouds stretching as far as the eye could see. No racing today, and I had to ride the bike 200 miles home in the wet. When the motorway dried out a bit, I squirted some nitrous into the engine and it went off the clock in top. I estimate going on for 120 mph) Two years on the bike is still going, Its been repainted, and it runs a standard top end now. Shes been retired you see. All in all Ive owned an X7 for 5 years now in standard and tuned forms, and raced it for two of those years, with nitrous oxide. Encapsulated below are the accumulated wisdoms. The X7 crankshaft is quite strong enough to take all that I could throw at it. The crankshaft seals failed on two occasions when bits of piston were inadvertently left in the crankcases after a blowup. Even with some scoring of the barrels, the engine is quite happy to run a few more miles just by popping another piston in, cheapish at 12:99, getting rarer now though. If you use a reasonable two stroke oil, an untuned motor will go on and on. Even the stage two tune that I was running (sadly now defunct through wear, 6 pistons holed in the final bores before running out of oil scarred them beyond redemption), was very reliable with road use only.
The only bearings which wear out with any rapidity are the Swing arm bearings which seemed to only last 1000 miles, but since Ive stopped locking up the back end with struts these have been fine. Tyre wear is very light, even after burnouts etc. the metzeler ME77 on the back has lasted 7000 miles so far, looks like its good for another 7000 and was second hand when I got it. The front wheel spends so little time on the road that front tyre wear is minimal, although for the record it is new compound yokohama which matches the metzeler very well and makes it very stable. The original suspension components are not very good but Marzochis on the back improve the bike so much that it is only necessary to preload the fork springs by 5 mm. If you are going to put nitrous oxide on a two stroke, it is essential that the inlet side of the engine is totally free from air leaks. It took me years and uncounted pistons/rebuilds to find out. over 5 years INCLUDING the nitrous oxide kit and all spares and goodies, and the two rolling chassis, even down to all the spark plugs, but not including oil and petrol, the X7 has cost 1432.42 to run. I call that Value For Money.
Would I have another one ? Im not going to sell this one !
