After only 12 hours on the rebuild i lost compression on the track. Just wanted to give a shout out to eric gorr racing. Although a twostroke engine has less moving parts than a fourstroke engine, a twostroke is a complex engine because it relies on gas. Build a factory race replica or maximize your stock motocross or offroad bike with expert techniques from tuner and columnist eric gorr. Zero problems so far in 2 years of ridingracing and eric always answers the phone when i call i try to get him first thing in the morning, before hes involved in anything. Book two the iremonger trilogy by edward carey 1au. Motocross and offroad performance handbook motorbooks. The operation of basic twostroke and fourstroke engines diagnosing mechanical, fuel, and electrical problems replacing parts, oil changes, engine tuneups, belt replacements, and more small engine repair for dummies is a plainenglish instruction manual for anyone with the. Tuning suspension is explained in detail, describing everything from changing fork seals and replacing shock springs to revalving and adjusting the compression and rebound damping. At high rpm, the engine needs a shorter effective stroke, longer exhaust duration, greater. Big bore by eric gorr tech helprace shop motocross. A myriad of different aftermarket accessories is available for you to custom tune your bike to better suit your needs.
Download yamaha 2 stroke ob 2 250 96 98 ebook in pdf, epub, mobi. Eric gorr is the author of fourstroke motocross and offroad performance handbook 4. The parts unlimited 2014 street catalog is more than just a book. Bigger carburetors, higher compression ratios, altered port timings and expansion. Buy motocross and offroad performance handbook motorbooks workshop 3rd revised edition by gorr, eric isbn. The most common mistake is to choose the wrong combination of engine components, making the engine run worse than stock. At low rpm, the engine needs a long effective stroke, which results in a high compression ratio. Fourstroke motocross and offroad performance handbook book.
In the model tuning tips chapters of this book, all the head specs quoted have msv ratings. Dirt and the author of motocross and offroad performance handbook, 3rd edition, also from mbi publishing company. Basic 2stroke engine tuning information joe hunt rc. The twostroke engine is widely used in both motorcycle racing and kart racing, and in very large numbers in model car, boat and aircraft competition.
The effective stroke is defined as the distance from tdc to when the exhaust port opens. Ive got an eric gorr 265cc 2000 cr engine in my 02 with his mo better porting. Ill try and get the ball rolling in here with a list of books i currently own on 2 stroke engines, and 2 stroke engine performance tuning. Porting for the following models, according to the specs of eric gorr, can be read about in his book. Its astounding how much more responsive and powerful it is than a stocker. Engine rebuilding transmission rebuilding clutch repair and rebuilding bigbore kits cam kits and valve timing and.
Fourstroke motocross and offroad performance handbook this thorough howto manual helps the offroad motorcycle enthusiast get the most out of their machine. It is designed to help you and your customers get the most out of your passion for powersports. It showcases the new, exciting, indemand products, as well. Two stroke tuners handbook 2 another mistake commonly made, sometimes even by those who have enjoyed some success in modifying two stroke engines, is to believe in a kind of mechanistic magic. Squish band width calculation on head motor 2 stroke. Custom built honda cr 450r two stroke by eric gorr and fmf eric has given authorization to post his response to a recent email conversation a thumper talk member had regarding his cr250 case reed engine big bore kit. Changing the power band of your dirt bike engine is simple when you know the basics.
Pdf motorcycle tuning two stroke download full pdf. Pete fl talking to one of the champ car mechanics and we were on the subject of 2 stroke versus 4 joke for racing. The following is an explanation of the basic operation of the twostroke engine. Eric gorr is famous for being an expert in 2 stroke posting. Eric gorr 144 kits full engines i rode the thing for about 1 month and realized that i am just not ready for the power that the thing puts out. I recognise that eric gorr is a world class expert in the area of motorcycles and 2 stroke engine mechanics, but anyone can make a mistake. Fourstroke engine rebuilding and tuning suspension setup and tuning carburettor jetting setup tips for latemodel motocross and offroad bikes from cover. Fourstroke motocross and offroad performance handbook. In the model tuning tips chapters of this book, all the head specs quoted have msv ratings designed for the intended power band changes. Basic 2 stroke tuning by eric gorr changing the power band of your engine is simple when you know the basics. Rev box to recurve the ignition timing 23 degrees advance tdc, portpolish intake and exhaust, head shaved.
He claims i rode the motorcycle for a year and this happened due to use, however, i did not get to ride the motorcycle very. Motorcross and offroad motorcycle performance handbook. Geared specifically for gp and kart racers, this hardcover treasure has turned out to be a great reference source for questions on the logic and concepts that pertain to tuning a 2stroke for maximum performance. If a twostroke engine could retain the same percentage of air, they would be twice as powerful as a fourstroke engine because they produce twice as many power strokes in the same number of crankshaft revolutions. Fourstroke motocross and offroad performance handbook motorbooks workshop ebook.
Motorcross and offroad motorcycle performance handbook by. Finally got out in a race with eric gorr tuning and did a very quick confirmation video. Fourstroke motocross and offroad performance handbook by kevin cameron, eric gorr and ron hamp 2011, paperback at the best online prices at ebay. He has served as a tuner for american and european offroad racing teams, and he resides near chicago, illinois. So i bought a cr 125 on cl and have been rehabbing it to get it in good shape for this coming season, once i am confident enough in my riding skills ill move up to the 450 again. Eric gorr author of fourstroke motocross and offroad. Pdf two stroke motorcycle engine maintenance and repair. Follow colton into garage 93 for episode 1, as he goes allin on his twostroke dream build and gets it dialed in for the fastest party in town.
Four stroke motocross and offroad performance handbook motorbooks workshop jul 10, 2011. I was really out of shape and the course was slick due to them being years old orv trails that had been. Second impression cylinder porting by eric gorr race. The most common mistake is to choose the wrong combination of. Topend rebuilding is the most frequem and cmtiy service romine on rwo stroke. Technology, properties, performance, and testing astm manual series, mnl 37 from brand. Fourstroke motocross and offroad performance handbook by. Basic two stroke tuning by eric gorr i think internal. Buy fourstroke motocross and offroad performance handbook motorbooks workshop by gorr, eric isbn.
Mini motocross and pit bike performance handbook by eric gorr 2008, paperback at the best online prices at ebay. Anyone interested in doing their own engine porting, or taking the time to learn the intimate secrets of 2 stroke engines should take. The mechanical simplicity of the twostroke engine gives it tremendous appeal, and makes it a tempting target for tuning operations, but the key to successful design, development and modification. Everyday low prices and free delivery on eligible orders. At high rpm, the engine needs a shorter effective stroke, longer exhaust duration, greater timearea, and a lower compression ratio. Eric gorr, who runs the highly respected motorcyclemodification shop forward motion and its companion website, is dirt riders dr. Meanwhile, eric gorr in his book 2 stroke top end and performance head squish band with a width of 60 % of the bore piston and compression ratio 9.
Eric gorr porting motorized bicycle forum motored bikes. Got home and found it broke the top piston ring at the exhaust port. Topend rebuilding is the most frequem and cmtiy service romine on rwostroke. The difference between twostroke and fourstroke carbs. First published in 1996, eric gorrs guide to maximizing stock motocross and offroad motorcycles and building factory race replicas has become the definitive work on the subject. An excellent academic book on the theory behind performance tuning for 2stroke motorcycles. Two stroke tuners handbook 2 another mistake commonly made, sometimes even by those who have enjoyed some success in modifying twostroke engines, is to believe in a kind of mechanistic magic. This onestop reference covers everything from basic maintenance to performance modifications, including. I throw the bullshit card eric gorr did all our super mini motors, mod 85s and our cr 144. Last winter i sent my cylinder to him for repair and plating. Because i am new to 2 stroke motorcycles, i trusted eric gorr at forward motion racing, and against my better judgement i installed the piston and cylinder when i could just feel by moving it around in the cylinder bore the piston was very sloppy and had too much clearance.
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