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Building a cheap dragbike

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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Greetings All
I am building up a cheap dragbike for a beginner racer. I have an old 78 gs 750 in the garage. I will line bore and re-ring the motor, do a good port job on the head, install some modern carbs (34mm cv's?) and a sidewinder pipe. The neck will be raked and the bike lowered and the whole thing will be lightened to under 400 lbs. I just want a strong reliable motor that will start and idle normally.
Any other internal engine mods you would recommend? Do these carbs sound right? All suggestions are appreciated.

Thanks, Paul
 
Hi Paul,
You shoud probably see how much you can buy a used GS1100 drag bike for. It may be withing a few grand of what you are going to spend on your 750. If you don't like that idea you could get an electronic ignition so you can rev the bike until it blows (without having the points bouncing about) and look into some new cams. People seem to like to "degree" there cams too but I don't know what this means. Most of the guys here like to modify their gear boxes for racing as well.

Where are you in Ontario? If you live in Ottawa you'll have to let me try out the bike in the spring. :)

Steve
 
Check for maybe a wisco piston kit. Leave the porting to the profesionals If you don't know what you are doing you can hurt preformance not help it. You are going to be at idle or wide open throtle, use the slide carbs to get you started. GS1000 did 154mph with them. Definatly go with a electronic ign. Manual cam chain tensioner is also a must for drag racing. cams can be degreed if you are looking for every ounce of power, what this does it to put them in the exact position called for in the blueprints. due to production tollerances they could be off slightly. You could also advance or retard them to change the power band/ move it up or down in the rpm range. Unles you know what you are doing set them to stock specs. Transmission gears are back cut?? Not sure exactly Less likely to miss a gear shift? Leave the neck alone, you will be looking for a new frame real quick. get an extended swingarm to help with traction an to limit wheelies. sometime they even put 5-10 lbs of balast on the front axel to keep the front down. There is nothing cheep about building a drag bike. SPEED COSTS MONEY / HOW FAST DO YOU WANT TO GO
 
Nasty, it is true you can buy a very nice drag bike cheeper than you can build one Don't even think about trying build that 750 go to (dragbike.com) then to photo classified you can get a good GS1100 drag bike that will self start for a beginner get a stock top end with a welded crank,under cut tranny,slider clutch,air shifter,two step,Dana ing.and coil shift lite with a crossover delay box and you will be set to compete as you get the need to go quicker just build the top end you should't have to spend more than around $4000.oo for a real nice one that will run 9.90's in the 1/4 mile. I have seen some good ones as cheep as $2000.oo


OHH YEA don't forget the wheelie bars or training wheels or what ever they call them things hanging off the back of the bike once you learn to ride you won't need them there just extra weight you only need wheelie bars to go in the low 7's like prostock

just my 2 cents
 
Now isn't there a universal law that says you cant have the words "Cheap" and "Dragbike" in the same sentence? Sort'a like that George Carlin line about Jumbo Shrimp!
GY
 
Hi everyone

Yea, cheap and dragbike are two words that can never be put in the same sentence. LOL. Anyways, I know I could buy a dragbike cheaper but I do have experience in bike building. I think the main reason I want to build is because I already have a reasonably good basis. A good stock 78-750 motor. Also because I can purchase parts as I can afford them and not have to pay out several thousand at one time to buy a bike already built. There's also the thing that if I bought it in the U.S. I would have to import it and there's all kinds of headaches there.
I can do most of the work myself, raking the neck is easy enough. (I can weld) and I won't even be using an extended swing arm if I have wheelie bars, I don't think I'll have enough power to worry about.
If I build my own wheelie bars and use as many stock motor parts as possible, all I should have to pay for is my electronics, and you see lots of that stuff used on the net. Also some expence for welding the crank and back cutting the tranny and the air shift . Here in Canada we must be more resourceful due to the cost of importing and the exchange rate.
Does anyone have any more ideas?

Paul Jones
www.nastyracing.ca
 
I don't think there's anything wrong with going this route. If you find that you need more speed one day, you can always drop in a 1000 or 1100. You'll have a chassis already. many racers use "mule motors" to dial in their chassis', so learning to drag with a 750 wouldn't be a problem in my book. Now for the fun stuff I would recommend; electronic ignition, rev limiter, hot coils, straight pipes(you can make 'em yourself), hone and rings, head port/polish, slotted cam sprockets(for degreeing), and mill the head for 12 to 1 compression. If you decide to swap motors, the 750 with 12/1 compression can still run on pump gas which could make a killer street bike, or you could sell it. more compression could make it hard to sell cause nobody wants to buy VP for their street bike. I wouldn't worry about new carbs unless you get a good deal on some flatslides. however, if you port the head, your carbs will be the choke point in your intake. straight cut gears won't be necessary with this motor unless you turbo or nitrous this thing. a welded crank would be nice but its not necessary if you keep your rev limiter at a reasonable level. One more thing is buy the suzuki clutch discs. nothing is better.

Have fun.
 
Cheap Dragbike

Cheap Dragbike

A "cheap" dragbike is possible!!! I bought a stock 82 GS1100e for $1200, I have no more than another $200 into it. Still street lagal, run high 10's, and win races (that's the important part!)!!! From my experience, the first things I would do if I was in your shoes again, before running the bike, weld the crank (my exploded), and get a Falicon backing plate on your clutch hub (that grenaded too - not a pretty site when you open the case). Stock Suzuki clutch plates work best, I used Barnett in my last drag bike, and they pulled me through the lights when I brought up the R's. I have seen some nice somewhat stock 750's do some damage to the faster, bigger bikes. My brother in law won the track championship three years in a row on a bone stock, nasty looking CB750 Honda running 14's. That was a free bike that leaked fuel from the floatbowls and was just the nastiest roach you'd ever seen. I think you'll do fine with the 750, be resourcefull like I have been, go to your local track come spring, and get parts from fellow races, or online like I have, make your own when you have too. GOOD LUCK, AND KICK SOME A$$!!!!!
 
Cheap Dragbike

Cheap Dragbike

A "cheap" dragbike is possible!!! I bought a stock 82 GS1100e for $1200, I have no more than another $200 into it. Still street lagal, run high 10's, and win races (that's the important part!)!!! From my experience, the first things I would do if I was in your shoes again, before running the bike, weld the crank (my exploded), and get a Falicon backing plate on your clutch hub (that grenaded too - not a pretty site when you open the case). Stock Suzuki clutch plates work best, I used Barnett in my last drag bike, and they pulled me through the lights when I brought up the R's. I have seen some nice somewhat stock 750's do some damage to the faster, bigger bikes. My brother in law won the track championship three years in a row on a bone stock, nasty looking CB750 Honda running 14's. That was a free bike that leaked fuel from the floatbowls and was just the nastiest roach you'd ever seen. I think you'll do fine with the 750, be resourcefull like I have been, go to your local track come spring, and get parts from fellow races, or online like I have, make your own when you have too. GOOD LUCK, AND KICK SOME A$$!!!!! :twisted: :twisted:
 
Just my 2 cents worth but here goes. If you're lowering the bike, eliminate the rear shocks and make some struts to replace them. No need to waste horsepower thru suspension compression or extension. Go with a 1000 or 1100 rear wheel for wider rubber unless you go with something fancy. Make sure the clutch basket is solid or you have a weak link. Rev limiter is nice because you can powershift without the overrev kaboom situation happening. If you can get an old header use it and just use the headpipe and make an extension in place of the baffle end. You can also tune it so to speak by smearing it with grease and cut the pipe where the grease stops burning off. A little low end torque trick I've used. Other than that it sounds like you've got it pretty much figured out. KICK A$$!!

Jon Kram
________________________

81 GS750EX and proud of it!!
 
Yea, these bikes are torquers not hi-revvers, so shift light will be set at 9000 rpm. I'll probably get the crank trued and welded anyway, it only costs 40-50 bucks and the motor is already apart. I have a header and will use a clutch basket and stock clutch plates from a gs1150. Also back cut the tranny. One thing I am considering is ceramic coating on some engine parts, pistons, valve stems. etc. Has anyone any experience with this? I can get everything done for about $200. This is supposed to help both power and longevity.Then I'll do the port and polish, you can do this at home if you only smooth out the ports and remove a little material. It really woke-up a 85-750es I owned. That would be it for the engine mods. How much can I plane off the head? Obviously, I still need to use hi test pump gas. Everyone's suggestions sound great so far.

Paul
 
Hi Paul,
who would you have weld/true your crank? I just bought an 81 1100E and it'll need that done at some point.

Actually, as Canadians I think we should spend a little bit of time to put together sources for good parts and work. I have no desire to order everything I want across the border.

I have been told Niagara Race Crafters in Virgil Ont does good work on GSs although they never mentioned that to me I was there.

Thanks in advance, Steve
 
porting

porting

Nasty, I say go ahead on the porting of the heads, polish the exhaust, but don't touch the intake side after porting. If you polish the intake side you'll pool up fuel. Found that out the hard way too. Little tip.
 
Since this engine is only getting mild mods, I won't be doing much internally. What I do need to know is how much should I take off the head? I have heard up to .30 thou. What do you experts say?
 
I'd strongly reccomend a rev limiter. Not so much to stop you over revving
it , but to act as a saftey net in case of a missed gear, gear popping back out and into neutral, or even breaking a drive chain. Some serious engine damage can occur in these situations making your cheap drag bike suddenly quite expensive, not to mention the inconveniance.
Get some good after market valve springs at least, and cams if you want to spend the extra. These made the single most biggest improvement in performance after much work on my bike.

Another tip, get a spare engine or two for pinching parts from as you need them.
 
GS 750 is a good place to start. Already has straight cuts, big plus. Do the crank, then concentrate on basics, good valve job, ring seal, valve timing, ignition timing etc. Cams and compression will give the most bang for the buck as you grow with it. If I remember correctly GS 850 cylinder and pistons will fit. A friend of mine has been drag racing a GS750 based bike for more than ten years. Even though there are easier ways to go real fast he insisted on the 750, it is currently capable of running mid 9's (only the lower end is still from a 750). Another testament to the strength, is that Suzuki used the 750 as the base for their 1000cc superbikes in the late 70' early 80's.
 
Hey GTM
Yea, the 750 is plenty stout enough for the rigors of dragracing. I would like it if someone had a good set of hi-c pistons for sale. The 850's will give me some more displacement, but not much increase in c.r.
How about it friends?
Paul
 
Using a '78 GS750 as the basis for a drag bike is not a bad idea, especially if a good one is readily available. There is a wealth of used parts available and many things that interchange with the GS1000-1100 or can be easily retrofitted. Additionally, the straight cut primary drive is already in place, kickstarter allows removing entire electric starter and charging system and there are many donor 850cc cylinder blocks available. My strategy would be to make it as light as inexpensively possible, make it reliable and consistent, then make it as fast as inexpensively possible. I recommend the following:

Chassis: Use spoke wheels (GS1000 has alloy rim for front; add WM6 rim on back with 5.5" slick) instead of the heavier mags with a single disc brake on the front. Extend the stock swingarm 3-4", install struts and a wheelie bar, leave the rake alone and shorten the forks to maintain a level chassis. Remove as much of the unnecessary stock components as able. Objective is long, low, rigid and as light as junkyard parts allow.

Engine: Weld crank, install HD springs in backing plate and weld stock clutch basket on back to fuse rivets and backing plate, HD springs on clutch pressure plate, remove flywheel and starter components (kickstart only), install 850cc cylinder kit from a shaftie, mill head .020" and freshen head with valve clean and lap and new valve seals, modify stock cam chain tensioner to make manual (30 minutes and no cost), degree cams for best power, Dyna S ignition and coils. Add stock GS1000 cams if they gain anything (I've got free ones if you want).

Miscellaneous: 4 into 1 header is a must, rev limiter optional (if you are sure of your shifting), air shifter optional (if you are sure of your shifting), 29mm Mikuni Smoothbores would be a definite plus (can be pricey but always worth their cost to resell when done with them), velocity stacks, new battery and new chain.

It can be done inexpensively without being cheap. I know because I've done it. Many of the parts can be bought used and later resold for near what you paid if maintained. This includes carbs, rear wheel, wheelie bars, etc. Once this combination is dialed and your ready to go faster I'd add nitrous. Or change to a GS1100 motor. No return on the cost of pricey pistons, porting, cams etc. on the 2v GS750, IMHO. Good luck.
 
I disagree with adding nitrous. Ive had nitrous on my 1150 for 16 years and found at the dragstrip the inconsistanty in et's with nitrous hurt me in bracket racing. if i wanted to be consistant and wanted to run close to my dial in i did not use it , but if i got behind due to bad launch or wheelspin or wheelie I would use the nitrous to make up lost ground . This only worked out for me a few times and usually didn't . and nitrous can be tough on parts (just had to install new cylinders due to nitrous wear and tear)
 
Speaking from experiance GET A REV LIMITER, one missed gear and your whole season (and a whole lot of work) can be left in tatters. 12,000rpm on an '82 1000Katana is not to be recomended :cry: :cry:
 
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