GT750 Drag Bike

rngdng · Post by **rngdng** » Wed Apr 29, 2009 4:59 pm

Kevin,

What year cylinders are those? The indentions for "Liquid Cooled" stickers would say 74 or later, but the flanges for the carbs?????? If you added those, you managed to get them to look like factory-original.

Lane

water cooled · Post by **water cooled** » Wed Apr 29, 2009 6:00 pm

Lane,

Yes, that's a 1974 cylinder block. I milled the back of it to change the intake angle so that 36 and 38mm Mikunis would clear the clutch hub. There is an aluminum adapter plate that was fabricated to allow the flange style mounts. It came out pretty good.

The barrel and cylinders have been modified and now lifted a bit higher...compliments of Cometics.

Kevin

tz375 · Post by **tz375** » Wed Apr 29, 2009 11:27 pm

Kevin,

You are making great progress. the bike is losing weight and making more power.

I can't find my handy dandy calculator for ET, but those H2's must be making a truck load of HP to get in the 9's and must be really light.

So the plan for next year is 120HP in that superlight chassis with a lightened crank, tiny Carbon fiber tank cover over a 4 liter alloy fuel tank, electric water pump with LC radiator to reduce weight, titanium axles and other hardware, lighter front forks, chrome-moly wheelie bars (if they are mild steel), alloy wheel bearing spacers, straight cut primaries.

Then we need a lock up clutch. Do you have an ignition interputer on that MRE air shifter for full power clutchless shifts?

Don't worry, I'll always be able to think of new ways to spend your hard earned money.

Phase two, we have go radical with gastric staples or wired jaws to reduce eating.

water cooled · Post by **water cooled** » Thu Apr 30, 2009 12:30 pm

I got the frame back from the welder this morning and we added the steering limit, new seat pan mounting straps, new battery box, air bottle shifter bracket and new tab locations for the MSD. I dont know what an ignition interpreter is but I don't believe the MSD multi-channel is designed necessarily for an airshifter. However, that said, Bill Baxter runs one on his world-class H2 with a shifter so there is a way to do it.
I dont think I want to kill power to the box since the ignition is retarding on a curve as the rpms increase. So shutting the box off might start to do some strange things to the curve. Bill offered to help me when the time comes so...I will need to contact him and see how he does it but I suspect, I would want to interupt the coils rather than the box.

As far as weight reduction, I have a better idea than wiring my jaw shut...my son only weighs 157 lbs and he has lightning fast reflexes. I just need to figure out how to keep my wife from finding out that I intend to stick him on this bike and have him take it down the track.

She has been cool to the idea of motorcycles since our last trip to the Medina hospital when his YZ250F got out from under him on a jump.

tz375 · Post by **tz375** » Thu Apr 30, 2009 6:27 pm

I'm sure Bill can help you wire up the quick shifter electronics.

Never mind the son, go straight to the lightest person in the family - your wife. Some of the fastest racers on teh drag circuit are women.

Just sayin'

water cooled · Post by **water cooled** » Wed May 13, 2009 10:39 am

Here are some updated images of the progress. Got the engine back in the frame, ran a compression test and then took the engine back out. Found two very small chips of gasket material sandwiched between the case and the first base gasket. Cleaned everything up, installed a new Cometics gasket and got the engine back in the frame. Started the enigne and chased 3 or 4 issues with the carbs and some wiring. I installed the copper exhaust gaskets from Cometics and used the VHT Silicone to finish off the installation of the exhaust pipes. Reprogrammed the MSD for a tighter ingnition curve to retard timing slightly at the higher rpms. Started installation of the air shifter components, located the fill valve on the oil pump cover, and shift solenoid near the MRE cylinder (not shown). I'm working on the wiring logic for the air-kill solenoid and will install that once I make a decision. Still a lot of work to do and I have given up on the idea of painting the bike before the race at Martin in mid-June. That may get done before Norwalk in October...anyway...here is where Im at.

water cooled · Post by **water cooled** » Wed May 13, 2009 12:34 pm

Getting ready to install a momentary switch on the left handle bar for the shifter. Need to cut some of the grip flange away for the thumb to have unfettered access to the button. I dont remember using anything sticky when I put that grip on but it sure doesnt want to come off. I think I need to drill a hole in the end of the rubber to let some air in before it will slide off.

water cooled · Post by **water cooled** » Wed May 13, 2009 1:16 pm

Here is a video of the bike startup. The engine has not been tuned yet...

http://www.youtube.com/watch?v=IC-g9NNx8KE

Still, more work to do before it is ready.

jaybob · Post by **jaybob** » Wed May 13, 2009 2:20 pm

Kevin, you do nice work!! I know you have spent many hours on it. I can't wait to hear about the results in your terminal performance.

BTW....Can I have your garage floor?? Please?

rngdng · Post by **rngdng** » Wed May 13, 2009 5:28 pm

From the seat's reaction to RPM, I'd say you have the classic GT750 2000 RPM shudder! I love it. It sounds just like BlueBoy, and that's a good sign in my book.

Lane

water cooled · Post by **water cooled** » Tue May 19, 2009 6:49 am

In the video posted above, you can hear a sharp snap or pop. That snap only occurs consistently in the middle pipe and occasionally, on the left pipe. I'm pretty sure that a fully tuned engine would produce that sharp snap on all three cylinders on every revolution. The cylinders are accurately timed the same so what creates that sharp snap and how do I get it consistently across all 3 cylinders?

tz375 · Post by **tz375** » Tue May 19, 2009 2:37 pm

Lane has more experience with those pipes than I.

There are many possible explanations depending on exactly which pop you are talking about.

The faster an exhaust port opens, the sharper the exhaust crack, so if one exhaust port has a softer more gentle top curve in teh port roof, if will sounds softer.

Slight differences in carburation from one to another due to tolerances or adjustment, might make a difference as would slightly different timing. If one cylinder is slightly later than the others it could make a difference.

next is unburned fuel popping in the pipe.

Next is marginal differences between the pipes. If one was longer or shorter than the others, that could make a difference too.

Overall it sounds "lazy" to me in that video. I would have expected a sharper, crisper response when you blip the throttle. Almost as if the timing is retarded or the carburation is off slightly.

Maybe Lane can add some insight or Suzukidave who has a set of modified Bassani pipes on the yellow GTXR.

Ogri · Post by **Ogri** » Tue May 19, 2009 5:19 pm

water cooled wrote:Getting ready to install a momentary switch on the left handle bar for the shifter. Need to cut some of the grip flange away for the thumb to have unfettered access to the button. I dont remember using anything sticky when I put that grip on but it sure doesnt want to come off. I think I need to drill a hole in the end of the rubber to let some air in before it will slide off.

Blow compressed air in between the grip and the bar. Lightly pull on the grip and it will come right off. Install the same way. It works well.

water cooled · Post by **water cooled** » Tue May 19, 2009 7:39 pm

Well, I programed the MSD ingition to retard 20 degrees at start up. I misunderstood the function of that switch setting. MSD advised that the ignition will not go back to the static setting (or the next programmed setting until after 1800 rpm...so you were correct. It was idling at 4 degrees BTDC in the video and then, once I gave it the goose, it went to 23 degrees and then to 22 degrees at 8000 rpm, then hit the rev limit and suttered there.

I reprogrammed the MSD box this evening and started up again. It sounded much better and the throttle response improved noticeably...but unfotunately, I spent the balance of the evening chasing a coolant leak and an oil leak on the breaker housing. When I started it back up, the RH cylinder was not operating until I got the rpms up above 2k, below that, I had spark but no combustion...I'll need to look at the carb in the morning. uuuurgghh. It seems like I cant move ahead fast enough.

Thank you guys for the advise...Ogri, I got the handle bar grip off and was able to install the Pingel switch. Great technique. I was tempted to cut it off and buy a new one. Thanks for helping me on this one.

Kevin

tz375 · Post by **tz375** » Tue May 19, 2009 9:01 pm

Kevin,

You are headed in the right direction. That carb is probably dirt in the slow jet or the slow jet outlet. Clean that up and you should be good to go. make sure the air jet is also clear.

An trick i use is to take two supposedly identical carbs and spray carb cleaner through the circuits one at a time on both carbs. Compare the flow from one to another. If they are more or less perfect, move to the next circuit.

9 times out of 10 you will find one that seemed OK (with no reference point) until you compare it to it's partner and the difference shows up.

GT750 Drag Bike

Progress

Pre-tune start up