Restoring a '75 GT750!

[pearljam724]

I agree with Richard with his explanation. If you are after the stock look, by all means the stock exhaust is the way to go.

For performance and sound I like the Jemco's. That said I have found that the single biggest performance gain that I have seen is gearing. These GT's (and mainly the later ones) are way over geared if you are wanting any kind of straight line performance. After my first ride on a Buffalo, I instantly had this feeling. For mostly around town riding with maybe a little countrcruisingng, a lower gear will really wake the bike up.

Absolutely, the best modification anyone can do to any bike. Especially, a two stroke that does not make much power in the low to mid rpm range. All bikes are geared high from factories. The GT 750's are ridiculous.

How many teeth for the front and back sprockets would you recommend?

What Ring_Ding said. Sprocket gearing vary on the 750's from model to model. Mine is the same as the teeth count he mentioned. I'm dropping one tooth in the front to improve torque at low to midrange rpms. I don't want to lose a lot of top speed. Therefore -1 on the front sprocket only. Is very suitable for my needs. The 76 750 is geared extremely high at the rear sprocket. Which improves fuel economy and top speed on a bike that simply does not produce good fuel mileage by todays standards. Therefore, I don't want to change the rear sprocket teeth count for those reasons also.

[Toast]

Was able to pull the pump and lines (octopus I'm told?) today following suggests from this forum. You guys are a great resource!

Everything looked pretty good. I rotated the pump a few times with the supply line still connected and got oil out of all the outlet ports. The oil was a little reddish. Is this something that happens to 2-stroke oil when it sits for a while? The octopus also got cleaned and re-filled. I'm thinking I'll swap the old oil for some fresh stuff before I give it a run. I'm hoping the initial run happens in the next week or two!



ooh, one more question. Are the o-rings different sizes? I tried to match them back to the port they came off b/c they looked to be different. Not 100% sure if I got them back where they should be.

[Toast]

So seeing that my thread has a bunch of boring, non-glamorous photos so far, I'll add a few shots of the other (and currently envious) Suzuki ride. Hey, its my thread, I can do what I want.







The Pacific North West is a great place for a dual-sport!

[tz375]

O rings are all the same. make sure they go in the oil port holes and not the mounting screw holes. And be sure that you don't drop the drive pin. Oil does oxidize given enough time, so if the oil is years old, I'd drain the tank and replace it with fresh oil - just to be 110% sure.

[pearljam724]

Where do you rotate the pump ? Do you turn the cylinder at the top, directly under the pump lid or where the cylinder attaches to the octopussy ? I read a couple articles about testing to see if the pistons are sticking. But, those articles I found to be a little vague. Can you use a nail set and try to gently push the pistons ? To verify that they are not sticking. Also, should the ends of the pistons be nearly sticking out of the holes at the bottom of the cylinder ?

[tz375]

I would point you to the Pinkpossum.com site, but the hosting company seems to have a problem (still).

The shaft sticking out of the bottom can be rotated by hand or by removing the drive pin and use a pin punch or long piece of stiff wire.

That shaft is part of the plunger assembly and the pistons are inside that plunger ass'y, inside the main casting. It's not possible to see them without stripping the pump. If oil discharges form all 6 outlets it's unlikely that one of the two pistons are stuck.

[pearljam724]

I would point you to the Pinkpossum.com site, but the hosting company seems to have a problem (still).

The shaft sticking out of the bottom can be rotated by hand or by removing the drive pin and use a pin punch or long piece of stiff wire.

That shaft is part of the plunger assembly and the pistons are inside that plunger ass'y, inside the main casting. It's not possible to see them without stripping the pump. If oil discharges form all 6 outlets it's unlikely that one of the two pistons are stuck.

Thank you, for clearing that up. The writer mentioned resistance needing to be felt. Where should that resistance be ? Once you turn the shaft ? Sorry, for the thread jack.

[tz375]

As the plunger and shaft rotate, the top surface of that plunger is shaped like a face cam and it rubs on a pin in the top cover forcing teh plunger to rise and fall - hence pumping the oil. The more the lever is rotated, the further the plunger will reciprocate as it rotates. That's where the resistance comes from and it's why the lever will not always return . It's "sticky" nature is when the plunger is on the cam.

Once you wee one in parts, it's easy to understand.

[oldjapanesebikes]

I would point you to the Pinkpossum.com site, but the hosting company seems to have a problem (still).

I have some of Richard's material mirrored at this link:

http://www.oldjapanesebikes.com/fieldgu ... lpump.html" onclick="window.open(this.href);return false;

[Toast]

Anybody have experience getting parts from knkcycles?

[pearljam724]

Anybody have experience getting parts from knkcycles?

I recently bought my tank pin stripes from them. Can't speak for accuracy or quality as I'm several months away from paint and yet to open the box. I could speak of one displeasure. But, I'd rather keep it to myself. Their website is worthless, other than contact info.

[Toast]

So between moving and my computer crashing, I haven't had a lot of time to work on the bike or post anything. However, I was finally able to get the bike together enough to do an initial run. Everything seemed to work fine. I am surprised how quite it is... guess I'm used to loud 2stroke dirt bikes. So, as per the Hayne's manual, I have the mixture screws out 3/4 of a turn from bottomed. Is there a technique to fine tune the mixture that doesn't involve a synchro gauge set? Also, is turning the mix screw in leaning or enriching? Here's what it looks like as of tonight. I'll post a video once I have a good one.

[pearljam724]

There are a few ways to synch the carbs without a manometer. You can easily make one, bench synch ( carbs not on bike) or by allowing the bike to idle on one cylinder and adjusting that cylinder accordingly. Here's a good reference site, if you have no manual. http://www.oldjapanesebikes.com/mraxl_G ... cover.html" onclick="window.open(this.href);return false;

[RING_DING]

I use the method described on Page 16 of that reference site (the Suzuki on-bike method) and I've found it works very well. I do a final check with a manometer and it is usually spot-on.

[pearljam724]

Ring Ding, prior to putting the carbs back on the bike. Did you adjust the pilot screws at a 1/4 turn like the manual suggests ? Reason I ask, I've read several other write ups stating 3/4 was the way to go.