GT250 AK project

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r5baker_
Still in the Driveway
Posts: 7
Joined: Wed Sep 23, 2020 9:51 am
Country: United States
Suzuki 2-Strokes: 1973 and 1976 GT250s

GT250 AK project

Post by r5baker_ »

Hi, I go by r5baker, a Yamaha forum name that stuck due to my first restoration. I'm new to the forum but drawn to 2-strokes.

I picked up a couple of new project bikes that are some deep basket cases and need a lot. I think the first is a '73 and the 2nd is a '76 both GT250's

https://photos.app.goo.gl/NmD699KpaRtCR1Za7
https://photos.app.goo.gl/DTtcMNj6M8u1AfZi6

Unfortunately the '76 motor is completely seized from what looks like water intrusion. The '73 looks actually very good after pulling the top end. I cleaned it up and put some new gaskets on to measure compression and was pleased with 122 and 124. I'm sure it needs new seals/gaskets and I'll probably have the cranked looked over.

The plan right now is to make one bike from two. I'd really like some decent pipes and bigger carbs to liven things up, but we'll see.

I have been looking around but have not found a good source for engine parts as these don't seem to be as popular as the old Yamahas.
r5baker_
Still in the Driveway
Posts: 7
Joined: Wed Sep 23, 2020 9:51 am
Country: United States
Suzuki 2-Strokes: 1973 and 1976 GT250s

Re: GT250 AK project

Post by r5baker_ »

This is a '71 R5 350 I did years ago that has an RD350 engine with a lot of Scott Clough's work on the top end. The pipes are his dimensions designed specifically for this porting configuration. The bike is also fuel injected based on an Electromotive TEC2 allowing for variable timing and temperature compensation.

https://photos.app.goo.gl/z7yCcnN4hEwhxELaA

I've had my hands on a few over the years fixing up toys to play on:

Suzuki JR-50
Kawasaki KD-80
Kawasaki KE-100
Yamaha Moto 4 80
Suzuki RM-80
Yamaha IT-250
Yamaha YZ-125
Yamaha R5's
Zunspec4
Expert racer
Posts: 1087
Joined: Tue Dec 16, 2008 11:37 am
Country: UK
Suzuki 2-Strokes: T500R, SV1000S, TS125, Seeley T500
Location: Trowbridge UK

Re: GT250 AK project

Post by Zunspec4 »

Hi r5,

A promising pair of project 250's. they're great machines :up: . Like the Yam too, the pipes look a bit individual compared to others I've seen for the R5. Any further info on their design ?. I'd like to hear about the fuel injection too, never seen those before.

Cheers Geoff
r5baker_
Still in the Driveway
Posts: 7
Joined: Wed Sep 23, 2020 9:51 am
Country: United States
Suzuki 2-Strokes: 1973 and 1976 GT250s

Re: GT250 AK project

Post by r5baker_ »

Here's a video of the R5 on the dyno back in 2015. There are a few photos of the setup which is all custom but based on two throttle bodies of a Yamaha FZ6R, throttle position sensor, fuel rail, WRX injectors, Walbro pump, and the TEC2 to control it all.

https://www.youtube.com/watch?v=qzVHgHJ9PWI

The pipes are Scott's dimensions that he developed in simulation. I then configured the layout, cut out the cone slices, and welding everything together. I think he uses the Vannik software for developments.

Cheers Eric
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jabcb
Moto GP
Posts: 4240
Joined: Mon Dec 13, 2010 4:32 pm
Country: USA
Suzuki 2-Strokes: 69 T350 thru 75 GT750
Location: southwestern Pennsylvania

Re: GT250 AK project

Post by jabcb »

You probably have the correct model years.
The 73 GT250 has a metal brake line at the caliper. Later models don’t use a metal brake line.
The 76/77 models have spigot-mounted carbs & no ram air covers. The headlight bucket is chrome on the 76 & black on the 77.

Use the VINs to confirm that:
http://www.ozebook.com/compendium/suzi/ ... /page1.gif
http://www.ozebook.com/compendium/suzi/ ... /page2.gif

Sweet R5 — that project was way beyond my skill set! :up:
Good luck with the GT250s & have fun.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
r5baker_
Still in the Driveway
Posts: 7
Joined: Wed Sep 23, 2020 9:51 am
Country: United States
Suzuki 2-Strokes: 1973 and 1976 GT250s

Re: GT250 AK project

Post by r5baker_ »

Hey jabcb, I like the look the look of your cafe'd 250. Very quality work. The rearsets you adapted really fit the bike well with the pipes.

When you disassembled the engine did you have the crank rebuilt or do any engine work? I am so tempted to have the top end ported a bit to enhance the performance on a set of pipes. Then again, stock can be good especially with the seeming limited sources of parts for these.

Have a good source for the seals/gaskets?

I have a lot to do but winter is coming - so many rusted solid fasteners...
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jabcb
Moto GP
Posts: 4240
Joined: Mon Dec 13, 2010 4:32 pm
Country: USA
Suzuki 2-Strokes: 69 T350 thru 75 GT750
Location: southwestern Pennsylvania

Re: GT250 AK project

Post by jabcb »

We did a complete engine rebuild. Used Suzuki OEM crank seals.
Unless you have some local two stroke crank expert, I would use Bill Bune: http://www.billbune.com

You can get lots of new & NOS Suzuki parts from your local dealer or an online discount dealer.
I use my local dealer & Partzilla: https://www.partzilla.com/catalog/suzuk ... aft-gt250k
2 of the crank seals are available there.
The 3rd is available on eBay — search for the word, “Suzuki” & the part number.

I use Suzuki seals unless I can’t get them.
I have not had good luck with older gasket kits.
eBay seller, cruzinimage_co, sells new gasket kits — I’ve had good luck with them.
https://www.ebay.com/itm/73-75-Suzuki-G ... xyPc5SCzR2
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
r5baker_
Still in the Driveway
Posts: 7
Joined: Wed Sep 23, 2020 9:51 am
Country: United States
Suzuki 2-Strokes: 1973 and 1976 GT250s

Re: GT250 AK project

Post by r5baker_ »

Pulled the engine over the weekend for the '76. Crank had water intrusion but got everything apart. I think the cylinders will bore out clean, but the crank has quite a bit of rust on the disks. Can a rust crank be saved or is it better just to find a donar?

https://photos.app.goo.gl/H7Euo2MyoSbc1HT18" onclick="window.open(this.href);return false;

Is there much advantage to running the '76 with the extra boost ports? The factory rating was only 1-2hp more but is there more potential with this configuration?

Anyone running the Vannik software and do some modeling with these engines and a set of pipes? I'd like to do some porting and add a set of matched pipes and was looking for a known good configuration. I may have to just buy a copy and model it.
User avatar
jabcb
Moto GP
Posts: 4240
Joined: Mon Dec 13, 2010 4:32 pm
Country: USA
Suzuki 2-Strokes: 69 T350 thru 75 GT750
Location: southwestern Pennsylvania

Re: GT250 AK project

Post by jabcb »

The 76 trades less bottom end for more top end. Which is better depends on your preference.

For more better, you may be able to turn your early GT250 motor into a T350 motor.
That would require T350 cylinders, heads, carbs & exhaust.
This has been done to T250s. Not sure if it can be done to GT250.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
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