GT380 Pics

[Tripleking]

Pics of my 75 GT380 after paint.

[Coyote]

Nice! I am about to acquire another GT550. I like that seat. Info?

[Tripleking]

Previous owner had the seat installed. I believe it is one of the seats made in Vietnam and is based on the factory seat pan.

[Craig380]

Sweet! Are the chambers Bassanis? How does she perform with them?

[Tripleking]

I think they are. The story behind the bike was the owner who did the seat, chambers and rebuilt the engine ran into some personal difficulties. He sold the bike to a gentleman who reconditions, collects and sometimes sells old bikes, particularly two-strokes. I bought it of off him. I repainted and added Rental low bars. I also rebuilt forks and installed new shocks.

The bike runs well with the with the chambers. However it runs out of steam at around 7000 RPM. I think it needs a richer main jet. It runs fine at all other RPMs. Plugs are normal and there is no popping, etc. Which would indicate a really lean condition.

[tz375]

I suspect that those are Bassani and on a 750 they boost mid to upper revs but cut off sharply at around 6500-7000 from what I have been able to determine. That may be the case with the 380 pipes as well.

[Tripleking]

I have been told by others that they appear to be Bassani chambers. My 380 comes on the pipe around 5500 and pulls to 7000, after which the power drops noticeably. Power is just ok below 5000. From 5500 to 7000 it is heaven.

[Craig380]

The characteristics of those chambers are similar to the J&Rs on my own 380 (stock carbs, airbox & filters) - performs the same as the factory pipes, with no flat spots etc until 5,000rpm when the exhaust note hardens from a drone into a scream, and she takes off. At 7,000rpm it's all over.

With some dyno time and a lot of fiddling with jetting, pods etc I'm sure it'd be possible to get it breathing better at the top end but the pipes work well for road riding, as they allow the bike to pull 6th gear up a hill or into a wind, which a bone stock bike will not do.

[Tripleking]

That describes the characteristics of my engine to a tee. What I would like to know is what is a god cruising rpm. On flat ground, I can cruise at 4500 Rpm. However, I live in a hilly area. To get home, I have to run a 5 mile gradual incline and half mile run up the mountain. On the 5 Mile run, the engine feels like it labors a little below 5500 and is very sluggish below 5000. I don't want to beat on the engine, but I don't want to lug it either.

[tz375]

.....
With some dyno time and a lot of fiddling with jetting, pods etc I'm sure it'd be possible to get it breathing better at the top end ....

For sure timing and jetting have to be spot on to get it running best at the top end, but analysis so far suggests that both J&R and Bassani pipes have a very steep cut off and no over run. There are two ways (after you get it spot on with a dyno session) to improve it. One is to shorten the headers and move the brackets, which will move the power band up the rev scale and he other is to gear it down a couple of teeth to let it rev a little harder.

It's a 54x54mm motor so it should be safe to 9,500 or more if it had enough port area to rev that high. Port it and shorten teh pipes and you could be looking at as much power as a good stock 750 with about half the weight.

[Tripleking]

I always worry about over heating the engine and (especially) seizing the middle piston. I think a little jetting work will help. Timing is spot on using a dial gauge and has been confirmed by a good vintage shop which specializes in two-strokes (albeit Yamaha RDs). Maybe when it is time for rebuilding I will do some high performance work on it. The engine has about 4,000 on the current rebuild.

[Craig380]

That describes the characteristics of my engine to a tee. What I would like to know is what is a god cruising rpm. On flat ground, I can cruise at 4500 Rpm. However, I live in a hilly area. To get home, I have to run a 5 mile gradual incline and half mile run up the mountain. On the 5 Mile run, the engine feels like it labors a little below 5500 and is very sluggish below 5000

For cruising on relatively flat roads without too many hills, mine's happy for mile after mile after mile between 5,500 and 6,000rpm. It's nicely in the power band and will hold those rpm at a bit less than half throttle. It will climb a modest incline or fight a headwind in 6th with just a little more throttle. If the road gets steeper, going down to 5th is all it needs. On my gearing, 6,000rpm is about 69mph in 5th gear and 77mph in 6th.

It's a 54x54mm motor so it should be safe to 9,500 or more if it had enough port area to rev that high. Port it and shorten teh pipes and you could be looking at as much power as a good stock 750 with about half the weight.

Now that would be fun 2mm oversize pistons are available for the 380, which would pretty much a full 400cc. Together with a little light porting work ... well, I'd certainly need twin disks up front

[Tripleking]

Hmm? My GT380 will accelerate in 6th on level ground fairly well as long as I am doing at least 50 MPH. She will accelerate modestly while climbing a very gentle grade in 6th. However, to really accelerate briskly, let's say from 50 to 60 mph, 4th gear is needed. To accelerate, 5,000 to 7,000 RPM is best.

[tz375]

To put that all into perspective, my almost stock RZ350 is happy in 6th gear down to say 30mph but if I want to get up and go, it needs to be dropped back to 4th, 3rd or maybe even second. Above 7,000 it makes a lot more power than it does below 7k.

[Craig380]

And this is why we love strokers