Learn Me GT380s

[Tripleking]

I think the chambers are Bassanis, which are street-orientated in their design ... shallow cone angles and long length means they work over a wide rpm range rather than stacking everything at the top end.

If the bike starts and idles well, the crank seals probably do not need any attention. Have a check of the spark plugs before making jetting changes ... in some cases, some bikes may need to go a little leaner, the plugs will tell you.

When was the last time Bassani made two-stroke exhausts? Also, I don't think I have a crank seal problem now, I worry about one developing. The bike will sit much during the winter (probably all winter). I also worry about the lubricating properties of two stroke oil. I want to make this last because rebuilding a two-stroke in my area is like finding a unicorn.

[Vintageman]

I also nervous about oil injection/lubrication. I had a pump blocked once (dirt in tank supply line) and have many times seen air in Suz oil lines. So make sue your tank is clean and keep and eye on those oil supply lines.

I also run about 64:1 to 80:1 oil in my tank. This is with the injection pump set to factory. The whole point is to alleviate a pump, oil line, or oil pump cable failure. This saved my ars this year with my R5. I noted some oil dripping onto floor which was light green (Motul 700). I saw the banjo fitting broke. I pulled head and exhaust and all was still fine.

Seals I would not worry if OK. Seams like 380 seals have a good history.

I do think your bike should run better than you have described.

[Vintageman]

I also nervous about oil injection/lubrication. I had a pump blocked once (dirt in tank supply line) and have many times seen air in Suz oil lines. So make sue your tank is clean and keep and eye on those oil supply lines.

I also run about 64:1 to 80:1 oil in my tank. This is with the injection pump set to factory. The whole point is to alleviate a pump, oil line, or oil pump cable failure. This saved my ars this year with my R5. I noted some oil dripping onto floor which was light green (Motul 700). I saw the banjo fitting broke. I pulled head and exhaust and all was still fine.

Seals I would not worry if OK. Seams like 380 seals have a good history.

I do think your bike should run better than you have described.

[sportston]

Went through this last year. They loosened up, but when I tightened the clamps the vacuum leaks went away. I sprayed carb cleaner around the clamps and there was no change to engine speed. Typically, the idle speed will rise when carb cleaner is sprayed if there are leaks. When I had the carbs off for cleaning last year, the rubbers were pliable.

Yes you are correct about checking for leaks best stuff to use is "Cold Start" or "Bradex Easy Start" for spraying with. Sounds like your have no inlet leaks, which is a good thing.
Do you have any trouble starting the bike from cold?
Have you checked out the ignition stuff as previously suggested?

[Tripleking]

No trouble starting at all. On warmer days (over 60 degrees F) it will start with one or two kick. On cold days (50 and lower) it takes three or four). Once the bike is warm, I merely need to push the starter with my foot and it fires right up. I have not checked the timing since it was set last year (about 300 miles ago).

[tz375]

Going back to the pipes for a moment, Bassani used to make pretty good two stroke pipes. J&R made pipes which looked similar but they tended to have a much narrower powerband and at least on the 750 signed off early.

If the pipes are J&R or copies, it is quite possible that the pipe design is an issue. If at all possible, beg, borrow or steal a set of OEM pipes and compare the performance on your bike of the pipes in a back to back test.

[Craig380]

When was the last time Bassani made two-stroke exhausts? Also, I don't think I have a crank seal problem now, I worry about one developing. The bike will sit much during the winter (probably all winter). I also worry about the lubricating properties of two stroke oil. I want to make this last because rebuilding a two-stroke in my area is like finding a unicorn.

WAAAYYYY back in the 70s. They're hard to find now.

Don't worry too much about the crank seals. Laying up the bike for 3 - 4 months is fine. If it's going to sit for a while, best thing to do is turn the engine over GENTLY on the kickstart a couple or three times, every two weeks or so, but don't actually start the bike. Just turning it over gently moves the oil in the cases around (there's always relatively fresh, unburnt stuff down there), keeps the seals moist with oil and stops the seal lips sticking to the crank. I'd also pull the fuel line off the tap to avoid the risk of it leaking quietly into the carbs and cases.

If you DO start the bike, you should really take it out for a minimum of 10 miles to get it properly warmed up. Just starting it and idling for a couple of minutes creates a load of moisture which isn't purged from the cases.

In terms of making the bike last, I've just had the jugs off mine to fix a weeping / blowing head gasket. After 12,000 miles and 6 years of hard use, the piston ring end gaps have only increased by 0.1mm, they're still less than halfway to the service limit. Taking it easy for the first 3 miles on the road, and using a good high-spec 2 stroke oil does wonders for engine life

[Tripleking]

When was the last time Bassani made two-stroke exhausts? Also, I don't think I have a crank seal problem now, I worry about one developing. The bike will sit much during the winter (probably all winter). I also worry about the lubricating properties of two stroke oil. I want to make this last because rebuilding a two-stroke in my area is like finding a unicorn.

WAAAYYYY back in the 70s. They're hard to find now.

Don't worry too much about the crank seals. Laying up the bike for 3 - 4 months is fine. If it's going to sit for a while, best thing to do is turn the engine over GENTLY on the kickstart a couple or three times, every two weeks or so, but don't actually start the bike. Just turning it over gently moves the oil in the cases around (there's always relatively fresh, unburnt stuff down there), keeps the seals moist with oil and stops the seal lips sticking to the crank. I'd also pull the fuel line off the tap to avoid the risk of it leaking quietly into the carbs and cases.

If you DO start the bike, you should really take it out for a minimum of 10 miles to get it properly warmed up. Just starting it and idling for a couple of minutes creates a load of moisture which isn't purged from the cases.

In terms of making the bike last, I've just had the jugs off mine to fix a weeping / blowing head gasket. After 12,000 miles and 6 years of hard use, the piston ring end gaps have only increased by 0.1mm, they're still less than halfway to the service limit. Taking it easy for the first 3 miles on the road, and using a good high-spec 2 stroke oil does wonders for engine life

This is great info, especially about how far to ride it. My typical jaunts are between five and ten miles. I will make sure I ride for ten miles minimum, for the good of the bike.


Also, I have been using Honda two-stroke oil lately rather than the Havoline available at Advance auto.

[Tripleking]

As far as I know the pipes were installed during the past decade. I do not know where they were made.

[Suzukidave]

Also, I have been using Honda two-stroke oil lately rather than the Havoline available at Advance auto.

I have also been running the Honda GN2 in my GT750 for several years now works well .

[Tripleking]

Also, I have been using Honda two-stroke oil lately rather than the Havoline available at Advance auto.

I have also been running the Honda GN2 in my GT750 for several years now works well .

I have yet to have a problem. The local dealer is a Honda/Suzuki dealer. Their parts and service departments have been excellent. The chief mechanic is in his 50s and remembers my old two-strokes when they were new. The dealer has been helpful with things I cannot or will not do myself. They have also been helpful finding old replacement parts at prices which rival those on the net. Their price for GN2 is about 50 cents or so more than the parts store price for Havoline. For that difference, I will go with GN2 every time.

[CBWELLS]

Here's some numbers to consider:
The GT380, first prod'n 1972 & OEM spec'ed at 38 HP at 7500 RPM w/conventional point & condensor ignition.

The CB400T first prod'n 1979 & OEM spec'ed at 43 HP at 9500 RPM with CDI ignition system.

Aside from the character differences of 2-stroke vs 4-stoke, these two bikes are technically worlds apart & probably very difficult to compare even if they were new. After 30+ years of real world (ab)use, there's really no telling what PO's alleged "improvements" have really done for their performance.

Here's just an opinion (& you know what "they" say about opinions)!

It doesn't surprise me that the GT380 pulls well from 5-7KRPM & then drops dramatically after 7500. Seems pretty normal! I wouldn't worry about running it in that range, although I wouldn't hold the throttle at the hi end for extended periods (nor would I do so on any other bike near it's red-line). As for the "screaming" exhaust & "tearing apart" you mention, I guess I would expect that as well. The triples do complain some at red-line revs & spannies are not known for quiet operation. They also likely contribute to some degree of non-OEM type vibrations thru-out the bike as well.

I suspect both your bikes are not at "optimum" performance levels. Few are! Could one or both be better?..... Probably, but it sounds like they're both doing pretty well. And I'd be more concerned about screwing something up in my efforts to "improve" things than about some minor difference between two old bikes that really aren't comparable anyway. Enjoy the rides, don't fix it if it ain't broke, & put the money you save in your kids college fund! You can drive yourself to madness & to the poorhouse trying to get the "n"th degree of performance from old machines. Don't worry. Be Happy....that they go as well as they do!

[Vintageman]

Here is what I mean when I say these bikes can do +9000 rpm pulling.

http://www.youtube.com/watch?v=acyDUr1HuEM" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;"

He is tough on that bike. Can't tell what he runs for pipes (sounds like JEMC0s)


Also here is gt380 and a Hawk together

http://www.youtube.com/watch?v=rRS7Yv7BUd0" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;"

Here's a gt380 3 into 1 getting 11,000 rpm
http://www.youtube.com/watch?v=aPqFQJFm ... 776B37D649" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;"

[Craig380]

I don't know how the guy on the green 380K is able to rev it so high, it must have chambers and other work. Of course, tachos can over- and under-read but you can tell from the exhaust note that he really is giving it the whip.

My own 380, when stock, would run to about 8,250 on the tacho but you could tell it had passed peak power at that point and was no longer pulling.

With the J&R chambers, stock carburation (which careful plug chops show is slightly rich), it stops at around 7,250rpm, but 6th gear is usable under any conditions and the bike will pull it, which a stock machine will not (on a stocker, you'll reach max speed in 5th unless you're on a long downgrade, or with a strong tailwind. 6th is an overdrive for cruising).

I could probably reach higher rpm by playing with jetting etc but I can't be bothered ... being able to hit 90+ any time I want is plenty fast enough on the standard brakes & suspension

[markush]

Hi!

I don't know how the guy on the green 380K is able to rev it so high, it must have chambers and other work. Of course, tachos can over- and under-read but you can tell from the exhaust note that he really is giving it the whip.

The green 380 on the race track: In a comment below the owner wrote about 28mm Carbs from GT550 on it. But I wouldn't rely on the tacho-shown revs. The needle-damping seems to be defective (needle oscillates), and then tachos tend to show more.
Its sound in the upper revs is like my own 380:

My GT380 revs up to about 9000 rpm, even in the upper gears.
# Original carburetor and jets
# ports unchanged
# 3 in 3 Exhaust system:
(original exhausts at the left and right sides and a modified original left exhaust for the middle cyl., mounted on the right side.)
# X7 pistons (piston shirt about 1.5 mm shorter than the original pistons. With these pistons the whole powerband was risen about 500 rpm)
# sprockets 14/42