Inlet mainifold. GT380 vs GT550

[losclarkos]

I bought my '76 GT550 nearly 2 years ago as a runner but neglected. It had a bad "prior life" and I've rebuilt the crank, new pistons and rings etc etc. It's back together and I've arrived at fitting the inlet manifold which doesn't. Fit I mean. It seems way too small. The distance between the two outer extreme edges of the left and right carbs (in other words the total distance across all three carb inlets) is 270mm. The same measurement, across the inlet manifold is less than 260mm. The manifold is old and pretty hard so there's no way of stretching it. The guy I bought the bike from had a GT380 which he'd moved on just before I bought this bike and I'm wondering if he did some fancy footwork with some parts and swapped them over.
So, my question is:- are the GT380 and GT550 inlet manifolds the same size and if so what size are they? If not, have I got a 380 manifold?

Thanks in advance from a cold and damp Andalucia.

Los Clarkos

[Alan H]

By 'inlet manifold' I guess you mean the air filter base. Yes tbe 380 and 550 are different, can't say what the measurements are as I'm about 5000 miles from home!
Worst case, there are usually plenty on ebay.

Your details suggest you have a 550 and a 380, perhaps you could measure yours?

[Coyote]

Put the rubber parts in boiling for a few minutes, then work with them while hot. You'll be amazed at how much the rubber will cooperate when it's good and hot. The image below is for the throttle slide setup for both bikes. This would suggest tat the 380 carbs are closer together than the 550 carbs - but not by that much. The real key is the air intake side (air boot side) of the 380 carburetor is considerably smaller than the 550.

[losclarkos]

Thanks guys. I thought I was heading that way. The dimensions you gave me match what I'm seeing and the carb inlet diameter on the 550 is, as you say, much to big to fit in the 380 manifold. So a new one it is then. When you take something off a running bike you kind of expect it to belong to that bike. Call me Mr naive.

GT550 money pit project Coyote? I've got one of those.