gt750 center mufflers

[tz375]

I am sorting through a pile of pipes here for a GT750A and realized that two of the pipes are from an L that I threw in the pile. Checking the parts lists says that L inner pipes were different to MAB pipes and I'm not seeing it yet. Does anyone know for sure what differences there are between L and MAB centers?

I can tell the outers because of the couplers and the L header has couplers but the pair of detachable mufflers look the same from here.

On the ones I have here, I know which were on my L because of certain damage/scratches etc but they are in better condition that the MAB sets I have to choose from. What I don't know is how different they are internally and how important that is. My guess is that teh difference is small and undetectable on the road, but I may be missing something.

[GT750Battleship]

I don't know if the lower pipes are different on the L model,but the later bikes certainly had the exhaust system made to hug closer to the frame for better road clearance when cornering.I "think" the factory achieved this by altering the radius of the header pipes ?

[tz375]

Correct, the header pipes are different from M model on. I had an L and M center mufflers on the bench and could not work out any differences from an external view so I just pulled the new baffles out of the Ls and slipped them in to the Ms and polished the pipes.

I checked the service bulletin and it suggests that all 4 mufflers changed from a 29mm baffle inlet to 20mm in the M upgrade. I'll have to check that out tomorrow.

[old racer]

My parts book tells me the baffles are the same in all models L to A. And probably B. inner and outer,
That being outer baffle,Part number 14510-31000.
And inner baffle part number 14610-31000.
The inner pipes themselves have different part numbers,
L model Left inner part number,14304-31200.
Right inner part number.14303-31200.

M.A.and probably B.Model part numbers.
Left inner 14304-31620.
Right inner 14303-31620.

[tz375]

Thanks for the part numbers. That's what I was seeing in the parts list too.

What was interesting is that early and later outer pipes are easy to spot differences in the header portion, but an L and MAB muffler portion of the exhausts look identical. The same with the inners (center pipe). Header differences are obvious but the mufflers appear to be identical - at least externally.

They look the same. Spot welds all seem to be in the same places. They use the same baffles. The only visual difference is that MAB are stamped GT750 and L are not. But they have different part numbers. And that's what was baffling I'll see if I can see the front baffle plate to see if they really are different diameter inlets.

[oldjapanesebikes]

Richard - if you use a maglite and look in the end of the centre pipe from the engine side, the opening that you can see on the first internal baffle plate is a larger diameter for the L than for the M (29mm changing to 20mm). The removable rear baffles are unchanged, and of course so are the internal baffle plates they slide into. To see it in the outer pipes you need an inspection camera, but again, its just the first baffle plate.

[tz375]

Thanks Ian. I looked in from the rear end with baffles out and can confirm that the front baffle plate has the smaller hole on MAB than on L models.

So the shells are identical as is the front wadding/mesh and the main baffle plates. The difference is that from plate as shown in bulletin GT-7 dated May 1 75. I should have checked that first....

Interesting. So I fitted the better pair of A mufflers to match the outers.

[pjmcburney]

Richard, I think the L inners are unstamped too.


That is, there's no 'GT750' stamping on them toward the rear of the muffler on the outside.
At least, that's the situation with my collection of pipes.


EDIT: - what you said!

I can't vouch for them being different internally as I've not really investigated that.

[tz375]

Yep. I was surprised that they were so similar. Because the outer pipes are so easy to spot, I wrongly assumed that the smaller center mufflers would have distinctive differences too. Turns out teh only external difference is "GT750" stamping and the only internal difference appears to be that first plate.