different length velocity stacks

[yamahansolo]

I have an 82 and dos 79's. The 2 79 models were both made in 78. One in april and one in july. The april one is my daily rider and its a beast when it comes to acceleration!!! Any way the airbox was removed 3 years ago when I bought the pods. The newly aquired 79 from july 's airbox has slightly shorter boots inside the airbox. A little over an inch shorter. What's up with that? I have swapped the april one onto the july bike because the chrome on it is in great shape.
Anyone else notice different legnths in thiers. All 4 are longer on the older one...

[natemoen]

I have an 82 and dos 79's. The 2 79 models were both made in 78. One in april and one in july. The april one is my daily rider and its a beast when it comes to acceleration!!! Any way the airbox was removed 3 years ago when I bought the pods. The newly aquired 79 from july 's airbox has slightly shorter boots inside the airbox. A little over an inch shorter. What's up with that? I have swapped the april one onto the july bike because the chrome on it is in great shape.
Anyone else notice different legnths in thiers. All 4 are longer on the older one...

From what I have read it seems some of the 79's were set up like 78's, could be that the 78's had a longer velocity stack than the 79's and that is another one of the subtle changes that took place between the two years.

Just thinking out loud...

[yamahansolo]

That was kinda my guess already. But also my carbs had different jets too it came with 140 mains 45 pilots and 210 airjets. That's a little different than what most of the 78's came with.

[natemoen]

just the main is different, should be 137.5.

[crazy steve]

Yamaha continually 'detuned' these bikes after the initial '78 models; why, I couldn't say. Could have been emission requirements, maybe an effort to get better fuel economy, possibly to reduce stress on the clutch/trans. Some of the changes were pretty obviously cost-cutting measures (deletion of the kickstarter, the much simpler and less 'tuned' exhaust crossover on the special exhaust), but hard telling why this was done...

[yamahansolo]

I know some of the 79's were detuned but not all. If you look mine came with140 main jets so to me that would mean if it needs more fuel it probobly makes more power. The other 79's had 137 mains. Also I have raced with a lot of bikes and this thing has huge balls even blew by an 80 standard. We were at the light and I was directly behind him. Light turned green and we all hammered it. The lane next to us became available and I blew by easily. When we stopped he said he was at 8grand when I blew by! His bike is in good working order as well. The bike in front of him was an 81 with a big bore kit his front wheel went up when he launched. After he got moving was when I started. I got right behind him but the lane ran out of room so I didn't get to blow by him...

I also noticed today the petcocks are diffrent. Mine come out straiht to the middle of the bike. The new one has one on the back left side and one on the front right side. And they are at an angle

[crazy steve]

I know some of the 79's were detuned but not all...

You are correct; Yamaha didn't do 'clean' model breaks, but seemingly 'used up' existing stock before making changes. I bought a '79 standard parts bike that other than color was identical to the '78s; 'tube-only' wheels, sealed beam headlight, etc...

[cywelchjr]

And of course you would blow by an 80, as the 80 was detuned in relation to the 79, and the 81 even more,although the big bore kit would probably more than make up for that.

[yamahansolo]

Aparantly it didn't make up enough