Hello and specs

[dnseal]

Agreed XSChris, strange though how they would drop (restrict) the HP by 11 hp from 38 to 27. I know the early post 70 muscle cars fudged the numbers to get by insurance issues, but bit did mortorcycle have to go through the same issues in the late 80's?

I did some comparisons with available specifications as printed in the Yamaha's Service manual Part# LIT-11616-XS-42 which has models from 360 (C-D) through 400's (D-J) and came up with the following. There is not enough of a difference to make up a 11 hp (24%) difference between the models.


The following is a quick review and jumping from page to page is hard on these old eyes, so accuracy is 98%;

compression the @ 9.3 to 1, with only the 400D being 9.2 to 1
Bore stroke same
Intake and Exhaust Valve sizes same
Cam lobes, lift, duration the same
Timing at 10 DBTDC at 1200 RPM same

Carbs had minor difference in pilot jets but the format of document made it difficult to verify this time around. I will research more later.

Exhaust? No way to determine flow restrictions, but again most likely minimal and nothing to cause a 11 hp difference.

Conclusion so far; put on and older carb or do some minor jetting and gain 11 HP.... smile. I really think this is a corporate/printing/reclassification type of error. I still refuse to believe the same engine can loose 11 hp without some sort of governor, rev limiter, ristrickor plate, etc doing so and if there is one where is it?


Be Well
Gil



As you can tell I'm ot on of those "climb the mountain because it's there" kinda guys.

 

[dnseal]

Agreed XSChris, strange though how they would drop (restrict) the HP by 11 hp from 38 to 27. I know the early post 70 muscle cars fudged the numbers to get by insurance issues, but bit did mortorcycle have to go through the same issues in the late 80's?

I did some comparisons with available specifications as printed in the Yamaha's Service manual Part# LIT-11616-XS-42 which has models from 360 (C-D) through 400's (D-J) and came up with the following. There is not enough of a difference to make up a 11 hp (24%) difference between the models.


The following is a quick review and jumping from page to page is hard on these old eyes, so accuracy is 98%;

compression the @ 9.3 to 1, with only the 400D being 9.2 to 1
Bore stroke same
Intake and Exhaust Valve sizes same
Cam lobes, lift, duration the same
Timing at 10 DBTDC at 1200 RPM same

Carbs had minor difference in pilot jets but the format of document made it difficult to verify this time around. I will research more later.

Exhaust? No way to determine flow restrictions, but again most likely minimal and nothing to cause a 11 hp difference.

Conclusion so far; put on and older carb or do some minor jetting and gain 11 HP.... smile. I really think this is a corporate/printing/reclassification type of error. I still refuse to believe the same engine can loose 11 hp without some sort of governor, rev limiter, restrictor plate, etc doing so and if there is one where is it?


Be Well
Gil



As you can tell I'm ot on of those "climb the mountain because it's there" kinda guys.

 

[dnseal]

Sorry for double posting, can somebody delete one?

By the way XSChris, check out the 1982 dyno sheet I posted from Cycle Magazine (PDF) earlier. It shows the 400 @ 29 HP on their Dyno, which maybe the just use provided numbers.

Again all fine and dandy, but where did the 11 hp go from 1977 to 1981? I think it just got lost in the printing ink somewhere and if not on the brighter side there is hope to better our bikes by 28% HP.


Gil

 

[xschris]

The 76-77 xs360 carbs is a much better carb for power than any xs400 sets. I know because I have tried them all. Remember we are talking stock non-modified xs400. The 77-79 xs400 exhausts where longer/bigger and less restrictive than the 80-82 short megaphone with a crossover pipe between then, good for mid range but thats it.

 

[dnseal]

Hello everybody.... I figured out how to get better performance from a XS400.

Get a XS650..... smile.

Love the 400, but because it won't do 100 (easily, reliably, comfortably) without investing too much and/or overstressing the engine I'm now in the market for a 73 to 77 xs650. Although I don't ride at 100 often, it the power range and comfort minimum I feel best with. When I want hold on for dear life speed, I ride my heavly modified V-Max.

I may sell the 400, trade it or pass it on to my daughter for a while. In the mean time, question to improve the 400 a bit. Would closing off the exhaust connector improve flow. My 81 has the shorter factory exhaust. Was thinking of capping off below, but understand this will affect the midrange. That said what improvement will be gained lower or higher rpm range?

I also was told that that 360 carbs are the best for these bikes, so does anyone have a set for sale?

Gil