Topic: dohc 750 Q:

[phil71]

working on a dohc 750f for a friend, and I  expected it to be a lot faster than the sohc. it isn't. So i looked at HP figures, and lo-and-behold, the claimed bhp is only about 3(!) more than the highest output sohc 750s. SO, I guess I wonder , why did they bother?
  Was it detuned for the times? It would seem that right around then, all the other J bikes were swinging for the fences with HP. What gives?

[JohnG]

from the magazine tests back then  (Cycle)  I recall the SOHC 750F having a peak horsepower of 58 at the rear wheel.  Same dyno,  the DOHC  750F  had 65.  Quarter mile times dropped from the 12.9 range down to the mid 12s and a little lower. Had an extra 1000 RPM to the red line. Engine sat higher off the ground for more ground clearance in curves.

It did have more EPA issues to contend with as you point out.

The overall package was perhaps better:  dual disks, transistorized ignition, oil delivery to head externally routed, better suspension, HyVo internal chains etc.

Not a revolutionary bike - more incremental.  The V45 Interceptor that followed was more along the lines of what you perhaps expected.  75 HP, water cooling, absurd ground clearance, fairing, 16" front wheel . . . .another 1000 RPM top end.

If you are fine tuning it, there is a small pilot jet hidden under a black cap.  This needs to be carefully cleaned for good running.  Replace the coils with 1998 or so CBR 600 coils for a much better spark  (about $40 on Ebay)  If it needs a valve job, go for a home equtiy loan . . .

[phil71]

Ha! Yeah got to those jets.. It was all pretty gummy, but a lo mile example.. Just sitting 4ever. It runs absolutely fine, but is certainly no world beater. In my estimation, it has a broader rpm range of usable power, but my '71 750 has quite a bit more seat-of-the-pants exhilaration in it. Smooth is awesome , but dull?

[JohnG]

A couple questions:

did you do the valves  and cam chains?  (takes shims. bummer)

Is it still box-stock ?  People mess with the carbs , filter and airbox to no gain.  The CV carbs are trickier than slide carb. Stock settings are best.

Stock exhaust?

I have a '79 DOHC 750, 76 SOHC.  I ride them to work regularly.  For that kind of riding, I find as you that the performance is pretty much the same.  The DOHC has the extra 1000 RPM of power band but I rarely have use for it.  Long ago I road raced one and could take advantage of it there.