Topic: Exhaust options for a 75/76 CB750F - AHRMA Historic Production

[Kickstart]

I'm hoping to take a course and participate in an AHRMA Novice Historic Production race this summer, but I need to do something with my exhaust.

From what I've read, the 75/76 CB750F model had a design issue with the stock muffler, where it will scrape on hard right-hand leans.  Since I don't want that happening (and I believe I need at least 40 degrees lean angle to pass technical inspection), I/m trying to figure out what would be the best replacement.

Anyone have any experience with this bike, or recommended muffler, or suggested whole exhaust systems I can use? 

I have to have some sort of sound reduction (open pipes are not allowed per the rules)... and I was hoping to not have to play around with the carbs, so it would nice to get something with similar back pressure as the stock exhaust.

I believe due to the rear disc brake, the mounting is different than a K, so that may also limit my options.

Thanks for the help!
Chris

[Old Scrambler]

I have not read the current rules................so.............I may be wrong .......................Historic Production is limited to 1972 and older design bikes.  Your F may pass if you change the rear swing-arm and install a standard drum-brake rear wheel. A 4-into-4 exhaust was required but 4/1 may now be allowed.

Read the rules and ask Bob Burns..........a member on this board.........for details.

[Kickstart]

I asked Cal Lewis (Chief Technical Inspector for AHRMA) about that... as I also figured an F wouldn't be allowed in the historic race, but he said it would be.  I'll double check... but I got the impression they were a little more forgiving on the novice races, as they're encouraging new members to join.

Regardless, I'm still going to take the race course so I still need to address the muffler/exhaust issues.

Any suggestions?

Thanks,
Chris

[turboguzzi]

talk with bob, aka big bob .. there might be pics of his bike in the forum, he was definetely running 4-4.

[Kickstart]

Thanks OldScrambler and Turboguzzi...

I'll reach out to Bob to get his advice.

Thanks,
Chris

[Big Bob]

Cal is a fantastic human being and really works his ass off for AHRMA.  Great guy.

But he's wrong about this one.  Not his fault.  It's not his responsibility to know what is and isn't legal for the roadrace classes.  AHRMA tech inspection is not about legality, it's about safety.

AHRMA Historic Production is open to bikes manufactured up to December 31, 1972 or like model.  What they mean by "like model" is if your later model bike is effectively identical to the 1972 or earlier model of that bike you're good to go.

A 1975 CB750K would be legal for the class since it's pretty much the same as a 1972.  Your CB750F is not the same.  Different exhaust, different rear wheel/brake/swingarm, different frame.

Acquiring a K model would be substaintially easier than modifying your F to run in Production class.  Or you could join me in Heavyweight Superbike, I can always use some company while I'm getting the crap kicked out of me by the dual cam firebreathers.

Alternately you could just go ahead and prep your bike and run it in Production.  It's only illegal if another rider protests you and for that to happen you have to beat them first.  I know about 70% of this years entries in the Heavyweight Production class and I can tell you that they'd be happy to see another bike on the grid no matter if it totally fits the rule book or not.

On the other hand there's always some a-hole that has to screw it up for everyone else.  Keep that in mind and be prepared to go run in Superbike.

I won't be at Jersey or Barber this year but if you decide to stick with it please don't hesitiate to reach out with questions.  I've sent my email by PM.

I have no useful advice for you regarding your pipe.  Sorry.  If it drags hang off more.

[Kickstart]

Thanks Bob...

Yeah, my main goal is to take the class... I'll just prep my bike as best as possible, and if I get to race in the novice production then great.  If not, I'm not so sure I'm up for the heavy weight superbike... might be pushing myself... I'll have to see.

I assume after the class they'll give me some advice as to what race I should sign-up for.

I now just have to figure out what to do with my exhaust and figure out how to fabricate an oil catch pan to fit my bike.

Thanks again,
Chris

[Don R]

 A 77-78 F pipe should fit, not sure if it clears better or not but it is different.