Topic: 1975 750F Custom - Engine Power/Performance Discussion

[carterjahn]

Hi,

New to the forum so I apologize if this is posted in the wrong place. Also new to building bikes, so go easy!

I'm curious about what people are doing to their builds to optimize power. I'm currently in the middle of an engine rebuild, and want to make sure I'm making the correct decisions to enhance the performance of the bike.

For starters, I'm going with an 832 bore with a set of new Wiseco Pistons. Do I need to upgrade connecting rods, or will the stock ones hold up okay? There's a high lift race cam in the head already, and I'm getting a valve job done so the whole top end should be flawless on the inside. (For those that care I'm in Los Angeles and Charlie at Charlies Place is taking care of that big job). Should I also be looking into things like sport clutches and pro cutting my transmission?

My other big question is carburetors. With all these power upgrades on the inside, will the stock Mikuni carburetors still do the job? I've seen a lot of photos of the Lectron carbs (like on the CycleX drag bike). Is this something I should look into? Probably going to be doing velocity stacks or pod filters for intake, and Exhaust will be the CycleX Sidefire.

I appreciate all the input I can get! I don't have many people to ask these questions to, and I stay up all night thinking about it!

[Don R]

 Stock carbs are keihen's rather than mikuni's. Mikuni's are available for them though.  Lectrons are mostly for drag racing. If you're going to run other than stock carbs and air filters do the research first. It's not as easy as it seems.
  Stock rods can hold up to an 836 kit but if you're revving it to the moon I'd put a set of good rods in it. Remember, it's almost 50 years old.

[carterjahn]

Sorry, I meant Keihins! I'm not looking to race this thing, just want to make sure the added power is going to sit well in other places of the engine. I appreciate the input!

[MauiK3]

These motors are pretty tough especially with a mature hand on the throttle. If you are not racing you can relax.

[Jerry Rxman Griffin aka MuthaF'er]

Stock carbs will work as will stock rods at 836. I have two 75 F's. One is 915 and the other 1000. General consensus says to upgrade rods after 836/850.

No to Lectrons. Full drag race only. Better options for your use if you go that way. When you take the next big expensive step and include some serious head work with bigger valves, and porting then get some bigger carbs and stronger rods.

What cam?

[carterjahn]

I appreciate the response. Recently figured out one of my conrods is slightly bent. So going to take that as a sign from the 750 Gods to just put some tough boys in there. Looks like I’ll just do a rebuild on the stock carbs and make sure they’re tuned to perfection (who wants to help me do that).

Cam is actually an old Norris High Lift Race cam, put in by the previous owner. Still in really good shape, and I think will match up well with the 832 Wiseco set.

For the future, what are the better options to explore in the carbs world?

[Don R]

 CR29's are one, some guys have used carbs from a 750 seca. Search those.

[Jerry Rxman Griffin aka MuthaF'er]

Or CR31's should work too. The Keihin CR's are available new.

[seanbarney41]

Got numbers for the Norris?  Only one I have ever seen was very radical drag race only territory=no fun on the street plus tons of expensive valvetrain mods for it to even have a chance of surviving a quarter mile at a time.  Lots of good info here

satanicmechanic.org/index.shtml

although nothing about the Norris

[Bankerdanny]

Spend $100 on Hondaman's (Mark Paris) book My CB750 Book. It is the bible on building these bikes and had substantial info on performance upgrades. http://forums.sohc4.net/index.php/topic,65293.0.html

[carterjahn]

Got numbers for the Norris?  Only one I have ever seen was very radical drag race only territory=no fun on the street plus tons of expensive valvetrain mods for it to even have a chance of surviving a quarter mile at a time.  Lots of good info here

satanicmechanic.org/index.shtml

although nothing about the Norris

Numbers on the Norris Cam are, 'K134' and 'J 8'. Had a couple mechanics look it over and it seems to be a pretty standard high lift race cam. Shouldn't have too many issues (I hope).

[carterjahn]

Spend $100 on Hondaman's (Mark Paris) book My CB750 Book. It is the bible on building these bikes and had substantial info on performance upgrades. http://forums.sohc4.net/index.php/topic,65293.0.html

Already have it! I've skimmed through once or twice so far. Used it to help me disassemble the engine. I'll keep on reading though.

[seanbarney41]

Got numbers for the Norris?  Only one I have ever seen was very radical drag race only territory=no fun on the street plus tons of expensive valvetrain mods for it to even have a chance of surviving a quarter mile at a time.  Lots of good info here

satanicmechanic.org/index.shtml

although nothing about the Norris

Numbers on the Norris Cam are, 'K134' and 'J 8'. Had a couple mechanics look it over and it seems to be a pretty standard high lift race cam. Shouldn't have too many issues (I hope).

ok, but I meant the actual measured amount of lift, duration, overlap.  This will tell experts whether that cam can be made to operate correctly in a street bike.

[seanbarney41]

carterjahn, from a quick google search, I found no information on that cam.  There is a few threads with information about Norris r2, and r3 grinds and those seemed to be in street territory.  But no answers about K134.  It appears Norris did a lot of air cooled vw cams and may still be in business?

I am not the most skilled google searcher...
Also possible to set it up in v blocks and dial indicators and measure it yourself.