1982 CB750 Custom: Overall Performance Question

[joshkh]

Hi!

At the beginning of the Spring I purchased my first motorcycle, a 1982 Honda CB750 Custom with 5,000 miles on it. Needless to say that I'm in love. I went from never owning a bike to fixing it up, getting a permit and then a license in NY. I also put 1,000 miles on it. Not too shabby for my first Summer.

One thing to note...

I wouldn't say that I'm mechanically inclinded, so it took me a while to fix up the Custom. The previous owner snapped the guards off the idle screws and mucked with them. He also rejetted from the stock 108's to 138's (yikes) and from the stock 72's (I think) to 86's. He also took off the airbox and installed cone filters. Finally, he installed 4 into 1 headers.

I jetted back down to around the stock sizes which vastly improved the performance, and I kept the 4-1 headers and cone filters on the bike.

Now, around the same time my girlfriend bought a 1981 Honda Saber v45 (750) at the same time and fell in love with it as well. Although the more we rode together, the more we realized something...

Her Saber eats my Custom ALIVE.

Off the line she destroys me, but further more she can hit 70 in first gear. And highways are not a problem either.. she can easily cruise at 100 mph with two gears to spare.

On the other hand, I can't hit 25mph without red-lining in 1st gear, and by the time I hit 40-50mph I'm easily in 5th gear. At around 80mph I'm pushing 6.5k RPMs, and at 100mpg I'm red-lining. First gear is so small that I usually end up shifting into second by the time I cross traffic from a red light. There also feels to be a considerable amount of drag on the bike... like it's pushing through sand, at least compared to the Saber.

I understand that the Saber is liquid cooled with a different engine setup, but they're the same size engine and the performance between her bike and mine is so drastic that I can't help but wonder if there's something wrong with mine.

Are my gears simply that close to eachother? Is it possible to change gear ratios in the transmission? Would the jetting have something to do with this? Is this just... normal?

I'll take any advice, thanks!!

- Josh

[Rodgil]

Hi Josh, if you go to "search" at the top of the forum, and type in "sprocket" you will get a lot of information on revs and gearing. I changed the rear sprocket on my '82 CB750F from 46 teeth to 40 teeth, it dropped the revs at 100kph (62mph) from 5000 to 4200. Always check to see if your question may already have been asked in the forum. Good luck.

[joshkh]

Rodgil,

Thanks for the response! Not being mechanically savvy, I wasn't even sure what to search for in the first place. Thanks for the point in the right direction! I'll check it out. :)

- Josh

[OTTODOCTOR]

The stock sprockets are 18 tooth front , and 46 tooth rear . These would put tachometer at around 4000 or so r.p.m. at 60m.p.h. , depending on tire size . -- Sounds like the P O changed the gearing for some reason or another . -- These bikes were set up to run about 130 m.p.h. flat out . -- Jetting changes will have no affect on this . ( GEARING ) -- If you can find a stock airbox and filter it will help performance as well . Pods don't work well with these carbs. -- ( Lots of posts on the DOHC forum about the pod filters .)

[woodsrider250-2]

In short, you will need some motor work to hang with the v45.  A spruced up 900f motor (which would bolt in) might get to be a good match.  Those v-4's are awesome, and to bat an eye at these days is a mistake.  Hard to compare peak HP #'s as well as the v-4 makes more torque accross the whole band.  You have to ride your I-4 like you stole it to keep it in it's true power....The V is more forgiving.  On the upside you can build up the DOHC pretty well if you sink $ into it.  There isn't much hod-rod stuff for the V's that's bolt-in.

[Re-run]

After you changed the jets, did you do a plug chop at all? As in check the plugs after running at various RPMs? You might be lean or there might be something else going on. I know looks-wise people like the pods but you will get better performance with the stock airbox and a k&n filter. Contrary to what might be though, jets do affect your speeds. If you are too lean or too rich, your bike will never perform well enough to reach its full speed or power.

[OTTODOCTOR]

I went back and clarified my post . Jetting will not affect gearing .