my new '81 cb750f

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my new '81 cb750f

dukes9989
Hey guys, new here, but I picked up a pristine 750f on craigslist a few weeks ago so I decided to join and hopefully take advantage of the vast amounts of knowledge you guys have to offer!


A little info about the bike---
The first owner babied this bike, keeping all his service and repair info for all 43k he put on the bike before suffering from dementia, loosing his license and ultimately forgetting about the bike and leaving basically the tank full.  From the records he's kept I can tell the last time the bike has been professionally serviced was back in 2008.  The second owner put all of 4 miles on the bike before selling it to me.  He said he bought it thinking he would like size of the 750 since he had been riding a cx500 for a couple years.  He basically did nothing to the bike expect attempt to clean the tank and carbs only to drop the tank and put a fat dent in it



So I got the bike back home, cleaned the tank with denatured alcohol and a couple pieces of chain.  The bike only needed a battery so after a couple days of waiting for that, I put it in and it started right up, full choke, but ran a little rough.  I had to play with the choke for a good while until the bike warmed up, still not idling without the choke about a third of the way out.  Since I've had the bike I haven't done much except clean the tank, exterior and change the oil and filter.  I've put some miles on it and it only seemsto get better but I still think it's not reaching it's full potential.  I'm thinking a carb rebuild kit is my next point of attack and I'm leaning towards the Randakk's rebuild kit.  Any suggestions? Comments? Ideas? Thoughts? Im all ears!!


Here's some more photos












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Re: my new '81 cb750f

motogrady

Nice find.....as far as running rough, I'd think carbs if choking, or enriching, it helps.

Some of these guys like the additive "Seafoam", you can get it at most car parts stores.

Maybe run a tank or 2 with it before you pull the carbs.

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Re: my new '81 cb750f

dukes9989
Thanks moto! I've run both seafoam and lucas fuel treatment through the tank now, putting a little under 300 miles on her.  
I reset the trip when I got her,
So that's why I'm thinking those bad boys are due for a cleanin!
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Re: my new '81 cb750f

sgtslag
I'd suggest cleaning as well:  SeaFoam can only dissolve minor deposits of varnish, and having run it through twice, that's about all it can do for you in the gas tank...  Be sure to run it once a month, after cleaning, for preventative maintenance, to absorb any water, and dissolve any varnish forming.

I'd also recommend running it through the engine, and transmission, by adding the proper amount to the engine oil.  Run it long enough to warm the oil, shift through all five gears, and then change oil and filter:  the i>SeaFoam will dissolve varnish, carbon, and other crud within the engine, and the transmission, which will be caught by the filter, and it will be suspended within the oil.  If using modern oils (SN, or better; the standard was around SF when this bike was made), you will likely never need to do it again.  You will know it is working if it turns your oil black -- that's the crud.  Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII
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Re: my new '81 cb750f

dukes9989
Thanks sgtslag!  Do you have any suggestions for the carb rebuild kit? or do you think the Randakk kit is the way to go?

I'll make sure to run that seafoam through my engine next time i go to change my oil and filter.

Also I've notice my auxiliary doesn't seem to be filling/working, could that be the petcock or the tank its self?

Thanks for any info!
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Re: my new '81 cb750f

sgtslag
I have not overhauled a carb yet.  I cleaned one set, last year, but that was it.  Sorry.

The reserve on your fuel tank is just a separated portion of the tank -- there is a ridge which divides it from the rest of the tank.  The petcock has a valve which allows gasoline from the reserve partition to flow out.  The fuel path from the reserve portion could be blocked, as well.  Test both channels of the petcock, then check the fuel path to the reserve portion.  Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII
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Re: my new '81 cb750f

Hoosier Daddy
I recomend Randakks to anyone who asks! Top notch materials. Plus Randall Washington is a Good Joe.
Take some time and read this over and over until you have a good grasp of whats entailed.

Sean G's Honda Carb Manual .pdf
81 Honda CB750C - Current Project
67 BSA Spitfire MkIII - Next Up (Full Resto)
81 Honda GL1100 - Bob / Cafe´
80 Suzuki GS750L - Bratstyle
72 Honda CB450K5 - Basket Case
73 Honda CB350F Cafe' (Gone but not forgotten)

Don't wait for opportunity to knock... kick the door down and drag the old harlot in!
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Re: my new '81 cb750f

seestheday
Damn that is a clean looking bike.

It might not need a rebuild, could just need a cleaning given how well it was taken care of.  If you want to be sure, do the Randakk kit.  If you don't mind spending a little time I would consider just opening them up and giving them a good cleaning without a kit.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals

My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.

My cb750 video site
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Re: my new '81 cb750f

dukes9989
Thanks for all the advice fellas! I've had the Randakk site tab up for about a week now, trying to decide if I want to go ahead and order the kit or not.

You're probably right sees, I just would hate to get them open to find out they need rebuilt.  But I definitely wouldn't mind NOT spending the $180+ for the Randakk kit.

Also I'm thinking about getting new handlebars cause I seem to have freak long arms and wouldn't mind some sportier looking bars. I don't think I want anything as far forward as clubman bars, any suggestions?
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Re: my new '81 cb750f

Hoosier Daddy
Take a look at Superbike, Daytona, and Euro bars dimensions...
81 Honda CB750C - Current Project
67 BSA Spitfire MkIII - Next Up (Full Resto)
81 Honda GL1100 - Bob / Cafe´
80 Suzuki GS750L - Bratstyle
72 Honda CB450K5 - Basket Case
73 Honda CB350F Cafe' (Gone but not forgotten)

Don't wait for opportunity to knock... kick the door down and drag the old harlot in!
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Re: my new '81 cb750f

cardinal430
In reply to this post by dukes9989
Do I see that the speedometer only goes up to 80 mph ? I know the bike is faster than that.
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Re: my new '81 cb750f

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Back in the 80's there was a law that mandated speedometers to only read up to 85 MPH.
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
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