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Hi there forum, thanks for all the wonderful posts on pretty much every single problem I have encountered with my 81 CB750 so far. However, I need to pick yall's brain because I am experiencing a very interesting issue.
What I've encountered might need a bit of explanation: When opening the throttle fully the engina revs up to about 6500 rpm, then suddenly the rpms increase without an increase in speed/power/accelaration. This goes along with a higher, whinier engine sound. It happens in every gear, from 1st to 5th. If the throttle is held open this whining engine sound and the high revs without any equivalent gain in acceleration persist until the engine, and here I am at a lack for words, "catches up" to the rpms it should be at.
The bike is a 1981, it idles fine, rides fine, gas flows freely, carbs just cleaned, stock airbox. When this problem occurs, and I can reliably reproduce it any time, the engine does not stutter or stall. Perhaps somebody has come across the same thing?
Cheers from TX,
TK.
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Administrator
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Your clutch is slipping. You will most likely need a new set of clutch plates.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
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
South of Eden (Kansas City MO)
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Well, that was easy. Thanks. (-:
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Be aware, that if you install new clutch springs, as well, your lever will pull much harder. Just sayin'...  Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII
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Administrator
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I would suggest getting honda plates if at all possible. People seem to have the best luck with those. Barnett plates are good too.
Stick with honda springs if yours are no longer in spec. The barnett springs can be very strong and really increase the lever pull.
The ride IS the adventure. The destination is just to get gas!
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Ok, I went the cheapest route possible. Ebay had a whole basket for sale for 60$ incl. shipping. Came off a 1981 CB750 with 13.000 miles. Mine has about 40.000 on it so I should be aok. Got suckered into picking up some CBR coils while I was at it, too. Lever pull is still very strong on my bike and I simply assume the springs will be fine.
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Administrator
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You can get brand new plates for that price. :( EBC plates and springs do well and the lever pull was very,very similar to stock on my SOHC. DOHC may be different,but I doubt it.
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well f me. I only looked at the ones over at Dynoman Austin, and didnt want to spend the high $$$. In any case, I dont have much time right now and this will hopefully be a quick and dirty drop in job. Thanks for the help fellas.
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On a side note, does the clutch only slip when I realize it during full throttle acceleration or is this a continuous thing that I am not even aware of while running between 3000 and 6500 rpm?
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Administrator
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Now that you know what it is, you will know when it is slipping.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
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
South of Eden (Kansas City MO)
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Nope, no additives. Changed the oil just a few days ago and it happened before and after. What did you use?
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Administrator
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What weight of oil? A typical 10-40 should be fine.
Some of us use rotella, either the conventional or synthetic. It is good stuff, AND is jaso-ma certified.
Not here but many people are stuck on using "motorcycle" oil mainly because of jaso certification. Well, rotella meets it.
The ride IS the adventure. The destination is just to get gas!
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what I meant was what additive did you use that caused this problem in your bike. Perhaps I misunderstood and you didn't use one because you had been told what would happen?
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Yeeha! Got the new (old) clutch in, installed CBR coils and changed the chain that was littering the driveway with o-rings.
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Administrator
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You will want to avoid using automobile engine oil that says anything like Energy Saving or similar. There are additional friction modifiers which will play havoc with a clutch. The clutch and engine in the CB750 share the same oil.
If you use/have used only motorcycle oil in your bike, then you're fine. If you're using car engine oil that's Energy Saving, the longer it's in there, the worse it is for the clutch plates.
I have been using Rotella 15W-40 in my bike with no issues and no problems. I think it's the diesel/synthetic stuff: can't recall, and I'm too far away from the garage to check.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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That's what I went for as it appears to remain a popular choice with the experts in this forum. Rotella 10/40. Been using it on my earlier 79 CB750 as well and never had any problems with it.
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Administrator
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I use Rotella in everything I own. Bikes,tractors,trucks,cars,mowers. I put 10-40 in everything but the bikes. They seem to like the 20-50 better. Once hot with the 10-40 the shifting gets a little clunky. Not so with the 20-50. It's what Honda recommends too.
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