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hi everyone.
i have had a 1972 honda cb 750 for just over a year now.
its a good looker and quite original in that it doesnt look as if its been tinkered much.
in the time that i have owned it, i havent ridden it too much but
it felt always aquite a strong bike, but always a tad difficult to start.
lately and as a consequence of this, i decided to get to the bottom
of it and get it looked at, as the starting problem was somewhat getting worse.
the mechanic who has a good reputation, has pulled the carbies and re seated them.
he also relpaced all the rubber tubes to and from the carbies and balanced them.
fuel tank was also checked for rust which there was non of.
new spark plugs and it ran like a dream for the first 15 minutes or so whilst on the expresway back home.
i could not believe how well it ran with plenty of power...plus.
almost like new!!!!!
after about 15 minutes, i heard a little backfire but i continued home.
i didnt think much of it and garaged it. the next day i went to start and it did but then it died. started again then died.
soon, i couldnt even start it.....i took it back to the mechanic,
he checked the compression which was good. he took out the new plugs that he installed previously and replaced them with new ones
as they were fouled up already.
it started first kick....i then decided to leave the bike with him and after a week or so he called me to tell me that it might need a top end
job, which would include valve stems, maybe rings and obviously a timing chain....
this came to me as a surprise because i rode the bike and it ran like new with plenty of power to boot. besides, i could never see any smoke
uphill, or downhill with this bike since the day i bought it....
has anyone gone through this experience or does anyone have any suggestions that might give me some direction....
cheers
met
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If the compression is good then you don't need a overhaul. Plugs fouled, points to the carbs running rich. Does it blow blue smoke? If not it's not burning oil. Just for a test I would take the air filter out and see how it runs (I assume you are not running pods). Also recheck the timing. The points could have moved.
Just my opinion.
On Tue, Oct 9, 2012 at 8:45 AM, met [via Honda CB750'S] <[hidden email]> wrote:
hi everyone.
i have had a 1972 honda cb 750 for just over a year now.
its a good looker and quite original in that it doesnt look as if its been tinkered much.
in the time that i have owned it, i havent ridden it too much but
it felt always aquite a strong bike, but always a tad difficult to start.
lately and as a consequence of this, i decided to get to the bottom
of it and get it looked at, as the starting problem was somewhat getting worse.
the mechanic who has a good reputation, has pulled the carbies and re seated them.
he also relpaced all the rubber tubes to and from the carbies and balanced them.
fuel tank was also checked for rust which there was non of.
new spark plugs and it ran like a dream for the first 15 minutes or so whilst on the expresway back home.
i could not believe how well it ran with plenty of power...plus.
almost like new!!!!!
after about 15 minutes, i heard a little backfire but i continued home.
i didnt think much of it and garaged it. the next day i went to start and it did but then it died. started again then died.
soon, i couldnt even start it.....i took it back to the mechanic,
he checked the compression which was good. he took out the new plugs that he installed previously and replaced them with new ones
as they were fouled up already.
it started first kick....i then decided to leave the bike with him and after a week or so he called me to tell me that it might need a top end
job, which would include valve stems, maybe rings and obviously a timing chain....
this came to me as a surprise because i rode the bike and it ran like new with plenty of power to boot. besides, i could never see any smoke
uphill, or downhill with this bike since the day i bought it....
has anyone gone through this experience or does anyone have any suggestions that might give me some direction....
cheers
met
American by birth. Cowboy by choice!
Vero Beach, FL
http://i373.photobucket.com/albums/oo172/grandpaslinger/HD%20Road%20Glide/IMAG0046.jpg
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Administrator
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If he ran a compression check, that should have told him right then if it needed a top end rebuild, or not. Definitely should not have taken a week to diagnose.
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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I would be questioning your mechanics diagnostic skills.
Were the plugs oil or fuel fouled?
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yes robs750.....im tending to agree.
its the reason why i have posted this,
so that i can hear what others might have to say, via experience, etc.
its interesting because the obvious question you raise as have a couple of others
of whom i appreciate all the input from, i simply havent asked yet and that is
whether the fouled plugs are oil or petrol based.
the bike is still with him as he awaits my answer in what we are going to do.....i will be sure to ask him this
obviously important question.
thanks for your input
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thanks tools1, he took ages to do the carbie clean up....maybe about a month and now, all this.
pretty pissed off with it all.
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the compression is good as he says.....and i ve never seen smoke coming out of this bike.
i will try the air cleaner trick and no im not running pods....thanks for your input, i will keep you posted
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Administrator
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Black and sooty plugs usually means a rich condition. Exhaust will usually be dark black smoke.
Black and shiny/slick usually means some oil is getting in there. Oil in the combustion chamber will be either black (usually valve guides or seals) or a light blue (usually piston rings and/or valve guides/seals).
The ideal color for plugs is a very light tan on the insulator. Bone white usually means a lean condition, and darker points to a rich condition.
Probably doesn't help you much, but I'm sharing my experience. Sorry you're having trouble, but maybe we can help you get your bike running better. I wish you well.
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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whats new with the continuing saga on my cb 750?
well....... the mechanic who has performed the initial carby re-seat, jet and clean,
and who has later suggested a top end rebuild because i complained of on-going starting and running problems after his work was done, has now decided to pull the carbies apart for the second time.
with this overhaul, he has now discovered that i might need new carbies....
he couldnt tell me exactly why but he will know more in a little while.
not much i can do for now but give him more time and just wait to see what he says.
(ohhhh i hate this)
anyway............stay tuned for more drama !!!!
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Administrator
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I seriously doubt you need new carbs. The only reason to need new carbs is if the slides are sticking or there are pieces of the carbs broken off. Sticking slides can be polished if they are not extremely corroded to the point of no return-RARE. I def would not spend money on new carbs.
Where are you located? Maybe one of us is near you and can give you a hand?
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thanks shinyribs for the offer but i live very very very far......
i m downunder sydney australia.
anyway the latest according to this mechanic of myn, is that he has tried working with these carbs and according to him everytime he screws something in, the body is so corroded that it just brakes and falls apart.
he says the only way out is to buy another 4 .......new or second hand.
i have no way of knowing whether he is telling the truth or not but he says that he will do the work from now on......for free.
i guess i have to look at it logically and think that it is a 40 old year old bike......and i cant prove otherwise, so i will have to surcumb to getting another set of carbs.
if anyone out there in this big wide world has a set of 4 to sell...............i will buy.
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You did not even tell us the mileage on the bike!
I would fire that mechanic.
Especially if he did not give you compression check figures.
Also it may have low miles but it is over 30 years old. Better be looking
in the oil pump screen for bits of rubber from the cam chain rollers.
Black plugs could be from the choke being left on too long.
On a Roadstar Adventure.
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Did YOU see the broken carb parts? And if a part broke ,WHICH PART? Did the mechanic show you the broken part? What was it????
Did YOU see a corroded part?
The mechanic says he will work for free!!!!????? (some kind of guilt?)
What a messed up story.
Lets see some photos of the carbs. Please.
On a Roadstar Adventure.
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Administrator
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Yeah,I've seen carbs that are so old and corroded that they crumble like that. I do have a set of just carb bodies if you are interested. If all your other parts are good then no sense in buying a complete set of carbs. I need to clean them up a little and give them a good look over for cracks or what not,but they should be good carbs.
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This post was updated on .
today i decided to visit my mechanic and finally see exactly what he is doing.
he didnt expect me which was what i wanted.
he showed me the row of 4 keihins in a stack which he had already taken of the bike.
he had already taken out their bowls and it was very clear that these carbs were corroding very badly.
he had at some point tried to tighten the screw and he had broken the shaft, but i am convinced this was due to corrosion and not negligence.....i just wish he had picked this up way before when he first put the needle and seats in, but anyway thats the latest.
i had asked him whether he thinks whether this was why the bike had not been starting due to fouled plugs, backfiring and flooding issues, etc. and he said maybe but regardless, this alll had to be done.
photos are now loaded
nabble_img src="IMG_0235.jpg" border="0"/>   
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