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So, I took the bike out to the movies the other night, but as soon as I pulled into the garage there at the theater, it started dumping gas out of the bottom of several carbs. It wouldn't stop until I turned off the fuel. I got it to putter along after the movie, but then it died while still in the parking lot. I rolled the bike into a spot, and left it for the night, since my buddy could drive me home. I hoped that I may have just dumped out all my gas, and came back today with more fuel. Still, no luck. I was able to get it started, but it would not rev much higher than 2k rpm, even with the throttle all the way open. Once I got rolling on it though, it would die as soon as I started to let off the clutch. Finally, I called by buddy with a truck to help me out. Since I am about to go on vacation, I decided to drop it off at a shop nearby that I have heard good things about. I plan to just meet them tomorrow, once they open, and explain to them all of the problems I have had, and ask them for a diagnosis. After that, I will decide what it is worth doing myself, and what I would like them to do.
I do feel a bit like I am admitting defeat with this one. Most of it is impatience. I think my bike is super neat, and would really like to be able to enjoy it. I have really learned a good deal more than I did about this bike and vehicles in general before I have started this adventure. I am sure that I will be doing more maintenance on this bike soon enough, and will let you know how I go about doing that. I would just really like to start from a good and reliable base line, so I know I will just be trying to solve one problem at a time. I will especially be hitting you guys up when I decide to get serious about restoring this bike and making it pretty.
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Administrator
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They are going to tell you $600 to $800. There is not anything wrong with your bike that a carb rebuild will not fix!
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 hope I did not let all you fine people down, but I did end up taking my bike to the shop. The poor girl died on me while I was out at the movies, pouring fuel all over the parking garage. I was sorta flustered and just gave up. After waiting about 2 months, they finally told me that the bike was ready to go, and I went to pick it up. It runs far better now. It starts and idles just fine. I also installed a new rear master cylinder, petcock, and choke cable.
However, all is not well in paradise. I took my bike out for a ride this weekend. I was following some friends. When we pulled off to rest for a minute, we went over a very dramatic speed bump. I heard something knock, but I figured it was my suspension. After that though, the bike started to run with difficulty. It starts and idles just fine, but when I get it above 3k rpm, it starts to lose out on much of its power. It accelerates very slowly, but sometimes I will get a popping, gurgling sound out of the exhaust and I will feel a short burst of power. My friends behind me also told me that there was a lot of smoke coming out of my right exhaust.
Cut to today, I went to investigate it further. I thought it kinda sounded like a spark plug issue, so I pulled each of them, inspected and cleaned them, then put them back. There was no difference. A lot of white smoke was coming out of the right exhaust, and I could see some leaking out around the #4 cylinder, where the exhaust meets it. From some brief research, this sounds like it could be the result of a blown head gasket. What do you all think? I have always thought of a bad head gasket as one of those repairs that make you want to seriously consider scrapping the vehicle, but I just got this thing out of the shop, so I would really like to avoid doing that. How hard is it to replace a head gasket, if this is the case? Note, I don't have access to a shop, nor special tools like a torque wrench or compression gauges. I am willing to take it into the shop again if necessary, but if this repair is going to cost $1000+, I would consider putting it off for a while.
I appreciate your help to get me rolling gang.
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Why do you think it's a blown head gasket? Because of the smoke?
That only applies to liquid cooled engines. White smoke from a car often means coolant/antifreeze is getting into the combustion chamber via a blown head gasket. This can't happen with your bike because you don't have any coolant/antifreeze.
White smoke for these engines usually means that you're getting oil into the combustion chamber somehow. The usual culprit is a bad valve stem seal, or rings that have gone bad.
You say that you checked your spark plugs. Were any of them oily? Also, you say that you saw white smoke leaking out around the #4 cylinder. Was it right where the exhaust header meets the head? That could just be a bad exhaust seal (e.g. the shop may have installed your header collars backwards or something simple like that).
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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Well, you see, now I am learning things. It makes sense, now that I think about it, that bad head gaskets are mainly a problem for liquid cooled bikes.
None of my plugs were oily. I even tried to swap out the plug on the bad cylinder with one from the #1 cylinder, with no success. I really don't think I am up to the task of replacing my valve stems or piston rings. From what I have gathered, those seem like difficult tasks for a layman without advanced tools. I was thinking of borrowing or renting a compression tester, and then doing a leak down test, which, from what I read, will at least let me know if I have bad piston rings, or bad seals. Either way, I am going to be taking the bike to a professional, I expect. My main question is how much you expect it ought to cost me to get it repaired.
My main concern is this. I knew that I would be fixing the bike up some when I bought it. That is why I was not too upset when I realized that the carbs needed major work. I thought, "Okay, I will just take it to a professional, they will get it done all the way, correctly, and then I won't need to worry about it." Now, less than a week after getting the bike back, I am now facing another major repair. My question is, how often am I going to have to do this? Can I reasonably expect to be able to rely on this bike at any point? Is it going to be unreasonably expensive to own if I am not a mechanic? I realized that vintage bikes would probably not be as good of a value as getting a modern one. I was willing to accept that cost in exchange for the history and retro feel. But if it is going to have breakdowns like this all the time, I would consider swapping it for a more modern bike.
So, what do you think guys? Should I press on with this adventure, or should I stop digging myself into this money pit?
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Why are you so set on taking it to a mechanic? The only reason I can see for doing that would be if you are short on time or don't have any kind of garage to work on the bike.
Buying the tools you need will be much cheaper than taking it to a shop. People here and other places will be happy to help you get it running strong.
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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Administrator
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Anything "vintage" is going to need some tinker time. Nature of the beasts. If you don't mind getting your hands dirty, you can do a LOT of the work yourself. Some of it may need to go out of house, especially if you're out of resources/tools/time to do it yourself. There's no shame in this. Some guys get the old bikes, take them to their mechanic, get them running, and then concentrate on riding. Some guys like to dig into them, get them working, and then sell them to someone else. Me personally, I work on stuff until I reach the limit of my expertise, then I raise my hand and get help from someone else (gas tank cleaning/treating, seat modifications, etc).
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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Alright, perhaps I underestimated the amount of work I could do myself. Would any of you be able to walk me through the steps and tools I would need to do something like replace a piston ring or a bad valve seal? I do not have a garage, unfortunately, but I do have a covered car port with a decent amount of space. I am happy to try to work on it myself, so long as I can be confident I am doing it correctly. My biggest fear is to somehow cause another problem in my attempt to fix my current issues. I would hate to be the one to break my bike.
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Here is a list of basic tools you will need, you likely have most of the basics already:
Set of screwdrivers
Set of metric box wrenches (a.k.a. spanners if you're in the UK) 6mm - 17mm
Set of open ended wrenches (or a combination set)
Metric socket set
Torque wrench (well worth it, fixing stripped bolts is more money/hassle than properly torquing them)
Tweezers
Set of pliers (needle nose, slip joint, etc)
Plenty of rags
Nice to have tools:
- Impact driver (the kind you hit with a hammer $20)
- Depending on what you do you may need a 19mm and some larger ones (I wouldn't buy them until you need them)
- Compression tester (~$30)
- Carb sync tool ($40-$80 needed if you need to sync your tools, buy it once and for the price of a single carb sync by a mechanic you can sync them yourself as many times as you want)
- Tap/die set (needed to fix stripped holes)
- Helicoils (buy as needed to fix stripped holes)
- oil change pan (you should really be changing your own oil)
I'm sure others will chime in, but that list should be a good start.
As for walking through, we can certainly help. Have you downloaded and read the FSM?
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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I have read what I think is the owners manual. It goes through much of this stuff in detail. However, please link me to the proper document you are thinking of. So far, this seems reasonable. I did just get my carbs synched and cleaned at a shop, so will I need to do that again after I fix the engine?
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As far as the bike being worth it is a question only you can answer. It depends on what you want out of riding. How much you are willing to learn and try to take on yourself. Personally I am not a great mechanic, I bow to the wisdom of Tools and Shiney and others on here. But I love having an old biek because I was raised on them. You want to talk about relability try owning a British bike. I love nothing better than and old Norton but I would never own one for my primary bike. A new bike is more reliable, but not perfect. I dmit I havent had my CB 900 for that long, but my last bike was a 82 Virago 750 That I got for free out of an old shed. I spent the winter scrounging parts, and rebuilding much of the bike. By spring I had and awsome bike that with just basic maint. ran perfectlt all spring, summer and fall. The following winter I did more major repairs and the following year was the same. If your willing to put in the time then I would say yes, it is worth it. There is nothing like the feeling of pulling up to a gas station and having a crowd circle you and check out your bike. The feeling is even better if you did the work yourself. These are awsome, rare bikes, and only getting rareer. If you screw something up, fix it! Then the next time you won't make the same mistake. Sorry to sound like a rant, but I hope this helps you make your decision.
It's only illegal if you get caught.
If at first you don't succeed, use more lighter fluid
95% of Harley Davidsons ever made are still on the road... The other 5% made it home.
New Baltimore, Va '82 CB900c, 1980 CB985F/K 'Mutt"
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Administrator
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Just read throughbthis whole thread. Sounds like your bike was tip top after leaving the shop, but you hit that speed bump, now you have problems again.
You're going to have to figure out what happened on that bump that created whatever issufe you have now.
Did it possibly crush a header pipe?
What hit?
Do you see any damage?
You CAN fix this bike yourself. Picking up a couple tools as you need them is way cheaper than shop bills and waiting til you can afford them probably wont take any longer than waiting for your turn in line at the shop.
You can do this. We can help you. Just hang in there and don't let it frustrate you! Fixing it will be a very rewarding experience.
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I thank you all for chiming in. I will admit I like the feeling, knowing that I fixed something. I replaced that rear master cylinder, and when I pressed that lever, and stopped my spinning tire, oh man, that excitement. I would love to do more of that. So, I think I am willing to give it a shot. Worst case scenario, I figure, I will have saved myself the cost of disassembly and parts at the shop, as I bring in a box full of my failed experiment. So, I bought myself the Clymer manual for the bike, and intend to read up on how this procedure is supposed to go. Any walkthroughs you can point me to would be appreciated (preferably with pictures). Within the coming weeks, I will be able to run that compression test, and once I get a fuller picture of the problem, I will be able to start in earnest. Thanks for helping me here guys. This really is a great forum.
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Shinyribs, I will have to look at the header. Please bare with me here, because, while I like to think of myself as mechanically pretty savvy, I am still new to working with engines. By the heads, you mean the exhaust pipes that connect to the engine, correct? I will get a good look at it as soon as I can. I know when I got it, I noticed one or two of the heads had some dents in them, from previous damage (perhaps other speed bumps!). The ones I saw were not on the #4 header, so I will take a look this time. Would a dented, but not crushed, pipe be causing this issue? Alternatively, could I have hit the pipe, and then jostled something inside the engine, like the valves? Again, I will have more info when I get a chance to do a compression test.
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Administrator
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Chicago Ted wrote
... Please bare with me here...
Certainly! You should have seen me when I first joined this forum. I was asking questions nonstop! It's how you learn.
As far as the terminolgy: Most people refer the the main four exhaust pipes coming off the engine as the header or head pipes. After that,you have the muffler or maybe just a tail pipe.
I have banged up my head pipes on speed bumps quite a few times. These bikes sit pretty low,IMO. Dents are not optimum,but it'd have to be pretty much crushed flat to do what you're describing. Even if it was collapsed the half of the original size I don't think it would show up as an issue. Unless maybe at max rpm.
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I should probably note that even after I got it back from the shop to clean the carburetors, I was never able to rev it over about 7500 rpm. When it got up to about 7000, it would sputter and dance between seven thousand and 7500. Could my old problem and new problem be related?
On Aug 29, 2013 12:33 AM, "shinyribs [via Honda CB750'S]" < [hidden email]> wrote:
Chicago Ted wrote
... Please bare with me here...
Certainly! You should have seen me when I first joined this forum. I was asking questions nonstop! It's how you learn.
As far as the terminolgy: Most people refer the the main four exhaust pipes coming off the engine as the header or head pipes. After that,you have the muffler or maybe just a tail pipe.
I have banged up my head pipes on speed bumps quite a few times. These bikes sit pretty low,IMO. Dents are not optimum,but it'd have to be pretty much crushed flat to do what you're describing. Even if it was collapsed the half of the original size I don't think it would show up as an issue. Unless maybe at max rpm.
Montvale,Virginia
Experience is something you get just after you need it.
To unsubscribe from '81 CB750F trying to get it road ready., click here.
NAML
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Well, good news. Sort of. I got all the stuff I needed to do a compression test, and just finished it this evening. The psi ratings, as far as I could read, were 112, 110, 95, and 120, for cylinders 1, 2, 3, and 4 respectively. I did a leak down test on cylinder #3, and it immediately shot up to 150 psi. So, from what I have read, that means I have bad piston rings, right? What are my next steps?
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Administrator
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Did you do a wet test, and was the throttle held open? Those numbers do not seem too bad to me. They tend to read low when you use an automotive compression tester. Also you need to be more concerned with differences between the cylinders compression. Yours are not that far off. Also when you did the leakdown test, did you remove the cams', or shim buckets, so that your valves would be fully closed?
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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So, when I mentioned a 'leak down' test, I meant that I poured about a tablespoon of oil down the spark plug hole, and then did the test again. Is that what you meant by a wet test? On cylinder #3, than led to an increase from 95psi to 150psi. So, you are claiming that 120 on #4 vs the 95 on #3 is not too critical? How low of a reading would I be seeing if I had bad piston rings or valves? I did not remove the cams or shim buckets. I had not read about that. How would I do that and what is it for?
Also worth noting, I forgot to keep the throttle wide open for the test. I did remember to open the choke all the way. Would you recommend I redo the test with an open throttle, in order to get a more correct reading?
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