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Post by Aerostudent on Nov 25, 2007 22:42:02 GMT -5
Ok, I know it's not scooter related, but I have finally gotten my 1980 Honda CB750K running again. I got it from a friend who let it set for about 4 years, the wife wouldn't let him ride it  . So far I have rebuilt the brakes, cleaned a lot of the electrical connections, new Yuasa battery, 91oct gas w/techron, cleaned out the carbs (all 4, yeah...), new plugs, and a few other minor adjustment such as cables, soked chain in oil for 2 days, etc. It starts now and runs ok, but it won't run for more than a few seconds without the choke on fully. With the choke on it runs at about 3200RPM at idle, but it sounds great. Also it doesn't like to rev much. I can get it to rev to about 7k some of the time (before I feel sorry for it and let off), but other times it will die out when it gets to about 4.5k. Is it just in dire need of professional tuning? Or is there something else that it really needs? Any help would be appreciated! Aero PS for those that are wondering, I finally moved it to my house using a moving, u-haul style, truck. |
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Post by guyruss on Nov 26, 2007 1:06:58 GMT -5
Good to hear from you aero, and I hope all works out well with the scoot. You might want to rebuild the carb, it has been siting for awhile. Might check the air-fuel mixture too.
Russ
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Post by swampsniper on Nov 26, 2007 1:14:28 GMT -5
You are gonna need to balance the carbs.
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Post by funderp47 on Nov 26, 2007 9:18:22 GMT -5
Did you actually make sure the passages (jet or carb body orifices) are free of gunk? Just cleaning the bowls won't help. Carb cleaners sometimes won't get rid of it either. The holes are really small and the gunk is sometimes like varnish and have to be mechanically cleaned. Careful use of a very small, stiff wire will work. I usually pull one from a wire brush smaller than the holes to clean them out.
Do you or anyone else know if it has slide or diaphragm carbs? Hopefully they are slides so you won't have diaphragms to worry about.
They make the single carb on our scooters seem simple, don't they?
Make sure the gas flow from the tank to the carbs through the fuel selector is free flowing.
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Post by Aerostudent on Nov 26, 2007 14:48:01 GMT -5
I did clean as many of the small passages as I could. The low speed jets were almost completely clogged through, only one was open enough to see light through. The needle jets seemed fine enough though I cleaned them anyway. I cleaned out the bowls too, and the drains, the drains were a little ugly, but still not too bad. For the jets, I used carb cleaner and a guitar string (high E, very thin string), which worked good.
I believe they are slide carbs, as I cleaned 4 slides ;D
I talked to a friend at my school that had a similar bike, and he thinks that they just really need tuning. I'm gonna look around for a local mechanic to tune and sync them for me, as I don't have the time or knowledge to do it myself, but if I had either one, I could probably do it (time to learn, or knowledge so it wouldn't take long ;D ). Later everyone!
Oh, yeah, for anyone interested, I should have my scooter back from ScootersFactory by Wednesday.
Aero
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Post by earlwb on Nov 26, 2007 14:59:08 GMT -5
Well that sounds like the inside jets or orifices still have something plugged up.
Oh yeah, check your intake manifolds (plural) for air leaks. Are the four diaphrams on the carbs still good? Sometimes they start getting pin holes in them after a long time.
Does it have a vaccuum operated fuel petock?
If it sat around for a long time, it might be sticking on you.
Also the fuel distribution tube could be clogged up some. The gas tank could be rusty on the inside letting all sorts of debris collect and clog up the fuel petock screen, dribbling down the fuel line into the carbs as well. Don't ya hate it, forget to clean out the gas tank real good and all that crud gets back in and clogs up the carbs again.
What I would do, is get a container of Carb Cleaner at the Auto Parts store. disassemble the carbs, remove all the plastic and rubber parts and soak the metal parts overnight in the carb cleaner container (it usually has a screen tray for making it easier). Then wash off the parts with hot water and let dry real good (blowing it off using a air hose is popular as you can force air into the air bleed holes etc).
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Post by lewtwo on Nov 26, 2007 18:48:54 GMT -5
> Does it have a vaccuum operated fuel petock? <<
Nope ... too old, straigh on and off valve ... but chek to make sure it is clean (there should also be a very fine screen filter in it).
Yep they are slide carbs.
One of the common problems is the slides sticking,
but your problem sounds more like fuel supply.
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Post by Aerostudent on Nov 27, 2007 16:51:04 GMT -5
Could it be so simple that it is just the fuel on/off needing to be cleaned out? My Manifolds are pretty old and crappy looking, so I bought some sealing tape stuff for a temporary patch for them. I might look into 4 seperate pod, K&N style, filters for them, but I might have to do some jetting stuff along with that and really don't want to mess with it. Got to get to class...
Aero
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Post by scooterollie on Nov 27, 2007 17:44:23 GMT -5
Aero;
My recommendation would be to trouble shoot, fix and get running good while in stock condition. Then think about spending $ on mods. When something stands that long unused, a lot of deterioration set in. Some because fluids are left in the machine and some because of aging of the materials. You may well have multiple problems contributing to the condition. I had a motor home for many years. It's systems could be in absolutely perfect working condition when put into storage in Dec. When removed three months later, six things would need attention. There are "Gremlins" out there that just wait to attack a piece of unused machinery!
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Post by Aerostudent on Nov 27, 2007 18:55:11 GMT -5
Yeah, I want to get it running good before doing anything like that, but if I have to replace the manifold, I might just go for some aftermarket filters instead, I really hadn't given it much thought. I think a stock manifold is about $80, which seems a little steep to me, so I thought that I might be able to get something aftermarket that was just as good or better, for less $$$. When I get home tonight, I will try tinkering with it a little more, maybe clean out the fuel valve, and seal off any leaks in the manifold, and see if those help any. Thanks for the suggestions and keep 'em coming!!!
Aero
EDIT: I forgot to say that I found one local shop that tunes and syncs carbs, but they want $85/hour at an estimated 4 hours + parts if neccessary (the parts I understand, but 4 hours at 85per, seems steep to me).
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Post by "Big Guy" on Nov 27, 2007 20:58:20 GMT -5
This may sound stupid, but stupid is as stupid does... ;D I might try running it from another fuel source other than the gas tank with a new fuel line. What would you waste, $2? Sounds like starvation to me, maybe crud in the tank or a collapsing line...  |
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Post by scooterollie on Nov 27, 2007 21:38:09 GMT -5
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Post by earlwb on Nov 27, 2007 22:18:55 GMT -5
Well you might try using a bunch of red RTV (the fuel resistant gasket sealer stuff) on the intake manifolds. That will last a long time if the rubber parts and seals are getting old but haven't started to disintegrate yet.
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Post by Aerostudent on Nov 28, 2007 0:12:56 GMT -5
I have a new fuel line on it so a colapsing line, while still worth checking out, is not extremely high on my list. The first thing on my list right now is to clean out the fuel valve, but I might as well check to make sure the fuel line isn't colapsing next time I fire it up. I also don't remember how well I cleaned out the point of connection between the fuel line and the carb, so that will be worth looking at and cleaning. How long should it take to synchronize 4 carburators? Keep in mind that I am fairly mechanically inclined, and a fast learner, but not extremely knowledgeable about what is involved in most mechanical procedures. Is it worth it to save a couple hundred bucks to try and learn to sync the carbs myself? Basically I'm a newbe that is willing to learn how to get my hands dirty (which has already happened quite a lot...Note to self: Don't bite fingernails...ever! ;D ) and I believe I have the ability to learn (studying aerospace engineering  which is why I have no time to tinker...but Christmas break is almost here!). I'll have to see about the tank and fuel valve. There is some rust in the tank that I just noticed yesterday, which might have an effect on just about everything fuel/carb related, think I should drain and clean it in addition to the valve? I Probably should. Thanks for all the help, and being patient through my questioning (read: interigating ;D)! Aero |
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Post by earlwb on Nov 29, 2007 6:47:43 GMT -5
Synching up the carbs, depends on a number of factors, esepcially the tools you use. I used to use a bank of mercury filled long or tall tubes to synch up the carbs. That let you see all the carbs at once and made it fast and easy. Be careful with the Mecury Manometers, if you use too much throttle, you can suck the mercury into the engine, which can lead to you hiring a decontamination team to clean your garage. But then a homemade manometer can be made using water: www.obairlann.net/reaper/motorcycle/manometer.htmlIf you still have all four separate exhaust pipes and mufflers..... A not quite so elegant or precise method is to use a homemade air speed indicator and go from one exhaust pipe to the other measuring the exhaust flow from each cylinder. A piece of paper that flexes in a cardboard frame works crudely. shamelessly copied from another site (http://www.motorcyclistonline.com/howto/motorcycle_carb_sync/ ), I didn't want to do all the typing this early in the morning. About those tools: You'll need a carb balancer, of course. Several types are available, including some inexpensive mercury manometers (tall glass or plastic tubes attached to a reservoir of mercury on one end and hoses that lead to the intake ports on the other), individual vacuum gauges and spiffy (but pricey) electronic items. We happened to have the purely mechanical Carbtune on hand. Plan to buy or fabricate a temporary fuel source, because on most bikes you'll have to do the syncing with the tank removed. You can also use the stock tank elevated and fitted with a long fuel line. Then find a long, thin Phillips screwdriver in that toolbox of yours. Start by clearing away as much bodywork as you can to gain access to the carbs 2..(Don't worry, this is the hardest part.) Some bikes will have screws filling ports in the intake tract; the most common size is 5mm, but some Yamahas use 6mm threads. Make sure your balancer has the right adapters. Still other bikes have nipples on the intake tubes, like the Bandit shown here 3.. Remove any lines or covers and attach the carb balancer lines, keeping track of the order; left-most cylinder to the left-most tube, and so on. Check to make sure the hoses don't get in the way of the throttle linkages or cables. See if the idle-mixture fuel (or air) screws are exposed and double-check that they're set correctly and equally. With the temporary fuel supply attached, start the engine and let it warm up. Resist the temptation to blip the throttle because the spike in manifold vacuum can draw the mercury out of the balancer. Look down between the carbs and you'll see a small screw head near the common throttle shaft. There are three of these on a typical four-cylinder bike to set the relationship of the adjoining carbs. Begin by adjusting the screw between the number-one and number-two cylinders to match the readings on the balancer 4.. Normally, the spec says to get them within 0.5 to 1.0 in. of Hg of each other but there's nothing wrong with setting them dead even. Gently blip the throttle to make sure the linkage has taken a set and check the balancer. Next, move to the number-three and number-four pair and balance them 5.. Finally, use the center adjustment to synchronize the left and right pairs. By now, you may have to reset the idle speed 6.. Don't be surprised if you have to go back and slightly tweak the settings one more time. As a final test, run the engine up to a low cruising rpm and see how the vacuum signals compare. (If they're way off now but fairly equal at idle, you may have a sticky slide, sloppy linkages or some other malady and syncing won't help.) Shut off the engine, remove the test gear and button it up, being careful to secure the manifold plugs and fuel connections. |
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Post by natefromogden on Nov 29, 2007 9:17:45 GMT -5
If you haven't found them yet- www.bikebandit.com is the place to get all the parts you will need. I used them extensively last winter fixing up that Suzuki GS850. You will discover that getting 4 carbs synched and running properly is more than 4 times more complicated than getting 1 scooter carb to perform correctly. I discovered that these old carbs are very sensitive to float height level and changing from stock filters to individual ones makes almost every sytem require adjustment. I would guess your intake manifolds are age cracked and shot too so plan on replacing them. And buy a socket head screw set for all the screws you will be removing because continually dealing with aged phillips head screws gets old too. |
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Post by Aerostudent on Nov 29, 2007 17:48:21 GMT -5
I also found another mechanic through a friend of mine that travels and only charges $45/hour, which is more reasonable. I might try the muffler version (still have 4 into 4 exhaust) and see if it helps some. But first things first, I will try to seal the intake manifold, and clean the fuel valve. Thanks everyone! I will keep it posted here as to what I am doing when I actual get around to doing stuff. Right now I have finals coming up, so I don't know how much time I will have, but I should be able to get some stuff done. Aero EDIT: Yup, I will definately be trying to salvage my intake manifold. I just checkd Bikebandit, and I dont think I want to spend $200  , even though it may be worth it... I could by a whole K&N HP intake set for the same price, so if I have to, I might just do that instead. |
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Post by natefromogden on Nov 30, 2007 9:54:54 GMT -5
You keep mentioning the intake manifold, but do you mean the air filter box instead? The 4 individual intake manifolds fit between the cylinder head and each carb. I think I bought 4 from Bike Bandit for about $18 each.
For the air filter box- try Ebay. I think I bought a stock airbox for the Suzuki for about $20. Then I spent a little more to paint it, replace the rubber boots and install a new K&N filter inside the airbox.
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Post by "Big Guy" on Nov 30, 2007 10:37:35 GMT -5
I still think you need to use a clean source of fuel, especially since you found rust in the tank. A new fuel line will not affect a bad tank with rust in it, or a clogged petcock. It's a simple 5 minute test that may help you narrow the problem.
If you have rust in your tank, it has to be removed and cleaned anyway...
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. So far I have rebuilt the brakes, cleaned a lot of the electrical connections, new Yuasa battery, 91oct gas w/techron, cleaned out the carbs (all 4, yeah...), new plugs, and a few other minor adjustment such as cables, soked chain in oil for 2 days, etc. It starts now and runs ok, but it won't run for more than a few seconds without the choke on fully. With the choke on it runs at about 3200RPM at idle, but it sounds great. Also it doesn't like to rev much. I can get it to rev to about 7k some of the time (before I feel sorry for it and let off), but other times it will die out when it gets to about 4.5k.
which is why I have no time to tinker...but Christmas break is almost here!).
, even though it may be worth it... I could by a whole K&N HP intake set for the same price, so if I have to, I might just do that instead.