Topic: A newbies Idle Problem

[Anti-Johnny]

I have owned my 75 cb750k for about five days now. It is my second bike. The first one was a much newer Yamaha that I never really had to do anything to. Just jump on and ride.

So far on this one, I have had to re run some wiring, clean it, and remove a windjammer fairing.

I was having some idle problems (the bike would die). So I took it to a local shop and the owner adjusted the thumbscrew underneath the gas tank. He told me I may need to adjust that day to day depending on weather or what have you. This fixed it, but today the idle was too high, so I turned it back a little. (I dont know if this information was necessary.)

I rode around a little then set to work rewiring the horn, when I smelled gasoline. I looked and I hadnt shut off the petcock, so I did that and it stopped. I tapped the sides of the carbs with my wrench to shake loose any sediment and went back to rewiring the horn.

So about an hour after trying to get the horn and light situated I took it around the block to see if the headlight looked any better. (by the way it seems to be just pointing a vertical light about 10 degrees off of center to the left. Piss...)  Now it sounds like I may not have a carb going. Like the syncopation is off. Is there anything I may be able to do or check to figure this out? I really can't afford to take it to a shop for them to charge me a couple hundred to say its fine. Or worse that I broke the damn thing in 5 days.

That is basically all I have done to the bike. Like I said, I am a novice with bikes and especially new to a bike like this. So any suggestions would be appreciated. The PO has been talking with me almost every day with questions I have. He said he had adjusted the carbs and checked everything before I picked it up from him. I guess I just want a second opinion or perhaps another point of view, at the least to better educate me.

[Anti-Johnny]

http://forums.sohc4.net/index.php?topic=76946.0

ive read through this thread but not sure if I am having the same problem. I am definitely weary to adjust anything like timing myself.

[nancy]

OK - start with the carbs. Remove the fuel bowls. Hold them carefully so u don't spill the fuel - so u can tip it into a small jar. Mark the level. Do this for each. This will indicate whether you have fuel or not for each carb...and if each has the same level. (Report your findings back). Then...look up into the carb and see the jets - one has a small slot in a nut - the other bigger. Unscrew, remove jets - clean - blow air, check again for dirt & replace - GENTLY. You might feel game to clean the float valves while you're there. If so, remove the brass pins holding each float - pull with small pointy pliers or similar - if you're lucky they won't be stuck. The floats drop down and will be followed by the float valve - so CATCH it! Now, unscrew the brass holder it fell from. This has a mesh basket on it to catch crappo from your fuel. Clean, blow, replace. Back in with the clean float valve and hold that sucker while you position the float back and push the brass pin back in...it's easy,..but needs a knack. Bowls back on. Check that they are seated good. Clip em up. Turn on your fuel. Check it out. Report back.
Regards
Mark
PS: Been there and done that - again and again...you'l get it.

[Anti-Johnny]

I havent taken the fuel bowls off yet. (Tests next week and my girlfriend and I only have one car at the moment, so I dont want to mess anything up yet) I did add some Sea Foam cleaner to my gas tank though.

I took this video to show where and how much gas is leaking. I dont think it looks like it is coming from the gas line or the nipple on the bottom of the carb.

I went by the bike shop and the owner showed me what the insides of the carbs look like and what to look for. He even told me if I have to take them off that I can come up to his shop and use his tools for free.

here is the video

[Anti-Johnny]

Just wanted to update this in case anyone comes along in the future.

bike mechanic says I have a loose O Ring in my second carb. He says if I do it myself, with not knowing what I am doing, to expect the bike to be down at least two weeks. The linkages have to be taken apart...

This thing is really leaking now. but other than this quirk I guess the bike runs fine. Hopefully I dont run into any other problems for a while.

[haggeo]

Just wanted to update this in case anyone comes along in the future.

bike mechanic says I have a loose O Ring in my second carb. He says if I do it myself, with not knowing what I am doing, to expect the bike to be down at least two weeks. The linkages have to be taken apart...

This thing is really leaking now. but other than this quirk I guess the bike runs fine. Hopefully I dont run into any other problems for a while.

the first time i ever touched a set of 750 k carbs i took them apart and put them back together in a couple of hours, not counting the time it took to soak them in simple green. the second set i did in 57 minutes, i know the exact time because i video taped the whole thing. if by linkages he means the choke, that's no big deal; 4 cotter pins, 4 washers and 3 link arms. don't let it scare you. get some o rings, maybe replacement cotter pins and have at it, if you get stuck someone here will help you out.

[bender01]

Bikes down 2 hours(days) at your house! If its the float bowl gasket its a simple fix. If the float is stuck Im not sure why fuel isnt going out the rubber overflow from the bottom of carb but it might be plugged with dirt, bees or who knows what. Take off the tank remove the throttle cables and the air box. Loosen the bands holding the carbs on and wiggle the whole rack off carbs off. Search carb cleaning here and go to town. You wont have to deal with the linkages . Your problem is simple but removing the carbs will be the easiest way to fix it. Procrastination is why these bikes can be had for low dough sometimes.

[Anti-Johnny]

the first time i ever touched a set of 750 k carbs i took them apart and put them back together in a couple of hours, not counting the time it took to soak them in simple green. the second set i did in 57 minutes, i know the exact time because i video taped the whole thing. if by linkages he means the choke, that's no big deal; 4 cotter pins, 4 washers and 3 link arms. don't let it scare you. get some o rings, maybe replacement cotter pins and have at it, if you get stuck someone here will help you out.

If you still have that video, I wouldnt mind watching it. haha. I should record mine from the top down as well in case I mess anything up.

Bikes down 2 hours(days) at your house! If its the float bowl gasket its a simple fix. If the float is stuck Im not sure why fuel isnt going out the rubber overflow from the bottom of carb but it might be plugged with dirt, bees or who knows what. Take off the tank remove the throttle cables and the air box. Loosen the bands holding the carbs on and wiggle the whole rack off carbs off. Search carb cleaning here and go to town. You wont have to deal with the linkages . Your problem is simple but removing the carbs will be the easiest way to fix it. Procrastination is why these bikes can be had for low dough sometimes.

Thanks both of you for giving me a better time frame. I live in an apartment so I have been putting off doing anything. I have only had the bike a week. It is mostly in great mechanical shape, I am just a novice so this is a little terrifying. I have spent most of the last week trying to figure out what all the bits and bobs inside the carbs are called and how to put them back together when I take them off. My last bike was only a couple years old so I never had to worry about maintenance outside of tune ups and oil changes.


I am fairly certain my carbs are stock. What should I be looking for in a kit that will have the gasket and the O rings? Trying to understand some of these posts about carbs is like reading algebra.

[bender01]

http://cgi.ebay.com/ebaymotors/HONDA-CB750-CARB-FLOAT-BOWL-GASKETS-1968-1976-_W0QQcmdZViewItemQQhashZitem33619efa32QQitemZ220681140786QQptZMotorcyclesQ5fPartsQ5fAccessories
 These might be all you need.Alot of the inside rubber pieces should be fine. At least reusable. Take them off before you order them. Maybe your float bowl is just loose.

[Anti-Johnny]

since it is just the one carb, could I get away with ordering this ?

http://www.vintagecb750.com/products/6/fuel-system

second item down. it looks like it comes with everything needed for a rebuild of one whole carb. Unless I can pick up an O Ring at harbor freight.

I saw another thread where the piece connecting the two carbs was cracked, it was plastic instead of aluminum. I dont know what that is called, but the guy in the thread got another forum member to use a lathe and make a new one.

I would like to order the gasket/ORing or this kit before I do it, just to try and insure that the bike is down for as little time as possible.

*edit* here is that thread http://forums.sohc4.net/index.php?topic=71015.0

He got a kit from honda that had the gasket and O ring together, it looks like. Going to see how much that is.

edit again* the rebuild kit I linked is cheaper than the honda kit for just gaskets and o rings.

[eastoak]

i got a metric assortment of (200 or so?)nitrile o rings at harbor freight for $3-4, i have not gone in to see if they have the right size for the carbs but i'd be surprised if it didn't.

[Anti-Johnny]

I ordered a set of Gaskets off eBay. Should have those in around Saturday. Pretty nervous about doing it myself but kind of excited as well.

Just wanted to update something.

The carb leaks now even while the engine is running. Instead of a steady drip it is now a steady dribble. Very descriptive I know....

Just wanted to check with you guys to see if this was indicative of anything more than just a leaky or loose gasket.

I am hoping I can swap this gasket out without taking the carbs off. If I understand the thing should set into a groove right?

When I take this bowl off, will anything fall out of it?

[nancy]

No - you can pull off the bowls easy as, no probs. Nothing drops til u remove the float pin to withdraw the float - that will allow the float valve to fall out of the seat. Place a towel/rag or flat lid under the carbs as u work.
The leak from the carbs - can't tell what the source is, but mine leaked a lot when the float bowl gasket was not sealing right. Either cos I refitted the bowl a little askew - not a nice fit..or,..the gasket had a slit, was hard and dry and naffed. Worse on the side stand in this case.

[Anti-Johnny]

Gaskets havent come in but I went down to see if I could figure out how to get the bowls off.

I did.

Here are some pics of the gasket and bowl. The bowl itself looks really clean. just the beginning of some gradou in there.

I think I figured out that the bowl is leaking from the rear. This might make sense because the gasket kind of fell out and is a little warped. here are some pics. Not sure if they look alright or not. Hoping it is just the gasket because I dont want to have to take the things off to get at an O Ring.

Just bought the bike want to ride it!




You can see in the second one that its a little bowed out. maybe its nothing, but again I dont know. Going to try to get it to fit back in the top part of the carb and see if I can reseat the whole thing.

I think I have read sticking it in the freezer for a bit can get it to shrink.

I dont have anything that measures mm, but I stuck my metal ruler in the bowl and its about 3/4"

[nancy]

The gasket should stick to the upper surface of the carb and the bowl drop away on its own. In my case anyhow. The upper surface has a recess for the gasket. So i'd suggest placing the gasket UP onto upside 1st and push the bowl back onto it - wiggle it till you feel it clank into place before pulling the wire clip back on. You may need to place a little something on the gasket surface to help it adhere upside down - a small smear of grease maybe..but make it sit nice before slamming on the bowl. I see no need to freeze it tho...

[Anti-Johnny]

I tried too shrink it back to a size that would fit in the groove. No dice. That picture shows that it's expanded quite a bit. This is my estimation of course

[cameron]

it is the gasoline that makes it too big.
It will dry out on its own and fit back in there.

[Anti-Johnny]

I found another thread where a fellow was having similar problems. here is what I posted there.

I just shot this video. The float and the float valve seem to be moving freely. I dont know if the float is in or out enough though. I can just see that it does slide up and down.

Its not in the video but when I hold the float up, even with the gas on, there is no leak. I dont know if this excludes the O Ring.

The second video is looking up from the bottom after I had the gas on for a few seconds to fill up the bowl. I can see that the leak is coming out from the gasket. This is the same old gasket that was in there and I may have not seated it properly. I need to get some grease to hold it in. So hopefully this may still mean it is just the gasket?

The stand pipe doesnt look cracked.

I can see in this picture that there is nothing attaching from the float valve to the float. In some videos, I see that there is a little loop of metal, but those may have been from different carbs.

I am waiting on my bike cover to come in before I take the carbs off. I park in covered parking and I dont want anything to blow up inside the engine. I plan on taping off where the carbs connect anyway, but just in case.

[flybox1]

your bowl gaskets will shrink after the gas they've absorbed evaporates.
use superglue in the corners of the bowl gasket tract to secure it in place.
i attached a picture of a float tang.  each of your carbs should have one.
this is what you adjust to raise/lower your float height.
I am unable to view your vids here at work, but if you are still getting leaks at the O-ring (the o-ring sealing your bowl to your carbs) the float valve is not closing.  if you can manually close it when the bowl is off, then its your float height that is incorrect, and not providing enough pressure on the float valve to fully close it.
lower your float by pressing/bending this tab towards the carb body.  this will make the float shut off fuel at a lower height. seat each of your float heights per your shop manual.
use the search function to see how to measure float heights.


edit:  home and finally watched your vids.  yes, your float valves are working properly, but if you are still getting a leak at the gasket seam, then the heights of the floats are set wrong. 
again, use the search function on how to measure and set float heights.