Topic: SOLVED Newbie Intro and Throttle Issues--Revving out of control

[cheeseman]

Hi Everyone:

This is my first post. First let me thank all contributors as I've perused these forums several times and the information is excellent!

I have had a '76 CB550 for about 20 years and have enjoyed riding it here and there, but nothing too serious. It really has no modifications and has always been reliable.  Most of my riding has been on the backroads around my farm in Wisconsin.

So last year I decide I want to take a trip with the bike, so I better finally get a motorcycle license!  It was an all day affair offered at a local Army base, and I learned a lot.  It was super chill as most of the riders were experienced, and we had a fun day on our own bikes--I of course had my 550 which the harley riders scoffed at, but seemed to take interest in the nonetheless!  The bike had performed well all day, and now it was time for the final road test.  About halfway through the test, out of complete nowhere, and at low speed (probly 2nd gear), the bike just screams and the rpms max out on the tachometer. Luckily my kill switch works and I shut it off. I I check the throttle cable and it seems fine, and I don't see anything unusual around the carbs. I start it back up and it screams up again. As I'm in the middle of a road test, I have no time for further diagnosis. What a time for the 550's first issue! Luckily one gentleman on a yamaha offered to let me use his bike to complete the test, so I earned my license.

I suspect something carb-related, but I haven't had time to pull them out and open them up yet.  Would you guys agree the issue is inside the carbs, and if so what should I be looking for?  And take not this wasn't just a high idlle. This is totally out of control engine screaming and tachometer immediately maxed out.

Also, after this incident, the bike is leaking oil while sitting. Seems to be weeping out of fins.  I haven't looked closely enough to see which fins/how high the leak is, but I know its not good. Would we suspect these things are related, and how so?  Head gasket maybe?  Would out of control rpm's blow a head gasket?  I was able to shut the bike off within 10 seconds, but maybe some damage already done?

Thanks and any suggestions would be most appreciated. I will post some pics when I get the bike out of cold storage.

[bryanj]

To scream like that something has to be wrong with the cables, take tank off and check properly that neither cable has anything wrong.

After that we will talk about oil leak

[Bankerdanny]

The only possible explanation for the bike all of a sudden revving up and not stopping is a cable issue. Everything is mechanical and the bike can only rev higher if the carbs are opened with the throttle. The carbs have a pretty stiff return spring, so even a broken open cable wouldn't cause it to randomly gain rev's.

[pjlogue]

You may have a frayed throttle cable which prevents it from coming back to idle.  Can't see it revving on its own.  You should check the linkage at the carbs to be sure it's free of anything that might get caught in it and also check your cables by unhooking them at the carbs and then gently working them.  They should be smooth as glass when you twist the throttle and not have any scratchy feel nor should the cable ends hesitate to extend when you push them out via a throttle twist. 

Great you got your license!

-P.

[cheeseman]

Thank you all for the responses. I will take the tank off and give the cables a good looking over.

Do you think the crazy revving could have broken something loose creating the old leak, or would you suspect they are unrelated?

[bryanj]

Leaking oil is probably coincidental but these bikes have always been known for an oil weep at the sides of the heads, its possible a seal has gone somewhere.
1st get the throttle sorted
2nd clean off the engine thoroughly
3rd check exactly where oil is comming from

I have been working onthese since the early 70's and some things are more common than others, pottering arround at lowish speeds for 20 yrs can do more wear damage than highway but nothing major.

[cheeseman]

Thanks again for all your replies.

You were exactly right about throttle cables. The lower one (push I believe) had actually jumped out of the retaining bracket down by the carb, which allowed the whole linkage to wrench the throttle wide open. I guess the nut somehow backed off and out she popped.

And the oil issue.  Well I checked the oil level and it was actually above normal on the dipstick.  So I'm guessing this dipstick at some point overfilled the oil, and then there must be some sort of overflow where it leaked out.  Its not leaking anymore.

When I fired it up and adjusted the idle a bit it ran like a top.  As much as I love ripping up the trails on my DR650, it sort of feels/sounds like I'm riding on an air compressor.  This little 550 just sounds like magic.

Thanks again everyone!

[bryanj]

There ya go, easy simple fix

[newday777]

The overfill of oil and leaking could be gas that has siphoned into the cylinders and past the rings from stuck float valve(s), piece of gunk/rust in the float valves. Does the oil smell of gas? If so, you need to rebuild the carbs. Do a proper cleaning of full strip down and deep soak, boil clean or ultrasonic clean and new Honda float valves and gasket sets or K&L carb kits.

[cheeseman]

So you mean gas can actually leak into the oil and end up in the oil system and raise the oil level to the point it could leak out?

[cheeseman]

I just thought of something. Last time I was using this bike my knee was bad and I couldn't engage the center stand. Instead it was always on side stand, making the bike lean. I bet I brain farted, checked the oil while bike was tilted, saw low on dipstick and added way too much oil.  Is that possible?

Oil does not smell like gas, although I have to shut off gas valve or gas will leak out overflows when parked--is that bad float valve/needle?

Thanks!

[bryanj]

Yes to both.
To be safe might be worth an oil and filter change. It is supposed to be done every 1500 miles or yearly

[cheeseman]

Great thanks!  I will change oil/filter

For needle/seat, do you recommend changing every needle and every seat, or just the ones that are overflowing or is there some evidence I am looking for?

From my limited experience, I have changed needles when they show some scarring or pitting or a ring around the tip. Have never changed a seat because they always looked good, but I guess I don't know the what constitutes good/bad in a seat.

I admit this is not a job I look forward to, as I don't like removing the carbs. I am always afraid I am going to tear one of those boots and it feels really aggressive yanking them out. If anyone has a trick/tip I would appreciate it. I know I tilt them a bit and rock them.  I think the first time I ever removed them I had to use a ratchet strap or something. Many years ago. 

Thanks!

[bryanj]

If its an outside carb and you can get the float bowl off you can change a float needle an seat in situ, awkward but it can be done

[ckahleer]

I added a vacuum shut off valve to my V65 Magna to correct the same problem. 8 years later its still working fine.
Or you could install a vacuum petcock.
Float valves are for regulating fuel height. While they will work as a fuel shut off 99% of the time, that 1% will get you.

[bryanj]

As an aside, when you change the oil filter first thing over the bolt is a spring, then a shim washer to protect the rubber seal on the filter frequently missing as it gets stuck to the filter and thrown away, if its missing dont sweat it just order one for next change

[cheeseman]

Thanks Bryan, great reminder on that washer.

My Honda Rubicon ATV has the exact same setup, but it reminds you of the mistake by leaking!  Lucky I hadn't thrown the trash out!

So for the carbs, would you recommend changing just the needle or always needle/seat combo, and should I do it on all carbs?

Any recs on where to source a quality needle/seat?  The prices were all over the map on ebay.

Anyone ever tried rubber tipped needles?

[bryanj]

Original Honda probably the best and to change the seat is only 1 extra screw. If you dont want to go original there is a firm called siriusonic in Canada and to me if only one outer leaks and you can get at it i would just do that one, if its an inner or you have to remove the carbs i would change all 4 and the fuel pipe at the same time, 5.5mm id by the way and not the see through reinforced crap

[Maraakate]

I have a 77 CB550K and I can tell you from personal experience don't bother with the aftermarket needles.  Yes, it sucks spending ~$80 for OEM needles (you need four), but the time saved in constant headaches of trying to get the aftermarket junk to kinda/sorta/maybe work OK made it worthwhile.

Get a digital micrometer (any cheapy harbor freight special will do) and set the float height accordingly.

[cheeseman]

Has anyone had any luck with 4into1 or K&L for carb parts?

[cheeseman]

So I'll answer my own question. Don't use 4 into 1. Cheap stuff.  Replaced the seats and needles as 3 carbs were overflowing when parked.

Well first the seats did not want to seat.  I had to put some oil on the o ring and then really had force it in to get the o ring in place, whereas the old seats slid in nicely. I didn't like that, so I thought I could use the new needles with old seat.  Nope, new needle was too big for original seat.  So I got them in place, adjusted float height to 22, and also replaced the main jets as they looked a bit rough. These slid into place better.

As usual, pain getting the carbs back in.  So it fired up ok, but clearly is not running right.  Less power, a weird sort of puffing sound from one exhaust, and the idle is wacky.  It will go up, then down, even stalled out once. I guess I should have been content with just shutting the fuel off, as it was running great before.  But everything else was excellent, and I wanted it to be perfect!  Lesson learned.

So, can anyone recommend a better supplier for more needles and seats?  Thank. you!

[bryanj]

Check one of my previous answers

[cheeseman]

Ah yes, thank you I will check those out.

What is really weird is that one of the exhaust pipes isn't even getting hot...

[cheeseman]

Any ideas on why the one exhaust pipe is cold?  Does that mean that cylinder is not working at all (it was before I messed with carbs). If so, would it be because the "new" main jet or needle/seat is not functioning?

Thanks for any input.

[Deltarider]

Check ignition first: spark plug and plugcap OK and well connected? Any arcing between HT lead and/or plugcap and the head? This is best seen in the dark.

[cheeseman]

Thanks Deltarider.  Yes, I did check out the ignition on that cylinder. It all looked good.

As this occurred immediately after I was messing with the carbs, I'm pretty sure that's the cause.

I'm just wondering if I should be targeting the main jet or valve/seat/float when I get them off again.  I'm seriously considering pulling that aftermarket junk off and just cleaning up the old main jets and using those. They were just a little corroded. And then get some quality needles/seats.

[IrocRuss]

I've been working on restoring a 1972 CB500 that I rebuilt the carbs on.  Bike wouldn't start (had aftermarket rebuild kit).  Posted a question about kit and HondaMan responded.  This is probably relevant to your issues.  On a second note (this is just my thought about cylinder that is cold), I had 3 of my 4 overflow tubes that were cracked, one was a more noticeable crack that went down the whole tube.  I wasn't clear if you fixed your gas leak to overflow tubes.  If one of these is cracked, and the float bowel level is always to low, I wonder if cylinder not getting enough gas for combustion?  Also on the float seats, they can get pitted (separate issue from dirt), one of mine was pitted fairly bad, I'm sure it wasn't sealing well.  I still haven't worked out the not starting issue, but seems the new aftermarket carb kit is the issue.  Here's a link to my original post:
[url][http://forums.sohc4.net/index.php/topic,182292.0.html/url]

[cheeseman]

Thanks IROC

Yes, I did check those tubes. Filled up the bowls before reinstalling and they held. I put the bowls back on the carbs and bench tested it by gravity flowing some gas into it from a gas can. They held.  After putting them back on bike and driving a few miles, one carb began to overflow, but not the "cold" cylinder. That junk seat or needle no doubt.

Thanks for the link--it helps.

Good luck getting yours running!

[newday777]

Any ideas on why the one exhaust pipe is cold?  Does that mean that cylinder is not working at all (it was before I messed with carbs). If so, would it be because the "new" main jet or needle/seat is not functioning?

Thanks for any input.

Did you set the float level when you changed the needle and seat sets? Float level needs to be checked/set with new needles and seats. Overflowing can be a float level issue or clog in needle seat from garbage/rust particles in the tank.