Author Topic: Blarg. Still hanging idle... 1976 CB550K (Read 5653 times)

Deltarider · « **Reply #50 on:** August 25, 2022, 01:10:46 AM »

Quote from: maxheadflow on August 24, 2022, 03:33:08 PM

I throw out how I do timing. Probably done a few hundred when these bike were new. It was part of the standard service.

First thing is to make sure the mechanism is clean and moves freely.

Make sure that the springs are tight and that they hold the weights up against the cam.. If loose, tighten the spring by using a pair of short needle nose and crush the spring loop on the pin. (arrows) During the time I worked on them never had to clip out a loop and reform the hook (except when I worked in a real crappy indy shop but mostly on Honda twins) . I'd expect that it would slow the advance curve sine the spring rate changes.

Rough gap the points and set the timing to the back of the F mark (8 deg?) See that at 1000 to 1300 RPMs that the timing is steady. If it bounces around, crimp the spring loop a little more..

With the timing set at idle see that full advance runs between the advance 2 lines. If not pull the points plate and using a hammer and a punch bend in the limit tabs.

Bikes always ran well. Came back to idle well.

When the motor and carbs are in good shape. You can set the idle mixture buy getting them all the same and after syncing, tweak them a little for best idle. You can then blip the throttle. If it comes back to idle slow, might need to richen up. If it comes back to idle and drops below, it's too rich.

Excellent advice. Never had to bend tabs however on a CB500/550. Running premium, I prefer to have 2 or 3 degrees extra advice. Also note that on most occasions readjusting the dwell (breakerpoints gap) is enough to arrive at the correct timing again: no need to turn the plates. So my working order would be to begin with (re)adjusting the breakerpoints gap. Only if you detect the advancer not moving freely, you need to unscrew the plates.

Scott S · « **Reply #51 on:** August 25, 2022, 02:41:19 AM »

Did you ever start over on the carbs? Seating the slides and then going for the 49mm?

Scott S · « **Reply #52 on:** August 25, 2022, 02:42:58 AM »

And this might seem like a silly question, but are the main jets in the correct orientation/direction?

OldGreyBeast · « **Reply #53 on:** August 25, 2022, 06:00:21 AM »

Yep, re benched the carbs with the 49mm deal. No change at all.

As far as I know the jets are in right. I put them in the same way they were in on all 3 bikes when I got em, so unless all 3 of those were wrong they're in the right way lol. I guess its entirely possible that happened, none of them ran when I bought them.

Anyone have a picture of the correct orientation?

dave500 · « **Reply #54 on:** August 25, 2022, 02:42:13 PM »

if your airscrews have the by pass hole it might be why it gives a lean or airleak type hanging idle,you can only cut off the air so far,if you have spares you can solder them solid if you dont have the solid type,this way you can enrichen the idle mix further if needed.

OldGreyBeast · « **Reply #55 on:** August 25, 2022, 03:40:12 PM »

It does have the mixture screws that have the air holes in it. I've noticed that the mixture screws make almost no difference at all. I looked through my spares bin and don't have any of the solid type, but have like 3 sets of extra mixture screws so I don't have anything against soldering up a set.

dave500 · « **Reply #56 on:** August 26, 2022, 01:55:21 AM »

yeah solder up a set,the ones with holes are like an emission thing?some models had the solid ones but i think all new kits supply the drilled ones?

maxheadflow · « **Reply #57 on:** August 26, 2022, 08:17:37 PM »

I would say the the carbs are not assembled right but you really need to go through and verify that the compression is good, valves set correctly and no intake leaks..

RAFster122s · « **Reply #58 on:** August 26, 2022, 08:38:46 PM »

You don't have any issues with your valve clearances, right? Worn eccentricity in rocker shafts on the 550 can cause strange running symptoms but usually isolated to 1&4 initially.

Most likely a carb issue where things are not moving freely I am betting.

OldGreyBeast · « **Reply #59 on:** August 26, 2022, 09:57:06 PM »

I've had the carbs apart 4 times and though I admit this is the first multi-carb setup I've ever worked on, I'm fairly mechnically inclined and have been working on cars/bikes for 15 years so I find it unlikely I did any assembly incorrectly. I mean for the most part things will only go together one way, so there's not really much that could be done wrong. Everything moves nice and smoothly. Throttle cables are smooth as butter and the return spring is strong with a good snap back to idle.

There are no intake leaks. Valves are set correctly and the rocker shafts are not worn (I do have a '78 rocker cover that I'll put on it for kicks if this continues). I'll check compression again after testing the soldered up mixture screws but it was fine about 1500 miles ago.

I can see how the mixture screws might be an issue so that will be my first test when I have some time to get back to this (hopefully Sunday), particularly since they really seem to make no difference (it's more of a binary thing, all the way closed kills the cylinder, but open .25 - 2.5 turns is pretty much the same, it revs a bit if you totally remove the mixture screw.

dave500 · « **Reply #60 on:** August 27, 2022, 12:48:22 AM »

just had a flick through the entire post,i have 4/1 pipe with airbox and run stock 100/40 jets with electronic,mine hauls arse,id drop that main down to 100 just because its not needed,not saying itll be your hanging idle issue though.

maxheadflow · « **Reply #61 on:** August 27, 2022, 10:36:08 AM »

Look at the screws on top of the arms. If they stick out too far, you won't get accurate slide positioning.. Also there are a bunch of parts in these mechanisms. If not assembled correctly, you are screwed..

95chris · « **Reply #62 on:** August 27, 2022, 01:41:56 PM »

Just chiming in here again to post an update on my situation. Bike finally returns to idle when letting go of the throttle!

Here the things I carried out when I pulled the carbs:

Verified needle notch position on all carbs.(#4, counting from blunt side). Did not have to do a bench sync, slide positions seem to not have moved at all after putting everything back together.
Installed the original Keihin pilot (#38) and main jet (#100). I opted to stay with the Keyster float needle with its seat and air mixture screw.
Installed a genuine main jet o-rings from Honda. Actually had to use a small teflon drift to install it! Used a bit of oil on it as to not damage it during install. It's also much harder to pull it out by hand unlike the Keyster mains.
Readjusted float height to 22mm, had it set to 20mm for some reason.
Completed a static timing.

Even after all that the bike would still hang after letting go of the throttle and I would have to bring it down by adjusting the idle knob.

So what worked? Backing out the air mixture screw by another half a turn out. Yep, literally the last thing I did after everything.

I had set a baseline of 1.5 turns out from fully in as per the Keihin setting chart in the Carb FAQ. So now the screws are now set to 2 turns out. I'm guessing the Keyster air screws are just that different then to the originals that they require slightly higher/lower adjustments to achieve similar settings to stock.

Maybe it's just me but I feel like the engine is much more quieter than when it was hanging, even at 1000-1500 RPM. Knocking is less pronounced and just sounds a lot more smoother. Pardon the commentary in the video, just glad some progress was made.

In case your wondering, the 350 gauge is sticking so that's why I have the 550 gauge sitting on the side.

I will say I'm happy I changed the o-ring on the main jet. I'm much more confident there is a proper seal now.

Best of luck on your bike! Hope it runs better soon, sure can be frustrating...

Chris

OldGreyBeast · « **Reply #63 on:** August 28, 2022, 01:44:13 PM »

Hmm maybe I need to try opening the idle screws up more after reading 95chris's post. I just got back from soldering up my mixture screws, and boy did that make a huge difference. Now I don't have the problem of the carbs "losing their sync" every time throttle is applied. I'm still chasing the hanging idle issue, but now instead of hanging forever it'll hang for like 5-10 seconds then start to stall out. Definitely making progress. The choke also nearly kills the engine when applied, instead of taking several seconds to do anything like before.

I was able to go through several 1500-4k cycles and turned the bike on/off 3 times and the carbs are staying very close on the vacuum gauges, so I think that problem is solved now. Moving the mixture screws actually makes a lot of difference now that they're soldered up. I had initially tried them at 1.5 and kept closing them off more thinking too much air was the problem. Next time I'm out there I'll try opening them to 2 turns instead.

I think the only thing different between my setup and 95chris is the 2.0 mixture screw setting and him being on the 4th position of the needle (mine is on the 3rd).

Thanks for all that have helped, I feel like we're finally getting somewhere.... hopefully can get this last bit nailed down.

Scott S · « **Reply #64 on:** August 28, 2022, 02:20:01 PM »

Can you show us a picture of the sync screws? How many threads are showing?

OldGreyBeast · « **Reply #65 on:** August 28, 2022, 02:44:58 PM »

1 and 2 both looks like 4 threads showing, 3 is 5 threads, 4 is 2 or 3 threads. Setting the mixture screws to 2 made it way worse. It's best at around .5 turns, but there's some smoke coming out of the exhaust so I'm guessing it's pretty rich at that point, and it won't idle for more than 15-20 seconds without requiring a throttle blip to keep it going. The video below is with the screws at 1.5 turns. It idles fine there, but does require futzing with the choke to get it to calm down.

1 and 2

3 and 4

News:

Author Topic: Blarg. Still hanging idle... 1976 CB550K (Read 5653 times)