Author Topic: 1978 cb550k running issues (Read 2799 times)

scottanderson76 · « **on:** May 31, 2013, 04:27:00 PM »

Hello all,
I hope somebody can give me some insight as I have been unable to track down any info on this site in regards to my current issue. I purchased this bike with the Mac 4 to 1 and pod filters and it was supposedly jetted for 500' above sea level. I currently live at 5000' and knew I was going to have to do some tuning. However every time the bike gets up to operating temp and after I have ridden for a couple miles it just seems to start bogging down and has no power and I have to limp it home with the full choke on. It also starts to leak a little oil out of the head (pic below). I am totally at a loss at what I need to do. Any more background info you think need to provide I would be more than glad to provide. Any assistance in remedying this would be awesome!

harisuluv · « **Reply #1 on:** May 31, 2013, 06:30:06 PM »

Head gasket leak is pretty common.

Sounds like something once hot enough is expanding and creating an issue, possibly a vacuum leak. I would check the carb to head manifolds, particularly the seal between manfiold and head, which is sealed with an o-ring, which is probably hard and. Once things heat up...

Spray something flammable i.e. brake clean while it's running around the seals and see if the rpms go up. Watch the paint..

Not saying for sure that's what the issue is but it's not a bad place to start and easy to check out.

scottanderson76 · « **Reply #2 on:** June 01, 2013, 07:01:32 AM »

Thanks harisuluv, I will try that out. Also, forgot to mention one of my float bowls had some damage to the inside near the drain screw so I decided to use some jb weld to fix it. This might be my problem, this was a temporary fix until I got a new one anyway. Do you think this is my issue? Lastly, so I would like to address the leak what do you suggest? I was thinking of getting a gasket set and I already have a oil seal set. Any ideas?

harisuluv · « **Reply #3 on:** June 01, 2013, 08:20:11 AM »

Just make sure the jb weld is fuel resistant.

The leak you have looks like it is more likely the rubber puck issue. Take the head cover off and you can see them, there are 6 of them. You can try that and maybe a retorque on the head.

All depends on how thorough you want to be.

scottanderson76 · « **Reply #4 on:** June 02, 2013, 07:00:16 AM »

Sweet, thanks....will give it a shot and report back with my findings

scottanderson76 · « **Reply #5 on:** June 12, 2013, 02:14:44 PM »

Quote from: harisuluv on May 31, 2013, 06:30:06 PM

Head gasket leak is pretty common.

Sounds like something once hot enough is expanding and creating an issue, possibly a vacuum leak. I would check the carb to head manifolds, particularly the seal between manfiold and head, which is sealed with an o-ring, which is probably hard and. Once things heat up...

Spray something flammable i.e. brake clean while it's running around the seals and see if the rpms go up. Watch the paint..

Not saying for sure that's what the issue is but it's not a bad place to start and easy to check out.

Ok, a quick update. I did take the carbs off and check those O-rings as you requested and they were toasted. Replaced those and re-jetted from 110 mains to 105's and tested and was still a little lean so went one more size down to 100 mains. This seems to be good but I did go up one size on my pilot jet and it doesn't hardly need any choke now (literally 15 seconds or so of partial choke) and throttle on 1/16 to 1/8 seems to sputter a bit (especially around 5k). I believe from what TT said in one of his posts that this throttle position is affected mostly by the pilot jet so I might go back down to the 42's and test again. Lastly, my throttle doesn't quite rev as free as it did before I made the jet changes...any ideas? Also, sometimes it doesn't return to idle and just dies. I think I will need to re-adjust my IMS screw again. Lastly, (I swear this time) I did a top speed test with the 100's and about 90 was as high as I made it. When I had the 105's in I was easily able to achieve the ton. I guess I can sacrifice some top end as I will never really need to go that fast anyway.

flybox1 · « **Reply #6 on:** June 12, 2013, 02:26:42 PM »

going from 110's to 105's will make your top end MORE lean.
if you are trying to richen up mid throttle and WOT, you need to go UP in jet size, and LOWER your needle clip position.

scottanderson76 · « **Reply #7 on:** June 12, 2013, 02:34:48 PM »

Quote from: flybox1 on June 12, 2013, 02:26:42 PM

going from 110's to 105's will make your top end MORE lean.
if you are trying to richen up mid throttle and WOT, you need to go UP in jet size, and LOWER your needle clip position.

[/quote

flybox, thanks for the info. I was under the impression the PD46C carbs i have did not have the ability to adjust needle clip position? Also, I was following a chart for jet sizes based on my altitude and the modifications I have on the bike. I believe I got this from a very respected member of this forum. Let me know if this is correct and I will address this with the comments you have made.

flybox1 · « **Reply #8 on:** June 12, 2013, 02:40:53 PM »

this might also help...
http://forums.sohc4.net/index.php?topic=112132.0

scottanderson76 · « **Reply #9 on:** June 12, 2013, 04:47:14 PM »

Quote from: flybox1 on June 12, 2013, 02:40:53 PM

this might also help...
http://forums.sohc4.net/index.php?topic=112132.0

Thanks flybox, I believe this will be helpful. The elevation thing is really stumping me but I want to stick to it. These mythical carbs will NOT get the better of me. Also, as I am new to this I was curious if you have a picture or could tell me where this mythical needle clip is on the PD46c carbs?

scottanderson76 · « **Reply #10 on:** June 17, 2013, 02:25:15 PM »

Could someone be so kind to assist with the discovery of the needle clip on the PD46C carbs? Picture? How to adjust the clip?

Bankerdanny · « **Reply #11 on:** June 17, 2013, 03:08:55 PM »

Take the cap off the top of the carb.

Remove the two tiny screws that hold the arm that moves the slide (you will need a medium length screwdriver, preferable magnetic).

The needle will be under the plate those screws go through.

The needle is brass, so a magnet can't lift it. However, the clip is steel, so you should be able to get a magnet on it to lift the needle free.

Scott S · « **Reply #12 on:** June 17, 2013, 03:23:41 PM »

The needles/clps can be removed with the carbs on the bike. It's a bit fiddly, and you must have the right screw drivers with a magnetic tip, but it can be done. I just did I t on my '78 last week in less than 30 minutes.

Remove the tops of the carbs.
Remove this screw:

Down inside the carb body are two small screws. Remove then and then you can flip the whole arm/assembly back and pull out the slide and needle.

The needle looks like this. Stock is 2nd groove from the top.

Put down a soft towel and use a small pick or screwdriver to push or pull the clip out of the groove. It simply snaps back in, using a small flat blade screw driver or a tiny pair of needle nose. Work somewhere clean and on that towel....these things can and will go flying and you want to be able to find them.

Pay attention to the cut out on the slide when you remove it. Make sure it's facing the same way when re-installing. Flip the arm/assembly back down and, using a small pick, align the two screw holes. I started one screw but left it slightly loose so I could align the other hole. Once both screws are in, tighten. Install the screw on the shaft that you removed in step one.

You WILL have to re-synch with vacuum gauges when done.

scottanderson76 · « **Reply #13 on:** June 17, 2013, 08:53:54 PM »

You guys are awesome! I can't tell you how much I have learned in such a short time of reading everything on this site. I will take what you guys have mentioned and apply, also I just spent the cash and bought a carb synchronizer for just such an occasion.

scottanderson76 · « **Reply #14 on:** July 02, 2013, 12:21:16 PM »

Ok...update. So I did what you guys mentioned and I have changed the needle clip position to the third position. I synced the carbs after that and I still have the same hesitation and flat acceleration starting at the 4500-5K area. I have completed the 3k tune up and nothing was out of whack. My current setup is:
110 main jet (90 stock)
45 pilot jet (42 stock)
3rd clip on the needle (middle)
floats set at factory 14.5MM
and I live at 5000' ft.

Am I missing something? One thing I thought of was, when I changed the needle clip position I could have put all 4 of the slides in backwards (opposite direction). Has anybody made this mistake before? If so, what are the reprecussions?

scottanderson76 · « **Reply #15 on:** July 02, 2013, 01:55:15 PM »

Quote from: scottanderson76 on July 02, 2013, 12:21:16 PM

Ok...update. So I did what you guys mentioned and I have changed the needle clip position to the third position. I synced the carbs after that and I still have the same hesitation and flat acceleration starting at the 4500-5K area. I have completed the 3k tune up and nothing was out of whack. My current setup is:
110 main jet (90 stock)
45 pilot jet (42 stock)
3rd clip on the needle (middle)
floats set at factory 14.5MM
and I live at 5000' ft.

Am I missing something? One thing I thought of was, when I changed the needle clip position I could have put all 4 of the slides in backwards (opposite direction). Has anybody made this mistake before? If so, what are the reprecussions?

I forgot to add that I have my IMS screws 1 turn out. I have been reading a few other posts and there are a few other PD46C carb owners having the same issues as I am with the sputtering and no power around the 5k mark. Most of you have been saying that the needle position affects this.

Scott S · « **Reply #16 on:** July 02, 2013, 04:46:28 PM »

Stock clip position is second from top. By going to the 3rd position, you raised the needle, which added more fuel. You may be TOO rich at your high altitude.

scottanderson76 · « **Reply #17 on:** July 03, 2013, 07:37:34 AM »

Quote from: Scott S on July 02, 2013, 04:46:28 PM

Stock clip position is second from top. By going to the 3rd position, you raised the needle, which added more fuel. You may be TOO rich at your high altitude.

Thanks Scott S...it seems the more I read the more I am looking at this as a potential culprit. I think I am going to switch to the 2nd clip position and re-sync and see where that gets me. I will report back with my findings.

scottanderson76 · « **Reply #18 on:** July 06, 2013, 02:29:25 PM »

Ok, what an adventure in head scratching and patience (thank you gin and tonic yesterday). So I discovered the culprit...it had nothing to do with clip positions or jets and everything to do with timing. I spent all day yesterday trying different combinations to no avail...so I went back to the drawing board and set the points and timed it for at least 2 hours this morning going back and forth on the exact location of everything before I got it perfect. The points are set at .014 feeler and the the timing light has everything spot on per what the factory manual states. This seems to be ideal as just listening to the bike she sounds spot on. This is what I have as far as my setup and is working quite well

105 main jet (90 stock)
45 slow jet ( 42 stock)
2nd clip from top on the needle
iMS screw set at 1.5 turns out
Floats set at 14.5mm
I live at 5000ft

There is no flat spot anywhere in the rev range and it pulls good in every gear. I will be doing more testing but the sync is spot on and the plugs look good for the minor amount of ride time I have in. If anybody has any questions feel free to ask.

K3Owner · « **Reply #19 on:** July 06, 2013, 03:40:26 PM »

So, can you again reach a ton on full throttle? I always set the main first so find your top speed. That, and I understand the setting for those late carbs for float level is 12.5mm so you're a little off. That said, if it runs really well and has pods and a Mac, you've done well, Pilgrim.

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Author Topic: 1978 cb550k running issues (Read 2799 times)