Author Topic: Need help please (Read 1961 times)

stevenwr · « **on:** June 19, 2012, 01:36:30 PM »

I have a 1978 CB550K. Everything is stock except the 4-2 Niche exhaust. I've rebuilt the carbs, 90 main and 42 slow jet, 12.5mm float height, pilot screw 2 turns out. I checked the float height externally and all good. I replaced the points, set the timing and the point gap. Set valve clearances and cam chain tension. Did a compression test and all cylinders are within 10% of eachother. I checked for spark at the plugs and all 4 cylinders are getting spark. The bike runs great, idles great...but these are my plugs: 1-4 from left to right. It looks like #2&3 cylinders have no combustion the plugs look new.

dave500 · « **Reply #1 on:** June 19, 2012, 01:49:02 PM »

2 and 3 look good,,check the 1 and 4 points again,the condensor might be getting old.

ekpent · « **Reply #2 on:** June 19, 2012, 01:52:59 PM »

Since you said please I will say they look lean compared to the rest.. It does look though that they may not be getting as much fuel as the rest. How is the tank and petcock looking.Fuel line routing ?? It is all a chain from the beginning to the end. Good place to start. Check the header temps with a damp rag to really see what is getting good fuel and getting hot.Sizzle good,no sizzle bad after a couple minutes of running. How much run time on them ?

dave500 · « **Reply #3 on:** June 19, 2012, 02:01:18 PM »

straight to the carbs?carb 1 and 2 share the one line and carbs 3 and 4 share one line,1 and 4 and 2 and 3 share the same ignition coil/points and condensors,i would be going right over the ignition again first.

ekpent · « **Reply #4 on:** June 19, 2012, 02:11:59 PM »

Dave makes that GOOD point as we all need to be aware of. Because the coil and points runs 1&4 and the other side 2&3 if there is a similarity between a pair,and a difference between both ,its a good place also to start the troubleshoot. I would also check those points,timing etc-----

stevenwr · « **Reply #5 on:** June 19, 2012, 02:15:14 PM »

The fuel tank I resealed and the petcock rebuilt all clean inside. Last night I removed the ign plate and cleaned/lubed the advancer/retarder mechanism. Since it's #2&3 spark plugs I'm thinking it's the ign., if a condenser is getting old could it put out a week spark?

TwoTired · « **Reply #6 on:** June 19, 2012, 02:22:41 PM »

If you think it might be a condenser swap them side for side to see if the problem follows.

I will ask if the carbs have been vacuum synchronized, and if you are sure the pilot jets are clean. Were they extracted from the body?

With the replacement exhaust, I'd bet you need larger main jets. #95 as a guess.

All the plugs will look lean and engine will run hot after you get the differences sorted.

Cheers,

lucky · « **Reply #7 on:** June 19, 2012, 02:33:10 PM »

I would use #105mm main jets with that set up.

Many other forum members have used that size main jet and got good results.
IE...Twisted Engineering, One Wheel Drive.

You have to set the floats by the book!!
NOT "I checked the float height externally"

??
How would you know the gas level in those float bowls?

Go to Clymers manual and Chapter SIX Page, P125 Figure 13.
Do it right.

Also the pilot screws for that model should be 1.5 turns out not 2 turns out.

You did not tell us if your model had the accelerator pump system and nozzles.
Do they all work correctly?

FACTS: 1978 CB550K.
Main jets?
Idle jets?
Intake system?
Exhaust Niche 4 into 2
Pilot screws 2 turns out should be 1.5 turns out.
Slide needle may be non adjustable on that model.

ekpent · « **Reply #8 on:** June 19, 2012, 02:33:30 PM »

Since you resealed the tank just make sure you did not glob up the gas cap bottom with a bunch of that junk. I use a rubber plug on top when needed as a last resort reseal to do, but have seen people fill their vent hole with the gunk if they don't. Carry on and back to the discussion----

stevenwr · « **Reply #9 on:** June 19, 2012, 02:50:37 PM »

Swapping the condensers is a good idea...thanks.
The float height I measured according to the Clymers manual using a vernier caliper and there exactly 12.5mm. I then took clear tubing and attached it to the float drains. I put the clear tubing beside the float bowl and opened the bowl drain screw...the tubing fills up with gas and that way I can compare float heights. The reason I turned out the pilot screws to 2 instead of 11/2 is to make it run a little richer since I have a 4-2 exhaust. The slide needle is adjustable but I haven't found any reference to where they should be for a 78 550.

stevenwr · « **Reply #10 on:** June 19, 2012, 02:55:12 PM »

Forgot to mention sorry....When I rebuilt the carbs I removed all jets, seats etc. and cleaned them in a ultrasonic cleaner, and the carbs have been syncronized.

dave500 · « **Reply #11 on:** June 19, 2012, 03:26:23 PM »

how old are the plug caps?if you have a multimeter check they are 5kohm.

lucky · « **Reply #12 on:** June 19, 2012, 03:33:31 PM »

Quote from: stevenwr on June 19, 2012, 02:50:37 PM

Swapping the condensers is a good idea...thanks.
The float height I measured according to the Clymers manual using a vernier caliper and there exactly 12.5mm. I then took clear tubing and attached it to the float drains. I put the clear tubing beside the float bowl and opened the bowl drain screw...the tubing fills up with gas and that way I can compare float heights. The reason I turned out the pilot screws to 2 instead of 11/2 is to make it run a little richer since I have a 4-2 exhaust. The slide needle is adjustable but I haven't found any reference to where they should be for a 78 550.

Sounds like you are doing a good job!

The adjustable needles on the 1977 should have the clip on the 3rd groove from the top or the middle groove. Yours may be a early 1978 since it has an adjustable needle.

BTW so you have the accelerator pump on carb#2?

stevenwr · « **Reply #13 on:** June 19, 2012, 03:53:59 PM »

The plug caps, wires and coils I'm embarrassed to say are original. I'll checked the plug caps...that's a very good idea. The PD46c carbs as far as I know don't have an accelerator pump. If the 4-2 exhaust means I have to increase the main jets...wouldn't all four spark plugs be showing a lean condition not just 2&3?

ekpent · « **Reply #14 on:** June 19, 2012, 04:11:45 PM »

Surpised the plug caps have not already just pulled off with a gentle tug as they do need a trim and refit if the bike has been a little neglected. Checking their electical value is a good idea while you trim back to some fresh wire on those old wires.

stevenwr · « **Reply #15 on:** June 19, 2012, 04:24:19 PM »

I trimmed the spark plug wires back because the caps were loose, I just never checked the caps.

TwoTired · « **Reply #16 on:** June 19, 2012, 04:34:39 PM »

Quote from: stevenwr on June 19, 2012, 03:53:59 PM

The plug caps, wires and coils I'm embarrassed to say are original. I'll checked the plug caps...that's a very good idea. The PD46c carbs as far as I know don't have an accelerator pump. If the 4-2 exhaust means I have to increase the main jets...wouldn't all four spark plugs be showing a lean condition not just 2&3?

PD46C does not have an accelerator pump. Beware of people recommending jet sizes used on early style carbs with your PD style carbs. The PDs have a different venturi shape and therefore require different jetting changes. There is a lot of "noise" on this forum lately from people who simply do not know what they are doing, but like to sound like they do, and still don't realize the differences between the CB750 and Cb550, let alone model year changes.

The 4-2 change will need to have the main jet size increased, simply because the new system holds less pressure in the exhaust than the stock system does. After you figure out why all 4 plugs are not showing the same deposit patterns (have you done a carb vacuum sync?), then it is likely they will all be showing lean conditions...leading to an increase in main jet size.

I know you said "All jets". But the pilot jets are pressed into the carb body and many overlook them because of that. Please verify that you pulled out the pilot jets to clean them.

Have you checked for induction system vacuum leaks yet?

Tell us about your air filter. And verify that all the sync port screws are installed and tight.

Cheers,

stevenwr · « **Reply #17 on:** June 19, 2012, 06:31:47 PM »

I took a chance and pulled the pilot jets out and cleaned them also. The air filter is stock. When I was battling a high idle I ended up replacing the intake manifold o-rings and new boots from the carbs to the air box. That solved the high idle problem. The sync port screws are all in and tight. When I get home from work I'm going to check the spark plug caps and swap the condensers.

stevenwr · « **Reply #18 on:** June 20, 2012, 04:56:07 AM »

I checked the spark plug caps- #1: 4.71 Kohms #2: 5.09 Kohms #3: 4.39 Kohms #4: 5.09 Kohms.
Next I'll swap condensers.

stevenwr · « **Reply #19 on:** June 20, 2012, 01:47:55 PM »

Well this is interesting...yesterday I started the bike up just at idle to see if #2&3 cylinders were hotter then #1&4. Today when I went to put the spark plug caps back on after checking them I pulled the plugs to make sure there's spark. All spark plugs are black/brown!

This tells me it's carbs...the main jets need to be increased, at idle it's using only the slow jets. I wonder why then at 3/4 throttle the plugs aren't all white? I read earlier a post of a guy who had problems with a couple of cylinders being rich and it turned out to be the needle seats, I wonder if that's what's happening.

TwoTired · « **Reply #20 on:** June 20, 2012, 01:53:54 PM »

Have you seen this chart?

stevenwr · « **Reply #21 on:** June 20, 2012, 02:29:37 PM »

No I haven't seen that chart....that's great.
I just swapped my condensers and now there's no spark to #1&4. I checked the wires to make sure the #1-4 condenser wires aren't shorting and there ok.

stevenwr · « **Reply #22 on:** June 22, 2012, 01:56:34 PM »

Thanks for everyones input....I replaced both condensers and now all 4 plaugs are the same colour. #1&4 plugs are the same colour as #2&3.

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Author Topic: Need help please (Read 1961 times)