Topic: ignorance is bliss........

[welnamark]

At least when it comes to compression....I have a 1978 CB550K that i bought two years ago with 6900 miles.  Now it has 12,000.  It's always been cold blooded,  i mean really cold blooded.  On cold start it will catch and stumble several times before holding it's idle and it won't even think about starting unless the the idle screw is cranked up about 3/4 turn.  It likes to be fully choked for at least 5 minutes and then will idle pretty nicely around 1500 rpm.

I always suspected that the pilot jets were dirty and that it was running lean particularly at idle. The pipes are bluing significantly. I have been trying to get the bike ready for a longish trip this summer and decided to replace the pilot jets.  Not particularly excited to pull the carbs i though a tune up was first in order to see if the carbs could be avoided. 

I replaced plugs, adjusted the valves, cleaned the points, adjusted the timing chain, and checked compression.  The readings were as follows. 

#4: 112 psi
#3: 105 psi
#2: 100 psi
#1: 110 psi

I nearly cried.  The bike only has 12,000 miles on the clock.  The exhaust looks great, never seen any blue smoke, so i suspect that the rings are fine.  There is no oil seepage on the head and again, no blue exhaust, so I assume the head gasket is fine as well.  ( My prior 550 had a head gasket so bad that it actually spit hot oil on my leg for most of the ride). 

The fact that I have suspected lean running conditions all along and foolishly continued to ride in concert with the lower compression readings in the center cylinders makes me fear I've burnt and damaged my valves.  I should be noted that i also took the #3 and #2 readings last because they were a larger pain so the engine was cooler at this point.

I would really appreciate some wisdom about how to proceed.  I've always subscribed to the philosophy that a person should be able to maintain their motorcycle and this belief has sometimes caused more harm than good.  Do you guys agree with the valve diagnosis and how should i proceed?

Thanks for the great community and a passion for cool bikes.

-mark

[Gordon]

Have you tried putting a little oil in each cylinder to see if/how much the readings change?

[tygrant]

if it were me i would just keep riding it. i know other people will disagree but if you tuned it up, fixed the lean condition and it still runs... run it.   

[Bob Wessner]

Was the engine hot or cold when you took those readings? What type of compression gauge did you use? Did it have a hose adapter on it, that could alter the readings.

[bryanj]

Did you have the throttle wide open?

[welnamark]

The engine was hot when I started taking readings.  The engine was fully choked and the throttle was wide open.  The compression guage I have has a rubber hose that is about 15" long I would image.  I will redo readings again tonight, dry, and with oil.
thanks,
-mark

[Sporkfly]

The choke completely defeated the purpose of having it wide open mate. The idea is to get as much air flow as you can.

So that along with the 15" hose might be hosing ( ) your readings.

Edit: Also you should have no more than 10% variation between cylinders.

[Gordon]

As you can see, there are many factors that can influence the overall reading.  Unless you're positive you're getting accurate individual cylinder readings, the main thing you're looking for is that there isn't a major difference between any of the cylinders.  

The middle cylinders are a little lower than the outer two, but not something I'd consider worthy of a rebuild unless I was just itching for a project or was trying to get the absolute most out of my engine.

[welnamark]

Thanks guys.  I feel better all ready.  I could hardly sleep last night. 

Sporkfly:  Thanks.  What you say makes sense.  I swear my clymer manual said to have the engine fully choked??

Gordon:  I'm definitely not itching for a project.  I just want to get the horrible cold idle issue sorted out.  I get depressed everytime i hear it idle when cold, and am obviously paranoid about running lean. 

The bike runs great when hot and it took me around Lake Superior last summer without a hitch.

I'll redo the compression readings tonight.

What does everyone thing about replacing the pilot jets.  Complete carb rebuild kits are $43 at SCI.  $172 OUCH!!  I have new pilots on the way for $22 for all four.

So the choke is supposed to be open?

thanks everyone.

-mark

[IHWillys]

...the main thing you're looking for is that there isn't a major difference between any of the cylinders....

Agreed.  I've run engines(not Honda 4s) with worse than that.  Low numbers on a comp test that are low across the board are not particularly concerning.  The test method may explain the low numbers.  Even if the compression is truly low, the uniformity of such leads myself to believe that no imminent catastrophic failure is indicated and thus the engine is safe to run without any specific increase of risk of inflicting other/further damage.

Focus on fixing the start/idle/lean issue.

Ken

[Sporkfly]

Thanks guys.  I feel better all ready.  I could hardly sleep last night. 

Sporkfly:  Thanks.  What you say makes sense.  I swear my clymer manual said to have the engine fully choked??

Gordon:  I'm definitely not itching for a project.  I just want to get the horrible cold idle issue sorted out.  I get depressed everytime i hear it idle when cold, and am obviously paranoid about running lean. 

The bike runs great when hot and it took me around Lake Superior last summer without a hitch.

I'll redo the compression readings tonight.

What does everyone thing about replacing the pilot jets.  Complete carb rebuild kits are $43 at SCI.  $172 OUCH!!  I have new pilots on the way for $22 for all four.

So the choke is supposed to be open?

thanks everyone.

-mark

Yep, you want a straight shot through your carbs with as little resistance as possible otherwise you aren't sucking enough air to give an accurate reading. If you've got the choke close you're restricting the air flow to pull more fuel. Fuel won't give you the compression reading you're looking for. I had similar readings on my bike prior to opening the throttle, once I opened the throttle it shot from readings of 90-100 to a reading of 135 even with the long rubber hose. Without something in the cylinders to compress the gauge will be wildly inaccurate.

Anyway, I'm just babbling now. Around lake superior you say? Did you pass through Marquette at all? If you did why the heck didn't you stop by!  

Edit: and agreed, fix your fuel ratio and ride!

[welnamark]

Sporkfly.  We went right through Marquette.  Two 78 CB550K's and a VFR.  We'll stop by next time to warm up.  It sure is cold up on the North side of the lake!

[Gordon]

What does everyone thing about replacing the pilot jets.  Complete carb rebuild kits are $43 at SCI.  $172 OUCH!!  I have new pilots on the way for $22 for all four.

What would be the cause for replacing the pilots?  You say you suspect that it's idling too lean, but have you confirmed this? 

If the pilot jets are clogged all you need to do is clean them, and make sure the jet passages are clean and clear, too.  Replacing the jets isn't typically necessary unless you need to change the size. 

[JLeather]

Length of hose to the gauge shouldn't matter.  You kick (or run the stater) until the reading settles anyway.  Unless your check-valve isn't working the reading shouldn't hardly change with a different length hose.

BUT, the choke is definitely a problem.  Try that again with the choke off and the carbs WOT.

And if it doesn't change, ride it anyway.  Ride it until it's either too slow to be safe or starts smoking like crazy and then rebuild it.

[welnamark]

Thanks Gordon.  Wouldn't the need for excessive choke and idle speed indicate a lean condition?  I guess other then that and the bluing pipes I don't have much reason for that assumption.  All the carb boots look good.  I don't think the carbs have ever been messed with.  I suppose it's possible they could need to be synced.  It just seems like the engine isn't getting enough fuel at idle to me and wouldn't that indicate the pilot jet?  While replacing or cleaning them i will also check for appopriate float height.  What else could cause such poor idling?
-mark

[Frankenkit]

MickeyX and I were cross-referencing carb rebuild kits, and if you just went the o-ring and bowl gasket route, it'd be $15 each (x4, of course) direct from Honda, I believe.  Then just get your float needles from Z1.  

IMO these later SOHCs are jetted SO lean that ANY gunk in your idle passages will cause you major grief.  Ask me how I know.  The 650s are the same or worse.  

TwoTired is our resident 500/550 expert (but not yet an expert on 650s because no one's given him one yet) but he can help you figure out your lean condition, too.

[Gordon]

Thanks Gordon.  Wouldn't the need for excessive choke and idle speed indicate a lean condition?  I guess other then that and the bluing pipes I don't have much reason for that assumption.  All the carb boots look good.  I don't think the carbs have ever been messed with.  I suppose it's possible they could need to be synced.  It just seems like the engine isn't getting enough fuel at idle to me and wouldn't that indicate the pilot jet?  While replacing or cleaning them i will also check for appopriate float height.  What else could cause such poor idling?
-mark

These are things that could be indications of a lean condition, but could also be other issues.  Clean off the spark plugs really well or install new ones and do a plug chop at idle to see what the deposits look like.  This will give you a much better indication of the idle fuel mixture.  Once you're sure the jets and passages are completely clean then you can make adjustments to the idle mixture screws to fine tune it.  

[welnamark]

I changed the plugs after doing the compression check.  The plugs looked alot like image #17 here:

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Although alot of the pics admittedly look the same to me.

I guess I'll start by checking compression again tonight with the choke OPEN to hopefully ease my worried mind, and when the new pilot jets arrive I'll pull the carbs to check old pilot jets, float height, etc. and see if that does anything for my idling problem

I'll get back tommorrow with tonights compression check and later with info about the internal state of the carbs.

thanks for everything everyone.

-mark

[Gordon]

I changed the plugs after doing the compression check.  The plugs looked alot like image #17 here:

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Although alot of the pics admittedly look the same to me.

I guess I'll start by checking compression again tonight with the choke OPEN to hopefully ease my worried mind, and when the new pilot jets arrive I'll pull the carbs to check old pilot jets, float height, etc. and see if that does anything for my idling problem

I'll get back tommorrow with tonights compression check and later with info about the internal state of the carbs.

thanks for everything everyone.

-mark

#17 is in the "best" range according to that chart, but you really need to start with clean plugs and do a chop at only idle speed to isolate that part of the fuel circuit.  Otherwise you're just looking at an overall deposit.  A carb synch could definitely help your idling issues, since idle speed is where un-synched carbs will have the most negative effect. 

[chrislib]

Here is a wealth of plug reading goodness, the guy is a BIG Mopar guy but spark plugs are spark plugs. As a side note, if any of ya`a have an older Mopar Don`s ignition box/coil combo is some of the best out there.
http://www.4secondsflat.com/Spark_plug_reading.html

[OldSkool]

I'll be watching this thread closely. It would make sense that the later SOHC engines ran more lean I guess to keep the hydrocarbons down for higher emissions standards. I have recently been going through the same problems as you and surprisingly also have a #1 getting pretty hot. I'd also like to keep from doing more damage to the engine and would love to also nip the lean idle problem in the bud, if I can offer up anything helpful I certainly will.

You're bike looks great by the way, hope things work out!

[alltherightpills]

Here's what TT had to say about compression testing equipment.  Might explain some of those low numbers.

From the Engine FAQ:
http://forums.sohc4.net/index.php?topic=369.msg476032#msg476032

[TwoTired]

The compression numbers don't look alarming.  Unless the tester check valve is right at the spark plug hole any volume the hose adds to the squish chamber in the cylinders changes the effective compression ratio.  That's why you only look for numbers within 10% of each other.

I don't think the numbers you posted are any cause for alarm.
Valve clearance adjustment can make a difference in compression tests.

Cold starting. 
It sure sounds like someone put D8EA plugs in your bike instead of D7EA as is proper.  OR, you aren't getting full choke butterfly closure when you pull the choke out all the way.  This is coupled to a fast idle cam, so I don't see why you have to change the idle setting for warm up.  (there is an adjustment for the fast idle cam.

Yes these have lean burn carbs.  In front of each carb bowl is an idle mixture screw.  You can turn this out to increase the idle fuel mixture.  But, if it runs properly after it is all warmed up, then it is likely fine where it is now.  1500 is too high, though.  Any cold(er) head pipes?  I would suspect some pilot jet blocking if the IMS is set out at 2 turns or so.  Stock idle jets are #42, which should be plenty if they are clear.

This all assumes you are still using the stock exhaust and air filter arrangement.

Cheers,

[welnamark]

Chrislib:  Thanks for the great plug info.

OldSkool:  Thanks for the bike comment.  It looked like new when I bought it, but has since suffered some wear.  I'll keep up with this post in case we have similar issues.

Alltherightpi: The link to the Engine FAQ really eased my mind.  My compression gauge has a long fat rubber hose.  I'm embarrassed i didn't find that thread on my own.  I really have thouroughly researched this issue. 

TwoTired:  Thanks for writing the Engine FAQ about compression and for your very useful thoughts.

I took new compression readings with the choke OPEN, WOT, dry and wet.  The results were slightly better.

#4:  120
#3:  115
#2:  105
#1:  115

The readings were the same with or without oil.  I took the number 2 cylinder readings last and the engine had cooled significantly by then so i think i could have squeezed a few more pounds out of that one.........

I have alwaysused, and just put in new, NGK D7EA plugs.  I'm going to start with rechecking valve clearances.  When i did them at the end of last riding season I found that I really had to bend or arch my feeler gauge to get it where it needed to be.  I think this may have added a little friction and my valves may be a bit loose.  The engine certainly has plenty of valve noise and sounds like a sewing machine when it's running smoothly.  I bought a motion pro feeler guage with a bent feeler which may make valve adjustments more easy and accurate.  It will be here in a couple of days so I'm going to start their.

When the new pilot jets arrive (#42) I am going to pull the carbs and do a thourough carb clean.  When the carbs are out I'll also check for full choke butterfly closure.  I hope that that will help my situation. 

Everything on the bike is stock except for the Krauser saddlebags.

Thanks again everyone.

I welcome and appreciate any other advice or suggestions.

I'll get back to the post when i get inside the carbs.

-mark

[TwoTired]

Those PD carbs should already have #42 slows in them.
Why are you replacing them with same size?

Where were you able to find replacement press in jets?