Verify my compression numbers are right

Hey guys - finally got around to doing the comp test.

Did a nearly cold test - had cooled off for about 2 hours.

Numbers:

1 & 4 were ~ 160PSI
2 & 3 were ~ 150PSI

After warming up the motor, rechecked:

All 4 cylinders across the board went up 1-4 PSI max.

The highest cylinder was #4, @ 160PSI, 160 after warm.

I know they are not LOW numbers at all, but are they too HIGH?
I know too high is a problem somewhere, but I forget.
But they seem good to me, please verify my results!

Thanks guys.

 

Standard 156
Minimum 128
Maximum 171

Max diff between cylinders 14

Sounds like you have great compression.

 

Did you shave the head? Have you run a little rich for a while? Either condition will bring those numbers up. The former is expected, the latter, not so good. Carbon buildup in the chamber can lead to hot spots, predetonation and cracked heads/burned pistons. Given that you are close to the high end (156psi max), I'd be concerned as well. What color are your spark plugs?

 

I have been running rich.

I just did a colortune w/o YICS to get the mixtures at least firing all the time at idle. Then put the YICS in, sync'd, and now I am ready for a final colortune again.

I did take a run around the block @ 3 turns out, when it used to run good at 6 turns. Idled like crap. Got it back, pull the plugs - #3 plug was TOUCHING the anode. WHAT THE HECK?!

Also mashed my plug hole threads a bit, but I kroiled them and they are a bit better. (only one hole)

Robert, you said 156 max, Bill says 171. What's right?

Carbon buildup is gone. Used to be a lot. When I did the comp test, it was gone. If I was getting predetonation, would I hear it?
If I was hurting my cylinders, could I see it? I have inspected visually my crowns they look nice and clean, even the etched symbols on the top are good.

So - The sync I just did, along with richening the 3 turn out setting to about 5, or so, really cleaned up the idle.

I think the run around the block real lean might have melted my plug tip on #3 so it bent closed? Is this possible?

 

DP, no expert, just opinion. What does your manual say the cold cranking pressure should be for your model? Do you always hold the throttle wide open when you crank it on each cylinder? The numbers you posted aren't that high for a modern motorcycle and a stock Harley runs around 150#. People run regular gas with CCPs around 170-180# so yours sounds good.

As for the side electrode touching the center electrode on your plug, something bumped it good or it was improperly gapped to begin with. Put another properly gapped plug in that cylinder crank it over for a second or two, pull the plug and stare at it. If the side electrode is again bent in to the center electrode, you have an obstruction on the top of that piston.

Your combustion chambers aren't going to get nearly hot enough to fry that electrode and somehow force it into the enter electrode. If it got that hot, you would have see-thru pistons already. I suspect the plug was improperly gapped or you bumped it against something putting it in.

Don't confuse pre-ignition with detonation. Pre-ignition is caused by a hot spot glowing in your combustion chamber and firing the mixture ahead of time.

Detonation is spontaneous combustion from high pressure, heat, cheap gas and your CCP numbers aren't way up there. I don't think your timing could be that far off (could it ???) and you'd hear a light knocking/pinging noise as you really get on it hard. The noise speeds up with RPM. If you're hearing that noise maybe your timing is way off.

 

My timing chain has never been checked for adjustment - mostly because I don't know what tool to get in there and loosen the nut etc.

I had a light noise between 1500 and 2000 the other day, but I think it is gone now.

I threw another plug in, gapped to 0.028 and it went in, fired up, and came out 30 seconds later, and it's fine... Maybe I just nailed it dropping the plug into the hole on the corner of the hole or something last time.

Idle seems better with new sync. Definately.

 

You have to take-off the Cam Cover and LIFT the Chain UP Off the Cam Chain Bridge to chech for SLACK.

The Chain shouldn't want to move at all. It should be nice and tight. If you can lift it off the Bridge you need to Adjust the Tension ... -Or- If the Tensioner is at the Limit ... the Chain.

Chains are usually good for 55,000 - 60,000 Miles.

 

Timing chain effects camshaft timing adn I don't believe that's your problem, DP. Your ignition timing (whole different animal) could be off. You might want to whip out the manual and check that since if it is too far advanced you can get detonation.

If you lug it down to 1500 - 2000 in too high of a gear, you could get the sound of detonation in a pretty good running bike engine. The cure for that kind of "detonation" is simply to drop down a gear. :wink:

I think your numbers are just fine and if the bike isn't running to suit you, the carbs might need a little more fine tuning or cleaning. Throw some Seafoam in the tank, ride it and see what happens.

 

My numbers are from the Haynes manual. The service manual only specifies 156 as the normal pressure. By the way these are always stated as at sea level.

 

Gee Bill, I pulled mine off of a 81 Service Data Sheet...for a 750...DOH! I gotta pay attention.
I pulled my Haynes off the shelf and confirmed your numbers off of page 37.
From the sounds of it Dpawl, you are in good shape!
Now I'm left to wonder if the specs on the Data Sheet are in error given the Haynes spec. I'm in agreement with Icantinaturner's logic. I'm gonna have to run a check on my 750...

 

Doug. Settle down. Your compression numbers are fine. Finish tuning the bike. RIDE IT. That was the whole idea in the first place. You've succeeded. Now go for a ride.

 

agreed.

 

I can't.

its running terrible again.

bogging etc.

how often does the cam chain need to be tightened? its a lot noisier lately, I think I may have stretched the chain a bit after riding real hard. the old owner rode it very easy. once I got the power back, I ran hard and probably shouldn't have. its chugging with low rpm and feels held back after that.

the mix screws are still way out, but its the only way I can get the colortune to fire without missing. 3 turns out and it was barely firing.

the sparks look weaker than before... this thing is driving me mad. seriously.

 

Chain self adjusts - the hand adjust process should not be required very often at all.

Your other issues still sound like you have some tuning to do. It's frustrating until you get it right. It is an iterative process. Tune, sync tune, sync etc.

Take a step back and relax - then jump back in.

 

Sync twice... tune 4 or 5 times.

Tune via colortune.
Colortune stays nearly blue the whole time.
But it DOES react. It changes as I move it, on all 4, exactly the same.

So my ports are not clogged - unless they are ALL clogged, EXACTLY the same amount, and none are completely clogged... because they all react, and react the same.

It's definately not right. Nobody on here has any clue WHY my bike runs pretty damn good @ 6 turns out on the mixture screws. Nobody can figure it out.

With the screws 3 turns out, it barely fires and runs real rough idling.

When I got the bike, the screws were that far out- figured brand new EVERYTHING in the carbs, fresh plugs, check for leaks, valve clearance adjustment, new valve cover... blah blah blah... would fix it. Nope. Not at all.

No way in hell it's running like this because the oil is nasty right?
I mean, there was a lot of carbon in the cylinders, and it's all gone now that it's been run a lot.

Still don't see oil causing it to run like that... ugh.

Piece of crap... errr.

 

i think that when there's no carbon on the cylinders that it means it's lean. I could be wrong, but i thought i read that somewhere.

 

You are gonna hate this answer - are you SURE you have your carbs surgically clean? (told you you would hate it)

Seems if you have it open that far some air or fuel passage has to be partially clogged. Or since you see it on all 4 could a jet be wrong or swapped? Got to be a reason here...

 

lol, i don't hate the answer, but i'm sure he will.

 

You DON'T adjust the Mixture Screws: "Turns, guarter-turns, etc."

You ADJUST the Fine Tuning a matter of DEGREES.

 

One Chance at Redemption.

You don't know what's-what because you are not doing the "Tune ONE Thing At A Time" Universal Rule of Fine Tuning.

Tune ONE thing. Observe results.
Tune More than One thing. You don't know what you did that altered the results.

So.
Let's eliminate ONE thing.
Mixtures.

Buy an Accurate Mechanics Ruler
Set the Depths of the Piot Mixture Screws to --> Precisely 27/100ths of 1-Inch Deep.
The Wings ... Not the Slot bottom.
Set the Wings on the Pilot Mixture Screws to: 27/100ths ... 27 ... Not 26 or 28 ... Get it On-the-money.

Test the Bike with Pilot Mixture Screws set to that DEPTH as measured form the FLAT Top of the Carb Body above the Screw.

Maybe we can find-out if your PROBLEM is something OTHER than the FUEL Part of the Ratio.