Topic: Weird Compression - Oh, Maaaaaan...!

[CycleRanger]

I've read that the coil mounts need to be grounded to the frame as well; I'll check again, but would any paint on the frame where the coils mount degrade the spark? I'm thinking that if the whole bike is indeed a 'ground', that might be a factor too....

The wiring harness should have a ground wire and there should be the large ground wire from the engine/frame to the battery.
Yes, paint is not conductive.

[Dr. Frankenstein]

Yep, got both of those, and they're where they should be. The harness one is connected to the front bolt that holds the coils, and the (new) ground wire from the battery connects to the upper right engine mounting bolt. Would it make a difference if the coil mounting itself is not directly on bare metal on the frame? 

[scottly]

I've read that the coil mounts need to be grounded to the frame as well; I'll check again, but would any paint on the frame where the coils mount degrade the spark? I'm thinking that if the whole bike is indeed a 'ground', that might be a factor too....

The coil mounts themselves do not need to be grounded to the frame, but some bikes have the green ground wire connected to the frame using one of the coil mount bolts.

[Dr. Frankenstein]

Yes, scottly, that's how I have it. Maybe there's not enough connection?
 

[Tracksnblades1]

It’s a wasted spark ignition…

I’d use a test light since you have points..
I think the service manual has the procedure in it…🤔

Like you wrote earlier it only take three things to make her run…
Timing is everything, when the carbs are working properly…😁

[Dr. Frankenstein]

Yes, but is that 105 - 110 lbs compression enough to make her run...?

[dave500]

You will never get a 150psi reading with thus gauge.

yes you will,so long as it has a valve at the start of the hose,itll only take a pump or two extra to fill that hose,an engines only a compressor,if the compressed air cant go back past that valve itll fill to max capable compression.

[dave500]

Yes, but is that 105 - 110 lbs compression enough to make her run...?

yes it is.

[Tracksnblades1]

Yes, but is that 105 - 110 lbs compression enough to make her run...?

yes it is.

👍+1

She’ll light if she’s in time and the carbs are mixing right..
Heck a Briggs/stratton and a ford 331y or 390fe will do it on 70 or less…😳
As long as the starter is good..🤪

[M 750K6]

Compression will be lower on a cold motor. Specs are with a hot motor. Watched a Brick House Builds YouTube video on his 750K5. His started at numbers like yours, one was down at 80psi (measured cold). After a few runs and an Italian tune up, he got to 160-165 hot.

[Dr. Frankenstein]

When I did the carbs I set the float height at 22mm; the only things I can think of rechecking is the grounds, voltage across the points and the air/fuel mix. I've only so far tried to get it to light using starting fluid sprayed directly into the airbox, and it 'chuffed', like I said, but I'll go back and recheck the air/fuel mix and probably scrape some paint off the frame where the coil mounts and put some actual gasoline in it and see what happens. When I bench-tested the fuel levels, I used the clear-tube method and the level rose to the carb bowl level before closing, so I'm pretty sure the floats are doing their job; IIRC, currently the mixture screw is set at 1 5/8 out or something like that - I know I set it to the spec in the manual, whatever that is - and I am getting a spark across all four, but a weak one. I asked a friend of mine who knows this stuff too and why I would get a weak spark and he indicated a poor ground as well.

Something else to note, that I discovered when I was trying to get the horn to work, was the horn button itself wasn't connecting and feels - not 'broken', but very loose. I took a look at the (new aftermarket) switch and noticed the little spring in there was not 'springing' like it should. The horn button acts as a ground for the horn, but would that have an effect as well? I tried switching out the spring with the OEM one that I took off the bike (the clutch mount was physically broken), but the spring, button and contact pin wouldn't fit. Everything else electrical - the lights, headlight, turn signals, brake light and Hi/Lo Beam switch works fine except the horn - but since the whole bike is basically a 'ground,' might that be a factor too? And would swapping the coil wires do anything? I haven't tried that yet, but I've read that can sometimes be the culprit.

[Ozzybud]

The coils do not need to be grounded.

[Dr. Frankenstein]

No, I know that, but I've read that the primary wires can sometimes be switched.

[Don R]

 The coils don't care if the bike even has a horn.
  You can swap the coil wires that go from yellow and blue in the harness to the coils.

[Dr. Frankenstein]

I tried swapping out the yellow and blue wires but that had no effect; I have spark, but as I mentioned it looks kind of weak, but it's there. I rechecked the timing and the points with a light attached to the points and they are dead on. I put some fuel in and got it to backfire twice but not start so I'm thinking I have either some crap in the carbs, or an air leak somewhere that is making a lean condition. The plugs are dry though, so I'm thinking something may not be sealed right, although everything looks right; the manifold boots are where they should be and tightened down. The mixture screws are set to 2 turns out, as per the manual - "set to 1 1/2 to 2 turns out" - so I'll try enriching it a little by turning them in a half turn and see what happens. Too much air in the mix, maybe...? Any ideas...?

Update: I turned the screws in a half turn to 1 1/2 turns out, and got more backfiring; I'm leaning towards cleaning the carbs again and seeing what happens. The manifold boots are new, but i haven't tried spraying them down yet with starting fluid to see if they catch, but I'll probably pull them again and go through them.

[Dr. Frankenstein]

HA!! SUCCESS!! I was doing some reading in here about the same problem, and I came across a guy who had simply mis-wired the two primary wires; I know I said earlier I tried that, but then I went out and went over the timing and points again, and I had misapplied the blue and yellow wires and was trying to time it to the wrong coil! DOH! It runs hot on all four too, which nice, but I can hear a sort of 'ticking' from the top - the sound of the exhaust blends with it so I can't really tell where it's coming from - cam chain, I think it is - and the exhaust is Loud! At first I thought the PO might've taken out the baffles, but they're the kind that doesn't come apart - here's a pic of the bike when I first got it, to show you what kind of exhaust it has. But it Runs! Finally! I changed those wires and it started right up! Cha - CHING!!

[CycleRanger]

Congrats! 
Now the real journey begins! 

[Dr. Frankenstein]

Yeah, Really...!    I changed out the old 25mm main glass fuse with a 15A blade fuse, too; I'm glad to see THAT's working...! Those right size 15A glass fuses are hard to find. Now if I can just get the horn to work...

[grcamna2]

Very Nice Dr.  'It's ALIVE' !!    sorry,couldn't help it 
I was thinking you might have some leaking exhaust header round gaskets? sometimes when they leak out of there it makes a sharp,variable noise that seems like 'ticking'.
Did you replace all 4) round headpipe gaskets with fresh ones?

[HondaMan]

Very Nice Dr.  'It's ALIVE' !!    sorry,couldn't help it 

Now, THAT's patina! Imagine ripping down the hiway, touring at 80 MPH, but it looks like it was left out in the rain too long?


Good job!
Did you, by chance, clean off the upper right rear engine mounting bracket of the paint between it and the frame? That might help the spark some. The one under the tank (over the coils) is similar, especially if someone painted that frame and didn't bare those 2 places.

About the horn: the handlebars have a hard time grounding in the 500, even when new, because it grounds thru the ball bearings in the steering head. If they haven't been moved around a LOT in a long time, they don't ground for beans. To test it (if you have some jumper cables), clip between the handlebars and the main ground with a wire, see if that makes the horn "meep"?

[Dr. Frankenstein]

Grcamna2 - yes, when I redid the bike I put everything 'new' in, including those gaskets (you're talking about the copper ones in the head, yes...?). I'll try tightening them up.

HM - Oh, it doesn't look like that Now - that pic was taken right after I got her home last year - in the meantime, I tore her down to the frame and repainted in Satin Black, took a Brillo pad and wire wheels to the metal parts that needed it, stripped the engine, vapor blasted the cases and carbs, repainted the engine, put in a new wiring harness (learned a LOT, there!), and I still have to strip and paint the gas tank - it's originally green, but I think I'm going metallic Orange; not necessarily the Flake Sunrise - that looks beautiful, but it looks a bit 'circusy' for me...maybe a burnt orange metallic, I don't know yet.

My problem is I'm always looking down the road - I have a 350F basket case that needs to go back together, but there's also a '74 CB550 I want to do too. I keep hearing my wife though saying "One At A Time...!" 

[HondaMan]

Having a "patina" bike in the Saturday night crowd in Peoria (in the day) was a blast: I had a 1967 SuperHawk that looked like everything but a truck ran over it, but it was my racer. I'd take it out to the crowd and dust the guys who didn't know me, riding their shiny new 350-something bikes.