Topic: Phaedrus: CB750 RestoMod - Update: 09/23/21 w/ new video

[MCRider]

It was a while ago, and they all clustered around 220 psi. We'll be checking that and valve lash and such before popping the carbs.

[PeWe]

oh yeah, Air/Fuel ratio was lean at the bottom, but by about 3000 rpm, it was no higher than 12 nor lower than 11, which the Mikuni manual says should be all right. So at least I shouldn't hole any pistons. I'll get the low range re-jetted.

Check cruising speed A/F ratio on the dyno is my recommendation for a street bike. You will use yours on the street too?
I had too rich needles that was revealed on dyno when the dyno guy checked the cruising behavior which is most important on a street bike. Earlier dyno runs were mostly WOT to check max power and A/F ratio.

Slowly increased throttle from 2000-6000 rpm. A/F ratio below 12. I lowered the needles 1 step but it was still too rich when cruising around in normal speeds in city and country roads, stuttering followed by bangs at decelerations. I lowered the needles 1 step more and finally bike ran really nice and even. I got it verified on dyno too. (plugs look better!)

I had too lean at WOT on 2 carbs. Same I had adjusted the fuel level on by clear tube. I changed back to make all 4 to use same main jet sizes.
All above can be seen on 3 dyno runs: http://forums.sohc4.net/index.php/topic,147350.msg1953508.html#msg1953508

- Compression test show 220PSI? That's a lot! Without cam?

I measured my last rebuild and got 175PSI, cam DP315. I guess the overlap reduce some. My 836 had around 190 with Action Fourss SS-1 cam with less overlap.

I hope this will help you to find the perfect tuning!

[MCRider]

We had it running great last year, dynoed at 79 hp. Everything spot on.

Then I changed the pipe, and removed the carbs to send them to be cleaned but never did. Adjusted the float levels (may have been a mistake) and now it runs like this.

IT has the wimpiest cam WebCam makes, a 41.

I wanted to ride it but got sick and can't ride, so a friend runs it at the drag strip. No cruising.

It really pumps, don't it?  My first 888, pumped 240.

[MCRider]

Valve lash was spot on. Cam chain spot on. Ignition timing spot on.

Comp Test: #1 = 90; #2 = 150; #3 = 210; #4 = 220

Sigh.      

[CBJoe]

Valve lash was spot on. Cam chain spot on. Ignition timing spot on.

Comp Test: #1 = 90; #2 = 150; #3 = 210; #4 = 220

Sigh.      

Bummer   

[Jerry Rxman Griffin aka MuthaF'er]

Did you notice a sudden decrease in power? Any top end noise? And I HATE to ask this - smoke? Frame kit? Put a real cam in it this time..... 

[Tintop]

Ron, have you now done a leak down test to determine if it's valves or rings?

[MCRider]

Did you notice a sudden decrease in power? Any top end noise? And I HATE to ask this - smoke? Frame kit? Put a real cam in it this time..... 

The Dyno run we did showed the loss in power. 49 now vs 79 last year. No noise, no smoke, Yes to frame kit, I'm ahead of you on the real cam.

[MCRider]

Valve lash was spot on. Cam chain spot on. Ignition timing spot on.

Comp Test: #1 = 90; #2 = 150; #3 = 210; #4 = 220

Sigh.      

Bummer 

Yup.

[MCRider]

Ron, have you now done a leak down test to determine if it's valves or rings?

Nope. It should be obvious once blowing it apart.

[Phoenix]

Ron
What do you think is causing the almost consistent rise from 1 to four?  60#, 60# then 10#.  Doesn't make sense.
Ed
ps. Are you still working the morning shifts?

[MCRider]

Ron
What do you think is causing the almost consistent rise from 1 to four?  60#, 60# then 10#.  Doesn't make sense.
Ed
ps. Are you still working the morning shifts?

I don't know, Ed. I have to concentrate my limited powers to add or detract on what is knowable. In this case, I only know I have to take it apart.   

Yes, we are. 10-12N every Sunday. We missed a few lately as I was out of town, or sick. But, its a firm schedule.

[MRieck]

Ron, have you now done a leak down test to determine if it's valves or rings?

Nope. It should be obvious once blowing it apart.

I would still do a leak down Ron before you disassemble it.

[MRieck]

Please leak it down while assembled.....it is a great diagnostic tool Ron. Please do it if you have the tool.

[CBJoe]

Hey Ron...I'm out of town until the 18th of Dec...but when I'm back I'm free to lend a hand..Just let me know 

[Tintop]

Please leak it down while assembled.....it is a great diagnostic tool Ron. Please do it if you have the tool.

+1 it will tell you were the issue is - intake valve / exhaust valve / rings.  I borrowed the 'tool' from my local bike shop.  Easy to do..Youtube.

[MCRider]

Please leak it down while assembled.....it is a great diagnostic tool Ron. Please do it if you have the tool.

I don't have the tool, but I'm inclined to get one if you think its important. I don't understand what it will accomplish, or how, but I've learned things before, occasionally.   

[Stev-o]

Please leak it down while assembled.....it is a great diagnostic tool Ron. Please do it if you have the tool.

I don't have the tool, but I'm inclined to get one if you think its important. I don't understand what it will accomplish, or how, but I've learned things before, occasionally.   

Ron - a leak down test will test exactly that - leakage from your valves, piston rings and head gasket.
I've done it on motors that I've acquired with no known history.

As a general rule:

Leakage under 5% indicates engine in excellent condition.
Leakage up to 15% indicates engine in good condition.
Leakage above 15% indicates that engine components are worn.

My brother also does leak down tests on his SCAA race car motor so he will know when it is ready for a rebuild

[Terry in Australia]

Sorry to hear it Ron, but I guess I was right in suggesting a compression test before you pulled your carbs, I'll be interested to see what's caused this issue, what pistons and rings are you running mate? I know how careful you are with your assembly, so I can't see how you could have busted a couple of rings in different cylinders during assembly, and it certainly hasn't done enough miles to wear them out, it's weird.......... All the best.

[MCRider]

Please leak it down while assembled.....it is a great diagnostic tool Ron. Please do it if you have the tool.

I don't have the tool, but I'm inclined to get one if you think its important. I don't understand what it will accomplish, or how, but I've learned things before, occasionally.   

Ron - a leak down test will test exactly that - leakage from your valves, piston rings and head gasket.
I've done it on motors that I've acquired with no known history.

As a general rule:

Leakage under 5% indicates engine in excellent condition.
Leakage up to 15% indicates engine in good condition.
Leakage above 15% indicates that engine components are worn.

My brother also does leak down tests on his SCAA race car motor so he will know when it is ready for a rebuild

But how does it tell the difference between valves, rings, or gasket?

[MCRider]

Sorry to hear it Ron, but I guess I was right in suggesting a compression test before you pulled your carbs, I'll be interested to see what's caused this issue, what pistons and rings are you running mate? I know how careful you are with your assembly, so I can't see how you could have busted a couple of rings in different cylinders during assembly, and it certainly hasn't done enough miles to wear them out, it's weird.......... All the best.

ARIAS pistons and I think they are Perfect Seal rings, sourced from Mike Rieck. Could have been me. But it sure ran good last year.

[Tintop]

Please leak it down while assembled.....it is a great diagnostic tool Ron. Please do it if you have the tool.

I don't have the tool, but I'm inclined to get one if you think its important. I don't understand what it will accomplish, or how, but I've learned things before, occasionally.   

Ron - a leak down test will test exactly that - leakage from your valves, piston rings and head gasket.
I've done it on motors that I've acquired with no known history.

As a general rule:

Leakage under 5% indicates engine in excellent condition.
Leakage up to 15% indicates engine in good condition.
Leakage above 15% indicates that engine components are worn.

My brother also does leak down tests on his SCAA race car motor so he will know when it is ready for a rebuild

But how does it tell the difference between valves, rings, or gasket?

If intake valve you will hear air leaking back through the carb / exhaust valve back through the exhaust / rings through the crankcase breather.

[MCRider]

Thanks! Something I can understand. Now to buy one. Got some leads in private email. motion pro, harbor freight, etc.

[MCRider]

Been remiss in my updates. Still tinkering towards a goal. Nothing done last weekend, called for flu bug scare. Brutal cold. I think my heaters would have been sufficient, but no enthusiasm to try. Warming up to the 20s tomorrow. Ice and rain forecast. We'll see if we can brave it.

We spent one shop day modifying the crate CBJoe scored for us to ship off the CB305 engine to a specialist in TX. Didn't take much modifications, and it is amazingly well engineered. It was originally for some kind of medical equipment that Joe works on. As expensive as they are, they are on;y used once, then thrown away.

Weeks before, I got the leak down tester. Silly, me. I jumped the gun weeks before by pulling the carbs and rocker box, preparing for removing the head. But Mike encouraged me to do the test first.

So, the test requires warming the engine. So... mufflers (removed to remove the rear wheel for unrelated service) carbs, rocker box had to go back on. That's done now.

Hopefully tomorrow, we'll warm it up, and do the leak down test. Catch up pics to follow.

Personally, business has been very good, and between that and the physical therapy for the Parkinson's, free time is dear. The "bradykinesia"  (slowness of motion. The individual's movements become increasingly slow and over time muscles may randomly "freeze") is frustrating, but we all have our battles.   

[Terry in Australia]

Well done Ron, I'm surprised that you're still working mate, what "Business" are you in? Cheers, Terry.