Author Topic: Ill-Advised Super Sport (CB750-F0) (Read 21558 times)

Jessamine · « **Reply #125 on:** October 29, 2018, 07:42:45 PM »

Well, big update after today's work. Got the engine reassembled, tried to fire it up... and got nothing but leaky carbs and a straining starter.

So I went in with the multimeter and found of course the points weren't set right anymore-- I'd inspected and greased the sticking ignition advancer, so the plate had been disturbed. Once that was set just so, and once I'd tweaked the float heights on the offending carbs, it fired right up with a strong idle.

The initial test runs, despite not having synced the carbs yet, were just brilliant-- breathtakingly fast.

Idle started to get a little shaky below 1200rpm after I'd ridden it for about twenty minutes, however. Carbs are slow to return to idle. And the plugs showed serious inconsistencies (1 rich, 3 lean) when I pulled them after riding stop and go thru the city. Definitely pulling out the fan and the manometers tomorrow morning to see if I can iron out the kinks.

1975 CB750F
1986 CN250
2005 KLR650

70CB750 · « **Reply #126 on:** October 30, 2018, 04:09:34 AM »

Congrats!

754 · « **Reply #127 on:** October 30, 2018, 10:08:35 AM »

Looking good. , next time make a felt pen mark on your points plate, then line it up when it goes back on.

70CB750 · « **Reply #128 on:** October 30, 2018, 11:12:11 AM »

Quote from: 754 on October 30, 2018, 10:08:35 AM

Looking good. , next time make a felt pen mark on your points plate, then line it up when it goes back on.

I use scribe in two places, no need to change anything with Pamco.

Jessamine · « **Reply #129 on:** October 30, 2018, 12:14:07 PM »

Alright, sync is done! Got them all spot-on even. Surprised at the quality of these gauges from CB750Supply-- all were calibrated equally (checked against carb #1), and the dampers were easy to dial in.

Video I took mid-sync: https://www.instagram.com/p/BpkFJ2Dn5Ax/?utm_source=ig_share_sheet&igshid=44p5p2r1olao

Have the idle set about 1200rpm right now. Bike starts to lope around 1000rpm and 1-2 cylinders start to get a little inconsistent, so I guess ill be doing an idle plug chop and setting the mix next. Bike didn't want to cold start before the sync with the air screws at 1 turn out, so they're sitting at 1.5 turns out currently. A little bit of overflow from carbs 3 & 4 again when sitting.

Bike rides feels good on the road, except that when I've got the throttle around 1/8 while cruising it stumbles a little.

1975 CB750F
1986 CN250
2005 KLR650

Don R · « **Reply #130 on:** October 31, 2018, 06:09:43 PM »

That's a pretty set of gauges. I may finally pull the trigger on a set.

Jessamine · « **Reply #131 on:** November 11, 2018, 09:34:52 AM »

Update, since my last reply got lost in a server error somehow:

Bike is on the road and running well! Had a lot of stumbling/hesitation around 1/8 throttle // 3500rpm/30mph, which was greatly improved by richening the needles to second-highest position from middle position, and opening up my idle air jets-- I'm going to inspect the latter more closely today, as they're around 2.5 turns out and that seems excessive. Haven't had the right stretch of road to do a perfect plug chop at the target speed yet-- Philly is pretty bad for that and it's getting colder now.

Suspension feels crummy, with insufficient rebound dampening on even small bumps. PO said he just replace fork oil to spec, but idk what weight/amount exactly he used so I'll be redoing that. Also planning to drill the caps and add air valves as suggested by Hondaman (my partner surprised me with his book as an anniversary gift!)

Clutch is a little wonky, tending to lurch into 1st but slipping over 70mph if I tighten it up enough to avoid the low end hard shifting. Reading threads about fixes right now-- I'll probably still the basket at a later date. Oil is dino Rotella T 15w45 right now.

PO also left me a lovely gift in the form of skinny 1" risers on the guages, one of which snapped the ear it was bolted to at the first proper pothole I hit. Gonna have to weld a new ear in place-- I just removed the risers and bolted it back on with large washers gripping the triple tree further back. Not sure what metal it is, but it seems real soft and crumbly.

Today at the workshop will mostly be about aesthetics and minor fixes; got an aluminum polishing kit for a cool $20 at Harbor Freight and I'm looking forward to shining up the engine some.

Look forward to some before/after pics soon, and I've attached a pic from my first real test ride the other day!

1975 CB750F
1986 CN250
2005 KLR650

seanbarney41 · « **Reply #132 on:** November 11, 2018, 04:21:19 PM »

Very cool that you are riding it...I suggest a front fender at the least, better yet a fork brace, or both, before you start messing with the front suspension

Jessamine · « **Reply #133 on:** November 12, 2018, 08:27:57 AM »

Quote from: seanbarney41 on November 11, 2018, 04:21:19 PM

Very cool that you are riding it...I suggest a front fender at the least, better yet a fork brace, or both, before you start messing with the front suspension

Good call! Any recommendations? I've seen reference to aftermarket ones but haven't been able to find one searching.

My main issue with the front suspension seems to be that it's overly stiff and rebounds too hard; not sure a brace would help with that, though I know that would improve the handling in other ways.

I realized yesterday my rear shocks are Progressive Suspension brand, so I think it's possible the fork springs got changed out for that brand too-- and from what I've read, those run real stiff. I'm a lightweight rider, so I usually lighten springs if anything.

1975 CB750F
1986 CN250
2005 KLR650

Don R · « **Reply #134 on:** November 13, 2018, 08:58:53 AM »

It's not uncommon to add a spacer over the springs to tighten things up a bit, someone may have done that.

Jessamine · « **Reply #135 on:** November 13, 2018, 10:24:30 AM »

Quote from: Don R on November 13, 2018, 08:58:53 AM

It's not uncommon to add a spacer over the springs to tighten things up a bit, someone may have done that.

Do those tend to be on top of the springs, right under the caps? Nothing there if so (already checked). Haven't pulled the springs and went digging in there yet though, if the spacers were installed beneath them.

Any guide out there on how to identify what type of springs (stock/aftermarket) I have?

1975 CB750F
1986 CN250
2005 KLR650

754 · « **Reply #136 on:** November 13, 2018, 11:34:06 AM »

Just pull one up, see if coils are spaced even or tighter on one end.
If you pull up till you see wet, slide a thin rod or screwdriver thru , springs let it drip off, avoid the mess.

Don R · « **Reply #137 on:** November 13, 2018, 02:32:27 PM »

Yes, usually on the top. Progressive springs are wound tighter on one end, stock ones look the same all the way. Some of us will cut an inch off of a tired spring and add a PVC pipe shim to restore the spring rate.
Get the weight off the front end first, and be ready when the cap threads off. It might be loaded and spring up. Those can be fun to get back in too.

Jessamine · « **Reply #138 on:** November 18, 2018, 11:25:16 PM »

Dug into the clutch today to try and solve the issues it was having with slipping. Was confounded by the special nut locking the basket into the bike, unfortunately, which was evidently overtorqued despite not having any of the finned retaining washer's tabs holding it in place. Using the prescribed hammer and chisel method to tap it loose yielded no results. I'll have to fabricate a socket to pull that before I'm able to access the plates themselves. In the meantime, though, I addressed some other issues...

It seems the cable tensioner at the cover wasn't seating properly and the part that should have been inset and spinning freely in the case was too large-- it rested just a millimeter inside the lip of the hole, and could skew sideways a little. I replaced that piece with a washer with an indent and a nut overtop, and those seem to fill the role alright. That piece may have been causing intermittent adjustment issues.

Springs all measured ~32.35mm, which should be within spec. I noticed that though they were all painted on one end with the same stuff used on the valve springs, half of them had the paint facing in and half facing out. I couldn't find proper orientation listed anywhere, so I took a guess and flipped them all so the paint was uniformly to the outside of the bike (as with the valve springs).

The outermost cork plate had a fair amount of old oil residue on the exposed (long, squared) tabs, so I figure there may be deposition throughout the pack which could contribute to slipping. I squirted some seafoam over the plates, and added some to the oil tank-- hopefully that will clean them up some until I can pull the clutch all the way apart.

Everything went back together fine, and the action at the lever felt a little kinder. Clutch sounded a little noisier when I fired up the bike, but it seems to drop into 1st gear easier with more slack in the cable. We'll see tomorrow if it's still slipping at high RPMs!

1975 CB750F
1986 CN250
2005 KLR650

70CB750 · « **Reply #139 on:** November 19, 2018, 04:05:37 AM »

You passed the test, lol. Putting clutch back together without cracking the lifter plate

Don R · « **Reply #140 on:** November 29, 2018, 09:57:23 PM »

I see what you men on the cable end. It looks better now, hopefully it'll work better too.

Jessamine · « **Reply #141 on:** January 25, 2019, 10:26:09 AM »

So the good news is: I found that second cam sprocket knock bolt that disappeared.

The bad news is: I found that second cam sprocket knock bolt that disappeared.

As the kids these days say, "Press F to Pay Respects."

I'd just gotten everything else on the bike to where I was happy with it too. I was out on a very triumphant test ride when I suddenly lost power and the engine died with a sad little whirr.

I'm still tearing it down to assess damage, but it's not pretty. The valve cover has a hole from shrapnel, the cam, sprocket, and chain are obviously toast, and those valves I just redid are far more bent than they were the last time.

Anyone got a spare engine they wanna sell me?

1975 CB750F
1986 CN250
2005 KLR650

kerryb · « **Reply #142 on:** January 25, 2019, 01:17:46 PM »

Sorry for your loss, that's a damn shame after so much effort!

Don R · « **Reply #143 on:** January 25, 2019, 02:22:35 PM »

Awwww, Dang. Fudge, but I didn't say fudge.

Jessamine · « **Reply #144 on:** January 25, 2019, 07:57:26 PM »

Can anyone tell me if there are fitment issues running a K engine in an F frame? Statistically it seems less likely I'd be able to find a running F engine than a K.

scottly · « **Reply #145 on:** January 25, 2019, 08:51:18 PM »

AFAIK, there are no fitment issues with a K0-K6 engine in an F0 or F1 frame. The K7-8 and F2-F3 engines have the drive sprocket mounted 10mm further out, requiring changes to the rear wheel sprocket carrier to get the correct chain alignment.

754 · « **Reply #146 on:** January 25, 2019, 09:15:29 PM »

Geez sorry to hear about your motor..
I am thing most damage is head gasket and higher, maybe pistons, unless the bolt went thru sprocket on the crank.

Jessamine · « **Reply #147 on:** January 25, 2019, 09:32:24 PM »

As far as I can tell, there wasn't damage until it reached the head, but that's difficult to verify. My biggest concern at this point is the fifth of a cam sprocket and the piece of aluminum valve cover I couldn't locate; I don't want a repeat of this issue due to unaccounted-for metal fragments. I'm concerned it would be difficult to fish out that metal scrap without splitting the cases on the engine, which I don't currently have the tools for.

1975 CB750F
1986 CN250
2005 KLR650

754 · « **Reply #148 on:** January 25, 2019, 09:44:40 PM »

There is only 2 special tools for a 750 motor.plus an impact hand driver.
Not sure right now about clutch, I think It can stay in. So if you remove point cover, clutch cover, dyno and transmission cover.. then there is one piece under the transmission cover, with 4 screws needs removing.
And your top case bolts, then flip engine over, remove bottom case bolts, and cases care ready to split.
Then you can check everything..

I have split them in an evening, back together next day and in the bike.

70CB750 · « **Reply #149 on:** January 26, 2019, 03:18:02 AM »

Quote from: Jessamine on January 25, 2019, 07:57:26 PM

Can anyone tell me if there are fitment issues running a K engine in an F frame? Statistically it seems less likely I'd be able to find a running F engine than a K.

My Red is K3 frame and 78SS engine. With your skill you can combine any SOHC CB750 frame and engine.

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Author Topic: Ill-Advised Super Sport (CB750-F0) (Read 21558 times)