Author Topic: CB750 K3F - AKA The Red (Read 118584 times)

MoMo · « **Reply #350 on:** May 04, 2015, 12:07:53 PM »

Quote from: 70CB750 on May 04, 2015, 05:24:52 AM

Quote from: MoMo on May 04, 2015, 05:08:12 AM
You think the switch was down too far and binding against the drum? Extra O-ring raised it enough to prevent that? Interesting fix, may try the same on the F engine in my K4...Larry

I suspect the shoulder of the switch against the drum groove edges, just dragging little bit.

But I polished the switch and gthere was no witness mark on it.

Very strange, your problem was all the time right? My 4th gear problem is only when hot.

Kickstart · « **Reply #351 on:** May 06, 2015, 03:37:39 PM »

Quote from: 70CB750 on May 04, 2015, 02:55:57 AM

Quote from: Kickstart on May 03, 2015, 07:39:18 PM
Great news!

Looking great... I like the way the comstars look on your bike.

Just curious... how did the double o-rings on the neutral switch cause the shifting problem... and was the neutral light always on?

The double O-ring actually allowed me to shift all the way up and down and smoothly. It tells me the problem is somewhere around the switch seating, but the shifting forks are - as far as I dare to say - okay.

Will try different switch now.

Oh... I read that wrong... the double o-ring solved the problem... interesting.

Was it an aftermarket neutral switch?

Does your neutral switch go on and off correctly after adding the extra O-ring?

70CB750 · « **Reply #352 on:** May 07, 2015, 03:16:19 AM »

It came with the engine, not sure, looks original.

It goes in easy and out too, I have another one coming from Bill Benton.

Will take her out on Saturday again and see what is what.

70CB750 · « **Reply #353 on:** May 09, 2015, 09:53:57 AM »

Put 35 miles on her today, now she shifts with just one o-ring on the neutral switch, seems like once I got her through 1-5 she fixed herself.

The speedo bounces around 60mph, will need to look into it, also the kick stand ďrags in left turns, need to tuck it in more.

Unlike the K0, that has significant kick at 4000 rpms, she pulls steady and without surprise from 1000 up. Did not push her over 5000 rpms, new rings and such, she seems to be happy there - 1000 higher than K0. Up hill in 5th there seems to be a hole, I may eventually go to 125 main jets.

The K0 pulls from stop like tractor, K3F needs more gas and clutch work.

She has an F3 cam advanced 4.5 degrees against original to bring the power band lower.

Overall, happy and pleased, hopefully I did not jinxed her.

Kickstart · « **Reply #354 on:** May 09, 2015, 10:42:19 PM »

Awesome!

Glad to hear the bike is feeling good through the shakedown/beak-in phase.

I wonder if the drum was just hanging up on some kind of debris that got in there during the build, and messing with the neutral switch moved things around enough to dislodge whatever was causing the problem.

Hopefully it's smooth sailing from here.

- Chris

70CB750 · « **Reply #355 on:** May 10, 2015, 03:21:09 AM »

Yes, Chris, I have the same gut feeling.

Stev-o · « **Reply #356 on:** May 10, 2015, 06:03:55 AM »

Good to hear you (hopefully) have it solved.

70CB750 · « **Reply #357 on:** May 15, 2015, 01:33:15 PM »

SOHC4 Cafe Racer Fan · « **Reply #358 on:** May 15, 2015, 01:56:16 PM »

Now we're talking!

70CB750 · « **Reply #359 on:** May 15, 2015, 02:19:05 PM »

Quote from: CB750 Cafe Racer Fan on May 15, 2015, 01:56:16 PM

Now we're talking!

It was one of those weeks, took the pictures last Sunday, posted them today.

SOHC4 Cafe Racer Fan · « **Reply #360 on:** May 15, 2015, 02:28:52 PM »

It looks much better up close.

MoMo · « **Reply #361 on:** May 15, 2015, 06:06:48 PM »

very nice Prokop...Larry

rtbmrgl · « **Reply #362 on:** May 15, 2015, 08:26:53 PM »

Very sharp!

Stev-o · « **Reply #363 on:** May 20, 2015, 07:40:44 PM »

+1 very nice. The 1 thing I like most about this bike is the uniqueness.

70CB750 · « **Reply #364 on:** May 21, 2015, 04:58:36 AM »

Quote from: Stev-o on May 20, 2015, 07:40:44 PM

+1 very nice. The 1 thing I like most about this bike is the uniqueness.

Thank you

It's not like I dreamed it up, it kinda shaped itself by parts availability.

One thing I want to find are wheels from 79 SuperSport. I believe they are tubeless Comstars and that's what I really want to have.

rtbmrgl · « **Reply #365 on:** May 21, 2015, 08:38:15 PM »

very nice, i like it!!!

70CB750 · « **Reply #366 on:** June 03, 2015, 04:02:56 AM »

With the engine split on the bench, I am going over the transmission step by step.

The clutch looks like it was messed with before, the tab washer does not look factory bent. Oh well, done the top end, I can as well rebuild the low end

Looks like Partzilla has tab washers: 90431292000

Restoration Fan · « **Reply #367 on:** June 03, 2015, 04:29:20 AM »

What happened? Why did you have to pull the engine?

70CB750 · « **Reply #368 on:** June 03, 2015, 04:32:04 AM »

This:

http://forums.sohc4.net/index.php/topic,147098.msg1688991.html#msg1688991

Basically the shifting problem never went really away. It seemed like I sorted it out, and it was good for ~100 miles or so, but it kept coming back.

SOHC4 Cafe Racer Fan · « **Reply #369 on:** June 03, 2015, 06:35:27 AM »

What a bummer - right during Summer riding season. I hope you get it buttoned up and back out on the road soon.

70CB750 · « **Reply #370 on:** June 07, 2015, 03:46:23 PM »

The tool can be bought for twenty or so bucks on ebay and other places, I spent several hours making it from chunk of 4140.

But it makes me happy

MoMo · « **Reply #371 on:** June 07, 2015, 08:22:20 PM »

Quote from: 70CB750 on June 07, 2015, 03:46:23 PM

The tool can be bought for twenty or so bucks on ebay and other places, I spent several hours making it from chunk of 4140.

But it makes me happy

Handy tool to have, I am fortunate enough to have one left over from my days of wrenching...Larry

70CB750 · « **Reply #372 on:** June 29, 2015, 11:36:14 AM »

Engine still open on the bench, working on the house instead.

70CB750 · « **Reply #373 on:** June 30, 2015, 03:47:11 AM »

The second tool for the clutch.

70CB750 · « **Reply #374 on:** July 30, 2015, 04:42:06 AM »

Careful optimism is in order.

Assembled the bottom yesterday, the drum movement and shifting is silky smooth.

Could not find anything wrong with it, only took it apart, polished the shifting drum and the rod forks slide on, soaked it all in 20W50 and put back together.

News:

Author Topic: CB750 K3F - AKA The Red (Read 118584 times)