Topic: I FIXED MY BIKE!!!! Yaaaaaaaaaassss (With Pics)

[BestBoy]

My bike has been running like turd since I got it in June. Ive been building it all summer, leaving the tuning/engine till last. Now its fixed!!!

WOW, its FAST!!! Not like my old R1 but seriously, for 1972, its awesome!! Way faster than I was expecting!

Things I did to fix:

Cleaned carbs, bought stock airbox to replace pods, new fuel lines, new spark plugs, float adjustments, airscrew adjustment etc.
The biggest culprits were two clogged breather vents in the bowls. Completly clogged up. Im assuming that's what the main issue was because thats the last thing I discovered and its now awesome!

Happy to share a few pics now its working. One question...

How high should this rev?

[Honda3]

My bike has been running like turd since I got it in June. Ive been building it all summer, leaving the tuning/engine till last. Now its fixed!!!

WOW, its FAST!!! Not like my old R1 but seriously, for 1972, its awesome!! Way faster than I was expecting!

Things I did to fix:

Cleaned carbs, bought stock airbox to replace pods, new fuel lines, new spark plugs, float adjustments, airscrew adjustment etc.
The biggest culprits were two clogged breather vents in the bowls. Completly clogged up. Im assuming that's what the main issue was because thats the last thing I discovered and its now awesome!

Happy to share a few pics now its working. One question...

How high should this rev? It looks like its easily going off the clock (13k maybe!?)

 I have a 72 as well. I am usually not a fan of modded bikes, but yours looks fine. If you want to preserve it, dont beat on it. Going fast a lot is not good. I NEVER get into the red zone on the tach...ever.

[BestBoy]

Thanks, yours looks great.

So, Im just realising that there's probs no limiter on this as its got no computer. I was wondering what the painted red bit was on the tach. Then it happily reved past it.

Ok, I understand now. Max hp is at 8K so no need to run into red zone.

[Honda3]

Thanks, yours looks great.

So, Im just realising that there's probs no limiter on this as its got no computer. I was wondering what the painted red bit was on the tach. Then it happily reved past it.

Ok, I understand now. Max hp is at 8K so no need to run into red zone.

Sorry. Let me rephrase that. Your bike is spectacular. really well done. like i said, I usually cringe when I see bikes chopped up, and can even reflect on when I hacked up a pristine CB350F - which I now regret. but yours looks amazing.

[BestBoy]

Haha, thanks man. To be fair, the donor was far from original so I didnt feel too bad chopping it a bit. Gave it a new life

[Honda3]

Haha, thanks man. To be fair, the donor was far from original so I didnt feel too bad chopping it a bit. Gave it a new life

My first bike. Top is AFTER. Bottom is BEFORE.

I was an idiot.

[Gene]

I typically keep my 750 revving between 3500 and 5000 unless stopped - preferably at the upper end. Yeah - don't go into the red zone. Glad you found the problem.

[seanbarney41]

If you guys ever read the manual, its ok to go into the red zone.  Just don't keep the engine there for extended periods of time.  Gene, if you never shift over 5000, you are missing out.  That is where the fun starts.

[Gene]

I've heard

Unfortunately, around here there's not too many places for me to wind it out. May be time to have some fun tho.

Happy for BestBoy.

[BestBoy]

Thanks guys!

Yeah its defs worth pushing over 5k

[jakec]

I saw your post on facebook about the rev limiter. It's kinda funny, how did you build the whole bike and then think there was somehow a rev limiter? Like a mechanical one, that would be interesting.  Like some guys on FB said, at high rpm you just get valve float.

I haven't had an sohc 750 but on the 400F you can certainly go to 12k no problem, the manual just says not to do it when you aren't under load.

[Keith]

Yep, same problem as mine...BIG difference!

[BestBoy]

I saw your post on facebook about the rev limiter. It's kinda funny, how did you build the whole bike and then think there was somehow a rev limiter? Like a mechanical one, that would be interesting.

I guess Ive never thought about what a rev limiter was. Everything Ive ever owned has had one so its not something I ever thought wouldnt exist. When I considered it for 5 secs it was obvious there was none.

In fairness, Ill bet there could be a mechanical limiter. Imagine a centrifugal spinning weight that only lifts to its highest point at a certain rpm. Connect the spinning weight to some gears to gear it so that at 9k rpm the spinning weight lifts high enough to bridge a gap that when closed, cuts the spark. I bet that exists.

[BestBoy]

Well... there ya go -

https://www.quora.com/How-does-a-mechanical-rev-limiter-work-when-was-the-first-produced-and-for-what-model-of-car

[RAFster122s]

Neighbor had a sport bike and would from time to time rev it to the moon sitting. One day he was doing this and it ended with a Pop and silence.  I suspect he blew up the motor and the pop was a rod letting go or coming through the block.
Bike had a rev limiter and he was bouncing it off the limiter for a long time.

Some people are just stupid or ignorant

[PeWe]

A CB750 must cruise at 5000 rpm to maintain the charge of the battery.
I had a cruise today on 3000-4000 rpm most of the time, very boring but for carb adjustment test and later plug check.
"Normal" riding shift at 6000rpm so something will happen   4000-7000rpm where the engine lives.
No problem to let it hit 8000 rpm  now and then which it will when passing cars. A stocker will not give any extra worth the wear after 8000 rpm

Many hot CB750 cams start to live from 6500-7000 rpm. This with better springs to enter 9500rpm.

[Honda3]

A CB750 must cruise at 5000 rpm to maintain the charge of the battery.
I had a cruise today on 3000-4000 rpm most of the time, very boring but for carb adjustment test and later plug check.
"Normal" riding shift at 6000rpm so something will happen   4000-7000rpm where the engine lives.
No problem to let it hit 8000 rpm  now and then which it will when passing cars. A stocker will not give any extra worth the wear after 8000 rpm

Many hot CB750 cams start to live from 6500-7000 rpm. This with better springs to enter 9500rpm.

Good to know. Thanks for this info

[BestBoy]

Yes, great to know this, especially the 5K charge level. It makes sense. Thanks.

In not knowing there was no rev limiter (I know, whatever... ignorance blah blah) I ran it out to about 11k and survived. I was just excited that it was running so well, having not. It pulled all the way. I actually thought it felt like a cam lift. Never gonna do that again of course I had it out today for a 20 mile run and it was 100%. I was shifting at 7/8k overtaking and 6k just riding about. Totally enough power to enjoy in that rev range.

Please dont comment saying Im dumb for reving to 11k. It happened... get over it and learn something. If my engine falls to bit in the coming weeks then Ill be on here asking for advise on fixing it. We'll all get on with our lives. Fingers crossed it stays in one piece. I see no signs of damage.

[WhyNot2]

Yes, great to know this, especially the 5K charge level. It makes sense. Thanks.

In not knowing there was no rev limiter (I know, whatever... ignorance blah blah) I ran it out to about 11k and survived. I was just excited that it was running so well, having not. It pulled all the way. I actually thought it felt like a cam lift. Never gonna do that again of course I had it out today for a 20 mile run and it was 100%. I was shifting at 7/8k overtaking and 6k just riding about. Totally enough power to enjoy in that rev range.

Please dont comment saying Im dumb for reving to 11k. It happened... get over it and learn something. If my engine falls to bit in the coming weeks then Ill be on here asking for advise on fixing it. We'll all get on with our lives. Fingers crossed it stays in one piece. I see no signs of damage.

ha ha.....like these comments.

Your bike, do as you please.

Wisdh I could get mine just to fire up. Ready for the fire pit.

[Jerry Rxman Griffin aka MuthaF'er]

It has a higher charging output at 5K but a solid system should charge below that but don't expect a whole lot of charging dogging it around town. Take it out on the road before you take it home