Author Topic: 1975 Supersport, performance cafe  (Read 119950 times)

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Offline jaguar

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Re: Hot Street 1975 CB750F
« Reply #175 on: August 28, 2010, 02:35:07 PM »
what coils are you running?

Offline MRieck

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Re: Hot Street 1975 CB750F
« Reply #176 on: August 29, 2010, 05:03:31 PM »
It looks like the new, mini Dyna coils. They work with the 2000 ignition.
Owner of the "Million Dollar CB"

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #177 on: September 14, 2010, 09:11:25 PM »
Finally had time to roll it on the dyno.  Did some loaded pulls to seat the rings and check for other issues before the real tuning starts.

Unfortunately Village Photos is acting up, so I can't show you pictures - but there were some interesting results.

First, the bike won't idle below 2k.  It just dies.  Didn't have time to make adjustments other than setting the mixture screws all to the same number of turns.  Should be easy to sort out, but wasn't on tonight's abbreviated agenda.

Second, the bench-synch on the carbs was awful "out of the box." Got it closer, but really need to get vacuum spigots on the carb boots to do it right. Poor synch caused cylinder 1 to run a bit cooler than the rest.

Third, the whole setup seems way too lean.  We need to use the AF sensor on each cylinder to see what we're looking at, but the plugs were incredibly white on the full throttle plug-chop and the motor fell flat just as it should have been coming on the powerband.

Finally, the moment you've been waiting for: the numbers.

Remember, no tuning has been done.  Limited the motor to 35 deg of total advance, Dyna2000 set to advance curve #4. Full throttle pull from 4k to 8k rpm.

68.17 rwhp @ 7k (flat or slightly dropping toward 8k)
51.18 lb/ft @ 5200 (50-ish lb/ft from 5k-8k, flat-as-a-pancake torque curve)

Wish someone could tell me exactly what my baseline jetting and settings should be for my CR29's, but I guess I'll have to figure it out on my own.  If there's another 20rwhp hiding in this motor, I'll be damned if I'm not going to find it.



Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #178 on: September 15, 2010, 03:45:40 AM »
Nothing too exciting, but here are the photos I was able to snap after the run.



Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando

Offline tweakin

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Re: Hot Street 1975 CB750F
« Reply #179 on: September 15, 2010, 05:04:34 AM »
Nice David.  I was curious to when you would pop your head in here again.  I still need to sync my cr's and tune them also.  I plan on putting in the spigots also.  I have a borrowed uni sync tools from Mike I will be using sometime soon to get them close until I am able to add the spigots.

Offline MRieck

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Re: Hot Street 1975 CB750F
« Reply #180 on: September 15, 2010, 05:33:54 AM »
I'd say there is more there...it is dead at 6,500 from I can see. I run a 125 main with 240 air jet.  I'll get back to you with the needle # setting but I cannot do it before Friday Dave. And yes.....you definitely need to synch the carbs using a vacuum tool.
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Offline tweakin

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Re: Hot Street 1975 CB750F
« Reply #181 on: September 15, 2010, 06:44:47 AM »
EDIT:  Found the link, ordered the parts...

Mike,  I searched and can not find the info/pictures on how you installed the spigots into your boots for syncing the cr carbs.

Do you have a link?  many thanks.
I'd say there is more there...it is dead at 6,500 from I can see. I run a 125 main with 240 air jet.  I'll get back to you with the needle # setting but I cannot do it before Friday Dave. And yes.....you definitely need to synch the carbs using a vacuum tool.

« Last Edit: September 15, 2010, 07:04:39 AM by tweakin »

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #182 on: September 15, 2010, 11:00:03 AM »
Nice David.  I was curious to when you would pop your head in here again. 

I'm on the board daily, just don't write much unless I have something of value to contribute.

Yes, I need 3/32nd hose barbs for my carb boots - along with a long list of other things to do before our next run(s).
Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #183 on: September 15, 2010, 11:02:03 AM »
EDIT:  Found the link, ordered the parts...

Tige, please share the link.  It's not coming up when I try to search for it.  Must be using the wrong search terms.
Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #184 on: September 15, 2010, 11:10:23 AM »
I'd say there is more there...it is dead at 6,500 from I can see. I run a 125 main with 240 air jet.  I'll get back to you with the needle # setting but I cannot do it before Friday Dave.

Jets are ordered.  Thanks.

What about the slow-jets? It idles with a bit of choke on, but won't - even with the air screws all the way in, with it off. Has anyone needed to use #65 slow-jets, or should the 60 be OK with tuning?

Next steps:
Change oil and filter
Adjust timing, 40 deg total advance
Jet carbs, raise needle
Adjust valves
Adjust drive-chain
Add vacuum takoffs to carb boots
Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando


Offline tweakin

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Re: Hot Street 1975 CB750F
« Reply #186 on: September 15, 2010, 04:41:54 PM »
Couple questions for you.

1.  What size rear tire you running.

2.  Who laced up your wheels and did they have to dish the rear more to the non drive side if larger than stock rear tire?


I have a set of 76f hubs, rims and spokes on order from Buchanans.  I am running a 120 Avon rear I have heard I might have chain clearance issues unless I dish the wheel over.  I am going to lace but want the wheels trued by someone who knows what they are doing.

Thanks.
« Last Edit: September 15, 2010, 05:01:07 PM by tweakin »

Offline MCRider

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Re: Hot Street 1975 CB750F
« Reply #187 on: September 15, 2010, 05:12:31 PM »
Couple questions for you.

1.  What size rear tire you running.

2.  Who laced up your wheels and did they have to dish the rear more to the non drive side if larger than stock rear tire?


I have a set of 76f hubs, rims and spokes on order from Buchanans.  I am running a 120 Avon rear I have heard I might have chain clearance issues unless I dish the wheel over.  I am going to lace but want the wheels trued by someone who knows what they are doing.

Thanks.

Seeing as how we can run a 150 on the Ks without chain clearance problems (it does hit the chainguard (throw it away) and the brake stay rod) a 120 should be no problem.

In fact, I have a rolling stock 75F I'll go check the rear wheel/tire size.
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline MCRider

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Re: Hot Street 1975 CB750F
« Reply #188 on: September 15, 2010, 05:22:58 PM »
Yeah, my 75F (I think identical to 76F?) has a 3.5x18 Akront (courtesy Buchanans), with a 130/80-18 tire. The first clearance issue is with the brake stay rod on the right, maybe with a 140, not the chain. With the 130 I could get a piece of cardboard between it and the rod.
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #189 on: September 15, 2010, 08:16:05 PM »
Couple questions for you.

1.  What size rear tire you running.

2.  Who laced up your wheels and did they have to dish the rear more to the non drive side if larger than stock rear tire?

I have a set of 76f hubs, rims and spokes on order from Buchanans.  I am running a 120 Avon rear I have heard I might have chain clearance issues unless I dish the wheel over.  I am going to lace but want the wheels trued by someone who knows what they are doing.


I'm using stock fitment rims and tires.  Buchanan's did all the work.  No clearance issues whatsoever.

The only change I'll be making, per Hondaman's recommendation, is to re-true the front wheel so that it's centered in the forks and not offset as it came from the factory.
Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #190 on: September 18, 2010, 08:20:11 PM »
Today's work:

Oil and filter change -- Oil that was drained had the usual amount of metal for a new engine.  A little frightening was the few bits of garnet blasting media that were in the oil filter housing.
Adjusted drive chain -- Not sure how much more initial stretch and bedding to expect from the DID 520 X-Ring on this bike, but I'm barely at the first notch with the axle adjusters.
Synched carbs -- Went through a simple "wire droop" synch.  Throttle response was much improved.
Adjusted valves -- They didn't move much from the initial settings, but all except cylinder 3 were noticeably off.

Still need needle position and slow jet recommendations.  Waiting on Main Jet and Main Air Jet for the next dyno runs.  Also, as its static timed only -- I really need to strobe the timing.

Had a nightmare the other night that the cam was way over advanced, killing my rpm capabilities.  Really hope the new jets and stobed timing wakes the bike up - or it's possible its not a nightmare, but reality.
Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando

Offline Doctor_D

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Re: Hot Street 1975 CB750F
« Reply #191 on: September 25, 2010, 02:05:33 PM »
Bad phone photo, but vacuum ports for carb synch installed today. 1/8" barb / 1/8" npt.  Drilled a 7/16" hole in frozen carb boots, then threaded them in with a little clear rtv. Almost too easy.



Carbs were rejetted, 125 mains, 240 main air.  Needles were in the 2nd groove when I opened them up (bad on me for not checking), raised to clip position 5.  Did a proper bench synch, so it should idle.

I'll strobe the timing Wednesday night and give it another flogging on the dyno.  If the power still falls off at 8k, then I have to assume the cam is advanced.
Take care,
David
___________________________________________
1975 CB 750F - Project page: http://forums.sohc4.net/index.php?topic=66026.msg725479#msg725479
1978 CX500
1971 Norton Commando

Offline 754

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Re: Hot Street 1975 CB750F
« Reply #192 on: October 02, 2010, 09:01:28 AM »
Has anyone heard anything from Dave ..??
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline MRieck

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Re: Hot Street 1975 CB750F
« Reply #193 on: October 02, 2010, 11:00:14 AM »
Has anyone heard anything from Dave ..??
I just spoke with him Frank. He is going to the dyno today.
Owner of the "Million Dollar CB"

Offline 754

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Re: Hot Street 1975 CB750F
« Reply #194 on: October 03, 2010, 08:54:42 AM »
Thanks, Mike..

 Dave, check your PM...
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline 754

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Re: Hot Street 1975 CB750F
« Reply #195 on: October 05, 2010, 09:08:08 PM »
  Dave, check your mail...
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Hot Street 1975 CB750F
« Reply #196 on: October 05, 2010, 10:30:26 PM »
Dave ain't here man  (where's that from?)
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Industrial Rat400f Killer

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Re: Hot Street 1975 CB750F
« Reply #197 on: October 05, 2010, 10:39:41 PM »
Dave ain't here man  (where's that from?)

Cheech and Chong

Offline 754

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Re: Hot Street 1975 CB750F
« Reply #198 on: October 07, 2010, 09:03:03 PM »
.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline MRieck

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Re: Hot Street 1975 CB750F
« Reply #199 on: October 23, 2010, 10:15:36 AM »
 I wonder if Dave got a chance to go back to the dyno. I sent him different needles and larger jets.
Owner of the "Million Dollar CB"