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Author Topic: Honda "l'arancio dolce" CB 750 Resto-Mod Project  (Read 787 times)

Offline Ryan Stecken

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Honda "l'arancio dolce" CB 750 Resto-Mod Project
« on: Nov 08, 2017, 04:08:24 »
Hey guys!

Looks like I got a new project!A good friend of mine asked me to help him with the resto-mod of his CB 750.
He has 2 ex-police Cb 750 bikes in his barn and wants to make one fully working nicely refurbished bike out of it.

Yesterday we took some time and started checking the bikes:

Electrical system seems to work to 80% (hi/low on the headlights,oil pressure,blinkers left and right,blinker relais)

Not working: Starter button,no spark,neutral light-->We checked the fuse box, all fuses are ok?

Any ideas how where to start on the NO SPARK problem?
Starter button is dead too, any ideas where to start on that problem?

We took a screwdriver and bridged the starter relais, the starter motor turns nicely with a fresh battery and the motor seems to have good compression (will check with a tool next time, what should this motor have psi wise in compression?).

Any advise in the right direction would be appreciacted!

First up will be cleaning the carbs and getting a spark going!

Motor:
CB750E 2734730

Frame:
Cb750K 2733839

Is it normal that frame and motor number do not match up with these hondas?
in the registration papers it is the same,just asking since on my old yamahas the numbers normally match up.

This is going to be a full rechrome,powdering the frame full-on resto...lets see where this will lead us!

Thanks in advance guys!
 8)

« Last Edit: Nov 08, 2017, 04:20:40 by Ryan Stecken »

Offline irk miller

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #1 on: Nov 08, 2017, 07:39:18 »
Most excellent. 

For no spark, start running through the ignition from the plugs back which means check the resistor caps.  The F model I helped get running recently had just that problem after sitting since the 80s.  The resistor caps showed infinity on the meter.  A quick change with a new set of caps and it fired up. 

Your starter button issue could be the neutral switch.  Did you have it in neutral with the clutch pulled in when you started it up?

And as far as the frame/motor ID, they never matched on Hondas.  That motor number (CB750E) tells you that is a facelift model.  E for European because Honda added Euro features. 

By those carbs, that looks like a 77 or 78.  I'm not going to lie.  Those carbs are a bitch to get clean because of the accelerator pump circuit.  Once they're right, they're awesome.  Also airbox for that year is only for that year.  It has a notch for the choke that other years don't have.

I hope you guys have fun with this one.  I still love the 750s, even though I turned mine into a chopper. 

Offline djmaynard

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #2 on: Nov 08, 2017, 09:46:30 »
I wondered what year also. I have a 77 Honda CB750K that was going to clean the carbs out this winter.


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Offline Ryan Stecken

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #3 on: Nov 08, 2017, 10:42:28 »
Most excellent. 

For no spark, start running through the ignition from the plugs back which means check the resistor caps.  The F model I helped get running recently had just that problem after sitting since the 80s.  The resistor caps showed infinity on the meter.  A quick change with a new set of caps and it fired up. 

Your starter button issue could be the neutral switch.  Did you have it in neutral with the clutch pulled in when you started it up?

And as far as the frame/motor ID, they never matched on Hondas.  That motor number (CB750E) tells you that is a facelift model.  E for European because Honda added Euro features. 

By those carbs, that looks like a 77 or 78.  I'm not going to lie.  Those carbs are a bitch to get clean because of the accelerator pump circuit.  Once they're right, they're awesome.  Also airbox for that year is only for that year.  It has a notch for the choke that other years don't have.

I hope you guys have fun with this one.  I still love the 750s, even though I turned mine into a chopper.

Thanks Irk for jumping right in!
Had bad sparc too on my XS750 project,ended up switching out caps,cables and ignition box.
Is there a way to measure the plug caps (you stated showing infinity) with a multimeter?if yes hwo doI need to set the mulitmeter up?thanks!

Offline irk miller

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #4 on: Nov 08, 2017, 10:51:58 »
Thanks Irk for jumping right in!
Had bad sparc too on my XS750 project,ended up switching out caps,cables and ignition box.
Is there a way to measure the plug caps (you stated showing infinity) with a multimeter?if yes hwo doI need to set the mulitmeter up?thanks!
Pull the caps off the wires, put one lead in the wire end and the other lead in the spark plug end.  Set the meter to 1k ohms.  For a 76 or later, they should read 10k ohms or less than 11k.  Any more than that and the caps are burned out.  Pre-76 will be 7.5k ohms and are burned out at 9.5k ohms.  You can get replacement NGK resistor caps at 5k ohms and improve spark.  It's not a bad idea to do it regardless. 

Offline Ryan Stecken

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #5 on: Nov 08, 2017, 12:23:15 »
Pull the caps off the wires, put one lead in the wire end and the other lead in the spark plug end.  Set the meter to 1k ohms.  For a 76 or later, they should read 10k ohms or less than 11k.  Any more than that and the caps are burned out.  Pre-76 will be 7.5k ohms and are burned out at 9.5k ohms.  You can get replacement NGK resistor caps at 5k ohms and improve spark.  It's not a bad idea to do it regardless.

Thank you irk!since we are doing a full nearly total resto we will go for fresh plugs and caps!I will however measure just for fun the caps!

As for the carbs: IŽve already been warned that these carbs are a nightmare.How would you go about?
The carb slides are stuck and donŽt move a bit, the bike however was well stored (the tank inside is immaculate) and I have hope that the engine wonŽt need a total rebuild...

My friend Der_Nanno advised me just to take the bowls off, clean the main and idle jets and leave the other things alone.
But I guess this wonŽt help me with the stuck carb slides....
I have access to a ultrasonic cleaner, but throwing the whole rack into the bath without "top end" dissassembly of the carb will probably ruin the carb i guess...
« Last Edit: Nov 08, 2017, 12:31:14 by Ryan Stecken »

Offline irk miller

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #6 on: Nov 08, 2017, 12:40:07 »
Just cleaning the main and idle jets doesn't usually work on these carbs.  PD carbs are unique in a lot of ways.  The biggest issue with these carbs is the accelerator pump circuit.  It's prone to clogging when left stored for too long, and it's vital to the performance of this motor.  You can try to spray through the circuit with carb cleaner, and if you're lucky, it will work.  But you need to get full spray on all for carbs coming from the pump nozzles.  The tendency is for #2, which is where the pump is located, to clear and the fluid just stream through that circuit.   The pump circuit is the rubber tubes that run between each carb.

Offline Ryan Stecken

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #7 on: Nov 09, 2017, 04:23:03 »
Just cleaning the main and idle jets doesn't usually work on these carbs.  PD carbs are unique in a lot of ways.  The biggest issue with these carbs is the accelerator pump circuit.  It's prone to clogging when left stored for too long, and it's vital to the performance of this motor.  You can try to spray through the circuit with carb cleaner, and if you're lucky, it will work.  But you need to get full spray on all for carbs coming from the pump nozzles.  The tendency is for #2, which is where the pump is located, to clear and the fluid just stream through that circuit.   The pump circuit is the rubber tubes that run between each carb.

Thanks Irk!That sounds really complicated...cleaned already a lot of carbs but never a bank of four with a pump...thinking about outsourcing this to one of few firms that specialises in overhauling these carbs...will cost some $$$ but since the owner is prepared to invest I think this is the way to go.
Is there someone in the forum that offers this service?
Do you have recommendations?

Thanks!

Offline irk miller

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #8 on: Nov 09, 2017, 07:49:02 »
You can do it.  It's more a pain in the ass then it is complicated.  Check the pump circuit first.  I may not be that bad.  That said, paying someone $150 to rebuild these carbs for you might be worth it. 

Offline Ryan Stecken

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Re: Honda "l'arancio dolce" CB 750 Resto-Mod Project
« Reply #9 on: Nov 09, 2017, 09:42:49 »
You can do it.  It's more a pain in the ass then it is complicated.  Check the pump circuit first.  I may not be that bad.  That said, paying someone $150 to rebuild these carbs for you might be worth it.

Yep,I will try, lets see..just had a word with a firm that does oldschool inline 4Žs and they charge around 500$ for that job....