Author Topic: 750 f1  (Read 343 times)

Offline Redders33

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750 f1
« on: May 06, 2020, 06:53:15 PM »
A up everyone, I’ve sorted my electrics and done a few other jobs so been out on the cb a couple of times (travel to work and shop).
I am really impressed how well it rides, handling is good and the engine is lovely.
Carburation is a bit woolly low down and feels like it could be crisper, it starts better without choke so I’m wondering if a bit rich or are they like that? It fine with a few revs and pulls very well. I’ve had the bowls off and blown all jets through didn’t look what sizes though .

Offline hairygit

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Re: 750 f1
« Reply #1 on: May 06, 2020, 07:03:52 PM »
Sounds a tad rich, check the air filter condition before messing with the carbs, you'd be surprised how different a new clean filter can be.

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Offline Redders33

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Re: 750 f1
« Reply #2 on: May 06, 2020, 07:19:18 PM »
Air filter is good, I’ve got a manual which will have standard jetting I’m sure?

Offline hairygit

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Re: 750 f1
« Reply #3 on: May 06, 2020, 07:20:56 PM »
Standard jets for 750F1 are 105 mains, what exhaust is fitted?

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Offline Redders33

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Re: 750 f1
« Reply #4 on: May 06, 2020, 07:30:40 PM »
It’s got a Marshall deep tone on it

Offline SteveD CB500K0

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Re: 750 f1
« Reply #5 on: May 06, 2020, 07:44:38 PM »
Hooligan


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Offline hairygit

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Re: 750 f1
« Reply #6 on: May 06, 2020, 08:13:45 PM »
Ouch, your eardrums after a couple of hours! If someone else fitted it they may have fitted oversize jets in an effort to clear a flat spot. Standard jetting in an F1 is on the lean side when they were new with standard pipes, emissions regs were starting to bite. Good thing with the 750 is you can check/change the main jets without removing the carbs!

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Offline Redders33

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Re: 750 f1
« Reply #7 on: May 06, 2020, 10:08:23 PM »
Cheers Hairy that’s a good tip, can the needle height be altered ?

Offline hairygit

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Re: 750 f1
« Reply #8 on: May 06, 2020, 10:28:00 PM »
Not with the carbs on the engine sadly, but at least you can check what jets are fitted before deciding what to do.

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Offline K2-K6

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Re: 750 f1
« Reply #9 on: May 07, 2020, 10:05:51 AM »
For starting and low speed (small throttle opening)  check how the idle circuit screws are set as they have most influence there.

If you also turn each one individually while it's running,  then you should get a response for each of the cylinders from turning the screw that's clearly heard in engine running.  If you don't get that from each one,  it points to that carb having its idle circuit partly blocked which could need cleaning to run effectively.

Offline Spitfire

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Re: 750 f1
« Reply #10 on: May 07, 2020, 01:55:20 PM »
Something sounds wrong on my F1 just like all the other 750's that I have owned they like full choke on start up.
Attached is some info on F1 carbs


Cheers

Dennis
1976 CB750F

1977 CB750F2 In bits

1964 BSA A65R In bits

2000 NT650V DEAUVILLE

Offline Redders33

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Re: 750 f1
« Reply #11 on: May 08, 2020, 04:54:53 AM »
Thanks for all the help everyone, few things to check eh, the idle screw is interest I think they are wrong ..so according to the chart it’s all the way in then out one complete turn ?

Offline Spitfire

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Re: 750 f1
« Reply #12 on: May 08, 2020, 12:39:56 PM »
That's the way I read it

Cheers

Dennis
1976 CB750F

1977 CB750F2 In bits

1964 BSA A65R In bits

2000 NT650V DEAUVILLE

Offline Skoti

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750 f1
« Reply #13 on: May 08, 2020, 04:46:47 PM »
'Carburation is a bit woolly low down and feels like it could be crisper, it starts better without choke'

Had exactly the same problem with my F1, tried everything mentioned here, but in the end it was new needle jets that cured it.

Part number 16012 392 004 (if you can still get them)



Good luck.
Motorcycling is Life, anything B4 or after is just waiting...


1976 Honda CB750F1
1974 Norton Commando 850 Mk II
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1992 Jawa 350 Blue Style
1981 Honda NF75

Offline Redders33

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Re: 750 f1
« Reply #14 on: May 11, 2020, 07:04:20 PM »
That's interesting Skoti, was there any evidence of wear on the knackered ones?

 

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