Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Redders33 on May 06, 2020, 06:53:15 PM
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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 .
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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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Air filter is good, I’ve got a manual which will have standard jetting I’m sure?
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Standard jets for 750F1 are 105 mains, what exhaust is fitted?
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It’s got a Marshall deep tone on it
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Hooligan
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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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Cheers Hairy that’s a good tip, can the needle height be altered ?
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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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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.
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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
(https://imagizer.imageshack.com/img923/1146/kQhC7o.jpg)
Cheers
Dennis
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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 ?
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That's the way I read it
Cheers
Dennis
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'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.
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That's interesting Skoti, was there any evidence of wear on the knackered ones?
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Yes ,by just holding an old and new needle jet up to the light for a visual inspection there was a fair difference in size.
Those were the original needle jets from new and had done 23,900 miles.
You'll probably find that you'll need full choke when starting and careful engine warm up after fitting replacements, also restores fuel consumption and nice smooth low throttle response.