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Messages - Mototech

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CB750 / Re: Mystery misfire
« on: June 25, 2021, 06:50:47 PM »
Quote from: philward on June 25, 2021, 05:57:56 PM
Stating the obvious - if its only a mis on 1 cylinder, its got to be that cyl HT circuit, that cylinders carb/inlet -
maybe sounds like float height/float valves (think thats what Julie might be getting at)
What model? HT lead in good order?standard airbox or pods? exhaust? Any recent rebuild/adjustments?

As 1 & 4 share a coil, I would have thought the misfire would have effected

It is 1977, all as it left the factory, I have stripped & rebuilt the carbs with new needles & needle jets & fitted electronic ignition, symptom is the same as before.

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CB750 / Mystery misfire
« on: June 25, 2021, 05:34:43 PM »
I have an odd misfire on cylinder 1, at idle & smallish throttle, it sounds like it isn't really running, with the odd chuff thrown in. I have checked ignition coil resistances & all appears to be ok, new plug caps & plugs, but still there. I also replaced the needle jets & needles as there was wear  evident, anyone have any more ideas?
I should also say, compression good & consistent on all cylinders & electromic ignition just fittted, but the issue is exactly as it was before I started!

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CB750 / Re: Running rich
« on: June 16, 2021, 02:34:21 PM »
Quote from: Skoti on June 16, 2021, 01:48:08 PM
Yep,

my F1 was once the same running very rich, after trying most things eventually new genuine needle jet kits cured it.

It's the only jet in the carbs that really wears out and most folk over look it.

https://www.cmsnl.com/honda-cb750f1-super-sport-1976-england_model14680/needle-setjet_16012392004/

Definitely worth a closer look, there is no obvious wear, but might be worth changing anyway.

4
CB750 / Re: Running rich
« on: June 16, 2021, 02:28:53 PM »
Quote from: K2-K6 on June 16, 2021, 09:19:11 AM
Welcome to the forum.

Have you checked air filter for condition? Even if it's been left stored damp it can affect it.

Do you know what jets etc are fitted in size and if they are original Kiehin manufactured.

All checked, filter new, jets all correct sizes.

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CB750 / Running rich
« on: June 16, 2021, 08:48:25 AM »
I've acquired a 1977 CB750 & it appears to be running seriously rich, plugsare very sooty. I have the carbs apart & from what I can gather,everything is as it should be. It has new electronic ignition fitted, new plugs & plug caps.   Are there any common issues I should look for?
Brian

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