Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Andrew-S on September 15, 2021, 09:20:50 PM
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Well, the K1 started up first prod after the carb rebuild, however when the choke leaver is down (fully open) then raised slightly it revs to about 3,000 rpm and when it's up (fully closed) it cuts out. I've checked the opening throttle cable and it doesn't appear too tight and the return cable is doing it's job. It will idle at 1,000 rpm at a little before the lever is fully up. I haven't adjusted the idle thumb screw yet so will look at all the linkages and idle setting tomorrow
In the meantime, any thoughts or suggestions gratefully received.
Video: https://youtu.be/KjWbOuseLOs (https://youtu.be/KjWbOuseLOs)
Thanks,
Andrew
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Well, the K1 started up first prod after the carb rebuild, however when the choke leaver is down (fully open) then raised slightly it revs to about 3,000 rpm and when it's up (fully closed) it cuts out. I've checked the opening throttle cable and it doesn't appear too tight and the return cable is doing it's job. It will idle at 1,000 rpm at a little before the lever is fully up. I haven't adjusted the idle thumb screw yet so will look at all the linkages and idle setting tomorrow
In the meantime, any thoughts or suggestions gratefully received.
Video: https://youtu.be/KjWbOuseLOs (https://youtu.be/KjWbOuseLOs)
Thanks,
Andrew
What you describe sounds like when I first had my 400/4 running - in my case I had inverted the situation in my head. When I pushed the choke one way I thought it was "more on" when in fact it was the other way around if you get my drift. The increase in revs was the fast idle cam, normal running when warm was off. I convinced myself it would only run when the choke was partially on in reality when I looked at the carb flaps it was off. My choke markings on the lever were confusing to say the least.
I could be talking rubbish - just shared my findings.
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Thanks Ted, I shared your frustration in thinking 'on' was 'off' and 'off' was 'on'...... :o
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The 750 has no lift of throttles when choke is used as it just drops guillotine type plates down into venturi on airbox side.
Throttle modulation is entirely on twist grip and rider control, usually you've got to juggle just rich enough to run with choke lever against how much you hold slides open until warm enough to run off choke. Choke lever down and flat against the carb body for fully open, no enrichment.
If you need someone else to come round and scratch heads in unison :) let me know as I'm not far and often going past near you.
Nigel.
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The 750 has no lift of throttles when choke is used as it just drops guillotine type plates down into venturi on airbox side.
Throttle modulation is entirely on twist grip and rider control, usually you've got to juggle just rich enough to run with choke lever against how much you hold slides open until warm enough to run off choke. Choke lever down and flat against the carb body for fully open, no enrichment.
If you need someone else to come round and scratch heads in unison :) let me know as I'm not far and often going past near you.
Nigel.
Hi Nigel,
I'm going to have another look over the weekend, but failing that a head scratching session in unison would be most welcomed, thank you. :)
Andrew
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The 750 has no lift of throttles when choke is used as it just drops guillotine type plates down into venturi on airbox side.
Throttle modulation is entirely on twist grip and rider control, usually you've got to juggle just rich enough to run with choke lever against how much you hold slides open until warm enough to run off choke. Choke lever down and flat against the carb body for fully open, no enrichment.
If you need someone else to come round and scratch heads in unison :) let me know as I'm not far and often going past near you.
Nigel.
Hi Nigel,
I'm going to have another look over the weekend, but failing that a head scratching session in unison would be most welcomed, thank you. :)
Andrew
Yesterday I fired the old girl up after readjusting the throttle linkages and idle stop both static and whilst running and it was only running on 2 cylinders, sometimes just one. ??? I've Just came back in from the garage having checked there is a spark at the points, at all four leads, that fuel getting to 2, 3 & 4 and the valves are opening and closing, and it's a 'yes' to all those.
That's all the time I have for it for today, so tomorrow I will pull the plugs and see if their fouled and go for there. Thing is, it was running fine and sounding great first and last time I fired it up back in Jan 19, but it wouldn't idle hence the carb strip and rebuild:
https://youtu.be/8aL1cXomjuk (https://youtu.be/8aL1cXomjuk)
Cheers,
'Frustrated from Farnham'
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The 750 has no lift of throttles when choke is used as it just drops guillotine type plates down into venturi on airbox side.
Throttle modulation is entirely on twist grip and rider control, usually you've got to juggle just rich enough to run with choke lever against how much you hold slides open until warm enough to run off choke. Choke lever down and flat against the carb body for fully open, no enrichment.
If you need someone else to come round and scratch heads in unison :) let me know as I'm not far and often going past near you.
Nigel.
Ok, so the plugs on 2,3 & 4 were fouled and no spark, but also the plug gap on No4 had increased to about 35 thou, strange?
All plugs cleaned and checked/regapped at 25 thou and it fired on all four pots, back-fired a few times then suddenly shot from 1000 to 4,000 rpm and stayed there so switched it off. Then on few restarts it fired up and stayed at 4,000.
I'm now thinking the carb bank will have to come off again...... :-\
Nigel,
I may end up taking you up on your offer of a head scratching session in unison whenever is convenient for you and when you're nearby.
Cheers,
Andrew
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PM sent to arrange.
Most bits you can get to without removal that change settings, hopefully we can figure it out as is with a bit of creative analysis.
Nigel.
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Look forward to seeing you tomorrow Nigel - the kettle will be on and the Hobnobs opened!
Cheers.
Andrew
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I hope you two chaps get it sorted, Hobnobs always help in the diagnostic process ☺️☺️☺️☺️
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Oooh cant handle hobnods, too bitty! now dark chocolate digestives, that of course i never have cos my doctor tells me off
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I'm with Bryan on the dark chocolate ones! or dark chocolate rich tea's. :o
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I'm not grown up enough for dark chocolate, but I do also have milk chocolate digestives, Kit-Kats and chocolate mini rolls but of course these are only here in case my sons pop in........ ;)
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Andrew, how can you not be old enough? ive preferred bournville since me teens( in the dark ages before anybody else sez it!)
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It's all ok, I'm accredited to war office standard in the removal and safe disposal ;D of a whole range of biscuits. It's a crunchy job but someone has to do it.
Draw the line at a Bourbon, pre french revolution bourgeois manifestation of a biscuit. Also a Garibaldi, which surely can't be counted as a real biscuit ;D
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Whilst on the subject of war and biscuits........
A true story.........A RAF Bomber pilot was shot down over Germany and when he was interrogated he was asked about the details of the aircraft he was flying (the Germans wanted to be aware of any new type of aircraft the RAF may have). Not wishing to give any secrets away the Pilot replied it was a Huntley & Palmer with Peak Freane engines. He was sent to solitary confinement for that remark!
Anyway, if Deans shortbread were being offered around with a mug of splosh I too would be offering to help Andrew and Nigel ;D
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The tea and Hobnobs went down well and the K1 is running on all 4 pots again, sounds much better and the linkages are pretty much where they should be. Although No1 needs its fuel/air mix adjusted (if not all), but in trying to adjust the air screws to see where they had all been set found the Keyster airscrews were such a tight fit that that No3 snapped the anticlockwise half of its head off. So once that little chap and the others are removed the original ones will reused and I'll go from there.
All-in-all, it was a very productive day and good to meet Nigel (K2-K6) who is a really nice guy and I very much appreciated all his help and knowledge (carbs are a black art to me!!) - we soon discovered that we shared many mutual interests, not least Hondas, motocross and F1.
Not sure where the time went (nattering mostly I think?) but it was 4pm before I realised and time to let Enzo the cat out............
I am in need of a No35 Pilot jet if anyone has got a spare one to sell as this will give the options of 40 (currently fitted) and 35 in final tuning.