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cb750 carbs
Bitsa (Ralph Wright - RIP):
Alan,
Yes I rebuilt the carbs but with all from DS not keyster.Hopefully tommorrow I will give her a thrashing down the road and hit the kill switch and check the outside two plugs.I will take a pic of the plugs and post and maybe everyones comments will be aired.Again stock manifolds,stock 341s,stock airbox and filter,gas 98 octane in fact There is no pattern parts at all.The only thing maybe is the plugs in France they recommend same as the USA D8EA.The engine to touch is red hot but if you take the dipstick out and splash the oil on your hand it is Luke warm no bloody hell that's hot.
Regards
Bitsa
Will post results Thursday if all goes well.
Bitsa (Ralph Wright - RIP):
Hi All.
Well today I did give her a run out over 30 miles.I started off with air screws out 1/2 turn.Ran OK warmed up OK but started to jerk about at low revs pull away etc.Gave it flat out hit kill coasted to stop pulled outside plugs.Photos 4 and 5.Looked lean to me and reset screws to Honda mans advice on k4s 7/8 out.Started off all over again screamed her stop and did not seem much difference photo 11.Good thing nice and smooth now with no jerking about good idle steady but still not happy with colour or as I said before paranoid?They are a close resemblance to the Haynes colours photo 13.According to a chart I saw on here my carbs are 657a main jet 110 years 69 to 76 don't know what year my k4 is.After that its F's with 105 mains.Got home ticked over perfect same after a handfull Had a bloody good time on it really nice.Question is do I stop worrying about it and just ride her?One other thing I did hear the odd burble at the back of the exhausts nice sounding burble not what you hear on modern bikes with go faster exhausts.Any comments Ladies and Gentlemen?
Cheers
Bitsa
Spitfire:
Looks a bit sooty (rich) to me, also what throttle opening did you have before doing the plug chop, were you wide open (on the main) ?
Here's some interesting stuff.
http://forums.sohc4.net/index.php?topic=5410.0
This is what I am getting at the relationship between jets and throttle openings.
More stuff
Cheers
Den
BigAl (Alan):
Hi Bitsa,
Looks a little sooty to me, bit if its running as you like it after 20/30 miles why worry!
Anyhow, the Haynes manual is based on the early CB750's upto K1...possibly K2 the exhausts are the (HM300) pattern and carburation jetting is 120/110
The K3 onwards there where a number of changes due to emission controls in the USA, carburation jetting size (105) advance and needle clip adjustment,also exhausts changes (HM341) style with 3 or 5 or 7 baffles...?
My CB750 book by Mark Paris page IV-8 the modifications through the K2,3,4,5,6 are well worth a read.
Question, are you sure your bike is a K4? the 657A carbs are the earlyer type as fitted to the K1 with HM300 exhausts?
Alan
Bitsa (Ralph Wright - RIP):
Spitfire,Big Al,
Thanks for your replies yes flat out for plug chop.I have checked engine number and it is a k4 motor but the bike was a k6 but the cylinders were shot.It was cheaper to buy a low milage motor than re boring in France.The carbs that I am using came with the bike on a k6.Maybe PO changed them don't know.As Al says I think I will live with it as she goes very well made me feel 19 again.Last thing to do in winter is to fix a poxy tiny oil leak in between 2 and 3 cylinders.
Thanks again
Bitsa
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