SOHC.co.uk Forums > CB350/400

fueling problems

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peteb:
hi im just starting to find my way round the site and have posted this plea for help some where else but i think it should be here so here goes again.I have just finished restoring a 400/4 and would love to enjoy riding it but i cannot get it to run properly.

from cold it starts easily and ticks over fairly well .when its warm if you crack the throttle open sharply the engine wants to die,if you open the throttle gently it will rev ok. it is not nice to ride in traffic as at low revs it seems a little gutless.

Ihave had the carbs ultrasonicly cleaned,fitted new jets etc,checked float heights,tried different neadle positions all the usual things

It does run better on half to three quater choke so would suggest weak mixture but the plugs look a little rich .

I have also fitted new coils,cam chain and tried timing as per book and alittle more reterded but nothing seems to make much difference.

In 40 years of fiddiling with things mechanical I dont think ive been so frustrated


HELP PLEASE

K2-K6:
Hello and welcome to the site hopefully someone here will be able to put their finger on something to help you get it going better.

Sounds as if you have reasonable confidence in the carbs.

I always find that retarding timing prevents any revs increase so would try it with a swing the other way to see what happens. If so you'd possibly suspect the advance/retard method as being stuck.

Are you certain about the cam timing? as this can run you in rings even if one tooth out.

Have you got any compression readings for each cylinder to verify general mechanical health.

Bryanj:
A bad or not fully charged battery can do this especialy if the regulator is sticking, also wrong grade plugs--they SHOULD NOT have an "R" in the designation no mater what the NGK book says

peteb:
hi thanks to you both for the replies,iforgot to say the bike is fitted with boyer ignition and seems to advance ok when checked with timing light ,battery is new but may be suspect as it wont turn the bike over so i will try to jump it from a good one tonight .as regards the cam i have replaced this with a new /second hand one as the original was very worn the only thing i dont know about here is that the original cam was marked as 360 and the replacement 359 but looked the same and i could not find any info on the relevance of the numbers.I have checked the compression but only on the kickstart an it read the same on all 4 pots at about 130 psi.When i had the head off it looks like it has had a rebore to .75 over size fairly recently but i will check compression again on the starter motor with a jumped battery as the book gives a figure of 170 psi but i assumed the lower reading was because i was only kicking it over.

perseverance furthers

thanks again and i will let you know how i get on.  pete

peteb:
hi, spent a while up the shed last night and have made some progress. I set the timing again but this time at 2500rpm and set it to the fully advanced marks which has made a huge difference.Iwill check the charging curcuit tonight and swap the battery from the old XBR500 which Iknow to be good and see if this irons out the last little bit of hesitation that remains when you crack the throttle open.


thanks again for your help

ps does any one arrange meets in the south east

Pete

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