Hi Guys,What are the standard jets for a 250 CB 72 //65 model, my plugs keep burning up, at the moment its running with #40 Idle speed Jet & #95 High speed jet. What height do you set the slide ( throttle) needle? will the mid range?of the five cuts do . This all started as we went into Winter. Any idea why the plugs go dead, is it due to the mixture being too rich,should I change it to a #35 idle jet & a #100 high speed jet. Any ideas?
Thanks,
Gordon.
Plugs Fouling
Hi Gordon
I think we need to differentiate between 'fouling' in your title - usually blackening due to richness or oil in the combustion chamber or 'burning up' which suggests a weak mixture and white colouring of the insulator. Send some pics - that really helps. 100 is a richer main jet than 95 so I think we need to get the diagnosis right first. G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
Plugs FowlingHi G Man, I think the fouling I presume is due to the richness of the mixture. Tho whole plug is black including the Procelain, no hard carbom deposits.
I have gone through six plugs, the bike stutters & the plugs burn up. I use a NGK//D8HA ,A mechanic asked me to use a hot plug Eg: NGK D6HA, but was advised aganist it, as might make a hole in the piston. I will be fitting 35 &100 Jets & a new Needle set at the middle cut. hope this works.What would you sugest? Thanks for your concern, Regards, Gordon.
Gordon
Going to a bigger main jet is going to make it worse. The smaller idle jet could improve things at low throttle openings but will make little difference from middle throttle upwards. I would try dropping (raising the clip) the needle one notch at a time with the existing main jet. That should reduce the richness at middle throttle openings. Have you checked the air filter? Does the bike use and oil? Smoke? G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
Plugs turning blackHi G, The Bike has been rebored & Honed, with new pistons & Rings, the gent who I bought the Bike from lives in Melbourne & I live in Sydney, 900Km away,so I cant take the bike back to him.He is sending me a set of new needles & jets by Monday
The bike does not use oil & does not smoke.The Air filter is new, but I washed it out,I even tried removing the rubber hose that goes to the Carbi:with no results I purchased the bike in April, & it ran with no problems, in early June when winter set in the problems started, I think I will take your advise, and run it with the original high speed jet,I think its a #95 & the 35 idle Jet Re: the needle I will start off from the middle notch, & drop it one at a time. The gent I bought the Hawk from used to be the Mechanic for his brother who used to race 250s & 305 in England in the 60s & 70s. Will inform you of the outcome with the new Jets & needles Thanks, Gordon.
Plugs FouligHi Guys, Thanks for all your replies, I tried them all with no success, as a last resort I wrote to Mr Honda, Bill Silver, he advised me to check on the cutaway, as the slides could have been swapped over, the cutaway should face the Air Filter, low & behold he was right, they had been swapped over. The Plugs don't burn up any more & turn black.
I think the Carbi: needs some fine tuning, I tied taking it for a ride,the bike hesitates & tries to cut out. The engine has been warmed up for about 7 minutes, so that could not be the problem The jets in the Carbi: are 35& 100 &the needle is set at the middle cut, I tried dropping it one with no change in take off. Thanks for all the concern, Regards, Gordon. Ps Attached is a Photo of the problem Child,
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