Author Topic: Strange engine issue that develops late journey  (Read 307 times)

Offline owain

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Thanks for all the feedback in my previous post. I managed to sort the richness issue out by replacing the 280 main jet with a 150 main jet. The spark plugs are looking a nice brown colour now with no carb deposits. In fact, the motorcycle was running so well that I decided to go for a longer ride around North Wales.

The bike was running great for the first 45 mins but then the engine started to die whenever I gave it more throttle. Instead of increasing in revs and sounding amazing, it sounded as if it is was muffled and starved of air. Very bizarre. Both fuel taps were open but this didn't resolve the problem.

I also noticed a bit of oil to the posterior side of the cylinder base. There was no signs of oil dripping from the rocker boxes or cylinder head. The only explanation I can think of for the oil is that it has managed to get pass the threads of the cylinder base studs?

The oil tank was also low on oil but was full when I left the house without any major oil leaks being evident. Perhaps the pump is drawing too much oil from the tank and not returning oil at the same rate? So the oil is accumulating and wet-sumping the engine? I'm scratching my head on this one guys, does these symptoms sound familiar to anyone?
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online duTch

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Re: Strange engine issue that develops late journey
« Reply #1 on: 13.08. 2018 23:56 »

 I'd think that a .150 main jet  be a bit small  *dunno*,  and depends how much stick you giving it... maybe starved for fuel not air ?

 Did you do anything to the pilot jet also, as starting was your issue if I recall ?
 I'm running a monobloc with I think a .240 main, but don't think i spend much time in that range...


Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online Triton Thrasher

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Re: Strange engine issue that develops late journey
« Reply #2 on: 14.08. 2018 06:45 »
How did you choose that main jet size?

Running weak then going funny once hot could be detonation, pre-ignition or seizing.

Or the fuel isn’t flowing enough.

Don’t let the oil level get low.  If the level in the tank drops noticeably in 30 miles or so, there must be substantial leaks or clouds of blue exhaust smoke.

Do more fettling local runs before heading for Wales.

Offline muskrat

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Re: Strange engine issue that develops late journey
« Reply #3 on: 14.08. 2018 21:34 »
G'day owain.
I agree with both duTch and TT. Also the fuel cap may not be breathing properly.
Cheers
Ps: valve clearance may also be closing up once it's hot.
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Re: Strange engine issue that develops late journey
« Reply #4 on: 14.08. 2018 23:21 »
yes fuel caps, I have a h h h o nda  CB 360 tank on mine and it stopped breathing while I was after a morgo 750 triton and bless her little cotton socks she was doing awesome until the insides of the cap rotated and starved her *problem*