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four (?) stroking ...
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b175er
saltfleetby
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July 27, 2019 - 10:35 am
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For a while now my B175's been plagued by four stroking at speeds up to the mid thirties. After that it's either better or inaudible; I'm not sure which ! I've changed the points, plug and condenser and experimented with the timing to no avail and at the rally my friend Chris - a more mechanically minded and adept person than me - stripped and cleaned the carburettor and jets and fitted a new float needle as he was confident that there was more fuel going into the engine than was necessary thus causing it to four stroke. However, his work made no difference. So, the other evening I changed the carburettor for one from my other B175 (a good runner) but, if anything, it seemed worse.

Having said all this, however, the bikes actually going well once it gets over forty; though not without a fair bit of vibration.

I'll be interested in any ideas anyone might have about it. Ken.

two B175s and a CB360

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Peterg
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July 27, 2019 - 11:19 am
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Has it been set up as a D14 with a No3 air slide?

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b175er
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July 27, 2019 - 11:31 am
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Yes, the slide is a no3. I probably should have said that since I've had it the bike's done nearly five thousand miles running perfectly well. It's just lately that the four stroking's started.

two B175s and a CB360

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johnsullivan
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July 27, 2019 - 11:33 am
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de coke would not hurt after 5k

67 D10. and a D7    2007 Honda Hornet FA. Honda CD200 81 93 Yamaha TTR 250 Raid, Sinnis SC 125.   75 Montesa Cota 247 an electric scooter of Famous make.

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b175er
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July 27, 2019 - 11:50 am
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Thanks John. It's my intention to have a look inside - as I should have done five and a half thousand miles - and twenty months - ago, of course, before I started using it !

two B175s and a CB360

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mike p5xbx
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July 27, 2019 - 5:30 pm
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b175er said
So, the other evening I changed the carburettor for one from my other B175 (a good runner) but, if anything, it seemed worse.
.  

Then it maybe nothing to do with the carburettor
as suggested try a decoke first and swap the silencer from the other good bike
you maybe surprised how much difference a silencer makes on a 2stroke

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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wildun
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July 27, 2019 - 10:41 pm
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Ken,

Interesting that you have swapped the carb from your other bike but with no improvement. So that must confirm no fault in your original carb in it's current condition.

Seeing as you have the advantage of another good running bike to borrow parts from then Mike's idea of swapping your exhaust system over is a very good suggestion. Seeing as this problem has crept up on you it may well be a slowly clogging up silencer causing your problem, similar symptoms. It is easiest to swap the whole exhaust system as a unit, especially as an experiment. You never know what you might find in an exhaust system !

How is your plug colour looking? You say that the bike runs well at higher speeds?

If after changing your exhaust there is no improvement then it is time to have a look inside the top of the engine.

1951 Bantam D1 125, 1954 Bantam Enduro, 1970 Bantam B175, all Bantams on the road and ridden regularly, 1995 Yamaha Diversion 900 and 2016 Honda Integra 750 scooter. Horses for courses, all very different to each other, but a bike for every occasion.

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johnsullivan
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July 28, 2019 - 11:38 am
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Decoking the exhaust is not fun but the agony can be reduced.The trick is patience and a two stage attack using white spirit and a cocktail shake for as long as you can stand it,drain then an overnight soak in a relatively weak caustic soda solution flush with plenty of water.the hard part is what to do with the effluent.

67 D10. and a D7    2007 Honda Hornet FA. Honda CD200 81 93 Yamaha TTR 250 Raid, Sinnis SC 125.   75 Montesa Cota 247 an electric scooter of Famous make.

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b175er
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July 28, 2019 - 4:43 pm
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Thanks everyone. I'll try my other exhaust system and let you know what happens. Ken.

two B175s and a CB360

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b175er
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July 28, 2019 - 4:49 pm
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wildun said
Ken,

How is your plug colour looking? You say that the bike runs well at higher speeds?

 

Hi Chris. The plug colour's not bad; light brownish, I'd say.

two B175s and a CB360

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nickjaxe
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July 29, 2019 - 7:18 pm
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Mine 4 stroked when I fitted a number 3 slide..only on light throttle openings....put the 3.5 back in and its fine...hot weather may make it worse...was it during that hot period Ken.

Choke is not stuck part on has it.

My Bantam video              https://www.you.....jpOFmzRZRI

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b175er
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July 30, 2019 - 9:09 am
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Hi Nick. That's a good question about the choke because that's just what it's like. However, the choke is pulling up properly. I'll try a different slide.

two B175s and a CB360

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nickjaxe
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July 30, 2019 - 10:27 am
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Ken is there anything you have changed on the carb recently.

Another possible...the needle and jet are wearing...allowing a bit more fuel in

My Bantam video              https://www.you.....jpOFmzRZRI

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b175er
saltfleetby
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July 30, 2019 - 10:52 am
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Hi Nick. The trouble has just seemed to come on lately (after 5,000 miles of good running) and I've tried almost everything - including a different carburettor, points, condenser and exhaust. Time to get the ratbike out again, I reckon !

two B175s and a CB360

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nickjaxe
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July 30, 2019 - 1:31 pm
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Odd...do you use old school mineral oil Ken...if so maybe yore right...a de-coke...

The other carb you used...was that off a bike that runs ok?

Mine only use to do it just as you wind back the throttle on getting to your cruising speed...most noticeable at 30ish MPH.

Is the vibration something new?

My Bantam video              https://www.you.....jpOFmzRZRI

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nickjaxe
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August 2, 2019 - 2:57 pm
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Has it got the tri-angle K+N air filter?...not getting a bit blocked by any chance...in fact whatever air filter you have Ken.

My Bantam video              https://www.you.....jpOFmzRZRI

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b175er
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August 2, 2019 - 4:29 pm
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Thanks Nick. I've tried it with and without the air filter; to no avail. I feel - rightly or wrongly - that the problem's an electrical one so I shall try a different ignition coil next.

two B175s and a CB360

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SpacedMarine
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August 2, 2019 - 7:23 pm
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b175er said
Thanks Nick. I've tried it with and without the air filter; to no avail. I feel - rightly or wrongly - that the problem's an electrical one so I shall try a different ignition coil next.  

Carburettor, points and condenser!What about the spark plug and check the battery voltage?

What's 7/16 in mm again?

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nickjaxe
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August 2, 2019 - 11:11 pm
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"Having said all this, however, the bikes actually going well once it gets over forty; though not without a fair bit of vibration"

Is that a new prob?

My Bantam video              https://www.you.....jpOFmzRZRI

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Peterg
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August 2, 2019 - 11:29 pm
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If it goes well over 40 it won't be an ignition problem, it will be running rich under 40.

They do vibrate like hell. Much worse than the D7. Make sure all the engine mounting bolts are tight, especially the difficult to get at ones underneath.

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