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New owner B175 - A few questions.
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Sponge
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May 10, 2020 - 10:28 am
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How frustrating but ....If it starts 2nd kick there is not much wrong with it  

From having a good read of this I reckon the problem is with the air/ fuel system / carburettor. It sounds like a blockage or a leak. 

Check the fuel system end to end ( eliminate any air locks - including the hole in the fuel tank cover)  

Check the air system - should be free flowing - no restrictions, blocked filters/pipes etc - check there are no leaks at the cylinder joint / carb flange face 

Check the carb is correct in all ways  ( is the needle going up and down with the slide, is the choke operating properly  ??)   - is it all there ? Is it the right carb (whats the number on it ?) 

Is the cylinder head tightened down ? 

Is the exhaust blocked ?  - I have seen a similar effect with a potato stuffed up inside the silencer on a Bantam.   

If all of this fails to produce a change or even a favourable result then get back to the forum and we can guide you onto the next stages. 

Sponge 

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Anthiron
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May 10, 2020 - 10:29 am
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Hi All, Cheers for the input.

@Sunny - I have plenty of carb cleaner and compressed air so that shouldnt be a drama.

@Spacedmarine - Yes choke is off pulled towards the rider. When it was running nicely It seemed to settle on the mixture screw 1.5 turns out. Thats where I have it now as well. No tuning of idle mixture is improving things currently though.

@AdrianS - Interesting. I need to get into the carb. I guess I will tear into it tomorrow and if I damage the gaskets I'll have to wait for the set ive ordered in the snail mail.

@Nickjaxe - Yeah looking at it it doesn't look too complicated. It's more that I don't have a gasket kit. One is ordered but its likely to take over a week to get here. No one local does Amal stuff. My grounds are good and solid have gone through the wiring. It's messy but its solid for now until I rewire it.
I haven't swapped the condensor as I don't have another 6v condensor to swap in. It has good solid spark though so I doubt its the condenser/HT lead/coil at fault here. I'll order a condensor anyway as a spare. Plug is brand new, clean and with 10thou gap. I think I'll strip the carb tomorrow and have a look see. If I destroy a gasket I'll just have to be patient waiting for the mail.

1969 BSA Bantam B175
2004 Harley Davidson Sportster
1998 Suzuki DR350
2007 Suzuki DR650SE
Grand Prix 160cc Victa Mini Bike

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sunny
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May 10, 2020 - 10:39 am
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 hi  Nick   i use  12vt   condeners  from  the  older  BMC  Mine   or  Ford  escort    work  fine  on my  external    HT Coil  d 5 & 7     the  sparkplug  should be  around   25   thow        not  18   like  the  older  bantams 

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Anthiron
Sunshine Coast QLD Australia
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May 10, 2020 - 11:27 am
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Hi Sponge - Thanks for the encouragement. I will pull the baffles tomorrow and check that too. I haven't checked the head bolts. I'll get onto that too.
Carb is a 626 17 which I believe is correct but I haven't checked the jets.

Worth noting here that I test rode this thing before I bought it a couple of weeks ago. It ran well and pulled through all gears. I doubt this is a problem with incorrect parts as much as it's a problem with something going bad with whats there correctly.

Sunny - Interesting. I might even have an escort condensor sitting around as I swapped an electronic ignition into my Mk 1 a while back. (Now sold and missed) I'll have a dig. My previous post should have said 25 thou for spark plug not 12. It is set to 25.

1969 BSA Bantam B175
2004 Harley Davidson Sportster
1998 Suzuki DR350
2007 Suzuki DR650SE
Grand Prix 160cc Victa Mini Bike

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nickjaxe
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May 10, 2020 - 11:43 am
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Dont let it fool you that your getting a spark....a duff condense with be eratic...they tend NOT to fail 100% right off...6v? not voltage specific.

The carbs are basic...don't worry to much about a dodgy float gasket...as long as the idle circuit is clear....have you checked that...does it idle ok???

does the carb fill reasonably quickly indicating no restriction to flow...don't forget the filter in the float base?

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

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SpacedMarine
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May 10, 2020 - 11:44 am
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If it ran well previously what have you changed?

What's 7/16 in mm again?

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Anthiron
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May 10, 2020 - 12:09 pm
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@Nickjaxe - Fair enough about the condensor. I'll see whether I can dig up a replacement tomorrow.
It idles ok usually when first started. Once you try to ride it and it starts playing up it gets a surging idle and stalls usually.
Video posted a couple of days ago was immediately before it started presenting this problem and it was idling sweetly while I put my helmet on.
Carb seems to fill quickly and I have checked the filter in the float base.

@SpacedMarine - Literally the only things I have done are check the points, check the plug, tighten all of the loose bolts and fit new fuel line with an inline filter (There was an inline filter fitted previously that had some debris in it so I replaced it. I have tried removing the filter and running straight fuel hose but no change. Fuel hose and checking the float bowl screen was the last thing I did and it was running well after the other things (up and down the driveway)

Before it was presenting problems I was just doing general checks and due diligence on a new machine rather than changing anything. My best theory is that when changing the fuel hose and checking the filter screen in the float bowl I have gotten some debris in there which is upsetting the carb.

1969 BSA Bantam B175
2004 Harley Davidson Sportster
1998 Suzuki DR350
2007 Suzuki DR650SE
Grand Prix 160cc Victa Mini Bike

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nickjaxe
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May 10, 2020 - 12:38 pm
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Sounds like the idle circuit is ok then...its a long drilling with a restrictor in it...well some carbs have the restrictor.

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

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stubaker58
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May 10, 2020 - 12:56 pm
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Hi,

as you said that tickling it whilst running almost made it stall is it running rich? Or at least over fuelling.

I found setting the fuel level in the concentric made a huge difference to how the engine ran, straightforward to do, instruction videos on line, but does need the Carb off and dismantled.  Whilst I was about it I made sure all the mating surfaces were flat to avoid air leaks.

Regards

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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stubaker58
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May 10, 2020 - 12:57 pm
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what I meant to say was float level!

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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nickjaxe
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May 10, 2020 - 1:56 pm
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Float level....not adjustable on a B175 carb is it???

If you flood it pressing the tickler till it floods the engine wont like it when its running....the trick is to tickle and stop before you flood the carb.

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

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Sponge
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May 10, 2020 - 2:34 pm
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There's not much that will make a Bantam run as bad as this. It has to be a simple thing. 

Have a think guys - if we wanted to make a Bantam run OK then die out after a few yards - what would we have to do to it ?

Sticky float needle ?

Restricted fuel feed ?

Blocked main jet ? 

If you dismantle the carb carefully you may get away with re-using the old gaskets until the new ones arrive.  If not you will have to wait for new ones.  I am convinced that the problem is inside that carb and its something simple. 

I recall a bloke had a similar problem a few years back. It turned out his needle was not going up and down with the slide because the little clip had come off the needle .  It started OK and ticked over because it was running off the pilot jet but when he opened the throttle it just choked up.  Fuel starvation.   This doesn't quite emulate your problem but its a good lesson just the same. 

I really hope that you get this sorted soon - its taxing my tiny brain. 

Sponge

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stubaker58
Sunny Felixstowe
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May 10, 2020 - 4:28 pm
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Hi,

on the concentric the float level is adjustable, the top of the float should be just about 2mm below the rim of the float bowl.  Briefly to adjust it you heat up the float bowl (hot air gun) and move the brass needle seat using a suitable drift and light blows with a small hammer!

On mine the float was level with the bowl rim, it’s now 2mm below and the bike is notably peppier and the plug has gone from sooty black to chocolate brown with no changes to the jetting etc.

Regards

(see Bushman’s Carb Tuning Secrets ** Please log in to view ** )

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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not henpecked
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May 10, 2020 - 7:25 pm
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Hi Ant & All

From what you have said so far your B175 was running OK before you decided to give it a good check over from sparks to fueling. In one of your replys you mention you have fitted a new spark plug. New plugs can be duff. Swap it for the old one so as a to eliminate this potential fault.

B175, on the road. Honda XBR 500, and ....... Suzuki Burgman 200 scoot! Nicknamed "The hair dryer" - by me I hasten to add; & great storage under the seat when you get to your destination.

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dienelt1
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May 10, 2020 - 10:01 pm
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 could be the coil playing up, had 2 go bad ,caused intermittent firing.

 

  DIENE.

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Blue Heeler
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May 10, 2020 - 10:41 pm
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dienelt1 said
 could be the coil playing up, had 2 go bad ,caused intermittent firing.

 

  DIENE.  

Me too. They can start to play up after a few mins running. Had one do that on my D14 & one of the coils played up on my Le Mans too, so stuck an old car coil on it & she ran perfectly again. One of my 350LC`s had intermittent misfire on one cyl, so I cut into the plastic twin-coil body to release the old HT leads & epoxy resined new leads in, right as rain again.

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Anthiron
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May 10, 2020 - 10:49 pm
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Hi all,

Early morning here in Oz land. I’ll get stuck into the carb today and see what there is to be found. As Sponge says. Hopefully something simple. 

when I said it has a new plug, I pulled the plug and it was clearly a new plug. I didn’t actually replace the plug, just gave it a squirt of carb cleaner and a 25thou gap. It was running well on this plug previously too both before and after pulling and checking the plug.

I guess it could be coil. I have had issues like that on a car although usually they work for longer and once hot start to misfire. This doesn’t feel like that but I won’t rule it out. 

1969 BSA Bantam B175
2004 Harley Davidson Sportster
1998 Suzuki DR350
2007 Suzuki DR650SE
Grand Prix 160cc Victa Mini Bike

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Blue Heeler
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May 10, 2020 - 11:02 pm
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Got a sis up in Cairns, & have lived in Bowen & Innisfail myself...breakfast-time Monday eh

Yeah, could be a faulty new plug, plenty of dodgy NGK copies doing the rounds.

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Anthiron
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May 10, 2020 - 11:09 pm
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@blue heeler - I did think you might have an Aussie connection with a handle like Blue Heeler. My old man grew up up there. Nice part of the world.

 

If I don’t have a win with the carb and manage to get it back together without busting gaskets I’ll go for a drive and find a new plug. Should be able to borrow the condenser from my little Chevy Luv Ute to rule that out. 

it really feels like fuel though. But hey I’ve been wrong before and I’m new to bantams. 

1969 BSA Bantam B175
2004 Harley Davidson Sportster
1998 Suzuki DR350
2007 Suzuki DR650SE
Grand Prix 160cc Victa Mini Bike

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nickjaxe
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May 10, 2020 - 11:12 pm
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Stick any old plug in just to test it just make sure it clears the piston top...I am ok with long reach plugs...some maynot be....start simple...work your way up.

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

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