A A A
Avatar

Please consider registering
Guest

Search

— Forum Scope —






— Match —





— Forum Options —





Minimum search word length is 3 characters - maximum search word length is 84 characters

Register Lost password?
sp_Feed sp_PrintTopic sp_TopicIcon
Concentric on a D7
Avatar
stubaker58
Sunny Felixstowe
Area Rep
Club Member
Forum Posts: 450
Member Since:
June 13, 2015
sp_UserOfflineSmall Offline
1
February 24, 2020 - 5:54 am
sp_Permalink sp_Print

Hi all,

Having identified the carburettor as the problem with my D7 I’m looking for some advice.

The bike is a bitsa, indeed the engine is a mongrel with a D7 crank in D14 cases and with a D10 barrel and head! The piston is flat topped. I’m running with a concentric not the D7 monobloc. As reported elsewhere the air filter was so clogged up that it strangled the engine but it was running rich even before this happened.

Quick question ... is anyone else running a concentric on (what is basically) a D7? And if so what jet sizes and needle setting are you using?

Many thanks.

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

Avatar
NeilB
Guest
Guests
2
February 24, 2020 - 9:41 am
sp_Permalink sp_Print

Off topic, but I thought the D14 had the points on the right hand side and a very different crank size? I'm guessing someone wanted the 4 speed and could only get the cases and gears, then fitted random parts?

Depending on your budget, I've seen a couple of Amal carbs come up for less than £50 on ebay, but I suppose the right jets and settings for any carb depend on what exactly you have and the mismatched everything (especially D7 piston with D10 head) will make deciding that more difficult. 

Avatar
bantammad
Top Gear User
Club Member
Forum Posts: 190
Member Since:
December 12, 2018
sp_UserOfflineSmall Offline
3
February 24, 2020 - 11:34 am
sp_Permalink sp_Print

Hi bantammad ere just a point of interest with the set up you have may l suggest you go for maybe a 624 concentric jetted to start with as D14 you can then reduce jets accordingly as a note l am running two bantams of different states of tune but both are of 186 cc capacity a little trick one has a 376 the other 626 both have ported barrels one has 6 ports there are also modified fore speed plus Tod head etc so as for carburettor settings start some where near standard then it’s a bit trial and suck and see happy days Les 

Avatar
Blue Heeler
Top Gear User
Site Member
Forum Posts: 2396
Member Since:
November 16, 2011
sp_UserOfflineSmall Offline
4
February 24, 2020 - 12:29 pm
sp_Permalink sp_Print

Hi Stu,

I`m guessing you`re running some sort of electronic ignition, am I correct? What deg timing?

My D-reg D10 runs a concentric, which I think is standard, if memory serves.

I ran my D14 (obviously also a concentric-wearing model), with a flat-top piston, after running out of domed ones. Engine was much smoother and just as quick. 

You are very wise to run the flat-top with a D7 crank, should be much less strain on it.

Based on that then, I would look up jetting for D10 and then factor in type of exhaust system you are running, diameter(my D10 is small bore front pipe with standard baffles in the silencer. Main thing is air filter level of filtration.

Have you a heat-block between your concentric and barrel flange?

Of course plug grade  and also even the make, can have a difference. 

Remember, with  D10 barrel and D14 crankcases,  you have upgraded porting, therefore better breathing, therefore better fueling. Did you blend the barrel ports into the crankcase cutaways...something I`ve always done with 2-stroke singles/twins/triples whenever I`ve rebuilt them. Important to cut the base gasket to suit, no overlap. Always made a positive difference with me.

There is a procedure to prepping the Bantam barrel-crankcase before this blending port work on a Bantam, if you`re interested.

For me with jets, it`s finding a starting point...in this case D10 standard jets, or even D14 ...and then it`s down to getting the airscrew and tickover set and mucking about with the slide needle position after runs...and then eventually plug chops for checking plug colour re the main jet.

If your barrel has been rebored by the best 2-stroke specialists, port radiusing and clearances should be fine. I have a copy of a bike mag where they road-tested a "restored" D7 the other year and it nipped up during the test. Reasons could be down to machine-shop/mechanic`s work(rough edges not removed/air leaks/carb not set up etc), being thrashed too soon etc.

Blue

Avatar
sunny
Norfolk
Top Gear User
Club Member
Forum Posts: 1473
Member Since:
January 9, 2013
sp_UserOfflineSmall Offline
5
February 24, 2020 - 12:32 pm
sp_Permalink sp_Print

hi    Stu    Bantams   dont  run   lean     ther   mower   engiens    with   big  wheels  on   so i  wold  enrich   the  bern  a  bit  ,.,was it  runing  ok  befor  you  chaged   the   filter

Avatar
stubaker58
Sunny Felixstowe
Area Rep
Club Member
Forum Posts: 450
Member Since:
June 13, 2015
sp_UserOfflineSmall Offline
6
February 24, 2020 - 3:37 pm
sp_Permalink sp_Print

Hi everyone, thanks for the responses. To answer a few of the questions ...

it was me , I’m guilty of the D14/D7 arrangement! Some years ago I read an article which praised the low down pull of the D7 but bemoaned the lack of four gears. It pointed out that to mate the two was not difficult. Now I had some bits left over after rebuilding a D3 SA (which had a D5 engine!) so I thought I’d have a go. None of the pieces were new or even refurbished, the barrel and piston were a matched pair however and I did my best to blend the ports into the crank cases. By changing the outer engine covers the old style Wipac generator fits and a D7 primary chaincase goes on by simply tapping the two holes that are already present in the D14 cases. 

(I think this conversion is/has been done for pre ‘65 trials use as technically the four speed box does not qualify and the later generator makes the engines less tractable?)

Its still on 6v with points ignition fed from a remote coil backed up by a 12Ah gel battery, much like the later D7s.

The Pope is small bore and feeds into a D3 torpedo silencer upswept in the manner of the Trail Bronc. The silencer could probably do with a clean too to help with the breathing.

It actually goes quite well and has not let me down but top speed has been a bit disappointing (53mph on my phone app) and the carburation has never felt that ‘clean’.

I’ll work through the various jetting permutations and let you know the outcome.

Thanks again.

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

Avatar
Geoffrey25
Top Gear User
Site Member
Forum Posts: 70
Member Since:
February 10, 2019
sp_UserOfflineSmall Offline
7
February 24, 2020 - 7:24 pm
sp_Permalink sp_Print

Hi Stu  I have a d7 with a d10 head and barrel with flat top piston  and

 a concentric 626 carb the best jet for me is a 160 with carb needle in position 2 the bike starts and pulls a way really well but I struggle  to get 45 out of my bike it seems to bog  down a bit at full throttle I use a pancake air filter on the carb regards Joe.

Avatar
stubaker58
Sunny Felixstowe
Area Rep
Club Member
Forum Posts: 450
Member Since:
June 13, 2015
sp_UserOfflineSmall Offline
8
February 25, 2020 - 5:57 am
sp_Permalink sp_Print

stubaker58 said

The Pope is small bore and feeds into a D3 torpedo silencer upswept in the manner of the Trail Bronc. The silencer could probably do with a clean too to help with the breathing.

 

Ooops! 🤭😂 No offence meant! ..... pipe is small bore .... autocorrect at its best.

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

Avatar
sunny
Norfolk
Top Gear User
Club Member
Forum Posts: 1473
Member Since:
January 9, 2013
sp_UserOfflineSmall Offline
9
February 25, 2020 - 9:09 am
sp_Permalink sp_Print

your  both   doing  welll   then    45    &55  out  of  a  bantam that  desined   to  run  all   day  at  30  MPH   ant   bad   is it ,, and  dont  for  get   sum speedos  dont  run   or  mach   up     well   so  well  done   then   a ,, to  both of  you  

Avatar
NeilB
Guest
Guests
10
February 25, 2020 - 9:17 am
sp_Permalink sp_Print

If I only get 45 out of my bantam, I'll be figuring out why! I expect it to get 55-60mph, and it's a 2-stroke so it's better when it's ridden hard providing it's been warmed up and is running right. 

Avatar
bantammad
Top Gear User
Club Member
Forum Posts: 190
Member Since:
December 12, 2018
sp_UserOfflineSmall Offline
11
February 25, 2020 - 11:14 am
sp_Permalink sp_Print

Hi bantammad ere I’ll go along with that statement NealB i think I’d be choked happy days Les 

Avatar
sunny
Norfolk
Top Gear User
Club Member
Forum Posts: 1473
Member Since:
January 9, 2013
sp_UserOfflineSmall Offline
12
February 25, 2020 - 11:35 am
sp_Permalink sp_Print

so   here s    the   thing  ,.,     ALL    kines   of   meters    with   a  needle  pointer     must     have    a   NO GO  space  at  the  top of  meter s  range  for the  needle  to  slow  down   coz  if  it   hits  the  top end  of  its  range  it  will   damage  the  meter      .,., so your   meter s    got   bilt  in  safty  wen it  comes  to    a speedo   with  a  top speed   of  80  mph     the  average   speed  range  of that   vechile     is about   30  to 55  this  levs  a good    slow  down   gap  so   the needle    dont  hit the  top   needle   stop  then  braking   the  meter  or its  internal  springs    ,.,likewize   amp  or  taco  meter   this  is  also  wy    amp  metrs are  NOT   recameded  for  m/cycles     and  thay  dont   show  much   anyhow

Avatar
NeilB
Guest
Guests
13
February 25, 2020 - 12:50 pm
sp_Permalink sp_Print

Not always sunny, I got my Sportster to the 130mph at the end of the speedo! With 80 on the speedo I'd expected to get 60-65 max speed down hill, but I'll keep you posted.

I guess it depends on weight too, on a bike that weighs a little over 200lbs, a heavy rider will make a BIG difference. Luckily I weigh around 160lbs in full kit, although less assistance downhill rolleyes

Forum Timezone: Europe/London

Most Users Ever Online: 223

Currently Online: Nick_S
12 Guest(s)

Currently Browsing this Page:
1 Guest(s)

Top Posters:

cocorico: 3412

Cornish Rooster: 3314

bart: 3130

Sprung Chicken: 2658

David Dale: 2485

Blue Heeler: 2396

Mags 1: 2356

Piquet: 2324

Munchkin: 2224

nickjaxe: 2100

Newest Members:

Terence7919

Forum Stats:

Groups: 9

Forums: 48

Topics: 12483

Posts: 108016

 

Member Stats:

Guest Posters: 1477

Members: 1632

Moderators: 0

Admins: 4

Administrators: Bantam-Super, JMD, Springs, Stoo63