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376/323 carb.
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Geoffrey25
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April 2, 2021 - 11:06 pm
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Hi all can anyone confirm if a 376/323 carb was used on bantam d 10 models of so does anyone have one they would possibly consider selling many thanks 

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FitzFortune
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April 3, 2021 - 12:06 am
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The 376/323 was used on early D10s, but if you need a replacement you may well be better off with a R626/2 as fitted to the majority of D10s.

Extract below is from the Amal Reference Catalogue. You can request a copy of the catalogue from Burlens, it's nominally free but they do charge a fair wedge for postage.

 - Ian (aka Fitz)

 

D10_1966_376-323.PNG

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Geoffrey25
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April 3, 2021 - 4:51 pm
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  • Thanks for that Ian I already have a 626 concentric carb but my problem is that I have a 1966 d7 which has a d10 head and barrel but what ever carb I put on it I can never get it to go full throttle I have used a wide range of jets and reset timing loads of times over the years but it just bogs down after 3\4 throttle.The other day I tried a mikuni vm 22 carb on the bantam and its the best so far but it still doesn't like full throttle but I do get a steady 40 mph out of it I would like to keep using the 626 but I just cannot get it perform at its best many thanks Joe.
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stubaker58
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April 3, 2021 - 5:52 pm
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Hi,

Can I ask what air filter you are using? My experience is that it makes a huge difference to performance to gave something free-flowing.  The pancake air filters can get gummed up with oil blowing back through the carb.

I was running a mismatch 626 concentric on a D7 barrel but went down to a 375 Monobloc so as to have no step in the inlet tract and it seems to have worked.

Regards.

“There’s nothing new under the sun”.

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FitzFortune
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April 3, 2021 - 8:01 pm
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Stuart's suggestion on the air filter is obviously a good one, and a partially blocked exhaust can also cause those symptoms. If your silencer has been on the bike a while, has it been decoked recently? If it's a replacement unit is it an Armours or some no-name clone? There have been several reports both here and elsewhere of the later being very restrictive straight off the shelf.

 - Ian (aka Fitz)

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Sponge
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April 4, 2021 - 10:15 am
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D7s do seem to be prone to this refusal to rev above an imaginary line syndrome and my own D7 in stock build configuration, apart from its haunted EI system, does indeed have its good days and bad days. It loves cold very damp weather and omps along, but I don't like cold and damp so we tend to fall out. 

Sensitivity to weather would, in my mind, indicate breathing issues and having been tempted to raise the main jet size I found that it made the situation worse. So I went back to stock carb settings and looked elsewhere.

I found that cleaning out the air filter made a slight difference but running without it completely made a big difference. I had a black painted silencer on it at the time and noticed that after a blast around the block the paint was all blistered on the last 6 inches of the silencer up to the cone indicating excessive heat there. So in a fit of frustration I got the hacksaw out and circumcised the silencer by the corresponding 8 inches. Inside I found a lot of black crud but none of the airways were blocked. However I got a 5/16 drill and put 8 more holes into the end baffle. Having rivitted the cone back on I then took it for a test......revelations it was now revving an estimated 750 useable RPM and an extra 5 mph on the top speed plus a looser engine. Also a lot more noise and for the first time in ages some dissaproving looks from old ladies as I wizzed past on my fire breathing D7.

Still not great performance though and a lot of head scratching and tea drinking led me back to the 375/13  carb. So I dropped the needle a notch and that seemed to give me a bit more revs and a better looking plug. It now pulls 46 Mph...a long way off its potential but it is work in progress and small steps in the right direction. There is no easy fix....that's my view anyway. 

Ref your bike....if you are running a stock D7 piston with a D10 barrel and head then you compression ratio will be very low. I would suggest either fit a D10 piston or a D7 head. Then test it and see what it feels like. After that you might need to pay attention to its breathing.

Sorry I cannot help further but stock settings ate always a good place to start from I find. Good luck with it.......

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Geoffrey25
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April 4, 2021 - 11:13 am
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Hi sponge thank you for your in depth reply here is a run down of my bike it's a 1966 d7 with a d10 barrel which has a 185 2ringed piston I have owned it 10years and tried all sorts of carb and filter configurations and old and new exhaust systems. So because of the barrel size I cannot use my 375 monobloc so 3years ago I purchased a new 626 carb and fitted a pancake air filter it seemed to run ok but not great then I tried a short belmouth filter that was about the same so then 2years ago I completely stripped and rebuilt the whole engine just in case there wa s problem with the crankcase seals and bearings.so after all that I found my original d7barrel and head  and had the barrel bored out to take a plus 40 new piston and rings ,great I thought now I can use my 375carb and matching choke slide air filter it had next to no compression ,board to start  and no good to ride . Now after all that I went back to d10head and barrel which is much better but it still bogs down after 3\4 throttle  so at t h e moment I am using a mikuni vm 22 carb that gets me to 40mph but still not full throttle my preferred choice is the 626 concentric carb which is run with 160 jet and  belmouth ,so as you see it is a real head scratcher .

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Sponge
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April 4, 2021 - 1:24 pm
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Its only my opinion but I would advise you to take it back to stock ad either a D7 or a D10 complete with a totally correct top end....including the correct piston, carb and exhaust. 

Then....get it rinning right as a stock engine. Once you are happy it runs OK then you can 'develop' it by changing only one thing at a time....only in this wau will you be able to measure the effecg of your changes. 

At present I would be suspicious of an engine with so many non-stock modifications. 

With a D7 bottom endand piston ..and a D10 top end...how have you se the timing up ? Have you tried retardinv it a touch because of the lower compression ?

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cocorico
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April 4, 2021 - 4:59 pm
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As ever, Sponge has a good way of putting things. I would add (after a pleasant lunch accompanied by copious amounts of good wine) don't ever forget that we are enamoured with machines that were originally designed in the 1930s, didn't have a great deal of money poured into development and were always entry level models designed for basic use. They can be improved by blueprinting the engine and by spending money on modernizing them in various ways, but they remain old, basic, technology. As said, it's probably best to get it back to it's intended running state before starting to 'improve' it. You may even find that a properly set up standard bike is nicer to ride.

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Geoffrey25
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April 4, 2021 - 8:26 pm
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Hi all I know what you mean about taking it all back to a standard d7 with original barrel ,head,and 375 carb I have done t his twice already the second time I put on a freshly rebored barrel and new piston and rings to match and it still wouldn't pull t he skin off a rice pudding.It definitely performs better with the d10 head and barrel today I went out on it for 8miles it ran quite well although it wouldn't go above 40 mph and t hat was with the vm 22 carb.I really don't know what to try next ,in all honestly what kind of speed should I get from a mid sixties 175 bantam?🤔

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stubaker58
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April 4, 2021 - 8:48 pm
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Hi,

With my D7 mongrel it would get up to 55mph before the circlip escaped. Now it’s been rebored and I’m running in so keeping the speed to 40 max on a very oily mixture but it feels like it wants to go faster.

The advice above about timing and breathing is key and getting back to a standard set up to start from makes sense.  Also is it possible that the crankcase seals are the wrong way around? It’s easily done.

Whereabouts are you?

“There’s nothing new under the sun”.

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Sponge
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April 4, 2021 - 9:06 pm
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Speed.....when I was a student and weighed a little over 9st7lbs my old D10A was good for 60mph and was quite zingy getting there. It would accellerate strongly in all 4 gears and I never really found out how fast it was because the speedo would start to play games at high speeds but my mate on his C15 said it wad good for 60 shakin and rattlin with bits dropping off. 

I first rode a D7 engine when  Mingo's upgraded his wheels with a 2nd hand D7 engine in his D1 stock chassis.  It was more 'strong' than fast....never a revver but that bike would easily maintain 50mph on a straight level run without a lot of fuss getting there. 

On a good day and with the original WIPAC S55 generator my D7 would give a solid 50mph but with my colossal bulk it would struggle going uphill.

A girlfriend at University got pulled up by The Fuzz in Didsbury doing a 'clocked' 60 mph + in a 30mph zone on a late model D7. It cost her £30 in fines plus costs but proves s D7 is good for a mile a minute. We all went down to the magistrates to watch her plead the case ...het defence was that a Bantam was not capable of 60mph but the traffic policeman won the day with the evidence from his calibrated speedometer. So there you have it !!

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GlenAnderson
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April 5, 2021 - 12:39 am
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When I had a D7 engine in my rigid D1 it would take the needle convincingly off the dial of the 55mph speedo on a downhill run, and would comfortably cruise at 50-55 all day long. It would take a big hill to see it dip below 50, and even then would normally slog up in top at 40 ish. 

I’m not a big bloke though, even if I am a bit heavier than I was 30 years ago. 

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Geoffrey25
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April 5, 2021 - 11:55 pm
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Hi stubaker I know that privileged for crankcase seals wrong in the last but I definitely know that they are the correct way round I can't really take it back to stock because most barrels of certain age would need a rebore and that is what I have already had done to mine and reset the timing to the best I can achieve.What I have done is order a short belmouth air filter with a gause mesh for my 626 carb as like you say the pancake air filter can be restrictive I will try this with a 160 jet and see what happens I do have almost enough spares to build a second d7 but am missing a decent d7crank maybe maybe if I find one then then I can start from the beginning ,by the way I'm near Chelmsford in Essex many thanks Joe.

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Sponge
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April 6, 2021 - 8:28 am
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I have just gone through this thread again and realising that this bike is bored out to 185cc I have a question. What size exhaust do you have fitted ?

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Geoffrey25
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April 6, 2021 - 9:04 pm
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Hi sponge I have 2 barrels for the bantam 1is d7 and the one on the bike is the d10they both have the thread that accepts the small down pipe the d10 barrel  has 26mm inlet for the carb which has a626 on it hope that helps.

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Sponge
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April 7, 2021 - 7:54 am
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Ok. So are you running a Suzuki piston in your D10 barrel ++

Reason I ask is because I have one here and a D10 barrel so I can do a bit of port mapping just in case I discover something. 

Have you ever done a plug chop on it ? I would expect a 160 main jet to be about right but taking it out to 180 might make a difference. Good or bad it tells you something so also worth a try. 

Final suggestions are: when you are riding flat out at 45mph and it is getting bogged down close the choke gradually and see if that makes it better or worse....also gives a clue as to weather you are running rich or weak at those throttle openings. 

Worth a try but deffo anti-social...if you can then remove the baffles from the silencer and see what effect that has....if it seems to be running lighter and revs freely then its also tells you something. 

Mark your throttle rotor with white marks at 1/4, 1/2, 3/4 open...its not rocket science but it will give you a reference point to measure against

Write down all your start point  settings and then only change one thing at a time.....test it, adjust, document, analyse, verify. 

Its a lot of faffing around I know but once you start to see measurable improvements it will start to fall into place. 

Once I get the ghost out of my electrics I will be going through the same exercise with my D7...happy days

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Geoffrey25
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April 7, 2021 - 10:48 pm
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Hi sponge I will strip down my 626at the weekend and swap the pancake air filter for my new belmouth with gause mesh and see what happens if no good I will change the 160 for a 180 jet .I have two exhausts unfortunately neither have removable baffles ,before I rebuilt the engine I had to set the points gap at 12 thou but now it runs on standard 15thou I did consider for a while to change it to electronic ignition but I like the fact that that part is still original many thanks Joe.

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Sponge
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April 8, 2021 - 10:28 am
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Just some other thoughts. You rebuilt the engine ....did you do any work on the crankshaft at all whilst it was in rebuild ??

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Geoffrey25
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April 9, 2021 - 1:44 pm
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No when I was rebuilding the d7 I took the crankshaft over to fd motorcycles to get check a d out and they told me it was good to refit as it is so I went ahead and did the rebuild which improved knocks and bangs of worn out bearings etc.I have now decided to rebuild my second d7engine which I have every thing for it except the main part the crankshaft I do have the one that came out that engine but a previous owner tried to remove the rotor without the correct tool which resulted in bending the timing side shaft so I need a replacement.

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