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
Help needed with D1 lack of power
Avatar
Martin Parry
Second Gear User
Site Member
Forum Posts: 18
Member Since:
April 19, 2019
sp_UserOfflineSmall Offline
21
October 22, 2021 - 4:02 pm
sp_Permalink sp_Print

Thanks to everyone who's posted - apologies for the lack of responses but I've been away with work for a week. 

Ibayyorkie - I get to around 25 in 2nd (when it won't go faster) and then shift up to 3rd, only for the speed to slowly fade away forcing me to shift back to 2nd.  It's not gearing, as I've tried smaller front sprockets.  Ref the fizz; I only mentioned it to demonstrate I was pretty handy with 2-strokes.

Number 6 - I'm definitely a pineapple!!

John - I only live a couple of miles from Bardney, so a bit frustrated I never saw the post - next time maybe??

Sponge - that's really nice of you to suggest meeting up; as mentioned above, I'll never make a meeting anywhere but will let you know when it's sorted. 

Stoo63 - thanks for the advice re electronic ignition.

Rusty - I'll see what taking the gasket out does first.

Avatar
GlenAnderson
Dover
Top Gear User
Club Member
Forum Posts: 471
Member Since:
August 27, 2013
sp_UserOfflineSmall Offline
22
October 22, 2021 - 10:22 pm
sp_Permalink sp_Print

You should see a bit north of 30 in second. Maybe 32-34, at which point, on the flat, the bike should happily pull top. With a following wind, or a downhill run, my D1 would easily top 50 even before I skimmed and reprofiled the head. 53-55 is quite possible and, once you’re over about 45 it will normally hold that on the flat. A headwind or an uphill gradient though will see the speed slowly ebb away. Once you’re below 40 then it bogs down and you’re back to screaming along in second at 32-ish. 

I would suggest that you check compression, timing and for general wear. Repeated stalling, or a seize at high revs, can make the mainshaft slip in the flywheel on the generator side, and put the timing way out. 

Avatar
Sponge
Lancashire (A chip shop somewhere near Preston)
Top Gear User
Club Member
Forum Posts: 754
Member Since:
November 6, 2016
sp_UserOfflineSmall Offline
23
October 23, 2021 - 12:03 am
sp_Permalink sp_Print

Martin, another thought about your D1. Check the carb.......GPO D1 bantams had restrictors to stop the telegram boys from ragging their bantams. I had an ex GPO bantam once and it too was gutless compared to my friend's fire breathing non-GPO  bantam. Comparing and swapping the carbs revealed the cause of the problem. 

Avatar
Number6
Lincolnshire
Top Gear User
Club Member
Forum Posts: 575
Member Since:
January 18, 2020
sp_UserOfflineSmall Offline
24
October 23, 2021 - 10:42 pm
sp_Permalink sp_Print

GPO D1 Bantam carburettor is 363/13, 0.475 inch venturi dia. Standard was 5/8" or 0.625 so yes a bit different.

Even with my old D3 you had to rev the snot out of it in 2nd before daring to try for third gear. Mind you it also had a 16 tooth sprocket to compound the difficulty.

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

Avatar
Martin Parry
Second Gear User
Site Member
Forum Posts: 18
Member Since:
April 19, 2019
sp_UserOfflineSmall Offline
25
October 31, 2021 - 12:49 pm
sp_Permalink sp_Print

Glen - I've checked the timing and all seems OK but thanks for the suggestion - I'll recheck before I try the next run.

Sponge / Number6 - I've swapped carbs with a working bike and that didn't cure it.

All - took the head off today to try without a gasket but didn't have any sealant to use; something I relied on in my youth!  Does anyone have a suggestion re applying sealant to the head before fitting - i used to use the red Hylomar compound.

Avatar
GlenAnderson
Dover
Top Gear User
Club Member
Forum Posts: 471
Member Since:
August 27, 2013
sp_UserOfflineSmall Offline
26
October 31, 2021 - 1:19 pm
sp_Permalink sp_Print

If the head and barrel mating faces are clean and unmarked, then you’ll not need any compound. I normally lap the head and barrel faces together with a little fine valve grinding compound before I fit them, but that’s obviously not possible with the barrel and studs fitted to the engine. 

very thin smear of silicone RTV instant gasket is normally enough if you get a leak without anything at all. 

Avatar
Martin Parry
Second Gear User
Site Member
Forum Posts: 18
Member Since:
April 19, 2019
sp_UserOfflineSmall Offline
27
October 31, 2021 - 1:52 pm
sp_Permalink sp_Print

Thanks Glen - I'll try first without but have a tube handy just in case.  Just need a day with dry roads now!!

Avatar
Sponge
Lancashire (A chip shop somewhere near Preston)
Top Gear User
Club Member
Forum Posts: 754
Member Since:
November 6, 2016
sp_UserOfflineSmall Offline
28
October 31, 2021 - 2:55 pm
sp_Permalink sp_Print

Hi Martin, glad that you swapped the carb and found no change...at least you know its not the carb. Suggest take a photograph of the top end whilst the head is off so that if removing the head gasket doesn't produce a result the next step could be a closer examination of the piston to check its provenance, porting, condition of rings/gaps/ bore etc

I just use a thin smear of High Melting Point grease on my head joint face.....so far no problems so long as the head face is flat to begin with. 

Avatar
Martin Parry
Second Gear User
Site Member
Forum Posts: 18
Member Since:
April 19, 2019
sp_UserOfflineSmall Offline
29
November 10, 2021 - 8:15 am
sp_Permalink sp_Print

Thanks Sponge.  Work commitments mean I'm away until mid December - I'll have a session on the bike during the Christmas break and let you all know the outcome.

Forum Timezone: Europe/London

Most Users Ever Online: 223

Currently Online: sunny
12 Guest(s)

Currently Browsing this Page:
1 Guest(s)

Top Posters:

cocorico: 3559

Cornish Rooster: 2917

Blue Heeler: 2434

bart: 2433

David Dale: 2144

Sprung Chicken: 2121

sunny: 1929

Piquet: 1846

Mags 1: 1753

mike p5xbx: 1688

Newest Members:

Cemoto

Forum Stats:

Groups: 9

Forums: 48

Topics: 10915

Posts: 96046

 

Member Stats:

Guest Posters: 1367

Members: 3506

Moderators: 0

Admins: 3

Administrators: Bantam-Super, JMD, Stoo63