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
D7 175cc misfiring/choking under acceleration
Avatar
BravoEchoNovember
First Gear User
Site Member
Forum Posts: 3
Member Since:
August 1, 2021
sp_UserOfflineSmall Offline
1
September 20, 2021 - 10:31 am
sp_Permalink sp_Print

Good Morning, 

The other week I bought the Amal gasket set and replaced all of the gaskets/seals and resurfaced all the warped faces on my surface plate , great news is that I repaired the leaking carb, bad news is that now under acceleration the bike chokes/misfires and looses power until the revs drop. I assume that maybe I put the needle in the throttle on the wrong groove, however after trying groove it's still the same. So I'm left assuming it's a timing issue, Note in the attached image that the spark lead is exactly 'attached' , however, I have zero knowledge on how to set the timing.

I'm based in Wantage, and ideally would like to have the engine completely overhauled, rid all of the leaks, and tune it properly. 

2 part question, would you agree my assuming of timing is correct and is there anyone, or company recommended that can help my fix my issue?

many thanks,

Ben

Avatar
stubaker58
Sunny Felixstowe
Area Rep
Club Member
Forum Posts: 756
Member Since:
June 13, 2015
sp_UserOfflineSmall Offline
2
September 20, 2021 - 11:04 am
sp_Permalink sp_Print

Hi Ben,

Firstly no picture! They must be below 1meg or they don’t load.(it’s there now, well done!)

Those symptoms are annoying, I’m currently working through a similar problem.  You don’t say how familiar you are with Bantams so apologies if it’s teaching grandma etc but what choke/air filter arrangements do you have on the D7? And are you on standard jetting? I had an after market screw on filter which was restricting flow so much that the bike was transformed when I removed it. I also went back to standard jetting on both the main and pilot jet (remember the main only really comes into play over about half throttle).

The ‘timing’ is pretty basic and could be the issue, as could whip on the end of the timing side crankshaft caused by a worn centre bush in the stator plate (a pretty easy fix). There’s stuff on here about how to set it (search using Google).

My last breakdown was caused by the cam coming loose on the crankshaft, it still ran until finally it was so loose that the tiny woodruff key fell out allowing the cam to rotate on the shaft.  Amazingly the key was there when I took off the timing cover and a few minutes fiddling got it going again.  

There’ll be someone nearer to you who will be able to advise.

Hope you get it sorted soon.

“There’s nothing new under the sun”.

Avatar
Number6
Lincolnshire
Top Gear User
Club Member
Forum Posts: 575
Member Since:
January 18, 2020
sp_UserOfflineSmall Offline
3
September 20, 2021 - 6:23 pm
sp_Permalink sp_Print

Did you mess with the ignition when doing the other jobs? If not, can't see why it should be playing up now. I'm assuming of course that it worked OK before. Although things can fail, e.g. could be a bad condenser.

According to the service sheet, Wipac/BSA designed it so that correct timing should be achieved simply by setting the CB gap to 0.015" (15 thou, as embossed on the casting nearby) and the 3 screws that lock the unit into the cover being in the middle of their slots. The slots do allow for some adjustment, but shouldn't be necessary, according to the service sheet.

So I am also thinking it's affected by the last thing you changed, e.g. carburettor.

I also notice in your photo how the heel of the CB, the part that bears on the cam, is looking quite worn. My D1's exisitng also looks like that and so will be replaced with a new one. Also the spring is very 'tired' (has quite a permanent bend).

Also your felt pad is missing, for oiling the cam, a bit of oil is added to it at periodic intervals.

laugh

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
Ringting
Newport Pagnell
Top Gear User
Club Member
Forum Posts: 93
Member Since:
January 1, 2019
sp_UserOfflineSmall Offline
4
September 20, 2021 - 11:44 pm
sp_Permalink sp_Print

Hi Ben. I'd put a Very thin smear of high melting point grease on that cam. As said check the gap but if this has only started since you worked on the carb (and that's all you've done) then that's most likely where the problem lies. I remember something about a washer on the needle valve that some monoblocks have and some don't. Fitting one if there shouldn't be or not fitting one where there should mucks up the float level so could give the symptoms you are experiencing.

Also I think the ht connection onto the coil should be soldered though I don't think that if causing your current issue. 

Do one thing at a time and if it works you've done it right. If it doesn't then something you've done has upset it.

Please do get back to us for further ideas or to let us know how you fixed it. Thanks,

Alan.

D1, D14/4, Guzzi LeMans, Guzzi V35, Triumph Trident 900, Maserati 160 t4. Mk1 Mini Traveller, Berkeley T60.

Avatar
GlenAnderson
Dover
Top Gear User
Club Member
Forum Posts: 471
Member Since:
August 27, 2013
sp_UserOfflineSmall Offline
5
September 21, 2021 - 1:02 am
sp_Permalink sp_Print

The HT lead most definitely does not need soldering. 

Soldering that joint will lead to a swift failure of the coil, as the tag will simply break off from the vibration. 

Avatar
cocorico
Central France
Top Gear User
Site Member
Forum Posts: 3559
Member Since:
June 23, 2013
sp_UserOnlineSmall Online
6
September 21, 2021 - 8:23 am
sp_Permalink sp_Print

Agree with Glen - don't solder, you are more likely to destroy the internal joint. The coil looks to be original, so possibly just an unfortunate coincidence of age related failure. You would need to use a DMM to check for a few kohms between the output tag and earth. I tend to carefully open up the hole on the tag to take a tiny screw, then attach the HT cable to it using a small crimp connector. Or  poke the bare copper wire through and carefully twist it enough to hold firm. The original models had a wiper contact arrangement for the Ht output, so you don't have to overdo it.

Carb problems have been discussed many, many times before if you search the forum, as has the missing felt lubricator.

Avatar
sunny
Norfolk
Top Gear User
Club Member
Forum Posts: 1929
Member Since:
January 9, 2013
sp_UserOnlineSmall Online
7
September 21, 2021 - 8:45 am
sp_Permalink sp_Print

hi  Ben  it  DOSNOT    sound  like   timeing   to me   did  you  clean  the  BYPASS  holes  in  each  of  the  2 parts  of the   carbs   body  ,

but  the photo  tells  me   the   c/shaft   oilite  bush   needs   atention  a  felt   pad  with  oil ect       the  needle  gos  on  the  4th  from  the top   monoblock  carbs   are  hard  to  set  up  being  a  4 stroke  carb     &      you  need  moor   homework

Avatar
BravoEchoNovember
First Gear User
Site Member
Forum Posts: 3
Member Since:
August 1, 2021
sp_UserOfflineSmall Offline
8
September 21, 2021 - 9:19 pm
sp_Permalink sp_Print

Hi all, 

Thanks for the advise, please forgive my lack of knowledge this is my first motorcycle, I'll have the felt ordered. 

I think I've solved the issue while discovering more, timing seems fine, so to does the carb settings. However I've discovered the fuel tap doesn't shut off fully, combined with what seemed a dodgy float pin, I found the crankcase had 300ml of fuel/oil. I drained out the case, had the carb cleaned once more, and it's fine, a little rough under speed but starts first kick and seems to have its full power.

Lesson learnt, check the case for fuel more often, on to the next problem rusty piston!

242446422_391279159177540_1708029624731940034_n.jpg242438087_222563576597813_4113254416931279269_n.jpg

Many thanks,

Ben

Avatar
Ringting
Newport Pagnell
Top Gear User
Club Member
Forum Posts: 93
Member Since:
January 1, 2019
sp_UserOfflineSmall Offline
9
September 21, 2021 - 9:59 pm
sp_Permalink sp_Print

Thanks for the feedback Ben and glad it's going okay now. It's not a difficult job to remove the head and barrel to give it a check and clean up. I found slipping a bit of thick card in between the cylinder fins supported the barrel on the studs and allowed me to carefully feed the piston and rings back into the barrel.

Maybe if you've done very few miles it's got damp in there and caused some rust. It has been said on here that mineral or semi synthetic oil stays on the surfaces while full synthetic doesn't so can allow corrosion. I use semi at 33:1 in the D14. (Oh no, I think I mentioned oil!!)

Alan.

D1, D14/4, Guzzi LeMans, Guzzi V35, Triumph Trident 900, Maserati 160 t4. Mk1 Mini Traveller, Berkeley T60.

Forum Timezone: Europe/London

Most Users Ever Online: 223

Currently Online: sunny, cocorico, El_presidente, Nick_S
13 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