BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
The Bonneville Shop JRC Engineering dealers
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
MotorEddy
MotorEddy
Lancashire, UK
Posts: 45
Joined: August 2011
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
31 registered members (Al Eckstadt), 266 guests, and 443 spiders.
Key: Admin, Global Mod, Mod
Newest Members
itomtom, Wristpin, Mom1, flyntone, RNORTON
10448 Registered Users
Top Posters(30 Days)
NickL 68
Jeff K. 60
DavidP 58
Popular Topics(Views)
732,808 mail-order LSR
Forum Statistics
Forums34
Topics68,575
Posts667,882
Members10,448
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
69 T120 R High RPM miss #734531
05/08/18 8:40 pm
05/08/18 8:40 pm
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I'm almost complete with a restoration of a 1969 Bonneville and have two issues I'm struggling with. The first issue is the bike miss fires at around 4,000 to 4,200 RPM. I have installed new .20 over pistons and rings, valves are seated and set correctly, the carbs are whistle clean, the floats are holding, new Champion spark plugs, new points set at .015 and clean, new condensers, checked plug wires for continuity (good), original coils, white wire on # 1 coil terminal, points on # 15 terminal. Check timing with a strobe, idle is 11 degrees, 38 (I believe it was 38 degrees, but I set where the shop manual stated) degrees at full advance @ 2,000 rpm, clean fresh gas, no air cleaners (at this time), choke off. Attempted to set low speed air screw, but it's idling a little rough at 1,000 rpm. Seems to run OK from 1,000 to 4,0000, then seems to load up and or start missing not wanting to rev any further. Previous Owner let primary case run out of oil, I had to replace the chain and sprockets and the clutch bearings, but the stater looked a little cooked but OK. The amp gauge in the head light shows discharging and charging. The coils seem to get very hot when the ignition is on. A volt meter connected between the positive post of the battery and the ground shows a 3/4 of volt passing when connected.
I planned on chasing down the voltage loss from the battery later but mention it now as it might be related to the miss firing. Any help would be greatly appreciated as it's getting warm outside...
Thanks
Mark

Support Your #1 BritBike Forum!

Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #734533
05/08/18 8:48 pm
05/08/18 8:48 pm
Joined: Aug 2001
Posts: 1,733
Jordan, NY
Al Eckstadt Online content

BritBike Forum member
Al Eckstadt  Online Content

BritBike Forum member

Joined: Aug 2001
Posts: 1,733
Jordan, NY
Make sure all your connections are secure. I once had similar symptoms caused by nothing more than loose spade connectors on the coils. Tightened all the connections with pliers and it worked fine.


Al Eckstadt
Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #734543
05/08/18 9:45 pm
05/08/18 9:45 pm
Joined: Nov 2012
Posts: 712
Isle of Wight, UK
K
koan58 Offline
BritBike Forum member
koan58  Offline
BritBike Forum member
K

Joined: Nov 2012
Posts: 712
Isle of Wight, UK
There shouldn't be any voltage or resistance between battery positive and ground. Maybe an idea to clean up the terminals and check the rest of the red wire system.

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #734546
05/08/18 10:24 pm
05/08/18 10:24 pm
Joined: Jan 2014
Posts: 4,091
Aus
N
NickL Offline
BritBike Forum member
NickL  Offline
BritBike Forum member
N

Joined: Jan 2014
Posts: 4,091
Aus
Classic symptoms of high resistance joints, as you rev the bike the coils require more current ant the more the resistance takes effect.
Check/clean the ignition switch and all the connections/joints, it'll take a while but it will be worth it..


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: 69 T120 R High RPM miss [Re: Al Eckstadt] #734564
05/09/18 1:18 am
05/09/18 1:18 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I’ll pull a gas tank and check them although I’m pretty certain I wrote very tight
I’ll look forward any other suggestions as well as I’m not very optimistic that that’s the issue
Thanks Mark

Re: 69 T120 R High RPM miss [Re: koan58] #734565
05/09/18 1:20 am
05/09/18 1:20 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I’ll give that a try as well thanks for the thought

Mark

Re: 69 T120 R High RPM miss [Re: NickL] #734566
05/09/18 1:23 am
05/09/18 1:23 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I’ll go through all the wiring connections again
The wife thinks I should be mowing your grass instead of sitting on my stool staring at the Triupmh wondering why doesn’t work right
I’m certain success is just right around the corner I just not want know which corner it is
Thanks Mark

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #734577
05/09/18 4:52 am
05/09/18 4:52 am
Joined: Sep 2001
Posts: 639
Great Southern Land
tridentt150v Offline
BritBike Forum member
tridentt150v  Offline
BritBike Forum member

Joined: Sep 2001
Posts: 639
Great Southern Land
Star the bike at night in the dark and make sure that your coils aren't jumping spark to the frame...seen it before.

Re: 69 T120 R High RPM miss [Re: tridentt150v] #734891
05/11/18 2:18 pm
05/11/18 2:18 pm
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
This morning I pulled the wire off the center of the rectifier to run just off the battery, no change, still misses at 4,100 RPM
Then I put a donor coil on the LH cylinder and it still misses at 4,100 RPM
I will switch it to the RH cylinder the evening and see if that makes a difference.

I did notice the gas line from the reserve petcock on tank to the LH carb is bent somewhat sharply, and I'm not putting a low of gas in the tank as I'm removing it frequently to check the electrics. I'm going to put a longer gas line on (without the tight bend) and see if the bike has been starving for gas. If that's the case, this thing sure is thirsty....

Mark

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #734897
05/11/18 4:45 pm
05/11/18 4:45 pm
Joined: Oct 2003
Posts: 3,703
Emsworth, sunny south of Engla...
D
dave jones Offline
BritBike Forum member
dave jones  Offline
BritBike Forum member
D

Joined: Oct 2003
Posts: 3,703
Emsworth, sunny south of Engla...
My 650 runs better with both taps on. Not thirsty but maybe the gauzes in the taps are a bit blocked.

Definitely best to check electrics first.

Once you have been through the electrics check the tappets and then the carb. Does it miss at 4000 revs whatever the throttle opening? If so it is the electrics.

Dave

Re: 69 T120 R High RPM miss [Re: dave jones] #734937
05/12/18 12:01 am
05/12/18 12:01 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I came home from work today replaced the fuel line was a kink in it and move the donor coil from the left-hand side the right-hand side after road testing it with a new fuel line and road testing it was a new donor coil
You’ll rub up to the high fours and start missing and then after that it just starts missing at 4100 RPM and won’t clear out
I’ll take your suggestion and try it with different bottle opening shift at RPM see if it keeps missing
I’m starting to wonder if the PO had messed with the cam timing
When I first got the bike I cleaned up the gas tank with lacquer thinner God it was so clean clean the carbs low speed high-speed main pilot jet everything seems to be clean
I have noticed that there’s a brown or oily substance coming out of breather tube when I fired up in the garage and take it through its paces before I take it for a road test
I don’t think it has too much oil in it oil tanks about 2/3 full
May be an exorcism
Hey more help or suggestions will be appreciated thanks Mark

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #734938
05/12/18 12:15 am
05/12/18 12:15 am
Joined: Feb 2006
Posts: 711
Qld, Aust and Otago,NZ
G
Ginge Offline
BritBike Forum member
Ginge  Offline
BritBike Forum member
G

Joined: Feb 2006
Posts: 711
Qld, Aust and Otago,NZ
Ignition key contacts and key ring flapping around in the breeze?


Ginge
Re: 69 T120 R High RPM miss [Re: Ginge] #734940
05/12/18 12:44 am
05/12/18 12:44 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I do have a little tab on the keys it does flapper around but engine breaks down the first year or second year or third year so the wind speed variesWhat engine always breaks down around 4100 RPM

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #734973
05/12/18 11:11 am
05/12/18 11:11 am
Joined: Oct 2003
Posts: 3,703
Emsworth, sunny south of Engla...
D
dave jones Offline
BritBike Forum member
dave jones  Offline
BritBike Forum member
D

Joined: Oct 2003
Posts: 3,703
Emsworth, sunny south of Engla...
Vibration certainly changes at different rpms and your 4100 could be affecting something. The ignition key contacts as suggested by previous poster are indeed a prime candidate. I dismantled mine and cleaned them.

Dave

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #735034
05/12/18 6:52 pm
05/12/18 6:52 pm
Joined: Jan 2017
Posts: 537
Pleasant Hill, California USA
T
TR7RVMan Offline
BritBike Forum member
TR7RVMan  Offline
BritBike Forum member
T

Joined: Jan 2017
Posts: 537
Pleasant Hill, California USA
Hi Dirtbikerider, Sounds like you've covered your bases on tune up & electrical for the moment.

At this point I might suggest mark your grip so you know exactly the throttle opening when bike falters. Don't look at RPM for this test. Just throttle opening.

Print this tuning guide by John Healy & put in your pocket. Go for some road tests & study guide. This will help eliminate carb problems.

https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf

Maybe carbs are good. I've found the carbs can mimic electrical problems & vise versa.

The key is marking the grip so you accurately know the throttle opening. I find it impossible to guess opening as you ride. I must mark it.
Don



1973 Tiger 750
Re: 69 T120 R High RPM miss [Re: TR7RVMan] #735415
05/15/18 4:49 pm
05/15/18 4:49 pm
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I'm trying to check the static timing (11 degrees BTDC) and the full advance (38 Degrees BTDC). I created a degree whee for the stater, and lined it up with TDC mark and the pointer on the primary case. I put the TDC tool in the crankcase and confirms TDH alines with the pointer and the mark on the stater rotor. Then I plotted the 11 degree and 38 degree points on the rotor and put small center punch marks on the rotor for each. I pulled the plugs, rotated the engine to 11 degrees on compression and then put an ohm meter on the points to check when they began to open. When doing so, I got 0 ohms when the points were closed and some degree of ohms when they were open. This indicated to me the current can pass even when the points are open. is this normal?

Thanks
Mark

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #735429
05/15/18 6:46 pm
05/15/18 6:46 pm
Joined: Jun 2007
Posts: 6,091
Maui Hawaii
HawaiianTiger Offline
BritBike Forum member
HawaiianTiger  Offline
BritBike Forum member

Joined: Jun 2007
Posts: 6,091
Maui Hawaii
You might expect to go through a couple of sets of plugs while breaking in. There's a fair bit of oil getting into the combustion chamber. My personal experience with this leads me to suspect Champion plugs that seem to oil/gas foul and can't be brought back by cleaning. So, I like NGK plugs initially as these seem to hold up, but then a switch to Champions because I'm more familiar with them and how they react to different carb settings.

Sounds odd, I know, but I never took it further than that. Perhaps just one heat range hotter Champions for break-in would have been the answer.

I just had this problem on my old T-bird. I rode around here on Sunday to keep everything working right. I went to pass a slow truck and the engine just quit at a wide throttle opening. Ran fine under that. I got home slower, but OK and cleaned the plugs. Problem solved. However, I have "unknowns" in my bike which are Bosch Iridium plugs since my local NAPA doesn't have the Champions I normally use. I'll be looking for a set of Champions now...

My problem was throttle and load related, not RPM. But, the solution to either is usually in the ignition.

Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #735433
05/15/18 7:02 pm
05/15/18 7:02 pm
Joined: Dec 2013
Posts: 4,503
ohio, usa
kevin roberts Online content

DOPE
kevin roberts  Online Content

DOPE

Joined: Dec 2013
Posts: 4,503
ohio, usa
i havent used champions in anything in almost 40 years. found a fouled set of N3G plugs in my tankbag a while ago, like a bad dream from the past. champions would always foul in my old T120, and would never come back.

NGK B8ES plugs always worked fine in the same machine. but i'm curious, so maybe i'll try the champions again. could be that whatever fouled them so long ago is fixed.


"Are bikes so nice as all that?" asked the mole, shyly...

"Nice? They're the only thing," said the Water Rat Solemnly, as he leaned forward on the handlebars. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about with bikes."
Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #735445
05/15/18 8:44 pm
05/15/18 8:44 pm
Joined: Nov 2012
Posts: 712
Isle of Wight, UK
K
koan58 Offline
BritBike Forum member
koan58  Offline
BritBike Forum member
K

Joined: Nov 2012
Posts: 712
Isle of Wight, UK
When the set of points that the meter leads are across are closed, there is the direct, virtually zero resistance route through the points.

When the points open, there is still a route to ground, which is back to the open points' coil, through its primary windings, then through the common supply to the other coil, through its primary windings to the other set of points which are closed, so to ground.

The resistance of that route will be twice the coil primary resistance plus any wiring losses. At a rough guess, I'd expect to measure something like 10 ohms.

Take care using the resistance function for this task. If you accidentally turn the ignition on, it may damage the meter. So it could be a good idea to take the fuse out or disconnect a battery terminal.

A safer way is to use the volts function with ignition on, in which case you will see 0V points closed, and ~12V points open.

Also, this should be done with the AAU locked at full advance.

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #736139
05/22/18 12:33 am
05/22/18 12:33 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I took Tr7RVman suggestion And investigated a carburetor problem in Lou of a ignition problem and he was right. I checked the carburetor main jetand it had 190s and the book said it needed 260s. I called Baxters to order new main jet and they told me the 190s or correct and the book is wrong. They then asked how many miles on the motorcycle I told him 60,000 and they said the carburetors all wore out and I need a new carburetors. After some convincing from them I lay down my $400 and bought two new carburetors which made a huge difference. Now the motorcycle will idle and rev up but doesn’t seem to have the correct amount of power for A freshly rebuilt engine. i’ve been checking the plugs and they seem to be running lean, they have a very very light gray look. i’m wondering if the 190 jet size horse for emissions and engine really want something richer. Does anybody have a device for re-jetting a fresh engine?
Thanks Mark

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #736140
05/22/18 12:35 am
05/22/18 12:35 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I meant does anybody have advice for rejecting I eat what jet size should try next
Thanks Mark

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #736142
05/22/18 1:12 am
05/22/18 1:12 am
Joined: May 2018
Posts: 11
Frederick MD
D
Dirtbikerider Offline OP
BritBike Forum member
Dirtbikerider  Offline OP
BritBike Forum member
D

Joined: May 2018
Posts: 11
Frederick MD
I meant does anybody have advice for rejecting I eat what jet size should try next
Thanks Mark

Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #736143
05/22/18 1:28 am
05/22/18 1:28 am
Joined: Jan 2014
Posts: 4,091
Aus
N
NickL Offline
BritBike Forum member
NickL  Offline
BritBike Forum member
N

Joined: Jan 2014
Posts: 4,091
Aus
How old are the condensers/capacitors?


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #736198
05/22/18 3:31 pm
05/22/18 3:31 pm
Joined: Aug 2001
Posts: 4,190
argyll. scotland, uk
gavin eisler Offline
BritBike Forum member
gavin eisler  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 4,190
argyll. scotland, uk
How old are the condensers/capacitors?

He says they are new at the opening post.

Are you still running with no air filters,? if so up the main jet 2 sizes.


Its a fresh rebuild , right?During the first 1,000 miles it will free off a lot, and will continue to do so for a few more.

Typical signs of leanness , if at full throttle ( surely not yet on a fresh motor!) the motor picks up a little as the throttle is rolled off , thats lean.on the main jet. Buy two pairs, 200s and 210. Not too spendy

At half throttle ,if acceleration could be better, no 8 stroking, clean running but slow to pick up maybe spits back as the throttle is opened, thats lean at the needle jet or needle position, try lifting the needle one notch and see , this is free, and what I would try first.

Most important, to seat the rings , a couple of bursts to 5K or more pulling hard on a hill, just there and back, this forces the rings to bed in, do not sustain this "hard work" just a couple of times is enough in the first 50 or so miles, after that run in as per normal.
Leave messing with the main jet until fully run in, it only has real influence beyond 3/4 throttle.

Mark your throttle twistgrip somehow, small triangles of coloured insulting tape is easy and removable when satisfied, , mark at 1/4, 1/2 , 3/4 openings, you will be surprised how much time you spend in the 1/4 throttle range, at this point the main jet has almost zero effect, this is the domain of the pilot jet and the throttle slide cutaway, adjusting the pilot mix to give optimum running will pay dividends here, if your carbs and pipes are stock its unlikely that the throttle cutaway will be far off, if its to the book.



71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: 69 T120 R High RPM miss [Re: Dirtbikerider] #736251
05/22/18 10:36 pm
05/22/18 10:36 pm
Joined: Jan 2014
Posts: 4,091
Aus
N
NickL Offline
BritBike Forum member
NickL  Offline
BritBike Forum member
N

Joined: Jan 2014
Posts: 4,091
Aus
Oops!


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Page 1 of 2 1 2

Moderated by  John Healy 


Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.6.2