- Joined
- Jul 20, 2017
- Messages
- 387
SteveBorland said:
I wish there were a 'Like' button for things like this, thanks for sharing!
Issue 850 MKII with motor cut-off after 3 km driving
- Thread starter Lorenz
- Start date
- Status
I wish there were a 'Like' button for things like this, thanks for sharing!
robs ss
VIP MEMBER
- Joined
- Aug 16, 2016
- Messages
- 3,495
Although not directly related to this original post I thought I might add this...
On my Norton 500 single 11.3:1 CR ( originally model 50 but now with BMW R80 barrel & piston...)
It used to kill plugs frequently (every month) for some reason (NGK B8SE) to the point I always kept a spare with me - they looked good but wouldn't spark.
I contacted NGK and sent them a "failed" plug but never heard from them again.
I changed to NGK Iridium B8EIS and have not had a failure since (4 years) - go figure!
Cheers
Rob
On my Norton 500 single 11.3:1 CR ( originally model 50 but now with BMW R80 barrel & piston...)
It used to kill plugs frequently (every month) for some reason (NGK B8SE) to the point I always kept a spare with me - they looked good but wouldn't spark.
I contacted NGK and sent them a "failed" plug but never heard from them again.
I changed to NGK Iridium B8EIS and have not had a failure since (4 years) - go figure!
Cheers
Rob
I think you may have two things happening or may be not. First off I think it's smart to do just one thing at a time. Open the fuel tap(s) and wait a bit. Take the bowl plug out. The bowl will drain quickly and then slow down but the flow should not diminish to just a trickle or drips. If it does this would tell you the flow is restricted either by an inline filter or the fuel tap screen (I am not sure if a Mikuni has it's own screen as an Amal does). This would mean you are simply running the engine out of gas. The time it takes to coast to the side and re-start allows some fuel back in and the choke (enrichener) picks it up from the bottom of the bowl so the engine starts and runs for a short while again. Repeating this a number of times means the engine is spending a lot of time "on the choke" and this could be the sole cause of the dark plugs. I would not go into the carburetor in an attempt to get the plugs looking "right" until the engine can be dependably run. Think about this: If richness and plug fouling was the cause of the engine quitting, it would not re-start with more choke.
It sounds to me as though the fuel tank is not venting quickly enough and the resulting low pressure in the tank is impeding the flow of the gas to the carburator. I think the vent is part of the filler cap. I remember having a similar issue with my old BSA A7.
- Joined
- Nov 30, 2012
- Messages
- 245
Fully agreing with Biscuit in saying that you should first check that fuel is correctly flowing from tank to carbs.
If not :
- No air entering the tank (reason why some of us advise you to do a test with your fuel tap open), creating a sort of air lock.
- Obstruction of the flow between tank and carbs: check (and clean if needed) every component (including the filter at the bottom of the carbs, and the jets).
or a combination of those both reasons.
The reason why your sparkplugs look too rich may come from that you have to use and re-use the enricher.
L.
If not :
- No air entering the tank (reason why some of us advise you to do a test with your fuel tap open), creating a sort of air lock.
- Obstruction of the flow between tank and carbs: check (and clean if needed) every component (including the filter at the bottom of the carbs, and the jets).
or a combination of those both reasons.
The reason why your sparkplugs look too rich may come from that you have to use and re-use the enricher.
L.
- Joined
- Nov 30, 2012
- Messages
- 245
I meant "a test with your TANK CAP open".
Sorry for my mistake.
L.
Sorry for my mistake.
L.
- Joined
- Aug 14, 2017
- Messages
- 105
Yes very sorry. Was a mistake. I measured the carb. It is 34 mmtriumph2 said:
Yesterday I check every needle and jet by a watchmaker glass:
35 pilot
6DH3 Needle
P5 Needle Jet
3 Slide
2 Air Jet
290 MAIN
Could be the size 2 air jet and Main 290 reason for the soot at the spark? :?
Ah by the way: What influence have the clip at the needle :?:
It was at position 3 from top.
And also I checked yesterday the aeration / vent hole of fuel cap .
Roughly 1 mm max 1.5mm.
I will drill a bigger vent hole into the fuel cap, something like 2 mm
Today I will reassemble everything. Weather in Germany is a disaster and it's dark outside when I'm ready with work.
So hopefully on weekend I can check.
- Joined
- Jul 20, 2017
- Messages
- 387
Oh how I know that feeling! It's not been great here in the UK either, you have my sympathy ...Lorenz said:
Lorenz said:
I can't answer those questions, especially as I am not familiar with Mikuni carbs.
But I will say this: always keep in mind that an engine NEVER requires a rich mixture in the combustion chamber, no matter how cold it is.
The choke/enrichener is used to compensate for condensational losses in the manifold and port when the engine is cold, so that the mixture is correct by the time it reaches the chamber.
By using the enrichener to re-start your engine when hot, you will be ensuring that the spark plugs will be sooty.
- Joined
- Aug 14, 2017
- Messages
- 105
Hi All.
First off all thank you for the input I got from you.
On Saturday I have done several tests.
Outcome
The gas flow out of the tank had an issue.
If I come under 5 liters gas in my tank the gas flow is not ok.
Over 5 Liter good flow.
I checked this by run out the gas and chewing if there is an issue by depression
Guess have to check the gas cock.
By reassemble the carb I set the needle leaner by moving the clip
Plugs are black still.
I ordered now some jets to make a new setup
By the way
I’m really happy with my tri-spark. No kick back, no fear!
Starts very good, cold even hot.
First off all thank you for the input I got from you.
On Saturday I have done several tests.
Outcome
The gas flow out of the tank had an issue.
If I come under 5 liters gas in my tank the gas flow is not ok.
Over 5 Liter good flow.
I checked this by run out the gas and chewing if there is an issue by depression
Guess have to check the gas cock.
By reassemble the carb I set the needle leaner by moving the clip
Plugs are black still.
I ordered now some jets to make a new setup
By the way
I’m really happy with my tri-spark. No kick back, no fear!
Starts very good, cold even hot.
- Joined
- Aug 14, 2017
- Messages
- 105
Hi there.
After a long and hard winter and a lot of thinks to do I fired up my Norton Commando this spring. The cutt-off after a while hits me again. So it was time tor investigate again th issue after I renewed the gasoline cocks and make changes at the carb. And what was the outcome: At the turn signal switch I had a short-circuit. What happend was that ground gets in contact with the frame (positive earth) and this brings miss fire abnd cutt-off by the ignition! Now the machine runs without cutt-off, but I have still issues with the set up of Mikuni carb. But for this I have to open a new thread.
After a long and hard winter and a lot of thinks to do I fired up my Norton Commando this spring. The cutt-off after a while hits me again. So it was time tor investigate again th issue after I renewed the gasoline cocks and make changes at the carb. And what was the outcome: At the turn signal switch I had a short-circuit. What happend was that ground gets in contact with the frame (positive earth) and this brings miss fire abnd cutt-off by the ignition! Now the machine runs without cutt-off, but I have still issues with the set up of Mikuni carb. But for this I have to open a new thread.
- Joined
- Jan 1, 2005
- Messages
- 195
Good job Lorenz! Never give up on your Norton. This group can help you fix anything(on a Norton).
Wrench On/Ride On
Dave
(by the way your English is way better than my German)
- Status
Similar threads
