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ET: Engine (Twin) Fuel and Carb Settings

Bill Thomas

Well Known and Active Website User
VOC Member
Just a thought, We built an old Bike with standard Carb's a few years ago, And the Slides were very slack in the body, Gave us a bit of trouble at tickover, The air was going round the slide ??.
It was fine when riding, But at tickover kept going on to one cylinder.
 

peter holmes

Well Known and Active Website User
VOC Member
Also when the slides are that slack you can normally hear them chattering back and forth, I think the bulk of the wear can be attributed to running without decent air filters, they may not enhance the look of the bike, but I would not run without them, think what it could do your bores.
 

Glenliman

Well Known and Active Website User
VOC Member
Since it fouled a set of plugs running around the shop, I'm hesitant to richen the pilot settings, but I believe it ran a bit smoother with the air levers pulled on a small amount.
If this is an Amal setup and the air levers are just "pulled" a small amount, the chokes will be just lifted that amount from the full choke position. Pulled all the way back is choke off.
Pushed all the way forward is full choke. Pulled up just a little will still choke it some when riding.
Could it be that you are running with the chokes on and this is fouling the plugs?

Glen
 
Last edited:

Bobv07662

Active Website User
VOC Member
No Glen, it fouled the plugs after a week of tinkering in the shop getting past, spigot air leaks, high float levels weak ATD springs and no road time to clear things out. Air levers fwd are on and down, levers back are off and up.
Thanks to the suggestion from Robert Watson, I applied non-hardening Permatex to the spigots and that has helped tremendously. The idle can now be lowered to a proper level, the pilot screws are much more responsive and the banging in the exhaust has been virtually eliminated.
Not claiming victory yet but I think I'm on the right path with all the help and suggestions I get from the VOC!
 

davidd

Well Known and Active Website User
VOC Member
VP Fuels C9 is 94 octane and C10 is 100. Premium is somewhere around 92, but will usually work on a 10:1 piston with a Mk2 cam.

David
 

Bill Thomas

Well Known and Active Website User
VOC Member
I am paying £1 .34p a litre, Instead of £1.06, Don't have a clue what it is, But can just hope,
The Bikes seem to run OK, They are 9 to 1s and Mk2 cams, Biggish carb's, Armours S/S straight though silencers.
 

Bobv07662

Active Website User
VOC Member
Was able to take the beast on it's first ride in New Jersey this AM...What a blast! Torque down low is very impressive, 3rd gear seems all you ever need.
Seriously, thanks to you all for all the help getting the bike sorted.
Now that I have a potato, potato, potato idle and no more vacuum leaks at the spigots a small issue has come up with the slide in the rear carb. Occasionally after using engine braking when coming to a stop it hangs up a tiny amount and the idle speed bumps up a bit. (100 rpm max bump) I can avoid the hanging up by coasting up to the stop or clicking the throttle closed a couple of times while slowing down. It appears the higher vacuum is pulling the slide a bit more than it is happy with. I can also tap the slide with my finger and it instantly returns to the correct lower idle speed.
Before I send for a pair of new carbs, has any one seen this before or know of any certain place to inspect the slide or carb body to look for the offending interference?
 

Comet Rider

Well Known and Active Website User
VOC Member
Hi Bob,
Be careful if you do decide to go for new carbs.
I know Greg Brullis has commented on new bodies being out of round.
You can get new slides which may overcome you problems without having to change the carb completely

Best of luck
 

Robert Watson

Well Known and Active Website User
VOC Member
Try lubing all the cables as if they have been sitting for a while they can get sticky as can the splitter box. Also if they are older cable there were some around that had lovely nylon liners. Trouble is nylon is hygroscopic and swells up with water making them stiff to pull. Also check to see if there are any small catchy edges on the slide and jet block. Taking carbs apart is fun!
 

Bill Thomas

Well Known and Active Website User
VOC Member
Just take the spring out and stretch it a bit.
Also see if there is a groove where the slide touches the stop screw, Maybe just file it flat there ?.
 
Last edited:

Bobv07662

Active Website User
VOC Member
Reporting in on the spring stretching...idle was better but still slightly hanging up but no where near as much as before. Just the rear carb. I have ordered a replacement AMAL cable return spring and will report back.
Bike is running quite well and continues to impress me. Hard to believe it's 70 years old!
Thanks again for all the support.
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Your persistence has paid off, sometimes it is the small things that make the difference.
If you haven't already done so check that the carburettors are balanced, i.e. starting to lift at the same time from tick over and the same amount with the throttles open. It can make a difference in starting and smoothness. I find using vacuum gauges to check is easiest and more accurate, pulling the same vacuum on the throttle stops and equal value with the throttles open a little. You can also do it manually without the engine running using maybe two drills the same size trapped under the slides and see that they are released together when you ease the throttle open.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Morning Bob, You are using the standard two into one small round box on the throttle cable ?.
Some people use two cables, Which I don't think is a good idea, You are forever readjusting those,
Just my thoughts.
The other thing is the run of the cables, Make the bends as smooth as possible, Could be your trouble ?,
They both have a tight turn, where the go into the carb's,
Some people make brass or something bends close to the carb's,
Good idea but I have never bothered.

I know what you mean about 70 year old, I sometimes expect TOO much :) .
 

Bobv07662

Active Website User
VOC Member
Ed, I've synced the carbs using both methods, manually with the drill rods and then while it is running with a Uni-Syn flow gauge. The balance is spot on and the bike does run quite well.

Bill, the bike does have the standard 2 into 1 splitter on the throttle cable. The cable routing is as smooth as I can make it. I purchased some snap-on plastic guides for the cables where they enter the top of the carbs but those seemed to require excessive force to get them to click on, so I did not install them.
As far as expecting too much, the way the bike runs now I'm happy with it and even rode it on the highway up to 70MPH this morning. It has lots of power, pulls smoothly and rides great. The brakes are much better than some of the other antiques I have. Happy days!
Next project will be to see if i can get a little more modulation into the clutch application but that's will be the subject for another day and another thread. Edit three.jpg
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Ed, I've synced the carbs using both methods, manually with the drill rods and then while it is running with a Uni-Syn flow gauge. The balance is spot on and the bike does run quite well.

Bill, the bike does have the standard 2 into 1 splitter on the throttle cable. The cable routing is as smooth as I can make it. I purchased some snap-on plastic guides for the cables where they enter the top of the carbs but those seemed to require excessive force to get them to click on, so I did not install them.
As far as expecting too much, the way the bike runs now I'm happy with it and even rode it on the highway up to 70MPH this morning. It has lots of power, pulls smoothly and rides great. The brakes are much better than some of the other antiques I have. Happy days!
Next project will be to see if i can get a little more modulation into the clutch application but that's will be the subject for another day and another thread. View attachment 36118
Looks good and goes good too. Nice bike.
 

Bill Thomas

Well Known and Active Website User
VOC Member
There is LOTS more left Bob, But if you want it to last, Don't go there :D .
I once did 124 mph in third on an airfield, Timed !!, On my tuned road Bike !.
6000 rev's is 110 mph in third !.

Super looking Bike Bob, Your mudguards fit better than I have ever been able to fit, Top Job.
 

macvette

Well Known and Active Website User
VOC Member
Morning Bob, You are using the standard two into one small round box on the throttle cable ?.
Some people use two cables, Which I don't think is a good idea, You are forever readjusting those,
Just my thoughts.
The other thing is the run of the cables, Make the bends as smooth as possible, Could be your trouble ?,
They both have a tight turn, where the go into the carb's,
Some people make brass or something bends close to the carb's,
Good idea but I have never bothered.

I know what you mean about 70 year old, I sometimes expect TOO much :) .
I use these ones my D twin only on the throttles. I have the standard cable splitter
Get them from Venhill, afew quid each code FB9
With a little fettling the tag is fixed by the scew for top of the20200726_074118.jpg20200726_074118.jpg slide
 

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