• Welcome to the website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Hon. Editor and Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this website.

    If you have previously registered to use this forum, you should log in now. CLICK HERE.

    If you have never registered to use this website before, please CLICK HERE.

ET: Engine (Twin) Inconsistent starting

Peter Salter

New Website User
VOC Member
My Series C Rapide has developed very inconsistent starting. I purchased the machine in 2009. It had only 20090 miles registered on the speedometer but it had been sitting since 1972 so was given a complete restoration by an expert in British motorcycle restorations. Since the restoration I have put 9500 miles on it and until recently it started easily and ran well. A couple of years ago, however, it became very difficult to start, a problem that was attributed to the magneto. Last year the magneto was completely rebuilt by a specialist and gives a good spark, but the inconsistent starting remains a problem. On some occasions, it will start first or second kick, sometimes without even priming the carbs. Other times I can kick it until I'm exhausted (I turned 80 a couple of months ago) with fuel dripping from the carbs after repeated priming. If left for a few hours, it will then often start on the first or second kick. The carbs are, as far as I know, the original Amal 276s and have been completely dismantled and cleaned. The fuel is ethanol free 91 octane and spark plugs are NGK B7ES. Once it does start, it very quickly settles into a nice even tickover with no spitting or popping. The pilot jets are open one and a half turns and the main jet and needle jet are 106 and 180. I always fully close the air slides when attempting to start the machine when it is cold.
Any suggestions for improving starting, short of installing an electric starter, would be greatly appreciated.
Peter Salter

Bill Thomas

Well Known and Active Website User
VOC Member
If you must use NGK I would use 6 not 7, I prefer Champion N5 or N9y, Only about 20 thou gap.
I have never got on with old type chokes, Although Brother Ron's Comet likes it.
I would not use chokes just flood it and try ?.
Good Luck, Bill.


Well Known and Active Website User
VOC Member
Peter, I have the chokes for my 276’s somewhere in a box. When cold I give the carbs a slight tickle, when hot I give the rear cylinder only a slight tickle.

Kevin Emery

Active Website User
VOC Member
Hello Peter

I have been chasing a similar problem for two years. I believe we have finally got to the cause of the problem. I was helped and guided by Andy Edwards, our section engineer. He is a very good engineer.
You may be interested in the story.
My bike was a pig to start but once started it ran well with a strong, slow, tick over.
I removed the carbs, ultrasonically cleaned them and checked the jets. No problems found and didn't fix the problem.
I had a problem with my magneto, the engine wouldn't start when hot. I believe this was a known problem with the original magneto. I also thought it could cause the starting problem. I replaced the magneto it fixed the hot start problem but not starting when cold.
It was taking so long to kick start the bike that I damaged my ankle and spent a month on crutches. Time to go to an electric start. I purchased an electric start kit and with the valiant guidance of Andy we fitted it. I thought that would do it. But even with a new electric starter it was still a pig to start when cold. Strangely it was easier to start it on the kick start that it was on the electric start. Dead end.
There were threads on the forum about the Magneto cutout cable causing starting problems if routed by the high tension cables. That was pursued and found to be another dead end.
Andy would not give up. He had an idea. If the engine wasn't starting it wasn't getting the initial extra petrol via the pilot jets. I contacted Burlen and they said no. If there was a problem with fuel flow rates it would also affect tickover. Mine was fine and strong. But we pursued Andy's idea and thought that the way to test this was to add some additional petrol at startup. We did this with a syringe of petrol squeezed directly into the carb. It worked. Squirt petrol in and the engine started first time every time.
The problem had to be the carbs.
Andy had two old worn carbs which we used to diagnose the problem. We replaced the rear carb and it made no difference to the starting. We replaced the front carb and it started straight away. Over the next week I started the bike at least five times a day and it starts first time every time.
I replaced the original rear carb and it still starts every time. The problem was the front carb. We inspected the carb and suspect there is a tiny amount of swarf crushed at the end of where the pilot jet adjuster screw is screwed into the carb body. But it is difficult to be sure and we have no way of removing it.
I have ordered another carb from Burlen. There is a 6-7 week wait on orders so I still do not have a replacement yet. When I get the new carb I will let you know how I get on.
In the meantime I am running on one nearly new carb and one very old and worn carb and the bike is running like a dog. But it starts first time every time. I am sure the running problem will be addressed when my new carb is fitted.

Keep going, don't give up and I hope you get your bike starting properly.


brian gains

Well Known and Active Website User
VOC Member
most frustrating fault is an inconsistent one.
regarding pilot jet; i was told and now adhere to cleaning the jet using purpose made 'cleaning' wire or fuse wire, it is not good enough just squirting carb' cleaner through and observing it at opposite end.


Well Known and Active Website User
VOC Member
Last year the magneto was completely rebuilt by a specialist and gives a good spark, but the inconsistent starting remains a problem.
A change from the B7ES to B6ES plugs seems to have done the trick.
There's no way the heat range of the plugs was responsible for the problem. However, my speculation is that when the magneto was rebuilt it was not remagnetized. That would mean the bike has to be kicked over faster to generate a spark than would be needed with one that was properly magnetized. Hmm, unless the new plugs happened to have a smaller gap than the old ones, which would allow them to spark at a lower voltage, i.e. lower kickover speed, than your old plugs.

There's never enough information given in questions like this to be sure about a diagnosis. But, everything you wrote is consistent with a magneto that wasn't magnetized after rebuilding. An easy piece of additional data you could add to your thread would be the gaps of both of your present plugs. Also, of your old plugs, if you kept them.

greg brillus

Well Known and Active Website User
VOC Member
The colder the plug the harder it is to clear itself of deposits........ These engines tend to run and should be run on the rich side, so they do tend to foul plugs. Even the Champions will foul up if the mixture is too rich........Once a plug fouls up, it can fail altogether, even if removed and thoroughly cleaned. Best to simply replace them and start over. It is very easy to flood these engines on start up.........ideally you should use the tickler or the choke but not both.........Engines with big cams can be hard to start due to the excess overlap........this is the case with my bike.......once running it performs better than most other Vincent's on the road, so I have to live with the starting issue.......It was difficult to start until I realized I was flooding it too much. I run Champion N5C in all these bikes now.
Last edited by a moderator:


Well Known and Active Website User
VOC Member
Inconsistant, tells me carbs. If the idle air screw is not effective it is an indicator the slides may be worn or...
I recently tried fixing a problem that did not need fixing. On advise from "Classic Motorcycles Elect. Man." I switched to NGK B8EGV plugs. This caused all sorts of problems, mimicking a bad magneto. Failing when hot. I swapped back to NGK B7ES and the bike starts up first kick, hot or cold.

Latest Forum Threads

Can't Find What You Need?

Buyer Beware: Fake or Real?

The Mighty Garage Videos

List of Forum Categories