Bike engine refuses to run!

[Pompey]

Hello All,

I am currently scratching my head why my bike will not run!

It is a 1960 G80TCS which I completely restored a few years ago and has been running fine until last year. When I went out to start it and other than a single bang would not run. It had been running the previous day when I had parked it in the garage. Since then I:-
1. Completely cleaned the carb.
2. Mag has been rebuilt and tested.
3. HT lead, cap and plugs changed.
4. Head off to check for any air leaks (inlet guide).
5. Checked piston, reground valves and has very good compression.
6. Carb face and heat spacer all flattened and checked on a surface plate so no air leaks there.
7. Retimed.
It will now start but only briefly allowing for a couple of “engine revs” before it just cuts out and dies. I have tried using the choke and advance/retard in different positions but no luck.

I feel that the problem lies with its 1 3/16” 389 Monoblock Carb which was purchased brand new from Burlen Fuel Systems about 7K miles ago. I can see no signs of damage or wear. It has been ultrasonically cleaned, all orifices have been blown and poked with fine fuse wire. The float level has also been checked and is OK.

So I have now run out of ideas and wonder if anyone can think of a reason why it will not run?

In anticipation,
Nick

[dave16mct]

I know you've cleaned the carb but it sounds like a blocked pilot jet. Is your tank clean inside? Any fine residue will block the pilot jet again very quickly.
Dave.

[ajscomboman]

I agree with Dave it's likely to be fuel related or a dodgy plug.

[Pompey]

Many thanks for the replies.

I can confirm that the petrol tank is clean with fairly new fuel. Also when I view the petrol in the carb below the main jet there is no sign of any muck.

I can rev the engine so it is passing out of the pilot jet area and into the needle jet zone.

Have tried several spark plugs being NGK, Champion and Brisk (that was recommended to me) with all exactly the same result.

Please do keep thinking of things.

Nick

[g80csp11]

Nick ,
could the valve lifter be set too close and once running valve grows slightly and you loose compression
Just a thought

[SPRIDDLER]

It sounds as though it could just be running on a carbfull (or a tickle's worth) of petrol. As said previously this usually indicates a blocked Pilot jet or drillings.
It could be that fuel isn't being replenished quickly enough in the carb. A simple check in case there's a partial blockage in the fuel line between tank and carb is to disconnect the fuel line at the carb inlet banjo and turn on the tap when fuel should run out freely. An even simpler check for an obstruction is to open both tank taps and see if the engine will run for longer - or forever.

[g80csp11]

if you want Nick , you can try my g80cs carburetor , i know yours is 600cc but it should at least prove its the carburetor

[OEW591]

Nick, Is the air-hole in the tank cap clear? I recently had a new cap on my Indian Velo where the air hole had not been drilled. A small hole drilled in the cap had things running sweetly.

[g5wqian]

hi nick ;
sounds like pilot jet is the problem , probably blocked and it may even require 2 or 3 times of cleaning it and running engine and cleaning it again .
the carb will have some very tiny holes in its mouth area just in front of the slide if you look closely , check these holes are clear and also take out the pilot jet and clean it .
if it runs for a bit then conks out , clean pilot again and test as it may be you need to clean jet out more than once .

my model 30 ajs had a problem last week when it started coughing banging and wanted to stop running , i thought i was low on fuel and put it onto reserve but although it did start to run reasonable to get me home i found i had some debris in bottom of the fuel line right at the end of pipe where it meets the banjo pipe .
although the fuel pipe is 1/4" bore , the banjo pipe going into it is NOT and i had a bit of crap from the tank blocking the fuel from entering the banjo pipe right at the ebd if the fuel hose .
luckily i use clear fuel hose and can see when there is any debris inside it , so it was a fairly quick diagnosis .

sometimes the float , if its plastic , can swell up from issues with this modern fuel , and the float touches side of bowl stopping it from coming up , there is also a bush on the shaft the float sits on which needs to be on there or else float and valve will not operate properly .

if you have a cut out cap on end of magneto , check this also for shorts or intermittent contact , i know a fella locally who has built himself a JAP engined supercharged vintage sprinter and had no end of problems starting the engine that he stripped it and changed piston and all sorts of things, and then when he got to a recent race meeting he spotted the problem was with the magneto cap and cutout , took the cap off and removed the problem bits and it has never ran better "".

my ariel NH used to conk out after 7 miles , then would run after few minutes , doing same thing all time , until i spotted the tank cap didnt have a breather hole in it , 1.5mm drill and solved it .

also would hesitate on throttle from idle , i have now sorted that by putting smaller needle jet in .

hope you get it sorted easily .
ian

[jackstringer]

Check you don't have any wires that are not accidentally earthing, I had this with mine where the use of the rear brake worked like a kill switch.

It is also worth trying to start the bike in the dark, with the fuel tank and seat off, it is a convenient way to see if the Coil or anything else has packed up and is now shorting to somewhere.

Take a look at the points and check the condenser isn't dead.

Also worth finding a hill and giving it a good old bump start for a few hundred meters, I have had bikes before that once given a bit of encouragement started and then ran fine.

If you could tempt some of the local group over with tea and cakes (or Beer) I am sure one of them will remember that one thing that happened to them once and how they fixed it. It is amazing the number of things you do when starting a bike but doesn't even think to tell someone because it's second nature.