tonytrev
Senior Member
Posts: 68
Registered: 7-11-2008
Location: Chorley Lancs UK
Member Is Offline
|
![[*]](./images/corporate/default_icon.gif) posted on 3-3-2010 at 03:17 AM |
|
|
Starting
Sorry folks but I am after the combined brains of the Cub fraternity again!
Engine rebuild gone well, engine in frame with good compression and spark, ign timing OK and when running it sounds fine, but starting it is a
problem. Symptoms are, does not want to fire but when it does after a couple of cycles it stops. The only remedy which sometimes works is to flood
the carb but it still does not want to run. However if I can get it running and the engine warms up then it settles down and idles and revs fine. It
seems that it has all the symptoms of a bad air leak or petrol starvation. I have tried the original Zenith 18 that came with the bike and another
almost unused one that I bought some time ago, either way the symptoms are the same! Since I am running out of options I am wondering if somehow I
have got the valve timing out by one tooth. The question I want to ask you gurus before I strip it down again is, would one tooth out on the camshaft
cause these symptoms? Any thoughts?
Tony |
|
|
birdman
Member
Posts: 45
Registered: 8-26-2009
Location: Jersey U K
Member Is Offline
|
| posted on 3-3-2010 at 01:40 PM |
|
|
Tony, what type of ignition system do you have, in the past i have experienced a similar problem and traced it to be a faulty condenser.
Ian |
|
|
connell1975
Posting Freak
Posts: 759
Registered: 1-18-2008
Location: winchburgh, scotland
Member Is Offline
Mood: always happy
|
| posted on 3-3-2010 at 02:36 PM |
|
|
Hi tony
Have you stripped and cleaned the carb seems like the pilot jet could be cloged up, or as ian say's try the condensor it may not be holding enough
power, But i would try your timing again I would advance the back plate a little and she should then start easier.
scott. |
|
|
T100
Posting Freak
Posts: 798
Registered: 3-3-2009
Location: Budleigh Salterton
Member Is Offline
Mood: A used Cub is a happy Cub
|
| posted on 3-3-2010 at 05:20 PM |
|
|
If it's doing the same on different carb settings then it can only point to ignition or valves - the only constant bits in the equation.
It'll be easier to fiddle with the ignition first and if not satisfactory then contemplate the valve timing.
Then again - could be the condensor!!
Martyn
It's no good being dead, RIGHT |
|
|
Chris Foster
Posting Freak
Posts: 365
Registered: 11-7-2003
Location: Garstang, Lancashire, UK
Member Is Offline
|
| posted on 3-4-2010 at 01:53 AM |
|
|
Hi Tony,
You say that when you have engine running it "sounds fine" ----- is response to throttle ok and free to any popping, banging or spit back? If so,
then I suspect it is not a valve timing issue.
Check that you have a good plug --- faulty ones are not unknown.
Have you set timing to fire at TDC or just a wee fraction before?
When I bought my T20 it had a fairly tired Zenith 18 which I replaced by a used Amal Type 32 as fitted by Triumph to later bikes. With both carbs, the
engine would only start from cold with full choke and if choke cancelled as soon as it fired engine died. If I remember correctly, the choke plunger
on Zenith has a mid position that you can use once it has fired to allow warm up. |
|
|
tonytrev
Senior Member
Posts: 68
Registered: 7-11-2008
Location: Chorley Lancs UK
Member Is Offline
|
| posted on 3-4-2010 at 03:14 AM |
|
|
Thanks folks, I shall try all the points raised before I delve into the valve timing. In answer to the question "what kind of ign do I have" It is
the original mushroom type as fettled by Chris Foster last year. I will keep you posted as an when things evolve!
Tony |
|
|
GBC
Posting Freak
Posts: 740
Registered: 2-25-2008
Location: NE Scotland
Member Is Offline
|
| posted on 3-4-2010 at 06:32 AM |
|
|
I thought popping and banging was only normal for a Cub......good luck Tony 
|
|
|
Chris Foster
Posting Freak
Posts: 365
Registered: 11-7-2003
Location: Garstang, Lancashire, UK
Member Is Offline
|
| posted on 3-4-2010 at 10:14 AM |
|
|
Tony,
Just a thought ---- on the Zenith carb, there should be an o-ring at the base of the counterbore where it pushes over the inlet stub on cylinder head.
Is the ring present and in good condition? When fitting the carb, push it hard onto stub so that you can feel stub contacting o-ring and tighten clamp
whilst holding.
Are you doing test runs with air cleaner fitted? If not fitted that can cause slightly weaker mixture.
Keep us posted ---- this virtual cub fettling is entertaining and far cheaper than the real thing!
chris. |
|
|
tonytrev
Senior Member
Posts: 68
Registered: 7-11-2008
Location: Chorley Lancs UK
Member Is Offline
|
| posted on 3-11-2010 at 09:27 AM |
|
|
Hi all, well I think I may have found the problem having tried all the suggested things with no success. On dismantling the inner cover to check the
timing marks something did not look quite right, the marks on crank and camshaft lined up ... sort of... so I took of the Timing Pinion and this is
what I found.
At some time in its past someone had damaged the small pip that fits into the hole in the crankshaft, in fact about half of it was missing which meant
that when the pinion was offed up there was play left and right = to about half a tooth, so when I fitted the pinion it may have been back a bit or
forward a bit. It seems I did not notice the problem at the time I fitted it. So I filed the pin down and drilled it out replacing it with a pin that
I made up that while not too tight allowed no free play.
So now when time allows I will put it all back together and see what happens. As they say "watch this space"
Tony |
|
|
Raggles39
Posting Freak
Posts: 1158
Registered: 9-21-2003
Location: Greenock Scotland
Member Is Offline
|
| posted on 3-11-2010 at 11:17 AM |
|
|
Well spotted Tony - the free play caused by the pin being damaged could well be the cause of the problem
Keep us updated
Jim |
|
|
