Author Topic: A10 is misbehaving  (Read 807 times)

Offline Lannis

  • A's Best Friend
  • ***
  • Join Date: Jan 2009
  • Posts: 90
  • Karma: 0
A10 is misbehaving
« on: 14.05. 2009 17:18 »
Trying to get ready for a 1000-mile weekend on the A10, and it's not doing right.

I put 1800 miles on it last summer in the UK and then shipped it here.  Rode it for a few days, but the cylinder base studs loosened and blew out the gasket. 

So I pulled the top end, freed up a gudgeon pin that was extremely tight in the small end, replaced all the gaskets, reassembled, set tappets and rode 25 highway and city miles into work.

Two things the bike is doing.  One is that when I run about 60 or 65 MPH and open the throttle, I get very little response.  The engine runs smoothly, but just sort of "bogs" and doesn't go any faster.  Since we never really got over about 55 MPH on the back roads we were on in the IOM and Derbyshire and Yorkshire, I never tested this before.  Needle position, you think?

The other is that when I come to a stop from a 65 MPH highway run, the bike will barely run, and sometimes cuts off.  Accelerating back up, the bike runs very rough, missing, etc, and gradually smooths out and runs OK again.  Spark plugs loading up, maybe?  I oiled them pretty good when I fired the bike up wet-sumped and oil puked out of the breather after it had been down a month or so.  I'll try a pair of Champion L10S in it and see.

The engine runs nice and quiet, tappets at .008 and .010 per spec, good compression, timing and point gap are on.

One more night of fettling and if it doesn't behave, the Guzzi will go play in the mountains instead of the A10 .... !

1961 A10 Golden Flash
1969 A65 Firebird Scrambler
1955 M21 Commodore
1935 Matchless Model X Project
1990 Moto Guzzi California III
1983 Moto Guzzi 1000SP
1986 Yamaha TT225 trail bike
1966 Morgan 4/4

Offline beezalex

  • North Carolina, USA
  • Valued Contributor
  • ****
  • Join Date: Jan 2008
  • Posts: 374
  • Karma: 4
Re: A10 is misbehaving
« Reply #1 on: 14.05. 2009 18:14 »
Lannis...I would check the timing again...just to be sure.  And make sure your point gap adjuster isn't backing off.

Otherwise, run it at half throttle for a few seconds, then hit the kill switch and pull in the clutch.  Coast to a stop, pull the plugs.  Put the plugs in your pocket and put in a fresh pair and ride home.  Now, with a hacksaw, cut the threaded metal portion of the plug off and all will be revealed.  Clean the insulator with carb cleaner and then have a look.  It should look something like this:

If you don't see the ring at the bottom of the insulator, you're too lean.  If the ring is more than .060-.080 wide, you're too rich.  Simple as that.

Too many BSA's

Offline A10Boy

  • Wise & Enlightened
  • *
  • Join Date: Jun 2008
  • Posts: 1075
  • Karma: 11
  • Solihull, Near Birmingham England.
Re: A10 is misbehaving
« Reply #2 on: 14.05. 2009 18:37 »
Its hard to diagnose a problem like this, they are normally resolved by checking the obvious things then progressively working through it from the obvious to the less obvious. It could be something as simple as a blocked filler cap breather or a partially blocked fuel filter - its happened before!

I would check everything you can check, starting with the carb, check everything including the size of the jets and level of fuel in the float chamber, is the slide actually lifting fully, is it sucking air from a loose or bent carb mounting flange ? With these types of problem you cant assume anything is right. When it plays up what happens when you loosen the filler cap or press the tickler, these things often reveal the problem. Do you have a colour tune ?

If its not the carb, then next is electrical, have you checked the sparks when its hot and its missing, often if there's a failure in a winding, a mag will show good sparks when cold then start to fail as it gets hot this will get worse. An engine under load needs a better spark than one cruising, so it could missfire until it gets to cruising speed then be ok - but as the mag deteriorates which it will, it will get worse.

A faulty condensor can show these symptoms to, are the points clean or do the look burnt, is the points pivot secure, they can come loose. One other thing, make sure your rockers are gapped right not too tight. Etc Etc

Sorry this has turned into war and peace and if you knew all that anyway. Good luck, let us know how you get on.


1958 Super Rocket
1974 Kawasaki Z1a
Yam XJR 1300