backfire on kickstart

[K steenst]

My 54 Airone continues to intrigue, amuse and annoy me.  I got some reasonable running yesterday though had to stop a few times as the plug carboned up.  Every 10 km.  Each time a new plug or a quick clean got it running again. I have tried a couple of different heat ranges (NGK) and 4 is too hot but 5 seems to go OK.  BUT... today I go to start it and i get massive backfires through the carb when I kick it over.  I got it started and idle for a minute or 3 but then it died and will not restart.  NOTHING was changed from yesterday when it was starting and running OK.  So now do I have a new problem or anohter symptom of the same one?  Probably running way too rich but it runs. Or used to.  Now i just get loud bangs and pops out of the carb as if the timing is suddenly out.  Or can this be a symptom of too rich as well?

[Dirk Van Ussel]

Do You still have compression when this happens?Valve clearance too tight?

Regarding plugs are You shure that You are not talking about the Bosch range?? seems very hot to me.

Have You polished and cleaned the magneto contact points? If not, dismantle them ,take a good look.Polish on a soft stone until clean.

Dirk

Op zondag 30 december 2018 09:37:24 UTC+1 schreef K steenst:

[baconsl...@gmail.com]

try a softer plug. Too hot plug will give the symptoms you describe exactly. It would be OK if the engine was warm probably.

[Paul Compton]

On Sun, 30 Dec 2018 at 08:59, <baconsl...@gmail.com> wrote:

> try a softer plug. Too hot plug will give the symptoms you describe exactly. It would be OK if the engine was warm probably.

Confusion often surrounds plug temperature ratings.

The plug electrodes need to run hot enough to burn off deposits, but
not so hot that they cause pre-ignition, or even melt.

The length of the heat path between the centre electrode and the plug
body determines the heat range of a plug. The shorter the path, the
more thermally conductive the plug is and the cooler the electrodes
will run. Higher compression ratios and higher specific power outputs
result in hotter burns, so a more thermally conductive colder running
plug is required.

The terms 'harder' and 'softer' get used too. A harder plug is a colder plug.

--
Paul Compton
www.morini-mania.co.uk
www.paulcompton.co.uk (YouTube channel)

[Andrew Nahum]

Check the ignition timing as a priority so at least you know it’s not that. The symptoms sound more timing related than anything else. 

There is no substitute for working through the variables systematically.     

(Although I confess I usually tend to jump on the first suspect thing that comes to mind.)

In my experience lean carb setting can give pops and bangs through intake. Rich mixture does not tend to if plug is clean. 

Ngk 4 heat range is awfully hot for an Airone. Others may disagree but I’d expect 6 to be about right. What colour is the insulator with 4?  I’d expect it to come out bone white. (Ie cooked). If it is black it suggests the motor is drowning in fuel. 

And there is always the capacitor/ condenser   which must be a suspect in any erratic running. Is the magneto a known quantity- has it been rebuilt?

It’s hard to get an Airone so overly rich unless the float valve is leaking (does it drip fuel?) or unless the pilot air passage is blocked.  Did it used to run well on current jets and main (slide) needle?  Which carb is it?

They are generally very simple and reliable engines - it should be easy to get it running smoothly and starting like a charm. 

Andrew 

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[Kst 099]

Thanks for the ideas Andrew. The 4 came out cooked. Running a 5 at the moment and comes out black covered in soot after 10 mins running. The bike hasn’t been altered since it ran the day before and started first kick each time. So unless the timing can slip out of adjustment by itself I can’t see that being a cause   I have a strong spark when resting it against the head.  Can’t adjustment could be in order. Drips fuel after I tickle it but not when running. So probably too rich but then it was yesterday too! If I get a lot of carbon on the plug the the piston crown must be covered in soot as well. Could it be preignitiion? Does it have the compression ratio to actually do that ?

Kristian Steenstrup +61 414 930 340

Sunday, 30 December 2018, 21:49 +1000 from andrew...@gmail.com <andrew...@gmail.com>:

[Kst 099]

Yes. Ngk 4 was a failed experiment as the 5 was fouling. But the 4 cooked in no time. But at least it was clean!  My confusion is that it should at least fire up with a 5 or anything really that gives a spark.   I just get a backfire through the carb like a pre ignition. Is there something I can do to clean the soot out of the combustion chamber without doing a full tear down ? Like some magic liquid and then kick it over to push it all out or am I being silly ?

Kristian Steenstrup +61 414 930 340

Sunday, 30 December 2018, 19:27 +1000 from paul.c...@gmail.com <paul.c...@gmail.com>:

[Kst 099]

I have good compression   Could the valve clearance have gone out by itself overnight ? Was running fine yesterday.  This is my first single so am learning all the time   I don’t suspect the magneto as I get a good solid spark 

Kristian Steenstrup +61 414 930 340

Sunday, 30 December 2018, 18:54 +1000 from vanuss...@gmail.com <vanuss...@gmail.com>:

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[Kst 099]

Ok. Will try a colder plug. Ngk 6.  I have had a few through it in the last week trying to solve the carbon fouling 

Kristian Steenstrup +61 414 930 340

Sunday, 30 December 2018, 18:59 +1000 from baconsl...@gmail.com <baconsl...@gmail.com>:

try a softer plug. Too hot plug will give the symptoms you describe exactly. It would be OK if the engine was warm probably.

On Sunday, December 30, 2018 at 8:37:24 AM UTC, K steenst wrote:

My 54 Airone continues to intrigue, amuse and annoy me.  I got some reasonable running yesterday though had to stop a few times as the plug carboned up.  Every 10 km.  Each time a new plug or a quick clean got it running again. I have tried a couple of different heat ranges (NGK) and 4 is too hot but 5 seems to go OK.  BUT... today I go to start it and i get massive backfires through the carb when I kick it over.  I got it started and idle for a minute or 3 but then it died and will not restart.  NOTHING was changed from yesterday when it was starting and running OK.  So now do I have a new problem or anohter symptom of the same one?  Probably running way too rich but it runs. Or used to.  Now i just get loud bangs and pops out of the carb as if the timing is suddenly out.  Or can this be a symptom of too rich as well?

--

[Rick Yamane]

While you have the head off pull the valves and make sure the seats are acceptably tight in the head. You may have to heat the head to make sure. I have heard of cases where seats loosen when the head gets hot and they fall out.

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From: guzzi-...@googlegroups.com on behalf of Kst 099 <kste...@gmail.com>
Sent: Sunday, December 30, 2018 8:22 PM
To: guzzi-...@googlegroups.com
Subject: Re: [guzzi-singles] Re: backfire on kickstart

 

[SED Sci]

Could it be flooded?  In my experience (Brit singles) gas dripping from a carb is flooded and won't fire but will spit out the carb.  If this happens with the Ariel the solution is to turn off the fuel, open the compression release and throttle and kick through half a dozen times, then close the throttle and do the cold start drill with the fuel off and no tickler.  

Or is it kicking back? Any chance you have mechanical advance and you are trying to start it at full advance?  Any chance you have centrifugal advance (MCR4 or similar mag) and the mag is stuck fully advanced?  

A compression test will tell you if a valve seat let go.

[ksteenst]

definitely could be well flooded.  lots of fuel dripping.

no kicking back (or rarely) and there is no advance adjustment on the old airone. But I dont know the inner workings of the magneto. Do they have a centrifugal advance?  that could be it.  but i dont really want to take the magneto out unless as a last resort.  I wonder if tapping it would loosen anything that is stuck ( i used to have to do that to the starter motor on an old ford I had)

[Andrew Nahum]

The combustion chamber will clean itself fine once you get it running well. The soot in there’s not a problem. A

Sent from my iPhone

[Andrew Nahum]

Pre-ignition only likely under prolonged load and heat. Not likely to be your problem. 

Ignition timing can slip. It’s not hard to check on flywheel outer diameter with a tape measure. Have you a handbook?

A

Sent from my iPhone

[SED Sci]

If you don't have a timing advance lever on the handlebar, it should have a centrifugal advance.  The mag should look something like the attachment - the case is an aluminum casting.  Earlier BL type mags have a smaller rounded top and are painted black.

You can see that this one has a centrifugal advance plate (#30 in upper diagram) so you should be able to grab either the points plate or the cam that opens the points and twist it to confirm that the advance mechanism is not stuck and the springs are returning it to the retard position.  - the twist will be against spring pressure.  If it is stuck, it is probably because #38 is stuck on the armature shaft.

While you are in there, check the point gap (0.012"-0.015"?).  Then check timing from the flywheel as Andrew suggests.  Then check good connection on both ends of sparkplup wire.  Then replace spark plug with new.  Check the gap - it should be 0.018"-0.020"  - gap will be too wide out of the box. 

[Andrew Nahum]

Hi Kristian

Forgive me if this is teaching you to suck eggs. You can check ignition timing from the flywheel outer perimeter with a magic marker pen and a tape measure.

Find top dead centre by taking spark plug out and insert a rod to feel top of piston. Rocking the flywheel back and forwards a few times lets you convince yourself where top dead centre really is. Then mark matching points on flywheel outer and on crankcase with felt pen.  Now you have TDC.

But make sure you are on the right top dead centre as this is a four-stroke and there are there are two - the exhaust top dead centre (when the exhaust valve is pressed down) - and the compression TDC when both valves are in up (closed) position. 

To double check you are on right top dead centre, take off the valve rocker covers.

Each valve rocker (rattle the inlet valve and exhaust valve rockers - or their  push rods) - each  should have some play (i.e. they should rattle or move when you push and pull them). You could measure the valve clearance but as a roadside barbarian I would just make sure there is some play at this stage because if not, the valve is being held open all the time which is BAD and eats the valve or head. It can also explain your backfire symptoms. (You can do the valve clearance measurement later, with feeler gauge but the important thing is to be sure that you have some clearance - to be finickity, it should be about 0.20 mm)

Then roll back the flywheel 1/4 turn opposite to the direction of rotation when the engine is running (or when it is kickstarted).

Take off the magneto points cover under the spring at the very end. Find the moving points arm. Open it gently with a small screw driver and insert a strip of cigarette paper between the moving point  and the fixed point. (Rizzla or Drum are good brands).

The strip of cigarette paper should now be held securely. Tug it gently. If it is not being held, the points are way too much open.

 Rotate the engine very slowly in the running direction using the flywheel.. Somewhere after about 30 mm advance on the rim the paper should come free showing the points have opened. I think if you have the magneto with automatic advance I think it should happen at 22 mm approx before top dead centre. Others please correct me if I'm wrong.

If paper does not come loose at all (or if it is loose all the time) it does NOT mean that the magneto has necessarily slipped. The points adjustment may have gone wrong because A) the heel of the cam wears, closing the points up.   B) The fixed point may move if the lock nut is slack so it can vibrate in any direction, probably open, C) the points can fail if a platinum contact button falls off the steel carrier, ) D: the points can burn and stop conducting especially if capacitor is failed.

The first thing to do is to set the points gap so the opening position is roughly reasonable.

Andrew

On 31 Dec 2018, at 04:15, Kst 099 <kste...@gmail.com> wrote:

[Ron Paterson]

Hi, Solve the flooding first as that's definitely going to cause a black sooty plug. If it drips the float needle is not sealing and stopping petrol flow to maintain the correct fuel height in the carb.
The backfire could be just excess fuel burning. I don't know your bike but many spark every time the piston is at the top (magneto direct on crankshaft), so the spark on the stroke where both valves are open can cause a fuel burn. My MV does this if I flood the carb too much, when cold starting.

[Andrew Nahum]

Don’t get too theoretical until you’ve worked through the  basic things and if they don’t help.

Check the mag points gap. If that doesn’t help, check ignition timing as per our previous.

 If the carb floods when you turn on the fuel but do NOT tickle the carburettor you have a float valve problem. If it does not flood or drip in those circumstances you don’t have that particular carb problem so put that worry aside. 

Centrifugal advances usually keep working quite well and don’t often seize. 

A

<MCR4Parts.jpg>

[ksteenst]

thanks Andrew for the detailed advice. I certainly need it!  New years day here and no I have had my dip in the ocean I am printing out your advice and illustrations to spend an afternoon in the garage. Fingers crossed!

[ksteenst]

Excellent practical advice as always.  I did as you said but worryingly it seemed to measure 80mm!  But that is close to the specification that i saw in my airone sport manual (see attached)  I checked points and plug gaps.  Both were too big and are now adjusted correctly. I also checked the idle mixture screw which was way out. 

BUT the really interesting discovery was that the head bolts appeared to be on the loose side.  When i was looking for problems I noticed dark stain where the head joins the barrel. It seems to have come loose. Bear in mind that I believe this bike had a full resto and rebuild 300 km ago before I bought it.  I did the full spanner check when I got it but obviously I need to be more vigilant and it probably loosened up or settled in after my recent short rides.  

And.... it started! and ran fine and actually idles now.  I rode it for about 15 minutes and apart from a bit of spluttering at the low end of revs it pulls fine in all 4 gears.  And it is quieter. So.... could it be that a gas leak in the head gasket would cause all these symptoms?  It is tight now but could something be damaged?

[ksteenst]

The carburettor has me puzzled now. It is not leaking at all, but definitely running rich.  BUT...There is a mysterious and non original rubber plug in the left hand side (see picture). I am not game to pull it out and I cant tell from the diagrams what should be there.  It is on the opposite side to the mixture screw. You can also see the soot that formed around the head gasket from the bolts not being tight which has now been corrected.

But from the look of the carb can anyone suggest what that rubber plug is doing?  

On Tue, Jan 1, 2019 at 7:02 AM Andrew Nahum <andrew...@gmail.com> wrote:

[Andrew Nahum]

How strange. The timing diagram I sent is from my own Airone manual showing completely different figures.  (Mike - what do use in mms static?????)1

That sports carb is ‘choke off’ when the side slide is up. i.e. the vertical slot is open to the air and you can see into that little side slide chamber. Is that how you’re running it?

Sent from my iPhone

<IMG_2010.jpg>

<IMG_2013.jpg>

[Andrew Nahum]

PS

That’s because the air bleeds from that side chamber down to a plenum round the main set and reduces the suction on the fuel. Slack cable = choke on and brass plunger down.   Warm running - cable tight.  Brass slide up. 

BUT I have had one of those carbs where the air passage was completely blocked and the Airone was running crazily rich. I stripped every component I could get out of carb. prodded out all muck I could reach and gave it ultrasound clean. That worked. 

Try choke positioning first. 

rubber bung is weird. Is it covering a pilot jet air feed? I’ve never seen one before. 

Andrew

[ksteenst]

Yes.. Vertical slot open when normal running.   And it is very intriguing that there are two timing diagrams in Airone manuals.  Maybe they radically changed it one year.  Mine is supposed to be a 54.

[Andrew Nahum]

Good. But Maybe it’s worth make sure the air passage is all clear from bottom of that enrichener slide all the way through to area round the main jet. If it’s blocked the ‘draw’ or suction on the fuel increases. 

I’d certainly want to see what’s under that odd rubber bung too. A

Sent from my iPhone

[Andrew Nahum]

PS.  Does it kick back through kickstart lever ever on starting? If not you can assume it is not disastrously over advanced. (Tho not necessarily totally correct. ). A

Sent from my iPhone

[Kst 099]

It did yesterday. But after fettling and tightening it does not do it today   So maybe the points gap being too big made it “virtually advanced “ and it is ok now.  Plus the loose head bolts did some weird things 

Kristian Steenstrup +61 414 930 340

Tuesday, 1 January 2019, 23:35 +1000 from andrew...@gmail.com <andrew...@gmail.com>:

[Andrew Nahum]

If it was over advanced double the correct mms. the kickback would be vicious. Where in Aus are you? A

Sent from my iPhone

[SED Sci]

The difference between the 2 timing marks is the difference in the magneto - manual cable advance or automatic centrifugal advance (MCR4 type in diagram I sent).  We figured this out on a friend's '51 Airone.

The earlier manual advance version is static timed at full advance (cable pulled tight) and uses the larger numbers. (just to be clear B are the correct numbers for magneto timing while A are when the intake valve starts to open for checking cam timing).  The later (after about 1952 if stock) auto advance mag is static timed retarded (because there is no rotation to through the advance weights) and uses the smaller numbers. 

My guess is that the spark plug gap was giving you the trouble - I've seen it before.  unless the points were very far out, they would only advance or retard the timing by a small amount (points open further up or down the cam).

I'd pull the rubber plug - it's blocking the idle air port. Remove and clean the idle mix screw, clean out the passage under the rubber plug with carb cleaner from spray can (it should squirt out from where you pulled the screw and into the throat of carb under slide) .  Then screw the idle mix screw in all the way - gently - and back out 1 turn or so and see if it starts and runs and doesn't foul plugs.  Turning in the screw will richen idle mix by cutting off air.

Good luck! 

[Kst 099]

Sunshine Coast Queensland. North of BRISBANE. Where are you at ?

Kristian Steenstrup +61 414 930 340

Tuesday, 1 January 2019, 23:42 +1000 from andrew...@gmail.com <andrew...@gmail.com>:

[ksteenst]

the restoration job on my bike appears to be very thorough so I have assumed that the carb was done as well. But maybe not.  And of course I can never be sure that some dirty fuel didnt find its way in there.  The rubber bung is definitely a recent "enhancement" but I am assuming it was a stop gap for a missing screw of some kind. 

[SED Sci]

Not a  missing screw. You've got the screw - the idle mixture screw comes in from the other side to restrict air through the air hole.  Under the rubber plug is a hole.  see the far right x-section with screw coming in from right:

Here's another diagram:

Only 3 reasons I can think of why it would be plugged - air slide&bore are worn and let too much air around at idle that the air screw can't make the idle mix rich enough, to make the idle mix richer to make up for a weak magneto (richer mixtures are easier to light apparently), the hole has been drilled oversized (don't know why it would be).  It's possible they used the plug until the bike started then removed it.

[ksteenst]

THANKS a BUNCH.  You guys are officially brilliant.  I cleaned out the carb after removing the screw and plug. It started first kick, pulls better though the revs with only an occaisonal cough.  no stoppages and a nice brown plug at the end.  That silly rubber plug must have been causing a lot of the problems.  I can sit on 80 kmh (indicated) now which feels fast enough on the Airone.   Very happy. 

[Rick Yamane]

Could it be the Carb was originally left hand and was converted to right hand, The plug sealing the original screw hole? If that’s the case the seat that the screw would meter through could be drilled out and the reason for the rich running. I am noticing the slide stop screw is on the left, at least it’s not on the right and Del’s usually have the screws on the same side.

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From: guzzi-...@googlegroups.com on behalf of ksteenst <kste...@gmail.com>
Sent: Tuesday, January 1, 2019 9:31 PM
To: Guzzi Singles

[ksteenst]

Rick

the hole was very small 1.5 mm  so not the original screw.  And after it was removed the bike ran great.  So it looks like someone plugged it and forgot to remove the plug and no one since has been game (at least not who I bought it from).  but thank to the advice on this forum it starts and runs perfectly now. 

[Rick Yamane]

Sounds good, just like how the new year should be starting off!

 

From: guzzi-...@googlegroups.com [mailto:guzzi-...@googlegroups.com] On Behalf Of ksteenst
Sent: Wednesday, January 02, 2019 3:04 AM
To: Guzzi Singles
Subject: Re: [guzzi-singles] Re: backfire on kickstart

 

Rick

[SED Sci]

Great - congratulations!  Now just need a photo or video of you flying down the road on it!

[ksteenst]

No action shots as I was testing solo. But here is a short stop in a local park to make sure everything was still tight and sound. Video later!  (back pack is for tools and spare plugs while I was looking for a reliable trial)

--

[SED Sci]

Outstanding!  It looks great.

[Rick Yamane]

It does look great.

I got a short New Year Day ride in yesterday. Hopefully Patrick won’t get mad because it was on my BSA but I got a nice shot overlooking the SF Bay.

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From: guzzi-...@googlegroups.com on behalf of SED Sci <doa...@gmail.com>
Sent: Wednesday, January 2, 2019 6:01 PM

[ksteenst]

Nice looking bike, and view!   I am all Guzzi here.  a 2006 Griso, 1984 Lario and of course the Airone.  Which is now well ahead of schedule as my aim was to get it reliable for the Distinguished Gentlemans Ride in September.  But of course there is a lot of time for something new to go wrong. 

[Rick Yamane]

Hahaha. That’s a problem by being ready too soon.

I think I’d rather be ready early though as opposed to using an organized ride as a teething run.

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From: guzzi-...@googlegroups.com on behalf of ksteenst <kste...@gmail.com>
Sent: Wednesday, January 2, 2019 6:46 PM

[guzz...@aol.com]

Hey Rick ,,,,,,,,,,, what type of clocks/gauges on the bsa ??

Tim

[Rick Yamane]

They are Smiths Chronometrics. Not the right ones either so they’re not functional.

I picked them up at a swap meet around a dozen years ago and some guy must’ve had his eye on them. He asked what I was going to put them on and I told him. He said they weren’t correct but he had the right ones he swap me for. I turned him down thinking these must be pretty valuable. In hind sight all these Smiths Chronos are valuable and I should have swapped but…….

One thing is the tach is a 10,000 rpm model. I think most of them were 8,000 rpm. It also spins the wrong way for me.

[Paul Waldman]

Back to that rubber plug in the carburetor... I think it should have a "Remove Before Flight" lanyard. I'm surprised it posed such a mystery for everyone — small holes like that are very attractive for certain mud-daubing insects and a plug is a smart idea when the bike is parked for extended periods. To remember it, a cork for the intake could be attached to the other end of a short string.

[Kst 099]

Good point though this looks like it has been stored well. I actually have it under a cover in an underground garage so minimal insects. I do however have a “remove before flight “ lanyard on my oil tap to make sure I remember to turn that on and off. 

Kristian Steenstrup +61 414 930 340

Friday, 4 January 2019, 04:47 +1000 from pwal...@gmail.com <pwal...@gmail.com>: