The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: wortluck on 25.03. 2017 15:25

Title: A10 GF power loss on hills
Post by: wortluck on 25.03. 2017 15:25
Greetings

Back on the road today after winter lay off - BIG SMILES  *smile*

Just one thing that keeps bugging me.  When winding the old girl up on a moderate to steepish incline, I start to lose power as if I'm running out of fuel.  In the worst cases, I get a fair bit of knock and the bike really struggles.  When the hill levels out, she goes like a bullet with absolutely no problems.  I'm using premium unleaded as the problem was worse with the standard muck.

My only thought is that it's some kind of problem with fuel supply.  Possibly that the incline is changing the fuel level in the carb so the main jet can't suck up enough fuel.  I've checked taps, fuel lines, etc, no issues, and the carb is brand new.  Could it be a problem related to altitude - the place where I've had the worst problems have been in quite elevated locations?

As I say, on normal roads and some steepish inclines, it seems fine.  On others it's quite bad.

Any ideas or suggestions?
Title: Re: A10 GF power loss on hills
Post by: bsa-bill on 25.03. 2017 15:53
are we talking standard compression ratio or has it been lifted, cause it sounds like pinking?
Title: Re: A10 GF power loss on hills
Post by: Triton Thrasher on 25.03. 2017 17:51
Greetings

Back on the road today after winter lay off - BIG SMILES  *smile*

Just one thing that keeps bugging me.  When winding the old girl up on a moderate to steepish incline, I start to lose power as if I'm running out of fuel.  In the worst cases, I get a fair bit of knock and the bike really struggles.  When the hill levels out, she goes like a bullet with absolutely no problems.  I'm using premium unleaded as the problem was worse with the standard muck.

My only thought is that it's some kind of problem with fuel supply.  Possibly that the incline is changing the fuel level in the carb so the main jet can't suck up enough fuel.  I've checked taps, fuel lines, etc, no issues, and the carb is brand new.  Could it be a problem related to altitude - the place where I've had the worst problems have been in quite elevated locations?

As I say, on normal roads and some steepish inclines, it seems fine.  On others it's quite bad.

Any ideas or suggestions?

It really sounds like you are in too high a gear for climbing these hills.

You can very easily roast your engine like that. 

Have you messed around with the sprocket sizes?
Title: Re: A10 GF power loss on hills
Post by: chaterlea25 on 25.03. 2017 19:51
Hi,
Check the ignition timing on both cylinders !
Maybe the engine is running a bit lean? these old bikes do not like lean mixture that would be ok on modern's

John
Title: Re: A10 GF power loss on hills
Post by: muskrat on 25.03. 2017 20:06
I agree with both TT and John. Holding the throttle wide open going up hill in a too high gear makes for a lean mixture and produce pinging.
Cheers
Title: Re: A10 GF power loss on hills
Post by: beezermacc on 25.03. 2017 23:15
Sounds like retarded ignition to me.
Title: Re: A10 GF power loss on hills
Post by: wortluck on 26.03. 2017 11:29
Thanks for the replies gents.

Engine is completely standard with standard gearing.  Plugs are proper tan colour when doing a 'run and shut off' test, although it does run slightly rich at tickover.  Sorry to sound a bit thick, but what's the correct procedure for checking the ignition timing.  I was under the impression that once the timing had been set, it wasn't likely to slip (I had help on this).  Also, I understand the '61 GF had auto advance/retard, so how would I end up with retarded ignition?

For the record, when I say I wind her up, I mean taking a run at hills to mitigate the issue. Obviously, when it starts to slow, I bang it down a gear.  Unfortunately, on the worst hill across the Derbyshire Dales, I'm often struggling in 1st and barely make it to the top.  All other times the bike runs like a dream??

This is my first restoration on a British bike so I'm still coming to terms with its eccentricities

Cheers
Title: Re: A10 GF power loss on hills
Post by: stu.andrews on 26.03. 2017 13:21
First run after a winter lay over. That gives the clue! It could very well be the petrol. I even had the same problem on a modern bike. Drain the fuel system, put in fresh petrol, tip the old in the car (it's not a diesel is it?), & make sure that the jets & passages in the carburettor are clear of gum.
Title: Re: A10 GF power loss on hills
Post by: chaterlea25 on 26.03. 2017 18:09
Hi All,
Speaking of bad fuel,
I visited a friend on Friday to try and resolve a problem with his Guzzi single,
Long story short, it died while out riding shortly after refuelling, it would fire but not enough to keep the engine running for more than a few seconds
After trying everything  *work* we tried the "petrol" in another bike, not even a "phut" from it
Tried it on some brake cleaner and it started instantly but would not run on the crap that was bought a couple of days previously
 *problem* *problem* *angry* *angry* *angry*

John
Title: Re: A10 GF power loss on hills
Post by: wortluck on 26.03. 2017 20:30
Sorry guys, not the fuel either.  I drained the tank as the ice set in so the fuel was straight from the pump to a clean tank.  Carb was drained of fuel too.  I know about how the crap we're ripped off for now goes dud pretty quickly, so I'm really careful in making sure I don't leave too much fuel in for too long.

Again, went for a 45 mile ride today and it was brilliant - just can't get why it fails on some hills (not all).  Will keep you posted on developments but any other suggestions would be welcome.

Cheers
Title: Re: A10 GF power loss on hills
Post by: chaterlea25 on 26.03. 2017 22:09
Hi
It could be the ATD sticking sometimes?

Title: Re: A10 GF power loss on hills
Post by: Clive54bsa on 27.03. 2017 03:08
I know this sounds a bit stupid, but after a rebuild of my '61 Super Rocket, I found after a while it would barely climb hills, 250's were flying by me.
Turned out I had the rear brake adjusted too much and had a slight drag, which got worse as it heated up.
Worth a look before you change anything drastic.
Clive
Title: Re: A10 GF power loss on hills
Post by: wortluck on 27.03. 2017 17:15
Cheers fellas - I reckon a sticky/faulty ATD is worth investigating.  Brake binding isn't happening as it freewheels easily when well warmed up!!

I'm planning to go to my hill nemesis sometime soon to see if the problem is still there (with a tank of full fat premium).  If it still struggles, it'll warrant a full check and a crate of cider. *angry*
Title: Re: A10 GF power loss on hills
Post by: wortluck on 19.04. 2017 20:27
Ok, so I took the GF to my nemesis hill with a tank of full fat premium after checking the tank and taps for gunge.  Steady run at the hill, changed down to third when it showed first signs of trouble and kept the throttle half way - went up no problem at 55 mph!!  Turns out I was trying to wring too much out of the old girl, just needed to keep her steady.  *conf2*

Also, to get all the, "I'm a pillock" issues out of the way, my bike runs a four spring clutch and not the six spring I originally said.  *doubt*

Thankfully, all the guys and gals on this forum are forgiving souls and can tolerate the odd touch of senile pillockry from time to time.  *dunno2*
Title: Re: A10 GF power loss on hills
Post by: Black Sheep on 14.05. 2017 13:54
I noticed that your bike is nice and shiny. Make sure your filler cap breather hole is clear - they can block with polish and produce similar puzzling symptoms.
Title: Re: A10 GF power loss on hills
Post by: TT John on 26.05. 2017 09:05
Cheers fellas - I reckon a sticky/faulty ATD is worth investigating.  Brake binding isn't happening as it freewheels easily when well warmed up!!

I'm planning to go to my hill nemesis sometime soon to see if the problem is still there (with a tank of full fat premium).  If it still struggles, it'll warrant a full check and a crate of cider. *angry*

I don't think you will get much success running it on cider!!! *pull hair out* *pull hair out*