Petter A1 Starting Issues

by Stu Pashley Mon Sep 21 2020, 18:21

Today I tried starting up my Petter A1 for the first time. Turned over but nothing. Fuel in the Carb and took the plug out and checked and a good blue spark at TDC. When I turn it over then stop it blows a fair bit of fuel out of the strangler(it's a Zenith 24T2 Carb which has been pretty much completely rebuilt) Strangler is spring loaded closed(is this correct, I have tried with it open and closed but no joy). Anyone any ideas(thought maybe a float issue)

by tony RA Mon Sep 21 2020, 19:59

The choke butterfly should be spring loaded open and closed to start may have been assembled wrong
good luck with it Tony

by Robotstar5 Mon Sep 21 2020, 21:50

As above, choke should be sprung in the open position, also check it's not flooding, I had to put an extra washer under the needle seat to lower the fuel level in the float bowl as it would drip fuel out the mouth.

Try a bit of fuel in the plug hole, if it fires it will prove the timing/mag are OK which just leaves the carb.

by Stu Pashley Tue Sep 22 2020, 08:20

Thanks. I will sort choke so it is spring loaded open!!. Also going to strip down carb as suspect may also have a stuck or leaky float so will check and as you say may add a washer under the needle. Any advice regarding carb settings. How about the slow running jet should this be fully in or out some turns? Will try the fuel down the plug hole to confirm it is a carb issue not a spark issue.

by Woodsman Tue Sep 22 2020, 09:46

Try screwing slow running jet fully in, don't overtighten, then open a couple of turns.
Have manual. PM me if you need a copy.

by Stu Pashley Tue Sep 22 2020, 10:01

Woodsman wrote:Try screwing slow running jet fully in, don't overtighten, then open a couple of turns.
Have manual. PM me if you need a copy.

Many Thanks just PM'd you.

by Robotstar5 Tue Sep 22 2020, 20:42

Woodsman wrote:Try screwing slow running jet fully in, don't overtighten, then open a couple of turns.
Have manual. PM me if you need a copy.

For the A1 or the Zenith carb?

by Stu Pashley Wed Sep 23 2020, 07:56

Robotstar5 wrote:
Woodsman wrote:Try screwing slow running jet fully in, don't overtighten, then open a couple of turns.
Have manual. PM me if you need a copy.

For the A1 or the Zenith carb?

For the Carb if possible. Have a manual for A1. Thanks

by Robotstar5 Wed Sep 23 2020, 11:51

Stu Pashley wrote:
Robotstar5 wrote:
Woodsman wrote:Try screwing slow running jet fully in, don't overtighten, then open a couple of turns.
Have manual. PM me if you need a copy.

For the A1 or the Zenith carb?

For the Carb if possible. Have a manual for A1. Thanks

I have a carb "manual" (only a few pages), if @Woodsman doesn't send you one, drop me a PM with an e-mail address and I will send it.

by Woodsman Wed Sep 23 2020, 14:34

Manuals sent.

by Stu Pashley Wed Sep 23 2020, 14:44

Woodsman wrote:Manuals sent.
Many thanks for that.

by Stu Pashley Wed Sep 23 2020, 15:14

So stripped the carb down and all looks ok. Float seems fine. If I take the spark plug out and turn over I have a good blue spark at TDC. I have taken the end cap off the magneto to have a look at the points. If I start at TDC(Magneto just fired and key way at bottom).As you rotate the flywheel, once you rotate through around 270 degrees the points begin to close then the central shaft seems to stop rotating even though you are still rotating the flywheel before it then clicks over on impulse. If I then rotate flywheel backward approx 20 degrees the points open. Is this correct as currently at a bit of a loss. I did also try dropping some fuel down the plug hole and a bit of pencil graphite on the plug and did get a nice flame out the exhaust so guess must have sparked.

by StuartTurnerSteve Wed Sep 23 2020, 16:34

The magneto will stop rotating while the impulse engages.
I ask this every thread about engines not running.... but have you taking a resistance reading from the HT lead to earth (Magneto body, cylinder head bolt etc)?

by Stu Pashley Wed Sep 23 2020, 17:53

StuartTurnerSteve wrote:The magneto will stop rotating while the impulse engages.
I ask this every thread about engines not running.... but have you taking a resistance reading from the HT lead to earth (Magneto body, cylinder head bolt etc)?

Just checked from Plug cap end of HT lead to earth is 0.02 M Ohms.

by Stu Pashley Wed Sep 23 2020, 18:15

Points are closing just before TDC should they be opening just before TDC? If so how do you correct?

by StuartTurnerSteve Wed Sep 23 2020, 18:57

Should be opening at tdc with the impulse, it will automatically advance the timing.

by Stu Pashley Wed Sep 23 2020, 19:24

So is that the problem the points are closing before TDC rather than opening even though impulse is firing at TDC. Anyone know how I correct this?

by Gaudin98 Thu Sep 24 2020, 09:19

The mag is fitted 180 degrees out.

by Stu Pashley Thu Sep 24 2020, 10:13

Gaudin98 wrote:The mag is fitted 180 degrees out.

Would that not mean it would then be firing at BDC rather than TDC. If I turn it over it fires at TDC put points seem to close before impulse rather than opening

by Woodsman Fri Sep 25 2020, 09:30

Magneto should 'fire' at 20 degrees before TDC. Slowly turn engine over compression. The impulse should click just before TDC. Loosen the bolts and rotate magneto to adjust timing - anticlockwise to advance. You could mark flywheel and body when at TDC, then measure circumference with tape - divide by 360 and multiply by 20 to give offset from TDC.
Good luck

by Stu Pashley Fri Sep 25 2020, 11:28

So at a bit of a loss. Magneto tweaked and now firing at 20 Degrees before TDC(Thanks Woodsman) and giving a good blue spark. Put the spark plug back in and try to turn over and still nothing. Points open after impulse then close again just before impulse, is this correct? Have checked the Carb and that all seems OK. Checked resistance of the HT lead and measured 15 K ohms(is this OK). There is a suppressor cap fitted, I know some say not to have these on a Magneto engine. I know I must be missing something just don't know what.

by StuartTurnerSteve Fri Sep 25 2020, 11:36

The impulse coupling retards the spark until just after the piston passes top dead centre for starting, so should be opening as the impulse clicks.

15k ohms sounds high, 3-7KOhms is what I tend to look for. Pull the suppressor cap off.

by maryalice Fri Sep 25 2020, 14:03

As told by my magneto repairer, Bin the suppressor they bugger magneto's.

Maryalice

by Woodsman Fri Sep 25 2020, 16:20

From what you say it seems to be failing under compression? Maybe the coil has a break in the wiring which can jumped when the plug is in air but not when under pressure. What is the resistance of the coil

Apologies just spotted that you have already measured coil resistance.

I'd be tempted to attach any old piece of stranded wire to magneto and use gloves, insulated priers, or numpty to hold the other end about 6mm from 'earth' and give it a whirl. If you get a decent spark try attaching to plug and give another go.

Just for interest - a nice description of the impulse mechanism here:

https://www.flight-mechanic.com/the-fadec-system-impulse-coupling/

by Stu Pashley Fri Sep 25 2020, 19:04

Woodsman wrote:From what you say it seems to be failing under compression? Maybe the coil has a break in the wiring which can jumped when the plug is in air but not when under pressure. What is the resistance of the coil

Apologies just spotted that you have already measured coil resistance.

I'd be tempted to attach any old piece of stranded wire to magneto and use gloves, insulated priers, or numpty to hold the other end about 6mm from 'earth' and give it a whirl. If you get a decent spark try attaching to plug and give another go.

Just for interest - a nice description of the impulse mechanism here:

https://www.flight-mechanic.com/the-fadec-system-impulse-coupling/

No I had only tested resistance of HT lead. But have since ditched the suppressor cap and this is now down to 5 K Ohms so may make up a new HT lead.
I have tested the coil. If I go from Magneto Body to the tab on the coil it's 5 k ohms. If I disconnect the LT coil lead and condenser and test it between Magneto body and LT Lead I get 5 ohms used 2 multi meters and have the same readings with both.

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