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AQ151C - Distributor faulty?

P

Paul McClure

Member
As part of the ongoing saga of getting my rebuilt engine running, it had been running and idling, but it didn't feel perfect, always a hint of a miss every so often and it died on me and wouldn't restart a few times. A few times it would just not start at all. I don't trust the thing to run properly when I'm out.

So today I bought a timing gun and went down to check the timing. The gun is the type with the pickup sensor that clips over the HT lead. However when I tried to check it, the strobe only lit up intermittently. Not the usual regular flashing on and off, but completely dead with a few occasional flashes. It's the same on every HT lead, however the one running from the coil to the distributor cap flashes constantly.

Items replaced (ignition circuit):

Ignition coil
HT Leads
Distributor cap
Points
Condenser
Rotor arm
Plugs

I also had a Pertronix electronic ignition module fitted, but there was no spark whatsoever with that, so it was pulled out and a new set of points and condenser were bought and fitted.

I'm beginning to think that pretty much the only part of the ignition system which hasn't been replaced is the distributor body, but does that sound likely with the symptoms above?
 
With the timing light sensing the coil's high voltage output lead, you'll see 4 spark events for every two crankshaft revolutions...... or 1,600 spark events in 1 minute.
Checking 1 cylinder allows you to see only 1 spark event for two revolutions.... or 400 spark events in 1 minute.
None-the-less, if it appears to be skipping, it sounds like your spark triggering is not consistent.
If triggering is consistent, then perhaps the rotor and cap are not working harmoniously.

Poor dwell angle from a worn and wobbling distributor shaft may be causing this.
I'd pull the distributor, and have it tested on a distributor machine.
Re-bush if need be, re-calibrate the progressive advance curve, and check the limit rpm.

.
 
If you didn't get spark with a Pertronix module installed it was either because of faulty module or wrong installation. That is, supposing that the ignition coil and all other ignition components are working and wired correctly.

Honestly, I would not use points and condenser in today's day and age.
 
Thanks Rick - I'm getting nothing like 400 spark events in a minute. It's often completely dead, with a few sparks showing up every 20 seconds or so. Given that the cap, rotor, points and condenser are all new, I'm guessing that the distributor is the problem. I'm in the UK and don't know anywhere that rebuilds or can test the distributor.

It's a Bosch unit, part number 0 231 178 019, centrifugal only model. Since I've swapped the Solexes for the Weber conversion, which has a vacuum pipe, I'm wondering if it's worthwhile changing the distributor to one with vacuum advance.
 
El, I'm going to test the Petronix model later, when it didn't work we reverted to standard points and condenser to try and isolate the problem. Not sure if it would have worked correctly is there's a problem with the distributor?
 
Vacuum advance is a no-no in marine applications, Paul. I would start checking the coil, the wiring and rotor and cap. Anohter thing that could be faulty, believe it or not, is your ignition key switch. To test that, just hotwire the + of the coil with the + of the battery and see if the symptoms disappear. Make sure you remove the jumper afterwards, because otherwise you won't be able to stop the engine by turning the ignition kee off. :)
 
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I got hold of a replacement distributor and there's no change. However we're pretty sure the problem is the carb. We're getting good spark on every cylinder, but the carb is still over fuelling.
 
"Carb" or "Carbs"? Unless you have converted to single carb, the AQ151 comes with a dual carb arrangement. In any case, those carbs are quite easy to overhaul.

Did you try hotwiring the + of the coil to the + of the battery?
 
It's got the Weber conversion, so it's a 38 DGES. I'm getting a replacement unit which I'll fit at the weekend. Last weekend I had it running off an electric fuel pump with a regulated pressure, then into another pressure regulator dialled down towards the bottom of the range, and it was still dripping some excess fuel and causing rough running. Without the second regulator, the tubes at the top of the venturies were still spraying a quantity of fuel and causing the engine to momentarily flood. It's like it runs for 10 seconds, coughs for a second, runs for 10....

I'll report back once I've fitted the replacement.
 
I fitted the replacement carb at the weekend. Ten minutes with a screwdriver and it's running fine. No over fuelling, even with the original mechanical fuel pump and no regulator.

This has been an expensive process and I'm sure the original faulty carb contributed to the engine blowing its big end bearings. I think I'll post a summary of lessons learned and things to check when moving to the weber conversion. I'm sure many points will be second nature to those working with engines on a regular basis, but for the DIY owner who rarely touches this stuff, it may save some time and money, not to mention a few wasted seasons.
 
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