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Old 18-07-16
erad erad is offline
Valued Member
Join Date: Mar 2015
Location: Cooma NSW
Posts: 3,343

A pressure relief valve would certainly help the air box situation if it worked quickly enough. Considering that there is an explosion, I doubt that it would, unless it was very close to the main butterfly valve. Still, it would be better than having the guts blown out of your airbox.

I had an NL on gas and had a lot of trouble with it. One time it backfired badly - I had Topgun HT leads on it and they were ultra KRAP. The positive pressure wave blew the guts out of the mesh inside the airflow meter. I had to panel beat the aluminium honeycomb mesh sections to restore them to some form of shape and airflow ability. Worse still, a positive pressure wave reflects from a solid surface as a negative wave (this is fancy Hydraulics/ Aeronautics stuff), and it sucked the choke from one of the resonators into the main air pipe. The engine would start & run at low revs but as soon as you tried to rev it it became ultra rich and stalled.

I was in Sydney at the time (a weekend), and took it to a taxi repair shop. The guy spent 2 hours on it, chasing everything. Eventually he replaced the gas converter and it still did it. Finally he took the main air hose off the manifold and by chance the offending choke bit fell out. It was about the size of a golf ball. It dropped back into position when the engine was idling or not running but as soon as airflow increased, it would pop up and cause major restriction and hence pressure drop. The Gas converter interpreted this as full power and hence gave lots of gas - too rich and it stalled. That exercise cost quite a bit of money and time.

It is VITAL that your HT leads by in top condition and that they do not come near the engine (rocker covers etc) or that they touch each other where they cross paths. Use the little brackets and carefully lay the leads out so that they do not cross or touch anything other than the support brackets. Also, set the plug gap 0.1 mm closer than recommended. This is a recommendation by Champion. Use top brand leads and plugs. I used NGK leads because they were numbered so that they were the correct length. I used Bosch leads but each lead was about 15 mm or more longer than original, and they drooped onto the rocker covers or they sagged and touched other leads. As said above, TopGun leads were absolute crap and caused all this problem.

Regarding spark plugs, I eventually got onto Iridium plugs. If possible, use a grade colder than recommended because the spark plug gap increases with time. The original plugs in my NL were replaced at 105000 km. The gap at the time was about 1.6 mm - huge. We also had a Magna on gas and I had no troubles with it at all because the HT leads were 7 mm diameter inste4ad of the 5 mm diameter leads used on the Pajero. I installed Iridiums in the Magna and my waife asked me the next day "What did you do to the car?" When asked why, she repiled that the car seemed to be running much better. I had noted this as well but didn't say anything, so maybe the Iridiums did give a better spark at low revs.

After years of trying, I finally sorted out the HT leads and plugsd on both cars and then eventually sold them both. Isn't that the way with everything - you get it all sorted and then move on...
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