Outer Limits 4x4 Board

Hi all,

Have done a search, and cant quite find what im looking for.

I have a GQ (mav) with TB42, Dual Fuel.

What are the timing settings that people are running with dual fuel setups? How far away from the factory nissan specs should i be running ?

The gas system is an older style impco so its not exactly the most efficient.

Interested to hear any differing opinions.

Cheers

Ok well this is a bit harder to answer as it depends on what you really want

My old baby was dual fuel but i ran it on LPG 99% of the time, only used petrol when climbing big hills with 35's on and towing, other than that it was gas all the way.

For this i had the Carby overhauled with special Gas seals put in so it didn't break down due to the dry LPG, had the head re-done with ceramic valves or whatever they call them that are dedicated gas valves so i didn't need flashlube at all.

Lastly i had the dizzy converted from Points to a pointless setup, Cranecam Fireball X700 was what i got.

To this i ran my engine at 13-15 degree BTDC. some people go as high as 20 degree with a re-done dizzy. at 15 degree i was powering on LPG with an average of 500K's around town and about 650-700 on the freeway.

This did present a problem when running petrol though having that far an advance. If i used normal unleaded (octane rating 91) when you put your foot to the floor or climbing hills, she would ping like crazy, this ment i had to run 96 to get it to a occasional ping on petrol or 98 to completly stop it (and that was using the United's Boost with Ethanol, Vortex 98 still pinged)

Dual Fuel is impossible to get 100% for both setups, you can only have one going perfect and one that is off, depends what you want, best idea is to have the LPG setup for the most power and economy as its cheaper to fill up and the more K's u get on it the better.

Having some entertainment on the LPG side too (as yet first tank down - great range but so little power up hills)...

I'll patch up my shoddy electrical system (new leads and plugs) and advance timing slightly to see how we go then.

Ok, another thing yo may want to know.

LPG setups are very sensitive to the electrical systems they are put on. Thats why if you are going to run points you will need to replace them more often then if you had a pointless setup, LPG needs for a better word, a clean spark

Bosch makes a range of leads that are designed for LPG, that being low resistance.

Also look at getting some Denco LPG spark plugs, they don't have any resistors in them, and they last a lot longer than the NGK or Champion plugs in my personal experience.

Also you will want to have the LPG system tuned properlly, however, Impco setups are really hard to tune due to the stupid mixers they use

My old setup as a dounut ring that bolted onto the carby top body and used the original air filter, just had 2 holes drilled through the bottom to allow the gas lines in. It then went to a splitter than converted the large gas hose into 2 smaller ones that led to the carby and the mixer, this splitter had a screw on the top to regulate flow. Then it was to the converter itself. I did all my own tune ups on my setup and while i don't have a dyno at home, i did notice when i did it myself i got it better than any one at the shop ever did

To do it i got the car to Normal Operating Temps and locked the revs at 1000RPM using the in cab throttle lock cable. I then went to the splitter and screwed it in and out till i found the maximum revs the engine would run at (if it would change at all).
after setting that part up it was over to the converter to play with the mixtures getting the engine to idle as well as i could. once i could tell she was getting extra gas with the slight popping from the back of the engine, it was then back to the splitter valve to open or close it off more to see if the engine revs would change

As stated i would start at 1000RPM, when i was finished i would usually have it finally at 1200RPM and if the mixtures had changed quite a bit (they tend to get bumped around a bit off road) i sometimes had 1800RPM on the clock,

Would then let the throttle lock off and adjust the idle speed screw to get it idling at specs again. had it down to a fine art by the end, sorry i rolled her, Diesel is alot easier, leave it alone

tj81 wrote:Hi all,

The gas system is an older style impco so its not exactly the most efficient.

Cheers

How old is the Converter also? it might be in need of a clean out of the sludge and the diaphrams replaced, i had that done when i had the carby serviced

Thanks for the comments guys,

a bit more info....

The LPG system has recently has a full service, convertor was replaced with a reconditioned unit.

New spark plugs, leads and points.

Carby has had a full reco not less than a few months ago.

As far as what im looking for, the LPG will be used mainly for round town stuff, and driving too and from trips away. Petrol will be used when track driving and in the bush, also will be used at minimum once a week on petrol even when round town. So i guess im leaning towards having the thing tuned as best as possible for LPG....

Try it at 15 degrees and see how you go. Mine runs great at 15 degrees on both lpg and petrol BUT on a hot day it will ping a little on petrol. I ahve now put some premium in the tank to see if it will help.

I found gas a lot better in the bush on steep hills. Wouldnt suffer any flooding or side slope surge.

Only ever used petrol to keep the system operational or as an extra to get home

Bazzle

discon the vacume advance and run 20 degree's
make sure you run 96/98 octane petrol

i had 13-15 degree and the vac advance on, it made a huge difference with it on.

Gas is a hell of alot better off road then carby petrol in some points. With LPG though since its all venturi action, when you put your foot flat to the floor you don't get the injection of extra fuel that you do on petrol, so it doesn't respond quite as well as petrol off road, however, you will not get any stalls when on hills or flooding when on extreme angles.

if i was ever to get a petrol based car again, i would defiantly have gas again. its too good

Does anyone know if theres a kit you can get to have 2 timing maps of sorts ? So one for petrol and one for gas. Something simple'ish not a full ECU or anything.