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Teething problems with Straight Gas

Started by _73LJWhiteSL_ , Dec 11 2005 10:36 PM

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8 replies to this topic

#1 _73LJWhiteSL_

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Posted 11 December 2005 - 10:36 PM

gday all,

just a couple of quires,

I am having a slight problem when reving and taking off from idle. When i put my foot on the accelorator when the car is idling it hesitants, and then revs fine. It doesn't do this when you are moving, even if you have your foot of the accelorator. I am thinking maybe something to do with vacum advance seeing as i was told that i don't need the vacum advance of the dizzy and so it is connected to nothing.

Is this right and if so where on the Gas Research carb should i connect the line?
If you don't think the problem is advance related, what could it be?

Also, When i was running on PULP i was running around 6.5 degrees advance which i found was the best position (7 degrees gave slightly better performance but also noticable more fuel usage). What should i set it to now that i am on straight gas? I have advanced it to about 12 degrees i think now, and the 'poping' from the exhaust pipe when taking your foot of the accelorator going down the gears has reduce quite a lot but its still there, which i think maybe means its running a touch lean.

I am interensted in any ideas you people have, so don't be shy, please post

thanks

Steve

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#2 _devilsadvocate_

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Posted 12 December 2005 - 05:37 AM

Did the people that did the conversion set it up and dyno tune it?
Dont think the vac advance is your prob, you could vary the initial timing, advance or retard a few degrees to simulate the timing setting it could get if you adjusted everything for vac advance, but doubt that would have any effect. I assume any vac lining going to the GR setup is plugged and its not leaking.
Sounds more like mixture related which 'could' have something to do with a relatively small motor and large mixer.....just speculation. or plug gaps havent been adjusted closer for gas?
Not quite sure of all the reasons for not having as much vac advance on a gas setup, most installers say you dont need it - though I suspect its easier for them than getting the dizzy setup properly. Apparently lpg requires less mechanical advance and to offset this the vac advance is disconnected in a budget setup. I had the dizzy on my 202UC recurved to suit my cam, lpg etc(I dont know how scientific they were about it), it runs less mechanical advance and about the same vac advance, so the intial timing setting is at 18deg.
Have ran my 173UC with both the vac advance(normal petrol amount) connected and disconnected, couldnt really notice any difference in driveability at all. Possibly if I did an economy trial on it might have seen a difference. In all I dont know if its worth spending the money on getting a dizzy recurved, the differences werent obvious to me.

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#3 _73LJWhiteSL_

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Posted 12 December 2005 - 09:43 AM

They did dyno tune it when they installed it, and it definately does not have vacum advance, the dizzy is not connected to anything.

From what i understand they choose the right mixer for the job, but i don't know. I was looking at a GRA.400 from ebay, but they told me it was too big for my stock 173.

I am running the commodore electric ignition with my plugs regaped to 1.3mm for the ignition. The ballast wire has been bypassed as well so the coil has 12V at all times, regardless of cranking or running.

I am planning on building a mild 202 sometime in the next 12 months and when i do that i will get an electronic dizzy recurreved for the cam.

I guess part of my wanting to connect vacum advance is to hook up the valve lube kit that i got when i picked up the car. I have heard gas is a lot harsher on soft valves than even ULP or PULP is, so i was thinking of running the kit just in the interim untill i get the 202 in as i will put hard valves and valve seats in the 202.

Steve

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#4 _devilsadvocate_

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Posted 12 December 2005 - 10:37 PM

If dynotuning it was part of the job, Id be taking it back to them and getting them to sort it, the dyno isnt just for getting max power, its for simulating typical driving scenarios and adjusting. The GR units have some finicky jetting science in them to setup properly, perhaps the just overlooked take off performance.
Re plug gaps, id only using 1mm on lpg with electronic ign and 0.8 with points.

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#5 _CHOPPER_

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Posted 14 December 2005 - 06:21 PM

I am having a slight problem when reving and taking off from idle. When i put my foot on the accelorator when the car is idling it hesitants, and then revs fine. It doesn't do this when you are moving, even if you have your foot of the accelorator. I am thinking maybe something to do with vacum advance seeing as i was told that i don't need the vacum advance of the dizzy and so it is connected to nothing.

thanks

Steve

Sounds like it's running lean in the LPG mixture. That's the most common cause, but there may be other factors. Return to installer and talk to them.

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#6 _73LJWhiteSL_

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Posted 15 December 2005 - 02:35 PM

Thanks Chopper, thats been my thoughts as well.

Steve

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#7 YiriSS

Forum Fixture

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Location:Melbourne
Joined: 08-November 05

Posted 17 December 2005 - 01:24 PM

steve ,

take it straight back to them and tell them to finish the job off properly!

it should be smooth power in any rev range with the gas research throttle body!

if they are not capable of finishing it off, pm me and i will tell you what to do !

with the plugs, gas seems to like a colder range!

cheers

mick

Edited by YiriSS, 17 December 2005 - 01:26 PM.

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#8 _73LJWhiteSL_

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Posted 18 December 2005 - 01:18 PM

Thanks Mick,

I have to take it back after 2000ks for a check up (which will come up this week anyways) so when they do that i will get them to fix the rest up.

I pulled the #1 plug out last nite, it was a nice grey sort of colour so i think it is running alright. I will look into some colder plugs.

thanks people.

Steve

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#9 _devilsadvocate_

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Posted 18 December 2005 - 06:40 PM

Yes, good pt about the colder plugs, I run the ngk bpr6fs which is one range colder than the bpr5fs. Dont think that will be the cause of your prob, running the colder plug is predominantly to eliminate any preign probs. Not a priority to replace them straight away, just dont have the timing set on the edge, youll probably find that your plugs will last for ever now you're on gas though!