Mixing parts with GRA..

Propane, Butane, LPG, GPL, C3H8, C4H10
C3H8
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Re: Mixing parts with GRA..

Post by C3H8 » Sun Jul 03, 2016 8:06 pm

Just got a reply. Proquip has one in stock if you want to give them a call.

gottago
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Location: British Columbia Canada

Re: Mixing parts with GRA..

Post by gottago » Mon Jul 04, 2016 12:04 am

Hey excellent! Will give them a call. I did glue a small rubber disk onto the flapper valve, that little one right in the fuel inlet that connects to a small tube that terminates beside where the secondary opens. Cured it, no more leaks or hissing but I wouldn't trust it to last.

C3H8
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Re: Mixing parts with GRA..

Post by C3H8 » Mon Jul 04, 2016 2:30 pm

A heads up. I did find out the kit is not cheap. Not sure of the reason as repair kits for most regs similar to IMPCO are reasonably priced. This might be a supplier issue combined with the Canadian dollar being at a disadvantage against the US dollar.

C3H8
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Re: Mixing parts with GRA..

Post by C3H8 » Mon Jul 04, 2016 2:39 pm

I did a little on line checking just for your info and for my own knowledge. I see that Century itself offers the kit for $101 US. Others on ebay have it between 90 and 100 US. Add exchange and shipping and the price here is comparable. A brand new M6 is 350 to 400 US.

gottago
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Re: Mixing parts with GRA..

Post by gottago » Wed Jul 06, 2016 12:09 pm

Yes, a bit pricey but at least available. On the verge of a mail strike here so will get someone to stop in at proqip.
re:
I have to assume the flapper inside the reg inlet you mentioned is the primary seat and it must be leaking which increases the primary pressure to the point that the secondary is force open.
This is a bit of a strange bugger in that there is a very small additional flapper valve right inside the fuel inlet controlled by its own spring and diaphragm. Haven't seen this on any other regulator. That's along with the conventional main secondary diaphragm and spring. On the backside where the two main springs go in is the other.

I have it working now with that little valve sealed properly, enough to realize how finicky and sensitive the gra mixers are to tune. Currently running 14.7 idle - 18.4 afr cruise.. Will need a bit more playing around but very smooth.

gottago
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Re: Mixing parts with GRA..

Post by gottago » Wed Jul 06, 2016 10:33 pm

Ohh boy, bit more tuning reveals a problem.. goes super lean for a short span right off idle. Idles at 15.9 now, 18 cruise, 14 under load but goes so lean it almost stalls out sputtering and near dead coming off idle. . Not so sure that's a regulator problem..

storm
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Location: NSW, Australia

Re: Mixing parts with GRA..

Post by storm » Thu Jul 07, 2016 3:00 am

gottago wrote:Ohh boy, bit more tuning reveals a problem.. goes super lean for a short span right off idle. Idles at 15.9 now, 18 cruise, 14 under load but goes so lean it almost stalls out sputtering and near dead coming off idle. . Not so sure that's a regulator problem..
That's the tip in through the progression circuit.If you have an O2 sensor in the exhaust they have a CTI system which includes a black box and an electric gas solenoid that will inject gas in to remove the stumble. My gut feeling is the progression circuit is to small or the idle port isn't large enough to let idle fuel flow just off throttle.
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Fuel flow requirements calculations viewtopic.php?f=5&t=1638

gottago
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Re: Mixing parts with GRA..

Post by gottago » Thu Jul 07, 2016 10:45 am

That was my interpretation also. I pulled all jetting from the progression hoses and still too lean. If I understand right, its sort of a common problem but you can drill out the idle port to compensate when jetting fails ? That would be the brass fitting in the port ?

storm
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Re: Mixing parts with GRA..

Post by storm » Thu Jul 07, 2016 6:04 pm

I'm sure you can but at the moment I wouldn't because you had it idling at 14.7 (I'm assuming your AFR gauge is set to petrol not LPG) and then you tuned it some more and it idled at 15.9, then you reported the lean stumble. So I'm wondering if the lean stumble is partly because of the leaner idle.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

gottago
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Location: British Columbia Canada

Re: Mixing parts with GRA..

Post by gottago » Thu Jul 07, 2016 10:08 pm

Yes, I'll check that, goes away a bit when richer.. and when timing dropped..
thanks

gottago
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Re: Mixing parts with GRA..

Post by gottago » Sun Jul 17, 2016 11:47 am

Stumble cured by going back to a richer idle. The twin gra system is incredibly sensitive to minor changes and quite difficult to tune but is extremely nice to drive so staying with it for now. The progression hoses change the entire afr curve wildly. Except for the too rich idle the afr is relatively stable and acceptable now. How rich is too rich if just at idle? 12.5:1 compression n/a stainless valves.. some overlap on cam

storm
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Re: Mixing parts with GRA..

Post by storm » Sun Jul 17, 2016 5:52 pm

Is your O2 gauge setup for LPG or Petrol AFRs? If it is setup for petrol AFRs 14.7 isn't to rich, it is 15.5 on LPG and 1.00 Lambda. I, personally, would go far from 1.00 Lambda at idle but that's just me.

I believe the progression circuit on GRAs need a better method of tuning. If you have a backfire and blow the hose off the car will run above progression but wont run at or below it.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

gottago
Posts: 200
Joined: Thu May 24, 2012 7:39 pm
Location: British Columbia Canada

Re: Mixing parts with GRA..

Post by gottago » Sun Jul 17, 2016 11:45 pm

Yes, that is 14 lpg afr. I do not want to run that rich at idle. I have tried both main jets in the kit bigger and smaller. Tried the idle jets and progression hoses but sort of stuck in the middle where it gets worse each way. I guess its time to mill the blank main they sent in the kit.

gottago
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Joined: Thu May 24, 2012 7:39 pm
Location: British Columbia Canada

Re: Mixing parts with GRA..

Post by gottago » Tue Jul 26, 2016 9:15 pm

Well I had a bit of time to retry tuning. I read some other forums and discovered as much as was available. Have to say that gra tuning is just a pitfa. I have decent numbers, performance is quite nice, very nice in spots but... idle rpm has now gone out the window. Closed down as much as possible, 1500 rpm. Tired of using spare time on this so.. adapter to impco is going on next, may still use one gra as the secondary. Feel sorry for those I read about in Auzzie land not finding any decent tuning shops especially for the dual setups. Should have read all that first. Non existent tuning assistance in North America.

storm
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Re: Mixing parts with GRA..

Post by storm » Tue Jul 26, 2016 10:11 pm

There are decent tuners round Australia for GRAs, I'm one of them 8) but I'm not currently working and won't start work in my current location because my place is for sale, but they are few and far between. Problem with stuff like this is remote service makes it really difficult to diagnose things. So many factors come into play and without seeing the parts and not knowing the engine combination everything is just guess work based on possible issues.

High idle, when did this start? vacuum leaks? what have you closed down? base timing? timing curve? how is the vacuum advance setup? what's the mechanical advance setting? if you're idling at 1500 rpm the mechanical advance will be operating making things worse and I'd say the vacuum advance will also possibly be operating as well.

I do agree that GRAs are a pain to tune but once you know how to tune them it's really not all that complicated.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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