TB42 on duel fuel

Post by **Froon** » Tue Nov 27, 2007 7:28 pm

Hi guys,

I've been having all sorts of trouble with this GQ since I bought it... I took it to an LPG mechanic the week I got it (it wasn't running on petrol when I got it) He fixed it up and it ran OK for a few weeks (barring water getting into the electrics) but as of Sunday, it runs on Petrol but as soon as I let the revs drop it'll stall...

The previous owner tells me that it was working GREAT until he got his carby rebuilt last year...

Was wondering if it is worth replacing the carby or whether the issue might be elsewhere... Just seems like the mix is adjusting itself.

Post by **PGS 4WD** » Tue Nov 27, 2007 9:04 pm

Common problem due to poor filtration, they get a blockage in the idle circuit, have to take the top off carby, remove a brass plug and pull out the idle discharge tube and blow it out with compressed air, have fixed heaps with this problem.

Joel

Post by **Froon** » Tue Nov 27, 2007 9:09 pm

Thanks mate...

Will give that a go on the weekend.

Post by **Black Trol** » Thu Nov 29, 2007 8:41 am

Hey Froon,

My GQ does the same thing every couple of months - idle speed on petrol drops and eventually dies. On each occassion the idle jet (or idle discharge tube)has been blocked. Clean it out like PGS 4WD says and its fine Have replaced filters many times more than I should have too but still the problem persists.

What I want to know is why? My mechanic reckons it might be the residue from the petrol once I have switched over to gas.

David

Post by **Froon** » Thu Nov 29, 2007 1:15 pm

The thing I've noticed about my trolly is that it will run fine while cold, as soon as it warms up it'll stall out.

The idle on the engine is unpredictable too, sometimes it'll idle at the 700rpm mark, othertimes it could idle closer to 1700rpm.

I've had this problem fixed in the past (lasted a total of two weeks before it reoccured)

Honestly, at the moment, I'm looking at putting in a new LPG mixer and carby...

I'm thinking it might be a little more serious than just a blocked line, as it splutters off the mark on LPG and there is a big power dip at around the 90% throttle mark... Seems the throttle return spring is going too, as I back off the throttle completely to clutch in, put the clutch in and the engine will rev out for a couple of seconds... Though this could be a fuel related problem too.

I've blown the top off the airbox a couple of times with backfires (replaced leads, seems fine now) but I'm wondering if I might have some carbon build up as a result... From what I can tell, the leads and plugs have been there for a few months before I got the car.

Post by **dwaynes** » Thu Nov 29, 2007 2:04 pm

Froon wrote:
The idle on the engine is unpredictable too, sometimes it'll idle at the 700rpm mark, othertimes it could idle closer to 1700rpm.

Does anyone know what causes this? as i get this issue now and then

Post by **tj81** » Thu Nov 29, 2007 3:43 pm

BCDD Valve, break it or turn it off, problem then goes away

Post by **ShaneGQ** » Thu Nov 29, 2007 7:25 pm

Mine is back firing through the carby on both feuls, now it wont idle on gas. I can run the gas at full revs while driving, but put it in neutral and drop the revs and she dies.

Post by **dwaynes** » Thu Nov 29, 2007 8:48 pm

tj81 wrote:BCDD Valve, break it or turn it off, problem then goes away

whats a BCDD Valve????

Post by **PGS 4WD** » Thu Nov 29, 2007 9:24 pm

Boost Control Decelleration Device, it bypasses air into the carby to reduce Hydrocarbons on deceleration.

If it runs fine cold, on the choke with enrichment it stilll sounds like an idle mixture blockage, did you fine the bleed I mentioned earlier. Usually when this is the problem adjusting the idle mixture screw has little effect and you have to idle on the hand throttle to prevent stalling.

Joel

Post by **j-top paj** » Thu Nov 29, 2007 11:16 pm

would going to EFI sort out all these problems?

Post by **Froon** » Fri Nov 30, 2007 6:45 am

ShaneGQ wrote:Mine is back firing through the carby on both feuls, now it wont idle on gas. I can run the gas at full revs while driving, but put it in neutral and drop the revs and she dies.

Hey Shane, I had that problem a few weeks ago... Check out the airbox, make sure its sealed, otherwise you're just losing LPG into the engine bay.

Since that happened to me, I found the most useful tool to carry with me in the GQ is a hammer... Saved my butt on the side of the M4 one day.

Also check your leads and plugs for corrosion, they may not be making clean contact and could very well be the cause of your backfires...

Post by **PGS 4WD** » Fri Nov 30, 2007 6:51 am

Going to EFI would but so would a carby rebuild, a quality air and fuel filter and some good sealing around the air filter, EFI is dear by comparison, better though and if you put on an aftermaket system or fit a piggyback ECU to tune it. I know where there is a TB45 computer loom and tank sender/pump for sale, all that would cost less than a MOTEC computer and accessories for yours.

Joel

Post by **Froon** » Fri Nov 30, 2007 6:58 am

I've regularly considered changing to EFI... Maybe its time to have a look into doing so.

Post by **ShaneGQ** » Fri Nov 30, 2007 7:46 am

Thanks Froon I will check it out today. Gas is just being a pain in the ass at the moment.

Post by **Froon** » Fri Nov 30, 2007 8:36 am

ShaneGQ wrote:Thanks Froon I will check it out today. Gas is just being a pain in the ass at the moment.

No worries mate, was the initial cause of all of my frustration, once that was sorted though, the gas has been very reliable.

Post by **j-top paj** » Fri Nov 30, 2007 9:45 am

Froon wrote:I've regularly considered changing to EFI... Maybe its time to have a look into doing so.

it will be better in the long run

dont want to be like simo and constantly fiddling under the bonnet to save a couple bucks but end up spending twice as much in the long run

Post by **j-top paj** » Fri Nov 30, 2007 9:45 am

mousie was telling me he found a efi setup for his tb42 for $500 and he was considering doing it

Post by **Froon** » Fri Nov 30, 2007 10:21 am

Little on the strapped side of things at the moment... will have to wait until after new years as I'll be replacing the front end to end shortly.

Post by **jessie928** » Fri Nov 30, 2007 11:05 am

you dont need to go efi man

just keep the gas in tune, keep the plugs filter and points in good condition.

run it out of gas every tank or every second tank and drive to the gas pump on petrol.

carby is more idiot proof than LPG. a big backfire on a carby is just a backfire, on EFI its probably going to cost you after a few.
Jes

Post by **Froon** » Fri Nov 30, 2007 2:11 pm

Thanks for the advice jess, I'll keep it in mind...

Looks like this'll have to be put on the back burner for a while... Got pulled over this morning and threatened that if a cop was to pull me over again, I would be defected...

So I suppose I better do some work to the thing, bunnings flares, mud flaps are probably good to have...

Post by **PGS 4WD** » Fri Nov 30, 2007 9:14 pm

Gas shouldnt be a problem, the remedies are simple, low resistance leads, electronic igniton of quality, low air gap rotor button, non-resistored spary plugs and a good dyno tune, so as to be sure its not lean as lean mixtures backfire. If you have a 300A with the crappy plastic air filter covers then make a sealed intake for the mixer and run a remote filter, all problems solved.

Joel

Post by **j-top paj** » Sat Dec 01, 2007 11:57 am

Froon wrote:
Looks like this'll have to be put on the back burner for a while... Got pulled over this morning and threatened that if a cop was to pull me over again, I would be defected...

how bad is your GQ? i still havnt seen it.
what did they threaten to defect? isnt it engineered?

Post by **Froon** » Sat Dec 01, 2007 1:45 pm

Its not engineered

Post by **dwaynes** » Mon Dec 03, 2007 4:38 pm

tj81 wrote:BCDD Valve, break it or turn it off, problem then goes away

If any one could help how can this be turned off as i would like to see if it fixes my over reving problem.

Post by **David_S** » Tue Dec 04, 2007 1:16 pm

Froon wrote:I've regularly considered changing to EFI... Maybe its time to have a look into doing so.

Haven't looked back since I went to efi with a Megasquirt ecu. Transformed the old P40 engine.

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TB42 on duel fuel

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