Fordmods Logo

running like a dog when swithced to petrol 

 

Page 1 of 1 [ 8 posts ] 

 
 Post subject: running like a dog when swithced to petrol
Posted: Tue Nov 23, 2010 9:44 am 
Stock as a Rock
Offline

Posts: 118

Joined: 22nd Sep 2007

Location: newcastle
NSW, Australia

I have recently rebuilt a 400 for my 72 galaxie LTD. it has a 780 holley, holley streetmaster lowrise single plane manifold, a 268DEH cam, TMI 9.5 to 1 pistons and 302 closed chamber heads with boss valve springs and 4v valves.
I initially did the aggressive break in on petrol, but after a trip to Newcastle and back where it gobbled up 20 litres of petrol (gave the missus a fright as it ran out 10 meters from the home town servo!!) I decided to refit the LPG mixer/tophat so I could afford to run it. it is a 425 impco and mixer. I now come to my problem. I managed to start it on LPG straight away with no adjustment to the timing and proceded to take it out for a fang. It still starts really wel.l
To my delight it went just as well on gas as it did on petrol. But now when I switch it back to petrol it runs like a hairy goat. you can nurse it up to revs,but give it a hit on the loud pedal and it misses and f@rt until the load goes off it. I have even tried disconnecting the fuel shut off and rehosing it straight in case there was a restriction there,but to no avail. There seems to be enough airflow as it goes well on the gas, but I don't understand how when it is switched over to petrol it is now so poor.
could it be the top hat mixer assembly after all and how do i fix it? i could just disconnect the LPG again and refit the aircleaner assembly and try it to prove a point, but again I don't get how it can have such adequate air flow on LPG and be poor on petrol. Again I have not adjusted the timing in any way. Help.
Top
 Profile  
 
 
 Post subject: Re: running like a dog when swithced to petrol
Posted: Tue Nov 23, 2010 2:59 pm 
Getting Side Ways
Offline

Posts: 6449

Joined: 11th Nov 2004

crsmith wrote:
I have recently rebuilt a 400 for my 72 galaxie LTD. it has a 780 holley, holley streetmaster lowrise single plane manifold, a 268DEH cam, TMI 9.5 to 1 pistons and 302 closed chamber heads with boss valve springs and 4v valves.
I initially did the aggressive break in on petrol, but after a trip to Newcastle and back where it gobbled up 20 litres of petrol (gave the missus a fright as it ran out 10 meters from the home town servo!!) I decided to refit the LPG mixer/tophat so I could afford to run it. it is a 425 impco and mixer. I now come to my problem. I managed to start it on LPG straight away with no adjustment to the timing and proceded to take it out for a fang. It still starts really wel.l
To my delight it went just as well on gas as it did on petrol. But now when I switch it back to petrol it runs like a hairy goat. you can nurse it up to revs,but give it a hit on the loud pedal and it misses and f@rt until the load goes off it. I have even tried disconnecting the fuel shut off and rehosing it straight in case there was a restriction there,but to no avail. There seems to be enough airflow as it goes well on the gas, but I don't understand how when it is switched over to petrol it is now so poor.
could it be the top hat mixer assembly after all and how do i fix it? i could just disconnect the LPG again and refit the aircleaner assembly and try it to prove a point, but again I don't get how it can have such adequate air flow on LPG and be poor on petrol. Again I have not adjusted the timing in any way. Help.


here is your starting point.

 

_________________

PERMANENTLY BANNED

Top
 Profile  
 
 
 Post subject: Re: running like a dog when swithced to petrol
Posted: Wed Nov 24, 2010 7:52 am 
Stock as a Rock
Offline

Posts: 118

Joined: 22nd Sep 2007

Location: newcastle
NSW, Australia

It's got to be worth a lash, but again as i wrote, there should be enough airflow at lower revs on petrol considering there is enough to suit LPG at over 4000rpm. At least at the moment I can leave it on LPG and run it around and save me some money.
Top
 Profile  
 
 
 Post subject: Re: running like a dog when swithced to petrol
Posted: Wed Nov 24, 2010 7:53 am 
Getting Side Ways
Offline

Posts: 6449

Joined: 11th Nov 2004

the carby was never designed to have a gas mixer sitting on top of it.

 

_________________

PERMANENTLY BANNED

Top
 Profile  
 
 
 Post subject: Re: running like a dog when swithced to petrol
Posted: Wed Nov 24, 2010 9:31 am 
Stock as a Rock
Offline

Posts: 118

Joined: 22nd Sep 2007

Location: newcastle
NSW, Australia

None of them do,but they still run dont they? If it was that bad they would never be fitted surely?
Top
 Profile  
 
 
 Post subject: Re: running like a dog when swithced to petrol
Posted: Wed Nov 24, 2010 3:47 pm 
Getting Side Ways
Offline

Posts: 6449

Joined: 11th Nov 2004

it's posible that the mixer has upset the tuning of the carby. Not all this stuff is bolt on and forget.

 

_________________

PERMANENTLY BANNED

Top
 Profile  
 
 
 Post subject: Re: running like a dog when swithced to petrol
Posted: Thu Nov 25, 2010 11:22 am 
Stock as a Rock
Offline

Posts: 118

Joined: 22nd Sep 2007

Location: newcastle
NSW, Australia

fair call. I will be running it on gas most of the time so it will be fine until I take it to my garage for its greenslip inspection. i was going to get them to check the LPG tune anyway, so maybe they can have an informed fiddle. It would just be nice to know if it's something stupid I could fix.
Top
 Profile  
 
 
 Post subject: Re: running like a dog when swithced to petrol
Posted: Mon Jan 31, 2011 9:47 am 
Stock as a Rock
Offline

Posts: 118

Joined: 22nd Sep 2007

Location: newcastle
NSW, Australia

As an update, some one has suggested that the diapraghm in the mixer (the bit bolted to the carby with the air cleaner on it) could be sucking closed causing the stutter down low and it only comes right once the air flow is up there keeping it open. I removed the afore mentioned diapraghm on the weekend and this indeed seemed to fix it. The only thing I haven't done is actually check the vacuum at the manifold as originally with help from this thread thought that it was screwing up the vac signal to the carby. Anyway is there a way to adjust or hold open the diapraghm to prevent it sucking closed at lower revs? It is an IMPCO 425, and it may be to small for the engine, but it should be fine in the lower rev ranges where it is tipping over at the moment.
Top
 Profile  
 
Display posts from previous:
Sort by  
 Page 1 of 1  [ 8 posts ] 

Who is online

Users browsing this forum: No registered users and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

 

 

It is currently Sat Dec 16, 2017 4:51 pm All times are UTC + 11 hours

 

 

(c)2014 Total Web Solutions Australia - Australian Web Hosting and Domain Names