Backfire?

This forum is specifically for engine and gearbox posts, please try to keep on topic in any thread to make things easy to find

Moderator: Board Moderators

Post Reply
User avatar
Hawaiis0
Senior Poster
Posts: 4130
Joined: Sun Jun 30, 2013 18:39
Model: Excel SA (No 3); Elite 504
Colour: BRG; Dirty White
Year: 1986
Location: West Oxfordshire

Backfire?

Post by Hawaiis0 »

Hi everyone. What causes back fires into the air box?
Nothing is fool proof. Fools are clever!

Pete Boole
Senior Poster
Posts: 3711
Joined: Tue Apr 04, 2006 21:28
Model: Elite
Colour: Monaco White
Year: 1974
Location: Nottingham

Re: Backfire?

Post by Pete Boole »

Timing usually.

Pete

User avatar
rbgosling
Senior Poster
Posts: 1702
Joined: Sun Jul 04, 2010 22:55
Model: Lotus Excel SE
Colour: Midnight Blue
Year: 1990
Location: Rugby

Re: Backfire?

Post by rbgosling »

Or possibly inlet valves that are worn/broken or not closing fully for some reason.
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2022 MG MG5 EV (not due to be a classic for quite a few years...)
2011 Nissan Leaf (Ragly - EV pioneer, must be due to be a classic one day)

User avatar
bash
Senior Poster
Posts: 2210
Joined: Thu Nov 03, 2005 15:34
Model: Se, V8
Colour: white
Year: 1986
Location: Doncaster
Contact:

Re: Backfire?

Post by bash »

Id go timing too, mixed up plug leads, distributor cap tracking or the infamous rotor arm.
Bash
Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.

User avatar
MetBlue
Senior Poster
Posts: 1401
Joined: Sat Mar 24, 2018 21:00
Model: Elite 74 & Excel 92 (SEish))
Colour: Metalic Blue
Year: 1974
Location: Northampton

Re: Backfire?

Post by MetBlue »

Another cause is juvenile motorbike fun.
Drive down a straight road. Kill the ignition by the switch Japanese manufactures always thoughtfully put on the handlebar grip. A couple of good twists of the throttle. Switch ignition back on.
Now watch the people on the pavement jump as a satisfying 'bang' - and occasionally a flame exit the exhaust 😀
Oh what memories.
Tony
What goes together.... Must come apart.

User avatar
rbgosling
Senior Poster
Posts: 1702
Joined: Sun Jul 04, 2010 22:55
Model: Lotus Excel SE
Colour: Midnight Blue
Year: 1990
Location: Rugby

Re: Backfire?

Post by rbgosling »

MetBlue wrote:
Mon Apr 18, 2022 12:33
Another cause is juvenile motorbike fun.
Drive down a straight road. Kill the ignition by the switch Japanese manufactures always thoughtfully put on the handlebar grip. A couple of good twists of the throttle. Switch ignition back on.
Now watch the people on the pavement jump as a satisfying 'bang' - and occasionally a flame exit the exhaust 😀
Oh what memories.
Tony
Ah - but that causes a backfire through the exhaust! Fill the exhaust with unburnt gasses, then ignite them.

Another good way to get a backfire through the airbox is to convert to LPG. I had an LPG-converted Subaru that used to do that randomly, scared the bejeezus out of me the first few times.
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2022 MG MG5 EV (not due to be a classic for quite a few years...)
2011 Nissan Leaf (Ragly - EV pioneer, must be due to be a classic one day)

User avatar
Hawaiis0
Senior Poster
Posts: 4130
Joined: Sun Jun 30, 2013 18:39
Model: Excel SA (No 3); Elite 504
Colour: BRG; Dirty White
Year: 1986
Location: West Oxfordshire

Re: Backfire?

Post by Hawaiis0 »

I now believe the correct term is SPITTING.

I will go with timing and associated parts first.

Thanks
Nothing is fool proof. Fools are clever!

Marten
Regular Poster
Posts: 127
Joined: Tue Aug 10, 2021 20:38
Model: excel
Colour: red
Year: 1985
Location: NL
Contact:

Re: Backfire?

Post by Marten »

rbgosling wrote:
Mon Apr 18, 2022 12:49

Another good way to get a backfire through the airbox is to convert to LPG. I had an LPG-converted Subaru that used to do that randomly, scared the bejeezus out of me the first few times.
Lean mixture will burn so slow it is still burning when the intake valve opens again. This works best with a fuel injected engine with a large plenum, but you can also melt a nice pair off double barreled Solexes

Post Reply