flame back fire through carb

[B-Hive]

Hi

Wont bore you all with all the lead up details, but in a nutshell the carb needed a look at because car would begin to splutter and miss after idling for about 30 seconds.

After an initial fiddle the car now struggles to stay running at anything below 2000rpm and when you do release the throttle and it coughs back through the carb and also shoots a flame back through..

Is this likely too much fuel pressure from the feed line (pushing past the needle valve) or is it more likely to be float too high from possible bending of the tabs when replacing the top of the carb..

How important is the fuel return metering. My carb does not use the standard fuel return outlet on the carb but instead has a t-piece on the inlet side that has a metered orifice back to the tank..

Really want to get this right or full on engine fire could result..

Thanks

[Way2go]

It sounds like your ignition timing is way out. If the timing is OK then you may have a burn't inlet valve/seat which you could detect by doing a compression test on each cylinder.

[Gibbo2286]

Firstly thoroughly clean the carburettor, this is a symptom of a sticking carb piston or blocked jet causing a 'flat spot' don't make any adjustment to the float level it won't help. Gibbo.

Should also suggest that you check the diaphragms on the carb for punctures/leaks

[B-Hive]

Ignition timing is fine as it ran fine prior to the fiddle (except for the struggling/splutter after about 30 seconds idling). Not valves again for the same reason.

As much as you say dont touch the float, I'm thinking I may well have bent one of the floats up down or sideways. as this issue only occured after lifting the top off the carb

[Tim Leech]

could it be the Autochoke sticking on and flooding it?

[citronut]

usual symton with floats to high is hard startting when engine is hot, are you sure the cam belt hasnt jumped a tooth or two,

as Way2go says certainly sounds like ignition fault to me,

or did you leave a jet or two out,


regards malcolm

[B-Hive]

are you sure the cam belt hasnt jumped a tooth or two,

as Way2go says certainly sounds like ignition fault to me,


regards malcolm

I always resist jumping to something that hasnt't been touched. The only thing I "played" with was the carb and that only involved taking the top off..

Now it does sound like a timing issue..I know it happens often that one fault can occur at the same time as rectifying another, but it kinda goes against my logic grain..

I was actually just logging on to see if the timing belt can slip one notch without calamity. Why I ask is now if I use the vacuum advance to manually advance the ignition, things are much improved in terms of idling and revving..(notwithstanding that it baulks and bogs down and almost dies if you need some moving power from it).

So yes it does sound like ignition ..I just can stand how this issue occured only after I popped the top off the carb..

Hoping that might also explain the extra din from the engine..

Just had a thought.. my initial mild issue may itself have been from timing having slipped on tooth..maybe it's now slipped 2 teeth.

[Gibbo2286]

It's very unlikely that it's slipped a tooth, I go back to what I said in my previous post, this is most likely a flat spot caused by a carb problem.

Difficult to explain without a picture but.....

With the air filter off and the engine stopped (don't do this with it running, you'll burn your eyebrows off) look down the primary venturi of the carb, there's a tube (the pump jet) that loops over and points straight down the middle, operate the throttle lever and you should see from that jet a good stream of neat fuel, if you don't or you get just a dribble that's your problem.

Take the lid off the carb pull out that tube and blow it out to make sure it's not blocked, if it's not blocked and you still can't get a good flow through it you'll have to look for why.

On the side of the carb you'll find the pump that supplies that jet, it's a square plate held with four screws with a plunger in the middle that's pressed by the throttle linkage when it opens, behind that plate is a diaphragm, if it's punctured the pump won't work and you'll also get erratic running because it lets air in and weakens the mixture.

That's all I can advise from this distance, best of luck. Gibbo.

[B-Hive]

It's very unlikely that it's slipped a tooth, I go back to what I said in my previous post, this is most likely a flat spot caused by a carb problem.

Difficult to explain without a picture but.....

With the air filter off and the engine stopped (don't do this with it running, you'll burn your eyebrows off) look down the primary venturi of the carb, there's a tube (the pump jet) that loops over and points straight down the middle, operate the throttle lever and you should see from that jet a good stream of neat fuel, if you don't or you get just a dribble that's your problem.

Take the lid off the carb pull out that tube and blow it out to make sure it's not blocked, if it's not blocked and you still can't get a good flow through it you'll have to look for why.

On the side of the carb you'll find the pump that supplies that jet, it's a square plate held with four screws with a plunger in the middle that's pressed by the throttle linkage when it opens, behind that plate is a diaphragm, if it's punctured the pump won't work and you'll also get erratic running because it lets air in and weakens the mixture.

That's all I can advise from this distance, best of luck. Gibbo.

Thanks for that but its more than just a "flat spot". I have checked that pump jet as you suggested and it has a strong steady flow of neat fuel down into the primary venturi.

If I'm getting backfire (literally) through the carb it means that theres still fuel in the pot and being ignited with an inlet valve still open. As I said i dont get the backfire issue if i advance the timing, but this is not the solution. How this all occured by taking the lid off the top of the carb just baffles me. If it helps too the backfire occurs only on quick throttle release, and in order to get the engine to rev i really have to baby the throttle and feed it in slowly

[B-Hive]

Hi



How important is the fuel return metering. My carb does not use the standard fuel return outlet on the carb but instead has a t-piece on the inlet side that has a metered orifice back to the tank..

Really want to get this right or full on engine fire could result..

Thanks

I'm quoting myself here because (touch wood) I have cured the problem. Our Australian delivered cars, with all their wonderful pollution gear, has a set up on the carb in as much as the fuel return outlet is blocked and the inlet hose has a metered return t-piece for fuel feed and return.

This part is apparently absolutely crucial to the correct running as without it all calamity ensues as I witnessed. The original t-piece snapped on disassembly.


So yes I placed an old carb jet into the return hose and hey presto back to where I was before. I am even thinking that my initial idling die/surge problem has been solved as a result of me examining every pollution vacuum hose etc..

So fixed...thanks for everyone's input.