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Back-firing

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Hi
I've not been driving my 912 much - round the block at weekends - and it's now coughing at low revs and back-firing at high revs.
Anything I can look at before it goes into a garage?
 
Hi Daisy,
timing, plugs, carbs...

Sounds like it might be timing if it is something new, if not then it may be leaky/blocked carbs or any other part of the fuel/ignition system. When was it last serviced?

G
 
Hi Gavin
Serviced and carbs rebuilt September. I've replaced the plugs. A similar thing happened a couple of months ago after I had taken the revs high. As I coasted down the motorway exit it back-fired a lot and did so for the two miles or so home. It was fine a coulpe of hours later. It starts first-time but doesn't tick-over very well at the moment.
Gary.
 
Don't know. Where will it tell me? The only markings I can find are: JFR4 or 963?

I've cleaned the carbs and it's running a lot smoother and not coughing. It did back-fire - not as much - when I took my foot of the gas when the revs were high.
 
back firing on the over run (foot off gas at high revs) can sometimes indicate air getting in to the system where it shouldn't be. Check all gaskets are good and there are no tears/splits in the fuel lines.
 
Thanks Chris.
There is a tear in one of the gaskets.
Waiting for new ones.

Gavin
My distributor is a Bosche 050. Does that sound right?
Sorry new to this.

Gary
 
Daisy,

Although I've got a different engine, I find if my car's been laid up for a while it runs a bit lumpy, This can be cured by letting the enigne warm up properly then going for a high-revving drive making sure you keep it up over the 3500 rpm mark, it seems to blow away the cobwebs. (not sure what the red-line on a 912 is though, maybe a 4 pot would explode above 3500rpm!![;)])
 
Hi Gary,
050 is an aftermarket distributor, but a good one (and no longer available) so should be fine. Sounds like the leaky gasket might be the culprit as Chris so rightly mentioned.

Here to help if we can so ask away, we are all learning, especially me! [;)]

Oh and I have to ask, why Daisy?

G

Oh and ignore the 6 pot folk, their just jealous of our excellent handling, unlike their cars with their large a*$es!
[;)]
 
[:D][:D][:D] shak'in and ass.....

Are you 100% sure you have the timing correct on the car?

Also rebuilt carbs?? how rebuilt.. if you just changed the gaskets then that's not rebuilt. Rebuilt to new is strip cemical clean, facture test, rebush the shafts and then rebuild the carbs is this what you did or had done..?

Are the points set right? How old is the fuel? is it unleaded ( not a long shelf life on unleaded, my Dad gets my old fuel over winter in his Polo to burn it up for me )

Correct spark plugs ? R Bray sold me plugs and I found out they were too long and kept closing the gaps up...

Keep us informed

Mark
 
I know Daisy is confusing and I don't know how to change it. It's my daughters name and I used it as my ebay name and consequently it became my login everywhere else. It has never caused any confusion until now.
 
Hello
Replaced to the top gaskets, cleaned out the carbs and replaced fuel lines which has improved things a lot but it still backfires. Waiting for bottom gaskets. I also have a 20mm spacer between the carb and the manifold. Why?
 
The spacers are to stop the heat from the maniflods effecting the cards, I gues you are running solxes if you have 20mm spacers.
 
Still could do with more info from you Daisy like the disy number and the plugs you used.

I know some engine stuff and the thing that comes to me quickly is that the back fire at high revs still sounds like it could be


incorrect valve clearances
incorrect timing

Carbs in need of proper rebuilding
incorrect jetting

give us an up date to where you are we would like to help get you on the road!!

can you get us a photo or several of the engine email them to me direct if you need to.

don't worry we all were newbie's to these at one stage. When I forst started to play with them I was looking for the water filler bottle[:D] joking......
 
Jon D has delt with Del's I have had Solxes and webers. If all else fails call Andy the 912 tec bod for the club in the back of the mag or have a look at Gav's site and look for AJP Engineering.

But get some photo's and somre more details. Then we can impress Andy with what we have all learnt from these flat 4's ...he still wount be impressed....[:D]
 
yes the correct way would be a start....[:D][:D]

er it's difficult to write it all down best thing is get a copy of harry's bit on timing ( pellow ) and find some one with a good stobe gun. with dig read out I am going to buy one as I have 3 flat 4 engines and i think it's worth it. Are you local to me?? Southampton.I can get a copy of detail to you I have a good photocopier in the office I am sure Harry won't mind if it gets your car going..failing that as long as you don't lose it you can borrow on the pain of death my Harry's how to tune your 912 engine video...
 
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