| Author | Topic |
|---|
Location:
Mackay, Nth Queensland
Registered:
June 2002
|
|
Pinging and Backfiring!?
|
Thu, 25 July 2002 03:31
|
 |
Just a few questions,
I have a modified 18-RGEU with twin 40mm Webers, electronic fuel pump and longer duration cams fitted to an st141 corona.
when at idle it usually backfires, mostly after a hard run and also when decelerating it backfires loudly - mainly when i change to a lower gear and revs high. i've heard that i may need an rpm transducer to stop the fuel pump at high revs or is there another way? Also how can i stop the car from backfiring when idling cause it puts the beast to shame. 
Also another problem is that it pings sometimes. the engine has been compression tested where the first 2 cylinders are at 120psi and the last two are at 60psi - i know these are low but am saving to fix them. could the pinging be from the type of fuel i'm using - unleaded - or has it got to do with the early detonation because of low compression?
One last question, is it possible to upgrade the carby jetters to match a 45/55mm dcoe webber to fit in the 40mm weber with a venturi size of 32mm? i've read that bigger webbers allow more fuel throughput and are suitable for high revving engines such as mine which should peak at 8000.
if anyone has any ideas or solutions please reply,
regards,
jarrod
|
|
|
Location:
Montrose, VIC
Registered:
May 2002
|
|
Re: Pinging and Backfiring!?
|
Thu, 25 July 2002 05:14
|
|
Well, to begin with, any 18r with webbers and cams is never going to idle like a Lexus! But with that kind of variation in compression (120psi aint exactly brilliant anyway, 60 is well below lawnmower class...) shows theres something wrong with your engine. It could well be that theres something up with your valves/head somewhere, upsetting the vacuum to all hell. My suggestion would be to find out whats wrong with your engine, might be time for a rebuild or head reconditioning. Once you've got that sorted, then check out the ignition (what dizzy are you using? does it need a regraph to suit your cams/carbs?) and try to get the thing on a dyno to get the carbs straightened out. Another suggestion would be to avoid running it on regular unleaded, personally I think that older engines seem to run like utter crap on it at any time.
Have you tried a vacuum gauge on it? But yeah, with that kind of compression it's never going to run at all well anyway.
Good luck!
|
|
|
I supported Toymods
Location:
Berowra-Sydney
Registered:
July 2002
|
|
Re: Pinging and Backfiring!?
|
Thu, 25 July 2002 05:19
|
|
Webbers are fun in the way they like to backfire as they are pumping so much fuel through, now its hard to say exactly whats causing this problem but i'll try listing a few things you can have a look at,
first of all your timeing may be wrong, i know with my car if you adjust it to far one way you get pinging where to far the other way and you get it to backfire.
check ignition leads you may find one has very high resistence causing a late spark or no spark.
check you haven't already got the webbers set to rich as when you set a webber up for heaps of fuel for when you are at high revs they tend to pump to much fuel in at low revs which may not all be being burnt,
but you also may find that all your problems is caused by the compression. standard they should have 171psi the maximum difference between clyinders should be 14psi and and the minimum compression should be 142psi so in other words your engine needs major work done to it, don't thrash it which such low compression as you will just cause more damage, and a main thing that affects the combustion in the cylinder is compression if you have something with low compression you want it to have high octane fuel where if you have something with very high compression you want to use lower octane fuel so you don't blow it up. you can't tune your engine as you have such big compression differences what fuel and air mixture might be right for the front two cylinders wont be for the rear two.
in other words either get a new engine or fix it. and your problems should go away.
|
|
|
