i seem to have just developed a bit of a backfire and popping out of my exhaust, only when my foots slighltly on the gas just cruising along at any revs.. all the jetting is correct as ive had it dyno'd a few weeks back, and they they left the jetting as it was cause it pretty much spot on... all the nuts on my exhaust are tight, inlet manifold nuts are tight etc..
so where do i start???
thanks, fabo.....
BizarreModeratorThe artist formerly known as blue74l
Backfire might also be caused by a vacuum leak at manifold or carb I think...
Could a backfire also be caused by very retarded ignition?
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remove and replace the ignition leads one at a time while the engine is running (from the cap). The motor should decrease revs everytime you remove and replace the lead, but you will find that one (or two) leads will make very little difference to the idle when you remove them. This will be the cyclinder with the blocked pilot jet. Remove and clean and it should fix the probs 😉
What HP did you get and where is your Dyno sheet ??
i have been running these jets for a year,with no probs so i dont think itsthe jetting.
i thought inlet leek shows up with eratic idling? ill spray some wd40 around...
ill check the idles as well as of today i felt a bit of a engine splutter down low on occasion...
craig, no dyno sheet,sorry,it wasnt a dyno denamics dyno. dunno what kind of dyno it was but i dont think it prints out HP numbers like the shoot out mode ones..the dyno guy did say its propably 100bhp maybe alil more but thats it... i might take it to one with shoot out mode to see,but not in this 42 degree heat here in perth....lol...
ill have a play saterday and let u knows.. thanks...
As above with blocked or partial blockage of a jet, maybe a small manifold leak, I doubt exhaust leak. Sometimes if the jets are clear the idle mixture screw is holding a little bit of foriegn material, set mixtures again and the movement of the screw will let the rubbish out.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
okay, i pulled all the jets out today and blew them out but the problem is still there...
ill pull the idles out again and give it a few revs when there out, maybe that will blow some crap out.if that fails ill try what matt said.if that fails , could it be a possible blockage in the fuel filter??
BizarreModeratorThe artist formerly known as blue74l
nope,. i was hoping this would be quickly solved as it does it while backing off when the revs are low and also when at a constant speed with my foot just on the throttle cruising along..
okay, i adjusted points and plugs today, all too tight...
pulled the carbs off to take them to a mates to blow some compressed air through them, and thought id pull the carb tops off to check the float levels. one was at 11-32mm the other 11-40mm, would this be causing my problems?.....
BizarreModeratorThe artist formerly known as blue74l
The backfire on light throttle AND backoff is definately a lean condition, mixture screws or jets, but valve adjust should also be done and definately NO exhaust leaks.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
Do you have a fuel pressure regulator fitted ? Any chance the pressure has been altered recently . As I recall fuel presssure on IDF'S is fairly critical (3 1/2 - 4 PSI ??)
