Backfire through the carb

[joebe1]

998 engine, hs2 carb, new coil, plugs, leads condensor, points, When u press the pin to lift the piston in the carb it revs slightly and drops back as it should, Timing light is brokin, but when it warms it seems ok, When u take it out the road she s dead in power low down bt not bad when u get it up the revs, but its poppin and bangin when u change gear, Accordin to the book it 4 degrees before TDC igition timin, Any ideas??????????????

[Merlin]

running lean I would say

[mad-mini]

what does that mean???

How do u fix that???




Steven

[Billy]

Adjust the carb to make the mixture richer. Check the Haynes manual.

[THOMAS]

Get another timing light,sounds like timing.

[keith]

there's a spring-loaded brass nut under the carb, that holds the fuel jet in place. turn that clockwise to lean out the mix, anti-clock to make it richer.

without moving the throttle turn until the idle is smoothest & and fastest. the re-set the idle speed to +- 900rpm and then turn the adjusting jet 2 flats (1/3 of a turn) leaner.

[joebe1]

Sound job, its only somethin simple, Was thinkin last nite, i no the head gasket was gone not so long ago, but i dont no how well, could poor compression have anythin to do it aswell

[swalker]

Set the timing static only a std bulb needed. Place it between gnd and the -ve of the coil, turn the engine over by hand. When the light comes on that's your timing. It should be 2 less than that at tickover.

[joe f murray]

id say its timing all right but i would suggest you get it done right cos my engine was running fine when i built it but after a few weeks started making noise . turns out cos the timing was so far out it done in the big end bearings so had to rebuild again. its up to you do. any good garage should be able to time it for you only takes about 15 minites and the power difference is unreal.

[Merlin]

[quote="joe f murray"]id say its timing all right but i would suggest you get it done right cos my engine was running fine when i built it but after a few weeks started making noise . turns out cos the timing was so far out it done in the big end bearings so had to rebuild again. its up to you do. any good garage should be able to time it for you only takes about 15 minites and the power difference is unreal.[/quote]

I'm Sorry Joe this is going to sound very rude of me but who ever told you, you need new big end bearings because your Ignition timing was wrong was eider completely out of his dept or was taking you for a ride. I have been build engines for the guts of 10 years now and never in all that time have I ever heard let alone seen an engine with failed big or Main bearings because of incorrect Ignition timing the Piston would have failed hours before the bearings would be effected.

an if the engine was advanced enough to cause a Piston failure the car would be almost Imposable to drive not as you put it "Running fine and then making noise"

[kona]

there's a spring-loaded brass nut under the carb, that holds the fuel jet in place. turn that clockwise to lean out the mix, anti-clock to make it richer.

On my hs4 Clockwise richens the mixture?

[keith]

On my hs4 Clockwise richens the mixture?

moving the jet up towards the needle weakens it.... away from the needle richen's...

[Deadly Dave]

The problem sounds like timing to me. Adjust your points first before you do timing though. The best way to do the points is with a dwell angle meter.

[joe f murray]

id say its timing all right but i would suggest you get it done right cos my engine was running fine when i built it but after a few weeks started making noise . turns out cos the timing was so far out it done in the big end bearings so had to rebuild again. its up to you do. any good garage should be able to time it for you only takes about 15 minites and the power difference is unreal.

I'm Sorry Joe this is going to sound very rude of me but who ever told you, you need new big end bearings because your Ignition timing was wrong was eider completely out of his dept or was taking you for a ride. I have been build engines for the guts of 10 years now and never in all that time have I ever heard let alone seen an engine with failed big or Main bearings because of incorrect Ignition timing the Piston would have failed hours before the bearings would be effected.

an if the engine was advanced enough to cause a Piston failure the car would be almost Imposable to drive not as you put it "Running fine and then making noise"

not rude at all . but i was given that info by mervin johnston. thought he might know what he was on about since he has been racing and fixin minis for the last 50 years.

[joebe1]

Had a look, i noticed the coil was arking which was causing a missfire, got a light today, i was fairly close by ear but there was a small bit of an adjustment needed, and i richened the mixture slightly, seems to be goin much better, but i ll see what its like from cold tomorrow cheers lads,

If the timing was too far advanced it would cause early firing of the plugs which would burn a hole in a piston, however if the bearings were nt fitted or torqued correctly could have caused ur problem

[swalker]

Did you clean it well before the build? If there was dirt in the oil galleries that could do it, or the oil relief I have seen get stuck open after a build.

[Merlin]

[quote="joe f murray"][quote="Merlin"][quote="joe f murray"]id say its timing all right but i would suggest you get it done right cos my engine was running fine when i built it but after a few weeks started making noise . turns out cos the timing was so far out it done in the big end bearings so had to rebuild again. its up to you do. any good garage should be able to time it for you only takes about 15 minites and the power difference is unreal.[/quote]

I'm Sorry Joe this is going to sound very rude of me but who ever told you, you need new big end bearings because your Ignition timing was wrong was eider completely out of his dept or was taking you for a ride. I have been build engines for the guts of 10 years now and never in all that time have I ever heard let alone seen an engine with failed big or Main bearings because of incorrect Ignition timing the Piston would have failed hours before the bearings would be effected.

an if the engine was advanced enough to cause a Piston failure the car would be almost Imposable to drive not as you put it "Running fine and then making noise"[/quote]

not rude at all . but i was given that info by mervin johnston. thought he might know what he was on about since he has been racing and fixin minis for the last 50 years.[/quote]

Its fair enough and he may well be building engines 50 years, but that still does not make it possible for over advanced Ignition to cause Main or Big end Bearing failure, I have literally seen engines with 2 Pistons completly Melted (as in missing) from over advanced Ignition and the crank in perfect condition.

As Swalker has said it is much more likely that poor engine cleaning or incorrect fitments caused your problem,

A very common problem I see that causes this is people not refilling the Oil filter on a new engine build, this allows a dry wipe bearing to accrue which will fail rapidly.
regards,
Paul.

[joe f murray]

sound. thats me corrected then so. sorry for the incorrect information. hope he got her sorted anyway.