rattle under acceleration and deiseling when turned off.

[unfamilia 1,938]

Hi I took falcon out for drive and was nice.

Seems to get rattle under decent acceleration and severe deiseling/running on when turn ignition off.

The 250 has flat top pistons

mild cam, shaved and ported head with over size valves.

im running 35 dwell reading and 6-8 deg timing as per specs.

idles smooth in d at 650rpm.

 

im using 95octane fuel and the stock stromberg.

 

Wondering what coukd be.

[VDO 124]

Crossflow or non crossflow..?

[n00bus m@x1mus 465]

Way too much comp for 95 ron fuel, its preigniting and running so hot that its running without ignition once shut off. You will need to run 98 with an octane booster and possibly even drop the timing right out of it. Are you positive the timing marks on the balancer are correct?

[unfamilia 1,938]

Yeah marks are right. Will try 98 and see. What booster is good value

[unfamilia 1,938]

Crossflow

[ando76 4,354]

What noobus said.  You may have to pull some timing out of it or perhaps lock it at 26 - as much as I hate locked timing.  also try the better fuel.

 

You have not indicated what head and how much it has been shaved and also deck height.  With flat top pistons and a shaved C2 head it is really easy to get comp into a x flow - which it sounds like you have if you are experience dieseling. 

[unfamilia 1,938]

Not sure was a 2nd hand engine and he gave me a bunch of receipts that dat to 1997 for head work and pistons were approx 2005 hypertechs

I used inspection down spark plug hole to confirm piston tops. Sump off confirmed brand.

 

how to lock timing

[Mr Polson 10,214]

Look between the intake ports 1-2 for a letter/number (E1,E2,C,C2,D) to tell the head type.

[unfamilia 1,938]

Is that under the rocker cover or on out side? If on outside the there is nothing. Probably machined off

[unfamilia 1,938]

This motor may not be what I need. I need a stockish motor for reliability. If it does ok on 98 (won't know til payday in 2 weeks) then might have to get another or look at 302 for sure.

A head swap could solve it to drop compression too I guess.

[gerg 10,871]

There was a problem with XF series 2 heads having a swirl-inducing wing in the combustion chamber. Detonation was a problem due to the wing having a pointy end and thus a hot spot. The fix was to pull off the head and have the point milled off to make it more of an open chamber. Yours, coupled with the other mods, may be asking too much of even 95 fuel. The dieseling tells us that no amount of timing will change the fact that your mixture is pre-igniting.

[Mr Polson 10,214]

Is that under the rocker cover or on out side? If on outside the there is nothing. Probably machined off

 

See the C2? That's where.

[Clevo120Y 815]

Well with no casting mark on the outside of the head between the intake ports and also running a single barrel strommy I would assume you have the first alloy head or even a cast head? both are an open chamber, are you also still running the points dizzy? to start with I would be setting initial timing at 10 degrees and limit the total mechanical advance to 32 degrees. the fuel cutoff on the carb may be faulty also (if the single barrel had this as I can't remember) either way your pinging and it's either up the octane or limit the timing.

[unfamilia 1,938]

Its xd cast iron head. No mark there so who knows what head it is.

Going to drain the tank and get 10 lt of 98 and try that first.will set timing again and disconnect vac advance.

Not sure how to limit mechanical advance.

 

Otherwise Anyone in the market for a warmed up xd iron crossy lol.

[unfamilia 1,938]

Oh yes points dizzy unfortunately

[gerg 10,871]

You can convert to Bosch electronic very easily. They are a brilliant unit for stock applications. You need to take off about 0.7 mm from the OD of the oil pump drive so it will fit in the block. You need to work out how much total timing your engine needs and work back from there. If it likes 28 deg total, then set it there and don't worry too much about idle timing until you want to start playing with dizzy weights/springs. Vac advance should be connected to manifold vac for best cruise/idle. Your dieseling/knocking might also be carbon buildup, hot plugs or valves. You could try an upper cylinder cleaner like the genuine Subaru one (I've used it to great advantage), or try a cooler thermostat. Also how breathy is your engine? Blow-by gases will cause your problem too.

[unfamilia 1,938]

Its not overly blowing by from breathers. No vapour really but some air as ive noticed from most high comp motors ive had before

[Crazy2287 1,886]

What booster is good value

This one:

[LJDB 103]

i was having similar problems before i decomped my engine alittle. i tried afew octane booster including the one above, i found this one to help with the pinging the best but to costly to use all the time. thats why i de comped mine.

[unfamilia 1,938]

Octane boost my 95 or just dump it and try 98. If no good boost that.

how much is that stuff anyway

[bear351c 10,273]

$20 a bottle.............

 

Cheaper to use 2 head gaskets.

[unfamilia 1,938]

Now ive had this discussion with datsun guy's and they dont belive this 2 gasket stuff. My mechainc says its a cheap fix for a couple years if your not going for outright power. Does it work with the ironhead crossflows???

Or just too dodgey

[bear351c 10,273]

Nah, old bush mechanics trick. You can get copper head gaskets made, whatever thickness you need, may bring down the comp ratio.

 

Just saves pulling the engine out............

[unfamilia 1,938]

Mmmm where to get copper gasket and price. Could be better with the 302 option if it doesn't run ok on 98.

 

Mrs wants me to sell if cant fix. If I sell of part then a 302 might fix it ;-)

[Crazy2287 1,886]

Bottle the 95 and use it in your mower or shopping trolly. Put 98 in.

 

Your 100% sure your timing is right? It's not 180 out or something dumb? Some of them balancers have marks at BDC and TDC, Thats tricked me before on an XG.

 

If you pull that head back off make sure you run the numbers and CC the chambers so you know what comp you have. Then you can adjust it to suit. Better then fkn guessing.