Spark plug problem:

[Anonymous]

Hi i have an XD falcon 250 Crossflow, its been worked, 30 thou over pistons its stroked, 3.3 rods compression is 10.5:1. I started off with a 600 holley. that was way too big i was getting flat spots getting bogged down low.. and lots of pre ignition, it would turn off sometimes. The block was deck to 0. Cam is a camtec stage 5

I then put on a 450 holley, i have had better economy and performance out of it but still down low it boggs, but i think thats cause of my gear ratios 2.92, im going to go to 3.5s.

I have another topic on PRE IGnition: but my subject now has got to do with a spark plug.

Since the motor was built cylinder number 3 from the front to the back of the motor in the engine bay has been having some trouble... the spark plug is coming out with all this all this excess stuff on it Lots of gathered stuff all over the spark plug... the rest of the spark plugs are fine... at first i thought it was excess carbon building up in that piston from the 600 holley... i have changed the spark plug twice with the 465 on and im still getting the problem.. Someone has suggested i put a warmer spark plug in. I have gone from a bp5es to a bp4es. I have been told this could be an oil control ring or it could even be the piston scuffing.

I have done a compression test on all pistons.. all come up with around 160. does anyone know the stock compression of each piston on a 250 crossflow?

Im going to let it go a bit with this spark plug and see what happens.. Does anyone else know what kind of problem this could be?

 

[Anonymous]

the bp5es is an NGK I presume? these are the best plugs of all to use. what colour is the deposit on the end of the plug?

 

[Anonymous]

could it be bad manifold distribution of fuel? what brand and type of manifold are you running on this engine?

 

[Anonymous]

believe it or not, I would run a rochester on this engine before a holley as the rochester will have better midrange due to it's air door system (intake velocity=torque=horsepower) and better mixture control due to it's needle metering system!

 

[addo]

A Dualjet or Varajet or Q-jet?

 

[DYNOED250]

QUADRAJET :> THere a great carby on a 250 with a 4 barrle... ujust gota get the tension on the secondardy flap right.. great fuel eccon.

 

[Anonymous]

IM running a redline manifold.. as it was all i could find. I dont particularly like it because i think it doesnt distribute the petrol properly. I think it distributes it unevenly

Im running a warmer NGK spark plug and trying it out for a while to see if this makes a difference. I have been having some pre ignition or detnation where the motor would not want to turn off... I found out that this problem was caused from fuel. I was running it on 98 octane and even with an octane boost it didnt like it.

Now i am running it on 100 octane Optimax the new one with 5 % ethanol and it is running a lot better and switches off smoothly. I took the spark plug out the warmer one BP4es and it seems to be fine.. just blacker then the rest of them.. As mentioned before i think this has to do with the manifold... or the carb might require a little more tunning

The soot that was on the one spark plug.. is a build up of stuff. Like thick crums that have stuck to the spark plug.. IM hoping that if my motor behaves properly now with this 100 octane that the spark plug will to.

I will then go back to the BP5es on the cylinder and see what happens.

 

[Anonymous]

the rochester quadrajet off a s.b chev (did they come on 308's?) is what I would use before a holley. if they came on a 308, I would use that. 253's came with a small 2 barrell stromberg which would be insufficient.
pity about the manifold as this is what I think is the cause of the problem as only one cylinder is running rich and it just also happens to be one of the cylinders which is directly under the carb for the least resistance for the fuel to travel along. some devcon or a welder and some experimentation might come in handy if this the only manifold available. maybe some longitudinal ribs on the inside base of the plenum to channel some fuel away from the affected cylinder. I thought that a cain manifold was/is made but I don't know if it is still being made.
the redline manifolds can be a bit shitty as I purchased one for dcoe triple webers and there were port mismatches requiring devcon and the manifold face was crowned by 28thou (like someone had not tightened down the manifold in the machine before facing it-good one!)
as far as the plugs, bp5/6es's will do the job. I think 4's will eventually be too hot.
the running on can be solved by sourcing a shutdown solenoid from the wreckers which either opens the throttle slightly on shutdown (ie XD) or opens a port to allow air into the manifold and prevent run on. it is caused by a lean mixture. to set the idle mixture, i have found if you pump the brake pedal when the engine is idling, several things will happen. if the mixture is too lean, revs will drop. too rich and the revs will rise. correct and the engine will hunt at the same idle RPM. this happens because each time the pedal is pushed, the brake booster admits a small amount of air into the intake manifold.
persist and then enjoy.

 

[Anonymous]

Very Interesting! Thanks for that ill have a fiddle around...