SAAC Forum

Cool

I'll have cold beer waiting for you.

Ross

Come to Australia I'll put you up for free 

Cap and rotor changed also

Sorry forgot to mention that.

I started the topic because it morphed from an earlier one re correct spark plugs and has had me chasing a backfire in my KR.

So in summary:

Engine starts, idles and cruises fine but it backfires when accelerating harder than just cruising.

Car was running fine until i had it stored in a workshop for 3 years slowly getting some work done when it developed a backfire once it was started.

Had the carby rebuilt

Changed points, condenser and coil, set timing, checked number of spark plugs and they're fine no sign of wear or fouling and the problem is still there.

Could be a vacuum leak causing engine to run to lean

Tilt away was fixed by changing the relay but now the relay is working but the tilt away wont tilt back so I'm thinking there's a vacuum problem in the system which could be related back to the backfire.

A couple of guys on the forum have offered some assistance which is much appreciated, thanks Shelbydoug and 1967 eight barrel

So this is the current position, I'm going to chase down a vacuum leak as my next step,

If anyone else has had a similar issue your feedback would be appreciated by me and also to assist for anyone else who may experience the same issue in the future.

Ross

Doug and Keith

I will start a new thread in regards to the backfire because I think this thread has changed direction from spark plugs to carby to vacuum leak

Doug by using my vacuum gauge would I be looking for a drop in vacuum reading and where do you suggest the best place to connect it would be....base of the carby?

Guys, Just as a side step to the carby backfire issue let me throw something out there.....

I had the tilt steering looked at and the workshop got it working. Apparently it was a bad relay.

The backfire problem has started since the tilt was sorted. Now the tilt away doesn't draw the steering to tilt away for some reason yet to be looked at but the relay is working off the door because  I can hear it switching when I push the switch in and out.

If there is a leak in a hose or if a hose is not connected to the vacuum canister on the tilt steering can this cause the manifold to leak so much that it would lean out causing the backfire I'm getting under load??

Guys what size power valve should it be running just in case the wrong size is in it I want to be sure i replace it with the right one?

I do agree regarding the pv howvere I put a new one in before having the carby rebuilt and the problem hadn't changed so I decided to have it rebuilt.

I guess I've got nothing to lose by trying another pv again.

Yes that was my initial thought but I had the carby rebuilt by a reputable builder and tested.

The problem began after sitting for 3 years in a workshop where the guys would start it when they needed to move it and it just idled and fouled itself.

Power valves dont go bad suddenly when not being driven but occasionally started so the diapghram which is the common cause of a bad pv is not the centre of the problem.

I have a mach 1 that suffered similar issues and after rebuilding that carby. The pro b lem continued so I elimated the car by as the problem at bolting on my gt350 715 to the mach 1 and the problem was still there. The cause was found to be fouled plugs.

So this path seems likely to me.

Once I've changed the plugs I'll eliminate that as an issue and get back to you all with my result.

Just pulled plug out of number 1 and found it to be a NGK AP6FS which on cross reference is a either a
Mototrcraft BF22 or BF32

Looks like its too cool for the driving I do.

My plan is to get to it next week.....once I've summoned the courage to tackle the tight fit.

Bob I have BRF42 CU plugs here would they be ok although not concourse??

I can't get the concourse ones here so I may even try the NGK AP5FS as they seem to be a replacement alternative.

Your thoughts??

Hi Bob,

Thanks for your prompt reply.

The car has origina 32,000 miles on it.

It doesnt get driven much at all. Lucky if I do 500 miles in a year and they would be highway miles.

I don't drive it hard so maximum horsepower isn't a priority.

Just the occasional squirt when I take it out and it warms up.

So BF42??

I have BRF42 CU Motorcraft but they are resistor type I think for al later model Australian ford.351 I think

Ross

Quote from: 1967 eight barrel on February 28, 2019, 09:42:34 PM
The issue with BF32's is they are a cold plug and the vehicles usually aren't driven enough. All dual quad cars run rich at idle.  I'll guarantee my ignition isn't weak with the igniter II and matching coil.  The NGK U groove is a much better plug than the BF32, and they are NOT available from the parts store.  Jay Brown and a couple other FE builders will also tell you to stay away from the BF32. If you're competing in Concours, then you might want to run them. Otherwise its plain stupid to waste 7-10 a plug on stock poor plugs.

Mine doesnt run a dual quad as its a KR with the Holley 735.

My issue is it currently backfires underload but drives along ok until I accelerate hard then it goes off with backfiring. Carby has been rebuilt, timing set, new points and condenser, coil is fine so the only thing left is the plugs.

I just want to make sure i put the right ones in due to the difficulty in changing them. If it was my 66 GT350 it wouldn't be an issue as access is easy.

So just to be sure is BF 32 the right ones that won't give me issues??

I bought 2 good spare caps back in 2014 for $200 that means they're worth $5350 now......better than the stock market returns