FE390 Head gasket?

[McBrain]

There was a bunch of weird stuff done by the PO, this could be another leftover. I did put a rebuild kit through the carbie a couple of years ago, but didn't replace the jets. I would have started at 1.5 turns on the mixture screw but it must have needed 2 1/8 to get the vacuum right.

Those 68 jets are from the FRONT metering block (front of car) That's with the 2.5 power valve. I will pull the rear and see what's there.

The cam is mild.

What do I rev to when tuning? ~3000.

This is what I will do:
Put #65 jets in the front and #68 in the rear.
Replace power valve with 6.5
Set mixtures screws back to 1.5 terms
I'll also check the fuel pressure.
Tune carbie and set timing.

If there's funny stuff with the timing we'll have to address that.

[barnett468]

The power valve is a 6.5 . 68 msins are mot typically too big fior a 390 edoecially if it has headers. Your power valve could be leaking fuel but this often causes a noticeably erratic idle in a small block engine but less erratic of an idke in a big block. Sone performsnce build shops have a power valve tester but even if it tests hood, the gasket on it could be leaking or the valve could be dry and therefore not functioning properly
 In your case,  since we can not see the parts in person  i would just but another 6.5 power valve and gasket and put a lite coat of grease or wd40 on the gasket before you install it then try number 66 main jets and check a plug after you drive it maybe every 100 miles to see the color, this is providing your choke is opening soon enough and opening all the way and that the float level is not too high, so check the float level as well.

[barnett468]

You must also set the timing to the optimum level. I can tell you how to do that.

[McBrain]

Thanks Barnett. I will try that. Picking up new plugs tonight and ordering some 65 jets and a 6.5 power valve.

If the cause of the issue does end up being carburettor combined with bad timing to cover it, why do we think that it's richer on the RH bank (more exhaust)? And the recent smoking in that one pipe per my original post? Unburnt fuel??

[GLENN 70]

With a 2.5 power valve yes it needed bigger front jets .  I would start with stock carb settings ,eg 65 front jets , 68 rear jets and the 6.5 power valve .  As I said the 670 carbs can run a bit lean from factory and that's hollleys way of saying how good these carbs  are  on fuel .

[shaunp]

how much vac does it have?

[barnett468]

Thanks Barnett. I will try that. Picking up new plugs tonight and ordering some 65 jets and a 6.5 power valve.

If the cause of the issue does end up being carburettor combined with bad timing to cover it, why do we think that it's richer on the RH bank (more exhaust)? And the recent smoking in that one pipe per my original post? Unburnt fuel??

you have not determined that one bank is richer because you did not remove all the plugs.

as i mentioned, the plug with the white porcelain could indicate that water is leaking into that cylinder.

[McBrain]

how much vac does it have?

With the plugs out and the float bowl off: zero! 

I will know when I retune with new jets. I didn't make a note of the vac when I turned in May.
I'm checking rubber plugs, etc for vac leak.
There was some surging when decelerating into roundabouts.

[McBrain]

as i mentioned, the plug with the white porcelain could indicate that water is leaking into that cylinder.

Ah, I missed that in your prev post.
Any check I can do on that cyl other than a compression test?

[barnett468]

Ah, I missed that in your prev post.
Any check I can do on that cyl other than a compression test?

yes, i posted that info earlier as well.

[McBrain]

Ok. Had a look in cyl #3 and there's a couple of mm depth of fluid in there.
Fluid is FUEL

Would there be that much in the cylinder just from it not firing?

[barnett468]

Ok. Had a look in cyl #3 and there's a couple of mm depth of fluid in there.
Fluid is FUEL

Would there be that much in the cylinder just from it not firing?

it would get emptied every time the exhaust valve opens. also, it shouldn't be gasoline because it would have evaporated by now, especially if it has alcohol in it.

[McBrain]

Piston is near the top and both valves closed so not emptied yet.

I would have though it would have evaporated too - maybe there was more before. I soaked a bit on a rag and it's very flammable like petrol. Guess it could be mixed with coolant but then the petrol would separate out.

[McBrain]

When I drained the primary bowl to check the jets there was hardly any fuel in the bowl.

Just drained the secondary rear bowl and the amount of fuel was what you would expect.

Could this indicate a leaking power valve on the front bowl?

[McBrain]

Rear jets are #86 

I'll put the 68s on the back and wait for the 65s to come

[GLENN 70]

Sounds like a front needle and seat problem too . Pull the needle and seat out and  see if you can see anything at the point then tap in your hand  and see if anything comes out . Refit and adjust . Start a bit low not high when you have it all back together . Side view holes must not drip fuel out when running but not too low either ,rocking to car side to side a bit the fuel should dribble out .  I'm thinking it all a carby problem and the jets won't be the main problem , needle and seats problems ,not adjusted correct .  Remember no BP 98 fuel in our old girls .  68s in the front would be ok with the 2.5 power valve but not with a 6.5 . Wow 68 to 86 rear jets .

[McBrain]

Bowl levels should be ok.

I will check the needle and seat.

No BP 98?? I ALWAYS use BP 98 too much octane? What's the issue?

[GLENN 70]

BP 98 can cause the carb to run rich  by flooding and fuel can come out the vent tubes . To many additives and cleaners etc etc for some old carbureted engines ,some not all seem to be effected .  When this happens it will foul the spark plugs    seen it to many times now .  BP is good in late model fuel injected engines .

[barnett468]

Rear jets are #86 

 
 
 
 

 

[GLENN 70]

Are you sure they were 86 rear jets ? Not 68 jets ? .  10 sizes up are max and if it needs bigger jets it needs a bigger carb .  65 front jets are a bit small  and original  but we have to start somewhere .  Later 670 hollleys came with 72 rear jets from memory as 68 were a bit lean . Not sure if the upped the front jets .

[McBrain]

Yep, they were 86 jets. (Would have been 98 if I'd got it upside down!)

A 670 should be plenty for a stock FE390. I think that someone just put in whatever they had , or maybe they were dyslexic and put in 86's instead of 68's.

I'm trying 65 to make sure there is a noticable difference. If it is too lean I can switch up again.

[McBrain]

Done

Put the 68 jets on the secondary.
Fitted new 65 jets and 6.5 power valve on primary
New air cleaner
New plugs NGK Ap5fs
Set idle mixtures to 1.5 turns

Started in half a turn. Choke works great and opens fully.

I ended up leaning the idle mixture to 1.25 turns based on manifold vacuum. I will check the plugs to make sure this is not too lean

Test drove and it drives great

Possibly a bit of pinging. I haven't re-timed it yet. Initial timing is a 20deg which is probably a bit much but that was the best setting prior

No rich fumes from the exhaust or smoking after shut down.

Seems to have done the trick. Thanks for all the help guys!

[barnett468]

I will check the plugs to make sure this is not too lean

Test drove and it drives great

Possibly a bit of pinging. I haven't re-timed it yet. Initial timing is a 20deg which is probably a bit much but that was the best setting prior

If it is too lean it will have a flat spot when you accelerate.

20 degrees btdc at idle, is WAAAAY too much for a 390 unless it has a massive cam or an extremely stretched timing chain. it should be no more than 12 for a moderately built engine.

disconnect the distributor vacuum advance if you have one.

[GLENN 70]

That's great news  . If it stumbles a little off the line you might have to go up in the front jets , 66 or 67 . Timing around 10 -12 deg at idle with vacuum advance hose blocked ,total timing 34 deg should be ok on 98 fuel . Road testing is the best way sometimes and just make sure it's not pinning at any rpm . Anyway it's good to see its running great 

[McBrain]

Yeah!

No flat spots, no hesitation.

I reduced advance to 12-13 initial, 39-40 total. Probably still a bit high but it drives nice as is. I will play again next time I take it out.