Carburetor feedback needed

I’m new to the forums.  I recently purchased a 1982 F250 4x4 6.6L with 139,000 miles.  It had a single owner and was pretty well taken care of.  Mechanically, it’s sound but some of the work done over the years was poorly handled.  I have some records on what was serviced but no idea why certain things were done the way they were.

The truck has many minor issues but there are a few keeping it off the road regularly.  These are: high and rough idle, sticky throttle, a/c is intact but doesn’t work, gear box/power steering/lower steering shaft are shot.

Today I spent a few hours trying to fix the idle issue which I suspected was partly timing related.  The factory setting was 3° of timing.  I bumped that up to 22°. I’m still not sure this was right but the roughness in the idle is now gone. I also managed to get the idle rpm down around 800 which is what the factory sticker listed.  A lot of people, here and elsewhere, state that without the smog equipment the timing needs to be bumped.   Many people also suggest increasing the timing until you start to hear engine pinging and then back off 2°.  I never heard any pinging but after small increments, 22° worked well.   My goal is a balance of fuel economy and power — I’m not racing just hauling stuff in the bed.

The two things I’m still working on are the sticky throttle and some minor acceleration hesitation.  The truck will start cold around 800 and after it warms up can creep up around 900-1000.  It also seems to stick in the same range at times when accelerating.  I’ve checked the linkage for issues.  It seems fine and I’ve lubricated it several times with chain and cable lubricant — that has helped some.  When it does stick like this, punching the pedal usually releases it.  Forcing the throttle linkage by hand also works and it doesn’t take much force.

As for the hesitantation in acceleration, the timing increase helped a lot.  When I first got the truck, it would frequently die accelerating from a stop or when trying to accelerate to heavy.  Some fuel treatments and a better fuel filter helped resolve some of that but the timing made an enormous difference.  The only hesitation now seems to be when accelerating from a stop.  The acceleration begins immediately and with good response but takes a quick dip and then picks back up as excepted.

The carburetor concerns me in general. This is the second rebuilt carb the previous owner put on it. The first one was done with a new main fuel tank and fuel pump.  The previous owner replaced the fuel filter at the carb right before I got it. Within a couple of days I had to clear the bowl of Teflon tape bits.  I’ve read that different jet sizes were available on the Motorcraft 2150. I think mine may be undersized for this engine but I’m not certain.  I am considering rebuilding it myself but first I want to exhaust my other options and make sure this carb is properly sized.

I’d love to hear your thoughts on these things. I’m curious what others have done or experienced in these situations.

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Wow!  22 degrees?  That is WAY too much for a 400.  Did you have the vacuum advance line pulled and plugged when you set the timing?  The M-Block engines are prone to run-on when you turn the key off, and too much initial timing seems to contribute to that problem.

One thing that usually causes problems with these trucks is cracked vacuum lines.  The addition of air increases the idle speed and frequently causes a miss if it is near one cylinder.  So I'd check 100% of the vacuum hoses very, very closely.  And maybe do the "smoke" test where you block off the carb and puff smoke from a cigar into a vacuum line - like the one to the brake booster.

As for a changing idle speed, a cracked vacuum line can cause that as well.  But another thing that will do that is a worn casting on the carb where the throttle shaft goes through.  That allows the throttle plates to hit the bore differently each time you close the throttle and the throttle will hang before hitting the throttle stop.

Anyway, I'd start with the vacuum lines.  I think you have a vacuum leak that is causing all sorts of havoc.

Gary, do the 351M/400 engines develop slipped balancers like other Ford engines? I think I would start there then check for timing chain slop. We are talking about a roughly 41 year old vehicle.

Bill - They absolutely do!  The one on Dad's 351M was cocked at an angle when I got it, meaning the outer ring had come loose from the inner one.

So you are right, the balancer has probably slipped.  So I'd bring the #1 piston up on TDC, using either a piston stop or some such, and check the balancer.

Some of this is beyond my current understanding.  I believe I can check for vacuum leaks and figure out the smoke test.  When you say to block off the carburetor, are you referring to the air horn?  Can I isolate non-essential vacuum, like A/C, vents, etc., temporarily?  There are still some bits and pieces left over from the smog but I don't think any of it is still hooked up.

I've never heard of a slipping harmonic balancer.  I have seen piston stop tools and I think I can handle that.  After that, I'm not sure what to look for on the balancer.

I have changed the vacuum hose for the vacuum advance on the distributor and the PCV valve.  The hoses definitely look old but none have fallen off when prodded.

Could you suggest a range for the timing since 22 high?  The factory sticker states 3 and the balancer is marked at 3.  When I started, the timing was set at 6.

The smoke test needs every port either connected to something or blocked off.  So you'll need to pull the air cleaner and fashion a way to block off the top of the carb, like a plastic lid to some container with a hole in the middle and it pushed down over the stud.  And yes, things that aren't in use can be left disconnected but their ports on the engine need to be capped.

Then you get a cigar and start puffing smoke into a large vacuum hose, like the one to the brake booster.  Soon, if there are leaks, you'll see smoke coming out.

As for the harmonic balancer, it is made up of a large center hub, and an outer ring that is supposed to be bonded to the hub via rubber.  But over time the rubber lets go and the outer ring shifts.  And since the timing marks are on it, your timing seems to change - but it really doesn't.

So use something like a piston stop and find TDC on #1.  With a stop you roll it gently one way until it stops and mark the balancer where it meets the timing pointer.  Roll it back the other way until it stops and mark the balancer.  Half way between those marks should be your TDC mark on the balancer.  If not it probably has shifted, although being off a degree or so isn't a problem.  But if you are off 10 degrees then the balancer has slipped and needs to be replaced.

Initial timing of 10 to 12 degrees BTDC is common on these engines.  Some will take 14 degrees but anything more and you are asking for pinging and/or hard starting.

Here is what a slipped balancer looks like:



This was in 2011 when I was converting the truck to MAF/SEFI

I was wondering what the rubber/gasket looking stuff was around the harmonic balancer.  I have never noticed that on a balance before.

Could you recommend a piston stop tool?  I don't currently have one and I can't decide between the whistle style on another one.  I'm concerned my accuracy may not be good enough with the whistle.

You may well have a slipped balancer - especially given the rubber that's sticking out of it.

Here are several piston stop tools on Amazon.  And I think a stop is better than a whistle.

If you just want to check that the timing marks are correct .

You can use a pencil in the spark plug hole while feeling the piston with the pencil, and bring the number one cylinder up to TDC on the compression stroke, and find the spot where the piston doesn't move and check if your marks are on.

 

I may try the pencil method because I have plenty of those lying around.  I think I'm going to locate TDC first and compare that to what I have on the harmonic balancer and my current timing before I go too much further.  I'll let yall know what I find out.

I was able to get a whistle quicker than a any of the other style tools.  Between that and a pencil, TDC seems to be around -7 degrees on the harmonic balancer's indicator.  That puts me around 15 degrees of timing.

If you are off 7 degrees today you'll be off more, or less, tomorrow.  Once the outer ring lets go it walks around and may eventually come completely off, destroying things as it does.  So I think it is time to replace it.

As an example, a friend of mine had an Opel Kadett in the 60's.  Someone had installed A/C and then he'd done a tuneup.  After the tuneup it ran poorly so he eventually brought it to my father.  Turns out that every time the A/C compressor came on it slowed the engine so rapidly that the outer ring of the balancer slipped and the indicated timing changed.

I'm not saying that yours is changing that often, but I do believe that it will change and the ring may eventually come off.  And that's a bad situation.  So I'd change it now.

I definitely want to replace it. The potential damage it could cause concerns me.  I know I’ll need an impact wrench and a puller.  I’d also like to inspect and potentially change the front main seal at the same time.

I think this is definitely something I can do myself. I’m still researching options for the balancer.  I think a stock replacement should be fine for my needs. I see that Dorman sells what appears to be pretty close to the original.

I have a Dorman balancer on my truck since 2008 and it hasn't caused me any trouble.

Often you can "rent" a puller from your local parts store, if you buy the part there.
Not much point in purchasing a specialized tool for a one off job.
But a 15/16" deep impact socket is a good thing to have, even if you just use it to turn the engine over.

I would definitely change the FMS at the same time.
Be sure to grease the lip so it doesn't start dry on your new damper.

I didn't have any trouble finding the Dorman balancer.  Did you replace the washer and bolt?  I've seen many people recommend they both be replaced.  I am having a hard time finding them.

You probably aren't asking me, but I've never replace the washer or the bolt and have not had problems.

I did not replace the bolt and washer.
They weren't badly corroded and came out fine for me the few times I've had my timing cover off to replace the timing set.

Perhaps you don't intend to go that deep, but it might be wise to check if there's considerable slop in your cam timing?

I need all the feedback I can get!

I would like to check the timing chain while I have the balancer off.  From things I have read, if I remove the timing chain cover, I might have to pull the oil pan to get it back on.  I'm pretty sure that will require pulling or lifting the engine, and I can't do either of those currently.  Those are things I may have to wait on my mechanic for.