Tune Up - What order?

[Jeff Elliott]

Hi All -

Truck is back together and I'm ready to do some fine tuning... I need to:

1. Adjust valves
2. Adjust idle (lean drop?)
3. Adjust timing (I have removed and reinserted the dizzy so I'm sure i'm off a bit)

Should I do it in this order or should it be 3,2,1 or 3,1,2, etc.?

Thanks!!!

 

[Tancruiser]

3 1 2 is the way I would go ,make sure to adjust the valves with a warm engine.

 

[65swb45]

132.

 

[lc69hunter]

Cold adjust valves.
Set idle so that it stays running, and adjust air/fuel mixture if applicable
Set timing.
Re-adjust idle.
Re-adjust valves on warm engine.

 

[handcannon]

I am not sure what motor you have, but if it has a points distributor you will need to set the points/dwell first as any change in the points opening will change timing a bit.

Don

 

[65swb45]

What did you end up with for timing? Vacuum? Idle speed?

 

[Jeff Elliott]

What did you end up with for timing? Vacuum? Idle speed?

Hey Mark -

I haven't had a chance to adjust valves, etc. yet... Will post here when I do. It may be next week based on how full the dance card is this weekend!

Thanks for checking!!!

 

[Jeff Elliott]

What did you end up with for timing? Vacuum? Idle speed?

Hi Mark - I finally got around to adjusting the valves and setting timing today. Here's how it went:

• First adjusted the valves - I had one or two that were a little out of adjustment but for the most part they were all good
• Then started it up and checked RPM with the timing light - result was 530 rpms
• Loosened dizzy and advanced timing - got to 14.5 or 15 degrees and rpm's were bang on at 650
• Checked vacuum - hovered between 18 and 19 with less variability than it had been having before the valve adjustment and advance
• Test drove - still have stumble when first giving it gas as before but not as bad. Power better and pulls hills at low rpm better.
• Arrived at destination ~ 5 miles away from where I had started and rpms were noticeably lower at idle (at least 100 rpms lower than when I set advance) - didn't have timing light so had to estimate based on tach. Ran ok but much rougher than before... Stumble much worse
• Headed back home - half way home (say 2 miles distance traveled), rpm's back to normal or higher at stop light. Engine now smoother.
• Arrived at home, checked advance and idle speed with light - 17 degrees of advance at 720 rpms. Adjusted idle back to 650 - advance now at 16 degrees.

The "runs right then rough" situation that I described above is the same problem I've been having when I had the trollhole carb on as well. I can't for the life of me figure out what's causing the on again off again issue. I have a super clean gas tank, new fuel filter, freshly rebuilt carb (thanks again for that!), etc. The only thing I can think of is maybe I need to replace the fuel pump? Also thought this might be related to faulty vacuum advance in the dizzy?

Appreciate any advice!
Jeff

 

[thebigredrocker]

Jeff I'm sure 65swb45 will chime in when he get's cell service.

I bet he'd recommend you check your points, make sure they are clean, check gap, then tell him what your dwell angle is.

1.Dwell is the REAL measurement; point gap is only a handy reference.

2. As the dizzy gets older, and the shaft vibrates more, the stated point gap of the FSM bears less and less resemblance to what is required to achieve dwell.

3. In all likelihood, you will have to reduce gap well below factory spec to achieve proper dwell. This increases the likelihood that the points will burn prematurely. I had a customer some years ago whose dizzy was SO WORN that gap had to be reduced to .008 to achieve dwell. I told him I didn't think his points would last a week at that setting. They lasted two.

4. Dwell is preset and optimized in the Pertronix; this is one of the many reasons I like the product so much.

Best

Mark A.

On the contrary, higher dwell=higher spark. While points are closed,voltage is building in the coil. Unfortunately,a small point gap increases the likelihood that the points will arc and burn prematurely. At .008" I wouldn't expect them to last more than a week of daily driving.

Best

Mark A

Think about this. Point gap is an approximation. What you are really after is dwell DURATION. Duration is a function of time and energy. So time is an element, even though not in the way you are thinking.

Check your work with a dwell meter. Not just at idle, but at 1200 and 2000 rpm. Your distributor bearings may be failing.

BTW, I finally put that hardtop glass back on the shelf you inquired about.

Mark

Similar symptoms? —> '71 fj40 carb issues

 

[thebigredrocker]

One more quote

You've got a good carb and dizzy combo. Make sure your dizzy is getting full dwell 38-41 degrees, rather than relying on point gap. Power time the dizzy with tips from the thread on setting timing, and LEAVE IT ALONE!

In the choice between the never-ending search for power,
versus longevity, I choose longevity!

Mark

www.marksoffroad.net

 

[Jeff Elliott]

One more quote

Thanks BigRedRocker - My truck is a '78 so the dizzy is electronic - no points to adjust. Although it could be time for a new rotor button and cap?

 

[thebigredrocker]

Ahh
Not sure this pertains to your dissy, interesting tech here though
Distributor rebuild--Worth it?

Some more dissy info

Some quick facts to help with actual timing settings:

The 79-80 dissy has total mech advance of 20-24*. This number varies depending upon the degradation of the stop pin bushing.
Primary vac advance of appx 18*.
Sec vac advance 6*.

If all 3 advances are available, there could be 48* of advance added to the base of 7*, yielding total crankshaft advance of 55*.

The generally optimal timing for the open chamber cylinder head is 36-38*

This brings up vacuum setup option #3.

Connect distributor sec vac advance to carb ported vac. Giving max advance of 6+(20 to 24), total available 26-30*.
Set base timing at 7*, total crankshaft advance is 33-37.

Rough idle can also be timing scatter. Watch timing mark w/ timing light, see if it moves at all when idling. If there is random movement, then dissy bushings are shot. Common problem on the small-body points dissy.

Really doubtful that the idle solenoid is a problem.

Like Mark said, if the problem persists w/ 2 different carbs and a repaired dissy, it's not the carb or dissy.

The coil or ignitor is the next thing to test. The 78-80 coils are supposed to run w/ a ballast resistor. If yours has been running off straight 12V+ for a while, maybe the coil is cooked. The symptom of dieing after running at speed can indicate an overheated or weak coil.

 

[thebigredrocker]

While reading I saw Jim mention if your dizzy has a 2pin connector it Federal spec and Cal spec has a 3 pin connector

 

[bikersmurf]

Were you checking your base timing with the vacuum advance disconnected and plugged?

16-17 deg seems too much for OEM timing... it's been more than 20 years since I had an F... but I remember spec at less than 10.

 

[bikersmurf]

2F timing question (RPMs)

Per above thread BB is at 7 deg, and should be set there. More info contained within.

 

[65swb45]

The numbers don't exist in a vacuum ( pun intended!)

If it takes that much advance to produce that vacuum, then there is something else going on.

 

[Jeff Elliott]

The numbers don't exist in a vacuum ( pun intended!)

If it takes that much advance to produce that vacuum, then there is something else going on.

Ok, let's try this again as I in fact had not disconnected the advance (though I still think I've got a gremlin somewhere):

• I disconnected vacuum advance and capped at carb
• loosened dizzy and set timing light to 7 degrees advance - adjusted idle speed to get about 670 rpm's. Was able to put TDC mark on flywheel right on the pointer (writing this to ensure I've followed the right procedure with the light). Result was a stable 16.5 - 17 vacuum. Engine ran very smoothly here.
• Then advanced light to 12, set idle speed again to ~670 and aligned pointer with TDC mark - result was vacuum in the 18 - 19 range. Again, smooth running engine. It's the first time I've experienced the "sewing machine" smoothness since I've owned this rig.
• FYI, this truck has low compression. In the 118 - 120 range per cylinder dry.

Here's a video of me starting the truck (note how hard it starts without being given some gas), the vacuum gauge at idle (at 12 degrees of advance), the rpm gauge on the timing light AND the off idle stumble (note sound and vacuum gauge). Would sure like to hear thoughts on what else could be wrong with this thing!

 

[thebigredrocker]

I hear that stumble. Does your innova light give you a dwell? My light looks almost the same a give dwell readout.

Was your engine hot when you performed the valve adjustment and compression check?

Have you checked around the carb base & manifolds for leaks?

 

[Jeff Elliott]

I hear that stumble. Does your innova light give you a dwell? My light looks almost the same a give dwell readout.

Was your engine hot when you performed the valve adjustment and compression check?

Have you checked around the carb base & manifolds for leaks?

No, no dwell readout available (looks like I needed to buy the next model to get that).

Engine was definitely hot for all of the above.

I've checked for leaks several times with several methods (i.e. carb cleaner, cigar smoke into vacuum line) - nada.

 

[thebigredrocker]

If I'm understanding @FJ40Jim's explanation how to setup a 78 dissy correctly using the best option "#3". With your engine revved up and your timing light set to 33-37* you should see your timing mark. If you don't see your mark in that 33-37* range something needs changed. Right now, at 12* you are +5* above factory spec. So your total advance might be 38-42*.