74 620 Throttle Cable wore thru sheath

[flatcat19]

Oi vey.

[distributorguy]

Bicycle guys use what's called a "noodle."  A 90 degree bent tube at the end of the cable.  

Stop melting cables with electricity and problem solved.  

[Cardinal Grammeter]

UPDATE:  STIFFNESS ISSUES:   I've got the Body Ground down to <0.1 ohms to the battery terminal so that is fixed.  However, when I push the gas pedal, it is stiff and I can feel the cable "stick-slipping" or "cogging" as I apply throttle.  It is NOT silky smooth like I would expect it to be.

 

I reached inside the cab to try to pull the cable end with my fingers and moved it maybe 1/4" with great difficulty - it should not be that stiff.  (The cable is a good used one that was totally free and smooth when checked in hand.)

 

The carb has 2 return springs on it:  The "watch 'spring" on the accl pump bell crank pivot AND the main vertical spring from a low bracket on the carb to the pushrod end of the accel pump bellcrank.  This latter spring is very strong.

 

TWO STIFFNESS THEORIES:

• Worn Throttle Plate Shaft to Base Plate:   expected since this is where the pushrod from throttle shaft to bellcrank is reacted.  But once worn, it will be stiff since the proper bearing surface shape has been lost.
• Wrong "Big" spring in carb.   Possibly for linkage throttle and NOT cable throttle?  One DCH340 pic shows 20 turns on the big spring - I'll be counting mine hopefully today.  EDIT:  Big spring is 20 turns.  Tried w/o Big and not enough return force.  W/o "Watch" seems like there was enough AND definitely less cogging.  In fact, when manually working the carb throttle shaft, there is cogging present obviously due to worn shaft(s), etc.

Edited August 3, 2018 by Cardinal Grammeter
UPDATE

[Stoffregen Motorsports]

So to clarify, there should be multiple grounds. One from the battery to the body. Another from the battery to the frame. and another ground from the engine to the frame and/or body.

 

Then all of the small grounds in the harness. If you have the frame, body and engine grounded, you shouldn't still be welding your throttle cable.

 

Have you tried twisting the linkage at the carb by hand? Those small linkage parts on the carb get worn over time and can feel notchy.

[distributorguy]

How ever many ground cables it takes to make you think you solved your grounding problem, double that number and make all the cables bigger.  Grounding is like a drainage ditch.  You can make a nice ditch that allows water to flow, but on occasion you're going to get a storm.  Plan ahead and make sure you don't just have something that COULD be functional.  How ever much opportunity you have for power to enter the block via ignition, sensors, etc..., you need a minimum of 4X that much volume of grounding to allow unimpeded electricity flow or your throttle cable will continue to heat up.  

 

In most cases, factory cars are under-grounded, at least until EFI became standard.  2 cables off the engine the same size as your battery cables are required - minimum.  Not old ones that "look good" either.  Tear apart your old ground cable to see what I mean.  It'll be green on the inside, invisible from the outside.  Overlap cables from the battery to the engine to the frame.  Feel free to weld a new bolt (head down) to the frame, then use it to fasten ground cables.  Then go to the local auto parts store and buy a 6-pack of throttle return springs in the "Help" section.  And pick up an assortment of black battery cables with eyelets on both ends.  It'll be your best $30 investment.  

 

With a little modification, this will fit beautifully:

https://www.amazon.com/Mr-Gasket-5657-Braided-Throttle/dp/B001QVTIM8/ref=pd_cp_236_1?pf_rd_m=ATVPDKIKX0DER&amp;pf_rd_p=fcaa6d12-8b2b-4ad7-b277-864b2da79f6e&amp;pf_rd_r=RQ2PDFWH1GZ2X06RC6AK&amp;pd_rd_wg=rc2OE&amp;pf_rd_s=desktop-dp-sims&amp;pf_rd_t=40701&amp;pd_rd_w=k9spN&amp;pf_rd_i=desktop-dp-sims&amp;pd_rd_r=25139553-97e7-11e8-8a63-ad2dc5335592&amp;pd_rd_i=B001QVTIM8&amp;psc=1&amp;refRID=RQ2PDFWH1GZ2X06RC6AK

Edited August 4, 2018 by distributorguy

[Charlie69]

I agree Distributor Guy, you can not have too many grounds and these grounds require cleaning contact points from time to time.  Just part of your basic maintenance schedule.

[banzai510(hainz)]

one should have a return spring at the carb and maybe even another helper spring

[datzenmike]

Then the throttle shaft wears out.

[Stoffregen Motorsports]

Which is what he is now talking about in another thread.

[Cardinal Grammeter]

On 8/3/2018 at 2:10 PM, Cardinal Grammeter said:

UPDATE:  STIFFNESS ISSUES:   I've got the Body Ground down to <0.1 ohms to the battery terminal so that is fixed.  However, when I push the gas pedal, it is stiff and I can feel the cable "stick-slipping" or "cogging" as I apply throttle.  It is NOT silky smooth like I would expect it to be.

 

I reached inside the cab to try to pull the cable end with my fingers and moved it maybe 1/4" with great difficulty - it should not be that stiff.  (The cable is a good used one that was totally free and smooth when checked in hand.)

 

The carb has 2 return springs on it:  The "watch 'spring" on the accl pump bell crank pivot AND the main vertical spring from a low bracket on the carb to the pushrod end of the accel pump bellcrank.  This latter spring is very strong.

 

TWO STIFFNESS THEORIES:

• Worn Throttle Plate Shaft to Base Plate:   expected since this is where the pushrod from throttle shaft to bellcrank is reacted.  But once worn, it will be stiff since the proper bearing surface shape has been lost.
• Wrong "Big" spring in carb.   Possibly for linkage throttle and NOT cable throttle?  One DCH340 pic shows 20 turns on the big spring - I'll be counting mine hopefully today.  EDIT:  Big spring is 20 turns.  Tried w/o Big and not enough return force.  W/o "Watch" seems like there was enough AND definitely less cogging.  In fact, when manually working the carb throttle shaft, there is cogging present obviously due to worn shaft(s), etc.

 

UPDATE:  Rubber accelerator pump does in fact seize in bore.

 

A long time ago I posted that the rubber accelerator pump piston would stick in the bore - I believe I said the blue one.

 

When I discovered I had the wrong check valve weight/follower in the pump nozzle, I somehow convinced myself the blue pump was now working - probably because I could make the pump shoot manually operating the piston.

 

NOT

 

The blue (and red/orange) rubber pistons both seize in the bore.  If you bottom the piston, the spring in the bore will not push the piston up.  On the bench, the only way to get the piston to move is pull the pump assembly out by hand.

 

When the engine was running, I felt this pronounced stick/slip every time I pressed the gas pedal.  Evidently what was happening was I would push the pedal down, the piston would not move at first, the overshoot spring was then compressed and finally the piston moved a bit.  I could get maybe 6 cycles of this to the point where the secondaries opened.  I also though the accel pump was not doing a good job.

 

The ONLY pump that worked was the leather one with the spring underneath.

 

With this pump

• Stick/slip was gone
• Accel pump worked a lot better
• Carb would come back to idle better.

So where to get a usable accel pump?  Both new carb kits I bot had the rubber ones (blue and orange/red)?