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Stuart_Snow

4.2 L first time start-up after re-build.

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After doing a long and careful re-build on my 77 CJ7 4.2 engine I expected it to spring to life. So far I'm only getting spitting and coughing through the carb but it did fire once for a second which gives me hope. I'll quickly run through the vitals here:

Fuel system: New gas tank and lines. I have verified that it is pumping fuel to the carb. The carb is a re-build Carter YF 1 barrel. It was dirty and needed a new accelerator pump  but in good shape otherwise. I used a kit from Mikes Carbs and did it my self which was pretty straight forward. I have spent a fair amount of time messing with the carb on my CJ-3b so I was familiar with it. It does appear that fuel is making down the intake but when I pump the throttle I'm not seeing anything from the accelerator pump so its coming back off to diagnose that. 

Ignition: Its a DUI HEI unit, I installed it per instructions and set it up to fire the #1 cylinder at TDC.  I verified it is working with my timing light. Using my remote starter switch I can see the timing mark and I'm able to run it up and down the the advance markings by rotating the distributor while I crank from 0 degress to 12 or more all it does is spit out the carb.  DUI recommends 12 degrees static as a starting point for racing or off road which may be a bit much for me until I get past emissions. I currently have it at 6 but have tried the whole range. My factory settings only call for 3 degrees +/-2 @500 Rpm . I'm guessing this is due to smog regulations of the day. Anyway I've demonstrated that the ignition is working and I can set the advance up and down with no results.

Valve train: I spent a lot of IMG_1556.thumb.JPG.687acf5eb011beca6131be7a4b1f63e5.JPGIMG_1556.thumb.JPG.687acf5eb011beca6131be7a4b1f63e5.JPGsetting this engine up and do not anticipate valve-train problems unless the springs are tired or something is sticking. I ran through all cylinders in firing order with a cheap press on gauge and got  100 psi or more on all. I do have an aircraft style differential compression tester which I intend to use once I modify it to fit auto plug threads. I did a thorough priming of this engine and verified the lifters were pumped up and oil was making it to all the rockers.

So I have a flame throwing ignition system and an anemic carb. I understand that spitting can be a symptom of a lean condition but I assumed that was for an engine that isIMG_1549.JPG.2f4910055f666ef0a38b6eddcab84cee.JPG already running.

I'll report back when I trouble shoot the carb and verify my compression is good when and where its supposed to be. No back firing  but lots of spitting and coughing up the carb. I have kept the air cleaner on to keep flames out of my face.

 

 

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Stuart...See my comments below...Moses

13 hours ago, Stuart_Snow said:

After doing a long and careful re-build on my 77 CJ7 4.2 engine I expected it to spring to life. So far I'm only getting spitting and coughing through the carb but it did fire once for a second which gives me hope. I'll quickly run through the vitals here:

Fuel system: New gas tank and lines. I have verified that it is pumping fuel to the carb. The carb is a re-build Carter YF 1 barrel. It was dirty and needed a new accelerator pump  but in good shape otherwise. I used a kit from Mikes Carbs and did it my self which was pretty straight forward. I have spent a fair amount of time messing with the carb on my CJ-3b so I was familiar with it. It does appear that fuel is making down the intake but when I pump the throttle I'm not seeing anything from the accelerator pump so its coming back off to diagnose that. 

Does sound like the accelerator pump...Look for the checkball that keeps fuel in the plunger bowl.  Verify that the carburetor bowl is full, float working properly at the right height.  Fuel filter looks new.  Check the fuel pump pressure at the carburetor side of the fuel filter.  Fuel volume is important, too.  Is the fuel tank and pickup (if there is one on your tank pickup) clean?  Note the fuel flow rate and pump pressure.

Ignition: Its a DUI HEI unit, I installed it per instructions and set it up to fire the #1 cylinder at TDC.  I verified it is working with my timing light. Using my remote starter switch I can see the timing mark and I'm able to run it up and down the the advance markings by rotating the distributor while I crank from 0 degress to 12 or more all it does is spit out the carb.  DUI recommends 12 degrees static as a starting point for racing or off road which may be a bit much for me until I get past emissions. I currently have it at 6 but have tried the whole range. My factory settings only call for 3 degrees +/-2 @500 Rpm . I'm guessing this is due to smog regulations of the day. Anyway I've demonstrated that the ignition is working and I can set the advance up and down with no results.

Six degrees is plenty if your vacuum advance is working properly.  Make sure your vacuum advance hose goes to a ported vacuum source, not a manifold source.  Disconnect and tape off the vacuum advance hose when verifying the base spark timing...If the vacuum advance hose routes through a thermal vacuum switch, check the switch and advance vacuum as you tip-in the throttle.  For the vacuum advance to work, the engine must be warm when there is a thermal vacuum switch in the hose circuit.

Check the spark output at the plugs.  You should have a real zap with the DUI.

Valve train: I spent a lot of IMG_1556.thumb.JPG.687acf5eb011beca6131be7a4b1f63e5.JPGIMG_1556.thumb.JPG.687acf5eb011beca6131be7a4b1f63e5.JPGsetting this engine up and do not anticipate valve-train problems unless the springs are tired or something is sticking. I ran through all cylinders in firing order with a cheap press on gauge and got  100 psi or more on all. I do have an aircraft style differential compression tester which I intend to use once I modify it to fit auto plug threads. I did a thorough priming of this engine and verified the lifters were pumped up and oil was making it to all the rockers.

Priming was done with the pushrods and rocker arms installed, right?  You want to make sure the lifter plungers are not overextended.  They will bleed down as the crankshaft rotates, so they should be normalized by now.  (Depending upon engine design, the concern is valve interference/bending valves if the plungers are hyperextended while cranking the engine.  Unseated valves, even if they do clear the pistons, will cause spitting back through the carburetor.  With no noise, you likely have the valves clearing the pistons.  Also, your compression check indicates that the valves are seating.)  Valve timing is crucial.  I'm sure that you were painstaking when aligning the timing sprockets...Always a concern, though.

So I have a flame throwing ignition system and an anemic carb. I understand that spitting can be a symptom of a lean condition but I assumed that was for an engine that isIMG_1549.JPG.2f4910055f666ef0a38b6eddcab84cee.JPG already running.

I'll report back when I trouble shoot the carb and verify my compression is good when and where its supposed to be. No back firing  but lots of spitting and coughing up the carb. I have kept the air cleaner on to keep flames out of my face.

Though seemingly elementary, re-check the spark wire firing order:  1-5-3-6-2-4.  The distributor rotor rotates clockwise. 

You were painstaking with the assembly, I'm betting the issue is simple...Moses

 

 

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It runs!  I had the distributor setup one gear too late so it was not lined up with the plug terminal exactly. All I was getting was the warm afterglow which was causing my spitting problem. It fires right up now. Turns out indeed my accelerator pump port was also clogged. Carb spray did not clear it so I used one of the welding tip cleaning wires to clear the obstruction.

It idles very smooth. I ran it at about 1600 rpm for about 20 minutes to mate the cam with the lifters. My break in oil is Rotella 15-45 and I used the Lucas break-in additive with ZDDP. It looks good after the break in run and nothing leaking out of the bottom.

I have a slight exhaust leak to deal with at the manifold. It sounds like a beast.  At least now I can work on fine tuning things. 

Thank you Moses for getting me to start thinking and looking at it closer. I'll keep you posted on my break in progress.

IMG_1560.JPG.194a4d619e48dfa572dae40dcdfb1d93.JPG

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Yea, Stuart!  Sounds like you nailed it...This will be a great engine.  Smart to use Lucas break-in oil with ZDDP.  The camshaft lobes-to-lifter bases represent the highest friction point per square inch in the engine.  Proper break-in will deliver many, many years of quality service! 

Congrats on a job well done...

Moses

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