Fuel Pump Woes and Questions

Old60Driver

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Good morning folks. I've actually got two problems I'll be asking about. Let me know if I should split them and have separate threads. :)

Rebuilt the Qjet on my 83 last weekend, and everything went well. The carb wasn't in too bad of shape, but I did notice that all of the bolts/screws were only finger tight. Anyway, she started right up after the carb rebuild with no issues at all. Choke seemed to be working, step downs and all. I thought I'd take her for a spin down the dirt road, and good lord, she just fell on her face! She would idle and rev just fine sitting in park, but under a load? She'd bog HARD, and try to die on me unless I backed off on the throttle. Like she wasn't getting enough fuel. Unfortunately, I had to get back to Oklahoma for work on Sunday, so I left her as is.

I get back to KS on Friday, and start tinkering with the fuel delivery system. I'm thinking either bad pump, plugged lines, or clogged fuel pick-up socks. I take a look, and sure enough, it looks like the mechanical fuel pump had been changed out (not sure when, but the pump itself looks new-ish). Continued to trace it back, and yep, it's ALSO got an electric Mr. Gasket fuel pump in there. Now, I wasn't surprised, as I had seen this all before during my walk down, but it got me to thinking. Why would there be a NEW mechanical fuel pump, AND an electric to boot??

I decided to test on it, so I disconnected the fuel line at the QJet, ran a line from it to a bucket, and turned the key to ON. Well, fuel came out, but it was slooooooow. Hmmmm. So I fired her up to run the mechanical pump until the bowl emptied. Not much better, if at all. Definitely not enough fuel to keep her going under a load. Tested the electric out of the vehicle and yep, it's shot. The inlet filter looks terrible. I'm guessing the mechanical is shot too, but I'll get to installing one later, and figured I could run an electric for now. Installed a new Mr. Gasket electric pump, and tested her again. Getting lots of good fuel at the QJet now. That's a good thing, right? Nope. Now I have a new problem. High idle. I could not get the idle to come down unless I tinkered with the high idle screw on the choke.

I got the idle down, but she still stumbles badly under load at about 35 mph. Pulled the dizzy cap, and sure enough it's pretty bad in there. Well, I have a brand new HEI dizzy, so I figured I'd just slap that in there. It was on my list anyway, so why not?

Brought the engine to TDC, changed out the dizzy, and wires, and fired her up. Set the timing, but I noticed she seemed like she had a miss. Traced it to cylinder #5. Double checked the rotor alignment at TDC. All good. Checked the plug, and sure enough, no firing. Popped a new plug in (maybe cracked ceramic?), but no good. Hell, I even put one of the old wires back on just in case. Nope.

After all that (and thank you if you're still reading), I have a couple of questions, and requests:
  • FUEL:
  • Is it possible that I need a regulator for the new electric Mr. Gasket fuel pump? Could the fuel pump be overpowering the float needle? Is that why the idle was so high?
  • As nasty as the the inlet filter to the old electric pump was, should I consider dropping the tanks for a cleaning and inspection of fuel gauge sending unit and socks?
  • CYLINDER #5
  • Going to be checking compression today. I'll update. If it's low, I'll be pulling the heads for a better look.
  • What are the odds of that cylinder taking a nose dive immediately after installing a new dizzy? Could I have caused it somehow? I can't see how, but...
Anyway, sorry the the novel I just wrote, and thanks again for y'alls time.
 

Snoots

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Yes, yes and yes.
Yes.
Could be a bad rocker. I'd check that before pulling heads.
Slim, I doubt it.
Murpheys Law
 

Old60Driver

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Yes, yes and yes.
Yes.
Could be a bad rocker. I'd check that before pulling heads.
Slim, I doubt it.
Murpheys Law

Roger that Snoots. I'll probably be pulling the fuel tanks and taking a gander in there at the socks. Having said that, I loosened up my fuel tank caps, and that seemed to have made a pretty difference. She still not perfect, but I was able to keep her moving without too much trouble. I'll be digging into the vent system and fuel caps today. Sound about right?

Checked the compression. Well, on the drinkers side anyway. 125 across the board. It's weird. Research continues.

And Murpheys Law. You couldn't be more right brotha. Still I'm having fun working on the ol' girl!
 

C10MixMaster

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Qjets dont like a lot of pressure earlier ones carbs starting with a 70 only like around 5-6 psi .later ones with a carb number starting with 170 can take 7-8 psi. im running 9# with no problems but thats the upper limit. so pressure test and run a regulator if needed.

before you pull the head in addition to the rocker make sure the cams not flat.

defiantly look at the distributor first since the miss showed up after that. one thing to check is make the coil screws didn't go through the cap (happens if the screws are to long). double check the firing order. ( xxxxxxx edit ) 18436572
 
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idahovette

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Qjets dont like a lot of pressure earlier ones carbs starting with a 70 only like around 5-6 psi .later ones with a carb number starting with 170 can take 7-8 psi. im running 9# with no problems but thats the upper limit. so pressure test and run a regulator if needed.

before you pull the head in addition to the rocker make sure the cams not flat.

defiantly look at the distributor first since the miss showed up after that. one thing to check is make the coil screws didn't go through the cap (happens if the screws are to long). double check the firing order. 18654372
My firing order on ALL my chevys is 18436572
 

C10MixMaster

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Old60Driver

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LOL No worries.

Re-adjusted my timing (without vacuum) to about 9°. Seemed to help. I also unscrewed the fuel caps. That helped a ton. Still, she's missing at at idle.

I should clarify, that I may have been wrong in my assessment of #5 not firing. I 'think' it's number five because it makes no difference if I pull the plug at idle. I didn't have a helper to put her under a load and pull the plug, but when I ran her down the road, I couldn't tell that it was misfiring. She just has a bit of a stumble at idle now. Unfortunately, I had to leave her in Kansas again for work in Oklahoma. Oh well, I'll continue to tinker with her next weekend.

Thanks again for all y'alls help and insight. It's much appreciated!
 

Grit dog

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The little electric pump is not too much for the carb. They’re only like 5 or 6 psi.
 

Ricko1966

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The little electric pump is not too much for the carb. They’re only like 5 or 6 psi.
And too much fuel pressure doesn't cause a fast idle, a fast idle is air. Either from throttle opening or vacuum leak.
 

Old60Driver

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And too much fuel pressure doesn't cause a fast idle, a fast idle is air. Either from throttle opening or vacuum leak.

Roger that, thanks for that Ricko!

Still, I think I'll tear into her this weekend, and get rid of the Mr. Gasket electric, install a new mechanical pump, blow out all the lines and maybe replace the fuel caps.

Speaking of which, is there a good way to see if a fuel cap is bad? I know that it ran better with the caps barely installed, but I was thinking that it was plugged vent lines. Thoughts?

Thanks again!
 

Ricko1966

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Roger that, thanks for that Ricko!

Still, I think I'll tear into her this weekend, and get rid of the Mr. Gasket electric, install a new mechanical pump, blow out all the lines and maybe replace the fuel caps.

Speaking of which, is there a good way to see if a fuel cap is bad? I know that it ran better with the caps barely installed, but I was thinking that it was plugged vent lines. Thoughts?

Thanks again!
Before replacing the pump make sure the pump push rod is moving a flat fuel pump lobe on the cam will make your mechanical pump quit working.
 
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Old60Driver

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Before replacing the pump make sure the pump push rod is moving a flat fuel pump lobe on the cam will make your mechanical pump quit working.

I was thinking the same thing. As I mentioned, the existing mechanical fuel pump looks 'new-ish'. IE, cleaner than the other components found in the engine bay. That got me to thinking as to WHY there was an electric pump installed in the first place.

With that being said, what's the best way to confirm that the cam lobe isn't wiped? I was thinking about:
  • Removing and inspecting the pump and push rod
  • If all is good, I was going to grab a short length of small OD pvc pipe and, after pulling the plugs, rotate the engine by hand to check for lobe movement
  • If all is good on the cam, install a new pump, and do volumetric and pressure tests on the fuel system
  • If the lobe is wiped, cap off the fuel pump hole, and keep running with the electric. A new RV cam is in my future anyway, if the lobe is wiped, I'll replace the pump when I replace the cam
How's that sound for a path moving forward? Also, how much should the fuel pump rod be moving?

Thanks, and good morning!
 

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