midnight mechanic

I've let the fuel pump run for a minute or two before starting. After ~10th crank, it will fire up, missing, gradually becoming smooth. My theory is the fuel pump is weak, and it needs the full 12 v to perform. This is because it is getting only 10 v when starting the engine. Plan is to change the fuel pump sat night. Fuel pump is +24 years old.

Whadda think?

Toruki

I don't think it's the fuel pump. You'll fill the bowls, even if it runs at a slightly lower RPM before starting. With full bowls you'd start and run out and die if the fuel system couldn't keep up, but it would start. And since it keeps running after you start, I think the fuel system is fine.

If your battery is only supplying 10V with just the load of the fuel pump, then that's a bad battery!

I don't know what would cause the car to not start the first 9 times. I would at least check the sight glasses on the bowls and I'd measure the battery voltage prior to ignition with just the fuel pump running (and also just ignition off). A good battery should be ~12.5 V DC give or take a couple tenths or so.

midnight mechanic

That makes sense. Fuel pump makes a lot of noise. Looks like it is off to Wally, AZ, or O'reily's for a battery test.

Benjamin4456

Battery definitely sounds likely, although 10V while cranking is relatively normal. Wasn't quite sure if you meant it was 10V cranking or just key on though. A good battery will still drop 1-2V when cranking, but if it's hitting the 9V range the battery is starting to head out. I'd certainly agree that the pump being weak would not cause hard starting given the carby setup.

Will be curious to see the results of the battery test.

Holdfast

Do a compression test. Hard starting is usually from low compression.

midnight mechanic

I replaced the old fuel pump with a delphi fd0037 , it is knocking or ticking , issued a return to mail order warehouse , problem is that the delphi fd0037 is the most expensive pump listed there. What other fuel pump can I install ?

Car starts easier with the new noisy pump.

Compression test? Good idea, only problem is that if it is bad, I have to pull the engine, and find another which is scarce.

Rx7bgs366

Check all lines . Then check fuel filter. If not go to autoZone or any parts store that test your battery and alt for free.

7aull

iTrader: (2)

Ancient battery cables will NOT help!! If you don't know their history - replace. All sorts of starting/running bugs from old cables...
Stu A
80GS (new cables!)
AZ

midnight mechanic

Thankyou. the battery cables are the thickest you can fabricate from Autozone (2 gauge), and they were replaced in 2006. Car is hard to start when it sits +12 hours.

I installed a new carter pump that isn't knocking & ticking. fuel filter is new.

7aull

iTrader: (2)

[Car is hard to start when it sits +12 hours.]


NOT a good sign. Classic engine-failure sign. Does she smoke when it DOES start?? If so, describe for us plse!
Good luck!
Stu A
80GS
AZ

j_tso

iTrader: (2)

I thought hard to start when warm was the big sign of compression loss.

7aull

iTrader: (2)

Hard to say. My 80, when parked, say for 30 min - is a bastard to start -loooong cranks - but always starts (this has gone on for years) and only a minor puff of BLUE smoke.
Am tempted (NOT an expert) to pass this off as carb boiling away over the reactor. It starts INSTANTLY if just shut off - or if the cool down time is longer (few hours for eg).
I have always been under the impression the No.1 Start that spells trouble is a Cold Start (eg overnite) with a lot of WHITE smoke. Usually accompanied by a lot of cranking to get her going...
Obv - to get definitive a Compression Test is The Thing.
Stu A
80GS
AZ

midnight mechanic

Mine has always been hard to start if it sits. Seems to do better with 21 pedal pumps while the fuel pump charges up. I don't see any smoke.

Years ago there was steam for abut a minute. I did the coolant leak fix, the aluminum 2 component one.

Stevan

iTrader: (17)

Replace the accelerator pump diaphragm. As was mentioned earlier, if the fuel bowls are full, the fuel pump doesn't matter. The fuel gets squirted into the intake by the diaphragm when you pump the pedal, then sucked in by engine vacuum during cranking and running.

midnight mechanic

how hard is it to replace the acc pump diaphragm? in 30 words or less? never done it before

Toruki

I'm not sure if you can do it without a rebuild of the carb, but here's RAD Potential video I stumbled onto


That link should bring you to the part where they put in the accelerator pump check ***** and weights, it's about 30:00 minutes in

midnight mechanic

thankyou Toruki. Can I replace it without removing the carburator?

mazdaverx713b

iTrader: (91)

The carburetor has to be removed to replace the accelerator pump diaphragm. If you're in it that far, I don't see any reason not to rebuild the carburetor.

I would however, start with a proper compression test with a rotary compression tester. You really need to know where your engine sits. If its well below spec there's no reason to waste money throwing parts at it in an attempt to mask the low compression. It it what it is at that point.

I've had just ok compression engines run very well for a number of years with a clean and strong fuel system with an ignition system that's also up to par with new components. Like Stu said, sometimes we just live with the small issues and enjoy the car. You're call there. Just know we are here to help you along the way.

Slow_sevens

Not sure I buy the accelerator pump theory. Try this test. If you can start the car and get it running, try blipping the accelerator. (Quick stabs on the pedal with your foot). If the accelerator pump is bad, the engine will stall when accelerator is blipped. I am in the ‘test the compression’ camp. Maybe if getting hold of a rotary compression tester is difficult, using a regular cheap tester with the none return valve removed will give you a broad idea of what the compression is like.

midnight mechanic

Blipping the throttle once the engine is semi warmed up doesn't cause stalls.

Compression? I'm in the camp of either a rotary has compression or it doesn't. Original engine ran fine, then suddenly failed because of apex seal.

Could it be, not using the choke?

Slow_sevens

I would do the easy things first. Don’t take apart the carb unless you have to. If the floats and needles are working best to not invite the gremlins by messing with them.
Blip the throttle whilst looking down the barrel
of the carb. You should see a squirt of gas each time you hit the accelerator. If so, accelerator pump is working at least partially.
Pull the choke **** and visually check that the flap the choke cable closes in the carb closes all the way. After a full engine and carb rebuild I had hard starting and took me a while to spot the choke was not closing fully, turned out the cable was frayed and sticking.
Buy a cheap normal piston engine compression tester, remove the none return valve. Run a compression test and video the dial using your phone. You should see regular equal pulses over 100psi. If less than that or irregular pulses eg 100 100 50 100 100 50 then bad compression and engine rebuild needed. I am a rank amateur and have only done a engine rebuild once, but from what I understand compression failure can be progressive as well as sudden.

Stevan

iTrader: (17)

I know you were probably exaggerating with the 21 pedal pumps, but do you push the pedal to the floor?
Try pushing it all the way down with each pump and see if that helps.

I don't why multiple pedal pumps would overcome bad compression, if that was the problem, and not flood the engine.

midnight mechanic

I push all the way down. Engine was hard to start in 1990. Was hard to start after an atkins rebuild. Use to take 3 pumps. Now 28 ! If it sits for 12 hours, it starts right up. 24 hours it doesn't start right up.

Probably should connect and use the damn choke?

The 24 year old fuel pump was making more and more noise, so was destined to be replaced. The OEM suddenly failed in 1998 with out making any noise.

Thankyou everyone.

Slow_sevens

Defn try the choke.
I just ran an experiment for you. Tried to start my car with no choke, would not start. Multiple attempts with and without pumping gas pedal. Would not fire up.
Then I pulled the choke out and held it there with my hand, as it was trying to pull back in automatically as weather is mild at 60 degrees. Two pumps of the gas pedal, turned key and vroooom. Started right up. Let go of the choke ****, and held the car using the accelerator at 1500rpm until warmed up.

j_tso

iTrader: (2)

When my choke magnet quit I used a nickel to hold the **** out.