Hard to start after 2 days, fuel drain is possible. Why?

Here is my current cam sheet. I am running with 1.6 ratio T&D roller rockers.

I will try focusing on seeing if fuel squirts with the accelerator pump immediately next time.

As for the tach operation, I understand wavering, but it is the quick jumping a few times observed in this video that I am referring to. I have seen it worse also. Real quick motions of the tach needle, that the engine is not replicating itself. That is making me wonder about my spark quality and reliability.

But the car is turning 12.40's at the track again now.

I will try exactly that Jim. I don't recall the motor being this finicky before though.





Additionally, I have been in a scenario before after sitting 1.5 - 2 hours, it would not want to start and then flood out when I give it a little gas to start. Now, as typing this... This may have been when I had a leaky well observed at the track one day.



Thanks all,
Mike

 

Larry

Jim Rodgers and I put stock jetting back in as I use this carb for my street driving and wanted to use less aggressive fueling for economy. And it is a 750CFM carb. It is smooth at take offs and going down the road, very responsive. It just runs rough for the first 10-15 minutes.



Mike

 

How easy it starts with no choke depends a lot on primary jetting and the actual fuel level in the float bowl.

These are both factors in how fast it draws fuel thru the intermediate and primary fuel circuits.

Priming the fuel bowl is the biggest factor for you Larry, but being right there with 2-3 good accel pump shots helps also.

Try it without opening the hood next time.. see what it takes..

Actual volume of the accel pump shots is important to.. not all q-jet accel pumps are created equally.

Every time we use a Q-jet on the dyno, we start it with no choke, and 4-5 shots of the accel pump, with a fuel fuel bowl, typically does the trick.

JW

 

Nice start video, Mike, that's exactly what I was looking for. While it's hard to see, it does not appear to be getting any pump shot. You can tell by the sound of the pump action - it sounds dry and there isn't much resistance when you are operation the throttle before your helper cranks the engine. When the fuel pump finally fills the bowl, the sound is different and the fact that after it runs for a while and hot-restarts without any other issues tells me that the accelerator pump is in good working order. The accelerator pump rod is in the correct "inner" position in the accurate lever also.

That's part one.

Part two is that the idle circuit is too lean, as mentioned.

Getting back to part one, it's clear that the fuel has "disappeared" far too soon and the fuel pump is not filling the bowl up quickly enough. I've had a qjet on my convertible w/o a choke for over 30 years so I'm pretty familiar with the characteristics. If you are using a stock Stage 1 mechanical pump, it can not only be causing a siphoning effect of the fuel when the car sits for a few days, but a faulty internal check valve will cause a very long delay in picking up the fuel again from the tank.

You can pinch-off the rubber "suction" line at the fuel pump and re-test in a few days. The other way to test a fuel pump check valve is to use a vacuum gauge on the suction port of the fuel pump and crank the engine. If the check valve is faulty, the vacuum gauge will will "bounce" to a few inches of vacuum and fall to zero until the fuel pump arm is activated again. If the fuel pump check valve is good, the vacuum will continue to build to a minimum of 5 inches or so and hold for a little while after the engine stops cranking.

 

What I find works well is pumping the throttle a few times THEN waiting a couple minutes and it fires right up. On my race cars if I do that they start instantly even after sitting 4 months. If I don't wait I get have to crank more and even then not a clean fire. (this is with an electric fuel pump on the race cars)

 

Google: "cylinder wash down" - and then confirm your bowl plugs aren't leaking.

 

Any updates?

 

I was looking to give it a try tomorrow evening. I wanted enough time to go by again.


Thanks for your help !

Mike

 

With that cam, as others have mentioned, you need to riches the idle circuits for it to idle correct. If you have to crank up the idle speed screw, then you are pulling from primary circuit and will have nozzle drip at idle. This will cause rough idle and loading up while sitting at idle. This may improve when engine is warmer to help burn off the excess fuel.

I don't run a choke. Pump a couple times and it fires off. Pedal for a bit and then it does great. My cam is similar to yours.

 

how many days can you let it sit and still be able to start it this way?

what rpms does primary circuit start at?

 

Update all

I removed my air cleaner. Used a light to illuminate the carb very well. I could see some fuel with the first pump, but it was squirting at an angle to the side of the tube housing. Then I saw nothing. I made another video to confirm that nothing was coming out. I did not attach a link to that video.

This video shows a very small amount of fuel squirt with the accelerator pump.

https://youtu.be/S3EE72hUp7g

I then put gas in the squirt bottle to put in the carb through a vent port. I could not find what was referred to as a place to put gas into the carb through a vent. I then went into the car and cranked the motor for 5-6 seconds and shot a third video. I can clearly see the fuel squirting onto the horns (I believe is what they are called). Here is the video of that.

https://youtu.be/5ZxwIDr3AWI


I then went back inside the car. Began cranking and gave 1 or 2 half throttle gas pedal pumps. The motor fired off right around 2 or 3 revolutions. It ran for a few seconds before it shut off, from being cold and I just didn't throttle well enough. I then cranked over for firing off again and kept it running just as it has in the past several months.


This very much sums up my issue is fuel boiling off and/or evaporating. I now know that 5-6 seconds of cranking puts fuel in the bowl. Then give 3-4 throttle thwaps to prime the intake system for now.

I am currently running a 750 CFM carb that Jim Rodgers has tinkered with that is functional enough for me. I have an 800 CFM that I have boxed up to send off to Mark to set up for me.



I appreciate everyone's help provided !




Mike

 

Again, if you are using a mechanical pump, pinch-off the rubber fuel suction line at the pump after the engine has warmed up and shut off. Let sit for a few days and check your pump shot. If the fuel pump is siphoning fuel off, another carb or another overhaul of this one won't help. Leaving the small wire needle hanger off of the needle will keep fuel in bowl from being siphoned. If this is all Greek to you, you can at least pinch-off the fuel line and check for a pump shot in a few days.

 

Thanks Bob !

I did just pinch off the inlet hose. Only, I did not run the car to warm up temp tonight to see if it may be boiling off. I will check again in 3-4 days for pump shots. If I do, I will start up and warm to running temp and repeat with pinching off the line to test in a few days longer.



Mike

 

any disadvantages to removing that clip? What is its purpose that it can just be removed? Isnt it for positively opening the inlet to let fuel in when the bowl level drops.

 

I would like to know that also.



I went to the car this evening. I removed the clamp on the fuel line, then I had good pump shots from the beginning. I cranked the car and it fired off for a second or two. I cranked it again and it did not fire off. I cranked for 4-5 seconds with no fire off. I pumped the gas pedal twice and cranked again and I saw fuel spray puffing into the air above the carb. Not a lean backfire pop like before, just engine turn over. I then cranked it again with a couple gas pedal pumps and the car fired off and I kept it running. It ran moderately smooth, with slight bouncing of the tach that the engine was not doing to represent. I kept the idle around 1800-2000 RPM and after about 20 seconds, the idle didn't jump around like it was in the very beginning. Within a minute, the car was running on its own at idle.

I let the car run for 15 minutes to get to operating temperature and then shut it off. I did clamp the incoming fuel line again to see what happens in 2 days.

I don't understand why it had good pump shots, fire off and then not fire off for a good amount of cranking. Unless it only had just a small amount of fuel to give those pump shots that I saw. That would lead me to realize that fuel is draining back, even with the inlet fuel line clamped off. Maybe draining back through the return line???



Thanks all !



Mike

 

The clip......
Back in the old days, the fuel would gum up when evaporated, leaving a sticky film and after years of evaporating, a thick gum and crud. The clip would lift the needle from the seat, so if the car sat long enough for fuel to evaporate, the needle wouldn't stick in the seat and prevent the bowl from filling on the restart. Today's fuel doesn't gum up, but does evaporate quicker.
If the clip is connected incorrectly, it can cause flooding issues.

I have over a thousand we have built running without the clip. Haven't added them in many years.