I will assume your electrical system is ok. Don't forget that the distributor advance not working correctly can cause a similar problem.
Your friend is probably correct. When you step on the gas an extra squirt of gas is needed and that is provided by the accelerator pump circuit. There is where I would concentrate your efforts. Make sure that the check ball is in the bottom of the pump well, if your carburetor needs one. The way to tell is to look for two holes. One will be slightly up the side near the bottom and that is the discharge hole. The other will be on the bottom and that would be the intake. The check ball that resides here will be the smaller check ball and it is often aluminum.
Test the check ball by taking the top off. Fill the float bowl. The check ball will lift up by the weight of the gas and allow fuel to flow into the well. For those that don't use a check ball, the well if filled by coming over the slot in the side of the pump well. In other words it splashes over from the float bowl. If the well doesn't fill up, then the passage is probably plugged up. Run thin wire through the passage. Ethanol will leave residue behind that cleaners cannot get out.
Take the venturi off, remove the main discharge T, spring and check ball (bigger check ball). Fill the pump well, then press the accelerator pump down to the bottom. The pump well check ball should seal the intake hole and fuel will be forced out to the main discharge. If fuel comes out of the main discharge, then the check ball and passage way is probably ok.
Replace the main discharge check ball and using a brass drift punch, hold the check ball down so that the hole seals. You should now get some resistance when pushing the accelerator pump down. If you get fuel out of the main discharge while holding down the check ball, then use a brass drift punch to gently tap on the check ball. This will reform the check ball hole. Don't hit too hard, or the check ball might get stuck.
Replace the main discharge ball, spring and T. Run thin wire through all of the passages in the venturi cluster and then replace it. Don't forget the gasket.
Now when you press the accelerator pump to the bottom fuel should squirt out of the venturi cluster holes.
Using Ethanol Defense will help eliminate your ethanol problems.
Wire from twist ties work well for the small holes. Cleaners and compressed air will not remove the ethanol deposits left behind.
I soaked and cleaned my 2 carb both the 1 inch for a chev . One of them starts and idles good but when you try to raise the rpms it swings frm 1000 to 3000 rpms. It accelerates good if you push the pedal down but if you try to hold the rpms at like 3000 it swings up and down. Ive set the pump and metering rods per your specs and cant make it any better.
My first instinct is that he has a vacuum leak . . . which could be downstream of the carburetors.
Only Runs With Choke Valve Partially ClosedSo your engine seems to crap out once the engine gets warmed up.
- Float level incorrect
- Float drop not dropping enough, which will keep the needle from opening. Set to specifications. Don't fudge.
- Fuel pump pressure is lot. Test the pressure with a fuel pump pressure tester. Around 4 - 4.5 lbs will do it.
- A passage may be plugged. Especially the small passages such as the idle vent passage. Make sure you can blow through each passage. Include the small passages on the venturi. Simply soaking a carburetor in a cleaner will not unplug a passage. Dried gas leaves residue behind, which will plug small passages.
This article only refers to the type of 4 jet that uses a check ball in the bottom of the pump well. Not all carburetors do.
When rebuilding your 4 jet you may want to test the accelerator pump circuit before closing up the carburetor. Here are the steps you need to take.Place the smaller and aluminum (when provided), check ball into the bottom of the accelerator pump well. Not all 4 jets will have this check ball. Fill the float bowl and the pump well with mineral spirits.
Put the pump in the well and push it down toward the bottom of the well. The check ball will seal the hole, keeping the fluid from going back into the float bowl and the fluid will be forced through the 2nd hole through the main discharge. You should see fluid come out of the main discharge.
The main discharge should have the bigger stainless steel check ball, then the gold colored spring (don't worry if it is bent), then the T. Stake the T so that it doesn't pop out.
Now test to see if the check ball seals by holding your finger over the main discharge hole and pressing down on the pump again. You should feel a slight pressure on the accelerator pump and there should not be any bubbles or some other sign that would indicate the check ball is leaking and fluid is being forced backwards.
The larger check ball in the main discharge tube must also be tested. Hold the check ball down with a brass drift punch and push the accelerator pump down. You might get but a slight amount of fluid past the check ball, but you should also feel a slight pressure.
Replace the venturi cluster and test again by pushing the pump down. You should get a strong squirt out of both sides of the cluster. If not run thin wire through the small passages. They may be plugged with ethanol residue and cleaners will not remove the residue.
To re seat a check ball, using a brass drift punch, hold the check ball down into the hole with the drift punch and tap a few times with a hammer. Don't get carried away, or you will get the check ball stuck. The hole in the carburetor you are trying to form is soft metal and doesn't take much to change.
Now you can be confident your accelerator pump circuit is doing what it should.
Is the check ball stuck in either hole? Turn the carburetor over and while heating the bottom where the check ball resides tap the carburetor bowl on the bench. It will most likely fall out when hot enough.
- If the idle RPM is too high then the idle mixture isn't going to respond. The RPM has moved past the idle circuit. Adjust he idle as per manufactures specs.
- Too much air, or too much fuel? Too much fuel will usually show up with a gassy smell.
- You may have a restriction somewhere. Remove the idle mixture screws and make sure they blow through to the bore and then to the venturi. The very small passages are usually the idle vent passages. Inspect the throttle body gasket carefully to make sure it isn't covering up a vacuum passage. The 4 jets used multiple types of gaskets and they are easily mixed up. Blow through every passage to make sure they are clear.
- Check around for vacuum leaks, intake, carburetor mount, vacuum lines coming off the carburetor, or intake. Use spray carburetor cleaner to spray around seams. A change in RPM indicates a leak.
- Too much fuel - too much fuel entering the float bowl can cause air/fuel mix problems. Check the float level.
- Look down the carburetor while at idle RPM. If you see gas dribbling out of the venturi then you have a problem with the discharge. Make sure the main discharge has the check ball and it seats. There should also be the spring and the T installed above the check ball.
- Bad thermostat - replace the thermostat - test by heating water and immersing the thermostat. The spring should move instantly at least 1/4"
- Hot air tube is plugged. It should be hot to the touch all the way up.
- No vacuum in the housing - vacuum supplied to the choke housing is used to suck up the hot air from the hot air tube. Take the thermostat off and with the engine running, blow a little smoke into the choke housing. It should get sucked up through the vacuum passage.