Carburetor New Hard Hot starts

[zyzx]

Need some ideas regarding a new issue that's got me a little puzzled. My 89 GW, which is bone stock with all emissions equipment intact, has recently started giving me problems with hard hot starts after replacing the carb.

Original carb was running fine however noticed a drop in vacuum to about 14 or so. Hooked up the smoke machine and found leak at the driver side gasket. Removed the carb and and installed new manifold to spacer gasket and spacer to carb gasket. Was not planning on rebuilding the carb or changing it. I reinstalled the carb (torqued to 15 ftlb) only to discover that the spacer had cracked and the accelerator pump was now leaking. This was the original carburetor that came when the car was new(5RHA2) judging by the both choke plate tag and manufacturing date and carb tag. In any case, I happened to have another 5RHA2 with another spacer that I had personally rebuilt. I installed that one and dialed it in to get 19 hg of vacuum. Everything works flawlessly and the car cold starts and runs fine, actually better than before. However, now when hot it will barely start but once started it will run fine. It takes a lot of cranking( 1- 2 min) with careful throttling to get it to finally fire.

Everything is exactly the same as before. I checked the timing and it's still at 12 deg. I clean in a professional ultrasonic cleaner followed by chemical dip. I used an original power valve in the rebuild which I tested with a vacuum pump before install. I also test my rebuilds with mineral spirits to check pump circuit so I know there is no issue there. I measure my float with a micrometer it's set to spec for an 89 per the shop manual. The idle mixture screws adjust fine.

The only thing I think might be the issue, is the second spacer that I installed is also 30 years old and I heard it crack when I torqued the nuts (trust me I really do use a torque wrench) There are no vacuum leaks there but I'm wondering if that would be enough to cause heat issues and the hot starting problems? I will pull the carb again next week and install a brand new spacer and change the power valve just in case, but was wondering if anyone had any other thoughts?

I've combed through innumerable previous threads but can't find any other ideas.

Edit: exhaust heat riser is operational as well as airhorn heat stove, always have been. The choke is fully open when warm.

[FSJunkie]

Do this the next time you start it hot and tell me what happens:

1. Open the throttle about halfway.
2. Hold the throttle steady while you operate the engine starter.
3. Release the throttle (and they key of course)when the engine starts.

Should take 2-5 seconds to start.

That is how most carbureted engines start best when they are hot. That is how the owner's manuals told people to do it. The fuel in the carburetor boils after the hot engine is shut off and the vapor fills the intake passages in a high concentration that is too rich for the engine to start on until it is cleared out. The quickest way to clear it out is by opening the throttle a little and cranking. As I said, it should clear out in a couple seconds. Some carbs are worse or better than others and there isn't a whole lot that you can do about it.

[zyzx]

This car used to start instantly and repeatdly in 100 deg weather and engine fully hot before. Never did this once. It seems oddly coincidental that after a carb change the problem has started. It's an identical carburetor with everything else being equal so this has to be a settings issue, or a a problem with the spacer.

This is not normal operating procedure.

[Ristow]

float height may be a little high. also ensure the check ball and weight are under the shooter for the accelerator pump.

[SOLSAKS]

mine did that on a 1988 wagoner w/360

it had recently had a new edelbrock 4bbl and edelbrock intake installed

but the installer failed to put an insulator between carb and intake

boiling out gas when parked after getting it hot

called edelbrock

they sold me a the correct part ( approx 1/2" thick spacer/insulator )

and it solved the problem for me.

hope yours is this easy to fix.

dave in nc

[ZackN920]

huh, I didn't know these spacers/insulators could crack...

Did you tune the last carburetor that ran the engine perfect for ya? Or had it not been touched by you prior (when it comes to the state of tune) I have found that sometimes some fine tuning is necessary and tuning exactly to "the book" doesn't always work the best.
My Jeep kept fowling plugs and running rich when the choke was set to book specs for 1990, but after a lot of trial and error, and more adjusting, it runs good from a dead cold start.
You may need to adjust the float or idle circuits a bit on yours. Also make sure fuel isn't boiling and emptying the bowl when you walk away from it for awhile. If the bowl is empty, its gunna take some cranking to fill it back up to get it to pop off.

Are you sure the power valve isn't leaking gas into the intake? Mine did this when I got the Jeep. Everytime I shut it down, it would take awhile to restart. Found that the bowl was always draining out and that there was a very strong odor of gasoline in the oil...

[zyzx]

I am waiting on the spacer to arrive on Monday before pulling the carb back off. There's no sense in taking it off now since I won't be able to put it back on to test.

I will check the float height once it's off the car but I think that's not the issue. It is worth rechecking though. I set it to 0.328 inches per the 89 TSM. I checked the old carb's float height and that was around 0.34 inch. So they are fairly similar.

The carb that was on the car still had the tamper proof caps on the idle mixture screws. I had not tuned it before. The spacers do break, its basically a plastic piece where a thick flange gasket sits on top and gets sandwiched between the spacer and carb base. This causes some uneven pressure at the bolt holes if the flange gasket is too thick or when you tighten the nuts, especially if the plastic is old and has gone through a million heat cycles.


I do think that the spacer cracking is the part of the problem. Could be that the crack, regardless of how small, is letting heat up. But the flange gasket is thick enough and is sitting right on top of that so it should still insulate enough.


I did find that the power valve gasket (the O ring on it not the housing gasket) is leaking yesterday and that's probably the second problem. When I applied vacuum with a pump the housing inlet, it held vacuum just fine but I did notice the slightest drip of gas. I drove it for a bit then rechecked to find gas when I removed the vacuum hose. I will replace the power valve and gasket as well. Hopefully that will solve the problem but who knows.

And yes, if you're washing your cylinders you'll thin out the oil quite a bit and may ruin your engine.

[zyzx]

It was a leaking power valve gasket. Changed the gasket and ran the idle mixture screws a touch lean. Problem solved. Interestingly, it was holding vacuum fine before I installed it the first time. Perhaps the combination of engine vacuum plus gasoline from the power valve opening was more than it could handle.

[Bluesj]

I have had the same issue. After I drive it I would have to push the throttle to the floor to get it to restart. But runs fine after it starts. Going to check my gaskets and power valve.