87blyota

Today my truck decided right at 2300 rpm in 1st and 2nd gear only it was going to have a bad miss. I have never replaced any ignition parts so I figured that I would replace the plugs, wires, cap, and rotor. This did not fix the issue, but I have noticed it only does it when it gets up to running temperature, and around the same rpm but only in 1st and second, any one have any other ideas? truck is a 87 pickup 22r stock carb.

millball

When is the last time it had a valve adjustment??

87blyota

I have no idea, but i just got back from driving it around. if i ride the clutch a little more than i used to taking off it wont do it. Also i did just upgrade to 33s so i might have to ride the clutch a little more when taking off?

87blyota

Drove it around some more today it is still doing it. Looking for some ideas on what to test next. i checked the aap and all was good there i also noticed some black smoke coming out the exhaust.

87blyota

bump.

87blyota

did a compression test today it came back 180 psi on all 4 cylinders.

Odin

That is what I was going to suggest. Now that it's out of the way it's time to look for CEL codes.

87blyota

Its a 87 with 22r I don't think it has a ecu to even store codes

bswarm

Is there a float level sight glass on the carb? It should look something like this...

The fuel level should be about center.

87blyota

Float level is correct I checked that after the compression check. I ordered a new ignition coil on a street bike I use to have it went out on it acted this way it was fine cold after it warmed up it would miss in lower rpm range when taking off

bswarm

And it's for sure only 1st and 2nd gear? Try disconnecting the EGR, see if it's better. If not reconnect it and try disconnecting the vacuum advance on the distributor. Reconnect them if it makes no difference. It's a longshot, but I did have a few distributors come in with a worn advance plate bushing causing a misfire on vacuum advance.

87blyota

I unplugged the egr last night and it made no difference. Also checked the timing advance its doing it's job too and yes only in 1st and second once I get going it doesn't do it anymore

87blyota

even when it does miss it's real quick it'll miss catch itself and go right on down the road then when i shift into second it does it again sometimes, sometimes not the longer im driving it the more it does it in 2nd but it has yet to do it in 3rd

bswarm

The 1st and 2nd gear only has me stumped, unless it has a vacuum switch connected to a transmission switch for one of the emission controls.
Check the coil tower for carbon tracks where the coil wire plugs in. Other than that you said there was black smoke out the exhaust, that's too much fuel and possibly carb overhaul time. Carbon buildup in the cylinders causing intermittent misfire? I'm out of ideas after this.

87blyota

Good to know I'm not the only one I've been checking plugs before and after its doing it and they are a nice light tan

Odin

Yea, then then there's that... Derp

At least that brings it down to basics. Like you mentioned, spark and fuel.
I know Holley's fairly well but not these carbs. Gunna throw out some guesses here because I don't know anything about the carbed models.

Make sure all your ignition and electrical connections are tight and corrosion free. This includes battery cables.
Either can cause loss of voltage = Spark
Check your fuel pressure.
If you're using an electric fuel pump voltage loss will normally mean a lack of fuel pressure so you'll want to check and make sure your connections are corrosion free and tight there too.
Check the fuel filter.
Make sure your air filter is good with no restrictions. Try driving without it.
Check to make sure the choke is functioning correctly.
If there are any vacuum connections make sure they aren't leaking or plugged.
With the engine and air cleaner off slowly move the carb to full throttle to see if there is a lack of fuel being added from the accelerator pump.
Check to make sure the secondaries are functioning/transitioning correctly.

I'm sure there's a few more I left out.

87blyota

Out of curiosity is it possible for a ignition coil to slowly slowly break down? Also could the fuel pump be going out even though the fuel bowl is at the right level?

bswarm

I've rebuilt many of these carbs, but that was many years ago. I do remember one odd thing, there's a vacuum sort of power valve that enriches the mixture under hard load, and if that rubber diaphragm goes bad it runs rich at idle and may cause a stumble. The way to check it was pull the vacuum hose off (it's on the carb) and if fuel drips out it needs a carb rebuild. It's the vacuum hose on the cover in this image, see the cover to the right of part#21667...
http://www.utoyot8.com/images/182703998/405309118.png

87blyota

Bswarm I believe that's the aap your talking about. Just as a up date got back from a long drive and it didn't do it at all.

87blyota

alright so i have filled the tank twice since this first happened and am half way through the second tank i know its a crazy idea but what about bad gas....