Oldsmoswede

I just did a comp test with warm engine, fuel line plugged and kept full gas when cranking. As I understand, thats the way to do?

I got values 160psi (on cyl#3), other cyl 180-190.
According manual my engine should have ratio 10,75:1 (engine# S272611G).

Don’t know how to translate that to ratio, but does that say anything about my engine?

I’m trying to get it running well, but it’s a struggle...

joe_padavano

The absolute numbers are less important than the cylinder-to-cylinder variability. Sounds like #3 is a little weak, but I wouldn't be too upset with those numbers.

Vintage Chief

As most compression tests will stipulate and as many Oldsmobile CSM manuals indicate (as Joe has suggested), the important consideration is the delta between cylinders. In general (quoted from an Oldsmobile CSM): " The lowest reading cylinder should not be less than 80% of the highest". Your highest = 190, your lowest should not be <152. You're groovy, but a tad low. The next time you perform the compression test (as you did this one dry I assume), squirt a tablespoon of oil in #3 (wet compression test). In general, if the compression increases, it can often indicate a slight/mild condition with piston rings. The oil acts as a sealant against the cylinder walls and the piston rings. If the oil (acting as a sealant) facilitates an increase in compression, it 'might' indicate rings are slightly worn.

Fun71

You can't really say a particular PSI reading equates to a specific compression ratio because the cylinder pressure in greatly affected by the camshaft profile, specifically the intake closing event. If you have two engines with identical compression ratios and one has a short duration camshaft / early intake closing event and the other has a long duration camshaft / late intake closing event, the engine with the short duration / early intake closing will have higher PSI readings.

Vintage Chief

That was awesomely well constructed. Nice job!

Oldsmoswede

Thank you guys for your inputs 👍 You help me to keep me motivated and hopeful 😊
That camshaft theory makes sense as well.

So there still might be hope to get it running properly. Think I can rule out bad valves then, and focusing on fueling. It’s for sure over fueling somehow, spark plugs pitch black and spitting out drops and lot of smoke from the exhaust pipe.

I have done the ignition setting and dwell angle according the manual but didn’t help.
Bought a rebuilt Rochester 4GC from Carboretor Center this winter. Maybe there has happened something with the floats during the long shipping to Sweden? It has for sure flooding tendencies. Don’t feel good to open up a rebuilt carb but can’t see anything else to be the cause any longer. My old carb did a LOT of flooding, but found out the reason for that, one of the floats was full of gas...

So now I’m just gathering some energy and self confidence to open up the carb. I hope I can reuse the gasket after opening it up ?

By the way, that gasket gets soaking wet when I start up the engine. Don’t know if that’s normal?

Charlie Jones

This thread may be helpful ;
https://classicoldsmobile.com/forums...c-carb-127376/

Ozzie

It sounds like the fuel is too high in the bowls. Check that and the choke to reduce the richness being delivered by the carburetor.

Oldsmoswede

Yes I have seen that thread also, thanks for helping anyway ! 👍
Have been watching some YouTube as well 😊

Oldsmoswede

I have noticed that the choke is not the issue in this case. But will open the carb and inspect the floats. Hopefully I find some issue there.
Thanks! 👍

Fun71

Also check the fuel pressure. The QuadraJet needs around 7psi maximum or else flooding can occur. I had an issue with a new fuel pump putting out 10+ psi and it caused fuel to overflow and cause the engine to run very rich and die.

Charlie Jones

We're not talking about a Quadrajet , this discussion is about a 4GC .
Although , excessive fuel pressure might be a problem .

droldsmorland

Snap some pics of the spark plugs.

Before you disassemble the carb make sure it's not under warranty.

Check the air horn screws to see if they are loose. If yes just snug them up. Be careful over-torquing is easy to do with large meat hooks.

Disassemble the air horn from the float bowl carefully... you should be able to reuse the gasket. If it tears new gaskets are readily available.

Verify both floats...float in gas.​​​​​​
Verify the needle and seat tappers fit together well.
Verify that the metal O ring is present under both "seats".
Verify float level and drop settings per spec.

When the air horn is off check it for warpage with a straight edge. This could be the source of the weeping bowl gasket.

Be very careful to not over-torque during reassembly or mounting to the intake. Re-check torque after about 300-500km, the gaskets will settle.

Oldsmoswede

I went by a workshop and picked up new spark plugs but noticed a difference in length. Going back tomorrow to swap. As picture shows, my sooty plug indicates over fueling.
I have checked fuel pressure as well, seemed normal, around 5,5psi.

Oldsmoswede

Thank you for advices, appreciate it 👍
Will continue with it tomorrow when I hopefully have the correct spark plugs.

About warranty. I contacted the company about it a while ago. They recommended me to open it up and check the floats. It just feels struggling and costly to ship it back.
But if there is something wrong inside the carb I will contact them again.

Oldsmoswede

l lifted the air horn, one of the floats was filled with fuel...
And, there was no pull clips installed to the needles??? 🙄

Charlie Jones

If it was me , I would demand the " rebuilder " furnish me with two new floats and a carb kit .
For the money some of these guys get , you think they should at least provide new floats .

Oldsmoswede

I emailed them, let’s see what they have to say about it. Hopefully they are serious and solve this smoothly.

droldsmorland

There ya go. It's hard to find a good carb rebuilder. Let's see how this one does for you? I'd insist they simply send you another carb with a new base gasket. You paid for a rebuild. You should not have to be opening it up to fix their screw-ups.

Do you have the original carb? If so you could send that out for a quality rebuild and use this carb until it shows up after you fix the problems.

If you decide to go that route there are a few good Rochester carb shops on this side of the pond. Though they all have a waiting list.