Hi have tried to adjust highest vacum on idle and this was the best i could get today :

Used this port on the carbs base plate :



Was about 10 when i started so i turn the screws counter clockwise some turns , maybe the engine have
going to lean before ? :



The sparkplug to the right is from cyl 8 and the plug next to it from cyl 2. New sparkplugs , cap rotor and points.
Dwell ok , ingition ok , have not testdrive the 98 yet.

( sorry for bad picture quality )

 

A steady 18.5"Hg at idle is good.

Plugs do look lean; idle mixture doesn't really affect that as much as main jets do. If you're using ethanol fuel the stuff runs inherently lean. If you don't hear any detonation or evidence of a burned valve you should be fine. That's taking into account lack of larger jet availability for 4GC.

 

Nothing I would worry about.

 

Your spark plugs look fine.

 

They are available from Daytona Carburetor ;
Daytona Parts Home

Tony at Ross Racing Engines recommended to me to run one or two sizes larger in a 4GC to compensate for Ethanol laced fuel .
I jetted my '63 one size larger on the primary side , and two sizes larger on the secondaries .
The jet sizes are stamped right the jet .

A " brown sugar " color on the plugs indicates that the carb is delivering the ideal mixture .
Those look a little too white .

 

Thanks for answers , when we have drive cruising this year the engine could suddenly stop
at low speed / low rpm in city driving but starts easy up again. This has not happen
earlier and also not responding to the throttle as before . Could the poor vacum from the carb do so
the vacum adjustment on distrubator not worked 100 % and this is the problem that the engine stops att low rpm in slow speed ?

Driving on the best quality of gas avalible here with max 5 % ethanol.
shell-v-power-98.pdf

Next month we have more ethanol in the gas here 10% ( E10 ) but the E5 we have now should
stay at some places , we don´t know were yet.

 

I poured a little gas into the carb today and the engine started up.
Checked the ignition timing with the vacuum line blocked from manifold to the canister and blocked on the
carb to distributor but the ignition lamp showed the same as before. Had 18,5 Hg on the vacuum gauge last i
checked and the idle screws almost dropping out of their threads.
Screwed them in clockvise until they sited and out 2 turns but the engine would not start until 3,5 - 4
out. have the vacuum gauge connected and got about 17 Hg vacuum now but the engine don´t run
smooth at all. So we´ll se what to try next .

 

That's a classic sign of a vacuum leak or clogged idle passages. Vacuum leak can also contribute to a lean condition as your plugs indicate.

I think a carb teardown, cleaning and rebuild is in order. Make sure to get a rebuild kit made of ethanol-resistant materials. Daytona Carburetors as Charlie mentioned should have these. Also look into increasing jet size if they're available.

Be careful when selecting the gasket between fuel bowl and throttle body. Different 4GC have different vacuum passages and the wrong gasket will make a 4GC do strange things.

Also check all rubber vacuum tubes for deterioration and if the car has vacuum power brakes, check the vacuum booster diaphram for leaks.

Only 5% ethanol in Europe and 98 octane. Wow. Looks like better gasoline stock to start with, and corn farmers don't have as much influence in Europe as here in USA.

 

You shouldn't have to pour gas in the carb to get it started .
Have you checked to make sure your accelerator pump is working properly ?
To do this , with the engine off , remove the air cleaner and hold the choke butterfly open .
Then look down the throat of the carb with the aid of a flashlight .
Have someone press the accelerator to the floor .
You should see two fine streams of gasoline pour into the carb throat .
If you don't , the accelerator pump is defective .
Since the accelerator pump is inside the carb , the entire carb should be re-built .
Here's a thread on re-building a 4GC carb ;
How to ; Rebuilding a Rochester 4GC carb - ClassicOldsmobile.com

 

Thanks for answers , yes the accelerator pump seem to work , i poured in a little
gas because it was so hard to start last time , but it started up and run fine some
seconds.

The carb is a rebuilt from Autoline C979 almost new , not many miles on it at all.

Have saved the carb rebuild link in my computer and should look at it , thanks.
Should check the hose to the vacuum booster brakes , all other vacuum hoses are new.

PS . the hose from intake to brakebooster was very bad and went off when i should
pull it off the manifold , replaced the hose with a new and checked the idle screws
again and got 18 Hg vaccum. But the engine shakes so you can feel it in the car.
So a new try another day.

I tried to clamp the new hose to the brake booster but no difference.

Was thinking maybe the carb don´t get enough fuel , hmm . Have looked after a new fuel
pump here but not so easy , sold out on several places.

 

Glenn - You did not answer Charlie's question though - this is critical to troubleshooting further. What is your answer to the following?

 

I answerd this in my last post , that the
accelerator pump seem to work.

 

You stated:

I'll take your word for it. From your answer it didn't appear to me (at least) you saw two solid fine streams of gasoline pour into the carburetor - which is critical. If you did see two streams, then the carburetor accelerator pump should be doing its job.

 

Glenn - I'm thinking perhaps you have missed something in tuning the engine and I say this because earlier in this thread you stated you can achieve a steady 18.5" Hg vacuum. If you can achieve a steady 18.5" Hg of vacuum you shouldn't/don't have a vacuum leak. I'm suspecting it's likely you have missed something in the tuning protocol.

I don't own a Ninety Eight, but it's not such a bad thing to review the basics of the tuning procedure. Each step is critical and each step MUST be performed in the correct order.

(1) Dwell. Ensure your Dwell is established correctly. My 350 dwell angle is set to 30°.
(2) Ensure the points set screw (the one which hold the points to the base plate hasn't moved). The points need to be set so that the points rubbing block is on one of the high points of the eight lobes of the distributor shaft. If the set screw isn't tightened down securely, the points opening/closing may have shifted significantly.
(3) My initial point gap is set to 0.019" (inches).
(4) Establish initial timing. Disconnect the vacuum hose at the distributor vacuum canister and plug that hose. If the air cleaner is removed, plug the vacuum hose fitting w/ tape. Connect tachometer & adjust engine speed as indicated on your tune-up label on the fan shroud (or as indicated in your CSM). Now, set the timing to the specification on the tune-up label by loosening the distributor clamp bolt & rotating the distributor until the specification is obtained. My 350 is set to 12° BTDC. After this, remove the plugs and hookup the vacuum hoses.
(5) Establish A/F mixture ratio. It does not matter what the current position of the A/F mixture screws are currently set to. At this point, turn each A/F mixture screw either in (clockwise) or out (counterclockwise) until you achieve the highest steady vacuum you can achieve.

It never hurts to review and perform it again in case something was missed.

 

Charlie and Redoldsman ( Glen ) helped me out rebuilding my 63 Starfire 4-jet. But in talking with Tim at Daytona I still must have an issue with the idle circuit-vacuum. Just cant put my finger on it. Starts right up but, no missing very smooth but as the choke begins to open as it warms up, it leans out and wants to stall. But if I partially close the choke by hand the idle picks up 1100 rpm and runs smooth again. Glen and I are scratching our heads on this one. We did everything we could do as far as a process of elimination.

 

Ok yes i could se 2 fine gas streams when i
turned the throttle lever. Would be intresting to
se how the gas flow from the pump is . Could
connect a small gas tank above the engine and
let gravety do the flow and hose from pump into a bottle, hmm. When my fuelpumps in my truck stopt working twice i had a lawnmower
tank under the hood to be able to drive the truck home.
Thanks for input , should check the adjustments again

 

That is some good ingenuity!

 

A friend of mine has a can of ether starting fluid strapped to his engine - I cannot make this stuff up! The truck is an old Ford F-250 (1991 maybe?). He assembled this labyrinth of metal angle iron mounted to the left front fender with nuts & bolts - yes, the bolts protrude directly through the fender to the exterior of the fender. He then installed this push-button switch in the solid metal dashboard which will strike the ether starting fluid can nozzle and disperse ether starting fluid into the carburetor to start the truck. Again, I cannot make this stuff up! You should see the expressions on the faces of people who ask him what that bolt is for protruding through the front fender. Of course, he's happy to demonstrate how he starts that beast.

 

That's MORE than shadetree !

 

He is more than a handful!

 

Try adjusting the choke thermostat a little richer .
Loosen the three screws and turn the black plastic thermostat slightly counterclockwise .
The initial adjustment has the index mark on the thermostat aligned with the top .
Try turning it a notch counterclockwise at a time until it is satisfactory .

 

Intresting to se some different solutions

 

Charlie, Glen and I have played the choke thermostat but maybe not enough? He maybe over tomorrow so we can play with it.

 

Got my new fuel pump from Texas and mount it and today and the top went down and
took a little testdrive. Have adjusted the idle mixture screws again and have now
about 18 Hg at idle warm engine. Should look in the chassies manual to se what
idle speed i should have , have around 700 rpm now in park.

But noticed when driving at slow speed that the engine rpm could vary ( fluctuate ? )
a little when throttle was at the same position. Have not noticed this before. a little
hesitation when pushing the gas pedal also. Looks like the streams from the
accelator pump is better with engine stopped than in idle

 

Is the vacuum port your reading from below the throttle plate? Can you tap into afitting in the intake manifold to take comparative readings?

​Good luck!!!

 

Hi , i used the vacuum port on the pic in the first post , should check if there are any avalible port
at the manifold.

 

There should be a small vacuum port on the top of the intake behind the carb . It provides vacuum for the heater system .
That is the one you should use .
The surging may be due to moisture in the fuel system . A bottle of Isopropyl fuel line de-icer will get rid of that .
18 " Hg sounds good .

 

Thanks Charlie , the only vacumport at the rear of the manifold i can se is the larger port to the
brake booster. The port to the heather system is in front of the carb.
Have adjusted and lubricated choke levers and throttle linkage / pedal so the car runs much better
now , a little hesitation left to check. Had a nice trip with top down earlier this evening. Should give
the mixture screws a little attention again next.