5998DownUnder

Hi everyone,
I have just returned from a 3 day expedition in my 1959 Ninety Eight Oldsmobile. (394ci). About 1000 kilometre round trip.
My nieces' year 12 formal (Prom) in Canberra.


I may have a carby/fuel problem.
After searching via search bar found similar things discussed, where people have rough idle when cold. However my problem is that when hot, my car will idle extremely rough and stall.


The car drives beautifully on the road and I sat at a comfortable 100km/h. No dramas, she did not miss a beat.


Totally different when I hit the Sydney traffic and traffic lights. When stationary and idling the car becomes extremely rough, and stalls of its own accord and can stall when I go to take off, so a little T.L.C was needed when moving off. (Neutral + brake + accelerator + engage drive).
Took the car for a 15 minute trip yesterday and same thing happened re the stalling and rough idle.


When the day cools down a little, (it is 9.50am and already 85 degrees) I am going to check , vacuum hoses for leaks, fuel filter, carb mixture screw and idle screw for blockages.


If anyone has any suggestions re the trouble or something else I should look at, please suggest away.


Thanks
John.

5998DownUnder

The Olds in action.

oldsboyDino

Try this simple test. Disconnect the wire to the alternator and see if your car runs better. Your regulator could be putting out too much voltage to the coil and it could wreck your coil if it hasn't already. You can also check the voltage going to the coil and make sure it's not much over 12 volts.

lazy394

That is a Gorgeous 98 !!!
The 394 has the exhaust ported through the intake and under the carb.(That would be the bit on the intake with the paint burnt off).
When they get hot it boils the fuel off, especially when you shut it down.
Mine is an AC car so it has the fuel recirculating and the carb has mods to cope with the increased temp and it did it as well. I fabricated 2 stainless blank off plates to block the ports off and so far no issues at all.
Not sure why they did that, as I thought the cooler the air etc the better?

Once again sweet ride and nice work !

5998DownUnder

Hi there Scott,
Thanks for the comments on the car.
I have the carby off at the moment so I will check that out what you suggested, not sure where to look but I'll drag the manual out tomorrow. I hope my new carby kit arrives tomorrow as well. (fuel leaking from both top and bottom carb body gaskets). Time for an overhaul.


These cars attract some favourable attention to say the least, as you would know.
All the way back to Newcastle from Canberra, constant: thumbs-up, smiles and nods, kids in the back of the cars-waving, mums in the front pax seat waving. Made people smile, that's the main thing.

D. Yaros

Interesting that you speed is in km, but your temperature reference was to degrees Farenheit?

5998DownUnder

Speed is off Garmin nav man, it comes up in Km/h for this part of the world. I have to go off that as Olds speedo is not working.


I converted temp from Celsius to Farenheit for your viewing pleasure, (to save you converting it).

5998DownUnder

Thanks for that tip, I'll get the carb together and in and give that a go.
John.

5998DownUnder

I notice there is a thicker gasket btw carb and manifold, about 5-6mm thick.
I only got a standard 1.2mm thick gasket for that in my carb kit, wondering if a much thicker gasket might work. Maybe reduce heat soak?

Charlie Jones

It sure will.
Also another thing to check is the heat riser valve at the end of the left exhaust manifold. It may be stuck closed. On one side of the valve there will be a spring. On the other there will be a bobweight. The bobweight should move freely and the spring should return it to the closed position.
If the heat riser valve is stuck you may be able to free it up by soaking it daily for a week or two with a good penetrating oil.
The heat riser system was used when the outside temperature is below 45 degrees, and gasoline vaporizes slowly. It diverts the flow of exhaust gases from the left bank of cylinders up and across the engine through a passage in the intake manifold that runs under the carb. The idea is that the exhaust heat would warm up the carb and make the fuel vaporize better.
In warm climates, and in the case of collector cars which are never driven in winter. The heat riser system can be rendered ineffective. If a heat riser valve is hopelessly stuck, The flap inside of it that blocks the exhaust flow might be removed. As mentioned before the heat riser passages can be blocked by special intake manifold gaskets, but, if you do this make sure the heat riser valve is open.

5998DownUnder

Thanks Charlie Jones, I will be checking this out.


Well,


1/ Carbi kit put through, Still leaked a little,
2/ I took it apart and used aviation sealant on gaskets I replaced and it leaked a lot.
3/ then pulled carb apart again and checked gaskets, I had been replacing the gaskets I removed from the carbi, like for like. Being a kit that fit a few types of carbs there were different variations of gaskets.
Someone had originally used the incorrect gasket (heavens knows how it lasted this long), and I was following their gasket. Yes, my fault I should have checked for correct gasket for carb body, so I found the correct gasket and used that, aviation sealant, tightened her up, put on car...NO MORE LEAKS.


Rough idle and stalling at standing and low speed was fixed by re-setting slow idle screw. Oh and probably no more air getting sucked in and fuel sucked out of carbi.


2 out of 3 isn't bad but not good enough. Appears to 'bog down', cough and lose power momentarily when accelerating from standing start either slow or fast. I have to almost prime the accelerator to keep the car going by just a jiggle of the foot.

lazy394

Pleased it was an easy fix!
Guess what mine bogged down as well, all the wear in the linkages make the accelerator pump open too slowly. My old school mechanic who is a genius with tuning old girls had to Drill another hole where the accelerator pump linkage goes from the linkage to the pump ( about 3 mm further forward ).
Problem solvered

5998DownUnder

Thanks Scott,
Just got in from checking and mucking about with that linkage and the 2 hole positions. I actually adjusted mine so the little rubber stopper was just above the hole. Hope that's right.


I found 2 threads on Rochesters' bogging down on acceleration.
Looks like I may need to pull the carbi off again and look at the Auxiliary Throttle Valve adjustment.

lazy394

Carbi's are a black art , have fun !!

5998DownUnder

Would anyone have a photo of Q-Jet tensioned secondary spring?
My manual and discs do not show where it is and been looking on the net and the info I get is that one already knows what it is.
Thanks.

D. Yaros

The carb bogging down is frustrating and elusive. On my '55 Cadillac the problem was caused by a defective distributor vacuum advance. A rebuild of the advance cured it. Just another item to consider?

5998DownUnder

Thanks Dave, taken that on board.


Its funny how prior to me pulling apart and re-kitting the carbi, I did not have this problem.


Pilot error on my behalf maybe. Perhaps I have buggered something in the process.
I do remember the Auxiliary Throttle Valve dropping onto the bench. Might have upset that.

5998DownUnder

It now does not stall when idling in gear like at the lights like it used to. That's fixed and don't know what I done there but only the bogging on take-off to go.

Kahuna

Be sure to check the Heat-Riser Valve on your exhaust manifold. If it's not working properly, the carb can overheat and cause the fuel in the reservoir to boil, especially on a really hot day.

5998DownUnder

Thank you for that and the diagram will take a look.
Would that have something to do with bogging down on acceleration as well as the stalling?


Thanks
John.

Kahuna

If the fuel is boiling, the carb will simply not function properly. Both stalling and bogging down can occur. I had this problem with my '62 Dynamic 88 (394 2-bbl) a couple of summers ago. Turned out the previous owner installed the wrong heat-riser valve, so the valve would not open or close fully. When I replaced it with the correct valve, the carb performed much, much better.

As a precaution, I later replaced the standard 4-blade fan with a 6-blade fan AND installed an electric fan (hidden between the rad and the grill) that kicks in automatically at about 190°F (thermostat is 160°F). I also installed an override switch inside the car, so I can turn the electric fan on well before it reaches 190°F, if I'm approaching heavy traffic on a very hot day.

5998DownUnder

Thanks Charlie Jones and Kahuna.


Checked it out, Manifold Heat Control Valve is locked solid.
I do not know yet if it is open or closed. I have soaked it in penetrant and moved the weight back towards the motor and hope to unbolt it tomorrow.


Now, big question for anyone who can assist me.


Do I need one of these valves if I am going dual exhaust? I cannot see the reason for it on duals.
I have my dual system ready to go on at any time just a waste mucking about with this valve if I do not need it.
I checked out the workshop manual and it gives me no indication if I need it on a dual exhaust system.


Oh, have got rid of all problems except bogging and almost stalling on acceleration at low speeds at intersections and roundabouts. Seems to be more prevalent on the upshift.


Thanks,
John.

Kahuna

Yes, the heat riser valve is required on both dual and single exhaust systems, as indicated on the diagram I previously posted. The purpose of the valve is the reroute some of the exhaust up through the exhaust passage (middle portion) of the intake manifold, in order to warm up the carb on cold starts. When the bi-metallic spring on the valve reaches a certain temperature the valve will open fully allowing all of the exhaust to be routed down the tailpipe (see attached diagram below).

As for the stalling issue, I also had this problem a while back. I simply adjusted the idle screw on the carb to register 50 RPMs higher than spec. To clarify, I'm referring to the warm engine idle speed, not the cold engine fast idle. This seemed to do the trick, in my case.

D. Yaros

Well I will disagree. The heat riser was in fact used on both single and dual exhaust systems. However, it is not required on either. The purpose, as stated, is to speed up engine warm up in cold weather.

They are noted for sticking closed.

If you are not driving in cold weather, you do not need it at all. Many folks remove the butterfly valve inside the device, or prop it open.

What is needed is something to fill the space occupied by the heat riser assembly in the space between the exhaust manifold and the exhaust pipe.

lazy394

I agree that it is not required. When I bought my car the heat riser assy was AWOL and it still displayed the same symptoms as yours. Even with the assy working a large amount of exhaust is still ported through the intake ( see Kahunas attachment to his post ). The problem was solved by blocking off the ports on the intake side of the head and adjusting the air fuel.
Last week I was out in 39 degrees with the AC on. The engine Watchdog registered the block temp to be between 75 to 90 degrees. Only when stuck in traffic and the temp rose to 100 did it start to play up, turn the AC off and it went straight back to 90 and it performed as normal.
As for the bogging down I have the same issue but mine is related to it short shifting into second ( its only in first for 5 or 6 mtrs). That's also on the 'to do 'list.

5998DownUnder

Yes, no real need for the valve here, doesn't get cold enough especially as I am on the coast. Fair enough they are needed where the cars originated though.


Lazy394
"The problem was solved by blocking off the ports on the intake side of the head and adjusting the air fuel".


Scott, can you tell me where these were blocked, I will do same.


Also


"As for the bogging down I have the same issue but mine is related to it short shifting into second ( its only in first for 5 or 6 mtrs). That's also on the 'to do 'list".


This sounds like what is happening to my car. What do you think can be done to rectify this?

lazy394

John,

Place a 0.6-0.8mm Stainless plate between the gasket and the intake to cover the opening. Trim to shape so its smaller than the gasket and wont be seen. Use plenty of the copper based sealant. The other bonus of this is the centre runner on the intake wont get the paint burnt off any more .

As for the Jetaway First gear drama I was led to believe it was a seal issue from the car being dormant so long, but im not sure...maybe a good subject for another post.