Stromberg question

[Henry Hopper]

I’ve just been out in the roadster and thought I’d do a bit of routine maintenance when I got home.
The car was running fine. I checked the plugs and found them a bit sooty .
I cleaned them and refitted them, gaps were fine... In my wisdom I decided I would adjust the mixture screws on the carb. I took them out and cleaned them off and reinstalled as we the manual.... I followed to text on how to adjust but I now have a popping in the exhaust... no matter how I adjust them it still pops.

The adjustment screws are easy to turn by finger pressure and in fact seem a tad loose in the treads.... I don’t know if this is normal or not.

Plugs are new NGK , new E-Fire distributor and new leads and coil a couple of months ago

As I said, it was running fine until I meddled with things. any ideas?

[Charlie ny]

Max,
Donde estas ?
Charlie ny

[Lawson Cox]

If it ain't broke. Don't fix it.

[Henry Hopper]

I’ve ordered a new carb so hopefully that’ll do it.

[drolston]

When does does the exhaust pop? At idle? When decelerating in gear? All the time?
The only thing that changed was messing with the plugs, which were a little sooty. Recently I have learned that "cleaning" plugs does not necessarily help, and can actually make things worse, like causing a cylinder misfire some of the time, dumping raw fuel into the exhaust. So before a new $300 carb, try $24 for new plugs. If a little sooty, maybe try a hotter range; like go from NGK 6 heat range to a 5. Worked for me.

[Henry Hopper]

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The plugs are new( about 120 miles ago).. the soot was soft and just brushed of with a scotchbrite pad, so I doubt I’ve done any damage to them, likewise the distributor was fitted new at the same time along with new leads and coil. The car fired up fine after putting the plugs back in it was only after I decided to try and “ fix” the rich mixture that things went south.
As they say,” a little knowledge is dangerous”��.... the mixture screws are pretty loose in the threads too... maybe I dislodged some dirt with messing?

I followed the procedure from the Stromberg owners manual on setting the screws ... I started by screwing them in fully and backing them out 1 and a 1/2 turns exactly... I then tuned each one in until the motor began to bog and then turned them out slowly looking for the motor to gallop.. but it didn’t, it just sort of sat back at idle.Figuring I must be somewhere near the sweet spot I revved the motor but every time it “pops “in the exhaust. I spent quite a time slowly turning the screws one way and another but no joy.

I decided to buy and fit a new 97 and see if that cures the problem.. if it does I may rebuild the old carb as a spare. I recently sold some parts for a decent return so in my mind the new carb cost me nothing ( I find it eases the pain ��)

Thanks for the input.... I appreciate it.

[Terry,OH]

The springs for the adjustment screws should hold the screws firmly. They should not be loose. The screws were made to turn by your fingers. The original brass adjustment screws do not have a full screwdriver slot.

[drolston]

Couple of easy and inexpensive things to try.
1) Let the engine idle a bit then shut it down and remove the top of the carb to check the float level. If less than 1/2" from fuel level to gasket surface of fuel bowl, adjust the float level and clean the needle valve and seat with some carb cleaner. Check your adjustment by dipping fuel out of the bowl and then cranking (ignition off) to see where the fuel level ends up when the needle valve closes. Keep cranking for 5 - 10 seconds to be sure the needle valve is not giving way under too high pressure.
2) Check those plugs again to see if any are sooty and/or wet, indicating misfiring in that cylinder. If any are suspicious, check for a nice blue spark that will jump at least 3/8". Check for continuity in that plug wire and be sure the connectors are fully inserted into the distributor cap.
3) Run some MMO through the carb while jazzing the throttle. If a valve is sticking that may clear it up.

[1931 flamingo]

AS Terry,OH stated, make sure the springs are there !
Paul in CT

[Henry Hopper]

I did notice that the springs were weak or short as they didn’t seem to be doing much in the way of compressing.

I went though the plug leads today just to see if I’d missed something but all are well seated in the distributor and onto the plugs .

I should hopefully have the new carb later this week and I’ll let you know if that’s solved the issue or not.

Just wish I’d left things alone now ��

[koates]

Henry, You do realize that those two mixture screws are for the IDLE SPEED MIXTURE only and have no effect on the engine mixture at anything above idle speed. Main mixture is controlled by the size of the main jets which are a fixed size. There are various sizes of main jets available. Too read the plugs you need to go for a long drive (30 miles) at a bit of speed and then check the plugs. The shit fuel we get these days could be the cause of plugs blacking up. Maybe a set of plugs one range hotter will help but I would not worry to much with plugs sooting up a bit especially if you do short runs around town all the time. Regards, Kevin.

[koates]

Henry, I hope the new carb you are buying is a genuine Stromberg 97, made in England. Its the ONLY one to buy. All others are somewhat inferior in quality. Regards, Kevin.

[Henry Hopper]

The carb is one of Clive’s .
I’ve also ordered a fuel pressure regulator and gauge as the car has an electric fuel pump and I’m half convinced this may be part of the problem.

We’ve recently ,last month, had this awful E10 petrol introduced and E5 is still available but very expensive... I put a few gallons in on Friday and it was £1.45 a litre!!! it was £1.24 a few weeks ago.... it’s 99 octane, it used to be called Super Unleaded until the recent change.

The price of a US gallon of the E5 at U.K. prices is $7.59 per gallon at today’s exchange rate ... most of it fuel tax!!!

[Henry Hopper]

Problem solved ... I fitted the new Stromberg and bought a Filter King regulator and gauge unit.... runs a treat now👍

[Cadillac_chris]

Yup speedway 97s are garbage