Random Misfire while cruising

[Mark Maras]

 Both are excellent suggestions. As I recall he has a reasonably new set of NGK wires and we tried swapping two wires. He eventually bought a Bosch cap and rotor and verified a hot spark. I hadn't thought of a helicoil. 

[jalexquijano]

Plugs 4, 5 and 6 after 5 to  7 mins stop and go traffic today! What next? Ngk Bp5es spark plugs!!

[Patcon]

If all 3 on one carb are like that, I would start there.

Maybe stuck choke or choke cable binding up

[siteunseen]

Yes, pretty much narrows it down to the rear carburetor.

I'm not sure if the SUs have an idle circuit but that's what it sounds like.

[Mark Maras]

 I agree with Cliff. It seems to be a rear carb mixture problem of some sort. How many turns down are the nozzle screws? However, that doesn't explain #5 and #6 looking like #4. As I recall, #4 alone was the problem child. @jalexquijano What was the outcome of changing the valve seals? Was one of the seals on #4 damaged and did you change them all or just #4?

[jalexquijano]

Just changed the seals on cyl 4

[Mark Maras]

 Well, it would appear we're back to the rear carb. How many turns down are the mixture screws on both carbs?

[jalexquijano]

On 9/25/2021 at 7:53 PM, Mark Maras said:

 Well, it would appear we're back to the rear carb. How many turns down are the mixture screws on both carbs?

Ill check on this today. Anyway yesterday while parking the car i decided to turn on the air conditioner and the engine started to accelerate randomly. If i turn the AC compressor off, the engine will go back to idle speed. Could the electric solenoid i installed a couple of years ago be faulty? 

[jalexquijano]

Just now, jalexquijano said:

Ill check on this today. Anyway yesterday while parking the car i decided to turn on the air conditioner and the engine started to accelerate randomly. If i turn the AC compressor off, the engine will go back to idle speed. Could the electric solenoid i installed a couple of years ago be faulty? 

How do i check on this? 

[Mark Maras]

The simple way would be disconnect the wires to the solenoid. Do you have any theories why #s 4, 5, and 6 are fouled now? As I recall #4 was the only fouled plug previously and changing a couple of valve seals doesn't explain #s 5 and 6 getting worse. Was anything else worked on or fixed during the valve seal installation?

[jalexquijano]

On 10/11/2021 at 7:31 PM, Mark Maras said:

The simple way would be disconnect the wires to the solenoid. Do you have any theories why #s 4, 5, and 6 are fouled now? As I recall #4 was the only fouled plug previously and changing a couple of valve seals doesn't explain #s 5 and 6 getting worse. Was anything else worked on or fixed during the valve seal installation?

Nothing else. Ill check on the fuel mixture knob to verify the amount of turns. 

[jalexquijano]

Checked on the mixture knobs of both 3 screws round SU CARBS and they had 4 turns clockwise each. I checked on the balance to verify both open at the same time and lowered the mixture knobs to 3.5 turns each. Now the car has less power and started popping / backfire in the exhaust when releasing the gas pedal. I believe it should not backfire has the mixture is leaner. Any thoughts? 

[Patcon]

If you went from 4 turns to 3.5 turns, you made it leaner!

 

[jalexquijano]

Then why the backfire when releasing the gas pedal if its leaner? 

[Mark Maras]

1 hour ago, jalexquijano said:

Checked on the mixture knobs of both 3 screws round SU CARBS and they had 4 turns clockwise each. I checked on the balance to verify both open at the same time and lowered the mixture knobs to 3.5 turns each. Now the car has less power and started popping / backfire in the exhaust when releasing the gas pedal. I believe it should not backfire has the mixture is leaner. Any thoughts? 

 When you say clockwise, is that viewing the mixture screws from the top or from under the carbs? Your thoughts on 3.5 turns down vs 4 turns being leaner is correct. You mention both carbs opening at the same time,which could be linkage related, are pulling the same amount of air at idle?

[jalexquijano]

From the top lowering the jet to allow more fuel.

[Mark Maras]

9 minutes ago, jalexquijano said:

From the top lowering the jet to allow more fuel.

 That's what I remembered. We've got to keep this in mind because most of us view (mentally) the m. screws from the bottom. I'm still curious to know if both carbs are pulling the same amount of air at idle.

[jalexquijano]

1 hour ago, Mark Maras said:

 That's what I remembered. We've got to keep this in mind because most of us view (mentally) the m. screws from the bottom. I'm still curious to know if both carbs are pulling the same amount of air at idle.

Well i did balanced both of the carbs with a synchometer and turning the right screw at the linkage. I can try again tomorrow 

[jalexquijano]

7 minutes ago, jalexquijano said:

Well i did balanced both of the carbs with a synchometer and turning the right screw at the linkage after turning the fast idle screw to raise the idle 2500 rpm. When both carbs measured the same i returned the fast idle screw to current idle.  Im i doing something wrong here? Should i disconnect the linkage before doing this? I also have a colortune device. 

 

Edited November 5, 2021 by jalexquijano

[psdenno]

The Colortune will give you a good visual check on what's happening during combustion.  When I used to adjust the carbs, I would follow the steps in the shop manual and then check with the Colortune for any final adjustment.  No idea if many people still use a Colortune.

[jalexquijano]

On 11/4/2021 at 9:33 PM, psdenno said:

The Colortune will give you a good visual check on what's happening during combustion.  When I used to adjust the carbs, I would follow the steps in the shop manual and then check with the Colortune for any final adjustment.  No idea if many people still use a Colortune.

Tuned both carbs at 1000 rpm, balanced them and adjusted fuel mixture knob at 3.5 turns clockwise. Ill take a drive to see if i need to open them more. 

[siteunseen]

It's counter clockwise.

You turn them clockwise to raise them, less fuel. Counter clockwise to lower the needle, more fuel.

The insructions say turn them clockwise towards the passenger's side until snug then counter clockwise towards the driver's side to 3 full turns for the base setting. If the plugs are white go down to 3.5 turns counter clockwise and so on, do half turns for the fine tuning.

Think of laying under the car when turning the knobs. Right would be towards the passenger's side raising the needle which fills up the tube with more needle there by lessening the fuel.

Hope that makes sense.

[siteunseen]

Just read Marks comments, sorry if I've confused the conversation but I always think about the needle going up or down into the jet that determines the amount of fuel/air.

The jet screws in and doesn't move. The needle is adjusted with the knobs.

Right Mark? Should I try getting my foot in my mouth?  I'm not sure I can do that move anymore.

 

Edited November 6, 2021 by siteunseen

[siteunseen]

Foot in mouth, figuratively.

The knob adjust the nozzle into the needle so I am wrong.

SORRY!

 

[jalexquijano]

Ok after taking the car for a ride and adjusting the fuel mixture to 3.65 turns front and rear carb at 1000 rpm, the car ran pretty well but presented the following issues:

1. Backfire at exhaust when releasing gas pedal at 2nd and 3rd gear. Pops, pops....

2. Car started stumbling after staying parked on idle for 10 minutes. Could be due to some problems with vapor lock we had discussed in the past and never solved.

I guess ill have to live with this problems and only use the car on weekends to avoid traffic jams during weekdays.

Spark plug 1 2 3 4 5 6

Edited November 10, 2021 by jalexquijano