Exhaust loud popping: Lean? Rich? Fuel? What else?

[TEM666666]

Need some help!
Cold engine, no problem. As the car got hot I got loud popping noise from exhaust.

Now I did monkey around with everything a couple months ago because it (she?) didn't start after winter storage. Ends up to be both float bowl valves jammed up. Free'd it up and got it running again. Since I turned the jet mixture nuts (probably shouldn't have?), So I went back to scratch.. I set the jets 1/8th (0.125") below flush with calipers and played with it from there (lifting piston with screw driver to check mixture). I drove 40mins home no problems (on fresh 87 octane gas). I didn't drive the car much since I brought it home. 2 weekends ago, I put in 93 octane gas (ethanol free! yay!).. Drove home, no issues.

Yesterday, I went for a drive. When the car got warm, that's when I got the loud popping noise on acceleration. Rules say that's running too rich (too much fuel). Today I checked the spark plugs, pitch black! I turned the jet nuts up (anti clockwise looking down from above) to lean it out a bit, push up the piston lifting pins.. Got to where if I pushed up, it did nothing, then after a few seconds the rpm's dropped and engine shakes like it's about to stall out. Also adjusted idle screws to keep rpm around 1100 since idle rpm changed when I changed mixture... I drove it between adjustments. Am I still running way too rich? Still popping randomly on acceleration. When it pops the car is jerky too.

What's the fix? I have driven last year fine on high octane gas (only ethanol free gas around). So I'm guessing it's not fuel? Or is it? Or still running too rich? I feel I may have pushed the piston lifting pin up too much so I did it wrong?

 

[Joe Schlosser]

It seems like no one wants to jump in on your issue so I guess I will
You sound like you are still too rich. Book says correct mixture when playing with the piston lift is it should speed up a little and then settle down.
The nominal starting point for the jets is 2 1/2 (15 flats) turns down from full up. I do not know how this corresponds to your 1/8 inch initial setting.
What else did you touch when doing the post winter startup??
Suggest that when starts popping shut it off and have a quick look at the plugs.
Is there oil in the carb pistons?? They could be opening up too quickly

 

[TEM666666]

It seems like no one wants to jump in on your issue so I guess I will
You sound like you are still too rich. Book says correct mixture when playing with the piston lift is it should speed up a little and then settle down.
The nominal starting point for the jets is 2 1/2 (15 flats) turns down from full up. I do not know how this corresponds to your 1/8 inch initial setting.
What else did you touch when doing the post winter startup??
Suggest that when starts popping shut it off and have a quick look at the plugs.
Is there oil in the carb pistons?? They could be opening up too quickly

Hello Joe,
Thanks for your input! But most of all, motivation! There is oil in the piston. I played with the mixtures and idle. Took off the needle, piston, fuel inlet hose and float bowls.

I started with the left carb, setting the jet flush with the rest of the assembly, after 15 flats, it was 0.118" down which is only 7thousands from 1/8th. What bothered me was on the right carb, turning the nut all the way up, the jet won't go all the up to flush. What is causing that? I lowered it to 0.118 to match the other carb. The car fired up normal and I gave it time to get warm.. Still monkeying around with the piston lift and listening for rpm. Seems the 2 carbs needed fairly different adjustments (6? 7? flats difference seem too much?). Not sure if I'm doing it wrong but doesn't seem to work out as described. I went out for a 10min drive but it's fairly cool out tonight. No popping but it didn't pop on the cool night i drove it 40mins home. I'll have to try it again on a hotter day. Kind of late now.. I'll have a look at the plugs tomorrow. How much am I supposed to lift the piston? Maybe I'll try to get video next go at it..

 

[nomad]

Joe was nice enough to jump in on this but i thought I'd add my .02. First thing to do is make sure the butterflies are opening EXACTLY the same. If they are not all other adjustments most likely won't match. Personally I start at 12 flats down and look for the idle to pick up after lifting the pin only about 1/16. Then leveling off and maybe going a bit lean after lifting more. To balance the butterflies I like to use a gauge of some sort like a drill bit. Either hold the dampner piston up with something or have it removed and then holding the throttle open a little I gauge the butterflies between the two carb's.

Is the popping a backfire or a miss? Could be ignition.

Kurt

 

[TEM666666]

Joe was nice enough to jump in on this but i thought I'd add my .02. First thing to do is make sure the butterflies are opening EXACTLY the same. If they are not all other adjustments most likely won't match. Personally I start at 12 flats down and look for the idle to pick up after lifting the pin only about 1/16. Then leveling off and maybe going a bit lean after lifting more. To balance the butterflies I like to use a gauge of some sort like a drill bit. Either hold the dampner piston up with something or have it removed and then holding the throttle open a little I gauge the butterflies between the two carb's.

Is the popping a backfire or a miss? Could be ignition.

Kurt

Thanks Kurt! I guess it makes sense to check the butterflies as well, I will give that a try. I think I will take the air filters of and make a gauge/spacer to lift the piston 1/16 and try it out. Speaking of balancing, I re-synced the idle speed using the vinyl hose to ear method. First time doing this myself and I was surprised how off it was. Any idea why jet 2 won't go up all the way? Not like I need it all the way flush but is this an issue that cause another problem?

Loud popping was from the muffler end. I took out plug 1 and it's the darkest spark plug I had ever seen so I assumed too rich. I thought it it pops on the intake end and the spark plug is white then it's too lean. Mis-fires? No idea...

 

[Joe Schlosser]

on the right carb, turning the nut all the way up, the jet won't go all the up to flush.

The jet may be stuck. It needs to move down when you pull out the choke and then back up when the choke is pushed back in. If it is not coming up all the way it could be stuck down. Make sure it is moving when you pull the choke. The jet should be flush with the carrier when the adjustment is completely up. If it is frozen then your adjustments will affect the mixture.
RE the butterflys opening at the same time I agree with Kurt, that is T=0 for starting out. Do what Kurt has suggested to make sure they are the same. If you want go a step further you can air balance with a flow meter.

 

[TEM666666]

on the right carb, turning the nut all the way up, the jet won't go all the up to flush.

The jet may be stuck. It needs to move down when you pull out the choke and then back up when the choke is pushed back in. If it is not coming up all the way it could be stuck down. Make sure it is moving when you pull the choke. The jet should be flush with the carrier when the adjustment is completely up. If it is frozen then your adjustments will affect the mixture.
RE the butterflys opening at the same time I agree with Kurt, that is T=0 for starting out. Do what Kurt has suggested to make sure they are the same. If you want go a step further you can air balance with a flow meter.

NEW PROBLEM! Car now idles high, 2000rpm. and I can't get it down. My idle screw on one side is not even touching the stop.

The jets aren't stuck.. They both move. one moves more than the other. I took out the piston to check the butterflies they look like they are matching. But whats T=0? Re-set the jets to 12 flats down.. Warmed it up, set the mixture, lifting the piston, etc... Now it's idling high and I can't bring it down. Online documents suggest loosening the throttle linkage nuts to set each side. Should I attempt that? I'm a bit overwhelmed by all the confusing gaps to be set (distance between throttle linkage and heat shield, etc, etc). Is there any straight forward way to do this?

 

[JPSmit]

Is the choke on? This sounds like it could be an issue with the cable and not the carbs. can you disconnect the cable - or slack it off a bit?

 

[TEM666666]

Is the choke on? This sounds like it could be an issue with the cable and not the carbs. can you disconnect the cable - or slack it off a bit?

The choke is OFF. In fact, after looking at it for a while, I think my jets not coming up flush on one of the carbs is the result of the choke linkage not set evenly on the 2 sides (one is up while the other one is slightly down). But assuming they are in the fully choke fully OFF position, my left jet starts flush, go down 12 or 15 flats, check with calipers and match the second side to first side I should be okay. (only down side is when my choke is open, one side goes lower than the other.

I'll make another attempt this weekend if I can gather enough information on how to set the positions and gaps. I don't understand how they can gap between the throttle arm and the manifold heat shield. Internet says something in the thousands but I have a large gap. And also there is something about 0.3mm gap between the throttle linkage pin to the bottom of the jaw where it sits that lifts the last linkage that opens up the butterfly. If I can figure that out, I will loosen both throttle linkage and both choke linkages and start from scratch.

 

[Joe Schlosser]

It looks like you need to look for a good Utube vid for setting up SUs
With the jet adjusting nut all the way up (what I called T=0), the jet should be flush with the holder/ bridge. If not then something is holding the jet down. It is most likely the choke adjustment screw or the tab on the choke bar to the carb is set different than the front carb. This needs to be fixed first. The position needle in the jet controls the mix. If you are starting our with the jet down you are automatically rich to start with.
You are probably correct that the choke adjustment between the front and rear carbs is incorrect/slipped. Remember these are two separate carbs and need to be set up correctly independently and then connected.
When set up correctly both the choke and throttle on each carb will work the same.

 

[JPSmit]

I'll make another attempt this weekend if I can gather enough information on how to set the positions and gaps. I don't understand how they can gap between the throttle arm and the manifold heat shield. Internet says something in the thousands but I have a large gap. And also there is something about 0.3mm gap between the throttle linkage pin to the bottom of the jaw where it sits that lifts the last linkage that opens up the butterfly. If I can figure that out, I will loosen both throttle linkage and both choke linkages and start from scratch.

I am not clear what you are saying here? do you mean there is a gap between the carb and the manifold? in which case that needs to be addressed first.

Joe is correct, the carbs need to be set first and then connected.

Not sure how far you want to go with this, but, if you remove the carbs and take the SU's apart you might want to confirm that the needles match. However, assuming it did run and now you want to make it run again,

1. disconnect the carb linkage from each other ( test to make sure it is not binding)

2. Confirm that the butterflies both close fully.

3. adjust the needles the same number of flats.

4. reconnect the carbs

5. see what happens.

 

[SaxMan]

Sounds like you're having the same issues that I was having (and still having to some extent). Mine are on deceleration, not acceleration. Three of my cylinders were sooty, one wasn't, but I have other issues going on with my motor. I'll probably recheck the valve adjustments. It's also possible there is an air leak somewhere after the piston chamber -- exhaust manifold or flange are possibilities.

 

[nomad]

JP not only make sure they will close fully but the when you pull up on the throttle cable they open exactly the same. First thing to do. The adjustment is the clamp bolts on the throttle shaft. All the bit about the clearance from the heat shield isn't really critical. I would suggest as Joe did...watch a you tube vid from university motors on adjusting the carbs and read up on it as well. Also I have found that for checking mixture with the lifting pins not having to isolate each carb give's one a pretty good idea. I think I have tried just covering the throat of the carb not being adjusted. I usually just concentrate on setting both carbs the same and all adjustments the same. Then the lifting pin test tells you if both carbs and therefore the engine, has the correct mixture.

Kurt.

 

[TEM666666]

So my plan of attack
-Remove dashpot cover, Take off the piston/needle.
-loosening all 4 nuts holding the 2 throttles and 2 chokes.
-raise the jets on both sides via the mixture nut on bottom.
-tighten the linkage nuts to the chokes. (hopefully that will allow the chokes to operate evenly.
-push chock knob in (off)

-Lower the jets same flats on both sides (12-15) but I will check both sides with calipers.
-put the needle/piston back in, install dashpot cover.

-start engine and warm up.
-set idle and mixture on both sides. (1100rpm sound right? and doesn't this even's out the butterflies? or is there a different adjustment for that?)
-pull choke and set highspeed idle on both sides item 7 (screw with spring underneath pointing back and rides on choke cam). (what rpm am I looking for?)
-shut off engine.
-gap item 3 on both sides and tighten item 5 nuts for the 2 throttles.

Please let me know if this makes sense! thanks!

 

[JPSmit]

BTW I am sort of going to be out your way tomorrow afternoon (Warden & 401) - if after - suppertime/ early evening you need an extra set of hands or eyes.... (I don't know any more than you I promise - but I am enthusiastic and can look at the engine in a particularly manly way) :grin:

 

[TEM666666]

BTW I am sort of going to be out your way tomorrow afternoon (Warden & 401) - if after - suppertime/ early evening you need an extra set of hands or eyes.... (I don't know any more than you I promise - but I am enthusiastic and can look at the engine in a particularly manly way) :grin:

Thanks for the offer JP! Unfortunately I'll be downtown most of tomorrow evening for a dinner gathering. I'd take you up on that otherwise! I think we'll probably get in contact in the near future!

 

[Joe Schlosser]

Yes your program should get you running
Some additional thoughts/hints
With everything loose and the jet nuts all the way up the jets should be flush with the top of the holder
Make sure the levers on the chokes touch at the same time when pulling out the choke. There is some slop in the levers. Not sure why you say push choke in. This should be done with the choke in.
With the throttle linkage tight start motor and warm it up. It is a pain to start it with the linkage loose.
After warm up with motor running Loosen the throttle linkage. Adjust the mixture
Adjust the throttle screws so that the two carbs are about equal, either a flow gage, listening through a hose for equal hiss or as close as possible by eye.
Tighten the linkage. Make sure the tabs are engaging the linkage at the same time.
This should put you in the ball park
Idle speed with the choke out is a matter of personal preference. I use about 1500 with a warm idle of about 1000-1100 (my cam does not like the idle any slower.

 

[JPSmit]

Thanks for the offer JP! Unfortunately I'll be downtown most of tomorrow evening for a dinner gathering. I'd take you up on that otherwise! I think we'll probably get in contact in the near future!

no worries - can also be around mid to late afternoon Monday - I golf in Newmarket at 10:30

 

[regularman]

I would make sure the exhaust header is tight and not leaking. If it can suck air in there when you let off the gas, it will pop and crack when slowing down. If it can't get air, it won't do that even if rich.

Kim

 

[nomad]

I would make sure the exhaust header is tight and not leaking. If it can suck air in there when you let off the gas, it will pop and crack when slowing down. If it can't get air, it won't do that even if rich.

Kim

Agree, Kim. That is why I was wondering if the "popping" was a backfire or a miss.

If the choke cable is holding one jet from going all the way to the bridge my first move would be to balance them. I emphasize balancing everything because that is just my way of doing the carb adjustment. These are very simple carburetors and if you think through the process rather than being overwhelmed by all the instructions I don't think you will have any trouble. I could use the "hiss" method on the larger SU's but never had any luck with the HS2's. The principle of the vacuum operated air and fuel metering to give the engine what it is calling for needs to be understood first then the adjustments make sense.

Kurt.