Looking for diagnostic guidance

[TpupNomad]

I have an 85 Turbo (USA) all stock.  It starts, runs and is drivable.  After it warms up it's hard to get off the line, it's easier if I pull the choke when starting off in first and then push the choke back in once I'm going.  It also stumbles at 2-3K a bit and I can hear some popping at idle and lower rpm.  The car is not right and I've had multiple shops look and work on it.  The latest service was in august and they did:

• Checked engine cam timing
• Set engine at TDC to check cam marks
• Check Distributor, make sure ignition advance is working
• Check and set ignition timing to factory spec
• Check and clean spark plugs
• Check carbs, clean fuel jets and drill out idle mixture screws
• Inspect fuel bows and clean
• Adjust fuel mixture and sync carbs at idle
• Check intake manifold gasket seals for vacuum leaks
• Check all vacuum lines for leaks
• Check fuel pressure
• Richen up fuel mixture and adjust ignition timing to get engine to pull clean revs

The car has 3,600 miles and sat for many years before being brought back to life 5 years ago.  It has never run right since then.

The question is what is the list of things you would check to figure out what's wrong with the car?

Thanks in advance!

Roy

ps.  I do have an electronic ignition kit that is not installed if you think that would help.

Obligatory engine pic...

 

[jonwat]

1 hour ago, TpupNomad said:

After it warms up it's hard to get off the line,

Once she's fully warmed up check the the coil, it should be cool to the touch. If it's not replace it.

The other thing to note is all that emissions kit, I have no idea what effect that would have.

Good luck  

[ADF]

Hi Roy,

Firstly nice engine bay, Secondly 3600 mls that's incredible given its age.

Sounds like they've checked and adjusted all the usual suspects for what sounds like a fueling issue.  My guess would have been air leak or carbs.

I am not lucky enough to own an esprit but for what it's worth I would do a compression check just to be sure all is well and gas analyser (analyzer, as your in USA) to see if its lean at idle then put it on a rolling road with the analyser but you need a good technician though.  Did this with the elan many moons ago to figure out why it was running strange under load.  It was really the chaps experience rather than the equipment that guided us (you can put a lambda sensor into the exhaust to check the mixture as you drive but unless you're into playing i wouldn't bother). 

None of this will tell you exactly what's wrong but it should help in diagnosing.  Nowadays I tend to try to figure out what's wrong with a few tests/checks before I start taking things too bits.  Often just by driving and visually and audibly checking the engine you may get a list of what it's doing and just as importantly what it doesn't do, if you can have a working theory you can drive in a manner (or check things) to confirm or discount it.

Best of luck with it, let us know how it goes and don't lose the faith.

Tony

[mike.griese]

There are lot of line items in your list about checking carb related stuff, but have they actually been removed from the car, cleaned and rebuilt?  These carbs have some special characteristics that may not be obvious to a mechanic that is not experienced with these engines.  The turbo "blows through" the carbs, which is not a "normal" configuration for turbocharged, carbureted cars.  In order to make this work, there are a bunch of o-rings around all of the jets and needle valves to keep the air and fuel inside instead of blowing out all over the place.  With so few miles, I would suspect the o-rings are no longer behaving properly.  They are tiny things, and if they glued themselves to the needle valves, they can tear when the valves are turned.

Slow acceleration indicates the accelerator pumps are not working properly.  These are located at the bottom of the carb bodies (you can't see 'em without a mirror) and tend to collect up any debris/varnish/clag/moisture/name your contaminant.  The accelerator pumps react to a quick application of the throttle and squirt a little extra gas into the intake to help with rapid acceleration.  Using the choke does a similar, if less controlled thing.

A stumble around 3k rpm indicates restricted or undersized main jets.  3000 rpm is a magic number as this is when the carbs switch from the idle jet circuit to the main jets.  Lotus sorta kinda undersized the main jets as a way to pass emissions, so if they get even a little varnish buildup, they are compromised. 

There aren't enough miles on the car for any appreciable wear, so I wouldn't expect to see any problems with worn throttle shaft bearings, loss of compression, or those sorts of things.  Time is not kind to gaskets, o-rings, vacuum lines and the like, and low miles over a long period of time would mean that fuel has dried up in the system at least a few times.  Balancing the carbs at idle is a useful thing, but won't indicate (or mitigate) problems with accelerator pumps, jets or pressure leaks.  I would recommend removing the carbs and having a full rebuild done as a base, then going back through balancing. 

Edited November 1, 2022 by mike.griese

[TpupNomad]

Thanks everyone!

@mike.griese - I cannot find any record of the carbs being removed, cleaned and rebuilt.  I agree that's a good place to start.  Thank you!

The guys who worked on the car for the previous owner were Porsche guys. The guy who did the work I outlined above is a Ferrari guy.  I spoke to him today and he confirmed that he did not rebuild them just did the items above.

Roy

[mike.griese]

It has been pointed out that there is an error in my post.  I should have said the idle jets needed to be upsized, not the mains.  I need a proofreader.

[ADF]

Best of luck Roy,

I misunderstood your original post, I thought that was stuff you had done fully.  If the carbs have not actually been removed or serviced that's gotta be a good place to start along with any vacuum lines / pressure feed.  Its fairly safe to assume at that age dry o-rings / seals can go brittle and crack. Unless you've checked it yourself never assume it's right. 

[jtmco]

If you are pulling the carbs, I would also replace the o-rings between the carbs and the intake manifolds. I rebuilt my carbs and still had a vacuum leak - it was the carb/manifold seal. 
 

Good luck ,

Jim