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Stock '71 Won't Start When Hot(-ish)


birdhouse

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I've been doing quite a bit of searching here, and other online resources, but can't seem to find anything that matches up to this scenario...  finally breaking down from passive reader to proactive post-er.    (Apologies if I've missed what I have been looking for.)

 

I am presently running an entirely stock-equiped 2002 that has been running fairly fantastically for far too long.   For the last month or two, I've noticed that it has been getting a bit grumpy about erranding/restarts:  now it is downright indignant about such things.

 

'71, stock solex with manual choke, stock air cleaner, still running pts / stock ignition.   She starts fine when cold, and seems to run great once she gets up to temp.   Boy, she just loves to run.   

 

If I stop though...  either a mile from home, or 40, I have to be prepared to stop for awhile.  What started with a 'grumpy' restart evolved into a restart only with starting fluid, to now a full on, get comfortable, maybe read war and peace parking lot stand-off.  ;) 

 

When in this state, the car will turn over.   (I get lots of offers for jumps, and they all seem so confused when I decline. )  Sometimes it will give the impression of almost catching as I come off the starter.  (This characteristic is so slight, I'm almost recalcitrant to include it.)  

 

She's got petrol: I can see it in the pre-pump fuel filter, and I can see the atomization when I manually move the linkage on start attempts looking into the throttle body.   In this state, it doesn't smell flooded.   I've once run the battery down attempting to start with no throttle at all to prove that.  I've done the same with chokes, and the normal, 1/3 throttle post-ignition kiss.   Nada.  No change in behavior.   Unless...

 

If she sits for long enough... say ~4 hours, then she'll start up fine again, like there's no problem whatsoever.   And run happy all the way home, where's she's put back in the doghouse garage, and left alone.

 

Any thoughts on where to go with troubleshooting would be greatly appreciated! 

 

Thanks in advance!

Really trying to keep it original.  Again.

"Speed provides the one genuinely modern pleasure." - Aldous Huxley

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Welp.  So, no useful forum hits in my original search on hot start issues...  but boy, use the terms 'carb upgrade', and they suddenly come out of the woordwork from the search engine!

 

So yes, looks like I've got a bunch new material to read through... I'd delete this post if I could, but it looks like the forum won't let me do that.  

 

Sorry for the redundancy!  ;)

 

rs

Really trying to keep it original.  Again.

"Speed provides the one genuinely modern pleasure." - Aldous Huxley

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Is it unusually hot lately in your neck of the woods? Is this mostly during the day, does it happen at night when it's cooler? Sounds kind of like a vapor lock issue. IIRC some people suggest placing a wet washcloth over the carb when parked.

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Edited by jmr_1602

- Project 67' 1600-2

- Pig Cheek 71' 1602

 

 

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I suspect flooding.

Next time this happens, try putting the gas pedal to the floor while cranking.

It seems counterintuitive, but helps clear the extra fuel.

     DISCLAIMER -- I now disagree with much of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book as timing maps for our engines.  I've also switched from using ported-vacuum to manifold, with better results.  I apologize for spreading misinformation. 

(3-28-2024)  

 

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I suspect flooding.

Next time this happens, try putting the gas pedal to the floor while cranking.

It seems counterintuitive, but helps clear the extra fuel.

 

Cheers for the tip!  I've never heard of that, but am certainly glad to try this approach next time I trigger this scenario!

 

Actually, it's funny that you write:  as mentioned above, I did find a few links on similar behavior once I changed up my search terms to drop 'warm start' completely.  You had a very comprehensive response on that thread regarding ignition, which I suppose might also apply here: 

http://www.bmw2002faq.com/topic/159541-hot-even-warm-startingrunning-issues/?p=1008738

 

It certainly may be time to look into my old vacuum advance dizzy... 

 

 

Is it unusually hot lately in your neck of the woods? Is this mostly during the day, does it happen at night when it's cooler? Sounds kind of like a vapor lock issue. IIRC some people suggest placing a wet washcloth over the carb when parked.

 

 

That's an interesting hack.  I've definitely worked to cool carbs on my race bikes, but never thought to try on the car.  Indeed, it has been substantially hotter than normal here.   I don't know that I've set out at night recently, which could be an interesting data point.  Might be interesting to try this out!

 

Cheers for the tips, guys!

 

rs

Edited by birdhouse

Really trying to keep it original.  Again.

"Speed provides the one genuinely modern pleasure." - Aldous Huxley

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Those single barrel Solexes rarely exhibit the issue you've described; that's the MO of a Weber 32/36.  However, yours is, so there's a problem, and one that has been gradually getting worse over a period of time.  ...a few things to check (all presuming your ignition is all up-to-snuff--plugs, points, wires, rotor, cap):

 

1.  Does your carb have the phenolic spacer (dark brown about 1/4" thick) between the carb and the manifold.  It's a heat block and prevents the hot manifold from heating the carb to the point where fuel boils in the float chamber.  If it doesn't have one, get one.  

 

2.  Where's your fuel filter?  Is it upstream from the fuel pump where it should be?  BTW, it rarely if ever is full, so low fuel in a transparent filter isn't cause for alarm.

 

3.  How's the condition of the fuel line between the firewall, fuel filter and pump?  If it's old (esp if it's the original cloth-covered line) it can be porous--mechanical pumps would much rather suck air than gas, and a porous line will allow that--even a small air leak will make starting hard.  

 

4.  Checked the carb's float?  I've had several Solex carb floats sink, or at least get partially full of gas.  This allows too much fuel into the float chamber so that it overflows into the manifold, causing flooding.  Checking is easy; unscrew the five screws that hold the carb's top on, remove the float and shake it.  If you hear sloshing, replace it.  Be sure to re-tighten the screws in a criss-cross pattern so as not to warp the carb top.

 

5.  Have you checked for vacuum leaks?  Uncapped vacuum ports, vacuum advance unit on the dizzy, and its hose, loose carb, worn throttle shaft etc.

 

That'll get you started; let us know whatcha find.  Be assured that Solex carb is very reliable and lasts forever (my 69 has its original at 224k miles).

 

cheers and happy troubleshooting

mike

 

PS--will your car restart quickly if it's only been sitting for a few minutes, getting progressively harder the longer it sits hot?  Or is a hot restart always difficult regardless of sitting time?

Edited by mike

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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Wow, thanks everyone for your comments--I will do my best to work through each in turn!

 

Slacked in putting my racebike back together, so got to spend some time on the suddenly-freed race weekend under the hood of the 2002.   In doing so, I did find a new nuance to the behavior:  on top of the other characteristics, the car *will* start to misbehave while running at low speed / load (i.e. running in my driveway, around the block).   Not sure if I've just gotten lucky in traffic, or if when it's running, she's moving fast enough to cool things down a bit to keep the characteristic in check.

 

The hot-running driveway misbehave manifests as an increasingly erratic rpm at idle that can hunt up, then down, and ultimately will stall the car.  (I even had this kill the car when manually adjusting the throttle rod to try and keep her running!)  

I've seen this kind of problem triggered in the old race bikes as an erratic air leak...  and bad coils.   Definitely in line with the suggestions already here!

On then: comments to your suggestions!

 

stock solex carbs do not like non stock fuel pumps, i.e. electric, is the isolation plate under the carb, prevents boil off,  it sounds like flooding either heat or float, coils can become weak when hot

 

Cheers for the tips! Alas, this little lady is still *all* stock.  Mechanical fuel pump, only about 5 years old.

 

Those single barrel Solexes rarely exhibit the issue you've described; that's the MO of a Weber 32/36.  However, yours is, so there's a problem, and one that has been gradually getting worse over a period of time.  ...a few things to check (all presuming your ignition is all up-to-snuff--plugs, points, wires, rotor, cap):

 

Indeed, I think I may need to look a little deeper into the ignition.  A few other threads I've found suggest that a coil might start to do this kind of erratic behavior as it gets hot.

 

1.  Does your carb have the phenolic spacer (dark brown about 1/4" thick) between the carb and the manifold.  It's a heat block and prevents the hot manifold from heating the carb to the point where fuel boils in the float chamber.  If it doesn't have one, get one.  

 

Yes sir.  Though, I did notice that the air-cleaner housing was showing wet at the base of this spacer... definitely suggesting gas getting out, and air is most probably going in.  Definitely a problem... Since they still seem to be available, I resisted hand-making gaskets and will order some replacements.    (Interestingly, this behavior did stop as the engine warmed up: i suspect as things were heating up, the expanded, and this self sealed.)   This behavior didn't correspond with the poor running.

 

2.  Where's your fuel filter?  Is it upstream from the fuel pump where it should be?  BTW, it rarely if ever is full, so low fuel in a transparent filter isn't cause for alarm.

 

Yep, there is one upstream of the pump...  though I've read a few suggestions that another should be placed between pump and carb.   (And the sediment in the carb bowl seemed to suggest this was also a good idea.)   Any concerns about putting a second filter on the far side too?

(Interesting to hear that it rarely is full: this was definitely concerning the first time I got to looking at it.)

 

 

3.  How's the condition of the fuel line between the firewall, fuel filter and pump?  If it's old (esp if it's the original cloth-covered line) it can be porous--mechanical pumps would much rather suck air than gas, and a porous line will allow that--even a small air leak will make starting hard.  

 

It is rubber... while not in great condition, it does not appear to be compromised.  No matter: it's a cheap fix, and a no-brainer safety update. False economy to use till it fails--I'll be replacing this, very shortly!

 

 

4.  Checked the carb's float?  I've had several Solex carb floats sink, or at least get partially full of gas.  This allows too much fuel into the float chamber so that it overflows into the manifold, causing flooding.  Checking is easy; unscrew the five screws that hold the carb's top on, remove the float and shake it.  If you hear sloshing, replace it.  Be sure to re-tighten the screws in a criss-cross pattern so as not to warp the carb top.

 

Ohhhh!  I clapped my hands together reading this one.  I've had more than a few bikes plagued by this issue (even with brass floats.)  I was fairly sure that you had it with this one and eagerly dived in.  Alas, the float seemed in good order.    Good one to watch for in the future, thanks!

 

 

5.  Have you checked for vacuum leaks?  Uncapped vacuum ports, vacuum advance unit on the dizzy, and its hose, loose carb, worn throttle shaft etc.

 

That'll get you started; let us know whatcha find.  Be assured that Solex carb is very reliable and lasts forever (my 69 has its original at 224k miles).

 

cheers and happy troubleshooting

mike

 

I read that the easiest way to check the vacuum at the dizzy was the clandestine blow/suck test at the carb-end of the hose:  this did appear to engage (and disengage) the diaphragm successfully.  Not sure if that has to be measured at a specific pressure, or...

 

Now, the throttle shaft is an interesting suggestion: I am not sure how to check if this is within expected tolerances--or what those tolerances are.  I'll do some searching and see if i can find any material on the subject!   Cheers for the tip.

At this point, I'm planning on going ahead and ordering new gaskets for the carb, and will just set about cleaning her up and bolting her back on with some new fuel lines.  That will at least rule out the confirmed manifold leak, and the candidate older fuel hose pre-pump.   Will try to demonstrate restraint at changing anything else until those two things are fixed.

 

 

 

PS--will your car restart quickly if it's only been sitting for a few minutes, getting progressively harder the longer it sits hot?  Or is a hot restart always difficult regardless of sitting time?

 

As an aside, this was an interesting question--I honestly didn't know the answer when I read it, because I'd be learning to keep her running no matter what.   Definitely tested this:

 

Restarting immediately after starting works fine.  

Restarting after running for a minute or two works fine.

Restarting after getting 'to temp' on gauge works fine.

Restarting after running for some period 'at temp' and then left ~2min seems to be about when the behavior is seen. 

 

And as a new bullet-point, with reference to the recently identified idle 'RUNNING' issue suggested above:

 

If the car stalls at it's hot idle, then the behavior is seen immediately, and until full cool down is achieved.

 

Thanks everyone for the comments and suggestions.  Hugely appreciated!

Edited by birdhouse

Really trying to keep it original.  Again.

"Speed provides the one genuinely modern pleasure." - Aldous Huxley

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I've observed this same issue with my semi-stock '70 model. Originally had 2 fuel filters: one before the mech pump and one after (between the pump and 32/36 carb). I was told that this is not a good situation by several trusted folks on here. I seem to have fixed my issue with a new mechanical fuel pump, but if it's very hot outside and I've driven longer than an hour -  I am still hesitant to shut the car off for fear that it may not start back up. Usually it starts, but not quickly or easily. I feel that it's a vapor lock issue 

1970 Agave work in progress

Born on May 14 1970 and delivered May 19th 1970 to NYC to Hoffman Motor Corp. Agave code 071

new guy

help appreciated!

other cars: 1991 318is / 1999 540iT

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Restarting immediately after starting works fine. Restarting after running for a minute or two works fine. Restarting after getting 'to temp' on gauge works fine. Restarting after running for some period 'at temp' and then left ~2min seems to be about when the behavior is seen.

 

I've had that same issue more than once.

 

I may be way off base here, but on the tii, if the points are not set perfectly, it resists starting when hot.  Re-setting the dwell to 59-61 degrees has cured that issue for me. 

 

Shot in the dark, but just maybe.

73 Inka Tii #2762958

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Its a 1 barrel stock solex right? stock fuel pump ? right  I use to have a problem with idle jet on mine back in 1971, the shit would get in the idle  jet and cause erratic idle, running, unscrew it from the side of carb, try  sucking through  the tapered end of the jet, you should be able to draw air through it if not you can clean with a jet reamer or fine wire, its like a ,035 mm. Bruce M-TUNER

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Couple of more thoughts...I had the same erratic idle problem on my '69--but it was intermittent.  Sometimes it idled just fine, others it ran very slowly or even stalled.  Took a long time, but I finally figured it out--vacuum advance diaphragm had a hole in it, and was allowing air into the system.  When you checked your vacuum advance, did you remove the cap and actually watch the points while you sucked on the vacuum line.  Did they move?  Did the line and capsule hold vacuum when you plugged the line with your tongue?

 

Bruce also made a good point about the idle jet.  My '69 came from the factory with trash in the fuel system (cars didn't come with a fuel filter) that kept plugging the idle jet.  Took nearly a year for all the crud to work itself out of the system.  An "idle" jet actually provides most of the engine's fuel flow up to about 2500 rpm, so a trashed idle jet will affect more than just the idle.  

 

But do make sure all your ignition components are up to snuff.  My late father-in-law, who taught me how to fix cars once told me, "Mike, you fool with your carburetor too much.  90% of your carburetor problems are in the ignition."  And he was (almost) always right, too.

 

cheers

mike

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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I'm suspecting a ground problem. Make sure the engine block is grounded to the chassis. There should be a large braided ground strap between the two. I had the identical problem and that was the culprit.

75 2002 (black) 1990 - 1993

73 2002 tii (malaga) 1994 - 2017

74 2002 tii (verona) 2023 - probably forever

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