Hot-start problem

DSpieg

True Classic
My '71 850 Spider has recently been showing a hot-start issue -- after high-speed (no jokes please, it's all relative) driving for at least 15 minutes, if I shut down the car will sometimes not start, as if there's a fuel delivery or spark problem. Kind of like vapor lock, but I've never had that problem before and haven't changed anything to cause it to start happening.

So far I've changed the ignition coil, rotor and distributor cap, with no effect. I've got a Crane XR700 optical trigger in the distributor, wondering if that might be failing when hot? Also have a Mr. Gasket electric fuel pump but it's definitely running when I crank.

I do have a drip tray under the carburetor which (you would think) should help reduce the engine heat going up to the carb.

Not sure how best to tell if I have a fuel problem or a spark problem, any thoughts?
 
Hot fuel?

One way to see if you still have liquid fuel in the carb is to operate the throttle and check for accelerator pump squirts in the venturi. If so, then there's liquid fuel in the carb and vaporization is not likely to be your issue.

When I had my 850 I re-routed the fuel line around the exhaust instead of under it to help prevent vaporization in general, but don't know if I ever actually had a problem with it. I also used an electric pump and made sure the return from the carb was functional. If the return is not operational (like a different carb) you can have fuel overflow into the intake when it's hot and cause flooding while it sits. This can be a weak needle valve but also caused by lack of fuel return or tank venting etc.

I'm sure you know to check the primary idle jet for debris, the stock size is tiny and upgrading to a 50 is recommended.

Use a timing light to check for spark when you have the problem. If you do then you you know it's something in the carb. A 12v test light at the coil will tell you if you have power (15 terminal should have key-on power) and distributor function (1 terminal should flash when cranking)

Good luck!
 
Thanks, Greg, all good suggestions, but the rub is that this problem has only occurred after driving for a while, and only away from home base -- I haven't been able to reproduce the symptoms where I could troubleshoot them (and I've been solo in the car so had nobody to crank the ignition while I went back to the engine to check things).

I've also rerouted all the fuel lines away from heat, so if there's vaporization happening it would have to be within the carb itself.

And it isn't plugging of the tiny idle jets, I know that problem well and frequently pull them out to clean them using a single strand of copper wire I carry in the car at all times (I wonder what regular non-mechanic people did to keep their 850s running 'back in the day'?).

I'll check the fuel return line but I haven't done anything with the carb, maybe I should check the float as you suggest. And the 12V test light is also a good idea.

I HATE intermittent problems, especially the ones that only occur on the road. It took me months to figure out I had an intermittent bad ignition coil on the Vanagon, and the clincher there was that the tach would sometimes twitch faster than any engine can respond, which made me realize it had to be the coil from which the tach gets its signal. Unfortunately I don't have a smoking gun like that with the Fiat yet.
 
Yep...

I hear ya on the intermittent issue diagnosis challenge.

Imagine how much worse it would be if you had to take it somewhere to be fixed and how frustrating it would be to have it act normally every time you took it in for repair. I hear this story a lot.

With a 12v test light with an alligator clip on the end of the wire, you could extend that wire with another one w/clip so that you could put the light somewhere where you can see it while cranking, that's what I do. Or, carry a remote starter switch.

Do you have the stock carb? I don't recall the DIC line having an idle cut-off solenoid but it sure sounds like something similar. Could be ignition switch even, that's why you need to use the test light and see if you even have power to the coil.

The only time my '72 850 stranded me was when I ignored some ignition misses and the dizzy pooped out on me while I was away from home. The cap/rotor/points/condenser were old. I think it ended up being the condenser of all things. Good luck.
 
I appreciate the sympathy as well as the advice, Gregory! Car has a mostly-stock 30DIC4A carb, with some of the vacuum ports on the manifold plugged (emissions-related stuff, boo!). Has been very reliable until (maybe) now. I don't think it's the ignition switch, the couple of times I had the hot no-start problem the fuel pump was running (I could hear it), and the starter was spinning of course. I guess that doesn't demonstrate there was power to the coil, but seems unlikely to have been the problem.

I've been reading up and am wondering if part of the problem is that my electric fuel pump is mounted fairly high along the front bulkhead (firewall), near the top of the fuel tank, and given that electric pumps don't suck as well as they blow, perhaps my pump is starting to get a bit weak when hot, and can no longer draw fuel up from the bottom of the tank (where I have installed a very large fuel filter), and cavitates?

The system has worked fine for five or six years, but perhaps the pump suction was marginal all along, and I'm only now seeing the effects. I've considered mounting the pump low near the fuel tank outlet, but then it's too close to the exhaust header, so I think I'm stuck with the current pump location. Am going to install a new Carter inline pump that I bought a few years ago as a backup but have never used, maybe that will work for a while.

I suppose as a last resort I could revert to the OE mechanical fuel pump setup, but I'm not thrilled about that (and it brings fuel hoses back into proximity with the exhaust header, always a bad thing).

Never a dull moment. Sure beats driving a reliable Camry, huh?
 
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My Coupe has had vapor lock on several occasions when I have been on the highway for extended periods and then stopped to gas up.

If you have low suction, it could be exacerbated by junk in the tank, poor venting (i.e. too sealed versus creating pressure) or similar.

I have always had a mechanical pump and overall trust them and the fuel lines on that side. I like mechanical pumps because they stop running when the engine stops running. I have never seen a fire on an 850 caused by an issue with the fuel lines, the only ones I have seen are when the fuel fitting pulls out of the carb (brass in zinc eventually will work its way loose). If you keep your lines in good shape I wouldn't worry about where they run personally.

Given the equipment on the spark side, I would think its likely your Mr Gasket fuel pump is failing softly or is getting clogged.

I would never drive a Camry. The minivan I have is close enough and I can't wait until its time to depart our garage/driveway comes. Its our first and hopefully last automatic transmission car and I cannot wait until I don't have to suffer it anymore, its been 11 years so far and likely a few more to go... :(
 
I converted a '63 Corvair from mechanical fuel pump to electric after getting vapor lock too many times. Wooden clothes pins on the fuel lines helps absorb some of the heat.
 
When I had my 850 I had a rotary electric pump mounted low on the frame rail, but away from the header. I think it's possible that you have some drain-back occurring, does the symptom align with low fuel tank level? Another possibility if it does is of a hole in the sender pickup tube. Also check the mesh sock on the pickup tube.

I have no experience with Camry's beyond working on my neighbor's on occasion. Booooooooring! :nana:
 
Last night I removed the Mr. Gasket electric fuel pump and replaced it with the Carter (mounted slightly lower along the bulkhead, but not much). Nothing to do now but drive the car for a while and see whether or not the problem rears its ugly head again.

If I find anything I'll report back.
 
Problem solved?

At the risk of pulling a George W. Bush "Mission Accomplished" boner....it's been a couple of weeks with the new Carter electric fuel pump, car is running perfectly with no recurrence so far of the 'failure to restart' problem, so for now, going to blame the problem on the old Mr. Gasket pump getting tired.

Hopefully will not have to report back with bad news and foot in mouth....
 
The old Mr. Gasket pump was a rotary type, as is the new Carter just installed.

FWIW my X1/9 came to me 7 years ago with a Facet 'cube' pump, which continues to work flawlessly.
 
Whuddeyetellyuh?

Sure enough, I'm back with my foot in my mouth. Got a no-start this morning, fortunately in my driveway. Changed fuel filters and cleaned the two idle jets, tried again, still no start. Went away for a while, came back in the early afternoon and tried again, still cranked strong (and gave off a bit of gas smell indicating some sort of fuel flow) but no start. FOOLED AROUND WITH THE DISTRIBUTOR CAP AND ROTOR, and the car started right away! What the heck?

I had installed new rotor and distributor cap a couple of weeks ago, car has run fine until today with those parts. But then had the no-start this morning and again this afternoon without changing anything else. Then changed back to the old cap and rotor (which had been on the car when I began having these issues several weeks ago) and this time it started!

I am so confused. But at least it appears to be more likely an ignition issue rather than fuel-related. Wondering if I should I go back to my original points + condenser ignition and disconnect the Crane optical trigger? What little data I've got seems to point to an intermittent ignition problem, and it's not necessarily heat-related because the car had been sitting overnight and was not hot this morning when it failed to start.

I could ask for help from my neighbor to crank the engine while I check for fuel and spark, but of course if the engine is mysteriously running right again, both of those will check out fine....
 
I have a really old Crane XR700 (actually it's from before Crane, it's an Allison) brain box, no idea if it's compatible with what you got but your welcome to it as a spare if you want it.
 
Yeah I have a real predilection for foot in mouth myself

If you install a starter relay back there you can add a momentary switch along with it to crank it over from back there.

kle318_1.jpg


I just did this and it is very convenient, just be certain it's not in gear, particularly not reverse...

I am in the process of installing a lobe sensing Igniter ignition system in mine, I will let you know how that goes
 
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Deal!

Thanks, Jeff -- I would be happy to take your Allison brain box, please send me an email with how much you'd need for shipping + handling + state & local taxes + fees + VAT + insurance +.....

dspieg*earthlink.net is where I reside electronically
 
Thanks Jeff, you are a prince among men!

In the meantime, in an effort to eliminate one of the last two (I think) remaining possible culprits, I cleaned up a spare distributor, installed a fresh set of points and condenser in it, and installed the dizzy in the car while leaving the Crane XR-700 box and associated wiring intact though disconnected from the coil. Car seems to run fine, but as always, time will time.

I believe the one remaining untested part is the ignition switch itself -- I guess it's possible that the 'start' contacts may be failing, so if the latest swap doesn't cure the problem, I suppose the ignition switch should be the next part to change out.

This is so much fun.
 
No problem, better in your hands as a spare for testing or emergency then sitting in my parts bin doing nothing, and unlikely to ever do anything again.
 
If I only had a brain (box)

Jeff, your excellently-priced Allison XR700 ignition brain box arrived yesterday, grazie mille! It looks somewhat different than the newer Crane version (which has a slightly smaller footprint and no external transistor) but the connectors and other wires appear to be the same.

I now have three ignition choices.....
 
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