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sratner

Rough Starting When Hot...I'm Stumped

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Let me start by saying that i've had my '74 2002 for 36 years, i know it inside and out and it's never done this before.  It has run great and has always been very reliable until this past year. 

 

It starts perfectly when cold, drives great but when i shut it off and come back an hour later it's rough to start. Turn the key and it starts for a second or two then stalls.  And, it does that several times over several minutes. Starts, sputters and stalls. Then after many attempts it finally starts and runs great until i shut it down and leave it for an hour or so and then the symptoms repeat.  So today when it happened i looked at the fuel filter which had some gas in it but the carb bowls looked dry. It's a weber 32 36, manual choke. I just can't figure out why this happening all of a sudden.  Anyone have any idea what's going on? I'd appreciate any thoughts?     

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46 minutes ago, sratner said:

I just can't figure out why this happening all of a sudden.  Anyone have any idea what's going on?

 

Do you know whether your carb has brass or plastic floats?  Plastic ones eventually saturate with fuel and get sinky.

 

The little needle that the float seats could be getting worn and not sealing as well as it used to.

 

Do you still have the fuel diverter valve sending excess fuel/pressure back to the tank after shut down?

 

If not, I'm going to suggest that you try adding a jeep fuel filter to serve that purpose.  It has two outlets and you run the second one to the fuel return line under the battery tray.  Then when you turn it off, the pressure can bleed off; as opposed to sitting in the line and vaporizing, due to the hot engine; pushing its way through the carburetor.

 

Here are some filter options, if you want to try one.

https://www.rockauto.com/en/catalog/jeep,1976,cherokee,4.2l+258cid+l6,1179266,fuel+&+air,fuel+filter,6200

 

If you use the search feature and the phrase "jeep filter" you get 50 hits... half of them are probably from me.  You can read a bit about the filter installations... and stuff.

https://www.bmw2002faq.com/search/?q=jeep filter&search_and_or=and

 

Whenever I start my car warm, I just put the throttle to the floor while cranking, to let a lot of air in.  It seems to help with any sort of flooding situations.

 

Tom

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thanks Tom.  this is very helpful.  i’m not sure about the floats or the fuel diverter valve.  what does the diverter valve look like and where is it? 

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My manual choke 32/36 Weber has always been a reluctant re-start after sitting--the warmer the weather, the shorter the interval between stopping and re-starting for the reluctance to appear.  I've checked down the carb throat, and working the linkage gives me a nice squirt from the accelerator pump nozzle, so the float bowl isn't dry.  And I do have a phenolic spacer between carb and manifold to prevent fuel boiling--and the factory air cleaner that draws in cool(er) air from outside the engine compartment.  

 

I've not been able to figure out the cause, only to observe that outside air temperature seems to have an important influence on the time it can sit before becoming hard to start.  Cooler = longer sit time before becoming hard to start.  But mine usually will fire after 5-10 sec of cranking, vs almost instantaneous when cold or a short off-time.

 

Interestingly my '69's one barrel Solex never exhibits these tendencies--always starts right up, hot or cold.  Go figure...

 

mike

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24 minutes ago, sratner said:

what does the diverter valve look like and where is it? 

here is one photo I just dug up.  Not great, but shows the valve and where it sits.

8ffbee2a7f0f536574d62c423131e3ab.jpg

 

and another thread on that topic

 

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thanks mike.  i wish my situation was more like yours. at least yours starts after 5-10 seconds of cranking. mine starts right away but only lasts a second or two before it sputters off. since it just started happening i’m wondering what Tom suggested regarding the floats might be my problem.  

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thanks for the photo.  that piece is long gone. since this was never a problem before I think your thoughts on the floats might be my problem. l’ll check it out over the weekend. thanks again.  

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When the engine is shut off, the fuel pressure between the pump and carb has to go somewhere.  As it heats up sitting in the line, more pressure could be building up.  Sinky floats, or worn needle/seat fitment could make it easier for the fuel to be forced into the manifold.  I put that idea out there in response to your question about "what might have changed?".  Some carb parts do wear down, eventually.  I've read that you can weigh the plastic floats to determine whether they are gas-logged.  (mine are brass).

 

Along the lines of fuel delivery, I also like to periodically check the tension on hose clamps.  If air is able to be sucked in through loose fitting lines in the trunk, it can cause fuel delivery issues too.

 

Just throwing out a pile of little things to look into.  

 

I do like my Jeep filter.  I don't like the idea of leaving that line pressurized.

 

Good luck this weekend.

 

 

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Global warming?

 

Hotter temps make for hard-hot-starting?

 

I'd check everything mentioned before. You can find the dry-weights of floats in the googles. 

 

Small anecdote, But Brunhilde cranks like a champ now. In my experience with a dead-cold motor, it takes 2-3 seconds, but when warm or in a 2-3h window from last shut-down it's instantaneous.

 

 I did a road-trip to Amsterdam and back this past weekend (7 hours each way), on what was the hottest week I've yet experienced in Europe. The drive back was like being in an oven, there was no respite from the heat. 

 

Anyway, Through the hilly parts around Cologne my temp needle was the highest I've ever seen it, maybe 7-12 (angle) degrees north of the halfway point on the gauge, and that was keeping speeds down in the 110-130kph range. 

 

When I pulled over for gas, I let it idle a min or two before shutting it off in hopes it would allow the temps to drop, then filled her up. 

 

When i turned the key, the gauge was prolly 20-25 degrees north of horizontal, and sputtered for the first few starting attempts. I finally just went WOT, cranked, and she fought her way to life. I'm pretty convinced it was a fuel boiling issue due to heat. 

 

That's my story. :)

-J

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Sounds like vapor lock (fuel boiling in line) or cracked fuel line. Do you smell gas in the car or trunk?

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I had thought vapor lock too but no gas smell and the fuel lines (trunk and engine compartment) are new.  i’m changing out the floats and float valve this weekend to see if that helps.  thanks.  

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(edited)
11 hours ago, sratner said:

i’m changing out the floats and float valve this weekend to see if that helps.

 

I've battled this same problem for many years with the hot Texas summers.  Others make good suggestions and I would heed them.  Mint and I have toiled with this question every summer...

 

I might add to change all your rubber fuel lines with properly-sized ones and tight clamps. (fuel lines should snugly fit over corresponding nipples...if they are loose, they won't seal very well)  Make sure the plastic adapter on the outlet nipple of the fuel sender is not cracked (per Mint, you can cut a piece of the plastic fuel line to replace that little piece). (edit... I see you replaced fuel lines)

 

I put an in-line check valve near the tank.  This insures the entire length of fuel line has fuel and the pump only has to stroke a few times to fill the bowl of the carburetor.

 

After you do all this, watch to make sure the mechanical pump isn't leaking fuel out the weep hole in the back... KenB corrected me some months ago when another poster had a similar problem. After new lines and such the leaking pump became very evident and spilled fuel all over the engine!

 

Best of luck, this can be a frustrating problem, but it can be whipped.

 

Ed Z

Edited by zinz

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All above suggestions are good, but when you study Weber installations paper didn’t suggest to omit fuel return valve, which was installed on later model years car. Of course worn out carb components and or float that Tom mentioned needs to be checked out too.

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I agree with Buckeye.  Leaving pressurized fuel in the line is not good.

 

Here are a couple of photos of my Jeep filter installation.  I also have a clear plastic filter inline, between the engine and firewall, just to keep the Jeep filter clean and let me see if there is any crud in the fuel.

003.thumb.JPG.9006baf0275b0c57b01e03a909b2138d.JPG004.thumb.JPG.601f3f0ac44171c88b04cfd0735e70b7.JPG

 

The black band around the filter is just a chunk of radiator hose, protecting the filter.

 

I also think it is important to keep the fuel pump's feed line up off of the manifold and not to install the fuel filter where it will get heat soaked by the engine. 

 

 

On a related note, the little stubby fuel pump that's sold as a replacement part really doesn't fit these cars; unless they are omitting the coolant line from the diverter to the intake manifold (dual carb installation, for example).  With that pump, the hose is up tight against the bottom of the pump, acting as a fuel-heater-upper.  (I bought one, thinking they looked cool and eventually put the taller stock style back in).

 

Crappy kind

058.thumb.JPG.33a4ddd3538f0d2729397e7cb2c05b4b.JPG

Happy kind

071.thumb.JPG.8677490a6ca5b6998eb8cb8f9f3aa65b.JPG

 

See how it is up OFF of the coolant line?

084.thumb.JPG.bf677616fc4068dd20503097611e5e9e.JPG

 

I suspect BMW put that thick black bakelite insulator under the pump to keep it from soaking up heat from the head.  They even added stepped 'washers' around the bolts, insulating them as well; which is a pretty neat attention to detail.

 

(I dislike the stubby ones, even though they look cool... because they get hot).

Tom

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well today i changed out the floats, needle valve, tightened all fuel line connections and replaced all fuel lines in the trunk and engine compartment.  car stated right up, drove perfectly and I was feeling pretty good. I did a few short trips turning the car on and off without any issues. although I did notice that the car took a little longer to start after each short trip.  so after a 30 minute drive i parked the car for about an hour came back it started right up, i drove it about 100 yards and it sputtered and stalled. i tried to restart it without any luck. after numerous attempts it finally stated 45 minutes later. this is defiantly outside temperature related. today was the hottest it’s been and the wait to start the car was the longest so far. do you think this is vapor lock? i just can’t figure out why this is happening all of a sudden? do you think installing the fuel return valve will solve it?  

 

 

 

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