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Heat in engine bay causes idle to drop?

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yeah... I was thinking the first thing I do is change the plugs and wires. Then clean up the dist cap, and check the coil, possibly replace the coil. Though, the coil shouldn't be going bad so quickly (approximately 1.5 years old now), IMO.

Thought about checking that diaphragm in the ZS as it is probably the oldest & weakest link in the system atm. I might even check that before heading home tonight.
 
Coil should be OK till it quits, not too likely.
 
well... had an experience tonight coming home. Stopped off at the neighborhood grocery store to get some 'fresh' eats, and when I got back out to the car it started but ran like it was misfiring. So, I gently rev'ed it up to clear its throat and it started running smooth. I backed out of the parking spot and when I went into first it died.

Popped the hood looked around and touched the carb and it was ~hot~ to the touch. So, I let it sit for 20 minutes, and tried again. Nada. Wouldn't idle. Let it sit for another 20 and still wouldn't start and idle. I gave up and called AAA for a tow home.

While waiting (30 minutes before one could get there) for the tow truck, I decided to trouble shoot a bit. I managed to get it started and idle after another 15 minutes of waiting, but like before it had a miss. Long story short, I found #4 was missing.

I'm not entirely sure what that means (yet), but I am definitely changing plugs, wires, dist cap, and rotor this weekend. It was too dark for me to pull the plugs and give them an accurate visual inspection.

The bright side of this ordeal is that the tow truck driver owns a "63 Midget with lots of extra parts" and is looking to sell it. Good guy, he was more apprehensive about using his truck to tow my MGB instead of his flat bed than I was. If I wasn't only a mile or two from home, I would have insisted on a flat bed.
 
My 74 MGB with an 18GK engine has the same problem. The engine has just over 10k on a rebuilt engine that's about six years old, and the HS4 carbs were rebuilt three or four years ago. The shafts are still tight. I replaced the jets and floats, and the heat shield. It also has a Flamethrower dizzy and coil.

The mileage is kind of low because I've driven it regularly only in the last couple of years.

When it's cooler outside like today, it wants to idle up around 1100, when I'd like to idle at around 900. On hot days like last week, it would drop down to around 650.

I've never been satisfied with my ability to keep it in proper tune, and will be posting to the forum about that shortly.

Thank you,
-Bill
 
wkilleffer said:
My 74 MGB with an 18GK engine has the same problem. The engine has just over 10k on a rebuilt engine that's about six years old, and the HS4 carbs were rebuilt three or four years ago. The shafts are still tight. I replaced the jets and floats, and the heat shield. It also has a Flamethrower dizzy and coil.

The mileage is kind of low because I've driven it regularly only in the last couple of years.

When it's cooler outside like today, it wants to idle up around 1100, when I'd like to idle at around 900. On hot days like last week, it would drop down to around 650.

I've never been satisfied with my ability to keep it in proper tune, and will be posting to the forum about that shortly.

Thank you,
-Bill
Click to expand...

I feel the same way sometimes. Temps really play havoc sometimes.
 
definitely! why can't it be 80deg all year long?
 
heh Doc would agree with ya... if you were talking DCOE ;P

Changed my plug wires, dist cap, and rotor today. Seems all that fiddling I did with the mixture the past couple of weeks was all for not. Soon as I got... Well, not as soon as I put the wires, cap, and rotor on. I made an attempt to clean the contacts on the + lead on the coil and it seems I didn't quite get it connected back properly, and ended up fiddling around trying to figure out why it wasn't starting. I had plug #4 out checking for spark and didn't have any. Quadrouple check the coil and balast resistor wires and I touched the positive wire to on the coil and the engine half turned over (ignition was on). Then I made sure the + wire was firmly connected to the balast and the coil and no sooner than I touched the key the engine was running... on 3 cylinders. I forgot put put plug #4 back in, OOPS! Shut it down, resecured plug #4, and cranked it up again.

So, back to my original statement with fiddling with the mixture. Seems I'm a tad on the rich side now. The engine is idling wicked low, like 500RPM or lower. Smooth as possible at that RPM, but it's too low for comfort, atm. I've scheduled time in a friend's driveway tomorrow. So, I'll take care of that then.

As for my culprit, I'd have to say it was most likely the dist cap and rotor. When I pulled the cap nothing struck me as out of the ordinary, but when I pulled the rotor the conductor was all black.

I'll have to go on a good test drive tomorrow to make sure I nailed everything down.
 
Just wanted to follow up. First off, I sent my distributor off to Jeff at Advanced Distributor. Had him recurve it, and stick a pertronix unit in it. Can't say it completely cured my problem as I originally stated in this thread, but the car does run much smoother, no doubt about that. Any hesitation on acceleration is gone. And when adjusting the timing with the strobe light the timing marks are dead still, where as before it jumped +/-5 degrees and was difficult to accurately tune. So thanks to all who suggested the recurve.

I think I agree with many of you about the engine loading up. Now that I'm confident with the ignition and timing, I'm playing with the carbs to get them right at the sweet spot. Right now I think I have them leaned out a bit too much as the plugs are a bit white in color so I'm hesitant to go any leaner, and the engine still loads up but less often.

Something else that's always been in the back of my head is instead of trying to tune the engine to run at varying degrees of air temperature, why not try to keep the air temperature more stable with an electric fan? Any input on going that route? I've researched it a little, and it seems to be hit or miss for some people.
 
Are you adjusting the mixture after the engine is at normal operating temp? That can make a big difference.

I've a "pusher" electric fan on our '64. It makes a difference, but we're in central Florida, "among the masses."
Stop-and-go at noon on a July day it can 'creep' a mite. /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

The fan helps.


And yes, Stewart, I can agree if you're talkin' DCOE. THEY BARK! That insipid DGV thingie just draws air... but at least it's got accelerator PUMPS! /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif
 
DrEntropy said:
Are you adjusting the mixture after the engine is at normal operating temp? That can make a big difference.

I've a "pusher" electric fan on our '64. It makes a difference, but we're in central Florida, "among the masses."
Stop-and-go at noon on a July day it can 'creep' a mite. /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

The fan helps.
Click to expand...

Yep, I let the engine bay get toasty when I tune the carbs, at least as toasty as I can get it with hood up! So do you have a pusher in conjuction with the belt driven puller?
 
Yup. It ~was~ on a 'manual over-ride' switch, now gonna hook it to a thermo-switch pasted to either the t'stat area or a flat spot onna rad. Still "considering my options" at this point.
 
I have myself a pusher fan + temp sensitive controller in route for installation on my '76 this weekend.
 
Goodonya! Is a relay part of the 'kit'?
 
I believe it does. The controller (made by Hayden) claims to be able to handle up to 2 fans or 30Amps. It also says the temp sensor is adjustable, and has an over-ride.
 
PM me the pertinent link/info?

Pretty-please? /bcforum/images/%%GRAEMLIN_URL%%/jester.gif
 
sent
 
Rec'd.

THX.

/bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
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