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MGB Properly starting a warmed-up or hot MGB

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wkilleffer

wkilleffer

Jedi Knight
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We've been experiencing 90+ degree weather here in the last few days, which seems to make starting my already hot MGB even harder.

Starting a cold one is pretty easy and well-explained in all the manuals. But how do you start one that's already hot? Mine won't start hot unless I either pull the choke a small amount of its travel, or put my foot on the gas. Either way, the exhaust smells quite gassy.

Am I doing something wrong or do I need to make more mixture adjustments? Any suggestions would be appreciated.

Thank you,
 
William - you must have a Weber because putting your foot on the gas pedal on an MG equipped with dual SUs or a Zenith Stromberg doesn't do anything - they don't have accelerator pumps!
 
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William - you must have a Weber because putting your foot on the gas pedal on an MG equipped with dual SUs or a Zenith Stromberg doesn't do anything - they don't have accelerator pumps!

[/ QUOTE ]

Nope, I've resisted so far, and also find it strange that doing this seems to make a difference!
 
William, What carbs do you have? Are they HIFs? If so, when were they rebuilt last? How is the idle when the engine is running, (normal)? Rough or smooth? PJ
 
Putting your foot on the gas will open the throttle plate some.Thus letting the engine breath a little more. It sounds like you may want to re-visit the carb settings. a hot start should be easy. Check the mixture and idle settings. It sounds like the car wants some more air (and/or) fuel.
How is it on cold starts? Full choke? half choke? That may help you. It really should require most of the choke for a cold start. If not it may be set a little rich.
It could be any number of other things too.
Check your ignition timing. If it's out of adjustment, that can cause a hard start.
Just some food for thought
Good luck Guv'na
 
Here are some responses to your questions:

My carbs are HS4's as the engine's not original to the car. Idle seems fairly smooth considering it's a 4-cylinder. The speed is lower than 1000 rpm and varies a bit with engine temps. The carbs were rebuilt fully about 3 years ago. I've replaced the floats and switched the needle valves for grosse jets. I also replaced the jets at the bottoms of the carbs when they started leaking and came apart. The shafts are still tight.

On cold starts, it requires the whole choke. Fast idle's between 1500 and 1700 rpm. Fast idle sounds a bit burbly, but the car drives fine. If I take the choke off as soon as the temp gauge reaches normal, the carbs might backfire a bit, but then it settles down.

The book says timing should be 15deg at 1500 rpm. Mine's a degree or two higher, and might could go a bit higher still. Seems sluggish at factory setting.

If I give it partial choke when starting after warm-up, it will start quickly and I'll take the choke off quickly. It might could go another 1/2 flat richer. I have to remember that this car's exhaust is going to smell gassier than a modern car, and that's not necessarily a sign that it's running rich. It will soon be time for new air cleaners as well.

Thank you for the advice so far,
 
William, You shouldn't have to do anything but turn the key on a hot engine and it should kick right off. I'm wondering if you have a weak ignition and not a fuel problem at all. Possibly the coil is weak? /ubbthreads/images/graemlins/confused.gif Just another theory. /ubbthreads/images/graemlins/rolleyes.gif PJ
 
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If I give it partial choke when starting after warm-up, it will start quickly and I'll take the choke off quickly.

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To a small extent that's no different that putting your put down on the accellerator slightly (the "choke" on the SUs doesn't enrichen the mixture immediately, it raises the idle speed to a point then starts enrichening).

Just to add my two cents: my twin-SU, detoxed engine starts immediately when warm/hot without doing anything but touching the starter. When cold I use choke until it starts (usually 3/4-full) then back off into the "high idle" range until it warms up/smooths out.
 
And it sounds like yours is spot on Scott. My Bugeye was always the same. Always wanted to start right up even after seting from a month or so TDY away to the far corners of the world.
 
You should be able to reach in through the window, turn the key, and start a warmed engine without even getting in the driver's seat.
 
...and I'll chime in and say Tony's right: even with a (shudder) Weber DCOE!

Sounds like there are other issues. And when you use the choke it lowers the jets as well as opening the throttle plates a bit on an SU, to *IMMEDIATELY* enrichen the mixture.
 
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William, You shouldn't have to do anything but turn the key on a hot engine and it should kick right off. I'm wondering if you have a weak ignition and not a fuel problem at all. Possibly the coil is weak? /ubbthreads/images/graemlins/confused.gif Just another theory. /ubbthreads/images/graemlins/rolleyes.gif PJ

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Well, the car has a brand-new Pertronix distributor and Flame Thower distributor. But this has been going on since before I made those changes.

A new set of plug wires and maybe plugs might help as they're around a year old. But the car's mileage doesn't reflect that as I didn't drive it all the time until about four or five months ago. New air cleaner elements might help too.
 
If I was a betting man...............carbs need set up ie adjusted properly. Get the book out and start over.
 
Yep, carbs.
 
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If I was a betting man...............carbs need set up ie adjusted properly. Get the book out and start over.

[/ QUOTE ]

Again!?! I swear I've spent two years of my life doing that, or at least trying to. No telling how much gas I've wasted.

The trouble is that *it doesn't really work the way the books say it does!* I have at least three books on the subject, one of which is dedicated to SU carbs. All of them have a different method and none of them work. If they are working, then the signs are too subtle for me to notice.

The biggest concern I have is that I spent some fat bucks to get the neglected engine rebuilt, and thanks to my inability to perform tasks like this, I might have ruined it after only a few years of driving. The rebuilders built it so nicely that it should last, but not if I blow it.

HOW DO I DO THIS THE RIGHT WAY? I'm sick of not knowing and sick of the frustration.

This almost goes beyond the I'm-getting-a-Weber to the I'm-getting-a-Miata. Not really, but it's hard not to think about that when confronted with how I haven't been able to experience the car to its fullest.

Thank you, and my apologies for yelling,
 
Well, I doubt you've ruined the engine...let's look at some basics:

You have HS-4's...to which carb does the gas flow first? Whichever that is, that's the carb you have to set up initially, then you can move to the 2nd carb.

Do you have an SU tool kit (Moss # 386-300)?

or a carburetor syncronizer (Moss # 386-200)?

Have you checked for vacuum leaks in & around the carbs & intake?

If you want to get it to somebody, I don't think you're too far from Winchester, TN...see if you can link up with Ben Pender in Winchester - he's a whiz with SU's.
 
Kind of hard to ruin an engine with carbs out of wack.

Take a deap breath and step back a bit.

This is not rocket science and you can do it.

Heck it has been running for how long now?

Take your time and follow the instructions. All the books are correct, many ways to get to the end position if you have no air leaks mostly. Oh there is some other stuff but should run and run well.

If it runs at all you are mostly there.
 
On cold starts, it requires the whole choke. (and that is correct)

The book says timing should be 15deg at 1500 rpm. Mine's a degree or two higher, and might could go a bit higher still. Seems sluggish at factory setting. (and so is that correct)

Could I suggest opening each carb about one flat from what you think is correct and checking that for hot starting? Pay close attention and let us know of any change.
 
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Well, I doubt you've ruined the engine...let's look at some basics:

You have HS-4's...to which carb does the gas flow first? Whichever that is, that's the carb you have to set up initially, then you can move to the 2nd carb.

[/ QUOTE ]

Gas flows to the front carb first. Seems strange to set them up separately due to their interdependence even when all connections are disconnected for this procedure, but ok.

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Do you have an SU tool kit (Moss # 386-300)?

or a carburetor syncronizer (Moss # 386-200)?

[/ QUOTE ]

The SU tool kit has those hollow rods that go into the pistons with wires that point sideways to indicate how the carbs are breathing, right? I have something like that, and a Carbbalancer.

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Have you checked for vacuum leaks in & around the carbs & intake?

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Yes, but that doesn't mean that I might not have missed something. I'll check to make sure the intake manifold is on tight as well.

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If you want to get it to somebody, I don't think you're too far from Winchester, TN...see if you can link up with Ben Pender in Winchester - he's a whiz with SU's.

[/ QUOTE ]

I'm about an hour from Winchester on I-24. That trip would probably be a last resort, but thanks for the idea.

Thank you,
-Bill
 
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Gas flows to the front carb first. Seems strange to set them up separately due to their interdependence even when all connections are disconnected for this procedure, but ok.

[/ QUOTE ]

???
 
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