Flat spot, hesitiation, call it what you will...

[Andre the Giant]

The saga continues. I've been battling this for a while now, but had to take a few weeks off from working on the MG to do basic household tasks like mowing, fixing things, etc. Now I'm ready to fix the problem.

The car idles fine, but when on acceleration, when the RPM reach 2,300 or so, the engine boggs down. To get the power to reach the next gear, I have to floor it. The power seems to pick up when its floored.

Here's what I've tried. (all of these have had little to no effect.) Replaced the carb diaphram (ZS carb), tinkered with the mixture, reworked the carbon canisters, tightened all vacuum/emissions hoses, installed new coil, dist cap, rotor, plug wires, plugs, checked the timing, checked the vacuum advance, (Its a CEI distributor, not an OPUS one) adjusted the clearance on the rocker arms, cleaned the carb including the fuel bowl, and checked the fuel pump and hoses.

My latest theories involve the auto-starter (choke) which I discovered has some stripped bolts, and the coil. The bolts that hold the heat mass/water jacket to the autostarter are stripped allowing the whole mess to rotate instead of staying in place and acting on the auto-starter lever. I have another auto-start assembly which I will install this weekend. A wise man on this board wrote that the Lucas Sport Coil isn't the right match for my ignition system. So I'm going to switch back to the stock one and see what happens.

If that doesn't solve the problem... I'll go absolutely bonkers!

Any other ideas?

[ 08-01-2003: Message edited by: Andre the Giant ]</p>

 

[tony barnhill]

go to my website & then to the tech tip on ZS carbs...once its set up correctly, you'll have no more problems...&, you're correct - its probably in the auto choke
https://www.theautoist.com/zs_water_chokes.htm

 

[John S Farrington]

I would recommend that you convert the choke on the ZS to a manual type. There are kits available to do this and this gives you positive control of how much choke you are getting. Moss or British Victoria offer such conversion kits for the ZS. The autochoke of the ZS is not a good piece of work and is probably causing your problem. It sounds like the choke is allowing more enrichment than you need and thus it is bogging down. Try the converesion. Hope this helps.

 

[adam90009]

if you have striped holes for the screws for the auto choke try taking out the washer so the screw will reach threads further down.

 

[tony barnhill]

ZS carbs with auto 'choke' weren't the fastest thing around...however, when set up properly they do exactly what they were designed to do...any problems with one are because the owner hasn't yet gotten the problems sorted out....I have a 1979 MGB with almost 100,000 miles on it...totally original in all regards...starts first time, runs out perfectly, very good gas mileage - never a problem with ZS carb that has been rebuilt 1 time!

Oh, car sat for 10+ years & all I did to carb was disassemble, clean, reassemble & adjuet!

Go to my web site, get the book on ZS carbs, put it back like it came from the factory & enjoy....if you've stripped a hole, contact me....I have old bodies you can use

...if you decide to toss it, toss it my way!

 

[Andre the Giant]

OK. I replaced the autostart assembly and followed the instructions on Tony's site, (thanks for the very detailed and helpful info by the way) I also replaced the Lucas Sport Coil with the old stock one. The car still sputters and loses power in the midrange RPM.

I've tried disconnecting the vacuum timing advance, rotating the autostart heatmass assembly away from the datum mark, none of these things seem to help.

I think I've been overlooking the obvious. My car has been desmogged. The only hoses running from the carb are the fuel line, vacuum advance, coolant hoses to the autostart, hose from the valve cover/evap canister, and I believe a hose to the evap canister from the fuel bowl. I discovered that the Valve cover hose is loose. It's probable that air is being sucked at this point, but I won't know if that's the cause until I get a couple of small clamps and torque that hose in place.

 

[tony barnhill]

Andre...Tom Bedenbaugh is now on the BBS...I'll try to get my friend JDW to come over...they're both pretty good with carbs....I've never had that problem with any of my ZS's...but, I've gotta ask a question: How many throttle return springs are attached from your carb to the air cleaner?

 

[Tom Bedenbaugh]

I need a little info. What do your plugs look like? Are you ajusting the mixture with the air cleaner on, and do you have a clean filter? One other thing are the flyweights advancing the timing when you bring the RPM's up?

 

[Andre the Giant]

I have one of the ramflo type air filters, it seems pretty clean, but I'll try running it without the filter and see if it makes a difference. As far as the advance goes, I have a timing light and when I rev the engine, the timing advances. I think its set to around 8 degrees BTDC right now. When the engine revs, it goes to the edge of the scale, (I think it's 16 degrees, I can't quite remember) and if I really rev it, it advances probably 25 degrees or so. The plugs were pretty clean, not too much carbon fouling and no glazing. Just in case, I decided to change the plugs, bought different brand, the problem didn't change much at all.

As far as the springs go, I'm not 100% sure what you mean Tony... I've got an aftermarket air filter, the stock components have all gone bye bye. There are no throttle return springs attached to the air cleaner. I know one of my autostart heatmasses is toast. The other one, (the one I'm using) seems to be in perfect shape, but I assume it could be messed up. (I tested it with the hairdryer and it did rotate slightly) I'll try the manual choke setup over the weekend to be sure.

I tightened the evap. canister hoses and nothing changed. I'm going to swap out the damper return spring and see if that makes a difference. About the only thing I haven't changed or tampered with is the CEI ignition amplifier, but it's a solid state deal, I wouldn't think it would go bad.

heck, I still don't know if its a carburettor problem or an ignition problem.

And I thought I was a smart guy...

[ 08-08-2003: Message edited by: Andre the Giant ]

[ 08-08-2003: Message edited by: Andre the Giant ]</p>

 

[Tom Bedenbaugh]

Boy Andre, you have covered all the bases that I can think of. I read somewhere that the stromberg doesn't work right with anything but the stock filter. That was on a B. I don't know if it applys to a Midget or not. I'm like you . An electronic ignition either works or it doesn't. I wish I had the magic answer, but I would have to play with it to figure this one out.

 

[Andre the Giant]

I overlooked the post from John S Farrington, (sorry) and I do have the manual choke conversion kit. I'll put it on this weekend and see if that changes anything. Maybe someday I'll stumble across the solution.

I've already got two carbs, two autostarts, two coils, spare distributor cap, wires, plugs, rotor. Swapping those components seems to make no difference.

I wonder if the CEI amplifier or the amplifier pickup (I think that's the right terminology) in my distributor may be damaged. I checked the gap with a feeler gauge and it was correct. But the distributor is about the only thing that I haven't replaced or overhauled.

Tony, do you have a spare CEI distributor and CEI Amplifier laying about?

[ 08-08-2003: Message edited by: Andre the Giant ]</p>

 

[Andre the Giant]

I replaced the entire carburettor. Different choke, different everything. It still has the same problem. In spite of that, I am finally convinced that the problem is mixture related, not ignition.

Here is theory # 57412. I think I have an intake/exhaust manifold gasket leak. Or maybe I've got a crack/leak in the intake manifold. Maybe the leak doesn't effect the mixture that much until the mid-RPM range. I'm going to rip the carb/intake manifold off and replace the manifold gasket, inspect the intake manifold and maybe replace the studs and nuts that hold the manifold to the head.

This has to be the problem... (I've tried everything else!!! I think

)

Hey, at least I'm having fun.

 

[Tom Bedenbaugh]

As long as it's still fun. Although it's not necessary to do all that. Fire her up and spray some carb cleaner around where you suspect a leak. If the RPM are effected that's where your leak is. It will be an ovious change. If there is no change then you are waisting your time and money. If your going to do all that I would replacee the tappet cover gaskets(use the rubber ones), and the rubber grommetts on the mounting bolts. The manifolds normally crack under the hot air intake shroud.

 

[tony barnhill]

I'm thinking your problem is in the air cleaner setup/manual choke...though 2 separate things, either oculd cause the problem...
...it takes 3 springs on a stock air cleaner for throttle return...witrhout them, the throttle isn't operating properly...also, there's a return spring at the accelerator lever (the moon shaped thing) - is it there?
how's the induction heater?
...is the manual choke keeping its setting or is it slipping?
...is the throttle disc properly weighted so it stays open/closed when the choke is operating it?
...lots of variables there

 

[Andre the Giant]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by tony barnhill:
I'm thinking your problem is in the air cleaner setup/manual choke...though 2 separate things, either oculd cause the problem...
...it takes 3 springs on a stock air cleaner for throttle return...witrhout them, the throttle isn't operating properly...also, there's a return spring at the accelerator lever (the moon shaped thing) - is it there?
how's the induction heater?
...is the manual choke keeping its setting or is it slipping?
...is the throttle disc properly weighted so it stays open/closed when the choke is operating it?
...lots of variables there<hr></blockquote>

I am so confused...

I've got a ZS carb on a 79 midget. The heat sheilds, stock air intake, EGR valve, Air pump, and virtually every other extraneous item has been removed. The air cleaner is a Longflow type and there are no springs that attach from it to the throttle linkage.

The choke is now stationary. I installed the manual choke and the choke seems to be functioning properly.

I'm not sure about the throttle disk...

What I do know is that the flat spot is kind of erratic. When I hit 2500 RPM or so, the engine loses power, but it's not like it completely bogs down, it has little surges. It's not missing, but the sound changes, and if I let off the gas just a bit, the engine seems to get a bit more power.

I'm going to tighten the manifold bolts today at lunch.

One of these days, old "Eliza" will be back on the road.

 

[iggy]

Suggestions:
1) Might be a worn distributor shaft - Hook up a timing light and check the timing. Is it rock steady or does it move back and forth? Check at various RPM's.
2) Fuel delivery - Is the flow steady and sufficient? The old tractor I traded for the B had a large dead insect in the gas tank that got sucked into the intake tube and caused me problems. Could be anything...

 

[Tom Bedenbaugh]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>if I let off the gas just a bit, the engine seems to get a bit more power.<hr></blockquote>
That is normally a sign the engine is running too lean.

 

[Andre the Giant]

I'm driving today.

There are four factors that I think contributed to the problem.

1) The choke was adjusted improperly up until a week or so ago.

2) The DPO put a fine thread nut on a course thread stud that holds the intake/exhaust manifold on, thus stripping one of the manifold studs. (Thus possibly causing a intake manifold leak) I still haven't fixed this, but I tightened the others manifold nuts.

3) The DPO put a plug in place of the EGR valve, but the sealant he used didn't completely seal it. This allowed small amounts of air to enter the mixture, leaning it out.

4) The "dreaded current owner" replaced the stock air cleaner with a Longflow one. This allows more air to enter the carb, so it tends to run lean.

Right now I've adjusted the needle to it's richest setting. The car runs pretty well, but it's still a bit on the lean side. I may block part of the air cleaner, or put the ugly stock one back on to richen things up a bit.

In the mean time, She's back on the road and its in large part thanks to all of you guys. Thanks for the advice, tips and knowledge!

Andy