'72 Midget Runs On 2 Cylinders at Highway Speeds

[Cloudbase]

I was thinking about just getting a complete rebuild kit. I read about it my Bentley Manual today. I might take it into my local shop for a solid diagnosis before spending the money on that though.

So nobody has ever had a fuel pump that pumped okay when there was no back pressure, but didn't pump when there was pressure load on the line. That was the best hypothesis my limited experience / knowledge could come up with today.

 

[aeronca65t]

You don't have a loose manifold, do you?

Sometimes on those engines, the manifold and gasket get loose over time and suck in air.

Start the engine and let it idle. Spray WD40 around the intake gasket area.
If there's a leak, it'll get sucked in and the car will stumble.

 

[JPSmit]

You don't have a loose manifold, do you?

Sometimes on those engines, the manifold and gasket get loose over time and suck in air.

Start the engine and let it idle. Spray WD40 around the intake gasket area.
If there's a leak, it'll get sucked in and the car will stumble.

That's what I am wondering too - Fuel either works or it doesn't. particularly old or dirty. The only exception to this would be something in the tank that gets sucked over the outlet - that could be intermittent and could I suppose if it was porous cause those symptoms -fuel starvation.

Other than that, if you have replaced the filters and the carbs work and the gas is clean you should be good to go.

To check if it is an "air" issue - when it is running roughly, place your hand over the carb air intake(s) - filter off. If restricting the air there makes the engine run right, it is getting air from somewhere else - perhaps the manifold as Nial suggests. This is what happened with me, it ran fine cold but once it warmed up, it stumbled very badly as the parts expanded away from each other.

 

[nomad]

If carbs are balanced perhaps it is electical. Theres an old adage that says most carburetion problems are electrical in nature. In other words, look elsewhere. Not to difficult to bypass all the add on's with a seperate wire. OTOH if the miss is constant and doesn't vary its probably a fuel issue.

Kurt.

 

[Boink]

Are you sure there isn't a sticky valve? This could do it (under load).

 

[smaceng]

When you say it is running on two cyclinders, do you know which two? As the midget as two carbs, one basicly for 1 & 2, and one for 3 & 4, is it common to the front two or the back two? If so, check when you rev the engine, each of the carbs pulls in the same amount of air. Also, with a mirror and the air cleaners off, you can check if the pistons in the carbs are going up evenly. Do both of the carb gas bowls have the fuel in it? About same level?
Good luck,
Scott in CA

 

[Cloudbase]

In my troubleshooting yesterday I did a lot of what you guys have mentioned.

I've used WD-40 / carb cleaner to trouble shoot vacuum leaks in my E30 BMW. I sprayed a little around the peripheral parts of the head to see if I could make it stumble, but didn't hit the intake gasket area specifically. I'll try it when I get home tomorrow.

I also tried covering the intakes by hand with the air filters off. At one point it did make the engine idle normally by covering the rear carb, but it was very brief and difficult to duplicate. The dampers are moving up slightly unevenly, but consistently under engine revving. The rear one lags slightly. I suspect the problem is the rear carb / cylinders. The rear bowl is getting fuel and with the engine running when I loosened the hose clamp on the fuel connector line between the forward and rear carb fuel sprayed out under pressure.

Lastly, I pulled the spark plugs to inspect them. The #3 plug was fouled more than the rest and slightly wet. I'm on the road right now, but I'll to the WD-40 test on the intake gasket.

 

[rkep01]

Lastly, I pulled the spark plugs to inspect them. The #3 plug was fouled more than the rest and slightly wet. I'm on the road right now, but I'll to the WD-40 test on the intake gasket.

Sounds like an over-rich condition in the rear carb or an ignition malfunction.

 

[JPSmit]

Lastly, I pulled the spark plugs to inspect them. The #3 plug was fouled more than the rest and slightly wet. I'm on the road right now, but I'll to the WD-40 test on the intake gasket.

Sounds like an over-rich condition in the rear carb or an ignition malfunction.

+1 can you lean up the rear carb a couple flats?

 

[Cloudbase]

If it was something as simple as a rich rear carb, wouldn't it present all the time, not intermitently? A sticky valve sounds like it would be more like my symptoms then a rich carb.

 

[JPSmit]

If it was something as simple as a rich rear carb, wouldn't it present all the time, not intermitently? A sticky valve sounds like it would be more like my symptoms then a rich carb.

when mine was running particularly rich, it seemed intermittent - can't remember if it misfired only on acceleration or only cruising (either with or without load) but I do know there was one set of circumstances where it was obvious and another where it wasn't. (how's that for vague?)

 

[Boink]

I'm stickin' with my sticky exhaust valve theory. You may not notice it at all until under higher speed load. I've experienced that. The car ran perfectly until that event... then there was sputtering. In my case, with a fresh 1275, it was a strange wear-in situation. Has there been any strange burping of oil while in this problem state (e.g., if a 1275 out the oil separator or elsewhere)? Does it ever let up when you let up off the accelerator?

 

[nomad]

I'm still suspect of ignition problems. Try a hot wire from battery to coil and see if problem changes. Change plug on number 3 and check distributor cap for tracking. My .02. Easy check on carburetion is a mirror with air cleaners off and blipping the throttle so you can see the fuel delivery.

Kurt.

 

[Cloudbase]

Thanks for the replies guys. I'm going to try to dig back into it today. I have 3 other car projects going on at the same time so I'm a little jumbled. I'll start checking the intake area for leaks, mixture adjustment, coil, then dig into the valve cover (I don't have a spare gasket in hand).

 

[Guest]

He also has a smoke generator that runs into the exhaust using an old coolant expansion tank and windshield washer pump. That I plan to hook back up some day.

Just what you need, the driver behind you not being able to see the two foot high car in front of him. Stick to the flame thrower and you won't have that problem. :wink:

 

[drooartz]

I'm stickin' with my sticky exhaust valve theory. You may not notice it at all until under higher speed load. I've experienced that./quote]
A quick compression test would show that, well worth doing. Simple and will at least allow you to rule something out if it comes back okay.

 

[Boink]

I'm stickin' with my sticky exhaust valve theory. You may not notice it at all until under higher speed load. I've experienced that./quote]
A quick compression test would show that, well worth doing. Simple and will at least allow you to rule something out if it comes back okay.

True... but I've had a sticky valve only show under a load (and not in a static non-running situation). Strange, but it's happened. When the engine became <span style="text-decoration: underline">warm</span>, it stuck... and then when opening the rocker cover, there it was stuck with a push-rod that popped down!

 

[Cloudbase]

Hey everyone here's a quick update. I just want to say I really appreciate everyone's input. I'm sorry for my delay in posting my progress. I have a few car projects going on right now, one of which was a set of KW Coilovers I had to move on or loose for my BMW M Coupe (the truest modern reincarnation of the XKE Coupe / MGBGT in my opinion). I've also been putting in a lot of work 4 states away on my TR6 trade which is a whole other story, but also my motivation to get the Midget running.

I got to thinking about it and before I delved deeper into the head or the fuel I figured I better replace all known quantities in the ignition system. So far I had replaced the condenser and points with a Pertronix Ignition along with a Lucas Sport Coil, and new spark plugs. The original cap and wires looked good so I didn't replace them initially.

Today I replaced the cap with a top entry and 90 degree high performance wires. No change.

It started really rough and took quite a while to stabilize at idle (still running like it is on 2 cylinders). When I started this thread the rough running presented only under a hard load like high speed on the highway. Now it does it all the time. I cannot get it to run smoothly.

I sprayed brake cleaner all around the intake manifold gaskets and could not get it to stumble any worse, but it was running really rough. So I tried instead to make it run better by spraying carb cleaner in the same areas. I was careful to try not to get any overspray into the intakes, even covering them with my hand. A few times it actually ran smoother, just while I sprayed - which makes me suspect an intake gasket leak. But I have to be honest, it could have very well been overspray mist that was too fine to see getting into the carb intake.

I'm going to order new gaskets for both sides of the heat shield and a new fuel pump. That will rule out the cheap Napa pump and intake leak.

I couldn't do a compression test tonight because my compression tester is on loan. I'll do that after I install the new gaskets and fuel pump. I'm headed to back to San Diego to do more work for my TR6 trade, so it might be another week or two until I can report my findings. Thanks everyone for your help.

 

[Cloudbase]

Update: Did more work today. I pulled the carbs and heat shield to replace the gaskets. I cleaned every surface thoroughly and used the opportunity to clean the carbs again. I let them soak in carb cleaner and scrubbed off the grime with simple green. I put it all back together and started it up. No change! Argh!!! I even tested all the new gaskets with carb cleaner and it tested like there were no leaks. I loosened the fuel line to the back float bowl and it momentarily ran right. It makes me think the back is running too rich. I also pulled the plug wires on #3 and #4 while it was idling poorly. It made almost no difference in the sound of the engine. It really is only running correctly on #1 and #2.

Pics:

Dirty Carbs

Cleaned

 

[Cloudbase]

I also got my compression tester back. Number 4 was a little weak but not terribly off the rest. #1 = 100psi, #2 = 110psi, #3 = 100psi, #4 = 90psi.

The spark plugs tell a different story. I let it idle (poorly) for about 25 mins. My wife came home after a really hard day and I needed to console. During my consoling it finally quit. The fuel pump sounded like it was pumping dry, but there was plenty of gas. Lot of carbon deposits and indication of poor temp range on 1,2,4. 3 has oil glazing. Edit: Plugs have less than 20 miles on them and wires are brand new. Here are the plugs.

#1

#2

#3

#4

I'm thinking my next step will be to replace the NAPA pump with an OEM Lucas one. Then take it in to my shop for some carb tuning. Adjusting the mixture is a little above me. I think I would just make it worse. What do you think?