Puzzling Engine Issue - '71 Midget

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Larry Kluss
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Puzzling Engine Issue - '71 Midget

Post by Larry Kluss »

I thought I'd post a puzzling engine issue Tyson and I were trying to diagnose with his '71 Midget. We finally solved it last weekend thanks to Dean lending a fresh set of eyes to the problem. Here is where we were at before we obtained Dean's help:

Issue - bad miss/no power under load. Seems like it's choking.
Also happens static with elevated RPM.
Idle is very good.
Symptoms are less with choke on, but still obvious.
Happens every time, very consistent.

Issue started after engine was reinstalled. Removed to address clutch issue.
The only engine work done was timing chain only replacement, oil pan gasket.
Carbs/linkage, and intake and exhaust manifolds removed.
Carb suction chambers removed for polishing.
Front carb jet replaced.
Re-used old carb-mount gaskets.
New intake/exhaust manifold gasket.
The head, valve lash, and distributor were untouched.

Checked so far:

Engine mechanical -
Compression - 155/165 - good
Manifold vacuum - 20" Hg at idle - good. Reads less than 10" when issue occurs - not sure what this means?
Removed timing cover and triple-checked the timing gear marks - already good
Remove head pipe to check for exhaust blockage - no difference
Confirm all intake manifold plugs are in place - good

Ignition system -
Check/clean/adjust points - was good
Inspect cap and rotor - good
Check coil connections - correct and good
Check condensor and internal distributor wires for resistance - good
Check spark plugs - good
Check plug wire resistance - good
Check/set timing - was pretty close
Check engine ground resistance and try jumper cable from battery - good and no change
Check all ignition wiring to the diagram - good
Run jumper from battery to coil to eliminate ignition switch system - no change
Check coil resistance - good
Try a known good coil - no change

Fuel system/carbs -
Center needles in jets
Check carb pistons - free and smooth
Adjust/sync carbs - idle good
Check fuel pump pressure - good
Check float levels and ball seats - good. Not flooding because no fuel coming out vents.


Any ideas?
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Re: Puzzling Engine Issue - '71 Midget

Post by Martin Keller »

Hi Larry and Tyson,
Well here is what I would check for.
Fuel filter installed backwards or clogged or a collapsed or crushed fuel line.
Reason I would look at these is the symptom gets a little better with the choke pulled out from your description which tells me it is a fuel flow issue I would think.
Most likely a pinched fuel line if I were betting.

:drive
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Steve Simmons
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Re: Puzzling Engine Issue - '71 Midget

Post by Steve Simmons »

It certainly sounds like a fuel-related issue because of the choke making it better, but the other symptoms make me think otherwise. So many things it could be without seeing and hearing the car in person. Maybe the plug wires were mixed up?
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Re: Puzzling Engine Issue - '71 Midget

Post by Larry Kluss »

Well, you guys are on the right track being fuel related. But it idled great and the vacuum was good. Here is a hint, I always go back to what did I touch or change right before the issue happened and that proved to be the case here. Though we didn't see it without Dean's extra set of eyes.

Again, here is what was done before the issue happened...

The only engine work done was timing chain only replacement, oil pan gasket.
Carbs/linkage, and intake and exhaust manifolds removed.
Carb suction chambers removed for polishing.
Front carb jet replaced.
Re-used old carb-mount gaskets.
New intake/exhaust manifold gasket.
The head, valve lash, and distributor were untouched.
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Re: Puzzling Engine Issue - '71 Midget

Post by Steve Simmons »

Based on that, I would suspect an intake gasket leak, or carb linkage installed incorrectly or misaligned.
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Re: Puzzling Engine Issue - '71 Midget

Post by Martin Keller »

Ok I have to agree with Steve about the gasket leaking but at the the carbs to manifold or maybe the gassket for the suction chambers was missing in incorrectly installed.
Just guessing at this point with out actually looking at the car.
:drive
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Re: Puzzling Engine Issue - '71 Midget

Post by tannyo »

Since you said it was something you touched, I'm going to guess that it was the front carb jet.
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Re: Puzzling Engine Issue - '71 Midget

Post by Larry Kluss »

Okay, so with Dean's help we recapped all we had done and came to the same conclusion that it was likely fuel/carb related. Again it idled great and the carbs were in sync.

Tyson and I had only moved the carb pistons slightly to check/adjust the mixture. Dean moved each piston, one at a time, a large amount. Something we had not thought to do. When doing so the rear carb would cause an excessive rich condition as expected, but doing so to the front carb had almost no effect. So we had an apparent fuel flow issue with the front carb only. Progress!

Next we rechecked the front fuel bowl and spotted a tiny bit of black peeking out of the feed hole to the jet in the bottom of the bowl. We removed the jet and picked out an o-ring in three pieces that was jambed in the feed hole. We think the o-ring was from the old jet and it got jambed in the hole when the new jet was installed.

We reinstalled the jet and resync'd the carbs, fired it up, and it ran great!

This issue was a valuable lesson for Tyson and it stretched my diagnostic skills to the limit. Tyson learned to be sure to account for all of the old parts, seals, etc, when replacing components, and hopefully he learned a lot about the diagnosing engine problems. And I learned it's always better to have another set of experienced eyes to diagnose a problem. Thanks again, Dean!
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