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Engine stumbling badly off idle
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67rustavenger
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PostPosted: Sat May 29, 2021 2:05 pm    Post subject: Engine stumbling badly off idle Reply with quote

So I am having a bit of an issue with my 2180 revving past idle.

Currently running 45 DRLA's and have cleaned them today, But the issue persists. The engine starts with difficulty and once running. I cannot get past the idle circuit without it acting like it's starving for fuel.
It runs so poorly that it will not idle long enough the set the timing.

Current jetting is,
70 idle. Yes I know this is fat for my setup. They were 57's last time I ran these carbs on this engine, so I am experimenting.
160 main
180 AC
.2 emulsion tubes
55 pump jets
38mm vents
All the carb presets done per the "Superformance" book.
New gaskets at the manifold bases.
CB hex bar linkage, synced.
I have the CSP center pull linkage that Torben dislikes. But the rods will not clear the dist body. So those cannot be used in the current ignition configuration.

Ignition is a MSD clone dist, Crane Hi6N CDI, Crane LX-92 coil. Spark plug gaps at .040"

Heads are Tims stage II 42I 37E
Webcam 86b cam gear at "0" advance
1.4 Scat rockers

If I manage to get past the idle circuit, the engine responds fairly well. But once back on the idle circuit it's hard to get up in the revs again.

I really would like to get to the bottom of what's going on this weekend as I have planned on a race next weekend at the NW Bug Run next week.

These carbs ran great the last time I had the engine in the car. So I'm a bit puzzled at the moment.

Any ideas? Lemme know what other info you might need to help out.
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mukluk
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PostPosted: Sat May 29, 2021 4:48 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

Sounds like a vacuum leak to me.

What do you see when you connect a vacuum gauge?
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67rustavenger
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PostPosted: Sat May 29, 2021 4:52 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

Sadly it won't stay running long enough to connect a vacuum gauge and check.
This is just a weird situation. That I haven't encountered to date.
I did install new manifold base gaskets and the manifolds are true at the head end of things.

This had ran great last time I had it running.

I'm gonna try swapping back to the normal ignition system. Just to eliminate that aspect of the issue.
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67rustavenger
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PostPosted: Sat May 29, 2021 5:36 pm    Post subject: Re: Engine stumbling badly off idle (DRLA) Reply with quote

Forgot to mention that the carbs are somewhat acting like Evan's carbs were.

Coughing out the top of the carbs (I can hear it). And backfiring out the exhaust pipe. To me this seems very odd and I am having a hard time figuring out what's going on.
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Turnswrenches
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PostPosted: Sat May 29, 2021 6:09 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

Do you have an old points distributor to try ? Just to see if the CD box is giving you trouble.

Your description sounds exactly like my recent issues.

My chinese ebay distributor had too much advance built into it.
If I set total to 35 degrees, it would fall back to 10 degrees at idle and barely ran. It popped, sputtered, etc...
I removed one of the weights and limited the other one.
Now i can set initial to 20 degrees and all-in it stops at 35 degrees.
The engine is much more responsive and idles much better.

Just food for thought.
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APPLEGREENVW
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PostPosted: Sat May 29, 2021 6:15 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

Are your idle jets clean?
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67rustavenger
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PostPosted: Sat May 29, 2021 6:46 pm    Post subject: Re: Engine stumbling badly off idle (Solved) Reply with quote

It was the ignition system.

For whatever reason. It worked great on my 1679 test bed.
But didn't on this engine. WTF?

I installed my trusty 010. And life is good again.

And yes I cleaned the carbs and idle jets today.

I just had it running for a couple of minutes. Just to see what was up. It's all in the tuning now! Very Happy

Thanks for the input guys.
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PostPosted: Sat May 29, 2021 7:10 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

Let us know, what the issue is with the ignition system. Confused
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67rustavenger
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PostPosted: Sat May 29, 2021 8:16 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

APPLEGREENVW wrote:
Let us know, what the issue is with the ignition system. Confused

I don't know yet.
I had the CDI as described in the opening statement. Working on my 1679. It worked as expected.

For whatever reason, on this 2180 engine, it didn't work correctly. Lots of coughing through the carbs and backfiring through the exhaust.

It's strange. All I did was switch the ignition from one engine to the other. All the wiring remained the same with the same components. Other than the larger displacement of the engine.

I reversed the CDI install back to the 010 and the engine fired right up and idled within 30 seconds.
I'm gonna regret typing this. Glenn will crow about the virtues of standard ignition systems. Lol!
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67rustavenger
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PostPosted: Mon May 31, 2021 6:56 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

So I have been able to get the engine to start and idle very well.

The issue I'm having now is, the carbs act like the main jet stacks have been removed. Much like when tuning the idle circuit.

Driving the car, it will accelerate as expected, crisp and a good pull in the idle jet circuit.
Push the fun pedal past idle into the transition and main circuits, and there is nothing happening. It's almost like the fuel is being shut off.
Back off the throttle opening and just before the engine recovers there is a rather loud single backfire out of the exhaust pipe.

There are no vacuum leaks, I use a Malpassi PR, fuel filters are clean and flow well, fuel pump is a Carter P60504.

I'm at a loss as to what's going on with this setup. As stated above, it worked very well last time I ran it. So this is a weird situation.

I can imagine that this is something simple that I am over looking.
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PostPosted: Mon May 31, 2021 7:12 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

Do you have a good chassis/engine ground ?
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67rustavenger
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PostPosted: Mon May 31, 2021 7:38 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

Turnswrenches wrote:
Do you have a good chassis/engine ground ?


Yes, I'm good in that department.

The plan today is to run through the ignition system this morning. Before it get's too hot to think. Just incase I missed something there.

010 dist, CB dry pack coil, CB 8.2mm leads, NGK non-resister plugs.
FWIW, I have used the dry pack coil on many different ignition setups, 010, 009, CB MagnaSpark II.
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PostPosted: Tue Jun 01, 2021 4:49 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

After running through the ignition system. I set the timing to 30 at 3K RPM. Point gap at .026".
The engine is still reacting the same as described above. Great through the idle circuit.
Then on transition to the mains. Nothing! As stated, it's like the main stacks have been removed.

My next move, out of desperation. Will be to install the shit 45 Emporto's and hope that they work decent enough to at least get to full throttle. They worked in that range the last time they were on the engine 3 years ago.

Otherwise, I'm at a complete loss at to what's causing the Dells no falter when accelerating into full throttle.
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PostPosted: Tue Jun 01, 2021 5:22 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

if it was IDF's I'd say check that the aux vents are not upside down, I don't think you can do that with Dellortos
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PostPosted: Tue Jun 01, 2021 5:36 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

Slow 1200 wrote:
if it was IDF's I'd say check that the aux vents are not upside down, I don't think you can do that with Dellortos

Correct.
Dells cannot be installed upside down. They stand proud of the top of the carbs body, if incorrectly installed.
Then the carb tops will have a rather huge gap when they are in place.
Found out the dumb way! Embarassed
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PostPosted: Tue Jun 01, 2021 6:22 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

What's the acc pump shot like? May need to increase the volume/ decrease, could be flooding the spark
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PostPosted: Tue Jun 01, 2021 9:38 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

66brm wrote:
What's the acc pump shot like? May need to increase the volume/ decrease, could be flooding the spark

I'm not an expert as I just had a problem with my own set of DRLA 45's that I couldn't figure out on my own... lol

But given what I learned in the process I would say it's most likely not the pump shot because that only happens when you blip the throttle when you need to accelerate quickly or from a stop. The accelerator pump does basically nothing during a normal smooth transition into the main circuit.

You say it now acts like as if the main jet stacks were removed? I would try to actually remove the main jet stacks and see if it responds exactly the same, similarly, or much much worse.

Could you have accidentally snagged one of the floats when you took the tops off the carb? I know they have a tendency to get hung up a little when coming out. That could have lowered your float level?

Dirty float needle?

Possibly still some debris in the passages in the holes that run under the float chamber and feed the jets. Maybe some more cleaning might just do the trick?

If they ran well before on the same engine then it can't be jetting.
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PostPosted: Tue Jun 01, 2021 11:48 am    Post subject: Re: Engine stumbling badly off idle Reply with quote

After discussing this with a coworker/ racer/builder.

He suggested secondary coil winding may be faulty.

Does this sound plausible?
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PostPosted: Tue Jun 01, 2021 12:01 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

My question is what do you mean by it feels like the main Jets stacks are removed, is it flooding out heavily does it feel flat does it fall on its face when you get into that main circuit? I would recommend what Evan suggested start is to remove the main jet stacks process of elimination and see if it's feels the same or different, as far as the secondary on the coil , anything is possible, but from your description it doesn't sound like it to me. Did you verify that your upper venturi's or not 180 degrees turn the opposite direction? Also verify your float adjustment is not shutting off way early and that they are set properly.
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PostPosted: Tue Jun 01, 2021 12:19 pm    Post subject: Re: Engine stumbling badly off idle Reply with quote

I'm gonna ask this question because I haven't seen you mention it...

Have you set the idle mixture screws?

3-5 whole turns from seated is where dellortos usually land.

If not set right, stable idle is impossible, popping out the carbs, tough to bring all 4 cyls back.
Sync is impossible.


Usually, any sort of ignition problem will be most evident at full throttle, not idle and transition.
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