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Discussion Starter #1
My '74 Spider is running great these days, starts easily, even in the cold, runs well and pulls strong.

I've been through Wes's tuning guide step by step and feel pretty good about where things are at.

The last thing I'm trying to troubleshoot is a bit of a 'flat' spot just off idle once the car is up to operating temperature. Pull away from a light and there is a slight pause and then once the revs come up it pulls like it should. During the warm up cycle this does not occur, it pulls cleanly (shockingly so for a 40+ year old car!) throughout the rev range, even right after it is started on a cold morning.

I am speculating it's either a mixture problem (I have attempted to set the mixture per Wes's 2500rpm method) or maybe a linkage issue? I'm assuming it's a little lean and the mixture is richer during the warm up cycle without the TA fully extended, then once it is extended I'm too lean? Once I get further into the throttle I'm into the enrichened portion of the fuel curve, correct?

I am hoping to borrow a wideband from Joe at Centerline once the weather warms up to more accurately set the mixture but wanted to get some guidance here before I start twiddling with things again.

Thanks much.
 

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Discussion Starter #3
Thanks Roadtrip, I will double check that.

I did go through that procedure shortly after I got the car a couple of years ago but let's just say I've made a lot of far better educated adjustments since then, definitely worth going through again.

Your thought is that I have slack in the mechanism and that's what's causing the flat spot when I apply throttle? I don't doubt that is occurring but if it were the cause of my issue, then why does it not happen when the TA isn't fully extended as the car warms up?

Any and all insights appreciated!
 

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If the stop screws are not correct the delta between the opening of the throttle bores (air) and the throttle arm on the rear of the injection pump (fuel) may not be correct. If you need to borrow the factory tool, let me know.
 

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I'll mail the tool today.

Also, check your injection pump timing. If that is off, it can cause flat spots.

To set the pump timing:

1. Set the #4 (number FOUR) cylinder to TDC on the power stroke.
2. Rotate the engine CCW until the "I" mark lines up with the index on the crankshaft pulley.
3. Line up the timing ticks on the injection pump pulley and pump body and install the belt.

Using the #4 cylinder at TDC of the power stroke is the same as the intake stroke of #1 . . . just easier to see #4 TDC of power stroke than intake stroke on #1.
 

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John, isn't it common that when well adjusted (a tad rich) that there is a slight 'hesitation' (for lack of a better word) with the SPICA setup coming off idle to heavy throttle? I tried like crazy to adjust it out of my 74 to no avail--- its very slight and after a few drives one gets used to it..?
 

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If all that checks out, did you confirm good timing and working advance? So many "fuel" problems are in fact ignition problems.
Andrew
 

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Discussion Starter #9
Good thought Andrew. I replaced the stock dizzy with the electronic one from Centerline and set the timing, which I hadn't done since my 240Z days. Much easier with these fancy new strobe lights with built in advance and tach!
 

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OK. Have you tried a half or quarter turn either way, lean and rich, see if that makes a difference? Quick and easy, can get back to your original setting too.
Setting the bellcrank is fundamental to all other settings. Once you've done that other rod lengths etc may need to change.
Andrew
 

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Agree that SPICA doesn't quite have the immediate response off-idle as with Webers. My memory is that Wes Ingram agrees with this.

John, isn't it common that when well adjusted (a tad rich) that there is a slight 'hesitation' (for lack of a better word) with the SPICA setup coming off idle to heavy throttle? I tried like crazy to adjust it out of my 74 to no avail--- its very slight and after a few drives one gets used to it..?
Yep. As the old-timers used to say: "90% of carburation problems are ignition"

If all that checks out, did you confirm good timing and working advance? So many "fuel" problems are in fact ignition problems.
Andrew
 

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I've always heard that, but in a properly set up car I've never felt it. Yes, it doesn't have accel pumps, but I have thousands of track miles in both Spica and carb cars, and with a good engine and set up pump, I never felt like Spica was losing out on throttle response.
Andrew
 

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Discussion Starter #13 (Edited)
I iterated a number of times on the mixture, attempting to follow Wes's 2500rpm method but I have never been that confident in the result. I would love to find someone locally with an exhaust analyzer but, failing that, Centerline has a portable wideband O2 sensor that Joe is willing to let me borrow ('Tis a privilege to live in Colorado!), just need the weather to cooperate.

The odd part is that it doesn't happen as the car is warming up, only once it has reached operating temp. I'll re-adjust the bellcrank with Roadtrip's tool, adjust the rods accordingly and at least eliminate that possibility, then move on to mixture if necessary. One crisis at a time :thumbup1:
 

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John, isn't it common that when well adjusted (a tad rich) that there is a slight 'hesitation' (for lack of a better word) with the SPICA setup coming off idle to heavy throttle? I tried like crazy to adjust it out of my 74 to no avail--- its very slight and after a few drives one gets used to it..?
Yes, when properly adjusted there will be a slight hesitation between throttle input and on-coming power. The operative word is slight and certainly not a "stumble." If you're getting carb-like throttle response, the mixture is probably too rich.
 

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Yes, when properly adjusted there will be a slight hesitation between throttle input and on-coming power. The operative word is slight and certainly not a "stumble." If you're getting carb-like throttle response, the mixture is probably too rich.
agree there is no appreciable difference between well set-up carbs and spica, the injection may have a slight edge. This being noted, for maximum performance tuning to lean is better, of course without going too lean.
 

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...
The odd part is that it doesn't happen as the car is warming up, only once it has reached operating temp...
That would seem to suggest that at temperature you are running lean at tip in. If the bell crank stops are set properly I would be looking for vacuum leaks. Check that the butterflies are completely closed at idle.
 

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My Berlina has a similar pause on tip in, and also it isn't as noticeable on warmup. I have a wideband so I can see it go a bit leaner then come back. Which makes sense to me, as you're opening the throttle I assumed you're getting more air faster than the fuel can catch up.

Other than that mine runs great, starts in cold weather, runs pretty close to 14:1 on the freeway, gets good mileage. One of these days I'll get the factory bellcrank tool and go back through and double check everything again.

I'm happy to post a video of the wideband if I get a chance.

Ian
 

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Discussion Starter #18
Success!

Roadtrip was kind enough to send the factory bellcrank tool to me and I was not surprised to find that the stops were quite a ways off. Adjusted everything using the tool, took the car for a short drive today and am happy to report all appears to be well. Time and weather didn't permit a long test drive but I did get it up to operating temp and went through several stop/start cycles and it pulled cleanly each time.

Many thanks to all, I still want to set the mixture using the wideband (and I'd love to see your video archeologist) but I am a quite happy with where it's at as is.

Cheers
 

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Glad to hear of the success.

To reinterate again, the throttle stop screws (idle and wide-open screws) are set in a particular place according to the factory tool. The idle stop screw DOES NOT control the idle speed like it's nomenclature might suggest. Idle speed technically is controlled by the amount of air admitted through the idle air system (which is notoriously poorly adjustable). If you're getting a 600-900 rpm idle, that's within spec. These stop screws are set with the factory jig and then NOT TOUCHED AGAIN.
 

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Discussion Starter #20
When I got my Spider the TA was dead. I suspect most, if not all, of the adjustments I've had to make, from pump gap, to mixture to CSS and now bellcrank stops, were the result of someone trying to compensate (badly) for an inoperable TA.
 
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