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 Posted: 01-29-2019 12:09 am
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Rick in Miami
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When you removed the JH tach, the white wires to the back of the tach need to be connected together as power to the coil went through the original tach. The sense wire to the SpeedHut tach needs to be connected to the negative side of the coil. The red pertronix wire needs to be connected to a 12v source. If using a ballast resistor, wire the pertronix to th 12v side.

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 Posted: 01-29-2019 06:03 pm
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DonBurns
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Thanks Rick - that was the problem. Actually half the problem as I had neglected to attach the end at the coil. For some reason the white wire from the JH tach to the coil is a separate wire that was added. I don't remember doing this so I think the shop that helped set up the new engine must have done it. Since then I have replaced the main wiring harness. I should probably figure out what's up with the white wires in the harness.

Back to spitting though. For those of you with O2 meters, what ratios are you shooting for at idle and above idle? I have read that you have to run a little rich to be safe. Is the reading steady? Mine bounces around a lot.

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 Posted: 06-12-2019 04:07 pm
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subwoofer
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It could be your Pertronix momentarily shuts down, try wiring the red wire from the Pertronix directly to the battery through a relay and a fuse, naturally.

--
Joachim

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 Posted: 06-16-2019 03:34 am
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CDA951
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I recently had the same issue with my car (#19250), and it turned out to be restricted idle jets. I know this sounds odd, but let me explain.

I rebuilt the engine over the course of last year, put about 1,200 miles on it and the engine ran great and pulled well throughout the rev range (2.0 engine, Dellorto DHLA45Cs, 9.5:1 CR, stock cams). The car sat for a month or more until I had time to re-adjust the valves, and I got it going again last week.

The original Smiths tach did not work (needle was physically sticking and I have a Pertronix Ignitor), so last week I also installed a universal Auto Meter tach, which worked, except I would get missing/hesitation during light load/cruise, but only at about 3000 RPM, and only before the engine had fully warmed up. The tach needle would "blip" at the same time as the miss/hesitation, which would normally point to an ignition issue. I double-checked everything ignition-wise, and re-wired the primary circuit, which I had planned to do anyway: no change. The next plan was to take the car to my shop and use the oscilloscope to properly check the ignition primary and secondary circuits.

However, as I drove the car a bit more, I noticed the hesitation/tach blips would really only happen during part-throttle and in the RPM range during which the Dellortos transition from the idle to main circuits. The engine would pull cleanly to redline once out of this range. Furthermore, the engine would occasionally pop back/spit during a long period of closed-throttle deceleration, and the tach would blip then as well.

I pulled the idle jets, and while they weren't completely plugged, they were restricted. Once cleaned out, the hesitation and "blips" were completely gone. The restricted idle jets would allow the engine to idle and run normally in the low-RPM range, but would cause a lean condition in the upper reaches of the idle circuit. Because more fuel condenses on the walls of the intake manifold and ports of a cold engine, this effect was more pronounced before the engine had completely warmed up.

I already run two fuel filters (one upstream of the fuel pump, one in the engine compartment) and an in-tank strainer on the fuel pickup, but I might add another EFI-type fuel filter as well. I cleaned out the fuel tank as well as I could before I ran the car, but CA environmental regs make it difficult to properly clean a fuel tank . . . .

Interestingly, the slight bog/hesitation that I get during brisk acceleration from a dead stop is slightly worse with de-restricted idle jets, which tells me that my 58 idle jets are probably too much for my particular engine setup. The carbs are otherwise balanced and tuned well, and my engine setup and carb jetting pretty much mirrors Lotus "Spec 5."

I am not 100% sure why the tach needle would blip during a lean hiccup, but it might have something to do with how the Auto Meter tach is constructed:

https://www.autometer.com/resources/index/faq_view/id/49

Last edited on 06-16-2019 03:53 am by CDA951

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 Posted: 06-16-2019 03:54 am
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DonBurns
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For what this is worth - I replaced both the original tach and speedo (which was not reading correctly in spite of rebuild by speedometer shop, replacing the speedo cable and "new" transmission) with new units from Speed Hut (GPS speedo - I highly recommend!), and have not seen any of the tach "blip" issues since. Limited miles since, though, so I'll update if this changes.

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 Posted: 06-16-2019 04:00 am
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CDA951
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DonBurns wrote: For what this is worth - I replaced both the original tach and speedo (which was not reading correctly in spite of rebuild by speedometer shop, replacing the speedo cable and "new" transmission) with new units from Speed Hut (GPS speedo - I highly recommend!), and have not seen any of the tach "blip" issues since. Limited miles since, though, so I'll update if this changes.
Interesting. In reading your first post, it seemed like you had slight misfires that would coincide with tach blips, but are you saying that it was tach blips only without misfiring?
It also seemed like your carb balance/tune was nowhere near ideal, so I was hoping this would help. My carbs were well balanced and sorted before this issue cropped up, but it goes to show that these old carb'd engines need regular care and feeding!

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 Posted: 06-16-2019 03:31 pm
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DonBurns
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Wasn't thinking clearly last night - might have had a beer by then. I think the blips went away when I discovered the wires to the distributor cap were not pushed far enough through the silicone boots, and the sparks were jumping, building up carbon on the contacts. In the meantime I had messed up the original tach trying to convert it from RVI to RVC.

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