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Wed May 07, 2025 6:15 pm

Buddy let me use his backup motor to get my car back on the road after many years of sitting on jackstands. I logged about 15 miles while I sorted out various issues not related to the motor. Recently after driving a few miles around the neighborhood the motor started to stumble during acceleration and cruise. The motor is basically a stock 1600 with a single 40idf and 4-1 headers. Fuel pump is a Carter(electric) and a regulator set at 2.5psi. Plugs are NGK(BR6HS 1/2” reach). Dizzy is a 009 with pertronix unit and Flamethrower coil.
The jets in it were:
* idle 65
* mains 175
* ac 200

I thought those are awfully large for a 1600 so I switched to:
* idle 60
* mains 145
* ac 180

I then cleaned(sanded) and reinstalled those same plugs and took it for a test drive and within about 4-5 miles the stumble is back. I let the motor cool for about 1/2hr and pulled plugs #4 & #2 and as you can see #4 is ok and #2 is black(dry). Also as I pulled the 2 plugs I noticed that the dual port intake on the 3/4 side was significantly hotter than the 1/2 side.

Suggestions??

Wed May 07, 2025 6:20 pm

both are filthy rich in my opinion. The 1 - 2 side just fowled sooner.

Wed May 07, 2025 11:02 pm

Twisted throttle spindle?
Different sized idle jets despite the markings being identical?
Air leak 3/4 side?

Thu May 08, 2025 4:27 pm

Switched out plugs to a set of slightly used Bosch plugs that I had in my spare parts bin. Checked for intake leaks by spraying starter fluid at intake couplers and manifold gaskets….no leaks. Replaced plug wires with a set of 8mm Taylors that were to go on my 2332 currently under construction. Took it for a test spin and the intermittent miss and stumbling upon acceleration was still there. Noticed that it was clearly idling on cylinders 3 and 4. This was also evident by the fact that the manifold for 3/4 is hotter than 1/2.
I feel like my current jetting should be close enough to not cause these issues.

My next step will be to pull the top off the 40idf and see if I have a plugged acelerator pump jet. Does this sound like I’m headed in the right direction?

Also should I be using the 1.5 or 3ohm Flamethrower coil with the pertronix unit?

Thanks!

Fri May 09, 2025 9:36 am

A plugged accelerator jet wouldn't explain why you're only idling on the left half of the engine.

Have you checked to see if the two barrels are synched? Have you tried adjusting for best lean idle, and if so, are both mixture screws close to 1.5 turns out when properly set?

Which coil to use depends on which version of Pertronix you have -- Ignitor 1 uses a 3.0 ohm, Ignitor 2 uses 0.6 ohm, and Ignitor 3 uses 0.3 ohm.

Fri May 09, 2025 10:51 am

I looked harder at your throttle linkage in the picture.

I can see you are twisting the throttle spindle with a throttle cable return spring attached to the opposite end of the throttle spindle to the throttle cable. This may be enough to slightly crack off one barrel of that rather oversized carburettor (for a 1600..), and unbalance the idle.

Fit the spring in line with the throttle cable, the carburettor should be quite capable of closing itself off without big springs. The throttle cable has the problem, not the carburettor.

Fri May 09, 2025 5:35 pm

OK here’s what I have done today and here are the results.

* moved the throttle return spring to the center of the carb.
* measured with my sanchro meter that both barrels of the carb are equal.
* noticed when I pulled a plug wire from the dizzy cap the coil wire would arc
to the +terminal. Replaced coil wire seems to have fixed this.
* switched idle jets(60) from 1 side to the other and all of a sudden side 3/4
became the weak side. Took it down the street and it was still stumbling &
when I nailed it I noticed a large plum of black smoke. This thing is
loading up something awful.
* limped back to the house & pulled the idle jets back out and noticed that the
one I moved to the 3/4 side was massive….obviously not the 60 that is
stamped on it…….MikeJames called that one!
* replaced it with a correct(60) idle jet and now it’s idling on all 4. I readjusted
the mixture screws.
* reving the motor in my driveway I was still getting a miss/stumble but at least
no strong gas fumes or loading up.

I suspect at this point it’s probably pointless to go any further until I replaced the probably foul up plugs with a fresh set.

Thu May 15, 2025 8:15 am

Still struggling with this issue. It still stumbles when you give it gas quickly sometimes with a pop and a puff of black smoke which indicates to me this thing is dumping gas. When taking it for a test drive & keeping the rpms at a steady 3000 all seems well until I hit the throttle and ask for more then it stumbles & belches. I switched coils from a Pertronix Flamethrower(3.0 ohm) to generic one in my toolbox because it seemed too hot to the touch with no change. Advanced and retarded timing with no improvements. Seemed to help a little when I dropped the idle jet to a 55.
My current jetting is:
Air Correction……175
Main…………………..160
Idle……………………..55

When I 1st installed the loaner motor with the larger jets as listed in the beginning of this thread I drove it w/o issue for about 30miles then all of sudden fouled plugs. The owner of the motor drove it for at least a year w/o issue.

At this point I believe my next step is to disassemble the 40idf and give it a thorough cleaning, check float level & fuel shutoff valve. Any other suggestions would be appreciated!

Thanks

Sun May 18, 2025 4:02 pm

While tinkering today I noticed that the fuel in my clear filter had a brownish tint. I had treated a used fuel tank a couple years ago and stored it while I finished my car. I removed the top cover of the idf and could see this reddish residue at the bottom of the float bowl which I believe to be rust. I didn’t treat the tank well enough. I have 2 inline filters but this stuff still made its way into the carb. I plan to let the carb soak in carb cleaner overnight. My question is what is this item with the lever held on by 2 screws.

My 40 hmpx carbs on my bus don’t have this & if it serves no purpose do I need to remove it b4 dipping the carb.

Thanks

Sun May 18, 2025 6:40 pm

Its a enrichment valve that used instead of a choke to give slight rich mixture at startup/warm up..... You can leave them on or take them off, but you need to leave the plunger(s) in carb body.... And put cover plate on inplace of mechanism....

Personally I would "fix" them in the full open position (off) and just run them....

Sun May 18, 2025 7:06 pm

So I can make my own cover plate to replace this mechanism. That would be great because it would allow me enough clearance to install and remove the 2 inner intake nuts w/o removing the fan shroud.

Mon May 26, 2025 8:43 am

I cleaned and treated the used fuel tank I purchased sometime ago but apparently not well enough and this is just a little of what came out of it.

I disassembled and cleaned the carb, replaced both inline filters & retreated the tank. Fired it up and it appears like my drivability problems are solved. Not quite responding well to idle mixture adjustments to cylinders 1/2 but runs good on the road. Since I played with jetting previous to finding all this sediment(rust) I going to take some plug readings and see if some changes are needed. My current jetting is:
AC……..175
Main……160
Idle………55
For basically a stock 1600 with a Spanish 40idf.

As fun as it is to drive I’ll be glad when I finish my 2332!