Engine will only run above 4000 RPM. Carbs or timing?

[mlc240z]

You originally said the engine ran fine. Which car did it run fine in?

Did it start to screw up when you transplanted it into a 240Z?

Could it have something to do with the 240 tach and wiring?

Sorry, not knowledgeable enough about the electronics but have read of issues with the older tachs.

Edited April 24, 2013 by mlc240z

[grannyknot]

You originally said the engine ran fine. Which car did it run fine in?

Did it start to screw up when you transplanted it into a 240Z?

Could it have something to do with the 240 tach and wiring?

Sorry, not knowledgeable enough about the electronics but have read of issues with the older tachs.

Bart, the L28 that I transplanted into my 240z was purchased last fall. I got to drive in the Z that is was installed in, it ran like a top. I watched as it was pulled and drove it home that day.

Yes it screwed up when I tried to start it, pretty sure I screwed it up with the true ground wire I put to the Negitive side of the coil.

The tach? I don't know, I did see the tach working while the engine was running a few seconds at a time.

[madkaw]

Swap away- just get it wired right!!!

[grannyknot]

Well, I couldn't get it going with the 240's dizzy and Pertronix pick up, then the new coil and HEI arrived so re-installed the 280 dizzy and new stuff, checked every variable I could think of. It just wouldn't start, in desperation I drove up to the local auto parts store and p/u new spark plugs and it started! But wouldn't idle, 1000-1500rpm is as low as it will go before dying. When the engine dies with a couple chugs there is usually smoke puffing out the carbs as well as fuel (on one occasion I got a good plume of fire instead of smoke).

I have checked the float levels, they are good.

I've tried the start up multiple times now and have found the best timing adjustment to be slightly advanced from the centre line mark on the dist.

Then I started with the carbs and quickly found out that the idle mixture screw turned down until they bottom on the seats makes no difference so I'm pretty sure it's the carbs I'm fighting now or more to the point, the jets. Bottomed idle mixture screws should cut off those pistons fuel supply.

Very strange, since really the only thing to change is now there is a hogged out cast iron exhaust manifold on it and last fall it had a header. I can see that that might cause a difference at high rpm but not idle.

So, my plan at this point is put the car back together enough to make it road worthy, have it flatbeded down to the Z specialist at Whitehead Performance,

let them re-jet and get it running and then drive it home.

I could order a bunch of jets smaller and larger than what is installed and have a go at it myself but these guys deal with triple carbs everyday, they'll have it purring in 15min. flat.

What do you guys think?

Thanks,

Chris

Edited April 28, 2013 by grannyknot

[grannyknot]

I'm not really sure if I did screw up the old HEI module now as the new spark plugs seemed to do part of the trick, ... multiple system gremlins.

At some point I'll go back and try the old module and coil. I removed and cleaned the spark plugs four or five times during this last week and most of them were wet with fuel and all were very black. I used compressed air to clear the cylinders and carb cleaner a wire brush and compressed air to clean the spark plugs.

Madkaw/Steve, the alternator was reading 14.30v or something close to that while the rpms were between 1000 and 4000rpm. So pretty sure the alternator is working.

[madkaw]

Have you actually looked at the spark when arcing to see the color of the spark? I would not start messing with carbs until you have tried EVERYTHING else-especially since you knew this motor ran fine before. The color of the spark will tell you if you are getting full voltage. What have you determined about the coil-do you know or have you tested it?

[grannyknot]

Not sure how to test the coil that's why I just bought a new one instead.

Can't I assume a new coil is doing what it's suppose to do?

[madkaw]

If you can-watch the spark and see what color it is. It's pretty ease to do.

[grannyknot]

If you have an ohmmeter, measure resistance from the positive terminal to the negative terminal and then from the center post to the negative terminal and post the results.

SteveJ, I just noticed this post, sorry.

So, with the ignition key on I'm getting 12.20v between the pos side of the coil and true ground.

With the multimeter set on the 200 scale of ohms I get 3.4 measuring between the neg and pos terminals of the coil and the reading is the same with ignition key on or off.

With the multimeter set on the 20k scale of ohms I get 9.50

measuring between the neg terminal and the centre post of the coil and the reading is the same with ignition key on or off.

I used those scales because they gave the best results.

I just p/u this spark plug tester today from NAPA and it has no instructions of any kind. It looks pretty straight forward but I'll hunt through youtube first to see some how to vids before I use it,

[grannyknot]

Just tried the spark plug tester on every plug with about and 1/4 of an inch between the fixed point and the screw in point, it looked like a decent spark with a bit of blue as it starts then yellow to white as it reaches the other side.

Just did it again, and I'm not seeing the white and yellow so much but more blue with some violet and orange. I haven't tried screwing the point farther out than 1/4", and I would say that all of the sparks are pretty consistent looking compared to one another.

Edited April 29, 2013 by grannyknot

[bartsscooterservice]

L28 engine with triple SK/OER carbs, running beautifully last fall.

Transplanted the engine into 1970 240z using the same ignition setup.

Have not altered timing or carb adjustment. I did adjust the valves but only a couple were out.

When I start the engine I have to floor it to keep it going, if I let rpms get under 4000 it dies with back firing through the carbs,

new RX7 fuel pump working fine.

Help please.

Thanks,

Chris

It could be the carbs... to much fuel or not enough fuel ( dirty carb from sitting to long ). Have you checked the plugs when the engine has been running for like 20 seconds at 4k rpm?

Compression test was okay, so it's either spark or fuel problem...

[Zed Head]

Just noticed the "new RX7 fuel pump". Maybe you're getting too much fuel pressure to the carbs. I don't know anything about SK/OER carbs. Maybe a defective/sunk float or bad needle valve. Most of your signs point to flooding.