Mystery stroker R16 falls on it's face at 3,000 RPM

[JacobWisdom]

Hi - I purchased a 1970 1600 that had, what I'm told, is a 2000cc R16

The chain of custody is spotty on the engine, the story I was told is it was built then quickly replaced by a modern EFI power plant by someone. It came from what looks like a black / midnight purple accented Roadster. There is no documentation but I'm told the build work was done by a shop. The SU carbs are pretty distinct as they are polished with a purple powder coated intake manifold and pulleys. I changed the oil shortly after purchasing it and there was metal glitter that was consistent with a new build. I'm told it's a "Stage 2 camshaft". I have not started measuring lifts to confirm, some of what I was told was found to be untrue but I believe it was genuine ignorance from the messenger.

The engine starts immediately and idles very well. Unloaded it will run through it's RPMs easily but on the road completely falls flat at 3,000 rpm...to the extent I would believe it had a rev limiter if I didn't know any better. I set the idle timing (vac advance disconnected) at 16 degrees and also checked it up to 4,000 RPM where it runs about 36 degrees unloaded. I ended up just replacing the distributor with an EI to rule that out, along with a new coil and spark plugs, no change in performance though. Confirmed I'm at 16 degrees of mechanical advance.

I synchronized and did some adjusting on the stock R16 carbs but didn't find that it made a difference. As one does with vintage projects, I bought a parts car that happened to have a set of loose 2L SU carbs included. Relative to the rebuilt/polished carbs on the engine they are in terrible shape but I have begun cleaning them in my ultrasonic in case I need to resort to using them. In the meantime unless someone with authority tells me it won't work, I'm going to try the 2L needles to see if I can at least get it to run through the full power band under load.

Beyond that, can anyone offer me pointers? I bought an AFR and will install that at some point but it seems to be pretty audibly running lean when it hits the wall (popping and such).

Might be a reach but if someone knows the owner of the black / dark purple accented car (attachments), please help me get in touch with them, because that would likely solve some mysteries.

[SLOroadster]

Will it eventually get though the dead zone or is that all it will do? What is the air fuel ratio doing? Where is the timing set to?

There is a possibility this is a harmonics issue that happens with some R16s with SUs. That said, it appears to only happen with the R16 SUs and NOT the u20 SUs due to the U20 ones having rubber pads for the float bowls. I ran into a similar issue on a '67 1600 race car. It would not rev past 5000 for love nor money. I tried everything, and changed everything except the insulators between the carbs and the intake. The early R16s had this issue from time to time and Nissan spec'd some flexible insulators like the G15 ones. Once I tracked a set down and installed them, the engine would rev to 7K with no issues. This is a rare issue, but it does happen, and might be your issue. It seems to affect specific engines even if they are built to the same spec as another that doesn't have the issue.

Good luck,
Will

[Gregs672000]

So it will rev to 6000 in the driveway but not pull past 3000rpms under load? And it backfires out the carbs (lean)? Does sound very carb/fuel related, as a lack of spark would not result in a lean condition, and you have already confirmed advance and good spark as it is. A wideband would surely help here and are worth having regardless. What do the plugs look like? Just for grins, please check your firing order... 1,3,4,2 counter-clockwise on the dizzy... I ran my U20 to 80mph with crossed sparkplug wires. Check your fuel lines for air leaks, particularly at the filter. Consider trying an electric fuel pump (3-4lbs... Mr. Gasket 42S for example at Autozone)... yes, you do have to cut a fuel line and mount it (best near the rear wheel, close to the tank as they are pushers, not pullers). Consider installing an inline pressure gauge to see if the machanical pump is OK (before swapping pump?). I also had running issues in the past when my stock fuel filter was leaking air... no power on hills.

There are known issues with miss-matched cam and crank gears. Hopefully it's not this...

[Curtis]

Not enough info to fully determine. Is it a H20 or cut down U20 crank and you're sure it is a stroker?

I have an H20 stroker. It would hit 3-4000 rpm and go flat and stutter. Get up above 4k and then go again. Three types of distributors, a fresh set of Z Therapy 1600 carbs and originals, check the fuel pump and so on, nothing would cure it.

Carb needle change didn't fix it, richening up the mixture seem to help but then run on.

Z Therapy told me that the 1600 carbs were fine for a stroker. Turns out that was wrong, at least for me. I had a hogged out 1600 manifold sitting around I had planned to use for bigger carbs. Borrowed a set of 2000 SU from a friend, put them on, end of problem. Thing really goes now. !600 SU simply aren't enough for this motor.

I used the how to in the 311s wiki for the linkage conversion.

[SLOroadster]

Not enough info to fully determine. Is it a H20 or cut down U20 crank and you're sure it is a stroker?

I have an H20 stroker. It would hit 3-4000 rpm and go flat and stutter. Get up above 4k and then go again. Three types of distributors, a fresh set of Z Therapy 1600 carbs and originals, check the fuel pump and so on, nothing would cure it.

Carb needle change didn't fix it, richening up the mixture seem to help but then run on.

Z Therapy told me that the 1600 carbs were fine for a stroker. Turns out that was wrong, at least for me. I had a hogged out 1600 manifold sitting around I had planned to use for bigger carbs. Borrowed a set of 2000 SU from a friend, put them on, end of problem. Thing really goes now. !600 SU simply aren't enough for this motor.

I used the how to in the 311s wiki for the linkage conversion.

Sounds a bit like the harmonics issue I ran into with the #44 car, but to a lesser extent. The reason the U20 SUs work is because the float bowl has a rubber insulator and that standing harmonics wave doesn't happen.

On the #44 car it would rev just fine in the driveway, but run into a wall at 5K on the track. I changed everything, exhaust, ignition, fuel pump, float level, nothing helped. Replacing the hard spacers with some early, soft R16 ones fixed it.

Will

[Curtis]

I have the hard spacers. That engine really sucks the air in. I tried some 45mm single throat Webers on there and it revved great but couldn't get the linkage right. In this case it was just not enough carb. I've had a couple other people tell me the same thing. I'm wondering about what my 1800 stroker will need.

[Daryl Smith]

I had no issues with my 1800cc stroker on the stock SU's for the short time I ran it with carbs. Rev'd past 6000 rpm...good power all through.

[JacobWisdom]

Will it eventually get though the dead zone or is that all it will do? What is the air fuel ratio doing? Where is the timing set to?

There is a possibility this is a harmonics issue that happens with some R16s with SUs. That said, it appears to only happen with the R16 SUs and NOT the u20 SUs due to the U20 ones having rubber pads for the float bowls. I ran into a similar issue on a '67 1600 race car. It would not rev past 5000 for love nor money. I tried everything, and changed everything except the insulators between the carbs and the intake. The early R16s had this issue from time to time and Nissan spec'd some flexible insulators like the G15 ones. Once I tracked a set down and installed them, the engine would rev to 7K with no issues. This is a rare issue, but it does happen, and might be your issue. It seems to affect specific engines even if they are built to the same spec as another that doesn't have the issue.

Good luck,
Will

It will not make it through. Interesting possibility, something I was unaware of and will keep in mind. Might just need to put the U20 carbs on...the AFR is not installed yet so I can't confirm where that's at.

I have several extra carbs, maybe one set has the correct part? Could you give me some details I could use to ID, or make my own? My company does manufacturing

So it will rev to 6000 in the driveway but not pull past 3000rpms under load? And it backfires out the carbs (lean)? Does sound very carb/fuel related, as a lack of spark would not result in a lean condition, and you have already confirmed advance and good spark as it is. A wideband would surely help here and are worth having regardless. What do the plugs look like? Just for grins, please check your firing order... 1,3,4,2 counter-clockwise on the dizzy... I ran my U20 to 80mph with crossed sparkplug wires. Check your fuel lines for air leaks, particularly at the filter. Consider trying an electric fuel pump (3-4lbs... Mr. Gasket 42S for example at Autozone)... yes, you do have to cut a fuel line and mount it (best near the rear wheel, close to the tank as they are pushers, not pullers). Consider installing an inline pressure gauge to see if the machanical pump is OK (before swapping pump?). I also had running issues in the past when my stock fuel filter was leaking air... no power on hills.

There are known issues with miss-matched cam and crank gears. Hopefully it's not this...

That's correct it will not go past 3000 under load. The firing order is good, I could check plugs. Fuel delivery is definitely one I considered, have several spare Facet pumps from our desert race vehicles that put out the right pressure so that is on my list to try.

Not enough info to fully determine. Is it a H20 or cut down U20 crank and you're sure it is a stroker?

I have an H20 stroker. It would hit 3-4000 rpm and go flat and stutter. Get up above 4k and then go again. Three types of distributors, a fresh set of Z Therapy 1600 carbs and originals, check the fuel pump and so on, nothing would cure it.

Carb needle change didn't fix it, richening up the mixture seem to help but then run on.

Z Therapy told me that the 1600 carbs were fine for a stroker. Turns out that was wrong, at least for me. I had a hogged out 1600 manifold sitting around I had planned to use for bigger carbs. Borrowed a set of 2000 SU from a friend, put them on, end of problem. Thing really goes now. !600 SU simply aren't enough for this motor.

I used the how to in the 311s wiki for the linkage conversion.

I haven't been able to confirm any of the internals. If there's a method of doing that which doesn't involve opening things up then I'm all ears. Really wish I could talk to the person that built or had built this engine. The issue you experienced seems similar to mine.

Noted on the U20 carbs, good to know that resolved it. Do you have a link to the article you used for the linkage conversion? I didn't see it on the "Fuel-Carbs" page.

Not enough info to fully determine. Is it a H20 or cut down U20 crank and you're sure it is a stroker?

I have an H20 stroker. It would hit 3-4000 rpm and go flat and stutter. Get up above 4k and then go again. Three types of distributors, a fresh set of Z Therapy 1600 carbs and originals, check the fuel pump and so on, nothing would cure it.

Carb needle change didn't fix it, richening up the mixture seem to help but then run on.

Z Therapy told me that the 1600 carbs were fine for a stroker. Turns out that was wrong, at least for me. I had a hogged out 1600 manifold sitting around I had planned to use for bigger carbs. Borrowed a set of 2000 SU from a friend, put them on, end of problem. Thing really goes now. !600 SU simply aren't enough for this motor.

I used the how to in the 311s wiki for the linkage conversion.

Sounds a bit like the harmonics issue I ran into with the #44 car, but to a lesser extent. The reason the U20 SUs work is because the float bowl has a rubber insulator and that standing harmonics wave doesn't happen.

On the #44 car it would rev just fine in the driveway, but run into a wall at 5K on the track. I changed everything, exhaust, ignition, fuel pump, float level, nothing helped. Replacing the hard spacers with some early, soft R16 ones fixed it.

Will

To be clear, we're talking about the spacers between the carbs and the intake manifold? How thick are the flexible ones? Shot in the dark, but if you know the durometer of the soft ones, I could reproduce them. Or relative softness, e.g. about as soft as a DOT tire tread.

[redroadster]

The 96-8 Mitsubishi Galant had a issue like described above , the intake manif. not aligned as even it should be would surge at highway speed almost like running out of gas or ign probs seemed only 1/16 th of an inch

[Curtis]

U20 carbs on 1600 manifold.

http://www.311s.org/pmwiki-311/pmwiki.p ... IntakeMods

[Gregs672000]

Will said " the U20 float bowl has a rubber isolator" so I don't think he's referring to the carb to manifold connection (I'm afraid I don't have an image or much recollection about SU set ups anymore as my car has been Solex style forever)... must be how the float bowl attaches to whatever it connects to...

[Curtis]

Where the bowl connects to the carb body there is an donut type insulator. A bolt of some kind goes through it.

https://www.carpartsmanual.com/datsun/s ... retor-(su)

[Datrock]

I noticed in your photo of the engine compartment that you have the fuel return valve installed on the inlet to the front carb, it needs to be installed at the rear carb. Not saying this is the answer to the problem but it should help by moving it to the correct place.

[david premo]

Bill is right the fuel line are definitely not hooked up correctly.

[Daryl Smith]

viewtopic.php?t=32977
JT - "There is a calibrated valve used on the rear carb that acts as a simple pressure regulator"

Sounds likely to be a problem....make sure to install it after the rear carb......