Tops out at 3,500-4,200 RPM. Suggestions?
 

Got it running ok. Shifts through the gears and takes off just fine. Cruises great. Only problem is that it tops out at 4,200 RPM in 1st gear and about 3,500 RPM in all other gears. This doesn't seem to take away from hill climbing abilities or affect overall ability to drive, but takes away LOTS of fun factor!

What should I check? Secondary air butterflies or fuel needles? Timing? Fuel pressure?

Could be secondaries. In the archives or maybe FAQ check out mechanical secondaries mod and just do the bread tie part to make sure the secondaries arent stuck shut. I had this problem and after I got them unstuck they started working correctly with vac.

A little insight as to what we are dealing with would be nice.
I am assuming you dealing with the 79 model listed in your sig, but no clue as to what, if any, mods may have been done........

Will it free rev past those rpms, does it sputter when reaching them? No sputtering, check the exhaust, sputtering, check fuel supply.

It free revs to about 6500 RPM.The secondaries open by hand when you push on the little vacuum pump on the front exhaust side of the carb. They are a little stiff though. Is there a way I can remove a tensioner spring or something to get them moving easier? Or wire them to another cam so the open better? I just have a single belt on the alternator. Could it be slipping and draining the battery?




Just to bring you all up to speed...

79 RX7 with all original motor parts.

-79 Nikki
-header, 2 1/2 inch exhaust
-holley electronic fuel pump
-MR gasket fuel pressure regulator (Ive tried 2, 2.5, and 3 PSI. 3 PSI seems to make the most and smoothest power)
-Point ignition. a little off time I'm sure, but seems to do just fine at speeds under 3-4000 RPM depending on current gear and load.
-2nd gen spark plugs BUR 7 and 9 (really seemed to help a tremendous amount)
-emissions removed.
-choke release removed. still has choke, manual release.
-rebuilt alternator
-old Bosch battery.
-single belt. no air pump, no PS, no AC.

have you been into the carb at all to inspect the fuel bowls or the jets? have you replaced the fuel filter?

I've replaced it twice to be sure about a month ago. I have one more unused filter I can try out.

I'm also running premix.

Would the timing have to be pretty off to not have a top end? The bottom end feels fine. I'm guessing it's the secondary butterflies. I'm going to try to zip tie the secondary cam like the FAQ mech secondary mod says.

Idle and mixture screws shouldn't affect how the car drives over 2000 RPM right?

Nobody has every cracked inside this carb so I assume the floats are fine.

you may have sediment buildup partially clogging the jets and it may be getting sucked in from the fuel bowls. you may want to order a carb rebuild kit and rebuild teh carb for good measure...

I was thinking about throwing a bottle or two of Seafoam in it and driving it for a while. It seemed to have gotten a bit better the more I drove it today. I put 20 miles on it. That's the most I've been able to drive this car.

... a clogged cat? maybe? ..not sure how that feels but i know it kills top end, atleast on my uncle's car it did lol.

Cat and exhaust is a couple months old. This car has a 2 1/2 inch pipe setup and a less restrictive performance header so there shouldn't be any problems with exhaust flow.

It has to be carburetor based. I'm going to fiddle with the secondaries tomorrow. I bet thats the problem. It had a Weber 45dcoe on it prior to me selling it and reinstalling the Nikki. It pulled hard all the way to 7000 RPM with that carb so I know it's not a problem with the pump, lines, or filter. It has to be the secondary butterflies not opening on the Nikki. Just wondering if anyone else had this experience in their years.

With the added info, it does appear to be something related to the carb. It could be gummed up inside from lack of use. Running the seafoam thru it would likely help, if that's where the problem is. You may find that you need to take the carb apart and give it a thorough cleaning to fully resolve the issue.
Also, verify that the throttle cable is adjusted correctly. If it is not fully opening the primaries, the secondaries cannot open.
If the car has sat for a while since it last ran good, the mechanical advance in the dizzy *could* be sticking, which would have a noticable loss in power above 3500 RPM. Easy to verify that it operate freely, just pop off the dizzy cap and try turning the rotor CCW. It should allow for a few degrees of movement.

I would also look at doing a fuel pressure and volume test. My friend's SE for idle perfectly, but would just crap out if your tried to drive it. He replaced the pump, filter, etc..made no difference. A shop wanted to put on a new regulator and a new fuel pump (since he had put on a used pump), but they didn't even bother testing pressure or flow..they were just guessing.

I went to his house and checked pressure, timing, etc. Everthing seemed okay. Then did the volume test. The SE pump should put out close to .5 gallons/min, and we were only getting maybe 10oz in 1 minute. We found that the pickup/return tubes in the tanks were nearly completely clogged.

So even if the filter and pressure are good, you still might have a partial clog that is killing your top end. It is an easy test to do. After that, I would look into the carb.

time to rebuild thta carb! same thing was happening to my 7. Got the nikki rebuilt...no problems ever since.

The stock fuel pressure for an SA 12A Nikki is 3.7 to 4.7 PSI... at 3PSI you could be starving it.

Volume spec is 1.16 quarts per minute minimum, open line.

Clogged jets, timing off, points out of adjustment, no leading ignition....

See, some other people on here told me the Nikki needs 2-2.5 PSI. I'll try bumping it to 4 PSI.

Would the car run as well as it does below 4,000 if it was just firing trailing? It honestly runs really good at cruising speeds. Just when you try to take it over 3500-4200 it stumbles and wont go.

BUT we do know that the Trailing ignition is firing right though correct? The Tach works... I'll check L spark later if after I inspect the carb cams doesn't fix the secondaries.

Loss of trailing probably wouldn't be noticeable. However, the more I think about this, the more it sounds like clogged jets.

I dealt with this same issue a few years back. Here is my 4 page thread of troubleshooting and symptoms, which might be worth the read for you. https://www.rx7club.com/1st-generation-specific-1979-1985-18/12a-power-loss-%40-full-throttle-316922/

And if you want to just remove the jets to inspect/clean them, then there is a fairly simple way to do it without tearing the carb apart. Just search for the term "toothpick jets", and you'll find instructions. Good luck...



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1979 models have the tach run from the leading coil. The trailing does not work at all times, as designed by Mazda. If the tach is working, the leading ignition is working.
I still bet the issue is carb related, with a possible timing issue playing a minor role.

80s also have the part-time trailing ignition. One of many emissions compromises SA's have to tolerate, if staying stock.

You can remove the secondary diaphragm cover (4 screws) and remove the spring inside. Replace the cover and the secondaries should kick in almost immediately when you press the gas. The difference should be obvious if they are working. Check for leaks in the diaphragm while you have it open. If you drive the car like this gas mileage will be significantly worse than normal.

Fixed the problem! Turned out to be the secondary cam as expected. It wasn't opening easy enough. I wrapped some wire and a zip tie around the cams so it would be forced open and it works now. Pulls great to 7000 RPM.

Thanks for all the suggestions.

weird...

NCross, any chance you could post a pic of your fix of the secondary cam?