bart_heemskerk

I am very happy the way the conversion turned out. It is on the road now and i use it regular to go to work. I have lots of confidence of the conversion and soon i will hit the road without taking my tools with me (and a can of coolant).



In case someone doesn't know what engine is in:


But i am still struggling with a huge lack off power. When the secondaries opens, it hesitates, coughs or dies. So i am driving now only on the primaries for 1500 miles. I have cleaned all the jets and pasages and played with fuel level on the carb. Checked ignition, fuelpomp, vacuumleaks but i cannot find the cause. I am about giving up and start looking for a weber 45dcoe or fit EFI.

Jeff20B

iTrader: (13)

Two things I would do if I were troubleshooting your car.

1. Try a different carb

2. Try a different exhaust

You must consider the possibility that all your problems stem from either a bad carb or an exhaust that is too restrictive. I would first swap the carb and if it made no difference I'd examine the exhaust and change some components or run it with an open header (discretely lol) just to be sure. I assume your fuel filter and fuel pump are ok, as are you spark plugs and timing.

bart_heemskerk

The header and exhaust are made of bits which came of the mazda rx-7. The header consist of two 1 3/4" pipes and after they joined together, a through type pre silencer is fitted and then it ends in the muffler which was already under the car. That muffler is now swopped for the muffler which was mounted on the mazda. With this muffler it performs a bit better but only on the primaries.

The complete exhaust which was mounted on the mazda was made of 1 3/4" pipe. So i choosed that diameter for my new header.







Thinking of it, the pipes are attached to the flange at an angle. Maybe this angle is causing a restriction?

multirotor

iTrader: (1)

The exhaust is an elford performance exhaust for the Rx-7. Made in England. This should be good up to 150hp. You will obviously loose "some" flow but it should still flow enough for a stock engine. I don't believe the problem is the exhaust.

RX744CSP

iTrader: (4)

Glad it's working out well! That's a helluva accomplishment, you can be proud.

Having this power loss happen only when the secondaries open tells me fuel starvation. It 'coughs' because it goes real lean all of a sudden. I guess you are using the stock Nikki carb, right? I had a Nikki on an '82 which looked fine but as soon as the engine warmed up and the choke turned off it wouldn't idle. I rebuilt the carb; I have been fiddling with carburetors since the late 1960's (showing my age!) and I like to think I know my way around one. Guess what- same problem after a thorough cleaning and rebuild. I got another carb, swapped the base plate onto the one I had already rebuilt, problem cured. It would be worth it to swap another carb for test purposes.

BTW: you mentioned a possible DCOE Weber swap. Webers are good carbs for many applications, I have had many on MGs, Triumphs, etc but they tend to be less than optimal on rotaries and on another of my favorite engines, the Lotus 907 in my Jensen Healey.

Both of those engines require an exponential incease in fuel volume on throttle opening which Webers have a hard time delivering unless you richen the idle circuit up to the point that your eyes water. This kills fuel mileage and can lead to low speed plug fouling.

I would recommend a 48mm Dellorto DHLA or the equivalent Mikuni sidedraft. If you can't find that, a downdraft Weber IDA will work better than a DCOE but will require a lot of fiddling with the jetting.

Jeff20B

iTrader: (13)

Hmm, I suppose that exhaust you constructed is ok on a stock ported 12A. I've had worse (more restrictive) and the secondaries always added a little extra grunt.

It's gotta be a carb problem. Check the base plate like RX744CSP mentioned and definitely try to get another Nikki. Maybe someone in the 1st gen section can send you one cheaply.

RX744CSP

iTrader: (4)

FWIW, I have two Nikkis taking up room in my attic over the Garage Majal. They can be had cheaply (just like me! ); the only killer would be freight to the Netherlands.

bart_heemskerk

Stupid question, What is the base plate? Is that the thingie where the vacuum ports comes out?

I have been contacted by multirotor , who lives quit close by. He have some carbs and we gonna do some trail and error.

I have done a lathe course for beginners, and here i proudly present: my oilcap.

RX744CSP

iTrader: (4)

Right, the base plate is the cast iron part of the carb that holds the throttle plates and shafts. A lot of the vacuum lines come out of the plastic 'spacer' plate that goes under the carb; not the same thing.

Very nice oil fill cap!

Maybe sometime soon I'll post some pics of my RotOpel (13B FI powered 1971 Opel GT) which is currently under the knife.

Jeff20B

iTrader: (13)

Yeah, the cast iron "throttle body" part of the carb has a few vacuum nipples. The phenolic spacer, which sits between the carb and manifold, has five vacuum nipples. Look into the rat's nest removal to see which nipples should be blocked and which should be used as a kind of PCV system. Also determine whether you'd like to keep vacuum advance or not.

bart_heemskerk

Update:
Was still strugling with the major hesitation when the secondaries open. Tried everything. Also tried other stock nikki's, without succes.

To connect the carb with the airfilter, i made a piece from some duct, sockets and elbows. The main piece is a reduction wich bolds op top of the carb and with a smaller socket. This has an offset. I had it mounted so the opening is straight above the secondaries. That way the air can flow freely into the secondairies, and that's best for the performance. The airflow to the primairies has to go around some bends.
That is the way it is fitted since the beginning.

Now i turned the offset socket around so the big hole is above the primairies. The airflow to the secondaries now has to go around some bends. And what a difference does it make! The secondaries are working !!!!

Am i crazy? Does the secondaries airflow need restriction? Does the secondaries needs some vacuum to suck fuel from the jets?

Before:


After:


Okay, the secondaries are working, but still i don't get the power it should give. I have ordered a manifold for a dcoe. I set my mind to dellorto or mikuni.....

d0 Luck

you can try switching to a 48 IDA. much easier to tinker with...

RX744CSP

iTrader: (4)

Glad that it was that simple! Yes, the secondaries need vacuum to pull fuel through the passages. From the top picture, I suspect your real problem was not from the secondaires but rather not enough air velocity through the primaries at WOT. Thus, you would pick up fuel from the secondaries but lose it from the primaries. The end result would be the same: fuel starvation.

If you go with a side draft, let me make a recommendation: try to get the 'two piece' Racing Beat manifold. Then, fabricate a 1" (25mm) spacer to go between the upper and lower manifold sections. This will raise the carb enough to allow installation of a heat shield. I run a Dell on my car, and when the underhood temps get high enough the carb has some symptoms of flooding.

TrackKingRacing

i know its old but thank you for the post OP I am working on a MR-S 13B swap and this information was very useful since I also decided to use the e153 a common mr2 transmission swap. kudos on a great car!