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Thread: No power after rebuilding 18RG engine

  1. #1
    Forum Member 1st year Apprentice
    Join Date
    Feb 2019

    Question No power after rebuilding 18RG engine

    Hi guys, Im newby and not a mechanic, also i can not do necessary repairs or measurements my self too. The only thing I have is a love for my 76 Celica RA28 :-)

    Originally I had a 18R engine in the car, but let it swap to an 18RG which was available in the guy who sold it also rebuilds it for me and installed it as well.
    Unfortunately, I feel that the car does not have the expected power/torque and really does not pull. It has poor power all over rev, 1 st and 2nd gear rpm goes up fluently, engine screams but no pull really. in 3rd and 4 th gear low end is good, but when flooring it has power gap around 3000rpm till 4500. The guy is located in Germany and i live to far away to bring the car to him again for checking. Also i do not have that much trust in the guy meanwhile.

    The oem 40 Mikuni Carbs are serviced with a complete overhaul set. Im wondering whether probably the jetting can be the issue?!

    The jetting is as follows:
    Main Jet 145,
    Main Air 170,
    Pilot Jet 60,
    Pilot Air 180,
    Outter Venturi 34,
    inner Venturi 10,
    Pump Jet 50

    Igniton Timing: 10 degrees Btdc.

    Only external upgrade is a 4-2-1 header with a Sebring rear muffler from a professional header mechanic.

    Should I experiment with different Jets first to overcome the power issue? Your replies and suggestions are very much appreciated.

    Regards, Sergi
    Last edited by OSS117; 18-07-2021 at 05:17 AM.

  2. #2
    Junior Member Automotive Encyclopaedia
    Join Date
    Dec 2005
    Tallahassee, FL USofA

    Default Re: No power after rebuilding 18RG engine

    What's the compression, what do the plugs look like?
    How do you know it's 10 degrees?
    Is idling horribly, missing, surging, no load RPM increase have big gaps & jumps & not progressive/smooth, exhaust smell worse then sticking your nose into the tank's filler, blowing black smoke: Don't F with jetting?

    Cam and/or ignition timing.
    Good luck.
    'I've scrapped better.' John stated when asked about the car by the guy with the silver tipped cowboy boots!

  3. #3
    Forum Member 1st year Apprentice
    Join Date
    Feb 2019

    Default Re: No power after rebuilding 18RG engine

    Did not check the compression so far, car runs rich as well, I know because i let the emissions check by and independent touring club.
    The CO value is 5.8%, should be around 2-3% I read and the HC measured too and that showed around 700. I therefore do not think that the plugs will show more then dark black signs, but will pull them out soon. They also measured ignition timing there. It showed 10deg with vac at 980-990 rpm and 10.7 without vac. I saw different manuals where in one says 5 degrees in another around 12 for the 18RG.

    Idling is lil to high as mentioned, but no jumps. When driving with constant mileage in 3rd gear you can feel slight surgings. No black or white smoke, but exhaust smells as described by you.

    i also suspect the clutch slave cylinder playing a part within. I changed it a little while ago after i saw it dropping, but it was not oem Toyota part and the mechs said the day had to adapt the guide pin to fit, since then, also effected my 18R back in days, the clutch pedal never felt like before. Its quite hard to press the pedal, it goes to early and from 1 to 2nd gear the release feels strange, not slipping but strange. I already ordered a new one, which should be available the next days.

    I finally talked to the guy who made the swap today and he was asking me whether i switched to electronic ignition module, which you fit into the existing dizzy. I said no, i thought thats a goodie for future tuning if necessary. Now i found out the the cap, rotor and contact points are not new as supposed to. So i do that first, but im still not sure how much degrees needed btdc, 5 or 12? After that im going to adjust the carbs again and check compression and plugs.


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