Working on a REPU
10-04-16, 09:51 AM
#1
Working on a REPU
I've had a REPU here at the shop for side work for about a week now. 1977, California spec, all stock.
The truck sat for 10 + years so fuel system is toast. Needless to say the truck would not start. The owner said he drained the tank and flushed it out recently (maybe 2-3 months ago). In addition to that he said his neighbor during the same time "rebuilt" the carburetor. He then had issues with the carburetor overflowing the secondaries.
So, using my Nikki knowledge and applying it to the Hitachi I determined the floats were tweaked and needed adjustment. While the air horn was off I blew compressed air through all the passages I could find as well as carb cleaner spray. I soaked the accelerator pump in oil (leather), reassembled it and tried to start it up. The accelerator pump pumps with a vigorous pump of the gas pedal, and the float bowls stay at a steady halfway mark through the site glass on both sides. The flooding issue is solved, however the engine only starts on starting fluid or pouring a bit of fresh gas down the venturis. To me this means the main circuit is restricted and engine vacuum is unable to draw fuel through the venturis to keep it running for more than 1 second.
Before I took it apart the engine would start and run quite badly due to overflowing secondaries providing enough constant fuel to sputter along for awhile.
So, here are my questions...
1. Other than an internal restriction what should I look at? REPU "technology" is new to me so is there anything else to look at to solve this condition? (electronics, ignition, vacuum routing or capping)
2. What modifications must be made to fit an RX7 Nikki to this manifold? It looks quite similar so maybe just a base plate adapter or redrill the studs?
The truck sat for 10 + years so fuel system is toast. Needless to say the truck would not start. The owner said he drained the tank and flushed it out recently (maybe 2-3 months ago). In addition to that he said his neighbor during the same time "rebuilt" the carburetor. He then had issues with the carburetor overflowing the secondaries.
So, using my Nikki knowledge and applying it to the Hitachi I determined the floats were tweaked and needed adjustment. While the air horn was off I blew compressed air through all the passages I could find as well as carb cleaner spray. I soaked the accelerator pump in oil (leather), reassembled it and tried to start it up. The accelerator pump pumps with a vigorous pump of the gas pedal, and the float bowls stay at a steady halfway mark through the site glass on both sides. The flooding issue is solved, however the engine only starts on starting fluid or pouring a bit of fresh gas down the venturis. To me this means the main circuit is restricted and engine vacuum is unable to draw fuel through the venturis to keep it running for more than 1 second.
Before I took it apart the engine would start and run quite badly due to overflowing secondaries providing enough constant fuel to sputter along for awhile.
So, here are my questions...
1. Other than an internal restriction what should I look at? REPU "technology" is new to me so is there anything else to look at to solve this condition? (electronics, ignition, vacuum routing or capping)
2. What modifications must be made to fit an RX7 Nikki to this manifold? It looks quite similar so maybe just a base plate adapter or redrill the studs?
10-04-16, 01:31 PM
#2
People are idiots when it comes to carbs. Especially in this day and age. That Hitachi could have been ruined by the guy's neighbor. Or the idle circuit in the baseplate is simply clogged. Or it could be some other unknown problem. I've had Hitachis do that same behavior too. I don't like them anyway. But that's fine because putting a Nikki on a REPU manifold is easy. You have to drill four holes straight and exact. Then cut threads. Then add channels to mimic a 79 manifold.
The Nikki itself needs to be hogged out. Why? Because all stock US-spec Nikkis have 20mm primary venturis while the 74 Hitachi had 22mm. Going with a stock Nikki is like a downgrade. You have to hog it out to get any kind of performance out of it. That much is proven over and over these days. See if you can do 24.5mm to 25.5mm. Or try 26mm if you are really confident, but be careful.
These trucks have a weak charging system due to the external regulator, the stupid brain box behind the bench seat, the long run to the battery under the bed, and a 40 year old aluminum starter cable that is 11 feet long and should be replaced with thick copper to get a faster cranking starter.
Oh and replace points ignition with direct fire like DLIDFIS. There are two wires that feed the coils. One is activated in the "ON" position, which runs through ballast resistors to save wear and tear on the points, which the other wire is activated in the "START" position which feed full batter voltage to the coils during cranking. You can jumper these two wires together so your new electronic ignition gets full battery voltage in "START" and "ON". But jumper the correct ones. The wrong one will make it crank as soon as you turn the key to "ON" lol. Been there, done that, had to laugh.
You need to do a long primary exhaust to get any usable low end torque if staying NA. There is a ton of room for components. Get an RB road race header and a dual pipe flange. Also two 2" presilencers and place them side by side under the cab. Then collect them to a single 2.5" and flow into a main muffler next to the battery, aimed upward to get the outlet over the rearend. Add a flange back here for easy servicing in the future. There are also hangers in this area. Use them. Lastly, a single large muffler can be placed after the rearend and exit the tailpipe under the side of the bed. Don't go straight back under the bumper because it is too prone to damage, looks cheap, and makes hooking up a trailer more difficult. This is 20 years of REPU experience talking. Good luck.
Oh, I just thought of more to talk about. Ditch the boat anchor heavy 30 pound REPU flywheel and get yourself a GSL-SE flywheel. You will need a new pressure plate and 225mm disc because the REPU stuff is different and won't work. Don't get stage one Exedy as I don't think it's required. Just get stock duty Exedy. Both my REPUs have this and after the experience of a stage one in my friend's REPU, never again. They don't make enough power to justify it, especially NA. The modern Exedy stuff is extremely well made compared to 40 years ago, and has similar grip without the heavy pedal effort.
The Nikki itself needs to be hogged out. Why? Because all stock US-spec Nikkis have 20mm primary venturis while the 74 Hitachi had 22mm. Going with a stock Nikki is like a downgrade. You have to hog it out to get any kind of performance out of it. That much is proven over and over these days. See if you can do 24.5mm to 25.5mm. Or try 26mm if you are really confident, but be careful.
These trucks have a weak charging system due to the external regulator, the stupid brain box behind the bench seat, the long run to the battery under the bed, and a 40 year old aluminum starter cable that is 11 feet long and should be replaced with thick copper to get a faster cranking starter.
Oh and replace points ignition with direct fire like DLIDFIS. There are two wires that feed the coils. One is activated in the "ON" position, which runs through ballast resistors to save wear and tear on the points, which the other wire is activated in the "START" position which feed full batter voltage to the coils during cranking. You can jumper these two wires together so your new electronic ignition gets full battery voltage in "START" and "ON". But jumper the correct ones. The wrong one will make it crank as soon as you turn the key to "ON" lol. Been there, done that, had to laugh.
You need to do a long primary exhaust to get any usable low end torque if staying NA. There is a ton of room for components. Get an RB road race header and a dual pipe flange. Also two 2" presilencers and place them side by side under the cab. Then collect them to a single 2.5" and flow into a main muffler next to the battery, aimed upward to get the outlet over the rearend. Add a flange back here for easy servicing in the future. There are also hangers in this area. Use them. Lastly, a single large muffler can be placed after the rearend and exit the tailpipe under the side of the bed. Don't go straight back under the bumper because it is too prone to damage, looks cheap, and makes hooking up a trailer more difficult. This is 20 years of REPU experience talking. Good luck.
Oh, I just thought of more to talk about. Ditch the boat anchor heavy 30 pound REPU flywheel and get yourself a GSL-SE flywheel. You will need a new pressure plate and 225mm disc because the REPU stuff is different and won't work. Don't get stage one Exedy as I don't think it's required. Just get stock duty Exedy. Both my REPUs have this and after the experience of a stage one in my friend's REPU, never again. They don't make enough power to justify it, especially NA. The modern Exedy stuff is extremely well made compared to 40 years ago, and has similar grip without the heavy pedal effort.
Last edited by Jeff20B; 10-04-16 at 01:34 PM.
10-04-16, 04:42 PM
#3
If it was mine I would do all of the above Jeff, but the guy I'm doing the work for wants to keep it as original as possible, so I have to respect that. I did manage to get it to start an run, although I have to keep my foot on it to hold idle... Now it sounds like a stuck seal. I do have a GSL-SE flywheel if need be 
I also have spare Nikki parts.
One thing that i need to look into a bit further is that when the choke is pulled it does not have fast idle like I'm used to on my old Nikkis. Possibly something in the choke is fubar.
I'm going to bleed the clutch cylinders tomorrow and see if I can drive it and pop the seals free.
Another thing... the tach is inoperative. Should I be looking at the coil connections or elsewhere?
I also have spare Nikki parts.One thing that i need to look into a bit further is that when the choke is pulled it does not have fast idle like I'm used to on my old Nikkis. Possibly something in the choke is fubar.
I'm going to bleed the clutch cylinders tomorrow and see if I can drive it and pop the seals free.
Another thing... the tach is inoperative. Should I be looking at the coil connections or elsewhere?
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NivekYnmiz
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