13b in gen 1
06-02-21, 12:23 PM
#1
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13b in gen 1
New to this site, have a 79 rx7 just had a 13b street ported and put into it. Mikuni 40/44mm PHH Type S5 carb, not sure on quality of tune. Idles OK, has huge hesitation off idle when pushing on accelerator. And after turning off engine must wait at least 15 minutes before it will start again. Person who built engine said it was tuned but can not believe the way it runs is how it is supposed to be. Was told it was jetted for the engine but doubt it is correct. Have some mechanical aptitude but not familiar with rotary tuning, or where to start with this. Help please
06-03-21, 09:08 AM
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Thank you for responding, Unfortunately I do not have data on the engine/build sheet as there were issues when I picked up the car from the builder. My best guess about the engine is it was a core from a 1985 engine??????? This is a fresh build, street ported, with new larger apex seals and the assumption compression is good????? I was told it is a new fuel pump but the specific model I do not know, and have no idea about pressure setting. After reading some of the posts I will be putting one in the system leading to the carburetor. The carb is a twin Mikuni 40/44mm PHH Type S5. I gave the car to the builder with a running 12a with this carb on it and was told it would flow enough air for the ported 13b, as to what jets he installed I do not know and have been putting off opening the carb until I knew where I stand. I am an A&P mechanic but not familiar with rotary, I am familiar with fuel metering and have adjusted Idle mixtures hoping to alleviate the stumble that happens when trying to accelerate. Your efforts are appreciated.
06-04-21, 02:54 AM
#5
no worries on the build data and such. 
i failed to ask the question i wanted to ask as clearly as i should have. that was my fault. i just meant was your engine 4-port or 6-port?
as for the compression, assuming it's good simply because this is a fresh engine could be a mistake. there are plenty of cases where people chased problems on a fresh engine, only to find that the problem was the engine. just keep it in mind.
fuel pump should be fairly easy to find and (hopefully) identify. if there are any labels or part numbers on the unit itself. if you don't see a regulator, that could be the problem. believe it or not, that's progress.
i failed to ask the question i wanted to ask as clearly as i should have. that was my fault. i just meant was your engine 4-port or 6-port? as for the compression, assuming it's good simply because this is a fresh engine could be a mistake. there are plenty of cases where people chased problems on a fresh engine, only to find that the problem was the engine. just keep it in mind.
fuel pump should be fairly easy to find and (hopefully) identify. if there are any labels or part numbers on the unit itself. if you don't see a regulator, that could be the problem. believe it or not, that's progress.
06-05-21, 06:22 AM
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I do appreciate your time, after some conversation I was able to get information. The housing is a S4 '86-88 13B lapped and street ported. Rotating assy, 13B S5 '91. Polished and balanced 3MM Apex and corner seals. And I am going to assume the engine is 6port as there is a 6 port 13B side draft intake. As for the carb. there is a Mikuni base plate adaptor, and jet kit. I have to get under the car to get specifics, the only thing I got on the pump is that it is an HVLP one. This is why I was hesitant to build this myself, I have set up many aircraft engines and modified my motorcycle and had to rejet it. So getting the jetting correct to alleviate the acceleration stumble and not have so much fuel in the system that the plugs foul when shutting the engine down. The having to wait 15 minutes before it will start again because the plugs are fouled with fuel is the most frustrating.
Your guidance is greatly appreciated.
Your guidance is greatly appreciated.
06-05-21, 02:21 PM
#7
okay, whenever you get under the car, can you get some photos of the pump? also, some engine bay photos might help as well. it's too early to make any solid conclusions, but fuel pressure is definitely something to look into. when i got the point where i was tuning my Dell'Orto 48, it certainly was one of my main issues. it's also relatively easy to make right.
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06-05-21, 08:58 PM
#8
I actually own Rotaries
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What part of NC are you in? I would be happy to have a look at it for you.