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Discussion Starter #1 (Edited)
Hello all, new here. ive been buliding a 86 second gen rx7 for about 2 years now, started with a stock 302 from a junk yard. I went threw 2 different 302's from 2 junk yards. They both went out on me so for the last 6 months ive been buliding a 347 stroker. Its got a 4 barrel eldelbrock carburetor, msd 6AL, msd coil and a msd pro billet distributor. KB hypereutectic pistons. Comp Cams hydraulic roller lifters, comp cams 0.544 lift roller camshaft. PRW 1.6 ratio roller rockers. D.S.S. racing main support system and windage tray. Flowmaster mufflers 2 1/2" true dual exhaust, bbk shorty headers. Re-built C-4 transmission, TCI torque converter. The carb is the only thing i didnt buy brand new it came on the stock non h.o 302 I dont know what cfm it is but i know i need a new one.

Finally got it in and got it running pretty good. Had some issues trying to time it. My timing pointer has like a bubble and a upper straight edge i wasnt sure which to get my timing from. But i think i got that figured out it runs decent and starts up every time. My problem is when i tap the throttle the carb pops really loud and kills the motor. Havnt tried to drive it yet its on jack stands still but if Im smooth with the throttle it revs just fine. It goes into gear too. Im using the stock fuel pump in the rx-7 but i have a fuel pressure regulator so im running around 5 psi. Any advice is very much appreciated!! i've worked very hard and spent all my money on this car. I really want to get it atleast drive able so i can take it to a dyno and get it tuned right. This is my first build so i could really use some help. Thanks in advance!

One more thing, I pulled my plugs out a few days ago and i noticed half of them were clean and half were dark black. There only a week old, this didnt seem right to me. What can cause this?
 

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Discussion Starter #2
BTW if there is a more appropriate section for swaps feel free to move it there, i couldnt find one. I put it here cause the 302 block came out of a 86 mustang. Also, please dont flame me for putting a ford v8 in a mazda i did this because the rotary needed to be rebuilt and it was going to cost just as much for half the power. I'm just a kid doing my first project and working with what i have. thanks again and if anyone would prefer to help me threw e-mail please feel free i get e-mail on my phone so i can respond right away.

e-mail: [email protected]
 

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Welcome, and congratulations—that's a lot of work! And, don't feel bad about a Ford in a Mazda as that's very common, and... Ford owns Mazda so they're in the same family. Anyway, it sounds like you have a several little bugs to deal with. With what you've said, it sounds like you should identify your carb using the numbers stamped on it so we know what you're working with. That will determine if you should do a full rebuild on the carb, or replace the carb as it's probably too small now.

Then get to the dyno where they can do the rest of the checks and drivability tuning. That is money well spent. Do not go there for a dyno RWHP number—only tuning. I guarantee your HP numbers will suck until you've had a really good full-range tune put on it.

Half the plugs light and half dark is either a carb issue or gasket leak on one side of the carb. If that's true, the plugs of one color will be in cylinders #1, 4, 6 and 7. The other color plugs will be in cylinders 2, 3, 5 and 8. Pull a couple to verify to verify. Also, a quick jab on the throttle causing a backfire, hiccup, or stall is again a carb issue, and may have some timing-curve issues in there as well.

David
 

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Discussion Starter #4
thank you so much for your reply! the numbers on my carb are 1406 2659. My dad and I rebuilt the carb about 2 years ago, I used it on a non h.o 302 for about a year with no problems. Then it sat on the shelf for the past year. I belive my plugs are as you say but i will pull them today to make sure. The very next thing im doing is getting it to a dyno, i was trying to make it so i can drive it there tho. I see your local to seattle I live in Kent, dont kno if you are familar with king county but ive already called 2 places. Blood enterprises and The Mustang Shop, have you heard of either of these or know of a good local dyno shop? Blood said there booked past august but the mustang shop said they could get me in, decent prices too.

When I do a quick jab of the throttle it backfires threw the carb and kills the motor most of the time. You think this is the carb or a timing issue, is there a way to tell? My dad usually helps me with timing but hes gone now so im all on my own now. So any advice is greatly appreciated.
 

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When I do a quick jab of the throttle it backfires threw the carb and kills the motor most of the time. You think this is the carb or a timing issue, is there a way to tell? My dad usually helps me with timing but hes gone now so im all on my own now. So any advice is greatly appreciated.
It could be either..The condition you describe could be a really really lean condition(check you accelerator pump and also for vacuum leaks) but I am guessing its probably ignition related..Double check all of your spark plug wires to make sure you have the proper firing order and that they are all good and tight..Are the wires and cap and rotor all in good shape?..Getting the timing set up is really not that difficult..With the engine idleing turn the distributor a little either way..The engine will smoothe out when your going in the right direction and should have crisp acceleration when you give it a shot..
 

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Discussion Starter #6 (Edited)
It could be either..The condition you describe could be a really really lean condition(check you accelerator pump and also for vacuum leaks) but I am guessing its probably ignition related..Double check all of your spark plug wires to make sure you have the proper firing order and that they are all good and tight..Are the wires and cap and rotor all in good shape?..Getting the timing set up is really not that difficult..With the engine idleing turn the distributor a little either way..The engine will smoothe out when your going in the right direction and should have crisp acceleration when you give it a shot..
I've had the distributor for 2 years and i've never replaced the rotor but its been on jack stands most of the time. I only drove the stock 302 maybe 20-30 times over the course of a year. I replaced the cap last week only cause I snapped a terminal off my old one when I had to pull the motor out. The only reason I didn't replace the rotor is the jegs guy said i didnt need to if it looked ok. I've got it running good I was just thinking that maybe its a tooth off and that could be causing the backfire threw the carb when i tap the throttle. I've got it timed to about 12* according to the upper straight edge on my timing marker. Is this correct? I wasnt sure if I go by the straight edge or lower theres like a circle or bubble. Anyone know what im talking about? i can take a pic if need. If it was off a tooth could it run good and only pop when i tap the throttle?
 

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Discussion Starter #7
I just thought about this, I bought my MSD Pro-Billet distributor for a 86 302 non h.o which would be a non roller block. When I built the 347 i installed a comp cams retro-fit hydraulic roller lifter kit. Is there any chance i need a different distributor now that its a roller? I apologize if this is a stupid question, if it is just tell me so. Im just trying to think of every little thing, might be over thinking it. thanks for the replies!
 

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Is there anyway to turn my motor over if i cant get a breaker bar on the crank bolt? I'm thinking the dizzy might be a tooth off. Since I put my 347 in I cant fit my breaker bar between the radiator and the pulley even tho i had no problem with the 302. Guess my new balancer is a little thicker. I've already done this 4 times in the last week and every time i have to drain all the collant pull the fan, radiator, belts, and shroud. So if anyone has any tricks to turning the motor over so i can find TDC please let me know.
 

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I disagree, as far as method of diagnosis. Timing could be another issue, but as I said, you know you have a fuel/air issue for sure, based on your different spark plug colors. I would take care of known issues before doing something else that may be giving conflicting symptoms. Seriously - you'll drive yourself crazy with multiple symptom sources.

David
 

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Discussion Starter #13
what can i do to fix the air/fuel mixture problem? Do you know what timing pointer im talking about? It has a upper straight edge and beneath that there is a circle. Trying to figure out which i get my timing from.
 

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What is your dizzy part no? Which advance bushing are you using? Have you checked to see if the mechanical advance is working? I ask because I have encountered many of their distributors locked up due to rust caused by moisture. I called them on it they statedd it is because I live in a high humidity area. Basicly left me with the fact they are in Texas were rain is less common. Said to them they might try testing there product in the nort west were it rains a lot. Sorry about the rant. Dont think I am too interested in there products anymore. Researching more info on CD ignitions I am ready to go distributor ..less.
 

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Your carb is a 600 CFM possibly a 750 would be a better choice. Not a fan of Eddelbrock carbs. Search there web site and find there needle and jet charts. Find out whats in your carb and go from there. More info on what is done to the engine might helps us?
 

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what can i do to fix the air/fuel mixture problem?
You're looking first for air leaks and fuel leaks. Fire it up, and look into the carb throats for fuel entering unevenly from one bore to the next. If nothing is obvious there, use a can of non-flammable spray cleaner to check for gasket leaks. Just spray it on sections of carb and manifold gaskets, and vacuum lines, a few inches at a time. Listen for changes in the idle that indicate you found one. If you find a fuel or air leak, fix that first and see what that gets you.

David
 

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Discussion Starter #18
I just talked to edelbrock and they said that i need a higher cfm carb and that using my carb which is for fuel economy could cause it to pop when i tap the throttle. I know i need a new carb i just figured i could make it work till i have the money for a new one. he suggested that i buy new metering rods and a step up spring kit. Im going to do what you said David and check for vacum and fuel leaks right now and see what that does for me. thanks for the replies everyone very helpful! keep em comin, thanks!
 

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timed to about 12* according to the upper straight edge on my timing marker. Is this correct? I wasnt sure if I go by the straight edge or lower theres like a circle or bubble. Anyone know what im talking about? i can take a pic if need. If it was off a tooth could it run good and only pop when i tap the throttle?
Don't worry too much about timing marks at this point..Just turn the distributor and the engine will tell you what it likes..It should idle good,start good and have quick crisp acceleration...Being a tooth off only applies if you physically cannot turn the distributor body to get you the timing you need...This is usually caused because the vacuum advance is hitting against something...
 

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Good news!!! finally got it to stop backfiring threw the carb! atleast it only did it once and i tapped the throttle like ten times so thats much better then doing it every time i quickly tap the throttle. I even took it for a test drive! first time driving it with the new motor. didnt have as much power as it should but im sure it needs more tuning but its closer thats for sure. All i did was go get a gasket for under the spacer plate beneath the carb and the edelbrock guy told me to adjust one of the arms on the carb so i did that and now its much better, thanks for all the help everyone! bottom line is i think i just need a new carb
 
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