What is your static compression ? Bore and Stroke ? Head Chamber size or CC and head gasket thickness ? Someone here pointed out that you are at about 15 to 18 to 1 at a 1 to 1 ratio. Let's get that straightened out and get you the right pulleys for pump gas.
5/16 fuel line?? really?? what size needle and seats? floats adjusted right? do you have power valves in the carbs? ever taken a vac reading at the base of the carbs at idle and cruise??
Take the 8-71 off, put on a regular 4 barrell and drive it until it goes out. Save your scratch and build amotor for the blower. Do some pulley research and set the boost for the motor. It that motor has worn out intake springs it'll hold one open and that may be the backfire you are getting. The faster the blower spins the more it forces in there. You are asking to really harm the blower which is alot more expensive than a worn out 305. Don't put a magneto on it, it'll add to your misery. I feel for you as a Blower is the ultimate in cool. But that motor isn't up to the task and you are asking for a long frustrating road with that combo. Non forged pistons hate boost, and a non forged crank hates it even worse when the pressures that high. Tim
Just one other thing unrelated to the back fire, is running 1:1 from what i know it is not such a good idea, i have always been recomended to run either side of 1:1, to reduce the chance of harmonics ?????
I agree with alot you have to say here except the idle screws, the carbs that are of the reverse idle system type are clearly marked above the needle screws with arrows for lean direction so I don't believe he would be asking the question., he has stated his are the supercharged version which are specifically tuned for superchargers and are not the reverse idle system type
Hey guys, back again. I just got a points eliminator kit for my distributor. It's not what I want overall, but it's better than nothing. I'm planning on getting a new dist cap later today too; hopefully it stops backfiring. Also, I know it's bad to bend a blower belt sharply, but would it wear out quickly if I used a 25-26tooth 1/2" pitch drive pulley? I'm running out of clearance on the water pump for anything smaller than 25-26t.
I had so much written out just now, and it got erased again, so I will just say I am planning on pulling all of this off and putting it on a larger and "real" motor very soon. I just didn't want to screw-up a decent motor while troubleshooting. Also, thanks to everyone!
Try typing in a word doc. Or note pad then copy and paste into the post. Helps the sanity on long techy posts. Wtf are you trouble shooting?
If it's a repetitive backfire without load, it may be a crossed or bad spark plug wire, and/or a dead cyl. Double check your wire routing & do a compression test.
My BBC with a 871 on it had to have 26 degrees timing and no more than 34 total. Until I did this it would pop and spit. Go luck
I've heard of blowing a spark out being possible, but I didn't know a street engine could have it happen. Good idea about the note pad. I'm trying to set it up rich/lean wise and timing-wise for a better motor (when I get one) without blowing a new motor up on the first try basically. If this current motor blows up from something that's wrong, it won't make me cry. =D
I just installed a Hall Effect ignition system today, seems to work, although I'm resealing the carbs and giving them a once over and a cleaning to make sure everything is kosher inside. The jets are 73 primaries and 74 secondaries. Hopefully once it's all back together, it'll be smoother. I also swapped out my distributor springs for the next step softer (less tension) for the advance to come on sooner. I still have to limit the total advance down yet; hopefully soon.
My wires are all new 8.8mm Accels. I've run them before on a 350 in a Willys and they seemed to do well. I'm planning on doing a compression test once I get my carbs back together. I always route my wires perpendicular to one another if they are close or touching, just in case. Nice video Temper Mental. Thanks for the chart.
intake gaskets probably not sealing, what intake are you using on them tiny heads. If your running the balancer on your 305, its allready spun the outer ring and your timing is not set to what you think it is.
Put a cheap tbi chevy dist with 6a msd box in it, cheap small and no advance, set to 36 degree and hold it to the floor till the snout breaks off, breaks a rod, push rod, valve, valve spring or lift the heads and blows both head gaskets or just plain breaks and melts the cast pistons, But it will be fun till then
My carbs don't have power valves. I put all new gaskets on everything. I'm running a Cragar manifold. The intake ports are pretty small compared to the manifold. I ordered a new damper about an hour ago because the old one started wobbling. It didn't spin yet, but you're probably right about it getting too close for comfort. Yup, I just traded my Nova "leftovers" for a Pertronix points eliminator kit and I'm happy with it so far.
Ha, for sure kkustomz. =D Once something bad happens; it's going to get a better motor under the blower. I checked the intake-gasket sealing surfaces before I put them on and it turns out they had enough sealing surface to be adequate.
A couple more things to consider. Boost will create a lot more cylinder pressure. You need to run a colder plug and narrow the gap down. It also can play havoc with stock valve springs. Everything becomes more critical on a boosted motor. Making major changes can spell disaster. Good luck finding a save and reliable tune.
Right on about the colder plugs. I'll be sure to change those. I'm planning on keeping it below 5,200rpm... mostly. Thank you! I'm hoping to get down to 12 psi max if I can get the pulleys and belt issue sorted out.
Two piece designs are not good for performance engines, a Fluid dampner or similar is fine and help with street driven engines that plan on seeing alot of miles, blower hubs are used on blown drag engines.
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