Okay, so I ordered the full monty rebuild kit for the HP750 (4150) and downloaded all sorts of information and will be getting on it as soon as the kit arrives. I removed the float bowls last night and they seemed to be squeaky clean - still no evidence of the gushing gas problem. It was jetted 78's all the way around.

Now, I find this guy who has a brand new in box with BG dual filtered inlet setup 750 Mighty Demon. They are supposedly jetted 76 in front and 84 in the rear. Guys says if flows 940 - but I don't want to get into that discussion. Reason he's selling it is he just horse traded for a thumper 555 (can you even make one of those?) and the 750 he bought for his 383 is now just another part he can't use. I'm going to take a look at it this afternoon - he swears it is brand new, still in the box, never been touched, six months old, and the fuel intlet setup is still in the plastic shrink package. For $350 this seems TOO good to be true.

My combo is 434sbc; 220/64cc aluminum angle heads; 10.5:1 srp high silicons on Lunati 5.85 h-beams; comp hyd roller-110 lsa-236/244 @.050-.525; MSD pro hei, forged crank, and....stuff.

Mike Lewis was kind enough to reply to a personal post and helped me validate what the BG tech line was saying about a Mighty Demon 825 for my motor, but now along comes this deal.

What say the experts? BTW, Mike, you're Kershaw is in a 3-day ride to you. Let me know if you think it's a tool or a toy. If you like it, I want to get a big batch done up so I can hand my clients something worth carrying. Pens are boring....

Best,

Can you enlighten me and tell me how you get 434 out of a small block? I never heard of that.

400 chevy small block poked and stroked. 400 chevy block bored 30 over and use a 4.00 stroke crank and a 6.0 inch rod.

434 is a popular combo. Now they're getting to 454+ small blocks, but with aftermarket blocks. Pretty cool, although pricey.

Mike, I'm running a somewhat similar combo to yours, although its 22ci smaller. I've got a 245* cam (about .550 lift), and 12:1 compression, and I mounted a 825 Mighty Demon on top of it. I haven't played with the jets yet, it's too rich right now (12.5:1 on cruise according to Wideband meter). Let me tell you though, it's one crisp feeling carb. Runs awesome out of the box! I will be jetting down two sizes and probably a power valve change, but that should be it. Squirters and pump cams seem to be pretty close. BG recommended a 750 Mighty Demon, but I too got a great deal on this one ($330, about six months old).

I highly recommend this carb for your application.

Cool - thanks for the info. I think I'll snatch it up regardless. Those filtered inlets on the line kit that the guy is throwing in are really nice and will theoretically prevent trash from getting into the carb - which is probably why my 750hp is shooting gas out the vents.

The 434 is a result of Joe's calculations - he rebuilt the engine. Started out as a 427sb (4" stroke x 4.125 bore). In line with Tom Mobley's advice, Joe went with 5.85 rods and bored it out. Pretty awesome engine - wraps up tight - none of the slop that came in the original "crate" package.

I'm liking the hp and the room in the engine bay :D Everyone says I'll get tired of sb's soon enough and want a 502 or 540, but heck, if I'm gonna go that route it's 572 all the way!

Best,

Glad to hear you've got that deal back together. The 5.85 rod gives a little more room above the top of the wristpin to get a decent ring package in there. It's really tight with a 9" block, 2" throw and 6" rod. It's not that it can't be done, but is it something a guy wants to have a lot of money tied up in? Not me. Especially not for a streetable car.

Tom

Man are you ever right about the rings. The carb has been running so rich and then the vent tube problem poured a lot of gas down the cylinders. Joe said we would have had rings-a-poppin if we still had those "skinny top" 427 pistons as he called them. Anyway, a lot to be said for a good set of rings that actually have support all the way around the skirt. I'm just parroting what Joe has said, but he wasn't worried when I called him and told him how much gas I drained out of the oil pan.

I'm learnin' - day by day...thanks Tom.

Best,

horsepower tv just built a 472 thats right a 472 sb about three weeks ago.did anyone catch that one??????
shane

Yes you can make a triple nickel smile.gif a 555 is a .030 over 540 :cool:

Not that good of a deal really. Look on e-bay. Stick with the Holley unless you have BG experience.

Well, maybe it's back to Holley again. I have 0.0 experience with BG - only the opinion of people on this board. I started dismantling the sick 750 I have and can find nothing that would be blocking fuel flow or causing floats to stick. I did find 78 size jets all the way around, but no signs of varnish, trash, gunk - nothing. I understand why it was dumping so much gas down the manifold, but have no idea what caused the vent tubes to start spitting - no - shooting gas in the air. I guess I can rejet, just put it back together, and move ahead. I thought they jetted it rich because the carb was too small cfm-wise for my motor, but that doesn't make sense to me.

Back to s-q-u-a-r-e one. As my mother used to say, Life's great - everyday's a holiday, every meal's a feast!

Best,

Mike

Stop by my house - I have another 750 that you can throw on and and use as long as you like.


Joe

Thanks, Joe. I'll get my butt over there. I want to see your car run anyway. Guess I've kinda been avoiding you because I'm embarrassed about the whole header thing. MaryBeth got tired of having them sit in the garage and took them to the UPS Store and returned them while I was in San Jose a few weeks back. She's seen me fill out the Summit form a hundred times so God bless her helpful little heart - she just didn't know WHY I kept putting them back in the corner. I did get actually get a refund from Summit though. Sorry....

Best,

Originally posted by Live466:
Not that good of a deal really. Look on e-bay. Stick with the Holley unless you have BG experience. Can you explain that? You tune a Demon just like a Holley. I haven't had problems with either.

And that's a darn good deal. The ones you see on eBay (usually Speed Demons) are remans. A $500 Demon carb for $350 w/ fuel inlet is a great deal.

Mike,

Pull the needle and seat out of the bowls and spray the needle down with carb cleaner or compressed air. If there is anything between the needle and its seat the float will not stop the flow of fuel and it will eventually overflow out the vents.

Well, guys - here's what I found. I'll update my "spraying from vent tubes post".

The secondary needle and seat assembly slide in and out with ease, unlike the primary which has friction going in due to the o-ring. I don't know if needle/seats come in different sizes, but looking at the secondary - it's just plain worn. Deceiving to the untrained eye, but the fit is sloppy and the tip on needle (gray rubber, I guess?) is rounded off way more than the comparison with the primary. So, then I come to the fact that the float is not "suspended" in either position - right side up or upside down. That leads me to the metering plate where I find and ugly corroded/rusted power valve!!! I mean, this thing has as much crap on it as an old water heater element. But how could water get in there unless they were driving it with the hood off in a rainstorm? Maybe the answer is - it's not a new carb like they charged me for. Maybe the answer is it's a carb off one of his roundy round cars. I'm glad you guys pushed me to look - nothing like seeing it for yourself. Hey, I got screwed WAY worse than this by mitchell, so I'm not gonna make a bitch session out of this, but....what they heck are people thinking when they pull stuff like this? Like I'm NEVER going to find out? They're either complete idiots or theifs. I go with #2.

Thanks for the help guys. Total rebuild is now definitely in order.

Best,

Well, you've completed the hardest part: Finding the problem. Good luck!