bsc

Do a compression check, My old 350mag supercharged detonated and broke three piston skirts, It idled perfect and ran up to 60mph perfect then it would drop right back down to 30 like somebody put the anchor out. After spending way too much money tearing the heads apart, new holley electric fuel pumps, all 5/8” gas line to the tank and what ever else I could purchase to fix the power loss. Problem was the timing was set wrong, (Yes I set the timing) that was a costly mistake. I hope I am wrong and your compression is perfect.

thsorens

Hey Liberator 21
Have you had good luck with Carbs Unlimited? I called the guy and he's kind of a dick! He does have jet kits, and the .147 needle and seats I need though. How long does it take to get parts from him? Also, you say you got rid of your carb filter huh? Are you just running an inline filter then? I hate to cut my hard line, but I could cut in a filter between the pump and the tank. Someone mentioned drilling out the fuel inlet? Maybe I'll see what you mean after I pull the carb tonight.
Thanks guys.
L8r
Tom

thsorens

Putting the old needle and seat seemed to take care of the running out of gas issue, and premium fuel seems to have taken care of the predetonation issue! I was still a little gunshy, but I ran it wide open with the engine hatch open for a good mile, and no rattle, no loss of power! I still need to check the total timing (initial is set to 8), and take a plug reading, and check the compression. It probably wouldn't hurt to go up a size in the primary jets, it has 70's now. My secondary rod hanger is a K and the secondary rods are DA's. Getting this carb dialed in will get me through the summer, but I think I really need to put my E-Brock performer intake on and maybe a new carb. I also need to change the exhaust, but performance exhaust would cost me more than the engine! I have stock manifolds with 3" risers and a 3" Wishbone. The only cheap thing I could do is run 3" exhaust hose straight out the back off of the risers. Would that really buy me anything besides noise? Isn't replacing the manifolds and the risers where the power would come from?

Thanks guys! Really appreciate the help! 383's rock! This think pulls like a friggin freight train!

Liberator21

thsorens,
Sorry I didn't get back to you sooner, I was on the boat all weekend.
I usually ordered my parts directly off the website, and had no problems at all and got them in reasonable time. I know what you mean about the guy though, I called him once with a question, and he seemed like a real jacka$$. In a previous post, someone mentioned about the needle and seat assembly in the off the shelf carb rebuild kits being small. I purchased a kit, and found that out when I compared it to my old one. I guess you found that out too! As far as the fuel filter goes, I removed the carb's internal one, but didn't want to cut my stock line either. So I bought some stainless line, and bent a new one, then cut that to make provisions for a larger external filter. I'd have to look it up, but I think I'm running 73 main jets, and possibly 42 primary rods. For me 70's were a bit lean. What cam are you using, and what kind of boat is it in?

Paul

thsorens

Good to hear that Carbs Unlimited is reputable. I am using Comp's XM262H (pn 12-236-3) and its in a 1984 Webcraft 23. I will probably order 2 or 3 different jet sizes from Carbs Unlimited from 71-73, and the primary rods that go with them. Do you have to change primary rods when you change jets? I think I might go to the .147 needle a seat too since I'm making an order anyway. It actually runs pretty good right now though. I put the original needle and seat back in, put in premium, and set the timing back to 8 initial. It was at about 12. I dont have an adjustable timing light, but I'll get one on it and check the plugs after a WOT run ASAP. Thanks again for the help! What about exhaust? Does it help to run it thru the transom with stock manifolds and risers?
Tom

Liberator21

That's the same cam I'm using. I think I could use more cam though. Do you notice that your engine pulls like crazy until around 4600 - 4800 rpm, and then just seems to stop there? I've used this cam in two different engines, and had the same result both times. As far as changing jets and rods goes, if you increase the main jets, and leave the same rods, you'll richen your idle and cruise mixtures as well. It's a balancing act. If you have a good cruise mixture, but you're a little lean at WOT, you would have to increase the main jets AND put in larger primary rods to compensate for the larger jet opening to keep the cruise mixture the same. The tips of all primary rods are the same size. It's the diameter above the step that changes with the different numbers. This way, changing rods won't affect WOT mixture because at WOT, only the rod's tip is in the jet. But at cruise where vacuum pulls the power piston down, the stepped area is in the jet, and there's your cruise mixture. These carbs are a bit complex, but very tuneable, and once you understand how they work, they're actually quite easy to work with. As far as the exhaust goes, there are people on the board with far more experience in that area than me. Hopefully one of them will chime in because I'd like to know what they think. I can only tell you that I went from log manifolds through the transom to stock center rise through the transom, and saw no difference. I am however running Rex Marine slip in silencers which I am going to remove one weekend to do some with/without comparisons with the radar gun. What prop are you running, and what kind of speeds and rpm are you seeing? One more thing, I have a great article on tuning the Q-jet. It includes spreadsheets of jet/rod combos, and how to figure out jet area with different jets and rods. Unfortunately the link is dead, but I think I have a copy on my home computer. I'll check it out tonight. I know I have a hard copy printed out. If you want a copy, I'll send it to you.

Paul

thsorens

Yes, I can run right up to 4600-4800 in no time, with 1 person or 6 people in the boat, but then it just kinda stops! I figured it was because I was running the stock intake manifold and exhaust, I think an E-brock performer and an aftermarket exhaust would probably get it up to 5000, but just guessing. I wouldn't go with anything higher than a performer though, or the bottom end would probably suffer. This is not really a fast hull design (1984), so I really should just be happy with 4600-4800 with a 21 pitch SS generic prop. My speedo isn't working, and I haven't been shot with radar, but I'm guessing I'm running ~55MPH. I can jump right on plane with a boat load of people and coolers and even pull tubers with the 21, which demonstrates the incredible grunt this stoker has, but I kinda thought the top end would be a bit better. Its somewhat easy to get a boat this size to go 50MPH, but it takes some $$$ to get em much faster! Send me a copy of that Q-Jet spreadsheet if you find it! Thats exactly what I need. Thanks for the explanation on the primaries. HAD A GREAT WEEKEND ON THE RIVER!!!!!!
Heres a pic of the ol girl!
http://www.omahariverfront.com/galle...kerrun/mc9.jpg

Liberator21

It sounds like you have a very similar setup to mine. I have a 383 with forged pistons, and 64cc stock heads with a bunch of port work. I'm using the GM performance parts High rise Z28 style cast iron manifold (I run in salt). My previous engine was a 350 with the same intake and another set of the same heads. It had a mild crane marine cam, and would easily spin up to 5000rpm with a 19" prop. When I did a valve job on the engine, I changed the cam to the XM262-H, and with everything else being the same, I lost RPM. The engine would run up to about 4700rpm then fall off.
Now with the new engine, and the same part number cam, I'm getting the same thing? I'm convinced it's the cam. I'm running a 21' Liberator with a 21" prop, and I'm seeing 60mph on a cool day with only me in the boat, and a light load of gas. Otherwise, with a load of people and gas, I'll see mid to upper 50's all day at around 4600 - 4700rpm. Like you said, it gets up to speed real fast! I'd like to see what difference the performer makes on your engine. I found a copy of one of the Q-jet documents here in work.
Shoot me an email, and I'll get a copy out to you, and anyone else who wants it for that matter! Glad you had a great weekend too!
email: [email protected]

Paul