sbc problem

« **on:** September 22, 2008, 08:15:02 AM »

So ive got this brand new chevy 350 engine and it runs good at idle and low speeds. The person I got it from said I would probly need to replace the carb soon but the carb doesnt really look dirty. I dont know if that means anything if its dirty or not because I am still learning alot about engines. Well when I took it out it starts up fine and idles good and cruises really good but as soon as I get it up closer to top speed you can tell it starts to hesitate and then I lose all power and the engine fights to stay on and then dies. The only way I can get it to start after that is with some engine start spray and then it will do the same thing all over again. Do you guys think its the carb? Can I take the carb off and do anything or look for anything to see if thats the problem? I have a camera and can take pics of anything to show you guys. I am trying to make one last river trip and this little problem is kind of raining on my river parade. Any help is appreciated.

« **Reply #1 on:** September 22, 2008, 09:29:08 AM »

Sounds to me like at high engine speeds you're losing fuel pressure. Check the fuel pump as well as the carb. Would be a good idea to hook up a fuel pressure gauge and monitor fuel pressure while you're running as well.

« **Reply #2 on:** September 22, 2008, 09:36:53 AM »

Sounds like your motor is flat "running out of gas" it either has a collapsing line plugged fuel filter restricted fuel fittling , pinched line , possibly it has still has an internal bowl screen etc etc More info , Bow tank? saddle tanks ? do the tanks feed simultaneously ? Happy to help Knowledge is power ! Tom

« **Reply #3 on:** September 22, 2008, 10:44:35 AM »

It doesnt have a bow tank and it has a switch to switch from tank to tank so im guessing there are 2 tanks on the sides. Where would be the first place for me to look? What should I take off and check for? Or do I just start to replace things? The boat is a classic day cruiser I/O. Thanks guys.

« **Reply #4 on:** September 22, 2008, 11:06:19 AM »

Quote from: Jetaholic on September 22, 2008, 09:29:08 AM

Sounds to me like at high engine speeds you're losing fuel pressure. Check the fuel pump as well as the carb. Would be a good idea to hook up a fuel pressure gauge and monitor fuel pressure while you're running as well.

This was my thought to. After 4000 + its starts to pop , right ?

« **Reply #5 on:** September 22, 2008, 11:17:05 AM »

Yes it does and then I lose all power and it dies. How do I check fuel pump and carb?

« **Reply #6 on:** September 22, 2008, 11:27:18 AM »

Quote from: gokartrder on September 22, 2008, 11:17:05 AM

Yes it does and then I lose all power and it dies. How do I check fuel pump and carb?

Its never died for us , but obviously (sp) the problem is getting worse.. I always suspected a bad fuel pump , it would have to crank over for awhile before the first start. That means all the gas was allowed to drain back into the line. A good pump won't allow that. Did you take the carb apart? I would ditch that Edelbrock and get something better, maybe even a little bigger.....

Mech pumps are cheap, who knows how old it is.... And check all the fuel lines, if they are really soft replace them...........

« **Reply #7 on:** September 22, 2008, 11:42:33 AM »

Ok....will do sir. What size carb. is this anyway? Is it 650?

« **Reply #8 on:** September 22, 2008, 11:56:02 AM »

Like others have already said a fuel pressure gauge is a good place to start, inline, right up by the carb. SEE if you have good pres. at high r's and go from there.

« **Reply #9 on:** September 22, 2008, 07:00:11 PM »

Ok I took off the fuel filter and the fuel is comming out fine on each side. I also took off the fuel pump. It still had gas in it and the gas dumped out of the inlet hole but not out of the outlet hole. Does this mean it needs to be replaced? I will probly replace it anyway but I just wanted to know if there was a way to know if thats the problem for sure or not. Thanks again guys.

« **Reply #10 on:** September 22, 2008, 07:26:44 PM »

i got a fairly new holley 600 double pumper for sale...thing was awesome ran on a tired SBC, but ran great...when i mean fairly new it was purchased a year ago

« **Reply #11 on:** September 22, 2008, 07:33:43 PM »

did you check the excelerator pumps!did it ever backfire?

« **Reply #12 on:** September 22, 2008, 07:56:18 PM »

Quote from: gokartrder on September 22, 2008, 07:00:11 PM

Ok I took off the fuel filter and the fuel is comming out fine on each side. I also took off the fuel pump. It still had gas in it and the gas dumped out of the inlet hole but not out of the outlet hole. Does this mean it needs to be replaced? I will probly replace it anyway but I just wanted to know if there was a way to know if thats the problem for sure or not. Thanks again guys.

Again...plumb in a fuel pressure gauge and go run it. While you're running it at different throttle settings, monitor the fuel pressure at each RPM setting. 3000, 3500, 4000, 4500...etc etc...all the way till you hit your top RPM. If you see the fuel pressure start to drop, you may very well have a fuel line collapsing while the engine is under load demanding more fuel. But ya have to run it to find out. If fuel pressure holds constant even up to the point where it sputters and dies, then that verifies the integrity of the fuel system from the tanks to the carb and helps narrow things down quite a bit.

Also...from what you describe about fuel dumping out the inlet but not the outlet, that could point to the check valve diaphragm on the outlet side being the culprit. What kinda fuel pump does it have? If it has a Holley, you may be able to take it apart and clean it out. Sometimes debris can get caught in the check valve diaphragms and cause them to hang open, allowing fuel to drain back down towards the tank instead of remaining pressurized in the line.

« **Reply #13 on:** September 22, 2008, 09:30:03 PM »

I had the same problem - it turned out to be the fancy clear glass fuel filter in line. It couldn't keep up with the fuel demands.

Change out the filters with some 3/8ths line ones (fram etc), if you have to look it up find a 70-72 Ford truck with a 460 in it.

« **Reply #14 on:** September 22, 2008, 11:00:08 PM »

Quote from: gokartrder on September 22, 2008, 07:00:11 PM

Ok I took off the fuel filter and the fuel is comming out fine on each side. I also took off the fuel pump. It still had gas in it and the gas dumped out of the inlet hole but not out of the outlet hole. Does this mean it needs to be replaced? I will probly replace it anyway but I just wanted to know if there was a way to know if thats the problem for sure or not. Thanks again guys.

If it has nothing to suck it can't blow (boy that came out wrong), the fuel sounds to me like its under a major restriction somewhere, if there is garbage in the fuel tanks, that would be a good place to start, go and pick up an inexpensive fuel pressure test guage or install a permanent one of good quality, and also pick up a water separating fuel filter kit that uses the spin on filter, you can get a Racor but they are expensive for what you get, I use the Aqua Power kit and it can be bought thrugh NAPA under the Balkamp line for like $35, also grab a spare filter don't forget to eliminate the existing filter. the fuel pressure should always be above 5# while running at full go-pedal, good place to start, the filter can be emptied to see what the hell is in the system, us a Ball (also called a Mason or Kerr jar, depends where you're from) jar to empty it and let it settle, you'll see the crap right away...

GT

« **Reply #15 on:** September 23, 2008, 08:25:24 AM »

It has water/fuel seperator with new filter installed..... and i think the fuel pump is stock

Like they said , get a guage and check the pressure, check the fuel lines, Tank etc...........

One other thing i want to add to this.... I didnt notice any change in the way the engine ran till we changed props

After that @ high rpm's i think the engine was working to hard trying to spin that prop. But i could be wrong..

Sorry Chad , not trying to step on toe's .... Just want to help out

« **Reply #16 on:** September 23, 2008, 08:37:01 AM »

I would have a hard time believing that the carb is the issue, it still sounds to me like the fuel volume is inadeuate for the motor, have you tried running an outboard tank on it to see if the problem magically disapears? Its a cheat, but who knows, it may eliminate half of the components it could be...if it wont run on a separate tank, replace the fuel pump...I don't remember reading it but what type a carb does it have? if it is the Quadrajet carb, I would check to see if it still has the small filter in the inlet, if that gets plugged it will never make enough fuel flow...

« **Reply #17 on:** September 23, 2008, 11:29:05 AM »

Ok.....you guys are great. Even helping me out alot knowing I went I/O...lol. Anyways...just getting information from you guys and remembering what hapenned at the lake really points to the fuel pump. It really acts like its running out of gas.....and another thing I remembered I had my friend drive as I watched what was hapenning in the carb and I remember thinking to myself there was hardly any gas getting dumped into the little bowls in the carb. My last boat I had bought a holley 750 so there was ALOT of gas dumping in on that one but even tho the carbs are different I still think there should have been more gas dumping into the carb then there was......I mean it was drops. As bahner says it is a stock fuel pump and I probly should replace it anyway. I read up on how to switch them out and it doesnt seem too bad. I already got the thing off. And yes....Bahner says its a new fuel filter and its already the big twist on kind and I took it off also and the gas was pouring out just fine out of both ends and was clean as heck. I am going to order my fuel pump from summit and install it and if thats not it then I dunno what the hell.....but I am pretty sure it is. I also read up on some other sites people talking about their fuel pumps going out on their old muscle cars and its exactly the same. It works untill the rpms' go up and then it just cuts out. Either way it should be replaced and its already off so I am going to do that and hope for the best.

Hey Nordic! How much you want for that carb?

« **Reply #18 on:** September 23, 2008, 11:32:34 AM »

I guess you won't know until you put a pressure gauge on it.

« **Reply #19 on:** September 23, 2008, 01:46:38 PM »

Quote from: gokartrder on September 23, 2008, 11:29:05 AM

And yes....Bahner says ...

He will always be 2sav around here

« **Reply #20 on:** September 23, 2008, 03:01:37 PM »

im new in this subject but does it shutdown or die off till u lift a little?
i own a boat repair shop an i work on all jet,i/o,vdrive an so on but again if u need any more or cant get it let me know

« **Reply #21 on:** September 23, 2008, 03:46:31 PM »

Quote from: SLCKREG on September 23, 2008, 11:32:34 AM

I guess you won't know until you put a pressure gauge on it.

I know.....I just dont want to put the pump back on just to do this test when I am going to replace the pump anyways...if that doesnt work then I am going to try this.

Quote from: racer316 on September 23, 2008, 03:01:37 PM

im new in this subject but does it shutdown or die off till u lift a little?
i own a boat repair shop an i work on all jet,i/o,vdrive an so on but again if u need any more or cant get it let me know

Yeah I lose all power but then if I pull off the gas it will struggle to stay on and sometimes will stay on but after a while it just died everytime acting like it was running out of gas.

« **Reply #22 on:** September 23, 2008, 06:27:47 PM »

Hey gokatrder, is this an enclosed motor? If so that needs to be a marine spec fuel pump....FYI

« **Reply #23 on:** September 23, 2008, 08:51:59 PM »

water in the fuel/carb can do the same all it takes is a few drops in the carb and it can do many diffrent things an with todays gas.Im gona figure ur tank is under the floor an with the weather we have now with a little water under the empty to half full tank it will or can rain in ur tank especialy if it was sitting for any amount of time

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