OMC 165 GM L6 250 CARB Question...

[DukesFin]

Not sure if I can post a carb question here, but...

I've got a Holley 4bbl MARINE carb on my boat and the boat/engine/carb "boggs" down when throttle is in the "middle". Hammered down, does fine... Idling, does fine, but I'd say the middle 1/3 of the throttle position, it boggs down. Also, boggs down when on the ocean in some good swells, when I hit the face of a wave, it has a hard time recovering. No backfiring, just bogging down!

Any ideas?

 

[Bondo]

Re: OMC 165 GM L6 250 CARB Question...

I don't mess with Holleys,... So I can't tell you How to do it,.........

But it Sounds like the Carb is having a Problem with it's Mid-range Tuning......

With the Merc./Weber/ Carter Clone I've got,.....
I'd be changing the Springs or Needles..........

There's Got to be some Holley Guys around here.......

 

[Autotech1]

Re: OMC 165 GM L6 250 CARB Question...

dont know what the marine holleys have fir vents, but it sounds like they are spilling into the barrels. midrange bog could be the transition slots.

 

[ziggy]

Re: OMC 165 GM L6 250 CARB Question...

i'm no carb guy. but i'm gonna ask anyways, i'm courious as you've got the L6 in omc, i've got it in mercruiser. i have a 2bbl. and you have a 4. is that the oem carb? did it used to run ok? maybe a number on the hollie carb would help so others would know exactly what you've got to work on. w/o knowing to much about carbs. seems like to much fuel, like at1 is thinking, would be my first thought too...mostly because i got the 2 and it works good, and you got the 4.....
i assume you've ruled out anything but the carb. yer tune up is good? timeing, dwell? compression is good?......

 

[DukesFin]

Re: OMC 165 GM L6 250 CARB Question...

Good questions... Let's see...

Timing is good. Aftermarket carb for sure and the manifold to fit a 4bbl on this engine ain't cheap (near $1K)! It used to run perfectly. It's definitely a carb issue. I love the feel when going from idle or low speed to "hammer down" though. Not just the feel, but the sound too.

I had asked a buddy of mine about this a while back and I couldn't remember his exact words but I think his idea was somthing to do with "high-speed jets"??? I have never "broken into" a carb before. I need to get the #'s off of it and get a manual, pictures, etc, and study up on it though.

Sometimes, running at full throttle even on smooth water, it will bog down out of nowhere. Sometimes, running the throttle up and down quickly will "clean it out" but it does not last... Sounds/feels like somthing is "sticking", (like a spring or valve maybe).

I'll get more detailed info and post it tonight or tomorrow.

 

[DukesFin]

Re: OMC 165 GM L6 250 CARB Question...

It's a Model 4160.

 

[ziggy]

Re: OMC 165 GM L6 250 CARB Question...

It used to run perfectly.

if that's the case, i would think, not messin with the jets (repaceing with different ones)would be a good idea. maybe it's just dirty and needs a rebuild. that it might need, includeing the jets that are there....

ya say the timeing is good. but ya didn't say the dwell was good. or the compression is good. dwell could be off and that would effect timeing......

don't know if this will help. under carb troubleshooting in my merc book. for acceleration flatness. for an oem carb. there are other discriptions too, bogging down isn't one of them, but hesitation or surge are listed if ya think it's not acceleration flatness that applys to your issue. this is for acceleration flatness,

1- power piston dirty distorted, sticking or incorrect part
2-power valve, dirty, sticking or incorrect part
3-metering jets, loose, pluggted, incorrect parts
4-venturi cluster, dirty, loose screws, incorrect parts.

i reckon ya can rule out the incorrect parts, part.....there are other options too. but these were the 1st 4, listed in order.....it also seems that it is the proper chart for the 4160 as it is listed in the merc service manual.

 

[ParallaxBill]

Re: OMC 165 GM L6 250 CARB Question...

Hey ziggy,
Does your manifold look like it has a built in base for a Quadra-Jet? Mine sure does but I'm still running the original Rochester 2GC on mine. Works fine, so I'm not changing anything. Just curious.

Since I am not attempting to hi-jack the thread feel free to answer me via email if you want. Just gathering information. Hopefully the original poster and all that read it will understand.

 

[DukesFin]

Re: OMC 165 GM L6 250 CARB Question...

Since I am not attempting to hi-jack the thread feel free to answer me via email if you want. Just gathering information. Hopefully the original poster and all that read it will understand.

Understood! No problem at all. I've gotten some good "starting points" so far, so feel free to hijack as needed!

 

[Autotech1]

Re: OMC 165 GM L6 250 CARB Question...

Holleys dont use power pistons but they do use power valves. Wasnt sure if marine apps had them tho.

My Dad says it sounds like its lean, hes been running Holleys his whole life.

Im not too good troubleshooting carbs, but I can rebuild them and I know how they work.

I dont think id run a Holley on anything, theyre just a pain in the arse.

 

[ron7000]

Re: OMC 165 GM L6 250 CARB Question...

I have a 4160, but on a v-8. If you can post the list # of yours I may be able to point you in the right direction for parts.
I've had the same problem with mine and with other carbs many times. Based on what you said, this type of problem is in the transition circuit. It can be caused by a handful of things, usually by sediment in the passageways. They are very small and can get fouled easily, when that happens fuel flow is restricted and the air/fuel mixture is leaned out and the motor loses power in that rpm range. Disasembly, carb cleaner and compressed air is the most guaranteed fix. In addition, what can also cause the lean mixture is the fuel level in the bowl being too low. An easy, and free, fix is to adjust the float so the fuel level in the bowl is a little higher. These two things 95% of the time will fix the hesitation/stumble/bog when you accelerate normally, as opposed to hammering down. If when you hammer down and it takes off good and reaches 4000+ rpm, and also idles fine, then it's not the power valve. But you can replace it with one that opens at a different (higher) vacuum level and that may also fix your acceleration problem, especially if you're not running a power valve that's in the right range to begin with. They're also cheap so if you're going that far in it's a good idea to replace it anyway to rule out all possibilites. Hope that helps. What is the top rpm the motor will hit by the way?

 

[DukesFin]

Re: OMC 165 GM L6 250 CARB Question...

With my 19 pitch prop, I can only get up to a "hair" over 3000 right now.

I really need to get me a 15 or 16 pitch prop. (It did the same thing with the old 15 pitch prop I used to have before I sheared the pin off of it).

Since I do not know the age of my Holley 4bbl, or its history, I was thinking about getting a new one. Prices on them isn't that bad.

 

[ron7000]

Re: OMC 165 GM L6 250 CARB Question...

Good questions... Let's see...

I have never "broken into" a carb before. I need to get the #'s off of it and get a manual, pictures, etc, and study up on it though.

Sometimes, running at full throttle even on smooth water, it will bog down out of nowhere. Sometimes, running the throttle up and down quickly will "clean it out" but it does not last... Sounds/feels like somthing is "sticking", (like a spring or valve maybe).

I'll get more detailed info and post it tonight or tomorrow.

just read your 2nd post,
From this description it sounds like the carb needs a cleaning out, which is normal. If you can get the list # to the carb you can look up the rebuild/renew kit you need for it from holley. That will have all the parts and gaskets you need. If you can pull the bowls off the carb and read the numbers off the main jets and power valve that will also help, and I recommend doing that first before you buy the wrongs renew kit.


http://www.holley.com/TechService/Library.asp
you can get an exploded view of a 4160 there, for free.
Haynes puts out an ok reference manual, if your lucky you can pick one up for < $20 at a chain auto store. It'll at least show you where that part goes you have left over after everything's back together.
http://www.amazon.com/Holley-Carbur..._bbs_sr_1/103-0854587-3591828?ie=UTF8&s=books

A couple more books I can recommend if interested is

Motorbooks: Carb performance how to tune & modify
http://www.amazon.com/Carburetor-Pe...ef=sr_1_1/104-1381085-0560723?ie=UTF8&s=books
might not be worth the price, probably going out of print which is why the price is so high, but it is a very good reference. Doesn't have rebuilding instruction but explains carb theory very well so you can understand and troubleshoot any carb, it also goes into the internal details and the how's and why's of holley's, roch, carters, webers.

SA-Design Super Tune Holley carbs, solely holley carbs. Your best bet pricewise for reference for rebuilding a holley plus understanding how it works and be able to troubleshoot. Has a section to rebuild and tune the 4160 and a parts listing and exploded view.
http://www.amazon.com/Holley-Carbur..._bbs_sr_3/104-1381085-0560723?ie=UTF8&s=books

SA-Design How to build horsepower vol 2,
talks on holleys + rochesters, carters, webers; goes heavily into manifolds, fuel, airflow, air/fuel ratio and engine science, very good for understanding your motor and how to either troubleshoot or upgrade your intake/carb/fuel systems; also breifly explains how a carb works. A very good if not better substitute for the carb performance book, definitely buy this along with the previous one and you'll be able to understand everything.
http://www.themotorbookstore.com/how-to-build-horsepower-2.html
http://www.amazon.com/How-Build-Hor..._bbs_sr_2/104-1381085-0560723?ie=UTF8&s=books

 

[ziggy]

Re: OMC 165 GM L6 250 CARB Question...

sounds like the general consensis is to get her a good carb rebuild ontoit. cleanin it up real good.

at1, i stand corrected. there is no power piston. an exploded view of the 4160 confirmed that. i have no excuse. that's why i'm here anyways, to learn from others. thanks. one more bit of info to store to the hard drive so to speak....

df, have you done a compression test on this engine?

pb, yep, my manifold looks to be preped for a 4bbl too. i don't know why. has a base plate reduceing it to the 2gc prep. this is true for both my 72 and 75, they are both 165 hp mercrusiers, same 2gc carb. i agree, i'm not changin carbs either. i run too good as is.......maybe it has something to do with the 4bbl mounted to df's set up. df, do ya have a pic of this manifold and carb. ya say its aftermarket, and pricey. what is it? got any links? opps, i'm gettin off topic,

best thing i ever did was get a new carb for one of my old cars that treated me real bad. till i got a new oem carb(bottom of venturis was wasted from throttle plate wear, throttle shaft end play). it ended up being a straight R&R and the fix. i have no idea if that idea would hold up for a holly in a boat. i certainly hate to compare autos to boats. but it may still be an option for ya....seems like a rebuild would be in order first though.......

 

[DukesFin]

Re: OMC 165 GM L6 250 CARB Question...

Here is a pic of the manifold... I can get a picture of the carb later today...

Oh - Compression is spot on...

This is while I was getting the new engine ready...