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Old 07-03-2020, 07:59 PM
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Default Need help with boat carb.

My '83 boat has a Rochester 2 barrel carb on the V-6 engine. I put a new accelerator pump on, but still has a hesitation sometimes. Checking things out I noticed no gas coming from the boosters, even at 3500 rpm. I think all the gas is coming from under the throttle blades.

Boat runs ok on the lake, but seems to not have good initial acceleration for water sking.

Very hard to get at the idle mixture screws, no idea where they are set. Is this where gas would be coming from when the engine is running?

I took off the venturi cluster and there are no emulsion tube inserts in the carb. Is that why there is no gas flowing from the boosters?

Thanks, Tom

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Old 07-04-2020, 02:46 AM
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WHICH V-6? WHICH 2-bbl carb?

Is this a 90-degree/4.3L with a 2-Jet, or a 60-degree/2.8--3.1L with a Vari-Jet? Are the idle mixture screws hidden behind a "tamper-proof" plug?

I wouldn't expect it to get to 3500 rpm with no gas from the boosters. The idle circuit wouldn't supply enough fuel to have enough power to go that fast.

But I've been wrong before.

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Old 07-04-2020, 05:18 AM
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The booster cluster must have tubes hanging off the bottom of it otherwise there is no way for the fuel to get from the power valve into and out of each booster.

I would bet that they have fallen out and are sitting down in the area there made to hang in.

This maylay happens all the time with Q- jets also when subject to excess heat and vibration.

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Old 07-04-2020, 08:03 AM
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Tom,
Most likely your needle , seat & float need replacement and the carb needs complete rebuild kit along with good cleaning process.
My shop has seen quite a bit of those carbs in just the past few weeks as it's now boating season.
Along with tri-power units been building, modifying & live testing these units.
One customer left the boat for tuning, replaced old fuel, build Qjet knock off, fixed ignition issues, water tested
Jeff
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Last edited by shaker455; 07-04-2020 at 08:35 AM.
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Old 07-04-2020, 11:03 AM
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The engine is a 3.8, the carb # is 17080050
The emulsion tubes are attached to the venturi cluster. I was asking about the thin metal tubes with a flange, that sit into the carb body wells, that the emulsion tubes would go in to. Those inserts are not there. Is that ok?
The 3500 rpm test was while the engine was sitting in my driveway.
I have a carb kit. The problem is I don't have the needed tools to take the carb off the manifold. Sea Sprite must have had some special wrenches. I don't use gas with ethanol, so what passages I can get at are clean.
I'll recheck the float level and maybe turn the idle mixture screws if I can get a wrench on them.

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Old 07-04-2020, 11:20 AM
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Your engine a Merc?..I'm going to look it up in my book,
Not all units have those inserts.
Did you have them and removed them at one point?
Found it OMC
Drawing does show those insets... did you remove them?

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Last edited by shaker455; 07-04-2020 at 11:37 AM.
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Old 07-04-2020, 01:57 PM
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Push/pull/twist on the carburetor and watch/feel for movement between main body and base plate. These things are bad about base plate to main body screws getting loose.

Also need to make sure the spring loaded rod, that works the power valve, isn't froze up and sticking in the up position.

Clay

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Old 07-04-2020, 05:23 PM
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I purchased the boat used. You are right, Jeff,OMC. This is the first time I have worked on the carb. The inserts were not in there. Do those inserts make the well diameter smaller to help with fuel flow?
I will do the push/pull/twist test. The power valve rod is moving freely.
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Old 07-04-2020, 11:25 PM
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Most likely Tom to reduce the volume of fuel for the engine size.
I just finished that black one for a 3.0 4 cyl and it had no inserts so I think you'll be ok.
Haha! the guy tried to build it himself and attempted to run it a few time unsuccessfully.
I found his accel pump check ball in the main jet passage behind the jet after I pulled it.....that's real bad!
And half the parts missing including the spring in the spring loaded needle & seat.
Please don't do what he did.
Jeff

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Old 07-05-2020, 07:10 AM
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You may not see fuel flowing from the boosters regardless of engine RPM if the engine load is very light. It takes a lot of throttle angle and pressure differential above and below the boosters to pull fuel from them. Stab the throttle quickly and you'll see a butt-ton of fuel flowing from them, otherwise the engine would stall out and not carry the load.

I rebuild thousands of Marine carburetors, some are 2GC units but most are Quadrajets. Matter of fact I've rebuilt 5 in the last 48 hours and shipped two to Fort Lauderdale to a boat yard and next day airing one to Washington State tomorrow. The season is short for many boaters so most are in a hurry to get them back. Many of the Marine Rochesters 2GC's are different than their automotive counterparts and I don't remember seeing any inserts in any of them. If you look closely you will find units with larger bores (big CFM) and larger diameter accl pumps than the automotive units. They were also used on a wide variety of applications and even saw use on Ford Marine engines. Just had one in here from a 1977 Century powered by a 351W engine. I even went out with the owner for a ride on a nearby lake to test it out. Nice to get out of the shop once in a while. His almost hit 50mph so those carbs have plenty of potential to make good power and plenty of CFM for the little V-6.

Marine carburetors lead a horrible life, get little use, stay dried up for weeks, months and even years between use, get a lot of stale fuel ran thru them, and usually down in a bilge under an engine cover with a lot of moisture around them. The drying up cycles plus the fuel sitting in the tank(s) takes it toll on them. Good idea to manual clean the idle tubes with a precision drill bit in a pin vise.

Just a note for anyone reading this if you have a boat that uses a Rochester Marine carburetor on the engine. Do NOT for any reason trade in or exchange your Marine carburetor for a "rebult/remanufactured" carburetor, even from Sierra. ALL of the carburetors currently being sold as Marine replacement and JUNK, and most if not all will be "automotive conversions". It is difficult to build an automotive carburetor into a successful Marine unit, and the companies doing them, starting with I-5 at the top of the list are CLUELESS when it comes to that task. In any and all cases, even if your Marine carb is a little "rough" completely/correctly rebuild it or source out a real Marine core and rebuild it instead. I have a whole shelf full of these automotive replacement Marine Q-jets folks have thrown good money at that aren't worth two squirts of duck poop. In ever case we sourced out some real OMC/Mercruiser or Volvo Penta Marine cores and completely rebuilt them instead and immediately and permanently ended all the issue they were having with their "replacement" carburetors.

Sorry to be so long winded, pretty important stuff if you are a boater and want to enjoy your boat instead of having grief with it.........Cliff
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Old 07-05-2020, 03:58 PM
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The carb was tight between the main body and the throttle plate. So I rechecked the float level and put the top back on.
Yeah, the acc ball behind the jet is bad. My day job is a tool&die maker, so I can be very fussy.
I was wondering with no load on the engine would be the reason for no gas coming from the boosters. I seem to remember seeing gas from the boosters on the car engine carb though. Anyway I did stab the throttle quickly and did see gas from the boosters. Keep telling stories, that is how we all learn.
I think the hesitation problem is because slight movement of the throttle does move the acc pump rod ( on the outside of the carb ), but no gas squirts out. I was shocked at the large amount of acc pump fuel coming out when the throttle is opened a lot.
Maybe this week I'll take the boat out. Holiday weekend will be over,the lake is more fun with less boats.
Thanks everyone.

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Old 07-05-2020, 08:19 PM
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That's right!
We are in the same trade

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Old 07-06-2020, 06:17 AM
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The accl pump is there to cover up a lean condition with quick throttle movements. Marine accl pumps are usually shorter than automotive pumps so most or all of the pump shot isn't used up with moderate throttle angles.

Go back to the basics and make sure that the accl pump check ball seats well in the casting and not allowing fuel to drain back causing a delay in delivery (common problem).

Early Rochester 2bbl units used an aluminum accl pump check ball on the feed side under the return spring. Great idea but not so good in actual use and they would often leak and allow the fuel to return to the main bowl instead of getting put in the engine when the pump moved down. I'll add here that don't think for a second that just because you replaced the pump with a new one or put a "blue" seal on the old one that you are good to go. Many don't last more than a few hours in this new fuel, swell up, stick, roll off the pump, rip, tear or quit working well if at all.

I actually like that issue because I get a lot of carbs sent here and get to sell a lot of accl pumps.........
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Old 07-06-2020, 09:31 AM
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Quote:
Originally Posted by tc View Post
Maybe this week I'll take the boat out. Holiday weekend will be over,the lake is more fun with less boats.
Thanks everyone.
Tom let me know when you take the boat back out.
See you in the water!
Jeff

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