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Rohester 2bbl, 1967, 153, MC1, carb questions

T

txgalzdah

Regular Contributor
1967 Mercruser, 120HP, 153 ci, 4 cyl, MC-1, 2bbl, Rochester, GC
1. On the throttle body assembly, what is the static setting for the Idle Adjustment Needles for initial startup? (Needles, ie 2) currently @ 1.5 turns.
2. Steps for checking for Air leaks.
The boat and drive train were completely rebuilt. We did about 9 hours of shake down, made some changes and she was burring like a kitten. Winterized the Gal and got laid off. She set for a year and a half.
I am dealing with bad gas issues. I put her up with 20 gallons of fuel and Sea Foam. I guess that may be good for one winter season but not 18 months.
I have siphoned the fuel tank as best I can, filled w/ fresh gas, flushed the fuel system with good gas, changed the filter, small flush for the filter, and rebuilt the carb. It was gummed up.
The throttle linkage is removed and she will start with my hand on the throttle. By ear I guess it is about 850 rpm. I have checked for air leaks with starter spray. The sound is real smooth to the ear but this is way too fast for idle and when I back her down she stalls. Plus at this rpm I can't tweak tune the ignition.
Even though I have checked for air leaks I am thinking I still have a leak some place. Any thoughts???

MercruserManual_1 (the free download that ya’ll pointed me.) PN: 90-68648 286
Section 4-Fuel Systems:
Page 11, Fig 1. 2GC Carburetor, This picture resembles the carb on my barge.
Page 13, Fig. 3. “2GC” Carburetor Assembly. This picture represents what I am working on with some exceptions.
 
Air leaks that cause high idle are either in the intake manifold (threaded plugs, base gaskets etc.) near the bottom of the carb. Anything above the lower half of the carb will not cause a "vacuum" leak to affect idle.

do not use starter spray!!!!!!!!!!!!!!!!!!!!! that is for specific starting issues not for testing.

use either carb cleaner or some spray oil such as wd-40. Do not spray it anywhere and everywhere. point and shoot it at a small area of suspission and a small shot and wait to see/hear if there is any change.

WHat you are trying to do is mask/seal off the leak to cause a change in idle. Not induce more volatile liquid into the air fuel mix. The supposed leak is already causing a high idle condition.


Also sea foam is not a long term gas stabilizer...........there are a couple of good stabilizers out there do some research (STABIL Purple) that will keep gas good for well over a year.

Also double check your point gap/dwell and timing to make sure they are not influencing the idle.

Most rochester air/fuel needle adjustment is always 1 - 1 3/4 turns out from lightly seated. If you need to go beyond 2 turns then you definately have a vacuum leak......in my opinion
 
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You checked the fuel pump, opened it up and cleaned the filter in there? The filter in the fitting that enters the carb is clean ? You may have to clean both a few times till all the junk and gunk is gone from the tank.
If you can't find a leak around the base and the lower part of the carb and linkages then i would think the idle circuit is clogged. Dismantle the carb again soak in a good solution.
Here is a good write up on this subject... I came back to post one other little thing...some carbs just can't be saved or something was overlooked in the rebuild, such as the ball bearing... the float not floating, or the float hanging up.
clean carb

 
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Hey Ya'll,
Thank you for the replies. There are some very important details here that I didn't know or overlooked. This is the proverbal rest of the story that I needed to proceed. I will stop using stop starter fluid and I will check out the clean carb article to make sure I have all the I's dotted.
We are looking at costs for a repacement carb so we can start saving up. One question: do carb replacments come with a new throttle body and idle screws?
Thanks again,
TxGalzDah
 
You don't need a new carb. These carbs are really easy to disassemble and clean. Try this first. Remove the two idle mix screws and spray carb cleaner in the holes. Now if you have compressed air and a nozzle try to spray the bleed holes in the venturi area of the carb (inside). Now reinstall the idle mix screws making sure when you bottom them out it is done lightly and back each one out 1.5 turns. If this doesn't work you'll need to disassemble and clean and reassemble. If your careful and not tear any gaskets you wont need a rebuild kit. Now go out and purchase some Startron Fuel Treatment and follow the directions for initial usage. Stabil is junk compared to Startron and it will help restore old crappy gas too. I use it in everything... boat, car, truck, lawn mower, chain saw. Keeps fuel fresh for at least 2 years.
 
This new fuel is eating everything....paint rubber and the insides of some gas tanks. Yep, the insides of some gas tanks years ago were fiberglass.
So what happens is... you can suck all the gas out of the tank, clean all the filters and rebuild or disassemble a carb clean it perfectly clean put it back together and run the engine and 5 minutes latter the carb and filters could be clogged again.

What to do ? What i would do is replace every piece of hose with new. Make sure the tank is clean..the vent is clear... and the anti-syphin valve is working and clear. The filter in the fuel pump is clean and the one that enters the carb is clean. The carb is clean. Run the engine.

I had to clean the filters 3 times and clean my carb 3 times when i first got my boat. I first cleaned everything up changed out the rubber hose and rebuilt the carb. Ran the engine on a external tank of fuel. Hooked up the onboard tank and the carb and filters got clogged up 3 times.

7-8 years latter and my boat is running good, start her up after the winter no problem. What i do is with the engine running i cut fuel to the fuel pump and let the carb run dry... just like i do with my outboard and my small engines. Never a problem leaving the engines for a month a year or five years.
The engines always start for me, i dribble a little fuel into the carb and the engines start. Some times i have to keep dribbling a little fuel till the fuel reach's the carb from the tank about 3- 4 feet away. With my engine i have points i sand them a tiny bit before starting up every year i bet i don't even have to do that but i check them anyway for wear and if they are still within specs.
 
A vaccuum guage is the best tool to sort out engine problems.If you know how to use them properly,they are invaluable.For a start,theyl tell you if you have an air leak,or if theres another area to look at.Plus you can measure your fuel pump pressures
 
Oh and I just noticed you said the throttle linkage is unhooked. Is it idling at 850rpm's with the idle speed screw touching the choke plate cam in it's hot run position?
 
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