Rochester 2bbl.

[towboater1]

I bought my first boat from my uncle who had an eng. installed last summer(2011).Boat was put in water 1 time and he sold it to me due to his age,upon Trying to use it I found the accelerator pump was bad eng.was hard to start all the time.Had carb. rebuilt and installed it myself.Now I have done some work on cars,trucks and bikes in the past but never on a boat.This is just a 4 cyl. automotive eng.anyway I never had to adjust the air,fuel and idle on a boat.With this being said I'm having a hard time getting it to idle at 650-700 I turn carb adjustments in till it stumbles,and back out till eng. smooths out.She stills idles around 850-900.(Boat is out of water) is the only IDLE adjustment on the linkage itself?

 

[superbenk]

Re: Rochester 2bbl.

There should be 1 (Mercruiser later versions, I think) or 2 idle needles (screws with springs on them) at the base of the carb to adjust idle mix. Have you checked timing?

 

[fmalott]

Re: Rochester 2bbl.

yes look for the idle screws at the base i rebuilt my 2bbl i can't remember if there was 2 or 1 i think i had two anyways the manual says turn all the way in then 1-1/4 turns out. just a thought after i put the carb back on my motor got it running but the idle was to high i adjusted it like you said back it off untill it almost stalled then turned it until it ran smooth but it was idling to high then i realized the linkage was not back off enough i adjusted the linkage and it idle perfect

 

[CharlieB]

Re: Rochester 2bbl.

The Mercarb and Rochester are almost identical, the major difference is R used two idle mixture screws, one one each throat, while the Mercarb used only one. Both work fine, starting setting is 1 & 1/2 turns out from lightly seated.

Idle speed is set using the screw on the throttle linkage, you may have to readjust the throttle cable/linkage to provide 'slack' in order to allow the throttle shaft to turn back down to lower the idle speed. Once idle speed is set, the cable/linkage must again be readjusted to give a 'slight' positive 'push' to ensure the carb always returns to idle.

If idle speed cannot be reduced, check for any vacuum leaks at the carb base/intake, also check the distributor mechanical advance as a sticking advance will raise idle speed.

 

[towboater1]

Re: Rochester 2bbl.

There should be 1 (Mercruiser later versions, I think) or 2 idle needles (screws with springs on them) at the base of the carb to adjust idle mix. Have you checked timing?

No I have not got into that as the boat runs fine,just the idle issue. She starts and throttles up great now that carb has been rebuilt.

 

[towboater1]

Re: Rochester 2bbl.

The Mercarb and Rochester are almost identical, the major difference is R used two idle mixture screws, one one each throat, while the Mercarb used only one. Both work fine, starting setting is 1 & 1/2 turns out from lightly seated.

Idle speed is set using the screw on the throttle linkage, you may have to readjust the throttle cable/linkage to provide 'slack' in order to allow the throttle shaft to turn back down to lower the idle speed. Once idle speed is set, the cable/linkage must again be readjusted to give a 'slight' positive 'push' to ensure the carb always returns to idle.

If idle speed cannot be reduced, check for any vacuum leaks at the carb base/intake, also check the distributor mechanical advance as a sticking advance will raise idle speed.

Ok this is where I cant figure out the deal.What screw on the throttle linkage? Upon inspection the only screw that's anywhere close to the throttle linkage is th small screw that screws in/out on the choke linkage.The only way I have found to adjust the throttle linkage is to take the last leg off the carb.itself screw it out or in,and I find it hard to believe you have to take this part Everytime you need to adjust the Idle....I dont see a mechanic doing this to get the idle right....Totaly frustrated last night and gave up.Will take some pics. and post for you.

 

[fmalott]

Re: Rochester 2bbl.

Ok this is where I cant figure out the deal.What screw on the throttle linkage? Upon inspection the only screw that's anywhere close to the throttle linkage is th small screw that screws in/out on the choke linkage.The only way I have found to adjust the throttle linkage is to take the last leg off the carb.itself screw it out or in,and I find it hard to believe you have to take this part Everytime you need to adjust the Idle....I dont see a mechanic doing this to get the idle right....Totaly frustrated last night and gave up.Will take some pics. and post for you.

the red arrow points to the idle adjusting screw the yellow arrow is the linkage i had to adjust

 

[towboater1]

Re: Rochester 2bbl.

That's the one's..lol so I'm on the right tract then. One other thing,should there be a return/tension spring on the lower end of the throttle linkage set up or not?I noticed the throttle linkage does not return to lowest idle position from the helm.I can move it back down about a 1/16 or so and it makes a big difference in the idle speed.

 

[Don S]

Re: Rochester 2bbl.

There is no return spring needed, the throttle cable should be adjusted by turning the brass barrel on the throttle cable so it puts a slight pressure on the carb linkage to the idle position.

 

[Bamaman1]

Re: Rochester 2bbl.

I had to rebuild the carb on a 1980 Mercruiser 4 cylinder, and I needed a base plate and carb kit. The parts came from a 1967 Chevy Impala with a 307 engine.

 

[towboater1]

Re: Rochester 2bbl.

OK thanks Don and all that responded...Will let you know how I make out with it...

 

[towboater1]

Re: Rochester 2bbl.

Got her to idle at 750-850 on the trailer,when she get's in the water dockside the rpm's should drop with back pressure on the exhaust or does that have any effect at all on your idle point?

 

[Don S]

Re: Rochester 2bbl.

It has some, I usually just adjust them to 725 to 750 rpm out of the water and they seem to work fine in the water.

 

[towboater1]

Re: Rochester 2bbl.

Alright....Thanks once again Don. Going to take her to the water this weekend,will let you know how she runs and if we catch any fish..

 

[towboater1]

Stumble

Stumble

Just put a rebuilt Rochester 2 bbl. back on my lil 140 Mer Crusier,set the idle about 750-800 and it runs fine so far at idle and high Rpm's 3000-3500.I notice when just at idle if I take and nail the throttle she wont take the fuel?Could this be a float issue with the carb.?

 

[towboater1]

Re: Stumble

Re: Stumble

Just put a rebuilt Rochester 2 bbl. back on my lil 140 Mer Crusier,set the idle about 750-800 and it runs fine so far at idle and high Rpm's 3000-3500.I notice when just at idle if I take and nail the throttle she wont take the fuel?Could this be a float issue with the carb.?

She wont even think about taking the fuel,just dog's down BAD....

 

[superbenk]

Re: Stumble

Re: Stumble

Sounds like a bad accelerator pump. Maybe it's time to rebuild the carb.

(and put spaces after your punctuation)

 

[towboater1]

Re: Stumble

Re: Stumble

Had it rebuilt Tuesday,installed it on Wed. and did some tuning in so far as the idle and so on.Rebuild kit had new pump etc.and took it to the shop for that.Now that's not to say the tech.may have seen something he thought didn't need to be replaced....I just cant nail the throttle but other then that she runs like a scalded ape.

 

[superbenk]

Re: Stumble

Re: Stumble

With the engine running & the flame arrestor off, pump the throttle while looking down the throat. You should see 2 solid streams of gas shoot into the venturi. If you don't or the streams are weak, I'd suspect the accelerator pump or something gummed up still. You could certainly check the float to be sure you're getting enough fuel in the bowl, but that doesn't sound like the problem to me.

 

[ENSIGN]

Re: Stumble

Re: Stumble

I doubt if it is the float. Make sure you have a strong stream of fuel comming out when you hit the throttle.it could be the pump ,a stuck check ball ,a clogged passage or improper adjustment.why did you replace the carb in the first place ??? Have you checked the timing and the fuel for water ?