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1985 carb identification

mark_searay

Contributing Member
"Hello,
Boat: 1985 Sea Ray SR


"Hello,
Boat: 1985 Sea Ray SRV255, twin 170's.

After two years of hard "resurrection" work, we are into the fine tuning stage and many thanks to the members here for help. I’m starting to work on better idle performance and starting, while it is now “good”, dependability in tight situations needs improvement. i.e. low idle, hot, tight busy docking maneuvering where it doesn’t die.

I know the carbs have not been touched since 1993 and probably not ever. First question is proper identification, the only numbers on the carbs (2-barrel) is a tag that is stamped MCM 170/470, 1389-8489; stamped on the side of the float bowl: 13898498 & 4703. There is NO manufacture’s casting mark.

Any source for a manual on these? And what should one expect to pay for a rebuild done by a reputable shop? This is not something I want to do myself if needed. I’ll discuss symptoms in a future post. (rebuild might not be needed)

Thanks in advance."
 
I had the same problem with th

I had the same problem with the same carb. It would start and run no problem but coming into the dock after running it a while it would die on me unless I kept the idle up a bit. Not easy manuevering. I spent an hour one when I was by myself and set the carb's air mixture to fairly lean and I don't have the problem nearly as much but every once in a while on a hot day. Maybe Guy's suggestion of a thicker base gasket might help. I may try it and report back when the weather gets warmer here. It snowed the other day so I don't anticipate getting out for a few more months.
 
PS:

If it's a Mercarb t


PS:

If it's a Mercarb then it will make a big difference especially setting the mixture. BTDT!
 
"Thanks Guy. Found the manual

"Thanks Guy. Found the manual portion through Bondo’s link on the 2B Mercarb also thanks on the rebuild suggestion.

I’ve got it back starting much better as opposed to “not” (electronic, matching coil, 8 deg timing, idle is 700+ in gear etc..) Chokes don’t shut much at all, which is a known issue but cold starting is not the problem, couple of pumps and she generally lights right up. The BIG problem is as you state, Puget, is after running and its hot it will die at idle at only the most in-opportune times unless you run above idle or shift to neutral and do an occasional blip-run up to keep her going.

If you replace the base gasket to the thicker version, other than what the Merc manual states as adjustment are there some other techniques to you have used get the mixture dialed back in?

Guy, any thoughts on good setting technique. It’s been two years on the fuel filters and that is on the list during de-winterization here in about 2-3 weeks. Is there a PN on this site that is the optional thick base gasket version?

Boat is getting new upholstery now, so maybe she'll "feel better" this seasson.
Thanks, Mark"
 
"Mark:

You need to get the


"Mark:

You need to get the choke working properly. It may just be worn out or lost voltage. The choke should close to 1/8" when cold. Check and set the timing if needed.

Adjusting the mixture: Using only your fingers, start out by turning the screw in CW until you start to feel resistance; now back it out 1.25 turns. After the engine reaches operating temp, SLOWLY turn the mixture screw CW again until the engine starts to stumble--make a mental note of the screw position. Now turn the screw out CCW past the beginning point until it stumbles again; compare this point with the other stumble point and turn the screw CW to the middle of the two points. Repeat as needed."
 
"This is my typical choke acti

"This is my typical choke activity, boat is used April through October averaging 3X per month on weekends, no use during the week. Idle is about 720+ in gear, warm (bit higher than I would like but necessary for semi-dependable close quarter docking without dying)

Starboard starting requires 2 pumps of throttle, return to idle and starts after 1-3 seconds of cranking.
Port requires 2 pumps / leave the throttle open and starts after 1-2 seconds of cranking with an immediate pull back on the throttle to keep rpm <1500 (hard to do and I am most uncomfortable with).

Sometimes starboard, if it doesn’t fire, requires the open throttle trick. Sometimes both engines will fire for 1-2 seconds, run through the accelerator pump shot and die, second start try succeeds. Will almost never restart without this sequence unless it is <5 minutes from shut down. Engines run smooth full range, max rpm: 4200

Typical Choke activity is: (voltage measured at choke) starting temp range is 60-95 F.
Key OFF, choke plane is always OPEN & will not move with light to firm finger pressure
Key ON, volts are: Star: 8.6; Port: 9.3, choke plane will not move with light to firm finger pressure
Key ON, NO throttle pumps, crank engine – NO start: choke plane does NOT move but will move with light to firm finger pressure. Volts are: Star: 9.2; Port: 9.4
Key ON, 2 throttle pumps, WOT – starts: choke plane does NOT move but will now move with light to firm finger pressure. (closing choke plane with finger pressure to proper closed position will stall engine)

Volts after start are: Star: 12.3; Port: 12.1,
Running voltage is: Star: 14.3; Port: 14.3,
Purple wires at choke are warm to touch.

when I got the boat it was apparent the choke springs covers had been off as they were missing screws and loose, I doubt the springs are engaging properly.

Thanks, Mark"
 
"Mark:

After reading your c


"Mark:

After reading your choke data, it seems that you need both chokes readjusted or better to replace them. You mmust be running a points ignition on each engine since the voltage to the chokes is taken from the resistance wires. These engines most likely came w/stovepipe chokes that used manifold exhaust heat to open them. Someone upgraded them to electric chokes. BUT, they did not use a 12 volt source.

Place the shifter in the neutral position. Remove the choke 9 volt wires and tape them up securely. Find a 12 volt purple wire source on the engine that is on w/the key in the run position. The opposite end of the resistance wire to the choke will be 12 volts. Disconnect the battery and connect the new wire to each choke w/a 16 ga. wire.

W/a cold engine, disconnect the throttle cable and loosen the screws on the choke cover plate. Now move the throttle on the carb to set the choke to the start position. Next turn the choke cover plate slowly in either direction until the choke plate closes all the way; now open it 1/8" by turning the cover plate in the opposite direction and tighten the screws. Set the mixture screw w/your fingers all the way CW until it meets resistance and back it out to 1.25 turns. After a few minutes of running turn the mixture screw in SLOWLY until the engine stumbles and note the screw position. Now turn the screw CCW outward past the beginning point until it stumbles again. Compare that screw position with the first stumble and set the screw between the two points. Repeat for the other engine.

Now start one engine using the throttle linkage to first prime the carb w/2 short pumps. While it is running watch to see if the choke plate opens. If it doesn't, replace the choke as long as you have 12 volts to it while the engine is running.

Repeat for the other engine. Reconnect the throttle linkages. After the engines are warmed to operating temp you can adjust the idle speed to specs w/the boat securely tied to the dock and the OD in forward gear; about 650 RPMs."
 
"Hello,
I converted to Petron


"Hello,
I converted to Petronix ignition, rotor cap, wires, plugs, matched coil on both two years ago and single wire alternator on starboard one year ago.

Attach nuts don't show much evidence of ever being turned. Have all the orginal paperwork, manuals and maintenance manuals all indicate boat came with electric chokes, would have had to been converted prior to '93. Don't know what to look for on stove pipe evidence.

Does that change your recommendation any?

Thanks !!

(see photos)
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YES! That carb is a Mercarb 2

YES! That carb is a Mercarb 2 BBL and it's an old one at that; 3 piece hsg. Try oiling the shaft ends of the choke and the linkage pivot points so all will move. If the choke housing does not get warm to touch then its heater is open and the choke needs replaced--I would replace it due to its age by looking at it w/the plate standing straight up. The base gasket is too thin; replace it w/a 1/4" thick one. Don't change any wiring but do clean dirty or corroded connections. Have your battery load tested; may have a weak cell and part of the poor start problem and clean all 4 battery cable ends. If it is near 3 years old; replace it. Your ignition choke should have 12 volts w/the switch in the on position and you don't. That is the purple wire. The pink wire is the resistor wire. It's wired right. You need a choke and a thick base gasket.
 
"Hello,

I'll chase down


"Hello,

I'll chase down the volt drop problem.
That would seem to address the starting issue, but it really starts fairly well all things considered. The big issue is stalling when hot at idle in tight/breezy docking quarters.

Is the idle mixture and base gasket improvement the prime items that will address that?

Or is there so much wrong its just rebuild time?
Thanks."
 
"Is the idle mixture and b

"Is the idle mixture and base gasket improvement the prime items that will address that?"

Yes and include the choke.
 
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