rough idle in gear merc 200 CARB.

[xs03mich]

Thought I might ask it here...03 merc. 200 CARB. with appox 10 hours. Problem is cold idle is appox 750 rpms. seems to idle fine then put it into gear it will soon stall out as rpms go to around 500-600 rpms. At this point you need to feather the gas to leave the ramp. Next go out on the water no problems it will hammer, heat the motor up then stop and idle goes higher appox. 1200-1400 rpms. you have to jam it into gear and it runs at 750 rpms. As you set in the water with out running the motor 15 mins. or so as it cools down, start it back up rough idle again. This is happens like clockwork with the rough idle. Seems to run fine otherwise. Maybe bad coil??? Maybe fuel??? Linkage seems to be fine. Any other ideas. Thanks in advance.

 

[merc2five]

Open up the exhaust above the waterline. That was what finally was the majic cure on the carb mota I had. It never idled worth a c#$% from the day it was new. Dwayne Roberie opened it up just above the waterline & never had another problem with that again.
It was loud though, but I like loud.

 

[79allison]

How much it run $$$ to open a merc up. old 200hp that is

 

[hack02]

79; go to S&F and do a search on open exhaust in the tech section. Alot of information over there.

 

[Yellowallison]

Sounds like yu might have some CHIT in yur carbs!!

I rebuild a set of carbs on a 150 XR-4 last week doing the same thing and fixed it..


Buy a can of Merc POWER TUNE and spray it in tha front of yur carbs.. Let it set for while.. crank motor.. repeat this once or twice.. also might try buy merc POWER Kleen and riunning through yur gas..

it works good also! Just a thought!

 

[79allison]

Thanks hack

 

[brotherxb03]

It could also be your primary timing which is your idle speed control because those mota's are designed to idle withe the butterflies closed. It is controlled by a screw on the arm on the side of the mota.Be carefull you get the wright screw if you fool with it cause the other one is for your your max spark advance timing.

 

[xs03mich]

Thanks for the help. A freind with a new 150 merc carb was having problems also. He suggested to order merc service manual. I have ordered it. It does seem most people think butterfly/ carb related. I will use the service manual and the power tune, plus go through the motor and check all the carb settings. I understand in the service manual there is a section after the break in period to do more adjustments, ie. carb..oil inject..timing. I should have the manual this week and will try to knock it out. I will post the news. Thanks again for the suggestions. Everyones suggestions are a great help. Greg.

 

[xs03mich]

Well it seems after talking with mercury and using a thru the hub prop for the exhaust that my problem is with the exhaust flow out of the prop area of the motor. So the winner with the correct suggestion is merc2five....open up the exhuast chest. That should work for me also....but still not happy with the erratic idle it still has. Thanks again for the suggestions. Greg.

 

[jimih280]

idle

opening your exhaust chest won't help your idle and will hurt your low end torque. your engine is in a semi flooded condition when idleing. at low rpm the fuel charge doesn't have enough velocity to open the reeds. it collapses in front of the reeds and puddles. the bleed hoses take the puddled gas and dump it directly into the cylinders. gas must be atomized to burn properly in a combustion engine so this liquid fuel just creates a flooded condition. until the engine eliminates this excess fuel, it has a rough idle and low power during initial acceleration. any prop that ventilates the blades enableing them to spin easier during initial acceleration will allow the engine to rid itself of this excess fuel. don't let your engine idle below 1000 rpms for long periods and the gas puddles won't build up.

 

[accortojim]

Hey Greg

Last we talked the boat was going in to dealer... is that their response after checking it out..

Also you aren't putting her away for the season yet are ya.
Went fishing on Pontiac Lake last Sunday evening. Didnt do to bad.

Not sure where this weekend.

Jim

 

[xs03mich]

Yes boat went to dealer...mercury said it was a prop problem as the exhaust leaves the prop area. Put on a mercruiser 23 pitch and it idles great in gear. Move up to the chopper a little bit worse. Then the new prop much worse. The tech is going to meet me at the lake next week....still haveing the rpms to high after engine blasts out on the lake...as it cools down rpms drop. A couple of other issuses, but I am finding out they maybe merc carb characteristics, my 2.4 just ran better. I will try to find a happy meduim...but may have to trade it in for something else. Went to hardy pond last sat what a blast. Although 8 hrs driving for 6 hours boating not so good, but hey lots of go fast out on the water.

 

[brotherxb03]

The carb motor are designed to idle with the butterfly's closed and the idle timing controlls the idle speed.