New Carb Instal **What am I doing Wrong* 5.0 0m012817

[rick3452]

I put the new Rochester 2bl carb on this morning using a new gasket (the thicker Mercruiser gasket) not the one the carb people sent me which is more like paper thickness, and when I started it up the EXACT same thing happened when I put the new carb on two months ago.( that I sent back because I thought it was bad) It was running really rich, soot in the water. Choke was closed on start up and opened properly as it warmed up, but still smoke, and rough. At proper operating temp I ajusted the needle screws on the bottom, as there are two on the Rochester. As I gently seated each (one at a time) it made no real difference in engine. I brought them both out 1.5 turns and still runs and smokes bad.

Any ideas are very much appreciated.........Rick

ps: I am using the specified Mercruiser gaskets, and Adapter # 807726A2 which is about 1/2" thick
Is it possible that I should just be using the thin gasket that came with the carb directly on the manifold??

 

[picklenjim]

Re: New Carb Instal **What am I doing Wrong* 5.0 0m012817

Sounds like the float level is to high.

 

[RogersJetboat454]

Re: New Carb Instal **What am I doing Wrong* 5.0 0m012817

Sounds like either the float is stuck open, the float height is too high, or there is excessive fuel pressure forcing the float open.

You haven't done anything to the fuel pump at all have you? No recent tune-ups where wires may have been crossed, or timing thrown way out of whack, right?

An old mechanic's trick they taught me in reform school is to give the carb a few light taps with a hammer if you suspect a stuck float. Speaking of stuck floats, you have a fuel/water separator, right? And it has been changed/cleaned religiously, correct? May need to crack open the carb if the float height is off.

 

[Silvertip]

Re: New Carb Instal **What am I doing Wrong* 5.0 0m012817

1.5 turns on the idle mixture is not a fixed number.

1) Warm engine - choke fully open.
2) Set the idle SPEED to spec.
3) Start idle MIXTURE adjustment at 1.5 turns from lightly seated.
4) Turn one mixture screw in (clockwise) in 1/8 turn increments, pausing for 10 seconds to allow engine to respond. During this adjustment the engine may either smooth or it may begin to run worse. If it smooths, continue turning inward until the engine begins to gag or become more rough. Note the setting (angle of the slot).
5) Rotate the mixture outward (counter clockwise) until the engine begings to again gag/bog/run rough. Note that position.
6) Happiness will be somewhere between the settings noted in #4 and #5.
7) Reset the idle SPEED if necessary.
8) repeat steps 2 - 7 for the other mixture screw.
9) Reset idle SPEED if necessary.

Important: If you do not notice any change whatsoever in idle mixture settings, there is a manifold leak or some other intake system problem. Rochester 2bbl carbs are about as simple as they come but "rebuilders" can still manage to muck them up. With the flame arrestor off, look down the throttle bore at idle. You should not see fuel spewing anywhere that would cause a very rich condition.

 

[Don S]

Re: New Carb Instal **What am I doing Wrong* 5.0 0m012817

Did you adjust the idle mixture after installation?

You really need to check the fuel pump pressure. If it's to high, you can change carbs forever and it won't fix it.

 

[rick3452]

Re: New Carb Instal **What am I doing Wrong* 5.0 0m012817

Thanks for the quick resposes...... I have done nothing recently to the engine, When I took the MC Carb off it was running smooth, when I took the Rochester off and put the MC Carb back on once again smooth (I know) so why do I want the Rochester carb on there?
Supposedly its a better running carb for the 5.0.. I have not tested fuel pump pressure, and fuel water seperator just done....and yes Don I did try to adjust idle mixture after warm-up
Thanks again......

 

[rick3452]

Re: New Carb Instal **What am I doing Wrong* 5.0 0m012817

Does anyone know what the the proper float height is for this carb.......