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need help troubleshooting mc 2150

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SteveP
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need help troubleshooting mc 2150

Post #1 by SteveP » Thu Mar 21, 2019 3:59 pm

I read that the mc 2150 carb with variable air bleeds is a better carb than the ones with fixed air bleeds so I got one to try out.
It's been giving me fits trying to get it to run right. On the highway it's great but when I stop it usually wants to die. Sometimes it will keep running. I have to feather the throttle until I get moving again, and then it will usually stumble and bog until I get rolling good.
Today I took it apart and checked everything over, checked the float setting, blew out the passages with air and carefully made sure all the adjustments are right.
I cranked the motor up with the air filter off and was looking everything over good and I noticed the the venturis have fuel dripping from them at idle, the left more than the right.
I didn't think they were supposed to do this. Am I correct in this? If so, what can cause it?

sdiesel
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Re: need help troubleshooting mc 2150

Post #2 by sdiesel » Thu Mar 21, 2019 5:27 pm

yes your floats are set too high, or your fuel pressure is overriding the float needle. the extra gas is generally directed to the venturi.
fuel pressure is often a sneaky culprit to lots of carburetor sins. and its equally as often overlooked.
generally when you have a factor installed fuel pump for that carb you will have no pressure problems.
a long love affair with the 300 six.
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SteveP
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Re: need help troubleshooting mc 2150

Post #3 by SteveP » Thu Mar 21, 2019 5:45 pm

I'm running a stock engine driven pump.
The float is set at 1/2" below the top of the fuel bowl.

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THE FRENCHTOWN FLYER
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Re: need help troubleshooting mc 2150

Post #4 by THE FRENCHTOWN FLYER » Thu Mar 21, 2019 6:39 pm

You can run the engine with the top of the carb off. Watch the fuel level to make sure it is stable and does not creep up. Note the level at which booster flow initiates. Be careful - keep an extinguisher handy.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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MechRick
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Re: need help troubleshooting mc 2150

Post #5 by MechRick » Thu Mar 21, 2019 9:52 pm

If one booster dribbles fuel before the other, double check the air bleeds for restrictions.

If the idle speed is set too high, fuel can dribble from the boosters, but both equally.
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THE FRENCHTOWN FLYER
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Re: need help troubleshooting mc 2150

Post #6 by THE FRENCHTOWN FLYER » Thu Mar 21, 2019 10:23 pm

Also check both throttle plates to make sure both are closed completely at exactly the same degree. Requires carb removal and retracting the curb idle screw. Maybe at some point in the carb's life the throttle shaft froze and somebody twisted it to the point of damage to the shaft.
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SteveP
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Re: need help troubleshooting mc 2150

Post #7 by SteveP » Sat Mar 23, 2019 7:55 pm

I was finally able to work on my carb again so here's an update.
I failed to mention in my OP that when I had the carb apart I found that the jets were mismatched. One jet was a 50F and the other was a 50, and it was slightly distorted from being overtightened. I replaced it with a 50F jet. At the time of my post I hadn't driven the truck yet, having only run it at idle and finding the fuel dripping from the boosters.
Later I drove it into town and the difference was like night and day. It idled well and seemed to have a little more pep, though still with some stumbling on takeoff.
Today I reset the float, lowering it about 1/8", and blew out the air bleed passages again, and when I test drove it I was surprised at the difference. It really runs great now with a good idle, plenty of power, and no stumbling or hesitation. It still has a little bit of drip from one booster but it runs so well I'm going to leave it alone.

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old28racer
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Re: need help troubleshooting mc 2150

Post #8 by old28racer » Sat Mar 23, 2019 10:31 pm

Well as you have made three changes to the carb it is a little hard telling witch one was the problem. Do you think that the Air Bleeds Passages being plugged might be #1, Float level to high #2 & mismatched jets #3? Glad you got it running good again.
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SteveP
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Re: need help troubleshooting mc 2150

Post #9 by SteveP » Sun Mar 24, 2019 8:38 am

I think the mismatched jets was the main problem with the float setting making it worse. I'm not sure the bleed passages were contributing to the problem at all.

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THE FRENCHTOWN FLYER
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Re: need help troubleshooting mc 2150

Post #10 by THE FRENCHTOWN FLYER » Sun Mar 24, 2019 12:19 pm

Generally speaking changing the main jet size has very little effect on f/a ratios at idle; on a 2150 only about 2% per jet size. In ancient times we used to change part throttle fuel/air ratios on dyno testing by attaching a regulated vacuum pump to the bowl vent and by varying the amount of vacuum above the bowl we varied the f/a ratio. I think maybe the fuel level in the bowl would be my guess. It would be an interesting experiment to vary the fuel inlet pressure with the carb top off and observe the fuel level - both with the engine off and running. With the engine off it would be interesting to observe the fuel level versus time at various pressures to see if the inlet needle is leaking. When they start leaking on my multi-carbed race intakes the first indication I have is the idle goes rich. At WOT, no problem if they leak.

I'd change the needle and seat.
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SteveP
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Re: need help troubleshooting mc 2150

Post #11 by SteveP » Sun Mar 24, 2019 1:03 pm

FTF,
I don't have any way to accurately measure the hole in the jets so I don't know if there's a difference. They have the same # so I assume they're the same. There is a difference though. The 50 jet is flat on the bottom and the 50F jet is not.

download/file.php?mode=view&id=3435

I don't know how this would affect how the carb runs but it seems to.
The needle and seat is new but, like any other part, a new one can be bad so on your advice I'm going to replace it. It's cheap and it can't hurt. Thanks.
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THE FRENCHTOWN FLYER
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Re: need help troubleshooting mc 2150

Post #12 by THE FRENCHTOWN FLYER » Sun Mar 24, 2019 1:16 pm

Anther experiment you might try:

Replace the original jets in the carb - only this time reverse their positions.
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SteveP
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Re: need help troubleshooting mc 2150

Post #13 by SteveP » Sun Mar 24, 2019 10:19 pm

Funny you should mention that. I was thinking of doing just that when I change the needle and seat.

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