Hesitation/Stumble with the new MC2150

[cuban11182]

So I purchased my carb off the eBay guy, and although it starts and idles fine, it has hesitation when I get on it, under load. Once it recovers from the hesitation, it launches like it should. I'm reading about jets and power valves, and the accelerator pump, but I need to know where to start and what to order. It only does it when I'm driving, but when I'm sitting and reving it, it does fine.

Oh, and timing is at 10* and carb idle quality screws were adjusted with vacuum gauge. Do I need to just open up the top of the carb and see what jet size I have?

Any help is greatly appreciated.

 

[Torxhead]

I am not familiar with the mc2150, but usually an issue like you describe is due to a gap in the accelerator pump adjustment. When you mash down on the throttle, that squirt of gas is needed immediately.

 

[cuban11182]

Thanks torx. I've read the power valve has a similar effect. Going to first disassemble to see what I have .

 

[DHugg]

Thanks torx. I've read the power valve has a similar effect. Going to first disassemble to see what I have .

Interesting to me; I have a new MC2100 that does the same thing. Yesterday I noted that the accelerator pump was half-compressed all the time, engine shut down. So I pulled the connecting rod, straightened all the kinks, and have it adjusted to hold pressure on the plunger before throttle movement.

Can't test the squirt cycle; I have the cooling system open to do a rust flush, vinegar first then citric acid.

 

[cuban11182]

Thanks for the advice. My carb is new, so linkages are all straight. I did test the accel pump and saw two streams of fuel with engine off and cleaner pulled off. I did set it to the top hole and it made a little difference, but she is still falling on her face and then picking up. I was told I have either a 47 or 48 main jet and a 7.5 power valve. Since I'm pulling about 21-22 in hg I think that I need a larger power valve.

 

[Fastatv]

I am not familiar with the mc2150, but usually an issue like you describe is due to a gap in the accelerator pump adjustment. When you mash down on the throttle, that squirt of gas is needed immediately.

Try what TH has said. What u are experiencing is usually the accel pump. The linkage may be in the wrong hole.

 

[cuban11182]

Thanks for the advice. I did put the accelerator linkage in the top whole this morning. It did help, but there is still a bit of lag. The jeep accelerates when I start off, its just when I"m cruising and hit it, there is a stumble and then she picks up.

I'm new to the concept of a power valve, but to me, based on what I've read it should dump in 10 times the amount of fuel and the main when you hit WOT. If I hit WOT, she stumbles HARD and then jumps.

When I tested the accel pump with the engine off, and air cleaner off, I hit the throttle and she dumps two streams of gas. If you like, I can make a video and put it onto youtube.

 

[Torxhead]

The power valve switch sounds like something to look into, making sure the ignition timing is advancing correctly would be a good thing to know also.

 

[cuban11182]

Advance is setup to 10* after trying it at 8*. Vacuum advance is working, but since we don't go that high on the marks, I'm not sure how high, but I can see it work with the timing light.

 

[Fastatv]

Torxhead covered the timing advance. I'm wondering if maybe your getting too much pump/squirt? The accell pump has two holes on the pump diaphragm cover, but there could be two or three holes at the throttle linkage. If so, you might experiment with those, moving the linkage from hole to hole, checking results. Choke is coming all the way off right? I'm assuming its an automatic choke, not manual.

 

[cuban11182]

My arm on the pump diaphragm only has one hole. Originally the arm was in the 3rd from the bottom hole. When it put it on the top hole (hits sooner) it helped. I adjusted it to the 2nd from the bottom hole and it got worse. I can only guess that this means I'm starving for fuel, and not running rich. I tried to adjust the idle quality screws in half a turn and it got worse also (did this test independently from the first). To me this is still too little of a power valve.

 

[Fastatv]

My arm on the pump diaphragm only has one hole. Originally the arm was in the 3rd from the bottom hole. When it put it on the top hole (hits sooner) it helped. I adjusted it to the 2nd from the bottom hole and it got worse. I can only guess that this means I'm starving for fuel, and not running rich. I tried to adjust the idle quality screws in half a turn and it got worse also (did this test independently from the first). To me this is still too little of a power valve.

If you take the a/f screws in, your going leaner. Adjust them back out to max vacuum, then an additional half turn....counterclockwise that is. And, you may have a power valve issue. Just seemed unlikely to me on a new carb.

 

[cuban11182]

I'll take care of that tomorrow.

Doesn't the power valve need to be specific to the vacuum if the individual engine?

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[Bent]

You have the 1.08 venturie size? I only ask because that kind of stumble can be caused by a carb that is too big also. I think the 2150 was only made with the 1.08 and 1.21 venturie size.
It still sounds like a accelerator pump issue though. Just because it's new doesn't mean the accelerator pump diaphragm didn't dry up while it sat on the shelf.
Does that have a two stage power valve?

 

[cuban11182]

I can only assume that they are the 1.08 that everyone else buys from him. Can you tell me where I can find the venturi cluster number plate/stamp?

It is a single stage Walker 7.5.

It's 1am here, but I thought a video would show it better, but I think my acelerator is working fine
https://www.youtube.com/watch?v=-iRXW5eosL0

Here is a quick video from Holly describing how you size your power valve. https://www.youtube.com/watch?v=mE_xTUXQJQ8
It states that you take your reading at idle, and half that to determine the size of powervalve needed. Mine currently has a 7.5, but draws in 21 in HG (well it did before I messed with the idle quality screws :-D). So to me I need a 10.5.

Ok back to sleep. Thanks for all the advice so far guys. Keep it coming.

 

[Bent]

I can only assume that they are the 1.08 that everyone else buys from him. Can you tell me where I can find the venturi cluster number plate/stamp?

It is a single stage Walker 7.5.

It's 1am here, but I thought a video would show it better, but I think my acelerator is working fine
https://www.youtube.com/watch?v=-iRXW5eosL0

Here is a quick video from Holly describing how you size your power valve. https://www.youtube.com/watch?v=mE_xTUXQJQ8
It states that you take your reading at idle, and half that to determine the size of powervalve needed. Mine currently has a 7.5, but draws in 21 in HG (well it did before I messed with the idle quality screws :-D). So to me I need a 10.5.

Ok back to sleep. Thanks for all the advice so far guys. Keep it coming.

The venturie size will be cast into the drivers side of the of the fuel bowl. Behind the accelerator pump linkage rod there will be a circle with 1.08 or 1.21 cast into it. That is your venturie size.

 

[cuban11182]

I didn't see that on mine. Is there a picture of where it us supposed to be located?

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[cuban11182]

The eBay guy told me that it came with a 47 and 48 but instead when I opened them up they are both 49s!! I contacted him via email and text and we will see how he responds. I was expected a simple bolt on, but I'm having to troubleshoot his kit, which is making me frustrated.

 

[DHugg]

The eBay guy told me that it came with a 47 and 48 but instead when I opened them up they are both 49s!! I contacted him via email and text and we will see how he responds. I was expected a simple bolt on, but I'm having to troubleshoot his kit, which is making me frustrated.

The MC2100 I ran on the AMC 304 in my CJ7 had 44's. I bought a new one, not a reman, and don't yet know what size in it. But to answer your earlier question, the late-manufactor body of the MC2100 just purchased doesn't have the venturi stamp. The paperwork says 1.08, just like the older one I replaced. Replacement needed because the last guy to overhaul the MC2100 put too long a screw into one corner of the accel pump cover, then gorilla'ed the screw through the aluminum side of the float bowl. Every time I'd turn a corner, the aluminum fragments would reposition themselves and some get into the float needle valve, changing the fuel feed rate, always for the worse, never better!

 

[cuban11182]

So I'm guessing that you ordered a replacement carb for your AMC 304 ? I've been trying to see what the part number is in case I have to order one myself and build the kit. I have no problem paying someone extra for a pre-made kit that works. If it doesn't work, then I'm not willing to pay extra.