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Old 12-17-2019, 12:40 PM   #1
Merc Cruzer
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Default Hesitation when accelerating from stop - Holly 1901 carb

The car (1953 Mercury) is an automatic - Merc-O-Matic. The car is stock, with no mods. Nothing has been changed except the setting of the float to the correct level.

In my prior post I had an issue with setting the float, of this same carb. That has now been corrected. Thank you all once again for your posts.

Now there is a new issue. When I accelerate, from a stop, the car hesitates. I have replaced the minimizer/power valve diaphragm/valve and the accelerator pump piston seal, with new ones. When the car ran rich I did not have this issue.

There is no hesitation, when accelerating at speed.

Looking for suggestions to correct the issue.

Thanks you,

Merc Cruzer
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Old 12-17-2019, 01:15 PM   #2
51 MERC-CT
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

As I recall there are 3 positions on the accel. pump.
If in the center position, move to the one farthest from the arm CL to give a longer pump shot.
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Old 12-17-2019, 01:37 PM   #3
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

My 52 has been running like that for so long I've come to accept it as normal and have just adapted my driving style. A couple of quick pumps on the accelerator when I want to take off never fails to work for me. But if I just try to hit the gas and take off, it will cut out and stall. I've tried several times adjusting the accel pump stroke but never seen any improvement.
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Old 12-17-2019, 02:14 PM   #4
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Some new accelerator pumps are to tight in the boar so the spring compresses but the cup doesn't move ,I remove the spring that is inside the cup,
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Old 12-17-2019, 02:21 PM   #5
Merc Cruzer
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Quote:
Originally Posted by 51 MERC-CT View Post
As I recall there are 3 positions on the accel. pump.
If in the center position, move to the one farthest from the arm CL to give a longer pump shot.
Mine is in the center, so it looks like I need to move it to the right, since that hole has the longest arc. (new picture attached)

RalphG, I will let you know if it correct the issue. It is going to get warmer over the next few days, so I should be able to take it out for another test run.

Worth a try.

Thanks
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Last edited by Merc Cruzer; 12-17-2019 at 03:03 PM.
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Old 12-17-2019, 03:57 PM   #6
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

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If you are still running the stock dizzy, make sure the vac advance is working properly too.
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Old 12-17-2019, 04:51 PM   #7
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Speaking of vacuum, I would check for a vacuum leak somewhere. Lots of advice on this in the archives. Remember the 3 R's; spark, fuel and vacuum.
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Old 12-17-2019, 06:39 PM   #8
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

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If you are still running the stock dizzy, make sure the vac advance is working properly too.
Thank you, considering I am at 8300 ft, the vacuum is great. Hit the throttle and the advance is immediate.

Now climbing up a hill and turn on the wipers, that is another story. Hence the reason I have the Electro-Vac, but that is another story all together.
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Old 12-17-2019, 06:54 PM   #9
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Where I've had problems with the similar 885 carbs for my 51 Mercs is with the vacuum circuit for the power valve actuator. If it has even the slightest leak, the power valve won't work right. Everywhere there is a gasket flange involved is a potential leak source. Don't you just love them high float bowl Holley carbs. When they work right they will stay that way for a long time but getting them right can be difficult to say the least.

The 885 has the vacuum circuit passing through the top shroud so getting it sealed can be a bear. The 1901 goes through the body but it's there just the same.
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Old 12-18-2019, 09:23 AM   #10
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

I am just wondering, if there was a underlying vacuum issue, would't it have been there (by way of the hesitation) when the carb was running rich? The hesitation issue only surfaced "after" I corrected the float height, it was not an issue previously.
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Old 12-18-2019, 11:56 AM   #11
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

I believe the bowl gasket forms part of the seal for the power valve actuator but I haven't worked on the 1901.
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Old 12-18-2019, 12:32 PM   #12
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

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I believe the bowl gasket forms part of the seal for the power valve actuator but I haven't worked on the 1901.
I am not sure, but here is a picture of the top of the bowl along with the minimizer valve (installed and another one beside it). It appears that the seal for the minimizer valve is formed by the rubber gasket in the top of it, along with the ring and the three screws.

FYI: The bowl is not leaking from the gasket, if that is a true test of the gasket seal.
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Last edited by Merc Cruzer; 12-18-2019 at 06:01 PM.
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Old 12-19-2019, 05:02 PM   #13
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

51 MERC-CT,

The temp was up today, to 48 degrees (almost put the top down), so I had a chance to take her out. Big difference, when leaving from a stop. The hesitation issue seems to have been resolved with the changing of the hole position on the accelerator pump arm.

Thanks again,
Roy Lange aka Merc Cruzer

Last edited by Merc Cruzer; 12-19-2019 at 07:01 PM.
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Old 12-19-2019, 08:09 PM   #14
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Merc Cruzer,


Followed this thread with great interest. Glad you got it sorted out. Thank you for posting what resolved the issue for you.
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Old 12-19-2019, 08:28 PM   #15
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Quote:
Originally Posted by RalphG View Post
My 52 has been running like that for so long I've come to accept it as normal and have just adapted my driving style. A couple of quick pumps on the accelerator when I want to take off never fails to work for me. But if I just try to hit the gas and take off, it will cut out and stall. I've tried several times adjusting the accel pump stroke but never seen any improvement.
RalphG,

With this simple adjustment to my carb and the difference it made, just a thought: you might want to replace the cup/seal at the end of the accelerator pump. My thought is that the gas is getting by the cup/seal, so no matter what adjustment you make, the issue still remains.
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Old 12-19-2019, 08:40 PM   #16
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Quote:
Originally Posted by Merc Cruzer View Post
51 MERC-CT,

The temp was up today, to 48 degrees (almost put the top down), so I had a chance to take her out. Big difference, when leaving from a stop. The hesitation issue seems to have been resolved with the changing of the hole position on the accelerator pump arm.

Thanks again,
Roy Lange aka Merc Cruzer
Glad to see it solved the problem for you.
Just for reference, the hole position you are now using is meant for cold weather conditions, the center normal and the other one for extreme hot weather (as the need arises)
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Old 12-19-2019, 09:01 PM   #17
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Quote:
Originally Posted by Merc Cruzer View Post
51 MERC-CT,

The temp was up today, to 48 degrees (almost put the top down), so I had a chance to take her out. Big difference, when leaving from a stop. The hesitation issue seems to have been resolved with the changing of the hole position on the accelerator pump arm.

Thanks again,
Roy Lange aka Merc Cruzer
I find the temperature of the engine makes a difference too. Its better when the engine is up to normal (or above) temperature. Mine has the heat riser valve in the right side exhaust manifold but I'm not sure if it actually moves much. That is supposed to help build up some heat under the carb I believe.
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Old 12-19-2019, 10:07 PM   #18
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

53MERC-CT,

Thank you for the explanation for the three holes. My book on the carb doesn't address them at all. I can see now why most cars use the center hole. Sounds like I need to get the book you use for carbs.

I have been doing the test runs, in temperatures of the 30's and 40's. It is supposed to get to the high 60's this Sunday, so I will get her out in warmer air for a run.

RalphG,

I have dual exhausts, so my original heat riser valve is gone. I do have the two heat risers on each side of the carb, but they are blocked off for summer, so the tabs need to go, until warmer weather.

It is a shame to waste the nice days and not drive it.
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Old 12-20-2019, 12:59 PM   #19
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

The heat riser for the 885 in the 1951 Mercs has the temperature operated damper in the crossover to force a bit more exhaust up through the intake manifold where the heat tube goes through there. The passages in the block can get blocked with carbon and the manifold tube can too. It takes a lot longer for the automatic choke to work if the system is restricted. It takes a around 5 to 10 minutes or so for the choke stove to warm up enough for it to fully open but that depends on the outside temps. All these old cars were a bit cold blooded.
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Old 12-20-2019, 01:59 PM   #20
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Default Re: Hesitation when accelerating from stop - Holly 1901 carb

Quote:
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RalphG,

With this simple adjustment to my carb and the difference it made, just a thought: you might want to replace the cup/seal at the end of the accelerator pump. My thought is that the gas is getting by the cup/seal, so no matter what adjustment you make, the issue still remains.
I can't remember if we replaced that part when it was apart a few years ago. Probably not. Forgot mention that mine was converted to manual choke in the 1960s. Generally less problems and better control assuming the operator understands how a manual choke works.
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