Hesitation from a stop
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Senior User
Joined: May 2009
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From: Chicago
Hesitation from a stop
<TABLE cellSpacing=0 cellPadding=0 width="100%"><TBODY><TR><TD class=smalltxt vAlign=top>I got and installed the MSD dizzy and man what a difference. It starts right up with no problem and idles right around perfect. I set the timing with the vacuum and idle with the vacuum advance disconnected and plugged. When I took it for a drive it ran great with snappy accelleration, except from a start it hesitates just a little. If I start out really slow and give it plenty of gas before starting up then I am fine but if I try to accelerate too quickly it bogs. This would be fine but I am afraid that some day I will go to turn out on to a street and hesitate and put myself in a bad situation. The carb has new accelerator pump that is gapped correctly, and a new power valve. I pulled it into the garage and when I give it gas I can hear the air suck in when it hesitates. Any ideas? Oh it is a '58 f100 292 with a holley 2300, msd dizzy, flamethrower III coil, new plug wires and plugs. </TD></TR></TBODY></TABLE>
Posting Guru
Joined: Jun 1999
Posts: 2,415
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From: Comox Valley, Canada
Could it be that the accelerator pump isn't giving a quick enough of a squirt? Try and change the the linkage to another hole on the arm to make the arm shorter to give a quicker response time to the accelerator pump......... or maybe the arm has too be longer to give a larger squirt by driving the pump farther........ or I may be out in left field again 
I can't remeber if the Holley uses adjustable arms or if you bend them to increase/decrease the distance....... sucks to have an old "rememberer"
I can't remeber if the Holley uses adjustable arms or if you bend them to increase/decrease the distance....... sucks to have an old "rememberer"
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Senior User
Joined: May 2009
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From: Chicago
yes I had this problem before the timing but it was any time I hit the gas hard. Now it is just off of idle.
I will look at the accelerator pump linkage, I believe that I already shortened the arm to give it quicker but may have the gap to far so that it isnt getting the full stroke. Will look at the pump linkage on friday.
Thanks
I will look at the accelerator pump linkage, I believe that I already shortened the arm to give it quicker but may have the gap to far so that it isnt getting the full stroke. Will look at the pump linkage on friday.
Thanks
Post Fiend
Joined: Mar 2007
Posts: 5,776
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From: springfield il
blown power valve , or maybe the pump isn't giving a big enough shot off the line /under quick acceleration to feed it . that's the only two things that are coming to my mind . i'm afraid as of late i'd have to agree with the statement about holley's . have not had much luck with 'em on street useage . racing , wide open can't find a better but other than that well ........ i had a 780 holley on my 70 bird as well as a750 and ended up putting in a what everyone thought was an extremely large pump , 50cc i wanna say , dont 'member , to keep that 429 cj from falling on it's behind off the line . it also only had to just sneeze a little and even with the check ball kit to keep it from happening , it would take out the power valve and it's have a huge hole under acceleration and off idle . i'd really be suspect of it first . just my 2 cents .
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From: Chicago
I am thinking it is the accelerator pump at this point. The power valve is new with a new check valve and when I screw in the idle screws it still dies (usually if the power valve is blown it wont die). I just dont have the money to get a new carb so I will be working on this until I fix it. Thanks for the advice, will start with the pump and see what happens.
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Elder User
Joined: Jun 2008
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From: N E Ohio
It is hard to see with the carb on the engine, but check the accelerator pump cam. It is a small plastic cam on the throttle lever that the accelerator pump link rides on. It could be loose, as it is held on with one small screw. It has two possible positions, you may want to try the other position. The problem could also be too much of a shot too early.
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Senior User
Joined: May 2009
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From: Chicago
getting gas too soon will cause it to hesitate? I thought this was a case of not getting enough gas? I will put the plastic cam on the list and I know about the two settings and will try the other one but I believe when I first had this problem I tried switching it with no success. "Usually", does bogging off the line come from too much gas too soon, or not enough gas right away?
Fleet Owner
Joined: Jul 2004
Posts: 27,291
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From: NM
Did you use the MSD with the vacuum can it came with? If it is like their flathead "ready to run" dizzies, it is a can with an advance range that is appropriate for a Chevy small block. It produces a lot of advance. Try disconnecting the vacuum line and plugging it, see if the problem disappears. If it does, you need an Accel adjustable vacuum advance can ($20+/-). Did you put in the proper mechanical advance springs?
They are anything BUT ready to run in reality.
They are anything BUT ready to run in reality.
Senior User
Joined: Jun 2007
Posts: 394
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From: Springfield, Il
First check the gasket under the carb. sometimes you have to use two of them. most of the time you can let the engine run and take your finger around the bottom of the carb and feel around for suction and also you maybe able to hear a high pitch sound change when you have your finger over a vacuum leak. good luck.
Posting Guru
Joined: Aug 2000
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From: S.C.
Don't know if this will help but I had the same problem with my 302 a mechanic friend looked at it and said the dist. was 180 degrees off he took it out and put it back in and that solved the problem. Before it started and ran fine just hesitated on acceleration.
Cargo Master
Joined: Apr 2007
Posts: 2,063
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From: Valley Center, California
getting gas too soon will cause it to hesitate? I thought this was a case of not getting enough gas? I will put the plastic cam on the list and I know about the two settings and will try the other one but I believe when I first had this problem I tried switching it with no success. "Usually", does bogging off the line come from too much gas too soon, or not enough gas right away?
Given you don't have a vacuum leak or some mechanical issue...... Is there any improvement or change when the pump is adjusted at the extremes ? That may point you in the right direction.
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From: Chicago
So, I was going to start working on the truck and systematicly go through the suggestions I got here, the y-blockforever.com guys, and a great carb site I found. One of them suggested starting by making sure I have the carb tuned correctly with max vacuum from the idle mixture at idle speed. So I did that and bam the problem was solved. So how I had the screws out different amounts, and by a lot. The one was set correctly but the other was like a full turn and a half to far out. I have no idea how I messed it up that much but it is fixed and man does it run nice. I can jam the gas any time I want and instant power. I used the timing suggested on Timmy's Y-block page (http://m571.com/yblock/index.htm) and I couldnt agree with him more on the tuning of the dizzy. I used his exact numbers and again the engine runs like a champ. Thanks all.