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Index > Engine/Drivetrain > Thread: Hesitation/miss with throttle application
Thread: Hesitation/miss with throttle application
Jeremiah


Revvin Up
Posts: 56
posted January 25, 2009 08:43 PM

Hesitation/miss with throttle application

This is my first posting. I have had my pickup since the end of summer and it has ran great up to now. About 2 weeks ago I noticed at full throttle application in any gear at about 6000rpm I would get a little blip/miss or 2 in my acceleration. It only did that like I said at full throttle, so I quit doing that. I used my truck to do some moving and in the process I had the problem get alot worse. It starts and idles great. When its cold I can drive it around the block just fine as long as I give it no more that 1/2 throttle. When the engine is up to temp I can hardly drive it. At anymore than very light throttle opening it sounds like its allmost detinating, the engine refuses to accelerate, and I have to floor it to get it "past" this point and then it lacks power, misses and generally gives you this very jerkey feel. I have replaced the plugs, checked and adjusted the timing and have tried different fuels. I have noticed the sight glass on the float bowl shows a fuel level slightly under the 1/2 way mark but I dont see how this could affect it unless the fuel level was lower. The engine is all stock, exept for a header. thanks in advance

       
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Klaus45


Redlining
On two wheels
Posts: 218
posted January 26, 2009 09:17 AM

Fuel delivery, and/or...

...possible vacuum leak (?)

I'd check/replace the fuel filter(s), (including cleaning out the two little cylindrical fuel screens inside the top of your carb., if you're running the stock Hitachi). That is, if your pickup tube in the tank/fuel line are not impaired by any rust flakes, etc. getting sucked in... If things aren't spotless inside your carb., it would probably benefit from a full, proper cleaning and rebuild, as well. Another thing to check is the output volume/delivery pressure of your fuel pump -- very important! Starvation under full throttle is pretty common...

If it's not any of the above, (and even if it is), it's a good idea to periodically go over each and every fitting/blocked off port/etc. that could possibly allow for any vacuum leak on the intake side... these are also a pretty common problem, as caps and hoses get hard and brittle with age...

Hope that info. helped!

       
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Jeremiah


Revvin Up
Posts: 56
posted January 26, 2009 09:50 AM

Thankyou for the help. It is the stock carb. I have checked the furl pump and it pumps great, I can hardly hold my thumb over it. I purchaced a rebuild kit for the carb but have been wondering if I can tackle the task by myself. I have also gotten a racing beat intake manifold and was wondering if I should just go ahead and replace the carburetor with a holley or demon, since those are so easy to tune etc. Thanks for the help, I will inspect it all today.

       
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Klaus45


Redlining
On two wheels
Posts: 218
posted January 26, 2009 11:33 AM

You're welcome, Jeremiah!

It might be prudent to get everything worked out/dialed in before any further modifications; wouldn't want to change things up only to find out that the original issue was still there...

       
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Klaus45


Redlining
On two wheels
Posts: 218
posted February 04, 2009 10:00 AM

Hey, Jeremiah --

Here's where every bit of the documentation I have on the hitachi carb. is available in the Gallery, (thanks, Brad!):

http://mazdarepu.com/Gallery/index.php3?album=Hitachi+Carburetor+4bbl+for+REPU&photo=uploads/Hitachi1.jpg

Hope it helps! ;)

       
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jeremiah


Revvin Up
Posts: 56
posted February 07, 2009 10:25 PM

Hesitation

I rebuilt the carb and it works great! It took care of my problem, although all I think it really needed was a float adjustment. Thanks for all the help, its now on the way to perfection...

       
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Klaus45


Redlining
On two wheels
Posts: 218
posted February 08, 2009 11:08 AM

Cool!

Glad it worked out so well!

       
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