So Close!! Not 100% yet...help!

[pismorat]

I have had my 500hp 383 full roller stroker motor in my truck for a little over a year and haven't really driven it much...some of you have seen it. The issue is that it stutters off the line, or if I power brake it, it stumbles at first. But once this thing gets going and it catches up to itself it takes off! I am thinking its a distributor issue. I don't know if it would be too advanced or retarded or if the weights are too heavy or what. Can anyone give me some help? I am starting to drive it more and an wanting to get it right for once. I am pretty sure the carb is set up right, the timing is just where I'm looking now.

 

[Chevy305]

I will tell you right now I will put $$ on that it is carb issue, more specifically the accelerator pump or the pump cam.

If the carb is a Holley then when it transitions from the idle circuits to the primary circuits it needs a small sqirt of fuel to smooth out the transition to prevent bogging down.

To fix this problem you can get a larger accelerator pump cam to deliver the squirt earier or you can get a bigger pump itself. Most of the time the accelerator pump cam needs to be larger.

 

[Hogback Fabrication]

Yeah, we need more information.

But if he can power break it, its probably not the accelerator pump and (IMO) just general carb tuning.

 

[pismorat]

It has an Edelbrock 750. The accelorator pump is working. I checked it and it squirts gas into the carb as expected. When there is no load the thing will rev up fine, but with a load it is stumbling until about 2k rpm, and once it hits like 3k rpm it will go to 6k without a hesitation. Then at a shift it has a tiny hesitation, but it will keep going strong. I had the distributor worked by a friend who worked at a dynoshop a year ago, so I don't know if he over estimated it or what may have happened. What's an easy way to diagnose it?

 

[original balzer]

Could your dist. be 1 tooth off? or 180* out i have seen people tune and tune till a 180* out dist. seams to run fine but cant ever get it just right but 1 tooth off sounds more probable. Where is your cam timeing set? also check your vaccume lines got the vac advance on the correct vac port on the carb? any vac. leaks? and personaly i didnt like edel. carbs Unless its the Q-jet, mine had a bad dead spot i never could get rid of. same with the carter AFB carbs. check to make sure all your carb linkages clear your air cleaner. Just a bunch of stuff to consiter without knowing the whole story

Balzer

 

[pauly383]

Most drag race guys add more fuel to it to overcome the bog , as stated above .

 

[Chevy305]

It has an Edelbrock 750. The accelorator pump is working. I checked it and it squirts gas into the carb as expected. When there is no load the thing will rev up fine, but with a load it is stumbling until about 2k rpm, and once it hits like 3k rpm it will go to 6k without a hesitation. Then at a shift it has a tiny hesitation, but it will keep going strong. I had the distributor worked by a friend who worked at a dynoshop a year ago, so I don't know if he over estimated it or what may have happened. What's an easy way to diagnose it?

Well Edelbrock carbs are uncharted terratory for me, but I can tell you that something is out of adjustment on the carb.

According to my Holley carb liturature, it says that the hesitation and bogging that you get can caused by: idle mixture, idle passages (dirty or clogged), metering jets, primary needle/seat malfunctioning, float level, accelerator pump passages (dirty or clogged), secondary linkage binding, or venturies are dirty or loose.

Not all of these will be the problem but, I really think that the accelerator pump is too small for your application. Trucks are a lot heavier than cars therefor are consistantly loaded heavier and need that little extra bit of fuel right off idle to start moving smoothly.

But before you go tearing down the carb to put in a bigger accelerator pump, I also highly recomend looking at your float level because the float level esentially controls the fuel curve. It could easily be possible that the floats are off slightly giving you more fuel in the upper RPM range.

Was the carb new when you installed a year ago? Has the engine sat for any period of time?

 

[pismorat]

I bought this engine from a guy who totalled his truck just after putting the engine in it. The thing sat for about a year and a half or so outside under a tarp in the mountains (sun & snow). I was curious about the carb as well, it just seemed to work properly and such. I might tweak the timing to try and see if I can make a difference...but then I will go into the carb. What's it take to put a larger accelorator pump in an Edelbrock 750?

 

[Chevy305]

I bought this engine from a guy who totalled his truck just after putting the engine in it. The thing sat for about a year and a half or so outside under a tarp in the mountains (sun & snow). I was curious about the carb as well, it just seemed to work properly and such. I might tweak the timing to try and see if I can make a difference...but then I will go into the carb. What's it take to put a larger accelorator pump in an Edelbrock 750?

If the engine sat for that long I can promise you that there is some at least some varnish, dirt, or other crap probably restricting passages that is most likely the root cause of your bogging and hesitation.