Holley 650dp, hickups when secondaries open

[85_SS_302_Coupe]

I can't seem to find the culprit here. I've tried different pump cams but that doesn't really change anything. When i'm driving normal it's fine but if i come off the line WOT it'll pull hard for a split second and sort of hesitate and then rip like normal. Could this be a jetting issue or something else? It's a 650dp with mechanical secondaries and i have the secondary rod adjusted just so that the secondaries are all the way open at WOT. It only does it on the way to WOT...if i get out and drop the clutch and mat it, everything is ok while it's at WOT, it's just getting there that it hickups a little.

[mustangboy]

I wouldn't adjust too much until you get the fuel pump swapped and the pressure down where it should be. Once you get that in check then you can start tweaking the carb.

[85_SS_302_Coupe]

Oh....this is actually MY car i'm working on for a change :lol:

So, this is the proper setup, mechanical pump and all that.

[MFIELD]

What gear are you running, what squirters are in it?

[85_SS_302_Coupe]

3.73s and the squirters are stock, so whatever comes in a stock 650 4150. I do think it needs jetting up a tad but it's not super lean or anything.

[MFIELD]

I had a very similar problem with mine a while ago. I ended up putting a bigger squirter nozzle in the rear, I believe I went to a 33 but that was long ago. You might want to try it, there cheap and easy to do. Hope it works out for you. Also I wouldnt just go changing jets right away, I used the ones that came in mine with alot of diferent changes and it worked fine. If you now anyone with a wideband see if you can borrow it and tune it in that way or go to Cincy Speed and have Craig put it on the dyno with the wideband. It should only take a few pulls to get it right and then you know what you got.

[85_SS_302_Coupe]

Yeah i wanted to put it on the dyno but funds are pretty tight right now. I've had a couple other people say to up the rear squirter so i may try that. I've played with the pump cams on the front....should i try changing out the rear and see if that helps?

[MFIELD]

I would, like I said there cheap. Also may want to see if the rear acc pump is a 50cc or 30. I think they are 30 so you can up that to if the squirter doesnt fix it.

[85_SS_302_Coupe]

I just went out and switched the stock pump cam to an orange and WOW what a difference, but there's still some hesitation when the secondaries open so i'll still try the squirters. It really is night and day difference with that pump cam swap...i can't wait to see what it'll do without that hesitation.

[85_SS_302_Coupe]

Well i found the problem...i guess you can chalk this one up as a rookie mistake. The first thing i should've checked was to see if the accelerator pump was even squirting gas when the arm is pressed down...which it wasn't :doh:

So i took the rear bowl off and took the accelerator pump apart and there was the problem...the rubber check valve actually broke the stem off so it wasn't holding fuel in the diaphram. Luckily i'm also taking apart an old 4160 and i snagged an old one off of it and it's working awesome! Now when you smash the gas it's like an on/off switch...no hesitation and it plants you in the seat.

:rockon:

[satan jamez]

Right on! Glad you fixed it. :bigthumb