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streetbeast351

350 holley on stock 1992 XF ute Having trouble with the tune

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Hey all Seeking a little advice on tuning the Holley on my ute, ive been threw 2 webbers and cracked it and threw on a redline manifold and a 350 holley, I put a fast kit threw the carb and put 57 jets in it ( they were reccomended to me) and a 6.5 PV <-- ( witch i think needs changing)

 

Now it runs and idles fine, but has a flat spot in it near 1/4 throttle Right when the clutch grabs and you go to give it abit more the dead spot sits right about there. ive had a vac gauge on it and it sits just under 20 at idle, but thats with the mixture screws only about 1 turn out ( maybe less) from being fully seated witch dosnt seem right to me, but if i open it anymore it looses vacuum and starts sputtering threw the exhaust, when its at the highest vacuum setting its allso really gutless more so then it was with the webber.. cars still running the EST witch could be my problem?

 

maybe a squirter size change may help me out but unsure on that most people have not seemed to mess with that ( from the threads i read) i know the Carb use to be on a speed way motor had 68 jets in it when i got it.

 

Motors stock as a rock besides the holley

 

ive done a fair bit of digging and seen some threads around but all i found seems to be the opposite with everyone having the mixture screws nearly all the way out to get it to run right

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No I think on a stock 250, a 350 should have 57s in it. The flat spot might be a pump problem, but you need to establish that first by slowly opening the throttle and seeing if the flat spot comes at a steady state or on opening only.

If it's happening while quickly opening the throttle, then the acc pump might need some tuning.

First have a look at the squirter size, if they are any bigger than 28, that might be your problem. 25s would be ideal. The squirter diameter along with the pump cam determines how long the shot goes for. If you have something massive in there, it will dump it all in too early and either not leave enough to cover the transition or be too much for the engine to cope with at once, and drown it.

Next look at the pump cam. There are charts available but I think the pink ones they normally come with are pretty good all rounders for most mild carbies. Also check pump arm adjustment and that the arm is engaging the cam. Sometimes these carbies were coming from the factory with the arm riding on the throttle return spring instead of the cam next to it. There is literature out there on the pump adjustment but briefly, open it to full throttle and check that there's a couple of mm clearance till the lever bottoms out the diaphragm. That's a ballpark method anyway. Adjust the little bolt with the spring on it.

After ruling out the acc pump, check transition from the intermediate circuit (fed from the idle circuit but not adjustable) to the boosters (main circuit metered by the jets) by running the engine and slowly rolling the throttle open so that acc pump fuel doesn't affect mixture. Keep bringing the revs up while looking down the carby and noting any harshness or lean spots before fuel starts dribbling out of the boosters. If there is a stumble just before you see fuel, you have a lean spot between transition and main circuits, which can be cured by raising the float level. If you have an externally adjustable float needle, happy days. If not, unfortunately you have to pull off the bowl and bend the tab on the float lever till you get this right.

Raising the float level does two things to the transition: it delivers fuel for longer out of the transition slots and has the boosters come on sooner in relation to throttle opening. In other words, it takes less airflow to get them working.

Also check that nobody has messed with the bleeds. That will have the same effect of bringing the boosters on later.

On a side note... It's a shame that you can't get hold of a good Weber. They are superior to the 350 in every way. If talking in 4 barrel terms, the 350 is really only 280 CFM. 2-barrels are tested to a higher vacuum (3”) than 4-barrels (1.5”) to obtain their maximum flow rating.

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Thanks for that gerg ill give those a go in the morning i have not totally ruled out webbers yet i was told the XE webbers were slightly better in some aspects id be willing to put a kit threw one as i have one sitting there if i cant get this holley right, the webber did seem alot smoother.

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Thanks for that gerg ill give those a go in the morning i have not totally ruled out webbers yet i was told the XE webbers were slightly better in some aspects id be willing to put a kit threw one as i have one sitting there if i cant get this holley right, the webber did seem alot smoother.
I once made a good one out of two, a hybrid each of XE and XF Webers and my brother reckoned the car had never gone so well. Mind you, I hadn't played with carbies much at the time, I just swapped bits left and right till I had something that resembled a Weber again. They aren't terribly hard to work with if you let go of the Holley way of thinking.

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I also recently mixed and matched an XE and XF one. i don't think there's much difference in a performance point of view, they share the same main parts, just the later they are the more pollution hoses on them.  i'll be sticking one on a gemini engine at some point i suspect, it will need jetting changes and dyno time.. had been told to consider a 38/38 weber for that combo(bigger cam, bigger ports and valves) they should also be good on a falcon, but not sure how easy the linkages would be to set up on a falcon.(is same bolt pattern as the 34ADM falcon carby)

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changed the spot on the pump cam and it seems abit better, had 31 squirters in it atm h ave some 28's out of a 600 holly but they look a bit different still fit, but dont have little nozzels on them but test fitted it and seemed to fit and squirt in the right spot.. ill test drive it tomrrow

 

i should have said in the op the stumble is only under load

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changed the spot on the pump cam and it seems abit better, had 31 squirters in it atm h ave some 28's out of a 600 holly but they look a bit different still fit, but dont have little nozzels on them but test fitted it and seemed to fit and squirt in the right spot.. ill test drive it tomrrow
 
i should have said in the op the stumble is only under load
yeah if i cant get the holley right before the weekend ill put some new diaphragms in a XE webber and put that back on had a look at the 3 i had and every webber had crusty as hell diaphragms and a few new gaskets just a minor rebuild i guess.
Yeah Holley squirters can vary in design, some have anti-pullover nozzles (stops airflow pulling fuel out at WOT), some have little doodles hanging down, but they all screw on to the same place and do the same thing.

Did you play with the float setting yet?

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float setting seemed correct, just dribbles out of the sight hole with the car idling but i didnt toy with it any more then just check that.
You could try bumping it up half a turn or more, just to try. The sight plug method is just a ballpark setting. Otherwise, they wouldn't give you the freedom to adjust the level if it was meant to stay fixed at that initial setting.

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