Ok guys how do I set my holly striaght!  I have just finished putting a 350 in an 87 ext cab s10 and have only one problem offroad. The carb floods when hitting bumps and ruts. How do I correct this?  It would seem that Lowering the float level would help but it wont because I would not be able to feed my 400+ beast.  I have already replaced the brass floats with some plastic ones I bought from holly and that did very little to help. In case anyone is wondering it is a 750 dual feed double pumper.  Motor runs just like I built it to but this is the first truck I have ever owned and have taken off road. I have always had a camaro to hot rod in and have never had to deal with this problem. Can you help me?  

Justspeed

put a big quadrajet on it. find one off a 454 and you'll be set if you have as much power as you say.  

You need to raise your bowl vent tubes higher to keep the fuel from flowing out.  I have seen it done a variety of ways.  The easiest is to add at least 3/4" of tube to the top of the vent tubes with some JB Weld.  The taller the vent tube is the more splashing you can have in the carb.   If you add those you can keep your floats set to the proper level.  

If you have the cash, swap to a different carb.  The before mentioned Quadra-Junk or an Edelbrock would both work better.

check out the ads in the mags for the truck avenger and offroad carbs. they have full page ads listing the upgrades to call them offroad carbs. i think they're vacuum secondary single feeds but you might get some ideas.  i used to run a holley, i just extended the vents and put a piece of gas line to connect them. It didn't work that well though. my carter is no better. i'm gonna try a q-jet and if that doesn't work i guess it's on to pro jection. the cheap(if you can call it that) 275 hp version.  

I have to agree with everyone else, get rid of the holly.

I built a 350+hp 350 for my old 82 full size truck, and I started out with a holly 750 carb.  the think was junk, it ran grate on the street, but the fuel slosh was so bad that if I was at any kind of angle off road, it would stall and die. I sold the holly and took the origional Q-jet (rated at I think around 800cfm) and re worked it.  larger accelerator pump, re worked vent passages, larger needels, and a few other things(there was an article in a past isue that gave some good tips for making the Q-jet work even beter off road)  I put on the Q-jet, and never had any more problems with stalling wile off road.

good luck,

mudrunner

Thanks guys.    No way I would give up this carb.  I have used many many carbs in my time. Nothing performs like a holly.  I would raise the vent tubes if I had any.....lol

I will build a new carb with long vent tubes.

I will let you know what happens  

On the holley carb. I'm assuming you have a center hung floats. On the vent extensions use a rubber hose and go vent to vent and notch a hole at top of bend as high as you can within air cleaner. On the floats the lighter the better. I even tried those titanium needle and seats. Bad problems, they both stuck and even had a carb fire once in the middle of a forest. Really could have been a bad situation. Both sets stuck open!! I believe they are to light for off road. If your gonna be crawling around and short burst in mud you can run a smaller dia. needle and seat. If you have a .125 maybe go to .110 needle and seat. This way you don't flood your bowls. Jet extensions help alot. Also went to a  1 to 1 linkage that helps make you smoother on obsticals. If your angle is to steep when going down hill your front jets will starve and truck dies with double pumper. If you go to 1 to 1 linkage half you carb will be working instead of nothing. Down hill front jets exposed and backs submerged. going up hill its the opposite. With a 1 to 1 it helps alot it costs about $40.00 to do this and works really well. Also your torque is almost double at idle. Your driving style will have to change because its like driving fuel injection. Also you'll need to square up jetting front/rear. .070frt and .070 rear. Add your jets number and divide by two. If you have 70frt and 76rear total 146 divide 73frt and 73rear. Good place to start and square up squirters like .031frt and .031 rear. Once you learn your truck for off road you'll adapt. I've done many of these carbs for 4wd application and work well. If you have any questions drop me a note. I'm very experienced with these holley's in 4wd world and hi elevation. I run a 472 ford 470+ hrsp with a 900+ cfm carb and love it. Their are more tricks you can do to help. Talk to you later.  

Forgot to mention the holley 4wd carbs have side hung floats and tend to better for 4wds. Thats an advantage over center hung. Side hung have better control of floats and fuel level when going up and down hills. Hope this helps out. Now you have more stuff to worry about.  

holleys are easy to fix on the trail compared to Q-jets. It seems you can find a gasket kits just about anywhere even in wyoming. The small bores in Q -jet up front hurts your lowend compared to the holley 750 square bore carb. I've even ran the holley Q-jet replacement 800cfm. It sucks huge in a 4wd lowend torque just like a q-jet. I run a 1 to 1 linkage and love it. the 1to1 is adjustable on how quick you want to bring on the torque. Their is also a progressive 1to 1 that works well. On your 400hrsp motor you'll love the 1to1 in 4wd world. If you have tunable air bleeds and metering plates you can get your mileage up also.