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i need a new carb but i'm looking for one specific to my project and i'm hoping someone knows which one will work best for me. i've searched around and looked at a few options but have not found one specifically for the route i want to go.

 

here's the criteria:

 

-its for a z24

 

-it is used for autocross... normal driving is not too important

 

-i want something that is as much as the motor will handle and i'll get a new fuel pump as needed

 

-i live about 6,000 ft above sea level (mainly a jetting issue but maybe a certain carb works better than another at altitude i dunno)

 

-future mods include a port and polished head and a new cam

 

-prefer a weber

 

i was personally thinking the 38/38... yes? no?

 

any help is awesome... i'm new to carbs but i get how to work on them... just not sure which one to go with yet

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i've heard before that they bog down at first... any idea if revving before the launch eliminates this since its 1. no longer at idle and 2. up higher in rpms? like i said it is for autocross so there's not a whole lot low rpm stuff

 

till what rpm does it typically bog down?

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You can also drill out the discharge tube for the accelerator pump to give a bigger charge of fuel. The 720 pump is fine but Webers, specially older worn ones, are sensitive to fuel pressures over 3 PSI which can cause them to flood. A fuel pressure regulator would be a good idea.

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A fuel pressure regulator would be a good idea.

 

 

i was planning on a mallory pump with a regulator... i've heard 2.5-3.0 psi is good

 

the 38/38 is fine.

Just there is a slight bog right off idle. You have to rev it up.before clutching it.

 

If on a hill it can be annoying as a daily driver. Might kill the motor. But otherwise I loved that carb. Pulls great!!!!!!!

 

3 questions... was yours on the 2.0 l-series? do you think it will bog as much on a 2.4 motor as much if so? and are you saying that starting on a hill may kill the motor or just driving up one?

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He means the motor will take longer and work harder to rev on take off, increasing the chance low speed bog or stutter.

 

You have an '85 KC? That would be a 3.70 rear end. Pretty low. A 4.11 from an earlier truck or even a 4.375 would make take offs easier and faster. Definitely a performance gear for auto-X.

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yeah it is an 85 king cab... odd tho because i was told it was the 4.11... i guess this means i have the smaller one because of the non-removable diff cover???

 

when i was told it was the 4.11 i didn't second guess it cause it seems like my gears don't last for shit... and 75 on the highway is noisy as hell

 

i've been too lazy to get under there and spin it to count the revs but i guess it makes sense that its the 3.70 since it doesn't have the removable cover

Edited by PEZi720
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Yup you should have an H-190-ML with 3.70 ratio. If it hasn't been changed or you're pretty sure it hasn't look on the aluminum tag under the right hood hinge on the inner pass side fender. It will look like this:

 

http://i138.photobucket.com/albums/q251/datzenmike/720%20stuff/720stuff060Large.jpg[/img]"]720stuff060Large.jpg

 

Near the bottom it reads TRANS/AXLE....FS5W71B... HF 38

 

The 38 means 3.889 ratio (this is from an automatic) Yours will prob say HF 37, 37 being 3.70 ratio. Check the yards for earlier 720s. I know the 2wd '82 long bed auto had a 4.11 and the early 4X4 had 4.375. Skip the 4X4 with Z24 ('83 and up) motors they had the C-200 axle with the removable cover. Only came in 4.11 anyway. Almost all 620s came with 4.375 ratio. Be sure to check that the Z24 driveshaft will mate to the diff you want.

Edited by datzenmike
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awesome! i'll check that plate and check the yards for a new diff...

 

i could use higher gearing for autocross yes but this almost makes me worry... i hit 3rd on some tracks as is pretty easy... the 4.11 would really get me up there :eek:

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just checked... its the 3.70

 

 

makes me wonder... prolly too annoying to drive on the highway with the 4.11... its already noisy as hell

 

i may do this once i actually get the build portion of the truck underway... first i'm doing the fuel delivery... then more suspension work... after that will be the build portion where i'll do a new cam and such then throw in the higher geared diff

 

at this point it will be trailered to the track and off the street completely so i won't care about the highway driving part

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Third gear on an auto-X means you are carrying two gears that are not even used! A much higher ratio would mean you have more selection of gears to keep the engine at an RPM range where it's working hard. No more long long pulls up hill in second with the the engine stuck at 3,000, throttle to the floor and white knuckles on the steering wheel. When not a DD you can do things to your truck like re-locating the battery to the box for better weight balance and lowering the center of gravity. Lightening the truck by removing the bumper, spare tire even the tailgate if allowed. Lots of stuff.

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lol... i already did all that stuff... no rear bumper or the last piece of frame rail... no spare... no tailgate... no interior... battery is where the passenger seat was... no power steering... no a/c... the list of little things continues on and on...

 

my basic build on this was lighten it and do the basic handling stuff... now i'm on to the fuel delivery for a little more power and consistency under hard cornering

 

future mods are custom torsion bars in the front and fiberglass leaf springs in the rear... 285 r-compounds all around... then comes the cam and port and polished head... more random mods will come after that such as bed tweaks and other random stuff

 

as far as the gearing... i never have the issue of having to floor it up hills... for being a stock carb mine runs pretty well... and at autocross i hit 3rd due to 2nd hitting redline at the end of straits

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Looks like you need either coilovers, or stiffer torsion bars, and more sway bar. also consider putting some more weight over the rear.

 

Consider a pathfinder LSD h233b rear end. I have one in my hardbody with 4.6 gears, and it's really good for autocross style driving.

 

Sounds like you need to decide which is more important, autocross or highway, by the looks of the interior, highway driving is bound to be uncomfortable in your rig. Might want to think about running TALLer tires in the rear if you need to travel to-from events.

 

Oh and traction bars, and link your drp blocks together.

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as far as the gearing... i never have the issue of having to floor it up hills... for being a stock carb mine runs pretty well... and at autocross i hit 3rd due to 2nd hitting redline at the end of straits

 

 

Looks like you need either coilovers, or stiffer torsion bars, and more sway bar. also consider putting some more weight over the rear.

 

Consider a pathfinder LSD h233b rear end. I have one in my hardbody with 4.6 gears, and it's really good for autocross style driving.

 

Sounds like you need to decide which is more important, autocross or highway, by the looks of the interior, highway driving is bound to be uncomfortable in your rig. Might want to think about running TALLer tires in the rear if you need to travel to-from events.

 

Oh and traction bars, and link your drp blocks together.

 

 

 

Ask anyone who races 1/4 mile, (I assume auto-X is the same but mixed with sharp corners so the truck has to handle well too) you want to cross the finish line in top gear and at red line. You really should go at least 4.375 if you DD with it. If more towards auto-X then Kiz has the right idea. Get a D-21 Hardbody axle with the monster H-233 gears. It's already set up for leaf spring. It's only comes on VG30 powered trucks and is available with clutch type limited slip if equipped with the optional 'Sports Package'. Standards come only with 4.375, automatics come with either 4.375 or 4.625 (though only the 4.625 has the LSD I believe) The WD-21 Pathfinder axle can't be used without a lot of work to remove the 5 link and coil springs and you would have to weld on leaf spring mounts, BUT.... both the 4.375 and the 4.625 DO come with an LSD option and can be swapped into the Hardbody axle. Oh yeah, the Pathfinder also has optional rear disc brakes that you can just swap the axles into the Hardbody rear end. The H-233 is larger than a FORD 9" and is friggin' heavy. I don't think the D-21 has a rear sway bar but the Pathfinder does and maybe could be grafted onto the 720? This would give you added weight for the light end, way better gears, LSD and rear discs that would be more fade resistant when hot allowing later and superior braking when entering a corner.

 

 

The engine room tags with the axle ratios are in the same place as the 720 so easy to search out the ratio you want. It does not say if it has LSD but there is a small orange tag on the back of the rear end 'bum' that looks like this:

 

http://i138.photobucket.com/albums/q251/datzenmike/720%20stuff/Pathfinder--D-21conversion034Large.jpg[/img]"]Pathfinder--D-21conversion034Large.jpg ... just wipe the grease off.

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yeah i'd love an LSD... i'll have to look in to what ones match up

 

as far as the handling... it just a money thing right now... since those pics were taken i put in new end links (the old ones were shot) and custom made stiffer torsion bars will come as soon as i get the new carb out of the way

 

as far as the weight over the rear... i'm in love with the way it handles right now... we'll see as things progress build wise as to what i do back there... i've seen some custom fiberglass leaf springs that look pretty good so we'll see

 

it will eventually be a full autocross car so the gearing will definitely be high... and it'll go to and from on a trailer once fully complete

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