SU's driving me crazy!

[supraman]

Hey Z member's,

I'm having SU issue's and I'm going nut's trying to figure it out.

My 280Z has rebuilt SU 4 bolt round top's.

Last weekend I replaced some fuel line's, installed a low pressure electric fuel pump and my 280 fired right up!

This weekend it wouldn't start.

The first thing I noticed was no fuel coming through the return line after the carb's.

So i banged on the side of my SU's with a small hammer (lightly) and it seem to free up whatever was blocking it or stuck.

Fuel slightly started to leak out the front of the carb's.

But this meant to me that there was to much fuel pressure.

The car start's up but die's at idle, it does fire well when gas pedal is applied and they rev good.

Is this a float problem?

stuck jet?

combo of problem's?

exhaust sound's like it spitting a little too.

[VITAMIN Z]

I was havig a similar problem with the carbs on my 74 260Z, gas was leaking out from the carbs. All I did was to add oil to them, in the dampening chambers, do you have these? just a thought. good luck!

[beandip]

Sounds like a problem with the needle and seat. There may be a little crud keeping it from closing and flooding the float bowl. this would account for the revving but not idling. As you said it could also be too much pressure. Anything over 5 psi could overwhelm the needle and seats. If there is no fuel coming from the return line on the fuel rail, then there must be something plugging the metering hole at the end of the metal line. Are you running a in line filter before the electric pump and one in the engine bay? If you do find that the rail has some crud blocking it , take it off and run some carb. cleaner through it and let it soak a little while.

[Bruce Palmer]

What is the history of the carbs? Have they been in service recently or sitting a long time?

Old gas and crudded up fuel systems can play heck with the proper working of the few parts in an SU. Then again it could be any of the things mentioned already.

A good pressure gauge can tell about that pump issue. 3 1/2 # is a good pressure for well functioning needles and seats.

[supraman]

What is the history of the carbs? Have they been in service recently or sitting a long time?

Old gas and crudded up fuel systems can play heck with the proper working of the few parts in an SU. Then again it could be any of the things mentioned already.

A good pressure gauge can tell about that pump issue. 3 1/2 # is a good pressure for well functioning needles and seats.

From what i understand, the carb's have been rebuilt and in use on a 240Z with little to no problem.

The guy i got them off of did a good job of cleaning everything and reuilding them.

He also hand polished everything, even the manifold's so i imagine he put a great deal of time and money into them.

So what's the best idea here, re-seat the needles and clean everything out with cleaner, or just rebuild these carb's over again?

I wonder how much Z therapy would charge me to fix them up if there already full of new part's?

[Zs-ondabrain]

In the engine compartment,

1) Disconnect all the fuel lines, blow them out and physically feel that each tube (nozzle) has sufficiant air flow,

2) blow out the rubber lines,

3) Remove the bolt on each float bowl and remove the Banjo neck (metal inlet) and clean them as well as the small (last chance) screen filter.

4) remove the drain plug on each float bowl and drain them

5) remove the small rubber tubes (from the bowls to the nozzles) and blow them out as well as using a cotton swab to clean out any clinging crap. (I use alcohol on a Q-tip)

Blow out the nozzles and check the needles for straightness and carefully clean them.

All this may seem repetative but at least you'll know that everything from the pump to the needles is clean and no longer an issue. The steps above are what I personally do EVERY time I work on a system, basically like Preventive maintanence.

After everything is clean, run the fuel thru them and then remove the piston and look into the nozzle for proper fuel level as stated by Bruce. Adjust accordingly. It takes time but well worth it in the end.

If you're running a fuel pump, get a regulator and adjust it to 3.5 to 4 pounds, tops. A small pressure gauge should help as well.

Dave

Edited April 11, 2009 by Zs-ondabrain

[Bruce Palmer]

Supraman,

Our JUST SUs DVD might be the ticket for you now to walk you through the take apart, chase gremlins and reassemble and dial 'em in part of the project. None of us know what's in them in the way of NEW parts so that will have to be up to your serch.

I'd guess you either have crap in the needles and seats (which would be coming from the final filter in the float bowl lid) or float level issues.

I'd also get 2 float bowl lid gaskets as yours may turn into potato chips when you remove the lid to remove the needles and seats to douche them out with carb clleaner.

All we can to carbs here is completely go through them to insure what's there in the way of parts, what's been done and the quality of the work involved. Of course the double sealed roller bearings is part of the deal as well.

Let me know how we can help...

[supraman]

In the engine compartment,

1) Disconnect all the fuel lines, blow them out and physically feel that each tube (nozzle) has sufficiant air flow,

2) blow out the rubber lines,

3) Remove the bolt on each float bowl and remove the Banjo neck (metal inlet) and clean them as well as the small (last chance) screen filter.

4) remove the drain plug on each float bowl and drain them

5) remove the small rubber tubes (from the bowls to the nozzles) and blow them out as well as using a cotton swab to clean out any clinging crap. (I use alcohol on a Q-tip)

Blow out the nozzles and check the needles for straightness and carefully clean them.

All this may seem repetative but at least you'll know that everything from the pump to the needles is clean and no longer an issue. The steps above are what I personally do EVERY time I work on a system, basically like Preventive maintanence.

After everything is clean, run the fuel thru them and then remove the piston and look into the nozzle for proper fuel level as stated by Bruce. Adjust accordingly. It takes time but well worth it in the end.

If you're running a fuel pump, get a regulator and adjust it to 3.5 to 4 pounds, tops. A small pressure gauge should help as well.

Dave

Thank you for your time, this seem's to be a good guidline to cleaning these SU's out.

I'll give it a try and see how well they run.

I'm sure it has fuel issue's cause they ran perfect the first day then I tried them a few day's later and have been fighting them since.

I noticed one of my carb's has no bolt on the float bowl.

they are both identical other than the float bowl's.

They are both 4 bolt round top's and the id numbers have been polished off so i can't really id the carb's other than 4 bolt round top SU's from a 240Z.

They seem to work very well with each other, until now.

When I rev they do seem to run as well but have to give the car gas to keep above idle so they won't die out.

Cleaning fuel line's today and filter's then trying again.

I'll have to keep everyone updated.

[supraman]

Supraman,

Our JUST SUs DVD might be the ticket for you now to walk you through the take apart, chase gremlins and reassemble and dial 'em in part of the project. None of us know what's in them in the way of NEW parts so that will have to be up to your serch.

I'd guess you either have crap in the needles and seats (which would be coming from the final filter in the float bowl lid) or float level issues.

I'd also get 2 float bowl lid gaskets as yours may turn into potato chips when you remove the lid to remove the needles and seats to douche them out with carb clleaner.

All we can to carbs here is completely go through them to insure what's there in the way of parts, what's been done and the quality of the work involved. Of course the double sealed roller bearings is part of the deal as well.

Let me know how we can help...

Bruce,

Thank's for the tip, if I fail at getting these carb's to run properly I will just rebuild them for learning experience alone.

I think your dvd will be on my list of tool's soon.

The double sealed roller bearing's are an aftermarket tweak I take it?

If so, could I order them and install myself without extreme trouble?

[Bruce Palmer]

The bearings are a ZTherapy specialty and are available in either the complete REMAN ZT100 format or just the bare body ZT110 with the bearings butterflies and throttle shafts fitted and you swap everything else over.

[Zs-ondabrain]

The 4-screw carbs were the early version. The float bowl with NO drain bolt is an earlier version. No big deal or difference, except that one is drainable and one it not. just pull the rubber tube to drain it.

[supraman]

The 4-screw carbs were the early version. The float bowl with NO drain bolt is an earlier version. No big deal or difference, except that one is drainable and one it not. just pull the rubber tube to drain it.

I have a set of 3 bolt round top's also, i could rebuild them too i guess.

Are they any better than the 4 bolt when using them on a 280Z?