700 double pumper on a road car

GJUK · Post by **GJUK** » Sun Aug 24, 14 7:18 pm

dustymopar wrote:Replace the sec needle valve

It was brand new with the rebuild kit!

dustymopar · Post by **dustymopar** » Sun Aug 24, 14 7:23 pm

Float puncture / knackered?

GJUK · Post by **GJUK** » Sun Aug 24, 14 7:26 pm

totally water tight brass float, moves fine when dry, held under water for 2 minutes no bubbles.

When it was flooding the float was stuck to the bottom of the carb...

Neither my friend or myself could spot why, everything seemed fine, took it out, checked everything, moved it up and down. Blew in to it and proved the valve works fine. All moved very free, no snagging.

Back in the car, add fuel and 5psi it just spazzes out.

dustymopar · Post by **dustymopar** » Sun Aug 24, 14 7:36 pm

Could probably send you another sec float bow, needle valve n float to try....

Worth trying that before doing that before buying a new one...

Bozwell · Post by **Bozwell** » Sun Aug 24, 14 7:51 pm

take the bowl off and post a photograph

sound to me like you have two issues.

losing fuel flow so the float drops but the float then sticks down when fuel pressure has returned causing flooding.

there should be a stop on the float so it doesn't drop too far causing the needle valve to stick.

Mick · Post by **Mick** » Sun Aug 24, 14 8:48 pm

Try swapping them round, readjust and see if the problem transfers to the other side and Check the stop against the side that's working ok.

GJUK · Post by **GJUK** » Sun Aug 24, 14 9:16 pm

Hi guys,

I've spent about 9 days trying to troubleshoot this problem recently, plus all the other time and faffing etc.

The floats do hit the deck of the carb, when empty - I assume this is a problem?

There are springs on the floats though they seem to do nothing at all, both sides, front and rear (primary and secondary)

It seems to get stuck on the bottom then the fuel barrels in flooding everything and leaking from the booster.

The valves are new (original holley items in the rebuild kit)

I'm about ready to get a new carb, fixing this problem might reveal another... I really do not know how old the carb is so it might be best to start with a new unit.

Jon Connolly · Post by **Jon Connolly** » Mon Aug 25, 14 8:01 am

GJUK wrote:Hi guys,

I've spent about 9 days trying to troubleshoot this problem recently, plus all the other time and faffing etc.

The floats do hit the deck of the carb, when empty - I assume this is a problem?

There are springs on the floats though they seem to do nothing at all, both sides, front and rear (primary and secondary)

It seems to get stuck on the bottom then the fuel barrels in flooding everything and leaking from the booster.

The valves are new (original holley items in the rebuild kit)

I'm about ready to get a new carb, fixing this problem might reveal another... I really do not know how old the carb is so it might be best to start with a new unit.

GJUK - I have a brand new 850 double pumper in the box here. I don`t need it on my build yet. Why not fit the new carb and then reassess the problem. You can borrow it for 1 month and just return it to me. If it runs ok with my carb then just buy a new one from Real Steel

GJUK · Post by **GJUK** » Mon Aug 25, 14 8:32 am

Jon Connolly wrote:
GJUK wrote:Hi guys,

I've spent about 9 days trying to troubleshoot this problem recently, plus all the other time and faffing etc.

The floats do hit the deck of the carb, when empty - I assume this is a problem?

There are springs on the floats though they seem to do nothing at all, both sides, front and rear (primary and secondary)

It seems to get stuck on the bottom then the fuel barrels in flooding everything and leaking from the booster.

The valves are new (original holley items in the rebuild kit)

I'm about ready to get a new carb, fixing this problem might reveal another... I really do not know how old the carb is so it might be best to start with a new unit.
GJUK - I have a brand new 850 double pumper in the box here. I don`t need it on my build yet. Why not fit the new carb and then reassess the problem. You can borrow it for 1 month and just return it to me. If it runs ok with my carb then just buy a new one from Real Steel

Hi there,

That is a very kind offer!

I've had a lot of PM's and offers of help/loan carbs so far, I am very grateful for everyone that's helped on this thread and via PMs and in person!

I am not sure if a 850 will be too big for the carb, I am now considering a 750 vac secondary as I understand they are more forgiving on a road car (which is where this will be 99% of its time) and with an auto box.

Thoughts on this guys?

Thanks

Jon

Les Szabo · Post by **Les Szabo** » Mon Aug 25, 14 12:21 pm

Jon, carb choice is not made on engine size alone. It depends on use, cam/converter/rear gears/transmission, heads etc.

That 850DP will run ok as you have gears and a cam, but not ideal, if you get used to it and then replace it with a 750 VS carb you'll be moaning about its lack of performance, so I would suggest that 750VS carb from the off, you can tune the secondaries to come in earlier if you want it by changing the spring in the rear can etc.

You can get a DP to run just as good and better with more performance with some specific tuning to your set up, but for street use only with a tight converter, all round best would be that 750 VS would be my thoughts in this case.

I ran an 850DP on my little 340 with great success, but I did have a .590 cam, 4.30 gears, a race converter with good heads and a race intake etc etc.

Les

Blue · Post by **Blue** » Mon Aug 25, 14 12:32 pm

Not keen on vac. sec. carbs on anything, just not as tuneable as a DP. I think Philth is taking off his 750VS very shortly, drop him a PM.

Jon Connolly · Post by **Jon Connolly** » Mon Aug 25, 14 3:12 pm

GJUK ... The offer of the carb was temporary, purely to " isolate " the problem

i.e. if it still shows the same symptoms with a brand new carb then start looking elsewhere.

Just as a side issue I once had a fuel pump / fuel pressure reg issue .. regulator guage was reading 6 - 7 psi until I put a calibrated guage on and found out it was actually 2 psi. Spent a bit more money than I wanted to on an Aeroquip regulator and guage and it was bang on, and problem went away.

Good Luck

GJUK · Post by **GJUK** » Tue Aug 26, 14 7:58 am

Thanks guys.

The engine is a 400 big block, low compression so I understand. The cam is a COMP Cams Magnum Hydraulic Camshafts 21-242-4. (http://www.summitracing.com/int/parts/c ... make/dodge)
The Converter is a 2800-3000 rpm stall street/strip JEGS item
The diff is a 4.1

I may change the diff at a later date to a more lazy item.
The engine will stay the same as will the converter.

The car is on the road 99% of its life.

Does this help me at all decide on a DP or a Vac sec?

Thanks

dustymopar · Post by **dustymopar** » Tue Aug 26, 14 9:13 am

On the basis that it is a relatively light car, having quick gears I would go for the DP all the way. The DP is easily adjustable to overcome most situations where as the Vac carb can become a little more tricky. The combo you have also satisfies the online carb selection thingy that used to be (or still is) on the Holley website for selection of a DP carb.

On the overhand, if you had a heavy vehicle such as a motorhome, then the bore wash scenario that Real Steel had mentioned to you might become a reality. You don't so I would recommend the DP

GJUK · Post by **GJUK** » Tue Aug 26, 14 9:45 am

750 in size as a double pumper would you say?

Cheers

Jon