Mechanical adv dist for Datsuns?

[phatdave]

I have been reading about tuning the bigger Weber carbs and they say to " Use an electric fuel pump and a mechanical distributor."

 

Given that Datsun dizzys are vacuum where does one go to get a mechanical dizzy?

Datdoug that sold me my Weber 45 and Cannon Manifold said he had tuning problems,and also said he was running a mechanical pump and vacuum dist. therefore I am looking at putting on a Carter 4070 pump and figuring out the distributor situation. The site I was looking at said to simply run a Pertronix with out vacuum adv..step in here Hainz....and set initial advance up to 12-15 degrees.

 

Anybody with any thoughts on this?

[datsunfish]

The tuning problems would probably have to do with puting race equipment on a stock motor.I would suggest that if you want to suck in all that possible air you should do a camshaft upgrade as well as up the exhaust size to at least 1 7/8" pipe.What size block?What head?210 wont work for shit.Unported a87 and w53 would suck too.

I have never heard of a mechanical adv. dizzy for a L motor.Hainz as well as many others run 2 of those carbs with a normal dizzy and a cam upgrade.

This is just my opinion since I have never run sidedrafts but it makes sense that a stock carb at around 30/34 going to 45/45 would probably be a bit much for stock cam.Unable to achieve the air intake potential.

Also chat with Doug and see if maybe it was half of a pair at one time.This would make the jetting way off.

[phatdave]

Mallory,for one does sell a Mech adv. for L series motors.

 

I have a L20 with header stock open chamber big valve head.....U67.

 

45's are run all the time on Spitfires,etc. 1300-1500 cc engines, pretty sure a 2 liter with header and good electrical can run a single 45, let alone a pair of them.:D

[datsunfish]

Yeah,I am sure it can handle it but how well will it react?You should still do a cam upgrade IMO.You want it more open and for a longer time to allow the carb to do what its there for.Performance.You will also need to use a synchronizer tool.The two barrels have their own adjustments.

I suppose I have heard of the mallory but only know one guy with one and he has a downdraft.They are dual points and hard to get points for I hear.

This is just one guys opinion,I have never used a side yet but read alot from those who have and they tend to say the same.

[DanielC]

Vacuum advance allows the engine to run better at part throttle, and gives you better fuel mileage, and allows your motor to run cooler. When you are at wide open throttle, the vacuum goes away, and you are running only the mechanical advence. So, why?

If the new carb does not have a vacuum port on it, manifold vacuum will work just fine.

[datsunfish]

I dont think thats right.You do not lose vacuum with open throttle it actually increases with the increase in rps or engine load.The vacuum advance goes through the carb itself.From the manifold would make it advance all the time.Take off the cap and hose from the carb and suck through it.You will see it doesnt take much to advance it.You only really lose vacuum when you jam it at lower rpms.You want your spark to ignite sooner at higher rps and under a load.

[mklotz70]

I don't want to get in the middle of the discussion, but DanielC is right about the vac disappearing at WOT. The vac sig is created at a small hole just above the butterfly....so that when the throttle is cracked open, you get vac signal. Most people don't adj weber dgv's correctly and end up with constant vac signal....or an extremely short duration of sig.

 

but he is wrong about being able to use manifold vac...for the reason datsunfish stated :)

 

Anyway......here's some prices on that dizzy.

 

http://www.importperformanceparts.net/imports/mallorydist-nissan.html

[banzai510(hainz)]

My yellowcar has a set of 44mikunis and DOES NOT have a vacuum adv port.

my 40mm on my Banzai car has a port and I use it(such a small port).

 

Be honest I swapped the yellowcar dizzy for a SSS unit and converted it to a Pertronix. If there was a imporvment IM sure it was cause of adding the Pertronix

as for the vaccum adv I could never tell if they ever really helped by adding a faster curve.

I know by using a DGV set up I had/ I had one L16 dual point that was stuck and put one that worked I could never tell the difference.

 

Just my opinion here but for a mild/hipo L motor I would not worry about it and save that 400$ (Mallorydizzy) and buy something else like headwork,cam porting,set of Mikunis ect

 

The nissammotorsport book has listing of different weights for the dizzys if needed if you want a faster adv.Most racers will take their dissy and and have it curved for a particilar application(high rpm use).

[datsunfish]

I guess I was half right.I know the hose always goes to the port above the throttle plate.I have had pinging and rough power under load only to find the advance hose hanging loose.More a vacuum leak issue.

[]2eDeYe]

The nissammotorsport book has listing of different weights for the dizzys if needed if you want a faster adv.Most racers will take their dissy and and have it curved for a particilar application(high rpm use).

 

This would be more of a racecar application?

By that I mean trailer your car to the track situation...not a race to work on monday thing ;)

 

I was always told (with chev's mind you), remove the springs and advance it to where you want it....discuss :P

[phatdave]

I guess I will try to get her running with out vacuum, but with a n electric fuel pump and see what it does.

 

In the mean time I have 700$ to buy a driver truck anybody have one to sell?

[banzai510(hainz)]

the stock type fuel pump is fine

 

My banzai car all it has is a a stock KOYOSAN but with 40mm dual Mikunis.

 

if electric then you got to buy a regulator . Most eleltrics are above 5 pounds and these carbs(weber DGVs Mikunis want like 2.5 to 3.5 pounds pressure)

 

Just make sure the fuel pumps works. Im sure it does

then see where the butterfly throttle adj(speed screw) is and see it its cracked open.

 

I DONT KNOW WEBER DCOES but all I would ck off hand is see if its squirting gas(Mostly hear it)when cycling the carb, then open the top and make sure the jet blocks are screwed in all the way

 

all I can think up next is fuel float or those mixture screws. turn the mixture screw(with tension spring) in all the way then turn it out maybe 1 turn and try starting it then do half turns untill something happens

 

IM always very leary of buying sidedrafts. I seen a set rebuilt and the guy install the accell pump diaphram in wrong where you would squirt gas when you cycled the carb but otherwise it was OK.