L20B timing problem

[dgi]

Need help getting proper timing on my L20B.

 

I bought a 510 with a L20B, Weber side draft carbs. The single point dizzy seems to operate fine, but the vacumn advance is disconnected completely. No vacumn ports on the Webers's. New spark plugs and wires, sufficient and even compression on all cylinders.

 

With a 10 degree BTDC setting, the car idles and cranks fine but stumbles coming off idle and doesn't pull very strongly.

 

I advanced to 15 degrees BTDC and car pulls a bit better off idle but lacks power above about 3500 rpm.

 

I advanced to 18 degrees BTDC but have a definite stumble between 2500 - 3000 rpm. Above that it pulls pretty strongly to 4800 rpm and then just goes flat. But no noticible ping.

 

I'm thinking that the total advance is still retarded, but without the vacumn advance I don't know how to increase it.

 

Anybody know how to deal with this issue?

[banzai510(hainz)]

accel pump working ok on the carbs???????????

 

vaccuum on sidedrafts are minimal on my opinion

 

take the dizzy out ans spin it incase the weights fell off.

 

all the jets screw in all the way and didnt back out

[dgi]

Thanks for your reply.

 

Yes, the accel pumps seem to be working fine. I've only fiddled with the idle air mixture jets. Don't know enough about the Webers to do much yet.

 

I will check the dizzy ASAP to make sure the centrifigul advance weights are intact and it is operational.

 

But, correct me if I'm wrong, the dizzy depends on the vacumn advance mechanism for about 7 degrees of advance. The rest comes from the centrifigul mechanism. I'm going to have to find some reference material on that. Don't know what the total advance should be on the L20B and don't even remember what it was on my L16.

 

I have been away from the Datsun world nearly 20 years. Sold my last street 510 about that long ago. It had 38mm SU carbs and I understood those. These Webers are going to be a leaning project.

 

Just sold the 1972 PL521 I purchased new last December, but it had been running perfectly for years in stock condition til then so my tuneup skills haven't been tested in a while.

[banzai510(hainz)]

dgi,

I have 44mm mikunis on my yellow car and put in a SSS dizzy ans it has no vaccum port on the carb so I dont have the vacuum line to the dizzy hooked up. From the other dizzy to this one there was no change that I could really tell.

 

My other 510,the banzai car, I had L20 dizzy and some other dizzs and I have ran them w and w/o the vacuum adv. I couldnt tell the difference myself.

these 40mm Mikkunis have a vacuum port. Some do some dont I guess. Its such a small port and going to just one intake runner its just so small amount of vacuum your gonna get

 

anyways the vaccum advance works at idle when there is more vacuum so when you punch it, the dizzy will RETARD cause the sudden increase in volume than vacuum,

 

anyway you said at 2500/3000 rpm you have proplems. I think you would have full mecanical adv by then anyways

 

 

I have mine set @ 12-15deg intial advance with a timming light.

 

nothing what I said is from a book. this is what I notice and have experienced with the setups I have seen and ran.

 

get a carb sync and sync the carbs also and see if that helps.

 

sometimes it could be just a crappy set of carbs.

[hogboy52]

Most conventional motors ran an advance of around 35deg.@ 3000rpm.

The '78 manual shows 12.5deg.@ 9.84 in. vacuum and 11deg.@ 950 mech.

(electronic dist.).

The '74 manual says 3.5deg.@ 9.84 in. vacuum (a misprint?) and 10deg.@ 2150 mech.

The vacuum can has an adjustment screw under some glop on the end.

Venturi vacuum increases as the airflow through the carb increases. Don't know with Webers but the passage might be pluged with a screw.

My own cruddy points type I tweeked in a bit extra adv. with a file on the weights and replaced the rotted vac. can with a Toyota unit. It wound up with 40deg. advance which ran OK but I moved it back to 35.

There are after-market units that have a full advance curve using only weights.

[datzenmike]

I don't think there is any vacuum advance at idle. The port is above the throttle plate. When you give it gas the plate moves up and exposes the port to varying vacuum for advance off idle. Somewhere between 2,000 and 3,000 the mechanical advance takes over as the vacuum drops off.

[dgi]

Thanks for the replies...

 

Here is a bit more info to work with.

 

Been doing a bit more exploring :)

 

Crankshaft at TDC on compression stroke. Pulled the cover and No 1 cam lobes are at 10 and 2. Pulled the distributor and looked at the slot in the drive shaft straight on from driver's side. Slot is to the right like this / at about 12:45 position. If I'm reading right and viewing Hainz's video correctly it should be like this at about 11:28, slightly rotated right from a line drawn between the distibutor pedestal bolts.

 

Would this be preventing me from dialing in enough advance? It sure feels like it is running retarded.

 

Need advice on the best way to correct this. Can this be done without pulling the front cover and retiming eveything? Can I just drop the oil pump and repostition the shaft?

 

Second problem, the distributor fixing plate is mounted on the distributor with the marked side down instead of up (flipped over). If I turn it over so the mark shows (it only has one in the center), then it is 180 degrees away from the bolt hole on the distributor pedestal (which points towards the radiator). Is that the correct orientation for the pedestal on a L20B single point distributor? I have loads of documentation for a L16, but nothing for a L20B in my possession. Any help there would be appreciated.

 

TIA guys

[Cuts metal like mad]

people commonly mix and match dizzy pedestals and plates... but only if they have the incorrect one.

 

You CAN drop the oil pump to correct its position, but you will need to retime your motor. If the plate is mounted upside down I would suspect a poor repair was made at some point... I would suggest getting a matching setup so you can set it up properly... possibly what happened is that the perso who own the vehicle before put in a new oil pump and did not line up the dizzy drive correctly and flipped the plate to make it run... you may be able to correct the dizzy drive position and flip the plate and get "lucky" and find that its right where it should be, but sounds like you won't.

 

GOOD LUCK! :D

[hogboy52]

If you want the "proper" setting you'll need to drop the oil pump but that changes nothing else. Is it at the end of the adjuster slot? Even if so you have 15deg. now and any more would put a stress on the starter I would think. If you have a dial-in timing light, I would see how much mechanical advance there is at higher RPM. With a regular light, set the mark to 15 and make another mark at zero. There is probably around another 10deg. but the weights can get pretty gummed up. Without a vacuum port you are limited unless you go with something like a Mallory mech only or even one with curve tunable dip switches, but that's $$$+++.

[hang_510]

but only if they have the incorrect one.

 

If the plate is mounted upside down I would suspect a poor repair was made at some point...

 

i have something on the dizzy that suggesst flipping the plate is a possible fix for the plate issue.

 

didnt work for my friend though, still have no idea how it ever worked before :unsure:

[racerx]

Yep..the dial type timing light is a good tool to have..no second guessing here. Set it at the degree you want and see the results...besides the 11.28 or 11.25 of oil shaft, you can also turn the crank and stick some toilet paper on number 1 cylinder, once this pops you are either on TDC or getting very close to it. Popping the toilet paper is an ol skool trick. Your cam lobes at front of engine should also be at 10 and 2 oclock. Doinf these will ensure that you are at TDC. Once this is done you can use the timing light and adjust your distributor to spec. You can always go higher than factory specs, maybe about 4 degrees advance, till it pings. Take it for a spin and hear it pinging if it does then back of a couple of degrees.

 

Oh btw if you have not watch Hainz video, I highly suggest it..he can mail you one and he only ask for a donation.

 

Good luck...

[dgi]

If you want the "proper" setting you'll need to drop the oil pump but that changes nothing else. Is it at the end of the adjuster slot? Even if so you have 15deg. now and any more would put a stress on the starter I would think. If you have a dial-in timing light, I would see how much mechanical advance there is at higher RPM. With a regular light, set the mark to 15 and make another mark at zero. There is probably around another 10deg. but the weights can get pretty gummed up.

 

Thanks,

 

Yes, I'm advanced to the end of both adjuster slots and only have a 10 degree advance at idle. I was hoping correcting the shaft would solve that problem.

 

Timing advance increases to about 15-18 degrees at 2000 rpm, around 25 degrees at 3000-3500 rpm.

 

Maximum advance is 32 degrees at 4500 rpm. I would have expected that about 3200 rpm myself.

 

Maybe you are correct about the weights being gummed up. Worth a look!

[banzai510(hainz)]

if you look on the back side of the dizzy there is a 8mm bolt that hold the timming plate on. YOu can loosen this also to move the timming plate more one way or the other(adv or retard) then use the regular timming slot if it was to far to ones side to get it running correct.

 

what happens is it will run near idle then you step on the gas and it will go out of time,then start missing ,ect.......

[dgi]

Thanks Hainz,

 

I have already loosened the 8 mm bolt and advanced the plate as far as possible. Then by advancing the normal adjustment slot towards advance as far as possible gets me 10 degrees at idle.

 

Without any vacumn advance, I can get only 22 more degrees of advance, but that only comes in around 4300 rpm for a total of 32 degrees.

 

Comes off idle OK, but pulls rather sluggish til about 3500 rpm. Under load between 2000 and 3000 rpm in 4th gear it is anemic and occasionly misfires and pops. No pinging is heard. Drop a gear to 3rd and get it over 3000 rpm and it pull strong to over 4000 and then it really begins to perform.

[banzai510(hainz)]

If this was me I would dial it up to TDC and ck the cam timming marks.

oil pump 1128 position. dizzy position and hopefully its at #1 plug wire right on and have have enough movement on my timming slight(should be in the middle between R & A) If this all correct then swap another dizzy.

 

Put ON a weber DGV downdraft to mke sure its not your sidedraft carbs.

Or borrow one with stock intake set up.

 

I have one withe the springs broke off the weights but still ran.

[dgi]

Thanks for all the advice.

 

It has taken me a while to get back to this because of job problems, so I am just finishing it up.

 

Replaced the distributor with a matchbox with the proper pedestal. Now I can actually adjust the timing. Replaced the coil with one for use without an external ballast resistor. Rewired the ignition circuits.

 

Found the oil pump was off a tooth, so pulled it and corrected the shaft alignment.

 

So, that is all good again. Now I can move on to the carb problems.

 

Thanks again for everybody's generous advice.