Need some tips on tuning a '72 510 SSS engine with Dual Hitachi SUs

[Will]

I drove up to Syracuse for Thanksgiving, and it wasn't running too well at all - it was okay on the highway, but not too keen in town. Hopefully someone out there can help with some tuning suggestions.

 

A few weeks ago I used a timing light and set the timing to the correct setting, and it hasn't been running too well ever since -

 

-harder starting.

-sluggish off idle.

 

I tried to set the fuel mixture on the SUs to see if that was the problem with the new timing setting, but that only made things worse.

 

-really slow and stumbling off idle, with some rattling from the carbs during acceleration.

-temperature varied more as I was driving - a bit colder than usual but it usually kept at the center of the temp gauge.

 

 

Does anyone have some suggestions about how I can get this car running right again? I don't have much experience tuning the Hitachi SUs, and using a colortune only succeeded in giving me an electrical shock. I need to drive back to Brooklyn in a few days!

[Sealik]

Read up.... :)

 

http://www.zcarz.us/TechnicalInformationPageCarburation.htm

 

This is where a Wideband O2 sensor earns its money.....

Instead of a Unisyn to balance the airflow....I just used a small funnel on the end of a 2ft piece of garden hose

[Sealik]

Are these rebuilt 38s?

If not....make sure there are no leaks around the throttle shafts.

Start tuning with 2 turns out on each mixture screw

 

...."with some rattling from the carbs during acceleration".....

Make sure SUs are mounted properly....no vacuum leaks.

If you don't have a heat shield....should invest in one ASAP

 

Also...the funnel on that hose goes next to your ear...other end goes maybe flush with the face of the SU after the air cleaners are removed.

Just make sure the end of the hose is in the same position from one SU to the other..

 

Here's a vid on setting them up...different carbs but same principles

I have lift pins on mine....so no need for a screwdriver to raise piston while tuning

 

http://www.youtube.com/watch?v=ASeMfXfjNpw

 

PICS

[ggzilla]

So it was running well a few weeks ago. Then you changed the timing and the problems started. You didn't change teh carburetors in any way and the problems occurred. Only afterwards did you adjust the carburetors which did not help.

 

That doesn't sound like a carburetor problem.

 

So why not change the timing back to where it was?

[thatguy]

Timing

[john510]

Another thing you might check is to see if there is any oil in your carbs !

[Will]

I didn't have a timing light when I first got it running - I just aimed the distributor towards plug #1, got it running and then adjusted it a bit more until it sounded like it was running best. I hooked up a timing light and the marker on the timing cover was pointing about a quarter of the way around the crank pulley from 12° advanced (clockwise... in a spot where there were no marks on the pulley.)

 

It must have been something like 35° or 40° advanced - the engine is pretty much stock - it there a reason why it would be running better with the timing advanced that much from the stock spec? Or did Datsun make some crank pulleys with the notches in wacky places?

[yenpit]

Yes, check that you have oil in the cavity under the small black cap on top.......fill up to the bottom of the threads (engine oil will work fine).

 

And yes, there were different crank pulleys & pointers between the L16 L18 & L20B, so unfortunately you don't know if yours is correct without verifying/comparing visually.

 

I agree with ggzilla & thatguy. When you altered the timing, do you remember if you advanced or retarded the ignition.......which diection you turned the dizzy? I assume you don't have your timing light with you? Move the dizzy back IN SMALL INCREMENTS, drive it a l'il, move some more if necessary, drive again, etc etc until it "feels" better (sounds like you already did some of this!). As long as you didn't change the carb settings to much, and that you didn't randomly develope a vacuum leak, bad gasket, or anything else, you should be able to get back home without incident.

 

Once home, get your hands on a good user friendly (novice) manual for the dual carb setup, like a Haynes manual.........very user friendly & very informative series of manuals! I simply Googled "Haynes SU carb", and found this.............

 

http://www.amazon.co...s/dp/156392157X

 

Although the Japanese Hitachi's (also called the Hitachi SU's) are NOT the exact same carb as the British SU's, they are very similar in the way they work, so a Haynes manual for the British SU's should help you out immensely. Worst case scenario, find a reputable British repair/resto shop near home, and ask them if they would consider tuning your carbs........that's assuming that they are NOT worn out & would require a rebuild. Watch those video clips over & over, and let that info soak into your brain. Hope that helps!

[Sealik]

..."When you first got it running"....

 

What is the history on the engine, SUs...etc

[Will]

Thanks for the tips everyone. I've almost finished reading that giant page about SU tuning. ...next up the youtube SU video. I did bring the Uni-Syn and the timing light with me, but the Gunson Colortune was left in Brooklyn. I didn't want to get shocked again.

[Sealik]

Once home, get your hands on a good user friendly (novice) manual for the dual carb setup, like a Haynes manual.........very user friendly & very informative series of manuals! I simply Googled "Haynes SU carb", and found this.............

 

http://www.amazon.co...s/dp/156392157X

 

I have that book....there is more info in that link and vid I provided

Don't pay anyone to tune your carbs, do it yourself.....read up.....pretty easy after the fact.

[Sealik]

You need to address the timing before tuning the SUs

Try retarding dizzy and increase idle speed.....<.....to 12 BTDC

 

 

Timing was advanced to compensate for the idle screws backed out all the way????

That's why I asked the history on SUs etc.....

[Will]

The SUs were running well, but the engine overheated (before I got it... It was already out of the car when I picked it up.) and I needed to have the head milled - I didn't really mess with the carbs when I put the engine back together. I watched the video, and that helped to actually hear what all of the write-ups were describing. I'll give tuning another try in the morning... before the snow gets here!

[Sealik]

Head shaved

Assuming you have cam tower shims...if not....that will affect 'timing'

[flatcat19]

Hell.

Is the dizzy installed correctly?

Is the chain dead on?

[wayno]

I agree with flatcat19, start with the basics, put the engine at TDC, check to make sure the cam lobes on #1 cylinder are at 10am and 2pm, look at where the rotor is pointed, that would be #1, firing order 1, 3, 4, 2 counter clockwise.

[Will]

Head shaved

Assuming you have cam tower shims...if not....that will affect 'timing'

 

I thought that the shims were only for heads that had major amounts of aluminum removed. Could it throw the timing marking that far off?

 

I could install a set, but I sure wouldn't be looking forward to re-installing the cam towers afterward.

[Will]

I'll do that today - I need to check and see if TDC on the pulley is the same as TDC for the piston.

 

I agree with flatcat19, start with the basics, put the engine at TDC, check to make sure the cam lobes on #1 cylinder are at 10am and 2pm, look at where the rotor is pointed, that would be #1, firing order 1, 3, 4, 2 counter clockwise.

[datzenmike]

Keep the following in mind:

The less gas and air in the cylinder the more advance you need. This is because the molecules are not packed tightly against each other and the flame takes longer to travel across the combustion chamber. By advancing the timing the expandng gasses reach their maximum pressure at a point after TDC where it can sransmit most of it's energy to the decending piston.

 

 

 

All motors since the '70s have no vacuum advance at idle but just off idle there is. It's purely an enissions thing. The motor would love to be at about 14-16 degrees but is prevented from doing so and is set to static 12 degrees. Take any properly running motor and at idle move the dizzy advance and you'll find that the idle increases and smooths out. Again it needs more advance but is not getting it. This is just the way it is.

 

Now if you should set your timing 'by ear' to where it is strong and smooth (probably above 16 degrees) and then rev it up above idle the vacuum advance will come on and it will jump too high and stutter because now the expanding gasses are closser to tdc and work against the motor.

[Will]

Thanks for the information everyone! I'm just about to head out to the garage and get to the bottom of this problem. I'll let you know how it goes.

[Will]

Okay - the progress so far:

 

I took out the plug for cylinder #1 (looked good, normal reddish deposits) TDC seems to be a bit off from this illustration that I found. Instead of this:

 

It's more like this (but this could just be because it was difficult to find the middle between the point where the piston is moving up and when it starts to travel down):

 

The distributor was aimed at plug #1

The vacuum advance moved when I sucked on the tube

 

The oil level in the carbs was the same front and back, right between the marks.

However, the carbs WERE out of sync - when I moved the throttle linkage, the front carburetor moved before the back carburetor.

 

I synced-up the carb linkage, now I'm headed back to the garage to play with the Uni-Syn and the infernal mixture-adjusting nuts. Maybe the out-of sync carbs could be causing trouble?

[Will]

Okay - got it running and adjusted the best I could. I hear some sort of clattering noise that I don't remember when I open the throttle, but other than that it sounds okay, and it doesn't bog down when going off idle like it did before.

 

It sounds kinda like noisy valves. ...I adjusted my valves not too long ago, so I don't think that could be the reason.

[Sealik]

Okay - got it running and adjusted the best I could. I hear some sort of clattering noise that I don't remember when I open the throttle, but other than that it sounds okay, and it doesn't bog down when going off idle like it did before.

 

It sounds kinda like noisy valves. ...I adjusted my valves not too long ago, so I don't think that could be the reason.

 

You sure that clattering is not your timing chain?????

I'b be pulling the valve cover and check the crank/cam timing

Set engine at 0 degrees TDC. Exactly.....do not go past and back it up.

The back of the cam sprocket has a notch in it, there is also a groove on the cam thrust plate

Look through the top hole of cam sprocket.....is the notch on the back of the sprocket to the left or the right of the groove?

As you can see here the cam notch is slightly to right.....new chain<good

 

'Useless trivia'.......

Another way to quickly check chain stretch is to rotate engine CW to 0 degrees, do not go past.....pull dizzy cap.

Very slowly....... rotate engine CCW while watching the rotor.

As soon as you see the rotor start to move...stop

Now look at your timing marks......how many degrees did the crank pully move?

I think anything over 4 degrees (?) is suspect.

[ggzilla]

You are referring to A-series timing marks (those illustrations).

You need L-series timing marks, don't you? For a 510 engine.

 

If the timing was 1/4 way round the pull that's 45 degrees out! The tming marks must not match your engine.

 

Put it back where it was, if it doesn't ping, and it runs great -- don't change it!

[datzenmike]

Valve lash noise does not come and go with the throttle.