B210 120y - More power please!! (Read 701 times)

[greenclaws]

Good work!...the valve stem seals always seem to go hard and then crack so the engine smokes on start up.
Yeh don't touch the combustion chambers aside from removing any sharp edges that might induce hot spots.

If you have time put your finger into the valve throat and feel the sharp corner where the throat opens out
and turns the corner into the port. Datsun's cutter used to form the valve seat pocket leaves a lot to
be desired in terms of flow. It's really important that these edges have a smooth radius put on with the
rotary file it only takes a few minutes.
No need for a smooth finish rough gives best results.
It doesn't take much time - don't change the shape just improve what is there already

PS Don't forget to back of the tappet adjusters before fitting the rocker shaft.

[dave45]

New oil seals have world a treat! There was blue smoke when left idling for a while. That's sorted! Power is up mainly down to advancing timing to 10 degree. There is still the issue of flat spot though. I can also feel a hesitation when holding mid throttle. Got to be the carb. There isa weber conversion available, but I bet it's pricey.

Would love a spare head, carb and manifold to really spend time on. Will keep scouring the net!!

Thanks for taking time to help me out. Really appreciated!!

[greenclaws]

Hope my ramblings have been on some help!

That timing should work better - these cars were designed to run on 92 octane 2 star petrol...95 standard unleaded
should allow more ignition advance.

Personally I wouldn't waste my money on a Weber conversion - the Hitachi is a good carb.
Much cheaper option is to experiment with larger jets - try a 150 secondary main jet from a latter sunny and
see if it gives more power. Easy job no dismantling needed

There shouldn't be a hesitation that could be an air leak - carb to manifold nuts might need a tweak or the
float level is a bit low or the accelerator pump is set on the short stroke...

The plugs need to be NGK BP5ES..Bosch or Champion plugs just don't seem to work as well.
I always set them to 1.0mm gap but the points and HT wires need to be in top shape
to do this. That often cured mid throttle hesitation for me.

Maybe your MOT place has screwed in the mixture screw to lower the CO - if the idle is set too weak it used to
make my cars flat spot worse.

[dave45]

Running on super unleaded to cope with ignitiontiming and stripped carb down. Interesting that you mention the accelerator pump short stroke. I noticed there are two holes for the linkage. Would you recommend the outer hole then? Plugs are ngk, new as are the cap, arm and leads. Dwell is perfect. Like the idea of jetting it different! Who would I get one from??

Appreciate your expert knowledge mate!

[greenclaws]

I'm no expert just a backstreet mechanic !

Did you skim 40 thou from the head ?

Sorry for the confusion I meant the lever on the accelerator pump should be kept short ...so don't use the
hole nearest the end of the arm you want maximum delivery.

The main jets in the carb are M5 X 0.8 if my measurement is correct.

www.ebay.co.uk/itm/Brass-Main-Jet-Round-Slot-Head-Type-Mikuni-Carburettors-Carb-range-of-sizes-/111662794018?pt=LH_DefaultDomain_3&var=&hash=item19ff9f0522

These look about right but you need to check the thread pitch is right !

The carb I have here has 98 primary and 140 secondary jets...just go up one size on what you have already and see if it makes
a difference...but don't overdo it on the jet size or the car will stink of petrol and the un burnt fuel will just wear the rings out.

Really needs putting on a dyno with a mixture analyser to see what the air/fuel looks like
A good operator should be able to tell you straight away what needs doing
to combat the lean misfire at part throttle and flat spots.
But changing the main jets one size shouldn't do any harm and might point you in the
right direction if you want to have a tinker

[dave45]

Yes I had the head skimmed 40 thou and gave it a grind to the ports. To be fair I'm now happy with the overall performance but want it running perfect. May be asking too much but hey ho. Don't know till you try!

Jet purchased! Got be worth a punt for that price! Will check the threads first!

[greenclaws]

It will be interesting to see what the larger jet does!.

I have come across a couple of cars where the bi-metal strip that bleeds air into
the inlet manifold at high temperatures has been bent up to get through the mot
CO test. Make sure that is sealing as a leaking idle compensator made my car
really hesitant.

I'm looking at drilling a 2/3mm hole in the primary throttle butterfly to
improve the throttle pick-up. My hunch is the mixture is weak between the
transition and main jet circuits. The hole should allow the throttle to be more closed
at idle effectively increasing the length of the transition slot...
I can always solder the hole back up again if it doesn't work! ....

[dave45]

Well after a couple of weeks testing with 150 jet I can reveal..... There's no change at all. Performance is the same so going to revert back to riginal jet.worth a shot and a jet for £2.50 is giveaway.

[greenclaws]

Sorry for my late reply!

Thats interesting it seems like the secondary side is rich enough for full power...maybe modifying the air box and
using a K & N type filter would make a bit more power. The pan type cleaner with a narrow air horn looks a bit
restrictive - I drilled a few more holes in mine years ago but you have to be careful not to overdo it as
you will lose the advantage of heated intake air in winter.

I have found that the standard Datsun exhaust system is best so maybe consider re-fitting the standard system.
Nothing I have found beats the standard system unless your running sidedraft carbs and racing cams etc at high rpm.
Modified exhausts just kill low down power and your fuel economy.

I recently took the larger diameter system of my 1171cc Sunny and replaced it with the factory system and was quite
surprised how much better it now goes.
The top end feels about the same but it now pulls so much better from low revs.
I had the same experience with an A10 Cherry when I cobbled together a system with larger pipes when I couldn't source an original - I guess these engines need a small bore system with high gas velocity to give their best...my 1/2p theory anyway!.

[dave45]

It's possible. Exhaust modifying is a science. Anyway I've sourced an a14 complete with box. Going to clean it up, new head gasket, shells if I can get some, lick of paint and fit it. See what happens

[Al Ramone]

Nice one. Much better way to gain a few horses

[dave45]

Looking forward to it al!

[dave45]

Well after buying another carb I've sussed out my problem... A missing ball bearing at the bottom of the acceleration pump.. Fit a new one and its cured!!

One happy man now!! Thanks everybody for tips and info! Appreciated!

[dave45]

Well here's a the A14 lump I opted for. Had a complete strip, honed the bores, new rings, regrind crank shaft with new big end and main bearings. Cylinder head overhauled, decoked with all rough casting metal removed. Painted with heat proof paint, powder coated sump and chromed rocker cover.  Gearbox is original but has been stripped and inspected. It was pristine inside but has only done 34k. Anyway hopefully it will go as good as it looks! Just need to sort out the manifold situation now. Not sure whether to keep original exhaust manifold or convert the exhaust to fit the violet manifold. Inlet isn't water heated and this may be a problem. Manifold hints anyone???

[randywanger]

Looks good Dave. Custom made manifold? Be about £500 - £700 but will look good and make some power.