1800: Engine Tune Up

[andrew111]

I have been trying to tune the engine over the last couple of days, and am having poor results. I need some advice.


The problems I face are:- idle speed too high, lumpy acceleration, and engine running on when the key is turned off.


I have set the various settings as below and would appreciate confirmation if these are correct:

1965 P1800S - Engine is twin SU HS6's B18B engine. With valve inserts for Unleaded fuel. Re-bored with new pistons, and head cleaned up, new plugs , contacts, pumps etc. Car has just been restored so most parts are new or refurbished originals. Otherwise standard.

Valve Clearances - Cold .5mm on intake and exhaust (this sound too clattery to me - but that's what the manual recommends.)

Timing 18 degrees BTDC at 1500rpm.

Trying to set idle at about 900rpm -1000rpm - but with idle screws all out, am still getting about 12-1500rpm. (although this is variable!)

When adjusting the mixture am finding that it wants to be more rich - so that when I lift the air pots the revs don't fall away too much. But as a result of the richer mix, the idle speed goes even higher and I cannot adjust this down.

Am waiting for a Colortune kit to be delivered to check the mixture - but fear I might end up at a professional tuning firm. Can anyone recommend a firm in the Warks. area or nearby?

Would appreciate any advice you can give.

[JP 1800]

This sounds like you have an air leak and as such the mixture will be too lean. Are the carbs reconditioned and importantly were the spindle bushes re-done. Also do not over look the adjusting screw for the choke cams, there should be a small gap between the screw and the cam as the gap can close when the engine heats up leading on to higher hot idle. Lastly check that all the manifold bolts are tight it is not uncommon for some to be loose after a restoration.

I am facing similar issues and suspect that my bushes will need doing in the future as I have recently rebuilt my own carbs.

JP

[andrew111]

Hi JP

Thanks for the advice - I will try and spray WD40 around the shafts while the engine is running and see if this alters the revs.
Will report back.

[Steve121]

Had the same problem a few years back, for me it was the spindle bushes causing the leak, hence high idle. Now it idles nicely and can be killed if the idle screw is out fully. And no running on anymore.
There was just the slightest bit of play noticable in the spindles, that's all it takes!

[andrew111]

Just thought I'd let you know how I'm progressing.

The colortune arrived and was put to good use. I am getting a blue flame - showing the mixture is OK.

Found that the idle was too high due to the fast idle screw interfering - now that has been corrected can get down to about 1000rpm.- but still a bit lumpy at idle & acceleration is also a little lumpy.
On the advice of a carb repair shop I brushed neat petrol onto the spindles - and this does result in an increase in rpm. So probably the spindles are worn as you advise and letting in air.

Having adjusted balance, mixture and idle speed again I now find the engine a little smoother - and it on runs on only momentarily before cutting out on switch off. But again the acceleration is a little uneven.
Am not sure whether to live with it or go for a carb refurbish. Although the prices I am getting are not far off a new pair of carbs from Simon at Brookhouse.

Can anyone recommend a decent carb refurber?, or tuner.

thanks

[arcturus]

Burlens but a long wait
http://sucarb.co.uk/?SID=77qakcejosd...l1&___store=su
Give them a bell

[andrew111]

Thanks - local knowledge all the way from Portugal.
Obligado

[arcturus]

Originally Posted by andrew111

Thanks - local knowledge all the way from Portugal.
Obligado

Da nada. Obrigado.

[swedishandgerman]

All things are pointing towards air leaking via the spindles, however, one thing before you spend all the money on getting them done:

Have you balanced the linkages?

This gets missed too easily.

I don't know what method you have used to measure airflow (induction speed) at idle, but you should do the same once you have connected up the linkages again.

You can get a good enough guess by looking down the carbs at the pistons, blip the throttle and make sure the pistons lift and fall harmoniously.

Otherwise and more accurate, get a wind speed gauge (anemometer) from Amazon for about £20 - fabulous bit of kit! Open the throttle a bit and make sure you have the same induction speed on both carbs.

If acceleration is a bit lumpy as you describe, one carb is running faster than the other. So it could be air leaking in or it could be that you haven't balanced them properly and one throttle is opening less than the other.

I would guess that your symptoms are worse at part throttle openings than when you give it full throttle?

Shame you're so far away. I'd love to get involved!

Just one other thing - are you absolutely certain you have set up your distributor exactly correctly? Poor idle and running on would make me investigate to make sure the distributor is advancing and retarding properly - if it is knackered, it will always give too much advance at low engine speeds (won't idle properly), will give you poor running at low rpm and runs on when you switch the engine off. Grab hold of the rotor arm and twist it - it should have good tension and when you let go, it should return with a good 'clink'. Is your points gap proper and correct?

[andrew111]

Thanks Swedishandgerman for the many useful points.

I have balanced the carbs using the listening method with a tube and I think I am getting good results - both pots seem to rise and fall in unison, and I can definitely hear the difference in sound with only the slightest change to the idle screw. I have balanced them after checking and adjusting the linkages.

You make a good point about the distributor as it is the original one with new points , rotor etc. - but just cleaned up. I will try the test you suggest with the rotor arm - Am I just looking for it to return with a good thunk?
Shame as you say.
Thanks Again

Andy.