Hesitation at a slow cruise

[Dazza the Stag]

I have something of a hesitation issue with the Stag. Its most noticeable when I'm cruising at say 30 / 40MPH and whilst the hesitation isn't enough to cause any major jerking of the car it simply feels as though something is holding it back. I took it to the local Stag specialised for the MOT recently and he took it for a test drive and agreed that it wasn't quite right but didn't have time on the day to look into it further.

He suggested I should change spark plugs, leads and filters which I have now done but it hasn't made any difference. He then suggested for me to take it back for him to look at the Carbs. The strange thing is when I'm driving at speed you don't really notice the problem and whilst I could just floor it everywhere its not very practical !!

Just wondering if there is anything else I could check before I take it back ?

Many thanks

Darren

[wilf]

Vacuum advance?

Is there plenty of oil in the carb dashpots?

[Phil S]

oil in the dashpots first look

[Dazza the Stag]

I believe the pots are ok - Im getting resistance when screwing them back in around 10mm from tightened. Wouldn't even know where to start with the Vacuum advance ( didn't even know I had one lol ) so maybe thats something the garage will check

These are two of the spark plugs I've taken out( a photo of each side or each plug ), is it unusual that it seems that one side is blacker than the other ? They have probably been in for a few years but have covered less than 500 miles i reckon.

[JeffW]

Hi

Appears to be running very rich - I had the same problem and eventually the plugs fouled over, so you need to get the CO checked. Colourtune works well for home use or the workshop will check it with their CO/emissions analyser.

Jeff

[Ian F]

Looks as though it’s running too rich and the initial slight “further” press of the accelerator is overfuelling it a little too much. If you continuously floor the throttle, the added air and fuel probably compensates. I would check air filter, check the choke is fully returning and then CO2 levels and have the carbs rebalanced and set.

However also depends how long the car had been running and how far before you took the plugs out?

ian F

[Phil S]

the vacuum advance is there for when you come off the throttle, you are suddenly making the mixture weak by reducing the air causing a weak mixture at higher rpm, this creates manifold vacuum and advances the base plate in the distributer as a weak mixture has a slower burn rate

[richardthestag]

electric SU fuel pump pushing too much pressure and overwhelming the float chamber valves?

I could not get my stag tuned properly as it kept bogging down at idle until I fitted a malpassi fuel filter and regulator.

[MandM]

Hi

Appears to be running very rich - I had the same problem and eventually the plugs fouled over, so you need to get the CO checked. Colourtune works well for home use or the workshop will check it with their CO/emissions analyser.

Jeff

I use colour tune, If you get 2 you can set both carbs at the same time as, a carb does 2 cylinders per bank, a co2 meter gives an average, I could be wrong

[DZP]

I wonder if I dare use my old Colortune plug, last used on my MkI RS2000 in about 1977!!
It has been out of the box a couple of times, but I am afraid it might self-destruct and end up in one of the cylinders.
I bought a Gunson Carbalancer just after I sold the RS and bought a Dolly Sprint and that is still working OK.
Den

[Lingen]

Sorry Phil, but the vacuum advance on the Stag is of the "Ported" variety, so there is zero vacuum when the throttles are closed. The take-off to the distributor is from the "Open" side of the carburettor, not the inlet manifold.
Mike.

[wilf]

When the throttles are "just cracked open", i.e. low speed cruise, that's when you will; get maximum vacuum advance. If it is too much, you can get "hunting". Had this on a RV8 in another car once, which had plenty of static advance, and the vac advance gave it too much.

Easy enough to check.

[MandM]

I wonder if I dare use my old Colortune plug, last used on my MkI RS2000 in about 1977!!
It has been out of the box a couple of times, but I am afraid it might self-destruct and end up in one of the cylinders.
I bought a Gunson Carbalancer just after I sold the RS and bought a Dolly Sprint and that is still working OK.
Den

The older ones in the black box, seem better to be fair

[Dazza the Stag]

Well the good news is that after a return visit to the garage to service the carbs etc the car runs lovely - better than I can ever remember, so maybe need to have these checked on a more regular basis. Thanks for the comments

[MandM]

Well the good news is that after a return visit to the garage to service the carbs etc the car runs lovely - better than I can ever remember, so maybe need to have these checked on a more regular basis. Thanks for the comments

Did he say what he found, too rich ?, ???