HS4 on Mk3 Spit

[MarkB]

As mentioned in another thread I have got the13.60 engine running in my Mk3 Spit. I am having some problems setting the idle as the car tends to all of a sudden start to rev higher and higher. No throttle linkage from the pedal is connected and the idol screws are wound right out and the cams are on their stops. Oil in dashpots, emission pipes to the rocker cover removed and blocked off, timing set. I can't find any air leaks in the inlet manifold or carbs. Choke has been disconnected. Initially the engine will idle for a period of time and then all of a sudden the revs start to climb and level off around 2 - 2500 RPM. I turn the linkage making sure the butterflies are closed but has no effect then all of a sudden the revs drop and if not caught the engine stalls. These carbs were running fine on the Mk4 engine I removed. I have a set of good HS4 carbs complete, and was going to fit them once I started to tune the engine. Would they be to big to run on a standard 1360 engine or could I get by if I leaned them off. I do have another set of HS2's that I could also fit if I can't track down a fault elsewhere on the carbs manifold etc. as a process of elimination.

Cheers

Blue

[thebrookster]

As far as my understanding if these things go, the HS4's should work, however they would lack on low down torque compared to the smaller HS2's without the engine mods to increase the breathing (and therefore flow through the carbs). I would expect them to be fine for higher revs on a standard engine, just lumpy at low revs as less of a vacuum will be formed in the throat to draw fuel in.

[James]

Use HS2s with everything standard and go from there- they will do you perfectly well up to a decent amount of power. Stops you having to mess with needles and fault find on non-standard components.

Having said that a 13/60 engine is going to have a different cam- so not sure what you should be using exactly (what did 13/60 come with?)

[CHRIS211083]

Pull your plugs and check your mixture. It sounds like an vaccum leak or bad mixture setting maybe wrong needles. These carbs will run fine on a standard engine. They just need setting up properly.

Chris.

[Clive]

Wear in the spindles (would need to be a lot of wear)
spray some wd40 or carb cleaner around the spindles and other suspect areas, engine note will  change if air is being sucked.
The pistons are dropping cleanly?
The butterflies are seating properly (loosen the butterfly screws, close the butterflies and retighten?)

Have you checked the dizzy and valve clearances??

But does sound like a leak. Manifold the head OK??

[sparky_spit]

jcarruthers wrote:

Having said that a 13/60 engine is going to have a different cam- so not sure what you should be using exactly (what did 13/60 come with?)

The 13/60 came with a 212359 cam which would have 18-58 58-18 timing and 256deg duration.

[Nick Moore]

HS4s will work on a 1360 engine - my Herald has a pair, but as Brookster says, low end torque can suffer. Add a better cam and higher compression and they'll work well and still give better than 35mpg on long trips.

[Velocita Rosso]

Have you had the inlet manifold off.......?

[James1500]

Would also check the piston isn't sticking and that the butterflies are actually closing to a fine tolerence (the edges are tapered IIRC) and they are centred, found all this out trying to set mine up Doh!  :X

[That Man]

Do your carb butterflies have the small spring-loaded valves in them, they could be leaking ?

[Neil MAC]

Also have the same set up 13/60  engine in a Mk3 Spit with HS4`s (brand new when fitted). Had no problems with the initial "by ear" set up but found a rolling road was the best way to get a great set up.
Low down torque does suffer a bit but over all it s a worth while compromise.
On last years RBRR I got 40mpg which I thought was excellent.
Regarding your over reving/idling problem it sounds like an air leak some where which is the problem I had with the old HS2s before I ditched them.
Neil MAC

[CP72]

Hi,

my girlfriend's Spit MKIII engine has been running on HS4s for many years without problems, needles were ABT. When fitting an tubular manifold and KN filters with stub stacks we changed to AAQ and later to AAM. Car goes very well and fuel consumption is reasonable. A nice conversion IMHO, but might need some tinkering with needles and springs to get it right.

Cheers
Christian