9 replies to this topic

[jon_dec]

My engine setup is as follows:

998 A+ (flat top pistons)
12g295 Head
MG metro camshaft
Standard A+ distributor
3.2 diff, and A+ gearbox

After some struggle getting the dizzy timing correct, it seems to be ok - 8º BTDC@1500rpm (according to Hayes) and 34º@4000rpm.

I'm having some problems trying to tune this setup using my HIF38 carb. It has an ABY needle, but I suspect this carb is not doing it's magic properly - the engine floods quite often (it has been properly serviced, so a faulty floater should not be the point here), and the "under load" performance is everything but satisfactory. Thereby, I'm thinking of switching carbs, and to not give another shot in the dark (or my foot), I ask for your advice.

Should I stick to the 1.5" carbs (thinking of rebuild an HS4 that already have), or is this engine setup too much for it, and should I move to a 1.75" - hif44 or HS6 ?

[lapider]

im sorry i cant really help you with your question as although i have a similar spec i have not had it running properly yet. im sorry to hi jack but my spec list is very similar to yours with the 12g295 head possibly a metro cam and a stage one, what sort of performance do you get from it, as in is there any top speed change or acceleration change or has this been helped by the change in diff ratio.

[jon_dec]

Hi mate,

my cam is "for sure" an MG metro one

The engine was (at first) an A+ 998, high compression, standard head, and 3.75 diff. It was "fueled" by a HS4, and ran perfectly (made the full 3500miles trip to the IMM without any problem). It had the standard 998 inlet and exhaust

After that, and after a head gasket failure, I found and rebuilt a 12g295 head, and changed to a HIF38 (that should be simpler to tune and more reliable). The manifolds where replaced by a full Stage1 kit, and had also to change the needle to a ABY.
This HIF38 has proven not to be the most reliable thing, since the car tended to flood from time to time.

Now, after a gearbox rebuild (syncros and diff changed to a 3.2 to be a bit more pleasant at motorways), I fitted an MG cam, and ever since, the car has been a real dog to drive (fuelling not being done properly). I really suspect the carb, since all the stuff is proven to be right (and done by pros), including cam and dizzy timing.

Regarding your question:

After fitting the head and stage1 kit, the top speed was unchanged, but the way it reached it was very different The engine felt alot more torkey, and could without much effort follow a friends 1275.
This 2.75 diff is a real dog concerning long travel motorway driving - thats why I changed to a 3.2 - planning to do lots of motorway.

Edited by jon_dec, 30 January 2012 - 04:29 PM.

[bmcecosse]

Are you sure the cam was timed in correctly?? The poor running seems to be after the cam swap? And was the 295 head skimmed to get the CR correct? The ABY seems richer at the top end than the normal 'starting point' AAA needle. Should run ok - but possibly not the best fuel economy......

[jon_dec]

Cam was timed correctly, for sure. Because it is a much more aggressive profile than the standard 998cam, it sucks much more air, thereby my question about the carb being the adequate for this kind of setup.

At the time of the head swap, it was skimmed to give an acceptable C/R (lowered from previous 10.5 with the A+ head to 9.5 with this one)

The problem of this engine is much more on the fueling side - the carb tends to flood the engine, like (sometimes) it is feeding too much fuel (especially at idle). The carb was dismantled several times, and a rebuild kit was fitted. It has a normal spring, and the dashpot is filled with something very similar to your 3 in 1 oil.

[jon_dec]

AAU with the 12g295 didn't work: not even by near The engine backfired all over the inlet (especially in mid range) - way too lean. ABY may be too rich in the top end, but the engine doesn't backfire. Perhaps I should try another needle (have the ADX in the toolbox, and probably will try the AAA, IF the 1.5" carbs are the ones to use.

My main question at this point is the size of the carb to fit.

[twrminisport]

Either a HIF38 or twin hs2's
Mine runs like a dream with Hs2's

Jesus

[jon_dec]

That is one more fact to the bunch of tings that are confusing me (the needle was an AAU for sure - I tried 2 of them, and the carb was adjusted for every needle tried, more than once - one of them was reprofiled by guesswork, and the engine improved, but then fitted the ABY needle and seemed to be ok, until i fitted the MG metro cam - the occasional carb flooding - and overflow - at low charge occurred now and then...)

If tuning a single carb is being such a pain in the... "arm"?, throwing a pair of HS2 at this time, will only add more doubts to the thing. Thereby, thinking of resurrecting the old HS4, unless a HIF44 is the way to go. Just wanting to have a nice traveling engine

[thebullet]

Thinking the same, I have a standard cam, 12g295, stage 1 and a single HS4. Soon swapping to HS2's

Still not running right, huge flat spot in the middle of the peddle.

[jon_dec]

This HIF 38 was fully rebuilt, don't thing is any air leak on the spindle. My guessing goes on the choke mechanism, but will definitively try the old HS4 with new needle.

@thebullet - that flat spot should be related with needle profile or oil thickness in dashpot. Have you tried a rolling road session? In the UK you guys have access to nice rolling roads, but here in Portugal I cannot have that...