Morris Minor Owners Club

I was going to do exactly the same set of mods to my 1098 but was then put off because when I chatted to the bloke at DSN (mail order) he said that when he did it he couldn't get the car to run properly. Give them a ring and see if he describes the same symptoms.

Thinking again though, that combination on a 1098 seeems a bit over the top. If the inlet manifold is 1 3/4" feeding a standard 1098 head (12G202) and the exhaust is a large bore LCB you could be causing a lot of disturbance to the flow because of the size changes at the interfaces between head and manifolds. Steps like this can encourage the atomised fuel to drop out of suspension and cause stuttering, weak mixture in the cylinders etc.

When I put a HIF38 on a 948cc it ran very well - but I did match the head/manifold/carb interfaces so that there were no sudden diameter changes.

Sounds like the needle is too rich. Does the power drop off on acceleration?

If you can, remove the carb and try a HS4 Mini carb with a AAM needle, that should suit your needs.

I have never run a HIF44 with a 1098 as it is a bit too big, so I don't know what needle sizes to suggest.

Also check for air leaks and make sure that you have sealed off the breather inlet on the carb just in case it is running lean.

If you can, get a colourtune. You can do your own tests then to see if it is running too rich or lean at different revs as you will be able to see the combustion flame.

The gas velocities will be all messed up when using big bore stuff on a 1098 head (as mentioned already be Peetee). The carb sounds big for the 1098,
If the flow is overly restricted due to the small valves, then the carb won't realise that you've gone above idle! Also the effect of the stop/start on the air through the carb will be worse as the carb gets bigger - generally there's a balance point where increasing the carb size reduces the power, as you can't get a constant air flow through the carb, and the air intertia acts against you (according to an aquaintance of mine who had a space frame mini hill climb car)

It would probably be worth trying to find a 12G295 head or the 12G940. Even if that's not the route cause, £50 for a 12G940 head would give you the opportunity to use the potential of your £300 mods.

generally there's a balance point where increasing the carb size reduces the power

Bang on Ray. I was trying not to get too technical just in case .
It's something called inertial ramming. The valves are only fully open for a fraction of the time so the engine relies on the speed of the fuel air mixture to help more mixture in as the valve starts to shut at the same time the drawing effect of the piston stroke is reducing.
Imagine you are in a crowd getting on a train. It's a strange train this because inside is a vacuum. The door opens and people are sucked in You're halfway there the vacuum is spent and the train appears full, those in front of you have nearly stopped, but the people behind you are still moving so you carry on even thought the door is closing. Not suprisingly some people still manage to get on the train. That's inertial ramming.
Meanwhile, way behind you the platform is much wider and people are less crammed together. The vacuum has less effect there because it's wider and there isn't a crowd so they don't get drawn is nearly as fast.

This gas speed has a big effect on torque. Anyone with experience of modern engines will know that 16V cars are often criticised for their pulling power. On paper their bhp is higher than a 8v equivilent. The extra valves provide extra mixture into the cylinder at high revs where there is less time to fill the cylinders. At lower revs however the inertial ramming effect is reduced because the mixture doesn't travel as fast into the cylinder as it does in an 8v engine.

If your intake system has changes in its diameter this can cause turbulence to the flow. Theoretically adding a large intake manifold to a small ported head can actually reduce the flow in comparison to the standard system because of turbulence. Not only does less mixture get into the cylinders but some of the fuel held in fine suspension (good) collects forming larger droplets (bad).
Add a few sharp bends in the inlet manifold and.... - but that's another story.

The above is true (of course!) but I still think you will benifit from using a 1 1/2" carb on the 1098 instead of the HIF44. I used to run a HS4 one on my 85BHP 1293cc mini and it was fine, so unless you are topping that sort of power a HS4 will do fine, whichever head you end up using.

The head I was using was an MG Metro, fully gasflowed and ported with 37mm inlet valves and 31mm exhaust valves. I was also using a 252 duration cam (not much lift but more than standard).

I am inclined to go with Cam on this one as I believe the 1 1/2" was even fitted to the 1st 1275cc Marina`s, the 1 3/4" is really only for the 1275cc and indeed the 1275cc can run with a 1 1/2" as 2 of our branch members do with their commercials, you should check with Vizzard`s book for more info, but I think you have over done it.

but I still think you will benifit from using a 1 1/2" carb

I agree. I wasn't suggesting in my rant that a 1 1/2 was unsuitable. In fact the 998 mini was fitted with one. I would think that economy of build was the prime reason for staying with the 1 1/4 when the Minor went to 1098cc. They found that the larger displacement alone made a significant difference to the power so they left it at that.

You should be able to find a HIF38 on e-bay quite easily. I just missed out on a HIF44 with manifold and K&N which went for about £20. That was for a 1300 Marina lump which may (or may not) reassemble itself as a usable engine in the near future.

I think the HIF38 was fitted to the 1.0 Metros. Surely there must be a few of those knocking about in the scrapyards near you? I think some late ones also had an anti-run on fuel shut off valve fitted which could prove handy.

i tried an hif44 on my last 1098 and it was awfull, swapped to a hif83 from 998 metro 1000 and all was well.

The 1098 with small valves cannot suck enough air throught to make the 1 3/4" carb work

The 1 3/4 is measured across the butterfly.

One advantage of the SU is that the carb is self adjusting for size. The piston will only rise as far as required so having an SU that is too big is no where near as bad as having a Weber that is too large.

If you are un willing to travel to a rolling road your only other reasonable way is to use a Lambda sensor and fix the sensor into your exhaust. This has the advantage that it measures the mixture at all conditions (a colour tune does only tick over unless you rig up a camera to see it while driving).

Then you need a book that tells you all about the SU needle (which parts of the needle do each part of the throttle opening). You also require a needle that is too weak (so you can file it to suit). Then get out on the road and play, for a long time while you get it correct at all operating conditions.

The above will probably cost you more and take you longer than travelling to a rolling road, and getting it done properly.

Your other option is to put everything as standard.

John