Morris Minor Owners Club

If you mean the exhaust rasp on over-run, then most of us try and find ways to keep it. It's part of the Minor's character.
Generally the more modifications you make to the A-series and the manifolds etc.. the smaller the rasp (probably ;-) )

I like the exhaust rasp, in fact I make a point of changing gear under bridges, just to get the echo off the exhaust!!

Could it be a manifold leak that's causing the backfire? What air filter is fitted, because that can make some difference to the engine note...

Yes, the standard Moggy exhaust will be too restrictive. Best bet is to get a large bore system from one of the Minor specialists. They are not cheap as they seem to only do stainless steel versions.

A popular one is the Falcon system from the Birmingham Minor centre. I have had nothing but trouble with these systems but I am running a highly tuned engine. I have spoken to other people and they seem happy with the systems.

Unfortunately you do loose the exhaust rasp on over-run which is a shame, but I guess you can't have everything.

Do you mean that the exhaust rasp and backfire are one and the same? I have experience of a tuned engine with extra rasp compared to a standard car but I never felt this was causing a problem or that it constituted a 'backfire'. You say changing down to a 1/4 SU didn't affect the performance - I would expect that it would and combined with a 'backfire' this suggests to me a mixture problem. Did you get it set up on a rolling road?

At the very least you should have a stainless exhaust system fitted. these do have a better flow because of the method of construction. I once cut through the silencer on a knacked mild steel system. the through pipe was pinched into a + shape and was clearly a performance killer.

As Cam says, your best bet is a performance system from Birmingham MMC or Maniflow but you might want to try a cheaper standard size stainless system (at about 1/4 price) if you don't have one already.
Good luck and keep us posted. I am currently refurbishing a 1300 lump myself and will be going down the same route.[/quote]

You say changing down to a 1/4 SU didn't affect the performance - I would expect that it would

when running a smallish bore exhaust, I am not surprised if there is little noticeable difference between the carbs. The 1300 still seems to run quite well when it's strangled!

The 1300 still seems to run quite well when it's strangled!

A well made standard bore system will be abe to exhaust a standard 1300 engine efficiently until quite high revs. Providing that engine is running efficiently itself ie the exhaust charge isn't contaminated by unburned fuel etc etc. That's why I asked if the car was set up on a rolling road.
I apologise if I appear to be picking holes in your description 1300moggyvan but I think it's important to establish if you are really backfiring or just experiencing the rasp we all know (and love?) magnified by a 1300 engine and the van body.

I understand that popping through the exhaust is a common symptom of worn valves or something unpleasantly expensive. However, I have had this occur twice on Phyllis - the first time, was an air leak around the manifold, the second was when the air filter was loose.

Whilst on this thread I'd like to ask a few questions regarding your conversion 1300moggyvan, I'm doing a similar thing to my van and need to know if the flywheel used is a converted minor item or a converted marina/ital one? Also what did you do to the rear minor engine plate to enable it to fit the ital block? I'm using a minor box until I locate a ford unit. Comments/advice from any of you guys? I understand there are so many ford options, anyone know of identification marks on a suitable gearbox?

Les, The Ford box is the type-9 as fitted to the 5-speed 1.6 Sierras (plenty in the scrap yards). For pictures I suggest you get a Sierra Haynes manual from eBay for a few quid as they are useful for torque settings etc. and if you have Ford front brakes.

1300moggyvan, have you plugged all the air holes on the HS4 carb?? it sounds like you may be running lean at higher revs. Also which needle is in the carb?? if it is the standard AAC one then it will lean out at high revs. If you are running it with a 1300 then a AAM should stop the leaning out.

If you have used a gas analyser to check the mixture did you do it throughout the rev range??

Of course a rolling road session will sort the problems out but that's the expensive route!!

Glad you came in with that Cam. I was trying to think along the same lines yesterday evening but I'd had too many glasses of wine by then
I didn't get my modded 948 rolling roaded but It did visit a SU specialist who sorted out the spitting carb and flat spot, and as you and I both know, it didn't hang around after that!!