10 replies to this topic

[floatintoast]

some will probably remember my previous posts but basically:

Have an 850 with: Hiff 44 water heated inlet and 2" lcb exhaust system + K&N air filter (1275 stage one )

Finally got round to changing the monsterously large Hiff to the original hs4. However now when running i am having some difficulties. The engine idles fine ( a little rough but nothing out of the ordinary) and also revs without any problem. However the car backfires constantly when i try to hold the engine at a higher rev.

I think that the problem is due to the (too) large exhaust system and other 'stage one' parts connected to the orginal - unchanged carb; resulting in the needle in the carb now being incorrect. However just wanted to make sure that this was the problem and not the carb malfunctioning, or something else perhaps.

(I will get round to replacing the exhaust system to a more suitable one in due course)

cheers

si

[minislapper]

Air leak can cause backfiring. Check it's all sealed properly.

[Dog]

to big of a stage 1 kit?

Some chav car with dustbin exhurst backfire loads due to having none or very little back pressure... I mean a 1275 stg1 kit on a 850!!! a 1100 would of done with a 850!

[floatintoast]

Thankyou for stating the obvious and telling me that my system was too big, clearly i didnt know that myself:

"Finally got round to changing the monsterously large Hiff "
"(too) large exhaust system"
"I will get round to replacing the exhaust system to a more suitable one in due course"

I do hope that "some chav car" was not in reference to my mini, as i would take offence to that and have plenty to say in reply.

Perhaps to your suprise my mini drove quite happily with all of the (please dont tell me its too big again) 'stage 1 kit' on, no backfiring or loud echoing exhaust note. It has only since i have changed carb that the problem has begun and for under £100 for the lot it wasnt exactly a bad deal.

Would be very greatful if people can help me answer my question, as need to get mini back on the road asap.

thanks

si

[pikey7]

yes Si. Your carb probably is too big and is causing your issues. You may want to take it to an RR and see if they can level it out a bit. It may be just "out of range" for the available needles though.

Before you do, check your timing is OK too though. In my experience, backfiring is also associated with pinging.

I hope that answers your question......


(annnnnnnnd relax! )

[Dog]

Don't even bother turniong this into an argument!

No I wasn't calling your Mini a chav mobile! I said most chav with dustbin exhursts backfire - refence maybe the reason urs in backfireing, due tot he oversized system!

And when I oridgeanly replied to your post, you had not said/stated you were going to change the exhurst system! I was simply stating this could be one of your problems...

It might of ran fine before, but it doesn't now!

I do not wish to turn this into a hangbag fight, but I think you got the wrong end of the stick!

[floatintoast]

sorry if i seemed aggressive, meant to be more tongue in cheek but made valid point.

get annoyed just everytime i bring up this point someone always tells me it is too big, which is why i put in all the references of it being to big. i did originally put the point that i was going to replace the exhaust but was late at night so you may have missed it.

feel we have both got at the wrong ends of the 'stick'.

God knows where i'd be without the mini forum

si

(thankyou for advice pikey)

[Purple Tom]

I'd first of all eliminate the air leak scenario...and then I'd get it down a rolling road.

Late 850's were actually fitted with the HS4, so the carb you've fitted in place of the HIF44 is fine. The needle will DEFINITELY (no maybe's) be wrong, and will need fettling to get the right fuelling throughout the range.

It really is impossible to get it spot on without the use of a rolling road, but if you have WinSU you can get somewhere near right, by driving the car, working out where the flatspots are etc, then getting a needle richer in that portion of its length to compensate - but its not easy.

As for the backfiring, it could be a possible mechanical fault (sticky valve, burnt head etc...), or it could be something as simple as misadjusted points, wet plugs, too lean - its quite tricky to say.

Although before having it RR'd you're right in saying replace the exhaust - a Cooper freeflow and 1.75" system should be perfect for that engine, and if you put your old system on eBay you'd probably recoup the money back!

[floatintoast]

am pretty sure that there is not an air leak problem, are we talking new gaskets etc and making sure manifolds are correctly tightened, or is there somewhere else i should check? Have made plans for the new exhuast system, basically i want the stage one exhaust system without the rest of the stage one (except needle), have found a few things for it. could anyone give me a link of the exhaust system just incase iv missed one.

am researching on winsu right now (new edition is pretty good) and will have a look at the carb to see if it sticking or something

thanks for the reply

si

[Dan]

A 2" exhaust is realistically too big for any A series up to and including a 1380 as you know so I'm curious as to why you are trying to keep it. Also this:

basically i want the stage one exhaust system without the rest of the stage one (except needle)

confuses me. A stage 1 kit isn't a lot more than an exhaust and a needle! You've already ditched the inlet presumably in order to fit the HS4. If you have stuck the HS4 on the HIF44 inlet then there's a good place to look for an air leak and the source of your tuning issues.

As Minis84 suggests, a Freeflow manifold and 1.75" exhaust would be nice. I'd go for a Mini Spares RC40 Millenium system, with only one box and a link pipe to the Freeflow myself. While you're there you may as well get their Freeflow manifold too.

And while I'm here...

Dogmatix, how would an 1100 stage 1 kit 'do' for an 850? The kits (if you buy them from a reputable supplier) are designed for specific engines, if it's not listed as being for an 850 then it isn't for one. If they don't list an 850 kit then you'll need to develop the engine for yourself rather than using the quick fix method.

Edited by Dan, 17 May 2006 - 07:33 PM.

[floatintoast]

I had planned to stick with the Hiff44 inlet as the Hs4 fitted (although only across two of the four bolts) fine. I do not want to keep my exhaust system, quite the opposite as it has caused me lots of grief in the past and i would love to have the correct exhaust for it and put my troubles behind me.

Should i change the inlet manifold over to the correct one, having now had the idea of keeping it questioned, in my head i can now begin to see problems with keeping it - change in size of carb and i.d of inlet. Or is it possible to stick with the inlet and make some adjustments with the tuning.

It seems to me the best thing to do would be buy a complete stage one kit. and sell all the parts i have on the mini at the moment on ebay to help fund the kit.

Si

(also could anyone suggest a reasonable figure i might expect to sell my current set up for: k&n replacement filter, hiff44,inlet and 2" lcb exhaust system) cheers