8 replies to this topic

[designermatt]

So ill start with , I put a second hand engine in my mini, which had the Head off so I could see the bores weren't great but Ive got her up and running good, although I havent done a compression test IM sure theres a bit of life left in her yet.

 

So I set her up and used all my good engine ancillaries to get her going, using New parts such as dizzy cap, rotor , condenser , points, spark plugs, and got a nice strong blue spark, and Ive set my ignition with a stroboscopic gun to 8' BTDC at about 1200 rpm.

 

Also had to open carb up and blast a lot of red rust silt out of the float chamber and pipes etc to clean it all out, now I have also fitted new gaskets on the carb so no air leaks.

 

Now Im trying to get the mixture correct for best running of the engine, and ive been turning the mixture nut alot but not found the best point, I have also alterred my idle screw.

 

Heres where Im up to , I can start her on full choke from cold and when shes warm I put the choke fully in and she will idle but not very smooth at all, a little bit choppy for idle, and when I rev it up it can be very spluttery and boggy , or sometimes she will rev very high and smooth like it should without bogging, however when you let of the gas there is a few pops from the exhaust which I imagine is unburnt fuel, when ive been altering the mixture nut, sometimes the exhaust is backfiring so loud it sounds like the backbox has exploded.

 

How do I set it up as best as possible without a colour tune or gas analyser?

What initial adjustments should I make to the idle screw in relation to the mixture and the idling?

Ive read haynes which says about some carburettor piston lifting spring which you lift at idle and says if revs increase then settle its okay, if it dies then too lean, if it revs too high then rich mixture. However I CANT FIND THIS LIFTING PIN SPRING THINGY ON MY CAR ?

 

If anyone could recommend steps to take to get her running as best before Mot that would be great.

Car is unmodified , completely standard 998 A+ and ive set the tappets correctly

[carbon]

Some of the later HS carbs don't have the lifting pin, yours may be one. Also sounds like you may be running weak (need to lower main jet)

 

Set the main jet so that it is 2mm below the bridge height with choke fully in (initial setting). Then try tuning up, but you need to do this with the engine fully up to running temperature.

 

For lifting the carb piston your best option may be to take off filter and inlet elbow, and then use a small screwdriver to lift the piston by about 1mm instead of using the lifting pin.

[designermatt]

 

 

Set the main jet so that it is 2mm below the bridge height with

is the bridge the lock nut above the mixture adustment nut? so a 2mm gap between the nuts ?

[whistler]

I have a HS4 on my old 850 and have similar symptoms. The jet, when wound up, does not reach up as far as the bridge. I have done the waxstat replacement trick of removal and replacement with 2 one pence coins.
Interested to see other comments on designermatt's post.

[carbon]

 

 

 

Set the main jet so that it is 2mm below the bridge height with

is the bridge the lock nut above the mixture adustment nut? so a 2mm gap between the nuts ?

 

Matt,

 

To check jet heights you need to take dashpot off the carb. Then using digital caliper or other measurement check how far the top of the main jet sit beneath the alloy bridge. Recommended starting position for initial set-up is 2mm below bridge.

 

But worth also checking how high the jet goes when adjusted fully up (see Whistler's post above)

Edited by carbon, 06 May 2017 - 09:18 AM.

[designermatt]

aha yes i understand, measure inside the carburettor and see where I am , thanks for the advice guys , I shall have a measure and see where I am at, also I think I will buy a colour tune aswell to see what its burning like at idle

[redhouse53]

I'm having the same trouble on mine, the only way I can get it to run anything like smooth is to richen the mixture until I get black smoke. Everything has been rebuilt/replaced so I'm thinking I might have an air leak somewhere?? 

 

Any ideas?

[carbon]

Check the vacuum advance can for leaks, the rubber diaphram inside ages and can split.

 

It's a double whammy, you get an air leak and the vacuum advance also stops working.

[redhouse53]

Check the vacuum advance can for leaks, the rubber diaphram inside ages and can split.

 

It's a double whammy, you get an air leak and the vacuum advance also stops working.

cheers, I hadn't thought of that. 

 

I have replaced the jet and rebuilt the carb, then set it up again with a colourtune and it is now running much better :)