12 replies to this topic

[adam_93rio]

I had this problem before I changed to this 1275 but it's been fine for a good 6 months now and recently started misfiring again.

I took my plugs out on Friday and cleaned them, they were really black, on Friday I tried adjusting the timing as I though that could've slipped but it didn't make a difference to the misfire.

Took my plugs out again yesterday, (about 10 miles of driving) and they were fully black again. I decided to lean off the mixture screw and adjust the idle screw accordingly

The idle screw was actually all the way out, so it must of been running too rich? As I couldn't get it below 1000rpm, it seemed to help a bit and now I can work past the revs the misfire is at, but it will misfire and bog down like I'm hitting a rev limiter if I give it full throttle

Am I right in thinking it's just been running too rich?
About a week ago I was in a hurry to work and I'd left my choke out by accident and when I'd stopped it sounded very lumpy and cut out so must've flooded the engine. It's been misfiring at high revs since then so I must've sooted the spark plugs up.

I'm gonna pull my plugs again today and have a look. But a further weakening might be in order?

[adam_93rio]

Oh, it's a hif38 carb on a 1275

[cal844]

Strip andclean the carb if it hasnt been done in a while

[Chance]

Are you on points?

If so check the gap...mine was doing that for ages and i found my points weren't opening

[adam_93rio]

It's not on points thank god. if it was originally I would've replaced them, I can't stand them haha

I will buy a rebuild kit for the carb and give it a good service

Weird thing is that it did this with my 998 that I had in for a while, ran worse and worse until it eventually cut out so I used that as a good excuse to get the 1275 back in. It's been running find for ages then suddenly that problem is back again

[timmy850]

Have you checked your electrical connections around the coil/spark plugs? I had a misfire and it turned out to be one of the wires on the coil being slightly loose and disconnecting every now and then (the tacho was also going crazy all the time)

[foggy]

I had a very similar issue. Im on electronic ignition too.all it was in the end was the dizzy cap.changed it for a new one it went away.but then it came back again so took a look at the new cap and found it was poorly maufactured and wasnt quite fitting correctly on the dizzy. So bought another and hey presto. She has been running well for a while now. (Touch wood) ;) might be worth a try for you.

[adam_93rio]

So I changed the dizzy cap today, didn't help. If anything the misfiring is getting worse

I have noticed that if I rev the engine from under the bonnet I can see slight air bubbles in the fuel line, could this be the problem?

[silve1999]

Yep

[cal844]

The fuel system is drawing air, change the pipes first, then if its still drawing air, id check the pump

[tomb1992]

change your plugs! had the same problem. recently swapped to electric ignition, new leads and dizzy and my mini kept misssing and stuttering at high revs mostly in 4th. my plugs looked okay but had degraded , swopped to a fresh set of plugs with 30 thou gap runs as good as new for me :) 

[KernowCooper]

If your plugs are that black then you need to know what your sting the mixture to, use the lifting pin and see where your at now, setting is in the FAQs engine section on setting the mixture which is the same as the HS series except yours you adjust the screw

[adam_93rio]

The plugs only go black if I let it misfire, whenever I clean them off I can see under the black that they are a golden brownish colour as you would expect from normal running

I have check all electrical connections, changed the plugs and re gapped the rockers while I was at it. Did a compression test which have me 152,142,150,172 which is weird. I don't think the head gasket has gone though, I'm thinking the rings are worn as I know the engine burns a lot of oil on overrun anyway

The mixture was set up fine not too long ago, and winding it either way hasn't helped

I changed the top bit of hose too as I was looking at it yesterday and when I touched it it sprayed me. Need to change the bit at the bottom too near the pump I think as I noticed that was a bit damp but my manifold is too got to do it today