Still having this problem despite all the suggested remedies. The car will start fine when cold, I have even added the cho.ke to aid this. However, once up to operating temp and under load, especially having been on wide open, it tends to die, struggling to start again and feling underpowered (sluggish take up etc.). Also, when snapping the throttle closed, it sometimes tries to stall. The problems are really only evident once the car is warm and has been 'driven' (don't worry folks, I was on an abandoned industrial estate along the road)

Now since the last time I have:

Added a choke

Drilled main jets to circa 1.5, aiming to run lean though

Mixture jets turned out 3.5 turns

Dismantled carbs and cleaned all jets

Added paper gasket in an aim to eliminate air leak (not sure this has been 100% effective)

Timing set to around 5 deg advanced

Colourtune shows all carbs running ok, if a little rich

Carbs sort of balance. Far from perfect, but similar enough (before, they were well out of balance and it still ran)

A few weeks back, the car seemed to be running hot. But the temperature seems to be better now, still above where it should be, but the fan brings it down better so I'm assuming some of this is due to the engine slowly wearing in. Also, if i put my hand over the inlet and breathers of each carb, the car tries to stall. However, when I put my hand over carb 2, the revs actually pick up a little. What might cause this?

Whats really gotten me is that the car drove a good few miles a few weeks ago, with bursts of wide open and I had no problems at all. In fact i was doing a little bit of testing to, starting and stopping and the car was fine. However, it died once (unknown reason, but I'm thinking the same reasons I'm having now) and its not been the same. Back then the jets were standard 1.35.

I'm now out of ideas, bar changing jets again etc. The increased revs of carb 2 when covered is a concern. What would cause this and would it cause these running issues I've been having.

Thanks to those who have already been trying to help in my build thread

Edited 26 August, 201214 yr by prankstar2003

The revs increasing over carb two is because of an air leak. Who made your manifold btw?

Mine was totally homemade, and, despite being constructed bolted to a metal bench, it still warped, and really badly. Had to get an engineering firm to skim it (because I don't have access to a lathe).

I had the same issue (and on carb 2, surprisingly). Now, no carb is affected with hand over.

Just out of curiosity, what's your fuelling method? Just after wide open (where the most fuel is being used), and then struggling to start/run, would suggest the bowls are emptying?

Sounds like a blocked jet on carb 2, had it on my afh.

Also have you tried a different dizzy/hall sender?

The jets can't be blocked, I've cleaned the buggers out! I suppose some other part of the fuelling circuit could be blocked. I don't have another dizzy (i broke 2 )

Manifiold was made by a professional stainless welder (a friend of mine). He dad it tacked to the bench during construction but it is slightly warped. I can't feel an airleak, and thats why I've made the paper gasket. Would some liquid gasket help here?

Funny you mention the bowls. when i drained them earlier, 3 and 4 seemed to have more fuel in than 1 and 2. I'm using the T-piece method.

It's just strange that it doesn't start up immediately after it dies though

I chucked all of my jets and tubes ect in boiling water to loosen up the crap

I used a pipe cleaner and a bit of petrol

Hmm, it could still be warped though; I guess the quick way to check would be a steel rule.. Although that's not that accurate.

I used liquid gasket because I knew it would work, mine holds solid, only used it once, seems okay.

Seems odd that 1+2 have less than 3+4 though. Surely you'd think the outer two would get less.

Possibly a blocked fuel line? I'm using the t-piece method, held for 3k now, seems alreeeet.

You could check when it cuts out, drop one of the bowls, see what's in it?

I'll add a smear of blue hylomar on the inlet then and see if that helps.

A blocked fuel line could starve one side i guess, and 1 & 2 they are on the same side. However, there may have been no difference in the bowls, and I was seeing things

with the car running spray some WD40 around the head/mani join. it shouldn't effect it, if it does then you have a poor seal

a mate had similar running issues to you on his mg midget. it would run good when cold but get sluggish and run rough when hot, it also used to run far hotter than it should of. iirc it turned out it was running lean, he set his carb's up properly and reset his ignition timing at the same time and it ran like a dream afterwards

i know you've already looked at these avenues but i thought it was still worth mentioning as it's so simular to what your experiencing. its also worth mentioning that a badly sealing inlet mani would cause it to run leaner as your getting more air than you should be

Iv not used an inlet gasket tbh

When making my mani it was bolted to some 1" thick steel plate, with little tubes to locate the inlet tracts.

Good idea yeah, but was stuck to the jig after!

Dunno if it's warped or not, there's enough bolts to hold it IMO.

I took all the fixings out of my inlet on the 6n after 3000 miles and tbh I don't think it needed bolts. The sealant I used had virtually bonded it to the head :)

Manifold should be made with recesses for O-rings. With individual chokes there's such small air space in the manifold per cylinder, vacuum levels are very high indeed.

I tried silicone - which ended up being fired out the exhaust, where your paper gasket is headed.

My gasket is 8mm thick hard rubber, now compressed to about 5mm. But I would like to mill recesses in for O-rings, that was the plan when this failed but it's held up.

My flanges on the eight valvers used O-rings, easy because I made them on a lathe.

Why will your sealant end up in the exhsust? Mine stayed where I put it tbh

Depends what it is, if it can easily be broken down by petrol/alcohol then it will deteriorate and end up sucked into the engine, I've had it happen with poor quality stuff before.

What sealant did you use Nick? I'm beginning to think the carb rubbers may not be sealing properly now on reflection. I'll check these.

Guy: I shall try the WD40 trick, but due to Mark's experience at autumn fest, I know it can not always give positive results. However, it's something to try so I'll give it a bash,

I have used the colourtune and gotten good results, but this doesn't show whats happening under load. Apart from an AFR, is there any way to measure this? I'm thinking no

Spraying carb cleaner all over the place showed small leaks on cyl3 and 4 (not bloody 2 as I was hoping!). These are now sealed and carb cleaner has no effect on running. The manifold seems well sealed to the head, which is reassuring.

However I'm still having problems with carb 2. Again, with the breathers in the throat covered, revs pick up. Engine dies with the others as before. Also, this carb has a tendency to spit fuel out of it whereas the others don't. This means too much fuel correct? How is the related to the blocked (?) breathers?

check butterly is matched to others, check that your ht lead isnt fucked, check your jets/emulsion tubes in that carb arent blocked

Just on it. Butterfly is matched but going to strip the carbs again.

Carb 4 actually how no effect when covered either. Doesn't die (like 1+3) and doesn't pick up (like 4)

Matched by eye is shit, the tiniest adjustment throws them out of balance !

I know, but it's close enough. Listening to them also gives a similar sound on each carb.

Blocked idle jet in no.2. Just checking the rest

It isn't the reason why your getting these running problems, but it isn't close enough, they need to be matched with the correct equipment.

A good trick for quickly un-blocking jets is to rev the engine up to around 3k, and then slam your hand over the carb mouth, this creates a nice big vacuum in the circuits and should pull and dirt that may be hiding there.

blocked jet? see, I'm a boss

Jets now unblocked, all 4 where blocked to some extend, but now it's running super rich :-0 I used a tiny drill bit to drill through the crap by hand (it was proper solid shite in there, no chance of blowing/sucking that out). Fearing I may now have taken a bit of material from the jet making it run mega rich. It doesn't idle at all, and foot to the floor just about keeps it running. Going to order some new jets

Edited 28 August, 201214 yr by prankstar2003

If its the idle jets were talking about, you can dial it out with the mixture screws to some extent!

Ah right. But these control low end fuelling too. Will try now any way

atleast youve found one of the main problems si!