62 replies to this topic

[krusher74]

Jaydee -- Gunson's vs AFR... yes that's why I invested in a AFR gauge (AEM gauge, with Bosch UEGO sensor fitted in the manifold's collector).

 

Krusher74 -- not quite sure what you means by 'running a manifold tube to with the megajolt' but I guess you mean do I have a vacuum tube between the manifold and the megajolt's MAP sensor. If so then yes (fitted to the inlet manifold - not the take off point on the barb's body which I've plugged). 18deg at idle... that's AC's MAP (and I bow down to his superior knowledge). What would you suggest/expect for advance at idle?

Yes I was referring to MAP. How much of that 18 degs is being added by the map? I would just expect it to idle easily at 18 degs,so sounds like fuel probs.

 

have you tried as its struggling to tickover spraying some easy start in and see if the revs rise or fall. in-complete combustion is going to give a nasty reading on the fuel air ratio gauge also.

[ACDodd]

Idling needs to be leaner than that you will damge somthing if this is not rectified.

 

Have your a normal dizzy you can fit to see if that improves matters? Have your varified the ignition timing with a strobe light?

 

AC

[colinu]

I'm on the scrounge to see if anyone in my local club has an HIF44 and a dizzy I can borrow (i.e. to prove/disprove if either my carb or megajolt is part of the problem).

Yes, I've verified the ignition timing with a strobe. One thing I still need to do is recheck is the cam timing just in case I had a brain fart moment when I dialled it in on the bench

Leakdown tester... off to buy one this afternoon (a measly $35 from my local tool supplier   )

 

   Cheers,

   Colin.

 

P.S.

Paranoia is setting in, but I'd rather have that than a knackered engine

[jaydee]

Colin, with 12 AFR at idle i'm not surprised you have such a lumpy idle, try to set it at 14, it will still remain a bit lumpy with bouncing readings 13.5/14, but still acceptable

[colinu]

That's my problem... if I lean out towards 14:1 the engine behaviour doesn't improve. Idle get's rougher, and if I blip the throttle then it's pretty much guaranteed to die (as opposed to barely recoveable if set to the mid-12's).

 

Also a little bit of education for me (and anyone else following this thread)... when setting for a lean run in how lean should it really be set? Are we talking slighlty lean of the stoich point (e.g. >14.13 for E10 fuel), or leaner than you'd run on a bedded in engine (e.g. >mid-13's)? Also I guess we should really be talking lambda as this is a UEGO (wideband) rather than having to convert to AFR (whose value varies depending which blend of ethanol is in the fuel... e.g. lamba for any fuel at stoich is 1; but AFR is approx 14.7 for 'pure' gaolene and 14.13 for E10).

Damn was that a geek moment! Way too much science... especially for a 60+ year old engine design

[colinu]

Just my luck - bought a leakdown tester, took it out of the box and even before I hook it up I notice one of the gauges is broken. Grrrr

[jaydee]

These engines run at best on the rich side, 12:1, but thats really NOT reccomendable during run in, anything from 13.5:1 to 14:1 AFR is enough really at idle, look for 13:1 through the stations and dont excessive strain put the car (like going uphill flat out). 

You cant expect from a 1380 with a hot cam to have low down pull during run in, its also supposed to not have its full top end power.

Flat spots during accelleration are pointing to wrong needle, this needle will probably be good for a bedded in engine and you need a slightly different needle for running in. But try a thicker oil in the carb first, like 20w50.

Edited by jaydee, 16 July 2013 - 09:09 AM.

[Earwax]

hi colinu 

 

have you capped the breather pipe and disconnect vacuum? when you do your AFR readings

[colinu]

OK, I think I'm officially stumped. Plan_B... I've found where I can borrow an HIF44 and dizzy from so will give them a try soon (i.e. to eliminate/verify if my own carb or mj ignition is the cause).

 

So what did I do today?...

• Leakdown test. All cylinders look good showing no more than 15% leak down. On the plus side I did find that I have a slight leak in the exhaust (at the clamp between link pipe and rear box)
• Rechecked that the timing was referenced OK (i.e. disconnect megajolt so the EDIS is in limp-home mode) and using a strobe the timing was rock solid at 10deg independent of rpm
• Last night I went looking for leaks in the carb/manifold. Sprayed a LOAD of easy start around the carb and found the revs change every so slightly when spraying the WOK side of the carb near the abutment plate. However it was drop in rpm (not a rise) and now in hindsight I think the rpm change was either overspary getting into the air filter or maybe because i sprayed the carb body with so much of the stuff it was getting cold and trying to ice???
• Trying to chase down the above 'psuedo-leak' I took off the carb and inlet manifold. I couldn't find any indication of bad seals or gaskets between the carb, spacer, manifold, or head.

AFR is still bouncing around and too rich, and inlet pressure is fluttering (megajolt MAP sensor is showing 50kPA with a +/-5kPA flutter at 950rmp lopey idle... and doesn't really improve if I take idle up to e.g. 1200rpm 1200rpm).

 

So here's hoping the carb I borrow behaves better, and if so then I'll ship my other one from the UK in the hope that it behaves better.

 

To answer other questions:

 

Earwax: Breather is capped, but I haven't bother disconnecting (and capping) the vacuum take off... with the vac disconnected it wouldn't make any difference to timing as the megajolt map is set for similar advance at 50kPA (idle) and 100kPA (i.e. MAP sensor disconnected and open to air)

 

Jaydee: Yes I do understand that once run in I'll want to set the mix slightly on the rich side... but I'm not that far yet (car still hasn't been out for a proper run... too much risk/paranoia that doing so will reck this newly built engine... so the only real live engine time it;s seen is sitting in the garage trying to diagnose this problem). As for dashpot oil... I did change from 3-in-1 to 20W50 a few days ago but as expected that made no difference to the 'stall after throttle blip' problem.

 

So say tuned to see how I get on with a loaner carb and dizzy...

[colinu]

I should be picking up a loaner carb & dizzy on Friday evening... however I think I may have found a likely suspect for the cause of my carb/idling problem:

 

HIF44 Piston drop test... I know I did it before and was sure it was within the 5-7secs for a 1 3/4" carb. However I guess I messed up that test. I retested today... and it's only 2 seconds!!! So basically the suction chamber or piston is worn way beyond reasonable use (i.e. FUBAR). I'm assuming there's no way to correct that other than replacing them (and they are like hen's teeth to find!).

 

Hopefully the carb I'm borrowing is within the 5-7 second spec - that way i'll be able to use it confirm if this is the only fault with my carb.

 

Stay tuned...

[colinu]

OK, so trying the loaner HIF44 hasn't solved my problem... it also gave erratic AFR bounce, and engine would still try to stall after a blip of the throttle. So either my problem is elsewhere, or the Gods really hate me and I've been unluckly enough to have borrowed an equally and identically bad carb (unlikely).

 

I also borrowed a dizzy and thought of trying that... but I forgot I don't have a coil, dizzy clamp, or dizzy drive in my parts bin so had to ditch that idea for the time being. So the only other way I could think of to (partially) eliminate the megajolt from the equation was to disconnect it so that the EDIS module is running in limp home mode (which stays rock solid at 10deg as shown by my strobe). However even with that the AFR was still bouncing way too much.

 

So time to move my attention elsewhere...

• Maybe I have a duff wideband sensor or gauge, or there's noise of the sensor lines? But even if that is the case the "throttle blip engine die" means there's definately a fuelling problem irrespective of what the AFR gauge is reading
• Cam timing - if that were out by a few degrees could that cause these types of problems? I still want to check that for peace of mind if nothing else 
• Continue the (futile?) search for an air leak on the inlet. I'll strip the inlet manifold off yet again, but I'll also tripple check I don't have a leak on the vacuum take off line (even as far as checking the MAP sensor on the megajolt board)
• If there is an air leak then why would the plugs be running on the sooty side (even with the mixture screw turned down lean)? FYI - plugs are BP6ES and gapped to 30thou, all this is being done with the car in my garage - no road-going load placed on the engine other than two quick spins aruns the block the other week).
• Then getting extreme... whip the head off and explore. Leakdown and compression tests showed it (and rings) should be good, but what would happen if I'd miscalculated the compression ratio during this build as say had 11:1 instead of the recommended 10:1 for this cam (I think the head gasket I used should have put it marginally over 10:1 but maybe I miscalculated... if the head comes off then I'll remeasure)

 

Getting close to my wit's end! All other suggestion will be received with open mind and arms :)

 

 

   Cheers,

   Colin.

[Gulfclubby]

Are you seeing any smoke? Just had an idea that your brake servo, if you are using one, might be leaking. Have you lost any fluid?

[colinu]

No smoke, no brake servo, no leaks or fluids lost.

[jaydee]

uhm..i have the suspect youre missing two points, that this engine is lumpy due to its nature and that prolonged idling will soot up plugs and its not reccomendable for an engine thats being bedded in

[colinu]

Yes I may be missing more than two points (no pun intended!), but I'm now down to asking some basic/dumb questions. Thanks for the above info.

• Yes I had suspected that sooty plugs was caused by prolungued idling, but really wanted confirmation of that. I'm still a little too paranoid to take it out on the road so as I can see the true colour of the plugs (apart from being unhappy/confused by the AFR, it's not registered hence I don't want to risk an unpleasant conversation with PC Plod)
• Lumpy nature of the cam. OK maybe I am expecting too much, but AC (whose cam this is) says is should have a lopey idle at 950rpm... unless I'm picking him up wrong I take that to mean "should lopey idle at 950rpm and not try to stall if you blip the throttle)
• Megajolt wiring... will check it again. Originally I had the VR sensor wires crossed (picked that up quickly on first attempt at starting!). But getting back to my 'hypothesis' of only running the EDIS in limp home... surely that proves that the megajolt module isn't the root cause of the AFR bounce (although doesn't 100% eliminate the MJ system as the EDIS and coilpack is still present). I did try another EDIS and coil pack a few weeks ago... but that didn't improve things

Thanks once again for being patient with me... I'm sure I'll get this solved (soon I hope), and even surer the cause will be a dumb oversight on my behalf    Meanwhile I have anther Mini to work on (wife's convertible BINI... whose sunroof has packed in... grrr).