Reco'ed Motor Woes.

[Tez]

Finished putting a fully rebuilt motor back into my MB on the weekend and not happy Jan.

It starts reliably and runs - badly. The motor itself I'm sure is sweet, but it will not idle. It misses. Timing it as best we can I've driven it a short distance and it pulls really well - the missing disappears as soon as any throttle is applied, and when the choke is pulled out for cold starting it purrs like a kitten but, with the choke in and on decelleration, it misses and can stall. The ignition system is all new (plugs, points, condenser, leads. (except the coil- I'm confident that is ok, but may well replace it to be sure).
I've been told by two different people I may have an inlet manifold leak.

One suggested spraying carby-cleaner around the manifold and to listen for any improvement, and spraying under the manifold near to the fuel pump does cause it to improve noticably and run smoother for a short while (tried this twice to prove to myself).

So this evening I began stripping bits away to get at the manifold bolts (WHAT a job with the motor in the car) and after much cursing got to the bolt underneath the manifold nearest the fuel pump.

Reaching under the manifold to the end of a 12mm open-ended ring spanner I managed to wriggle the ring end onto the head of the bolt and pushing with my thumb only I got this bolt to tighten nearly a quarter turn. Trying the other bolts, the one under the manifold in the middle went up maybe an eighth of a turn and the one nearest the timing belt cover a little less. The three across the top hardly moved at all.

Now. After about an hour and a half, I have new coolant all over the garage floor and some totally inaccessable heater hoses removed, and various other bits off.

Have I fixed my possible leak? - If I go to the bother of putting all this crap back on, re-filling the coolant and starting it, do you think It will run smoothly now, or have I just made my task a little harder and I really
do need to take the manifold off completely and do a new gasket and refit it....

From your experience, what would you do?

Thanks for any help...

[Brayden]

Your problem could be an inlet manifold leak, and yes the easiest trick is to spray some carby cleaner or hard-start spray around the manifold while it is running. I doubt the leak would be at the manifold gasket though, because they tend to leak water if there is a problem.
Don't forget to check the simple things, like vacuum connections.

I'd also be looking at the carby, particularly the idle circuit. Have you rebuilt it? If not that would be a must.

[Tez]

Hi Brayden.
Thanks for your reply - Yes we put a new kit through the carby late November however, when we were trying to get the car to start on the Saturday we found that there was a fuel issue - firstly the mechanical pump wouldn't prime and so the float bowl was dry - when we took the top off the carby we found the bowl dry and it had some sort of gunk in it - it was definitely pristinely clean when we rebuilt it, so that was a bit odd. After we sorted that out (by removing the mechanical pump from the motor and vigorously operating it by hand for about a minute to get the fuel up!) it seems to manage to keep up ok. I guess I could strip the carby down again and check it over, but Pete the automotive machinist who rebuilt the engine for me felt it was ok - he had rebuilt it for me last year and it was running very sweetly until the head gasket gave way due to corrosion in the head causing the rebuild two weeks before christmas.

[Brayden]

If you rebuilt the carby last November does that mean you're using an F5A carby on an F8B motor? If so I should warn you that the F8B carby has larger jets/venturis/etc, and the F5A carby will make the motor run lean.

[Tez]

Hi Brayden - Sorry - I wasn't too clear - the motor is bog-standard F5A.

[Brayden]

My apologies, I automatically assume F8B because not many people rebuild the standard donk.

If you have another carby laying around then try it out. For some reason I installed a carby that was working in a Hatch onto a fresh motor and it wouldn't idle no matter what. I swapped to another carby and it ran like a dream.

[Tez]

I wish I had a couple of carbies to swap about, but alas, I have only the one.
So do you think I might have nipped up the manifold a bit (maybe it wasn't leaking there in the first place, coz no water leaked out) and I should concentrate on the carby...? But if that is the case, why did the rpms improve when I did the carby-cleaner thing?

I did use a chain from a bolt in a vacant hole on the front face of the bellhousing over the hook to a plate I had slipped through the slit in the manifold between cylinders 1 & 2 to suspend the motor (If you follow where I've gone with this) when I withdrew the motor, and to replace it - I figured that would be plenty strong enough, but maybe the manifold moved a whisker, supporting the weight of the motor...?

I'm just not looking forward to pulling the motor out again, or trying to remove/refit the manifold in-situ. Even tho' the manual says it can be done in the car, it doesn't say HOW

What to do?

[Brayden]

I can't say for sure if your lifting method would have bent/damaged the manifold, but it is possible. (I avoid even using the standard lift hooks on the motor in favour of two 500kg ratchet straps underneath the sump/box.)

I guess you'll just have to use a process of elimination. Frustrating and slow, but without being able to hang my head in the engine bay I'm not much use in diagnosing the fault. The inlet manifold can be removed without removing the motor, I've done it a few times. It is a mongrel job that I resorted to cutting a cheap 12mm spanner in half to accomplish.

[niiko]

I know it is a silly question but, have you tryed adjusting the air fuel mixture screw?

[Tez]

Not a silly question at all. I know Pete adjusted it on the Saturday we tried getting the motor going. To be honest, I don't know where it is set a.t.m. I'll take a look at that tonite. Won't I feel a dick if that's all it is...

[Jermaine]

if u said there was a bit of shit in the bowl, there could be some blokin somethin in the carby still causin it to not idle..

[Tez]

True enough. I haven't had a go at the carby this evening, but I did put all the crap back in and refilled the coolant and started it. - I set the timing as close as I could get to 10 btdc and it still doesn't run well - just better than it was... But, FFS!!! talk about exasperating bloody machine! - i took it out for a quick burl around the block - just to convince myself that the thing is running better than it was and now... NO BRAKE PEDAL!!! ARGGGH! - It's enough to drive a man to drink I tell ya.

So now. Brake issues also. - I'll start another thread on that. Goddamn I musta killed a chinaman in another life...

As for the motor - It's still running rough, but I might concede defeat on that and take it to a carburettor specialist a few suburbs away from here and get him to sort it out for me (at great $$$ I'll bet).

Cheers

[ceej]

Timing belt all lined up correctly? What about all of the earth straps to the engine? All there and in good condition? Just a few more ideas to get the brain storm happening!

[Tez]

Hi Ceej.
Thanks for the input - yes, with great difficulty we managed to get the timing cover off in situ and check the timing belt - Pete thought he might have been a tooth out - he wasn't - it all lined up perfectly. But one more thing we could tick off.
as for Earth straps etc. there's the braided copper line from the rocker cover bolt to the front valance, and the main Earth from a Gearbox bolt back to the battery. These are in place, in good condition and in fact I took the opportunity to clean all the contacts before re-assembling them. That's all that were present when I received the 'boy... Are there any others?

Keep the ideas coming - I'm not keen at all on the idea of having to take the inlet manifold off... Which is what it's starting to look like needing...

[Brayden]

There should be an earth from the body to the battery as well.