Help! Valve sealing issue.

[haison]

Hello again.

Once again I'm having issues with this bloody 5ME.
For those that don't know, i have a 4MU carby attatched to this 5M (don't ask) and so far so good.

I can get it to start and idle for short periods of time, but I'm having backfiring issues. Once it's warm it'll idle/fast idle for about 10 seconds then it'll backfire, sending flames out the carby. The higher the revs the bigger the flame.

We nutted it down to the valves not sealing properly (being my first head service i scraped some of the carbon off the valves and seats but didn't grind them properly).

I was told to keep starting it and rev it hard to hopefully settle them down.

I've done this for about an hour now and although it's got a bit better it hasn't solved the problem.

Anyone know any tricks to help it along?

I've loosened the tappets off a bit to make the valves hammer into their seats, other than that I can't think of anything.

Also could there be any other issues that'd cause this?

Thanks heaps guys.

EDIT - it only backfires out the carby, not the exhaust afaik.

EDIT 2 - I don't even know where to start searching on this sort of info!!

[MWP]

You sure the cam & ignition timing is correct?
You should make 100% sure they are right first.

[haison]

Yep. Checked, and checked again, then again.

Also I'm pretty sure its not a vacuum leak but is there any way to test this for sure?

[oldcorollas]

done a compression test yet?
comp should be down.

turned the motor over slowly yet?
it should "leak" faster on cylinders with leaky valves

[Mathew]

I think that you should check the cam lobes are in the right place when the piston is at top dead centre and also the distributor is set properly - the point being not to trust any timing marks or what the manual says should be correct - check it yourself and make sure!!

If you think it is carbon and crap making the valves not close properly there is an old wrecking yard trick that is pretty nasty but certainly clears all the crap out. Mix 50 / 50 auto transmission fluid and water and then whilst holding about 2000 revs slowly dribble down the carbie a small amount of the mixed brew. Note that it will blow heaps of smoke as it scours all the crap out, don't overdo it! Two or three goes at the most. I was amazed to see this work on an old v8 motor that had been sitting for ages and tested with very low compression, afterwards when tested the compression was up and the motor idled smoothly!

[mrshin]

Subaru upper engine cleaner, much better than water can ever hope to be.

[30psi 4agte]

I can vouch for the wreckers trick. Not something idd suggest but i had a similar prob years ago on a 4k. It did end up working........ to some degree. The suby cleaner is a far better option.

You can check for vac leas a few different ways.
One is to use a long vac hose like a doctors stethascope(prob not the right spelling)
Stick it in your ear and put the other end around all of the possible leak spots. You will hear a leak if there is one there.

This is a particular good way to check for exhaust leaks as the can clearly be heard blowing out but not always perfect for a vac leak as they suck air in and can be hard to pick.

For a vac leak the best way to check it is to get a coke bottle fill it with water and put a hole in the lid. Then squirt the water around the carby / inlet manifold etc etc if there is a leak the engine will suck in the water and will run like crap and hence you will know you have a leak and where it is !


Id be doing a comp test or better yet a cylinder leakage test! This will tell you for sure if it is a valve seating issue.

[haison]

Thanks a heap guys. I'll keep all that in mind in the morning when I give it another shot. Bloody neighbours complaining about the noise.. i mean constantly revving at 4k rpm doesnt make that much noise! sheesh

+rep for all

[haison]

Well looks like it's sorted. Couldn't find that subaru cleaner, used contact brake cleaner instead. Figured it's designed to remove carbon and it's flammable.. gotta be on the right track there.
Checked for leaks, there were 2.. basically 2 vacuum hoses i forgot to hook up, it actually didn't make a difference with the backfiring but it helped it idle better.
After a good hour of revving it's seemed to settle down. Last couple of runs didn't backfire at all. Yay!

I'll let it cool down a bit and give it another shot later.

Thanks again guys!

[Merudo]

so now that's taken care of, what's with the 4MU carby on the 5ME?

[haison]

Lol. Well the 5M is just temporary to keep it moving so I can go get/build myself a daily. Probably a AE71 seeing as i have a nice silvertop 20v sitting here.
Seeing as I butchered the 5M EFI gear getting it out thinking i'd never use it again it was easier for me to use the 4M carby my mate had sitting in his garage.
Like WAY easier.
Plus the induction noise is cool.
Woulda been cooler if we managed to get the triple carby setup he had working