incomplete combustion diagnosis

[ghosthunter]

no oil..just dry carbon deposit except for 1 plug. its an old 2T engine btw

definitely do a compression test.

[janmike]

been digging the net and i have read a few possible causes as to why. this include over rich a/f mixture(carb), ignition timing, valve leaks and intake manifolds including low compression. additional info is the engine eats up lotsa gas, carb obviously not in good condition, no knocking, pinging or hard starting, smell of unburned gas in exhaust, backfires on decelleration and loss of power on steep climb.



*ghosthunter
if bad compression is found would the engine require overhauling? TIA

[janmike]

i started fiddling with the engine beginning with the carb, i'm going to test first for a very rich mixture diagnosis that may cause the incomplete combustion. visual inspection and looking down the throat of the carb gave me a picture of how it works. with a bit googling and youtube class i had a good idea where to start. float seems to work fine (i can see fuel in the bowl and looks like it's closing because the flow of gas stopped on my soda bottle).
my question is, before i start tweaking, when we talk of A/F mixture adjustments are we talking about the idle mixture screw? and what does it regulate the air or the fuel? like if i fully closed it does it mean i'm starving the engine of air or fuel? or both?
help please!

[kinyo]

If you have a rich mixture, wouldn't ALL spark plugs be affected?

[4JGtootsie]

You have a fine old school engine.
I would simply begin with valve adjustments, good compression will greatly rely on good seating of the valves giving a tight seal, worry about worn piston rings and walls when you have already done all the other test.

The cylinder head gasket will be the next.
The third will be cylinder head check up (dismount head from block), take a close look of the valve condition, seats, guides and seals. Warpage and leaktest of the head should also be checked.

[janmike]

You have a fine old school engine.
I would simply begin with valve adjustments, good compression will greatly rely on good seating of the valves giving a tight seal, worry about worn piston rings and walls when you have already done all the other test.

The cylinder head gasket will be the next.
The third will be cylinder head check up (dismount head from block), take a close look of the valve condition, seats, guides and seals. Warpage and leaktest of the head should also be checked.

tnx! i really like this engine for it's simplicity and raw power (if i can manage to tame it ). your advise is highly appreciated sir, in fact i had it already on my long list of to do's. as of now i'm on top of my checklist and having it DIY. when it comes to your advise it's best i leave it to a professional - though i may still try to do it myself - but will see . Good thing for now is that i'm not experiencing white/black smoke (signs of internal engine problems), pinging, knocking or overheating (signs of wear).

Correct me if i am wrong please:

Idle Mixture screw - regulates the amount of gas flow? air(vacuum) flow? or both instantenously?

Which part of the carb countinously pours gas on idle - main jet or pilot jet?
where is it located in the carb?

TIA

[4JGtootsie]

tagat ko na dispatcha corolla liftback ko but i think the lowest screw is for air by pass and above it is Air fuel. You can do a lot of things to that engine pwede mo gawin 1800 by replacing the crankshaft from a 3t. Pwede rin gawin twin cam by replacing the head from a 2tg.

[janmike]

If you have a rich mixture, wouldn't ALL spark plugs be affected?

Theoretically, yes it should. that is what's puzzling me until now. i have searched for a number of info's regarding this and how to fix it. for now i am trying to DIY and hope to gain some valuable experience regarding this matter. My plan is simple elimination starting with most accessible, most obvious and serviceable part - the A/F mixture. if it does not show any significant change then on to dwell(point gap) and timing because late timing can also cause incomplete combustion.