Logo
FULL SITE MENU

Correct timing or just good valves

S

sinkingnswimming

New member
"Hello again... My question is

"Hello again... My question is that if the timing is off on my (aq125b), will it still have good compression in all cylinders? Still in question about the timing, *(no timing marks on my head to line up with the cam pulley)*, however my compression is...
#1= 170
#2= 170
#3= 170
#4= 170"
 
"[b]"My question is that i

""My question is that if the timing is off on my (aq125b), will it still have good compression in all cylinders? "

Are we talking about camshaft indexing?

I'd have to suggest that when indexed correctly, the valve timing is optimal for building good cylinder pressure. If anything, being out of index may create a lower cylinder pressure.

Your readings are very consistant with one another. This is good!
However, it is no substitute for verifying that the indexing is correct!

."
 
"Thanks for the fast response.

"Thanks for the fast response... The motor fires strongly(without turning over a complete rotation), however it still runs sluggish around 2000RPM... It has already fouled out one set of plugs, and it's not backfiring, but it is popping back through the carb(very rich)... I have tried turning the distributer both ways, and it does change the rough idle to a smooth idle, however when checking the throtle response(going from idle to WOT), after about the third time, it starts poping back thru the carb... I recently changed the timing belt, do to it breaking... The head, nor the valve cover, have any marks to line up with the cam gear... I am just trying to eliminate the timing as a possible cause, so i can move on to the carb... Carb was built at the end of last season thats why i'm a little hesitant...

Thanks again for all the advice/tips, and HAPPY BOATING"
 
"You are very welcome.... and

"You are very welcome.... and we'll get you through this.

If I may, let's refer to the cam as "indexing" or "cam timing"..... and the ignition as "timing" as to avoid any confusion. Fair enough?

You may have an issue in two areas here, and I welcome input from El P on this.

First, the camshaft must (capitol MUST) be indexed correctly, or you will get no where. So this must be verified before going much further.... or any further for that matter.

Secondly, the ignition timing must reach the correct TA range (total advance).
If your ignition is not advancing correctly for a given RPM, then it may be causing what you are describing..... I.E., falling flat at 2k rpm.
The spark advance must do so as RPM increase!
See your OEM specs for TA or TAT.... total advance timing.
It will give you this in "degrees", and will offer an RPM at which this is to occur.
If the ignition system is not delivering this, then you will not get any performance from this engine..... Simple as that.

It could be as simple as rust within the distributor, or a broken spring, etc.
It is a very critical part of your engine being able to perform well.

Again, first the cam "indexing", then once that is either corrected and/or verified, move on to ignition "timing".


Anything past that may lead you to a fuel delivery problem...... but that is another topic.

."
 
"Thanks again.. I have tried e

"Thanks again.. I have tried everything i know to verify that the cam is indexed corectly, but without any marks, so far impossible to be SURE(beyond reasonable doubt)...

I will for sure be checking the TAT today, and will post ASAP with the results...

You guys have been very helpful, and appreciated..."
 
"Ricardo has it just right, ju

"Ricardo has it just right, just want to second his plan. My gut feeling is that you have a spark/spark timing issue. An indexed cam on that boat would be surprising, since you cannot index the stock cam gear, it would have to be custom made or an obvious after-market mod.

You can get an engine fired with goofy timing, but as Ricardo says, you will get no performance from improper ignition spark timing once you start revving. I managed to get my 125a running great in a bucket with timing advance 25 degrees BTDC, but I had loaned my timing light out that week, so I stupidly assumed all was well and took the boat out for a test run...pow! blam! etc...ran great all the way up to 1200 RPM under load :). SO now I keep my friends and my timing light closer by...

Jonathan"
 
"Chris, two things you may wan

"Chris, two things you may want to do:

1) Open the distributor and ensure the centrifugal advance weights move freely and the two springs are in good condition.

2) Check that the accelerator pump in the carburator is working as it should; that is, that it squirts fuel all the way during acceleration.

When you installed the timing belt, you should not have any problems with valve timing if the two lower timing gears (crankshaft and distributor) were correctly positioned, then you used the mark in the belt to slide it in the groove by the dot in the top timing gear."
 
"Jonathan, when I used the ter

"Jonathan, when I used the term "idexing", I was referring to Chris' camshaft and crankshaft being indexed! I think that Chris' issue is the no marking on the cylinder head to align his cam pully with..... hence, not being able to index the cam to the crank.

Seems to me that one of my manuals has an image showing a center line method.
El, you may be more up to speed on this.
The image shows an imaginary center line through: cam pully notch/cam center/crank pully notch/crank center.
If I recall, when all four of these align, the cam is phased/indexed correctly to the crankshaft.
This leaves only the counter shaft to index and that can be done with the markings on the belt.

Does this sound right?

."
 
"Ok guys, i would like to star

"Ok guys, i would like to start by saying thanks for all the imput here... I have performed many test and would like to share the results...

-Again i installed a fresh set of plugs, and it fired up with ease...(less than a complete rotation)...

-Checked the ignition timing and (idle to WOT) it runs its best at 27degrees BTC???... STILL POPPING BACK THRU THE CARB

-Checked the TAT(total advance timing) and of course it is way off the charts (looks to be working properly as it is advancing it a good 20degrees)...

-Took the distributer apart, cleaned the cintrifugal advance and inspected the springs (all working properly)... Checked for rust and corrosion to the ignition module base (found none)...

-Took the intake off and carburator base (replaced gaskets)... Noticed a puddle of gas in the intake...

-The spark plugs i replaced, are very black, almost like brake dust... The manual says this is a sign of rich fuel mixture...???




After running it yesterday for a hour or so, i tried to start it this morning(cold start), no luck... Ran three batteries dead trying to start it... I'm pretty sure that it will fire right up with a fresh set of plugs, as this has worked twice in the past week...



Thanks guys again for any and all help/advice...!!! HAPPY BOATING"
 
""-Took the intake off and

""-Took the intake off and carburator base (replaced gaskets)... Noticed a puddle of gas in the intake...

-The spark plugs i replaced, are very black, almost like brake dust... The manual says this is a sign of rich fuel mixture...???"

Plugs are not wet also? Just sooty?

Just a thought....
I think I would verify my mechanical valve timing (camshaft indexing) is correct (El & Ricardo's posts). If that is correct, a flooding condition as you describe, I would think, should blow out the exhaust and not through the carb unless there is preignition (electrical timing), an open on the intake side (bent/sticking intake valves), or a very remote possibility of a restriction in the exhaust system (sticking exhaust valves, plugged manifolds, etc).
Hope this helps,
DS"
 
I have had a similar problem w

I have had a similar problem with my AQ261 and a Holly carb. Everyone swore it had to do with the ignition and ended up replacing everything with no change. Once I replaced the Holly with a rochester the problem went away.
Shocked everyone.
The best guess was that the Holly needed a #2 or #3 power valve to deal with the fuel load required for acceleration. 3 different carb shops all had tried/or used a #6 or #10 power valve.
It may not be your problem but worth checking at this point.
 
"Chris,

Sorry for not comi

"Chris,

Sorry for not coming back to you before.

Let's try one thing at the time. First, verify that you have aligned the marks correctly in all the 3 gears. This picture is not for the marine engine but the marks are in the same spots:

http://www.threefattigers.com/Protocore/Volvo/TimingMarks.htm

After you verify that the timing belt has been installed correctly, please run a leak-down test to see if one of the intakes is not closing. A compression test will not reveal this.

Once you are 100% sure that all the above is correct, please post again and we will deal with the ignition and the carb.

One thing you should keep in mind, though. Your type of engine carb is prone to flooding if the engine runs for a long time at idle and the idle mixture is not correct. If that happens and you try to start as you normally do, you will waste your time and in addition you will drain the battery and possibly ruin the starter. One thing you can try in cases like this is to put the throttle lever at 75% to 100% and crank the engine; and once it starts running, bring it quickly back to idle.

Also, if the valve timing is correct but the ignition timing is not, you will have a hard time trying to start the engine.

Anyway, let's try one step at the time..."
 
"Eduardo, Excellent! That&#39

"Eduardo, Excellent! That's the image that I referenced in my above post..... I could not find for the life of me! Thank you!
I've ear marked it now!

."
 
"Thanks guys for all the help.

"Thanks guys for all the help... The boat is now running better than ever, and has been for a few days...

-Found the problem to be the pick-up inside the distributer(over years the old points wore down the lobes on the shaft)... The little black pick-up did not fit tight against that shaft anymore... Fixed it with 2" of electrical tape wraped around the shaft believe it or not...


Again, thanks all and HAPPY BOATING!!!!"
 
"Chris, The pick-up unit is th

"Chris, The pick-up unit is the stationary piece. The Hall Unit is what rests on the points cam and rotates.
I'd be afraid that the electrical tape adhesive will become gummy when warm, and the tape may allow this unit to slide on you. If it does, the spark lead may wonder a bit and the alignment may change again unexpectedly!

Why not try a bit of epoxy between the unit and the points cam?"
 
Back
Top