High rpm miss AQ 260 350ci

"motor runs and idles perfect

"motor runs and idles perfect until 3400 to 3500 rpm and then it starts to miss badly. changed wires and plugs ,cap, rotor,rebuilt carb,fuel pump.pulling my hair out,can anyone help please."

"Does the distributor have poi

"Does the distributor have points or is it electronic? In either case, make sure the advance weights are not seized and the springs are not broken.

Also, you should

1) checked that the anti-syphon valve in the fuel tank is not stuck;

2) make sure the fuel filter and the fine strainer inside the carb are clear;

3) the flame arrestor in the carburetor is clean;

4) make sure the ignition coil is in good condition.

5) make sure the ignition switch is in good condition, and

6) verify that there are no loose/corroded connections between the overload thermal fuse and the ignition switch, and between the ignition switch and the ignition coil.

There are no doubt more possible causes for your problem, but I think the above is a good start."

"it has electronic ig. all new

"it has electronic ig. all new filters. I ran a wire from + coil to + battery,no difference,new coil. Ill check out the mech.advance tommorrow.Thanks very much!!! Cam"

"Cam, If I may........ our Mr

"Cam, If I may........ our Mr. El P makes some good suggestions.
You have not mentioned whether or not you have checked the anti-siphon valve and/or the fuel tank pick up tube screen.
All are important aspects of this.

Also, by chance have you replaced fuel lines to a fuel line capable of combating the ill effects of E-10 fuels?
This crap can cause issues ranging from a break-down of the rubber to internal hose delamination ..... any of which can cause issues.

If you take these measures, you'll be well on your way to a P of E....... (process of elimination.... one item, and one item ONLY at a time until you find the problem.)
You particularly want to use the P of E for the issue you describe. It may not be fuel related! But this is certainly a place to start.

Also, and I'm just throwing this in the mix here.... (and I have no idea as to which ignition you have)...... but I'm not a fan of an Ignition Conversion.... I.E., an electronic conversion kit such as the Pertronix kit.
People tend to think that these cure distributor problems..... they may not if the distributor is worn out.
These kits are not as accurate as a true electronic ignition distributor.... photo eye or magnetic....... IMO.
I'd suggest that you eliminate fuel related issues first......, and then look at ignition if the problem still exists.
Again, IMOO here. "

You are on to it I think. I re

You are on to it I think. I removed the Electronic ig. to find the small spring in 4 pieces.nothig open on Sundays in my little town so made one. 90% better! yipee. Question? should there be slop between springs and weights with engine stopped.I can shorten small spring more but large spring sloppy to.thank you so much as I cant afford to keep changing things.Mr. Ricardo and Mr. El Pes you guys are the best Cam

"Cam, you are welcome, and tha

"Cam, you are welcome, and thanks for the compliment. The correct way to fix your problem is to remove the distributor and take it to a shop where they can put it on a testing machine and ensure they install the correct size of springs so that the advance curve remains as per specifications. Alternatively, you may want to check with NAPA/Echlin (not sure what auto parts stores are available at Powell River) and see if they have spring sets for your distributor. Maybe even a Mercruiser dealer may have them, as most distributors for marine V8 Chevys have the same advance curve (I assume yours is a Prestolite IBM 7011A or IBM 7013A, check the plate on the distributor). Once you install the springs, give them a small coat of grease so that they don't corrode.

Also, to answer your question: yes, some of the springs may be sloppy."

"I agree with Eduardo.... And

"I agree with Eduardo.... And will further this by suggesting that too light a spring, and your advance curve and limit will bring the full out advance on wwwwway too early! This will cause detonation, possible burned valves and/or pistons!

Either replace this distributor with a new Marine unit, or have it completely over-hauled by a reputable shop who has an old school distributor machine..... and by one who knows how to use it.

Then re-time your engine for not only BASE, but for Total Advance as well.

."

question? I managed to get a s

question? I managed to get a spring today and the following advice:idle timing between 10 and 15 degrees and at 2200 rpm I should be at 35 degrees max.If my boat was lighter as high as 38 degrees.He said set timing at 2200 first to 35 degrees and then see if it idles between 10 and 15 Do you guys agree????? Cam

"Nope. The idle timing should

"Nope. The idle timing should be 8º BTDC and 30º at 4200 RPM. However, the curve in between those two points is important, and it can only be verified in a machine. My advice: find if someone who has a distributor testing machine in Powell River and pay him to do set your distributor. It will be money well spent (cheaper than ruining an engine anyway)."

"NO.... totally disagree!
35

"NO.... totally disagree!
35 degrees max @ 2,200 rpm is a recipe for detonation...... the most destructive force that you could allow your SBC Marine Engine to undergo!!!!!
This is ill advice for a marine SBC!

Try to gather advice for this from trusted marine people..... people who know the difference between marine and automotive.

While I refuse to quote an actual curve spec, or TA for you..... I'll make a suggestion to you:
With a known engine using a Q/E (quench effect) style piston/head configuration, these will work well with a base of 6* to 8* ... and a TA (total advance) of approximatley 28* to 30 * @ 3,200 RPM.

As RPM increase, you will want to see a fairly straight advance curve up to your TA RPM.
If she climbs slightly higher after that, I'm OK with a little more TA.... but not much.
<u>(See your OEM specs for YOUR engine on this!)</u>

Bottom line...... and generically speaking, you want a fairly straight curve, and a limit of approximately 26* to 28* @ 3,200 RPM if the piston selection is unknown....... ( the dreaded "dished" pistons/small chamber heads, for example)
If you know that this engine is using a Q/E piston/chamber combination, you can bump this to about 30* @ 3,200 RPM.

Also, you should see NO mechanical advance until after 850 to 1,000 RPM..... there is no need for any mechanical advance until this RPM, IMO.
This makes for setting low idle speeds more consistant.

I agree with Eduardo..... If hell bent on using your existing distributor, have it set up on a machine by someone who knows what the heck they are doing!
Better yet, buy a new distributor that is factory set for SBC marine use.
The YLM 624 AV is a good magnetic reluctor style ignition system for the average std rotation SBC marine cruiser engine.

Hope that helps you.

."

"The curve in your distributo

"The curve in your distributor should look like the thick black line on the picture. Remember that, to the values indicated in the graph, you have to add the basic idle timing setting (7º-8º BTDC) to have a reading you could see with a timing light....

"

"Yes.... Thanks, El P.
It&#39

"Yes.... Thanks, El P.
It's good to at least look at an advance curve graph to see what we are talking about here.... maybe show this to your marine guy friend!
Not to rub it in, but to share the info.

NOTE: (and this is redundant) When reading an advance graph like this, you must note that the vertical scale for degrees is minus BASE advance.
IOW's....... when looking at the 3K RPM scale, and the intersecting vertical scale of 20 degrees......, note that this is absent BASE advance!
If you add a BASE of 6* or 8*, you now have a TA of 26* or 28*.... of which is just about where you want to be unless you run low octane fuels.

Note that the graph shows @ 3,700 RPM, the TA is at/near 30.5*."

"thanks so much.Its not that I

"thanks so much.Its not that Im "hell bent on using it" but to change it I have to pull the motor for enough headroom and another 391$$$ im JUST TRYING TO BE SURE this time.,I cant thank you guys enough for all your facts.Thats what I needed. Cam"

"Cam, you are very welcome. We

"Cam, you are very welcome. We're just trying to help you avoid a very expensive repair should you not get this correct.

Quote: "Its not that Im "hell bent on using it" but to change it I have to pull the motor for enough headroom and another 391$$$ <u>I'm JUST TRYING TO BE SURE this time."</u> Unquote.

Well, we want the same for you!

Cam, call me bull headed on this if you will! This is not my ego trying to talk you into something here.
This is just dang good information that I am passing along to you.... and from 40+ years of experience!
It's too dam important to foo-foo or forgo.

While it may seem like a big ordeal or task (or an expensive one) to change and/or correct this now, the cost to replace or correct this distributor now will be paled by comparison to the cost of engine repair from damage caused by "Detonation" later on!
And you WILL be pulling that engine if you have a failure!

While you may think that replacing these little springs, and getting them to perform at the prescribed curve, is easy............ it is at best difficult to do any internal distributor advancing mechanism work while still installed in the engine.
And even if..... you now must do the testing "ON ENGINE!"
Can it be done???? Yes, if you know what you are doing!!!!

Detonation is what I am trying to help you avoid here.
**Detonation is very difficult to hear from the helm.
**You've got an engine hatch doing some sound deadening......
**You've got the distance from engine to helm station.......
**You've got other sounds .......
**Often operating temperature will not go up quickly enough to give you a reading at the helm before damage occurs.
**Piston and/or valve damage from this can happen in a matter of seconds.... not necessarily minutes or hours.

There are just too many things going against a chance of an early warning prior to this occurring.


Example: a TA of 30* coming in full-out by 2,500 RPM, can cause detonation while under load..... especially on an engine using dished pistons and small chamber heads!
Marine engines have no "coast" time (no "low load" time)..... they are always under load no matter which speed, other than hull speed.
The typical cruising RPM that we tend to run at just happens to also be in the range where detonation can be most destructive!
Hence the need to pay particular attention to checking TA on any gasoline marine engine.

Bottom line...... if you were to remove this distributor now, and have it set up correctly..... (or replace it with a Mallory YLM)..... you will never know exactly what damage I am speaking of..... and that is a good thing!

I'm hopeful that Eduardo would support this line of thinking given your particular scenario here.

I'm done! I won't interrupt your thread any further if you prefer.
Good luck. I do hope you get this resolved. "

"Cam, in addition to Ricardo&#

"Cam, in addition to Ricardo's wise words, let me add that testing your distributor should cost you no more than $30-$40, and if the problem is just replacing one or both springs for new ones of the appropriate tension, the total bill should be around $50-$75 depending on how much time they spend setting the correct curve. However, if your distributor is original and you intend to keep your boat for a few more years, it may be money well spent getting a new distributor. It is not the first time I send an older distributor to adjust the curve and spend over $100 on it, only to find later that there are other issues with it that make it virtually unusable or very unreliable.

Personally, and if like me you are budget minded, I suggest you may want to take the distributor for testing and talk to the shop tech first, making it clear that you don't want any work done on it if they have to do more work than just changing a couple of springs and lubing the bushings and centrifugal weights ping. Remember that if your distributor is very old, you already got value for it, so if it looks "iffy" it's probably time to bite the bullet and replace it. A new Mallory would be a good choice IMO. "

"More info and some images her

"More info and some images here including a new YLM 624 AV. I'm "2850Bounty" on this forum.
http://www.baylinerownersclub.org/forum/showthread.php?p=345772

In this thread, there is a link to a seller who has a killer deal on a YL points style Mallory! Contact him, he may still have some YLM's for sale. I bought several of them from him earlier this year just to keep on hand.

There is also an image of an old school Sun distributor machine.... kind of fun to look at.
And these still work well.

. "

JUST A QUICK NOTE: Ive ordered

JUST A QUICK NOTE: Ive ordered a new dist. and will pull motor next week. Thanks again Cam

Which system did you buy? Just

Which system did you buy? Just curious!

"Its a mallory, marine,with el

"Its a mallory, marine,with electronic ig. Thanks again guys. Cam"