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  #1   IP: 164.44.67.4
Old 07-11-2010, 11:58 PM
doralda doralda is offline
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Engine full rpm neutral but dies when shift to Fwd

Have a 1973 Bristol 30 w Atomic 4. *Have jumped primary circuit, checked firing order, have 50-80 psi compression, have removed and cleaned fuel tk, replaced fuel lines and filters, new hose clamps, removed and sprayed fixed main jet and cleaned carb. Am using AV 100 aviation gas - no ethanol, very clean. points look good, new plugs, see no cracks in cap, distributor advance mechanism cleaned and lubed. Mystery oil in gas, pulled intake manifold off gasket looked good, added form a gasket and replaced, reinstalled carb. new mech fuel pump last yr. Also replaced coil "at sea" when engine died for no apparent reason. worked for another half hour but had to sail up to mooring. Ideas?
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Old 07-12-2010, 02:47 AM
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Quote:
Originally Posted by doralda View Post
Have a 1973 Bristol 30 w Atomic 4. *Have jumped primary circuit, checked firing order, have 50-80 psi compression, have removed and cleaned fuel tk, replaced fuel lines and filters, new hose clamps, removed and sprayed fixed main jet and cleaned carb. Am using AV 100 aviation gas - no ethanol, very clean. points look good, new plugs, see no cracks in cap, distributor advance mechanism cleaned and lubed. Mystery oil in gas, pulled intake manifold off gasket looked good, added form a gasket and replaced, reinstalled carb. new mech fuel pump last yr. Also replaced coil "at sea" when engine died for no apparent reason. worked for another half hour but had to sail up to mooring. Ideas?
1. Wasting your money using AV 100 gas and you may not achieve peak performance with hi-octane fuel in a low compression engine;

2. 50 - 80psi is much too low for an A4 - should more in the 90 - 100psi range;

3. How much form-a-gasket did you use?

4. Did you properly set the timing on the engine?

Cheers!
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Old 07-12-2010, 10:08 AM
Trysail Trysail is offline
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Are all four cylinders firing? Mine will start, idle or rev like a champ on three cylinders and still start and idle, a bit rough, on two cylinders. Things don't go so well on two or three cylinders when I put it in gear.

I'm having a "low power/RPM in gear, yet idles and rev's fine in neutral" problem.

I started with the exhaust, checked everything else, now I'm going back to look for an exhaust blockage again.
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Old 07-12-2010, 10:41 AM
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I would do the oil in the cylinder method to determine whether you have low compression do to rings or valves. Doing a valve job on an A4 is not a bad job, and if you are lucky, you can do it with the engine right in the boat.

In the mean time, you could use a hotter plug like the Autolite 437 to get you through.

David
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Old 07-12-2010, 11:11 AM
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100 octane avgas has no ethanol and lasts about a year before going stale. I think that is why the OP uses it. The extra octane will do nothing for an A4, and if my 6:1 compression ratio O-200 is any indication, it will lead foul the hell out of the plugs and likely the valves too. You'll need to buy the Alcor TCP additive to prevent that.
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Old 07-12-2010, 01:54 PM
doralda doralda is offline
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Doralda A4 troubleshoot

The extra money for the cleaner w/ no ethanol AV 100 gas I feel is worth it considering I am not going thru fuel filters like kleenex now. Tank cleaning and new lines and filters helped. I will try the additive but is a hotter plug advisable with the higher octane gas? I am far away from the Eureka moment with this problem and need to look at it from a new angle. Any angular thoughts woul be appreciated. Motor will race or idle in neutral but still stalls in gear.
I live in Camden, ME. The warm season is short here. The blackberries need pickin before the birds get em. Maybe I'll eat some w yogurt for lunch and I'll get a clue...before I row out to the mooring and stare the engine down again.
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Old 07-12-2010, 05:15 PM
Dave Neptune Dave Neptune is offline
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Lightbulb No start warm?

Did you check for spark when she failed?? If no spark and you already changed the coil change the condensor. The condensor can fail and restart when cooled off just like the coil. Worth a try.
My engine has about the same compression and you can't really trust most guages, so don't go there yet. However you can drop a bit of oil in the cylinders and see if the compression comes up then you will no wheather you have a valve issue or a ring issue. Your numbers are not bad enough to cause the engine to not run.
No you will not need a hotter plug for the Av-gas. The nicest thing about the Av-gas is the shelf life. I suggest a good quality regular gas. Your marina supply of gas could be a problem, some are good and some suck!

Dave Neptune
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Old 07-14-2010, 12:29 PM
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Firing order?
IIRC, it will do something like this with 2 wires reversed.
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Old 07-14-2010, 08:28 PM
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Dora, if you have 50 - 80 psi compression in that motor then a slug will beat you in a race.

There is something badly wrong in those comp figures - forget the yogurt and berries and stop staring down that A4...trust me, I have tried and it does not work!
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Old 07-14-2010, 10:34 PM
doralda doralda is offline
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Engine full RPM in neutral but dies in forward

Thank you to Ken in parts, and Don Moyer for his patience on this situation, helping me reason issues out, identify core problem - hesitation before coming up to full speed, and suggestions for the remedy. OK, new carb and fuel pump last year, checked firing order and wires for spark, firing order and correct install, jumped primary circuit, left jumper on overnight, burnt out coil, put in new one, flushed carb main jet to mason jar using manual fuel pump, no grit super clean AV100 fuel, lubed advance weight mechanism in distributor, power timed engine found timing was where it was supposed to be. squirted mystery oil to #2 cylinder - 50 psi - to hopefully loosen up stuck rings or valves, bought and installed knurled needle primary adjust screw and it is 11/2 turns out - Don said turn it in even though I told him the engine idles ok - said engine should idle perfectly and primary side of carb controls engine. bring it in 1/4 turn at a time even if I have to go all the way in since carbs are each slightly different and got to match mixture to this engine. Plugs pulled and all were dry and looked as if theyd been running hot. Will be in Maine on Saturday to try adjustments. Fingers crossed. Thanks for ideas.
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Old 07-14-2010, 11:16 PM
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Was there any punctuation in that response?

Good Luck and provide us some feedback...Don & Ken are gems!
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Old 07-25-2010, 11:04 PM
doralda doralda is offline
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I am running out of ideas. Best idle is w idle screw off seat 3/8 turn. Engine is responsive and comes up to speed quickly in neutral but dies when put it in fwd gear. Still ever so slight hesitation when indrease throttle but not as pronounced. Took carb off and put in a working carb from a friends boat - worked worse than mine. Took mine 1 yr old apart again blasted it w carb cleaner, put it back together again pumped a full glass jar of fuel thru it let gas settle in jar - pure. poured it back in tank. remounted my carb tuned it in to best idle again w idle jet screw engine sounds great then dies when put it in gear. Power tuned distributor, it was at right spot. Opened distributor removed points and condensor look good, plate to spray mystery oil lubricant on them worked the CA weights w a screwdriver tip they seem ok. Put the cap back on for the evening will put it all back together tomorrow. Foggy / Sunny w occasional TShowers here today at the mooring. Be nice to take a trip and have confidence in this engine! ANy fresh ideas would be appreciated. Thank you. Doralda.
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Old 07-25-2010, 11:12 PM
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Have you inspected your exhaust system looking for restrictions?
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Old 07-25-2010, 11:28 PM
doralda doralda is offline
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I there a quick way to do this? Water and the usuakl smoke comes out the stern.
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Old 07-25-2010, 11:33 PM
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Talking

I guess the really elegant way to do it would be to buy the low pressure gauge kit from Moyer Marine. Otherwise you have to get inside components. I am not familiar with your exhaust system, but I have heard on this forum that collapsed rubber hoses are often at fault. It seems that the collapse of the inner liner cannot always be detected from the outside.
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Old 07-26-2010, 01:30 AM
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I'll say it one more time - until you can sort out what is causing those very low cylinder pressure readings that engine won't fart its' way out of a wet paper bag.
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Old 07-26-2010, 12:20 PM
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I thought the quick test for exhaust restriction was to rev the engine in neutral. If there's blockage it won't care if the engine is under load or not, it just won't let the exhaust gases out and the engine will bog down.

I agree that the low compression readings are the thing to investigate.
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Old 07-26-2010, 07:13 PM
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Quote:
Originally Posted by Baltimore Sailor View Post
I thought the quick test for exhaust restriction was to rev the engine in neutral. If there's blockage it won't care if the engine is under load or not, it just won't let the exhaust gases out and the engine will bog down.

I agree that the low compression readings are the thing to investigate.
Assuming the head's not warped or the rings aren't completely shot, are the head bolts dogged down to the correct torque (40 ft/lbs. if I recall). They need to be torqued in a certain order, or so says the Seacraft manual. I get a quarter turn on mine every spring.

The gasket could be flawed, too. 90-115 PSI is nominal, not 50-80.
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Old 07-26-2010, 07:57 PM
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I don't like 40 lbs on the head nuts - stick to 35 per the MM manual - some are even happy with 30.
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Old 07-26-2010, 07:59 PM
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Quote:
Originally Posted by Baltimore Sailor View Post
I thought the quick test for exhaust restriction was to rev the engine in neutral. If there's blockage it won't care if the engine is under load or not, it just won't let the exhaust gases out and the engine will bog down.

I agree that the low compression readings are the thing to investigate.
BS, another 'quick' test is to pull one of the spark plug wires. If it runs better on 3 cylinders than 4, (25% less exhaust being pushed out) that can be an indicator of a plugged exhaust.
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Old 07-26-2010, 10:59 PM
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Prop is not fouled. Current at mooring will spin prop shaft seems to spin freely in almost engaged position either fwd or reverse. Have to position lever just right to see shaft stop turning.
Squirted MM oil into cylinders w squirt can aimed at alternator side of cylinder. 5 full squirts each cylinder, replaced plugs and started engine. White smoke cloud was emitted from stern exhaust, then faded after a bit. Repeated process 4 times. Still stalled going into fwd gear. Had a beer, let engine cool.
Pulled carb and main jet hex nut from bowl, did not loose gaskets into bilge. Unscrewed main jet and replaced it w a new one from a friends moyer rebuild kit. flushe it into mason jar. very clean installed hex nut w gasket and reinstalled carb. A4 Friend came by the mooring as I started engine. I told him I was hopefull the new jet would fix all, Started engine and it ran well. When warm and while ramping up speed w speed control lever I finess shifted into fwd gear. Engine bogged severely and I was able to get it to continue to run but at low rpm / had no power to accelerate.
Friend listened to exhaust and said he heard some low audible pops coming from the exhaust which indicated to him that I should remove the side cover and look at the valves he suspected one was stuck and clean out all the accumulated gunk and mush. Making sense but getting nowhere. Doralda
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Old 07-26-2010, 11:14 PM
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doralda, I would recommend letting the MMO sit in the cylinders for a few days. I squirt it into the cylinders and then turn the engine over (by hand) or blip it with the starter but don't let it start. Then let the oil sit for a few days. They key is to get the oil into the valve stems to break them loose.

Mine had a stuck valve I think last year and it took several MMO treatments over a few weeks every time I used the motor, I 'stored' it with an MMO treatment, and then one evening it 'popped' and ran better the rest of the season.
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Old 07-26-2010, 11:22 PM
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Quote:
Originally Posted by doralda View Post
Have a 1973 Bristol 30 w Atomic 4. *Have jumped primary circuit, checked firing order, have 50-80 psi compression, . . .
67's comments are not lost on me
Quote:
I'll say it one more time - until you can sort out what is causing those very low cylinder pressure readings that engine won't fart its' way out of a wet paper bag.
but neither are Dave Neptune's
Quote:
My engine has about the same compression and you can't really trust most guages, so don't go there yet.
Question for doralda and Dave Neptune: how many cylinders have 50 psi and how many have 80?

I'm starting to think you're chasing external systems to compensate for internal issues. Kinda hard to diagnose fuel and ignition components when the air pump ain't-a-pumpin'.
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Old 07-27-2010, 08:24 AM
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Question

I think Neil reminds us of the real issue we need to chase down first.
Another trick to diagnosing bad rings, which I learned on this site, was taking dry & wet compression numbers. If your compression numbers change when performing the two tests, it can be telling.

Get a good reading for each cylinder with the motor cold & with dry cylinders, & then squirt some MMO or I've also heard a teaspoon of motor oil into the cylinders and do a compression check again..if the numbers magically go up with the oil in there, it indicates ring problems...one could be stuck, or could be broken, or could otherwise be compromised.

Make sure to close the raw water intake for this procedure...we won't be starting the motor, and we don't need to compound the problem by backflowing water into the engine via the exhaust while cranking the starter.

Once we have good reliable numbers, we can move forward.

One other comment...I do not think you'll find gunk & mush underneath the valve cover. If they are sticking, it is more likely up in the block where the guides are located. IMO - the extended MMO treatments are the best way to tackle that issue for the time being.
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Last edited by sastanley; 07-27-2010 at 08:27 AM.
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Old 07-27-2010, 10:06 AM
baileyem baileyem is offline
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After using aviation fuel, with its heavy load of lead, I would change the plugs no matter how good they looked. A little fouling goes a long way in an engine with poor compression.

Mike
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