Still having power issues - Round two

[Oaktown27]

I did follow most of the process you outlined. I tore down the carb, cleaned the jets with a wire, cleaned the bowl, new gasket. Didn't adjust or check the spacing in the float. Perhaps this is something I missed?

Did not replace the jets or needle.

Going out again tomorrow, soe will see if the fuel pressure is constant under load.

[Jo Ross]

Originally Posted by Dave Neptune

Two questions.

#1 Are your plugs still white?

#2 What are you doing when you "clean" the carb?

Rebuilding the carb is essentially disassembling cleaning and checking the float setting then putting it back together with a new gasket. The needle and seat is seldom replaced unless it is leaking and replacing the shaft seals should only be done by a pro or very skilled carb mechanic. This is what lead me to question #2.

Dave Neptune

How am I looking here?

I had the hull cleaned and checked for foul and while dirty it wasn't a foul and I'm still having capped power issues. I also pulled the carb and cleaned with carb cleaner through the jets. Still having the exact issue where my throttle only goes about half way with a change in response and the rest is just doing nothing. RPMs capped at around 1600 and when I did a pressure test on each cylinder I couldn't get any above 90psi.

[Dave Neptune]

The plug still looks to be running rich. Did you set the float?

1600 ~ 1800 is not uncommon on most A-4's with a direct drive. If you have the Indigo prop or a 2 blade with a 7~8" pitch you should reach 2200 with the 2 blade and 2400 plus with the Indigo if the engine is running well. My Volador with less compression than yours could get 2700 with the Indigo however I did a lot of fine tuning and carb work of which I am very experienced in doing.

You are missing something in the carb or ignition timing. I think you may have the float set to high which will run rich. I set mine 1/16" low and liked the gain in power.

Take along look at some posts on finding TDC and setting the timing, it really makes a difference in performance . If you still have points check the dwell as most of these old A-4's have very worn out distributor cams that can no longer be set by gap alone . That is a good reason to upgrade to an EI, once you do you will not look back and the "tune" will last for many years!

Dave Neptune

[Jo Ross]

I'll look at those things.

For my pressure drop, is there a thread I can look at that talks about the compression rings? I don't know what that actually means but I ran this thing extremely hot on my last outing and I'm worried I did some damage that needs attention.

[Dave Neptune]

Your compression numbers sound fine. No worries there.

How hot did it get? And are you raw water or HX cooled?

Dave Neptune

[Jo Ross]

I ran it with a compromised coolant pump gasket for like a half hour total. The dark gold paint started turning black on top of the manifold.

Raw water cooled and I fresh water flush after every run.

Actually, now I am noticing that it gets very hot very fast even though I have good coolant flow. I'm not very excited about that.

4th cylinder spark plug shows a lot more soot than the other three but I can't find any reason for it.

[Dave Neptune]

The back lowest plug will look blacker especially if the engine is running rich because the excess fuel will go down hill to the back due to gravity. How far out is the idle air screw? Try opening it a half turn to lean the idle a bit.

Did you try closing the bypass if you have a valve to force more water through the block? You can pinch the hose with a C-clamp carefully if no valve.

If you have a t-stat check it to be sure it is fully opening so it closes the bypass off. Remember it is a double acting t-stat not like the ones in cars. If you have an automotive type get rid of it. Many of us here run without a t-stat in raw water cooled engines.

Any air being sucked in by the pump will drastically reduce water flow!! Install a new gasket before running again.

Dave Neptune

[Jo Ross]

What does it mean to "set the float"? I realized I don't know what that is talking about. The float valve in the carb? Or the idle jet screw?

[Jo Ross]

And could the polishing filter being old be a cause of low power?
I never have great luck finding these in the auto stores so I don't have them on hand.

[Dave Neptune]

The float controls the level of the fuel in the carb for proper metering. If the float is set high the carb will be rich and if set to low the carb will be lean. It is a very important setting and instructions are included with most any carb kit. When adjusting the "tab" on the float that controls the needle and seat care must be taken. Only bend the tab by holding the tab with a pair of needle nose pliers and then bending the tab with another pair. Do not just bend it against the float. The bending must be done carefully and when done the float should be parallel with the body when the needle is closed. IE the bending into position is a 2 part for both height and parallelism. I like setting the A-4 about 1/16 of an inch low to lean down the overall mix across the throttle settings.
Follow the directions in the rebuild kit. It is not hard you just need to be patient bending the little tab for float height and also the float angle for parallelism.
Just remember to bend only the tab by holding with 2 needle nose pliers. Bending the float side for parallel and the tab end for height.

The idle air screw on adjust the idle, out for lean and in for rich. It adjusts the air in the fuel not the fuel itself.

Dave Neptune

[Dave Neptune]

The only way to check your filter is with a pressure gage (cheap) and it would not contribute to a "rich" mix. It can reduce power only if it is plugged up and reducing fuel pressure to feed the carb when power is applied with the throttle.

Note the A-4 will achieve full power with a direct drive well before fully opened as the carb is capable of far more power and used on much larger engines too.

Dave Neptune

[Jo Ross]

I'm convinced that the pressure in the cylinders is the problem.
I can achieve extremely high RPM in neutral with absolutely no issue. The carb is clean and I think working fine. The spark plugs all have spark. But I can't get pressure in any cylinder above 60 at idle (the 90psi noted earlier was with ignition coil disconnected and fuel line shut after multiple starter turns measuring with the gauge firmly in the spark plug place). Hull has been cleaned and prop verified not fouled. Fuel filter had no effect when bypassed. I looked at the valves through the galley and they all have full travel when the engine is rotated.

The engine is not able to achieve power above a certain point and in fwd gear it peaks at 1500 rpm.

I guess I'm going to just soak every valve in PB blaster overnight and try again in the morning to see if I break some sort of residue clear.

If anyone has overcome this weird capped throttle response please let me know what you did.

[Dave Neptune]

To do a compression check all plugs should be removed, batteries fully charged, the throttle set to wide open and the choke fully open. This is so the engine can "breath" which it can't do if the throttle is closed. 90 psi is good compression and do you have an accurate compression gage?

It is normal for a direct drive to not respond after about 1/2 throttle and 1500 is close to normal depending on the pitch and diameter of the prop.

The mix is to rich so subtract a couple hundred RPM's right there. If the spark is not at the correct time (timing) another couple hundred RPM's can be attributed to that too.

What type of ignition do you have EI or points? Have you checked to see that the centrifugal advance is working smoothly (another couple hundred there too)?

What was it getting as far as RPM's before you had this trouble.

The prop that was on my Volador when I bought it would only get 13~1400 once it was properly tuned. I changed it for a smaller 2 blade (10" pitch) and got to 1800 RPM's then I went with the Indigo and got 2600+.

Stop revving the engine to high RPM's with no load it is very hard on the engine and yields absolutely no information.

Dave Neptune

[Jo Ross]

I guess I should clarify that the lack of throttle response is NOT normal for the history of this engine. I've had it four years and have never had an issue revving high in FWD gear well beyond 1500 when needed. Cruising rpm has always been right at 1500.

Re-performed the compression check as you laid out and got closer to 100psi. Still lower than I'd like but I'll accept that it should be high enough to support power. Back to square 1.

I do have electric ignition and electric fuel pump. I have no experience or knowledge checking timing on that though. It's never been an issue but if this fails I guess I need to learn.

Agreed on not revving in neutral. I only did that to verify it was possible for the carb to keep up at speed.

Any tips on an easy way to inspect my exhaust to verify no blockage?

[capnward]

I would suggest you get one of those compression testers that actually screw into the spark plug holes like the plugs do. I have one and it is nice to not wonder if I have a tight enough seal on the plug hole. I always get readings over 100, and I had a bad overheating episode several years ago.
Timing involves turning the distributor, a procedure which is independent of whatever type of ignition and fuel pump you have. Good that you have EI.
Any Autoparts store will have metal inline fuel filters. They may not call them "polishing filters", but they work. I have two and replace them every year, they are cheap. And yes, once they get clogged even a little, they will restrict fuel flow.
Good luck on getting over 1600 RPM with a load. My maximum is about 1800, and I am fine with that. I have an Indigo prop.
Sounds to me like you are doing fine, with compression around 100 and cruising rpm of 1500. A little more available RPM would be nice but not essential. Try leaning the mixture by turning out the idle screw, turning in the adjustable main jet if you have one, or rotating the distributor counterclockwise a bit while running at cruising rpm. A leaner mixture will make the engine harder to start without the choke but may give higher maximum rpm with a load. Also make sure the centrifugal advance weights are clean and lubricated by turning the rotor. It should turn easily and snap back into place.
In my experience, adding MMO to the fuel keeps the valves clean.

[Jo Ross]

Welllllllll I just pulled the leg of exhaust piping between the engine outlet and the box thing and tested the engine and it appears to be back to normal. There is clear bubbling in the leg of piping which probably compromises about half of the cross section, maybe more, and that has to be it, right? Going to replace that and then I'll report back on performance.

Thanks for your help on this so far, Dave. I feel dumb for not checking that sooner.

[Dave Neptune]

Wow, good find. From your posts I was thinking a fuel or tune issue from what you were chasing.

What you have is the "Sneaky Pete" of performance drops. It is usually a slow process where performance drops outing to outing over many months. The excess back pressure will also cause your wet black plug.

Replacing the exhaust is rather a straight forward process. Remember to use "black pipe" an not galvanized as the galvanized will "off gas" some really nasty bad fumes. Stainless is also good but must be tightened securely as it will not do a "rust-seal" making it a bit tougher to fabricate and install however it will last a long long time.

And when cobbling the pipe together they do not have to be very tight and to get to some of the angles required that extra turn on large pipe may not be possible. No real need for sealant even in a sorta loose (hand tight) fitting. with in a couple of runs the rust in the pipe threads will seal it up "tight".

Dave Neptune