What would cause an A-series 1100 to fall flat at 4000RPM?

[curmudgeon]

It's been 30 odd years since I've played with minis but definitely go to an 1-3/4" exhaust. Mildish 998s seemed to like that size best, warmer 1275s liked 2"..
The grade of oil in the SU dashpot will have no real effect on steady state mixture so I wouldn't waste too much time with different oils. It only affects transient response, like an accelerator pump.
If you're using the same needle and spring as the rest of the world then mixture is unlikely to be a problem. And a quick test with a standard points dissy will uncover any ignition problems.
Even with the bigger pipe I wouldn't expect a standard cammed 1100 to be still pulling hard much over 5000, but it should spin through 4k fairly quickly.

[Dave75]

From the SU service manual:

Lack of power at high revs...rich mixture
weak mixture
sticking piston...won't rise properly
bent needle
incorrect setting of mixture nut
sticking choke control.. in down position
clogged air cleaner
****FUEL PUMP GIVING INADEQUATE SUPPLY****try an electrical pump [4 -7 psi]

[BMWTurbo]

Ta Dave :-

Chokes fine and returns each time, was one of the first things I checked.
I have checked the needle and seats previously but will do it more thoroughly
Tried without the air cleaner, bugger all difference

The fuel pump did need priming when we first started it after siting for a while, but the fuel filter is always full of fuel, which suggests the pump is okay, the bowl should be able to store enough fuel to rev out at least once though.

Shouldn't take long to check the bowl, piston, damper, seat etc tonight.

[pauly24]

- If it was leaning out, it would get hot and knock.

- If the AFRs are spot on, and you advanced the timing a shit loads, it should knock.

- So it leaves one thing, its rich!

[Andrew Bolt]

Fuel filter
cam timing

[Jim]

Stop fucking with the carby. The fault will
not be carb related. Check the coil and distributor setup
properly before you do anything else.

[BMWTurbo]

Spent an hour removing the carby and cleaning and resurfacing the internals faces etc to confirm it's all working ok this afternoon.

Car now revs cleanly to about 5000RPM but the same seems to happen at this point. It would probably go more if I held it, but you can feeling the power nosing over.

I found it has an 'ADF' needle inside it but the only other needle I have is a 'BDK' which is noticeably finer in the high end. Seems to be the factory fitted needle for late model 998's Link

Checked piston after strip and rebuild and it moves up smoothly and without the damper in it moves upwards to the limit with a blip of the throttle.

Also did the drop test and took longer then 5 seconds each time for the piston to almsot fall out with the holes blocked.

Jim :- I'll investigate the coil and distributor when I get a chance to dig an old out out from the parents place to substitute.

I also dropped the plugs after a blat around the block to keep the rev's/load up and they were all a nice shade of grey, which didn't suggest too lean, nor too rich.

One other thing I noticed that when I was paying attention to the clear fuel filter I could see bubbles coming through the fuel feed line when the engine was idling. I'm not sure why the diapgram pump qould create bubbles, unless there's an issue with the pump or it's sucking air pre pump.

[Dave75]

Thanks Dave, I'll try that tonight and see what happens. I hadn't thought that the piston might not be reaching full height...

I was looking at getting a new needle and seat for it to trial however.

Gerry, I'll investigate that also, looks like it might just be easier to pull the carby off and test on the bench, I don't think it's going lean though as you say it 'should' have pinged it's head off with 3X degrees of timing if it was running lean.

Before you do that, work out what the problem is..too rich/too lean.. needles & jets @ $55 can get a tad expensive..can't be returned for a credit.

Also, invest in a Colour Tune kit ...lets you see the colour of the ignited fuel in the cylinder.Adjust accordingly while the motor is running.

Alsox2...remove the filter & using a mirror, watch the piston when the engine is revved.Should move Smooooothly

???needle & seat or needle & jet???

[Dave75]

I can get 7500 revs [ Needs a rev limiter ] out of mine but it has bigger valves, 3:2;1 exhaust, 1.75"exh, 731 camgrind, 60 th oversize pistons[1150cc] Revs "cleanly" right to the top, but could probably be improved with a proper Dyno Tune.

[BMWTurbo]

Needle and Jet. When I pulled it down the jet was about 1mm below the seat in the carb base and that was where it idled the best.

Next on the list will be to test a std dizzy and see how that goes, if no change, I'll make an adaptor for the WB02 and check the mixtures.

Hopefully if anything it's lean and I can hone the needle down to suit.

I actually read vizards tips for a 'home dyno' and using the brakes and a Colour Tune today when looking for needle info. Interesting, but I'm not keen to pour money into this as it's very much a second car that doesn't see much use, but I'm happy to try and get the most for a modest outlay.

I am also tempted to drop a bund into the exhaust to check the backpressure of the system to see if it's a concern or not. The exhaust is very uninspiring, when you have gotten used to 3inch systems.

Your engine, sounds very similar to my old 1100 I had the injection on. Same dizzy and coil, but I'd locked the mech advance and let the ECU take care of timing.

[BMWTurbo]

I'm starting to wonder if the bloody tacho is wrong...

With a steady lowish idle it reads 900RPM. I've just assumed that it liked to idle higher but it doesn't sound like it's idling fast.

Pretty sure it's a 3.44 diff and it shows around 4100RPM at 100kph. 165-70-10 tyres.

Speed Calculated RPM
50kph 1880RPM
60kph 2260RPM
100kph 3760RPM

At 5000RPM+ (tacho) it really sounds like it's turning pretty hard.

[9triton]

my dwell meter (good old piece of kit) has a low and hi range tacho on it-

if you have one can check the dash tacho

[cheapracer]

Have you actually put a strobe light on it to check the advance?

Possible the Civic is designed to turn the other way and the weights are not throwing out?

[QABB]

Fark me you guys talking about 7500rpm + 1100cc engines are mad - that's huge revs for such a long stroke engine!

I'd expect a stock 1100 to fall over at about 5000rpm anyway...

[BMWTurbo]

I screwed up my calcs above, pretty sure they are 145-70-10's not 165-70-10's

Calculated is 4000RPM at 100kph with a 3.44 diff.

Measured as below :-
Speed Calculated RPM
40kph 1800RPM
60kph 2700RPM
70kph 3000RPM
80kph 3400RPM

Suggests 4200-4300RPM at 100kph.

Should read 4000RPM in a perfect world with the above details at 100kph.

Think I have another tacho floating around that I can connect temporarily to check actual RPMs, worst case though it might be reading 10% out which still suggests something isn't quite right.

Engine will rev out to 5000RPM much easier now, but it really stops pulling at this RPM.

Batfink :- I have checked the advance direction a long time ago, the honda dizzy is designed to spin anti-clockwise, the same as the mini distributor. You can see in the attached the weight are designed to spin in an Anti-clockwise rotation, although that break-down is for the pulsar, the internals are the same.