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Author Topic: Top end power loss  (Read 210 times)

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Steam

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Top end power loss
« on: March 10, 2020, 11:11:46 AM »
Hey Guys
Please see this post for info on work done
https://www.mokeforum.com.au/index.php?topic=13962.0
Now all misfires are gone and mixtures set and it drives well and hard to 100k just under 4000 rpm and cruises perfectly but when putting the boot into at 100kmh to overtake etc the response is very slow. Does not bog down or misfire, just does not really respond at all. It will slowly increase in speed.
Previously it would accelerate well from 100 4000rpm, that was with a ramflo air filter.
I am wondering if it is not getting enough air through the now stock new filter.
As we found so  many faults I am unsure where to look for this problem.
Any Ideas most welcome.
Cheers, Dave

Halfpint

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Re: Top end power loss
« Reply #1 on: March 11, 2020, 12:38:09 AM »
Hey Dave,
Is the Distributor a vaccuum advance type? Im wondering if you have a vac leak that isnt retarding your timing enough at 4k +?

From your trouble shooting post "The dissy is a 65dm4 A+ converted to a series."
These electronic dizzy's are fitted to later A+ Minis and Metro's.
What size carbie? The Metro had the HIF44 from what I have read.
I also assumed it to be a 1275? Is this correct?
HP
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Steam

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Re: Top end power loss
« Reply #2 on: March 11, 2020, 07:42:08 AM »
Yep 1275 with a HS4 carbie, may be a tad on the small size but ran fine before the air filter change.
I have had twins on before but they are just too much hard work.
The dizzy is A+ checked to be OK when the drive dog was changed.
The thing is that even with all the faults, with the ramflo it would pull fine from 4000.
I may put the ramflo back on as a test or to eliminate.
I had to change the carb end of the vac advance pipe to an elbow for the airbox, will check for leaks & correct operation.
Cheers Dave.
Cheers, Dave

Halfpint

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Re: Top end power loss
« Reply #3 on: March 11, 2020, 09:26:11 AM »
Would be interesting to swap the air cleaner just to see if anything changes.
I cant think of why the air cleaner would make such a big difference, they have served the A series well for many years.
HP
The happiest of people don't always have the best of everything, they just make the best of everything they have.

matpaul

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Re: Top end power loss
« Reply #4 on: March 11, 2020, 10:28:06 AM »
Probably not the problem but a quick read through the work done says that you did change the SU needle? if it has a different profile then the mixture at that airflow setting could be different i.e. too rich or lean? Does pulling a bit of choke help with acceleration at 100 K's? Just something else to try perhaps.
Cheers,
Mathew.

Terry

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Re: Top end power loss
« Reply #5 on: March 11, 2020, 10:39:42 AM »
Would be interesting to swap the air cleaner just to see if anything changes.
I cant think of why the air cleaner would make such a big difference, they have served the A series well for many years.
HP

Airspeed and volume. The Ramflo allows more air to travel in a straight line. The donut gets things a bit dizzy but doesn't have the same amount of air. Kieth Calvert did a review and showed a modification to get similar results. It was something to do with drilling holes in the stock cleaner.

Terry
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Steam

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Re: Top end power loss
« Reply #6 on: March 11, 2020, 10:50:35 AM »
Probably not the problem but a quick read through the work done says that you did change the SU needle? if it has a different profile then the mixture at that airflow setting could be different i.e. too rich or lean? Does pulling a bit of choke help with acceleration at 100 K's? Just something else to try perhaps.
Thanks for the thoughts , I ended up with the same needle back in after trying variuos others.
I would expect misfires throughout if the needle was not right.
Pulling the choke out is a great way to check for leaning out but made no difference this time.
Cheers, Dave

Steam

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Re: Top end power loss
« Reply #7 on: March 11, 2020, 10:59:23 AM »
Airspeed and volume. The Ramflo allows more air to travel in a straight line. The donut gets things a bit dizzy but doesn't have the same amount of air. Kieth Calvert did a review and showed a modification to get similar results. It was something to do with drilling holes in the stock cleaner.

Terry
Thanks Terry, I seem to remember Calver saying the standard housing was better due to strange shock waves which the elbow/housing even out. He found a cone filter actually showed a reduction in HP.

However your post has made me wonder, planting the foot would open the butterfly, if the su piston does not rise then surely it should lean out.
Can the airflow fail to increase if the cutterfly is opened
Am I thinking this right or not?
Cheers Dave.
Cheers, Dave

Terry

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Re: Top end power loss
« Reply #8 on: March 11, 2020, 12:57:02 PM »
Hi,

why would you think that the piston wouldn't rise if the butterfly increased the air flow?

The increase in air passing through should lift the piston and provide more fuel, that is the design of the carby.

You could try a thicker or thinner oil in the dashpo to see if it changes things. I normally run engine oil in mine but have used air tool oil and auto transmission oil and they can make a difference(not always for the best) however it might help you work out what is going on.

Terry
I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is.


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Steam

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Re: Top end power loss
« Reply #9 on: March 11, 2020, 02:16:09 PM »
Hi,

why would you think that the piston wouldn't rise if the butterfly increased the air flow?

The increase in air passing through should lift the piston and provide more fuel, that is the design of the carby.

You could try a thicker or thinner oil in the dashpo to see if it changes things. I normally run engine oil in mine but have used air tool oil and auto transmission oil and they can make a difference(not always for the best) however it might help you work out what is going on.

Terry

Thanks again, the description in the SU tuning book I ha e suggests the piston stays down, I will have to go and read it again.
Funny you should mention the oil, I was thi king last night that we may have changed it when we had the dashpot off.
I will check to see what was used, I normally use 10W air tool oil.
Cheers Dave.
Cheers, Dave

Steam

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Re: Top end power loss
« Reply #10 on: March 11, 2020, 08:04:58 PM »
Managed to get an bit of time in the shed after work tonight and the oil in the dashpot was NOT my usual 10W.
Not sure what happened but No1 son did tip the piston over while we were changing needles and the oil drained out. We must have put some oil in out of the small oil can used for general lubrication. Think it may be 20W50 engine oil but it was way thicker than normal. Drained nd refilled with 10W tonight.
Won,t get a chance to test this weekend but I will report back.
Cheers Dave.
Cheers, Dave

Steam

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Re: Top end power loss
« Reply #11 on: March 22, 2020, 02:38:59 PM »
The oil that was in the dashppt was 20W60.
Changed it to SAE10 but that seemed to miss somewhat on hard acceleration up through the gears.
I have ended up with SAE20 after trying 30 and finding the top end problem again.
The 10 was fine with the ramflow but the standard air filter prefers 20.
Cheers, Dave

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Re: Top end power loss
« Reply #12 on: March 22, 2020, 05:25:42 PM »
 Hi Steam,

On the dashpot damper thing, try drilling a couple of extra holes in the plastic screw in top.  I have 3 holes in mine, all the same size as the std one. If that hole blocks the vacuum inside the dashpot will have a hard time trying to get the piston to rise against the pressure in the damper rod tube.

What colour spring are you using?

Chinese electronic distributor?

Do you check the timing with a light?  After you set the timing reconnect the vac advance hose and watch what the advance does, give it  rev and see how far the timing marks go.

Cheers
Dave

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Re: Top end power loss
« Reply #13 on: March 22, 2020, 05:54:15 PM »
Hi again, you mentioned changing the coil, i think with electronic distributors the resistance has to be at least 1.5 Ohms, low resistance coils are a no no.

Thought it might be worth mentioning.

Steam

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Re: Top end power loss
« Reply #14 on: March 22, 2020, 08:22:47 PM »
Thanks Dave, the dissy is a lucas 65dm4 commonly found on A+. Converted drive dog, checked for correct advance for engine. The coil is now the one specifically for that dissy.
 I set the max advance to suit engine, timing light can dial in so also do decel check.
I will defo check the damper breather, I hadn,t considered that.  I have a few spare dampers here so might experiment.
But it is now running well, and no induction roar.
Cheers, Dave